Ion implantation (I/I) is a key technology for preparing semiconductor devices. In the case of GaN, I/I is still under development. The formation of n-type and p-type regions remains a major challenge. In this paper, we will focus on analyzing the effect of structural quality, represented by the threading dislocation density (TDD), on the diffusion of implanted silicon (Si; donor) and magnesium (Mg; acceptor) in GaN. Four (0001) GaN substrates with different TDD, varied from 103 cm-2 to 1010 cm-2 will be used. Substrates with different TDD will be implanted with Si and Mg. The samples will then be annealed at a few temperatures at the same high nitrogen pressure and time. Analysis of the diffusion profiles of the implanted dopants will allow, using the finite element analysis (FEA), to determine D and the activation energies for GaN as a function of TDD.
Gallium nitride (GaN) crystals of the best structural quality are grown by ammonothermal method in a supercritical ammonia solution inside high pressure autoclaves. This lecture will focus on the basic ammonothermal growth. The growth mechanism in different crystallographic directions, growth morphology and structural quality of GaN crystals, will be discussed. Structural properties and shape of the seeds will be shown. The influence of the crystallization run parameters, the internal configuration of the autoclave and the structural quality of the obtained GaN will be discussed. The path from bulk crystal to finished substrate of GaN will be presented. All challenges and difficulties to grown bulk GaN from ammonothermal method will be demonstrated. Scenarios for the further development of bulk GaN crystallization will be presented.
The results of complimentary time-resolved photoluminescence and positron annihilation measurements on Mg-implanted GaN on GaN fabricated using various I/I sequences will be shown to identify the species and quantify the concentrations and minority carrier capture coefficients of major midgap recombination centers (MGRCs) created by the I/I processes. Because vacancy clusters comprised of Ga vacancies (VGa) and N vacancies (VN) such as (VGaVN)3 were assigned as major vacancy-type defects and the room-temperature photoluminescence lifetime for the NBE emission increased with decreasing their concentration, (VGaVN)3 are assigned as major nonradiative recombination centers with electron capture coefficient of 5×10-6 cm3s-1, which is an order of magnitude larger than the hole capture coefficient of VGaVN in n-GaN (6×10-7 cm3s-1).
Financial supports: CSTI-SIP, MEXT (JPJ005357, JPJ009777, JP16H06427, JP21H01826), PNCRD TECHMATSTRATEG-III/0003/2019-00 and PNSC 2018/29/B/ST5/00338.
In order to fabricate gallium nitride (GaN) substrates, bulk crystals of the highest structural quality have to be grown. Today, three GaN crystallization methods are mainly applied for this purpose: Halide Vapor Phase Epitaxy (HVPE), sodium-flux, and ammonothermal. This work will cover basic ammonothermal and HVPE crystallization of bulk GaN. Properties of crystals and substrates will be shown. Limiting factors as well as recent progress in the two approaches will be presented.
In this work we presents effect of ultra high pressure annealing on Si-implanted GaN n-type and p-type epilayers on ammonothermally grown bulk GaN substrates. Samples were blanked implanted with different Si ion fluences from 3x1014 cm-2 to 3x1015 cm-2 and then annealed using UHPA at temperature of 1200, 1300 and 1400°C for 5 minutes at 1 GPa. Ion distribution before and after annealing where investigated using SIMS method showing no Si diffusion in p-type GaN along with Mg diffusion from epilayer and very low Si diffusion in n-type GaN epilayers. X-ray diffraction studies shows that not all defects were recovered after annealing, especially for high ion fluences. Annealing at 1400°C causes changes in implanted GaN morphology. The surface roughness where increased after annealing especially for samples implanted with 3x1015 cm-2Si dose. Our results shows that more work is needed to optimize UHPA parameters for defect recovery in Si-implanted GaN especially for high ion fluences.
It is demonstrated that Borrmann effect X-ray topography (XRT), based on the anomalous transmission of X-rays for high-perfection and high-absorption crystals, is a robust method to benchmark the structural perfection of GaN substrates. GaN substrates prepared by ammonothermal method or HVPE were investigated. Substrates for these growth methods were analyzed on the basis of native seed or alternatively on the basis of foreign seed. The study shows that only GaN crystals prepared with a native seed approach, both by ammonothermal method and HVPE, exhibit a Borrmann effect and proves the high perfection of the substrate produced in this way.
Low angle bevelled-mesa structures are crucial for development of high quality GaN p-n high voltage diodes and photodetectors. However, there is lack of details of development of such a process in the literature. Here in this work, we present results of optimization of bevelled mesa fabrication process for vertical GaN p-n diodes using plasma etching through photoresist mask prepared using reflow process. Developed process of formation of low angle bevelled mesa structures was integrated in the vertical GaN p-n diodes on bulk GaN substrates fabrication process. Very low leakage current density below 10-9 A/cm2 and very high Ion/Ioff current ratio over 1013 was obtained. Low values of ideality factor down to 1.5 were obtained as well. These prove applicability of developed process in technology of vertical GaN p-n diodes on bulk gallium nitride substrates.
Three dopants (Be, Zn, Mg) were analysed in terms of diffusion through the crystal lattice of HVPE-GaN. Different crystallographic directions were investigated: [0001], [10-10] and [11-20]. Ion implantation was employed to create a thin layer of strongly doped GaN which acted as the diffusion source. Annealing in high nitrogen pressure was performed. Secondary ion mass spectrometry (SIMS) was used to measure the post-annealing depth profiles of implanted species. The measured profiles were used for calculation of diffusion coefficients and activation energies for all dopants and crystallographic directions. A strong dependence of diffusion on crystallographic orientation and impurities composition was observed.
Behaviors of vacancy-type defects in ion-implanted GaN were studied by means of positron annihilation. Si or Mg ions were implanted into GaN to obtain 300-nm-deep box profiles of the impurities. The ion-implanted samples were annealed up to 1480°C under a N2 pressure of 1 GPa (ultra-high-pressure annealing: UHPA). For as-implanted GaN, the major defect species was identified as Ga-vacancy-type defects such as a divacancy (VGaVN). After annealing above 1000°C, vacancy clusters, such as (VGaVN)3, were introduced, and they were found to be remained even after 1480°C annealing. For Mg-implanted GaN with [Mg]=1018 cm-3, no large change in the depth distribution of Mg was observed before and after annealing at 1400°C. For the sample with [Mg]=1019 cm-3, however, Mg diffused into the bulk, which was attributed to the over-doping of Mg and their vacancy-assisted diffusion. The Mg diffusion was suppressed by sequential N-implantation, which was attributed to the reaction between Mg and vacancies under a N-rich condition. Interactions between vacancies, Mg, and H during UHPA were also discussed.
Silicon diffusion process was investigated in GaN layers crystallized by metal-organic vapor phase epitaxy (MOVPE) on native ammonothermal substrates of the highest structural quality. N-type (Si-doped) and p-type (Mg-doped) layers were implanted with Si and treated with ultra-high-pressure annealing. The morphology of the layers was examined at each step by optical microscopy and atomic force microscopy. The crystallographic structure was evaluated by X-ray diffraction measurements. The diffusion of Si was analyzed basing on depth profiles from secondary ion mass spectrometry. Temperature-dependent diffusion coefficients, pre-exponential factors, and activation energies for Si diffusion in n-type and p-type MOVPE-GaN were determined and compared.
Co-doping with manganese and carbon was performed in gallium nitride (GaN) grown by halide vapor phase epitaxy (HVPE). The crystallized material was examined in terms of its structural, optical, and electrical properties. Basing on Raman and photoluminescence spectra of the samples it will be presented that in the GaN:Mn,C crystals Mn is in a different electrical state (Mn^(3+/4+)) in comparison to Mn in GaN:Mn (Mn^(2+/3+)). This change is due to the presence of carbon, which forces manganese to change the oxidation state. This phenomenon will be analyzed and confirmed by the examination of the electrical properties of obtained crystals.
Implantation of Ga ions into ammonothermal GaN crystals is proposed as a method of controlling the concentration of gallium vacancies. Ultra-high pressure annealing (UHPA) is expected to facilitate the diffusion of the implanted Ga ions into the entire volume of the crystal. Gallium vacancies are expected to be replaced by the Ga ions. Since Ga vacancies act as acceptors in GaN, reducing their content will result in a higher free electron concentration in the crystal.
Gallium ion implantation and UHPA processes will be presented in detail. Values of the main parameters of UHPA allowing for the complete replacement of the Ga vacancies with Ga ions in GaN crystals will be determined. The morphology as well as structural, optical, and electrical properties will be compared for samples without any treatment and those implanted and annealed. The ultimate goal is to obtain highly conductive GaN crystals with the lowest possible Ga vacancy concentration.
Diffusion of Be was investigated for the main crystallographic directions in HVPE-GaN: c [0001], m [10-10], and a [11-20]. Be was implanted into the samples at room temperature with a dose of 2.9e15 cm-2 with energy of 200 keV. Ultra-high pressure annealing (UHPA) was performed to repair the post-implantation damage and activate the dopant. The annealing was performed at different time (15 and 30 minutes) and temperature (1200 – 1400°C). Depth profiles of Be were measured by secondary ion mass spectrometry (SIMS). Diffusion coefficients were calculated using the complementary error function (erfc) or Boltzmann-Matano analysis. The determined diffusion coefficients were summarized in an Arrhenius plot: D(1/T). From this relation the pre-exponential factor D0 and the activation energy were calculated. In addition, it was possible to calculate the formation energy for interstitial Be as well as gallium vacancy defects.
In this paper we would like to report the recent progress in basic ammonothermal GaN crystal growth. Growth on ammonothermal GaN seeds is presented. Structural properties of the seeds are shown and discussed. A new shape of seed crystals is proposed. It allows to eliminate the appearance of cracks in the growing GaN. The unwanted lateral growth is restricted and controlled. A higher growth rate, both in lateral and vertical directions, is obtained. Generally, the high structural quality of native seeds is maintained. In case of crystallization in lateral directions the structural quality of the seeds can even be improved. The influence of the crystallization run parameters, growth direction and configuration on the structural quality of the obtained GaN will be discussed.
Vacancies in Mg-implanted GaN were probed using positron annihilation technique. Mg was implanted into GaN with [Mg] = 1E19 /cm3. For an as-implanted sample, the major defect species was identified as Ga-vacancy related defects. The sample was annealed under a nitrogen pressure of 1 GPa in a temperature range of 1000–1480C without a protective capping layer. Comparing with the sample annealed with the capping layer, although no large difference in the defect spices was observed, their concentration was decreased by the cap-less annealing. The diffusion of Mg during annealing was influenced by the presence of residual vacancies. H was unintentionally incorporated into the sample during annealing, and its diffusion property were also affected by vacancies and Mg. A part of this work was supported by MEXT “Research and development of next-generation semiconductor to realize energy-saving society (JPJ005357)” and the Polish National Science Centre through project No 2018/29/B/ST5/00338.
Recent progress in bulk GaN growth technology will be presented. New results of basic ammonothermal GaN crystallization and halide vapor phase epitaxy (HVPE) of GaN will be shown and analyzed. The advantages, disadvantages and challenges of both methods will be discussed. An influence of lateral growth on critical thicknesses and structural quality of crystallized GaN layers by both methods will be demonstrated. Reduction of lateral crystallization and growth only in one crystallographic direction will be shown.
HVPE can be used for growing thin, up to 200 µm, GaN layers of high purity and low free carrier concentration. Deposition of such material on conductive n-type GaN seeds results in a structure which is the basis of some vertically operating electronic devices. It should be stressed that thickness of this GaN with low free carrier concentration influences the breakdown voltage of the devices. Therefore, HVPE becomes the main epitaxial technology for crystallizing such layers. The method allows to crystalize GaN with a relatively high growth rate of about 100 µm/h. It makes this technology crucial for preparing transistor structures with breakdown voltage higher than a few or several kV. The main goal of this paper is to investigate implantation of beryllium (Be) acceptors into thin (10-100 µm) unintentionally doped layers of GaN crystallized by HVPE on native seeds. A nitride structure comprising of an n-type layer of low free carrier concentration with implanted regions with p-type conductivity or semi-insulating and a highly conductive n-type substrate will be obtained. Basic parameters of HVPE-GaN growth processes (reagent flows, growth temperature) as well as parameters of ion implantation will be determined. Post-implantation damage, which occurs in implanted layers, will be removed by high-temperature (1400-1480°C) annealing at high nitrogen pressure (1 GPa). Basic structural, optical, and electrical parameters of implanted and annealed GaN will be investigated. The samples will be characterized prior to and after ion implantation.
Ion implantation (I/I) and annealing techniques to enable high carrier doping into selected regions are one of important research fields for realization of GaN power devices. However, particularly difficult research challenges are present in Mg-I/I into GaN as p-type doping technique. First problem is related to nitrogen vacancies (VN), crystal defects introduced by Mg-I/I . [1] Second issue is connected to degeneration of GaN surface by pyrolysis reaction during high-temperature annealing process. We examined Mg/N co-implantation into GaN as p-doping in order to compensate of VN defects. Research on ultra-high pressure thermal activation process to maintain equilibrium conditions at high temperature was conducted to avoid degradation of GaN surface.
We prepared Mg/N co-implanted GaN-on-GaN samples with 300-nm-deep Mg-box-profile of 1E19 cm-3 and with N-box-profile of various concentrations in the range 0 ~ 1E20 cm-3. The samples were annealed without a protection cap layer at temperature between 1300 °C and 1480 °C under 1 GPa in N2 atmosphere. Samples capped with sputter-AlN were treated by conventional lamp annealing at 1300 °C for a comparison purpose.
We obtained the dominant Green Luminescence (GL) emission at 2.3 eV and the recessive Donor Acceptor Pair (DAP) emission at 3.2 eV from a low-temperature cathodoluminescence (LT-CL) spectra in Mg-I/I samples without N co-implantation. This is in good agreement with results published before.[1][2] In addition to this, we found that the Mg/N co-implantation, for optimized N-ion dose, suppresses the GL intensity while maintaining the DAP intensity. Furthermore, in the ultra-high pressure thermal activation process, the DAP intensity markedly increases with anneal temperature and GL intensity suppression is also visible. These results strongly suggest that the origin of GL is related to VN, and the VN defect compensation occurs by N co-implantation. We also compare the AFM images of GaN surface roughness. The ultra-high pressure annealed surfaces were as smooth (RMS = 0.2~0.3 nm) as the as-implanted samples (0.3 nm), whereas surface treated with conventional lamp was rough (1.9 nm).
We can, therefore, conclude that Mg/N co-implantation and ultra-high pressure thermal activation process allows activation of the Mg acceptor and recovery of p-GaN crystal quality. Such treatment results in VN defect compensation and a smooth surface of the annealed sample.
This work was supported by MEXT “Program for research and development of next-generation semiconductor to realize energy-saving society.”
[1] A. Uedono et al., Phys. Status Solidi B 252, No. 12 (2015)
[2] K. Kojima et al., Appl. Phys. Express 10, 061002 (2017).
A review on doping with acceptors of pure and structurally perfect HVPE-GaN single crystals grown on the native Ammono-GaN seeds will be described in this paper. Solid iron (Fe), manganese (Mn), magnesium (Mg) or methane (CH4, precursor of carbon) were used as dopant source to crystallize semi-insulating HVPE-GaN. Carbon-doped GaN was highly resistive at room temperature (exceeding 1×108 Ω.cm at 296 K) and became p-type at high temperature. Activation energy of 1 eV was an experimental confirmation of theoretical calculations for CN (deep acceptor). Doping with manganese also led to very high values of resistivity. In this case the activation energy was close to 1.8 eV. Resistivity of GaN with Mn concentration of 1017 cm-3 exceeded 108 Ω.cm at room temperature. Hall measurements revealed n-type conductivity at high temperature. Co-doping of HVPE-GaN with Mn and Mg led to highly resistive material at room temperature (exceeding 1×108 Ω.cm) and p-type at high temperature. The activation energy was 1.2 eV above the maximum of the valence band. GaN doped with Fe was also highly resistive at room temperature (3×107 Ω.cm with free electron concentration of 5×108 cm-3). It showed n-type properties at high temperature and activation energy of around 0.6 eV below the minimum of the conduction band. Structural, optical, and electrical properties of the resulting semi-insulating HVPE-GaN will be examined, presented, and compared in this paper.
Gallium Nitride (GaN) substrates gained much interest because of their usefulness in making devices for microwave high power electronics, as well as electronic devices of high operating voltage (above 1000V). Among many techniques of GaN crystallization, ammonothermal method is regarded as a key technology of bulk GaN production. In this method, GaN is deposited on native seeds in supercritical ammonia solution at high pressure (4 kbar) and temperature (600 °C) conditions. Intentional doping allows to obtain crystals of wide spectrum of electric properties (n-type, p-type, highly resistive). In case of the latter ones, compensation of unintentional oxygen donors by shallow and deep acceptors is used. It enables to fabricate 2-inch highly resistive semi-insulating substrates of thermally stable resistivity of at least 1011 Ω cm at room temperature. Those substrates are characterized by outstanding structural quality (flat crystal lattice, dislocation density of 5x104 cm-2). Semi-insulating substrates were successfully used in fabrication of high electron mobility transistors (HEMT), operating at 22 GHz..
The main objective of this paper is crystallization of AlGaN by HVPE method. Source of Al will be metallic aluminum. Hydrochloride flow will be set above the Al source at temperature of 500ºC and as a result of reaction AlCl will form. Aluminum monochloride will be transported to the growth zone of AlGaN. The following growth parameters will be established and analyzed: i/ growth temperature, ii/ flows of gas reagents (HCl above gallium, HCl above metallic Al, ammonia), iii/ carrier gas composition (N2 or nonreactive gas). Determining proper parameters should result in a stable growth of HVPE-AlGaN layers with a desired composition of aluminum (Al content from 1 to 25%). Distribution of aluminum will be uniform in the grown layers. HVPE-AlGaN will be thick up to 100 µm. Their diameter will depend on the used seed – up to 2-inch. Structural, optical and electrical properties of HVPE-AlGaN will be examined and presented in this paper.
The main objective of this paper is crystallization of semi-insulating material with resistivity ~109 Ωcm in temperature range between 296 K and 1000 K. No free carriers should be activated at elevated temperature. Source of Mn dopant will be metallic manganese. Hydrochloride flow will be set above the Mn source and as a result of reaction MnCl2 will form. Manganese dichloride will be transported to the growth zone of GaN. The following growth parameters will be established and analyzed: i/ growth temperature, ii/ flows of gas reagents (HCl above gallium, HCl above metallic Mn, ammonia), iii/ carrier gas composition (N2, H2, mixture of N2 + H2, or nonreactive gas), iv/ temperature of metallic Mn source. Determining proper parameters should result in a stable growth of HVPE-GaN:Mn crystals with a desired morphology (hillocks). Distribution of manganese dopant will be uniform in the grown layer. HVPE-GaN:Mn will be thicker than 1 mm. Their diameter will depend on the used seed – up to 2-inch. The layers will be removed from the seeds by slicing procedure and as a result free-standing HVPE-GaN:Mn will be obtained. Structural, optical and electrical properties of this material will be examined and presented.
Hydride Vapor Phase Epitaxy (HVPE) is the most popular method for fabrication of high structural quality and high-purity GaN substrates. The technology of obtaining a low level of impurities together with high crystallographic quality of HVPE-GaN crystals enables the next step, namely introducing intentional doping to the growth process and obtaining semi-insulating crystals. This work describes developing a method for incorporation of acceptors (carbon or iron) into HVPE-grown GaN while maintaining high structural quality and low level of other impurities in the material. Ammonothermally grown GaN crystals and substrates will be used as seeds. All growth processes will be carried out in a home-built quartz horizontal HVPE reactor. Methane (CH4) will be used as the precursor of carbon. The FeCl2 precursor will be created inside the reactor chamber by an HCl-stream over elemental iron. HVPE crystallization runs with different flows of acceptor precursors will be performed. HVPE-GaN:C and HVPE-GaN:Fe crystals will be characterized with X-ray diffraction, Raman spectroscopy, low-temperature photoluminescence, optical as well as transmission electron microscopies, Hall measurements, and Secondary Ion Mass Spectrometry. The properties of crystallized HVPE-GaN:C and HVPE-GaN:Fe will be compared in detail. It will be shown that concentrations of impurities (carbon or iron) in the new-grown material is always very uniform across the (0001) surface and along the c-direction. This result together with a high crystalline quality of the crystallized material will allow to obtain the semi-insulating HVPE-GaN crystals with resistivity of the order of 109 Ω.cm at room temperature.
Laser diodes fabricated from the AlGaInN material system is an emerging technology for
defence, security and sensing applications. The AlGaInN material system allows for laser diodes
to be fabricated over a very wide range of wavelengths from u.v., ~380nm, to the visible
~530nm, by tuning the indium content of the laser GaInN quantum well, giving rise to new and
novel applications including displays and imaging systems, free-space and underwater
telecommunications and the latest quantum technologies such as optical atomic clocks and atom
interferometry.
KEYWORDS: Semiconductor lasers, Gallium nitride, Laser applications, Telecommunications, Defense and security, Free space optics, Data transmission, New and emerging technologies, Free space optical communications, Diodes, Data communications, Laser systems engineering
Laser diodes fabricated from the AlGaInN material system is an emerging technology for defence and security applications; in particular for free space laser communication. Conventional underwater communication is done acoustically with very slow data rates, short reach, and vulnurable for interception. AlGaInN blue-green laser diode technology allows the possibility of both airbourne links and underwater telecom that operate at very fast data rates (GHz), long reach (100’s of metres underwater) and can also be quantum encrypted. The latest developments in AlGaInN laser diode technology are reviewed for defence and security applications. The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v., ~380nm, to the visible ~530nm, by tuning the indium content of the laser GaInN quantum well. Ridge waveguide laser diode structures are fabricated to achieve single mode operation with optical powers of <100mW. Visible light communications at high frequency (up to 2.5 Gbit/s) using a directly modulated 422nm Galliumnitride (GaN) blue laser diode is reported in free-space and underwater.
Laser diodes fabricated from the AlGaInN material system is an emerging technology for defence and security applications. The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v., ~380nm, to the visible ~530nm, by tuning the indium content of the laser GaInN quantum well, giving rise to new and novel applications including displays and imaging systems, atomic clock and quantum information, free-space and underwater telecom and lidar.
The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v., ~380nm, to the visible ~530nm, by tuning the indium content of the laser GaInN quantum well, giving rise to new and novel applications for medical, industrial, display and scientific purposes. Ridge waveguide laser diode structures are fabricated to achieve single mode operation with high optical powers of >100mW with high reliability. Low defectivity and highly uniform GaN substrates allow arrays and bars of nitride lasers to be fabricated. We demonstrate the operation of monolithic AlGaInN laser bars with up to 20 emitters giving optical powers up to 4W cw at ~395nm with a common contact configuration. These bars are suitable for optical pumps and novel extended cavity systems. An alternative package configuration for AlGaInN laser arrays allows for each individual laser to be individually addressable allowing complex free-space and/or fibre optic system integration within a very small form-factor.
Gallium Nitride laser diodes fabricated from the AlGaInN material system is an emerging technology for laser sources from the UV to visible and is a potential key enabler for new system applications such as free-space (underwater & air bourne links) and plastic optical fibre telecommunications. We measure visible light (free-space and underwater) communications at high frequency (up to 2.5 Gbit/s) and in plastic optical fibre (POF) using a directly modulated GaN laser diode.
Advanced Substrates consist of a 200-nm-thick GaN layer bonded to a handler wafer. The thin layer is separated from source material by Smart CutTM technology. GaN on Sapphire Advanced Substrates were used as seeds in HVPE-GaN growth. Unintentionally doped and silicon-doped GaN layers were crystallized. Free-standing HVPE-GaN was characterized by X-ray diffraction, defect selective etching, photo-etching, Hall method, Raman spectroscopy, and secondary ion mass spectrometry. The results were compared to HVPE-GaN grown on standard MOCVD-GaN/sapphire templates.
Gallium Nitride (GaN) laser diodes fabricated from the AlGaInN material system is an emerging technology that allows laser diodes to be fabricated over a very wide wavelength range from u.v. to the visible, and is a key enabler for the development of new system applications such as (underwater and terrestrial) telecommunications, quantum technologies, display sources and medical instrumentation.
AlGaInN laser diodes is an emerging technology for defence and security applications such as underwater communications and sensing, atomic clocks and quantum information. The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v., ~380nm, to the visible ~530nm, by tuning the indium content of the laser GaInN quantum well. Thus AlGaInN laser diode technology is a key enabler for the development of new disruptive system level applications in displays, telecom, defence and other industries. Ridge waveguide laser diodes are fabricated to achieve single mode operation with optical powers up to 100mW with the 400-440nm wavelength range with high reliability. Visible free-space and underwater communication at frequencies up to 2.5GHz is reported using a directly modulated 422nm GaN laser diode. Low defectivity and highly uniform GaN substrates allow arrays and bars to be fabricated. High power operation operation of AlGaInN laser bars with up to 20 emitters have been demonstrated at optical powers up to 4W in a CS package with common contact configuration. An alternative package configuration for AlGaInN laser arrays allows for each individual laser to be individually addressable allowing complex free-space or optical fibre system integration with a very small form-factor.
The latest developments in AlGaInN laser diode technology are reviewed for defence and security applications such as underwater communications. The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v., ~380nm, to the visible ~530nm, by tuning the indium content of the laser GaInN quantum well. Thus AlGaInN laser diode technology is a key enabler for the development of new disruptive system level applications in displays, telecom, defence and other industries.
KEYWORDS: Gallium nitride, Semiconductor lasers, Laser applications, High power lasers, Quantum wells, Indium, Free space optics, Laser development, Waveguides, Near field optics
The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v., ~380nm, to the visible ~530nm, by tuning the indium content of the laser GaInN quantum well. Low defectivity and high uniformity GaN substrates allows arrays and bars of AlGaInN lasers with up to 20 emitters to be fabricated to obtain optical powers up to 4W at 395nm. AlGaInN laser bars are suitable for optical pumps and novel extended cavity systems for a wide range of applications. An alternative package configuration for AlGaInN laser arrays allows for each individual laser to be addressed individually allowing complex free-space and/or fibre optic system integration with a very small form-factor.
The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v., ~380nm, to the visible ~530nm, by tuning the indium content of the laser GaInN quantum well. We consider the suitability of AlGaInN laser diode technology for free space laser communication, both airborne links and underwater telecom applications, mainly for defense and oil and gas industries.
The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v., ~380nm, to the visible ~530nm, by tuning the indium content of the laser GaInN quantum well. Thus AlGaInN laser diode technology is a key enabler for the development of new disruptive system level applications in displays, telecom, defence and other industries.
In this article homoepitaxial HVPE-GaN growth in directions other than [0001] is described. Three crystallization runs on (11-20), (10-10), (20-21), and (20-2-1) seeds were performed. In each experiment a different carrier gas was used: N2, H2, and a 50% mixture of N2 and H2. Other conditions remained constant. An influence of the growth direction and carrier gas on growth rate and properties (morphology, structural quality, and free carrier concentration determined by Raman spectroscopy) of obtained crystals was investigated and discussed in details. For all crystallographic directions a lower growth rate was determined with hydrogen used as the carrier gas. Also, the highest level of dopants was observed for crystals grown under hydrogen. A possibility to obtain highly conductive GaN layers of high quality without an intentional doping is demonstrated.
The latest developments in AlGaInN laser diode technology are reviewed for defence, security and sensing applications. The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v., i.e, 380nm, to the visible, i.e., 530nm, by tuning the indium content of the laser GaInN quantum well. Advantages of using Plasma assisted MBE (PAMBE) compared to more conventional MOCVD epitaxy to grow AlGaInN laser structures are highlighted. Ridge waveguide laser diode structures are fabricated to achieve single mode operation with optical powers of <100mW in the 400-420nm wavelength range that are suitable for telecom applications. Visible light communications at high frequency (up to 2.5 Gbit/s) using a directly modulated 422nm Gallium-nitride (GaN) blue laser diode is reported. High power operation of AlGaInN laser diodes is demonstrated with a single chip, AlGaInN laser diode ‘mini-array’ with a common p-contact configuration at powers up to 2.5W cw at 410nm. Low defectivity and highly uniform GaN substrates allow arrays and bars of nitride lasers to be fabricated. GaN laser bars of up to 5mm with 20 emitters, mounted in a CS mount package, give optical powers up to 4W cw at ~410nm with a common contact configuration. An alternative package configuration for AlGaInN laser arrays allows for each individual laser to be individually addressable allowing complex free-space and/or fibre optic system integration within a very small form-factor.or.
The use of GaN crystals grown by three methods (and their combinations): Hydride Vapor Phase Epitaxy (HVPE), high
nitrogen pressure solution (HNPS) and ammonothermal method for optoelectronic (laser diodes) and electronic
(transistors) devices is presented. After a brief review on the development of the three crystallization methods, the GaN
crystals’ uniform and unique properties, which allow to use them as substrates for building devices, are shown. The
Metal Organic Vapor Phase Epitaxy (MOCVD) and Molecular Beam Epitaxy (MBE) technologies for growing the
nitride quantum nanostructures as well as the structures’ properties and processing of devices are demonstrated. Future
challenges and perspectives for application of bulk GaN as substrates in building quantum nanostructures for some
electronic and optoelectronic devices are discussed.
The latest developments in AlGaInN laser diode technology are reviewed. The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v., i.e, 380nm, to the visible, i.e., 530nm, by tuning the indium content of the laser GaInN quantum well. Advantages of using Plasma assisted MBE (PAMBE) compared to more conventional MOCVD epitaxy to grow AlGaInN laser structures are highlighted. Ridge waveguide laser diode structures are fabricated to achieve single mode operation with optical powers of >100mW in the 400-420nm wavelength range that are suitable for telecom applications. Visible light communications at high frequency (up to 2.5 Gbit/s) using a directly modulated 422nm Galliumnitride (GaN) blue laser diode is reported. High power operation of AlGaInN laser diodes is demonstrated with a single chip, AlGaInN laser diode ‘mini-array’ with a common p-contact configuration at powers up to 2.5W cw at 410nm. Low defectivity and highly uniform GaN substrates allow arrays and bars of nitride lasers to be fabricated. GaN laser bars of up to 5mm with 20 emitters, mounted in a CS mount package, give optical powers up to 4W cw at ~410nm with a common contact configuration. An alternative package configuration for AlGaInN laser arrays allows for each individual laser to be individually addressable allowing complex free-space and/or fibre optic system integration within a very small form-factor.
The latest developments in AlGaInN laser diode technology are reviewed for defence applications such as underwater telecommunications, sensor systems etc. The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v., i.e, 380nm, to the visible, i.e., 530nm, by tuning the indium content of the laser GaInN quantum well. Ridge waveguide laser diode structures are fabricated to achieve single mode operation with optical powers of >100mW in the 400-420nm wavelength range with high reliability. Visible light communications at high frequency (up to 2.5 Gbit/s) using a directly modulated 422nm Gallium-nitride (GaN) blue laser diode is reported. High power operation of AlGaInN laser diodes is also reviewed. We demonstrate the operation of a single chip, high power AlGaInN laser diode ‘mini-array’ consisting of a 3 stripe common p-contact configuration at powers up to 2.5W cw in the 408-412 nm wavelength range. Packaging of nitride laser diodes is substantially different compared to GaAs laser technology and new processes and techniques are required to optimize the optical power from a nitride laser bar. Laser bars of up to 4mm with 16 emitters have shown optical powers up to 4W cw at ~410nm with a common contact configuration. An alternative package configuration for AlGaInN laser arrays allows for each individual laser to be individually addressable allowing complex free-space and/or fibre optic system integration within a very small form-factor.
KEYWORDS: Semiconductor lasers, Gallium nitride, Laser applications, Defense and security, Laser development, Quantum wells, High power lasers, Near field optics, Thermal effects, Indium
The latest developments in AlGaInN laser diode technology are reviewed. The AlGaInN material
system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v. to
the visible, i.e., 380-530nm, by tuning the indium content of the laser GaInN quantum well. Of
specific interest for defence applications is blue-green laser diode technology for underwater
telecommunications and sensing applications.
Ridge waveguide laser diode structures are fabricated to achieve single mode operation with optical
powers of <100mW in the 400-420nm wavelength range with high reliability. Low defectivity and
highly uniform GaN-substrates allow arrays and bars of nitride lasers to be fabricated. In addition,
high power operation of AlGaInN laser diodes is demonstrated with the operation of a single chip,
‘mini-array’ consisting of a 3 stripe common p-contact at powers up to 2.5W cw in the 408-412 nm
wavelength range and a 16 stripe common p-contact laser array at powers over 4W cw.
The latest developments in AlGaInN laser diode technology are reviewed. The AlGaInN material system allows for laser diodes to be fabricated over a very wide range of wavelengths from u.v. to the visible, i.e., 380-530nm, by tuning the indium content of the laser GaInN quantum well. Ridge waveguide laser diode structures are fabricated to achieve single mode operation with optical powers of >100mW in the 400-420nm wavelength range with high reliability. Low defectivity and highly uniform TopGaN and Ammono GaN-substrates allow arrays and bars of nitride lasers to be fabricated. In addition, high power operation of AlGaInN laser diodes is demonstrated with the operation of a single chip, ‘mini-array’ consisting of a 3 stripe common p-contact at powers up to 2.5W cw in the 408-412 nm wavelength range and a 16 stripe common p-contact laser array at powers over 4W cw.
HVPE crystallization on ammonothermaly grown GaN crystals (A-GaN) is described. Preparation of the (0001) surface of the A-GaN crystals to the epi-ready state is presented. The HVPE initial growth conditions are determined and demonstrated. An influence of a thickness and a free carrier concentration in the initial substrate on quality and mode of growth by the HVPE is examined. Smooth GaN layers of excellent crystalline quality, without cracks, and with low dislocation density are obtained.
Role and influence of impurities like: oxygen, indium and magnesium, on GaN crystals grown from liquid solution under high nitrogen pressure in multi-feed-seed configuration is shown. The properties of differently doped GaN crystals are presented. The crystallization method and the technology based on it (for obtaining high quality GaN substrates) are described in details. Some electronic and optoelectronic devices built on those GaN substrates are demonstrated.
We demonstrate the possibility of fabrication of InGaN laser diode with an extremely thin lower AlGaN cladding (200 nm) by using high electron concentration, plasmonic GaN substrate. The plasmonic substrates were fabricated by one of high-pressure methods – ammonothermal method or multi-feed-seed growth method and have an electron concentration from 5x1019 cm-3 up to 1x1020 cm-3. New plasmonic substrate devices, in spite of their extremely thin lower AlGaN cladding, showed identical properties to these manufactured with traditional, thick lower cladding design. They were characterized by identical threshold current density, slope efficiency and differential gain. Thin AlGaN devices are additionally characterized by low wafer bow and very low density of dislocations (<104 cm-2).
Highly n-doped GaN is a material of a reduced refractive index which may substitute AlGaN as a cladding layer in
InGaN laser diodes. In this study we focus on the determination of the optical absorption and the refractive index of
GaN:O having the electron concentration between 1·1018 - 8·1019 cm-3. Though the measured absorption coefficient for
the highest doped GaN are rather high (200 cm-1) we show, using an optical mode simulation, that you can design a
InGaN laser diode operating in blue/green region with decent properties and low optical losses. We propose to use
relatively thin AlGaN interlayer to separate plasmonic GaN from the waveguide and thus to dramatically reduce the
optical losses.
GaN epilayers were implanted with Eu to fluences of 1×1013 Eu/cm2 and 1×1015 Eu/cm2. Post-implant thermal annealing
was performed in ultra-high nitrogen pressures at temperatures up to 1450 ºC. For the lower fluence effective structural
recovery of the crystal was observed for annealing at 1000 ºC while optical activation could be further improved at
higher annealing temperatures. The higher fluence samples also reveal good optical activation; however, some residual
implantation damage remains even for annealing at 1450 ºC which leads to a reduced incorporation of Eu on
substitutional sites, a broadening of the Eu luminescence lines and to a strongly reduced fraction of optically active Eu
ions. Possibilities for further optimization of implantation and annealing conditions are discussed.
We studied light-current characteristics in InGaN laser diode subjected to aging process. We observed
anomalous behavior consisting in apparent increase of bimolecular recombination constant B. We proposed that
the existence of a carrier escape mechanism proportional to N2 can fully account for this paradox. We show that
it is possible to observe cathodoluminescence contrast in the degraded laser diodes. This contrast has uniform
character through all the area of device. Our laser diodes are also characterized by deep defect center lying 0.82
eV below the conduction band minimum although we don't have yet a direct evidence of the existence of this
level with device degradation.
In the present work we demonstrate a concept of a "weak plasmonic cladding" for the improved transversal optical confinement in the
structures of nitride lasers diodes emitting in the violet and blue spectral region. We show that by using highly doped GaN:O or
GaN:Si layers we can induced the reduction of the refractive index by around 1-2% comparing to a lightly doped material. Such a
material can be effectively used as optical cladding replacing thick, highly strained AlGaN layers. Plasmonic claddings can be grown
by two methods: first of them is High Nitrogen Pressure Solution growth (an introduced donor is an oxygen) and Molecular Beam
Epitaxy with silicon as a donor. In the both cases we can reach a free carrier concentration of up to around 1020cm-3. MOVPE method
so far did not show capabilities for achieving so high doping level. We demonstrate the use of such layers for the construction of the
violet and blue laser diodes and laser diodes mini-arrays showing a total suppression of the substrate mode leakage.
Violet and blue Laser diodes, as well as highly efficient high-power Light Emitting Diodes (including any UV
emitters) can be constructed using low-dislocation-density freestanding GaN substrates, either produced as thick
HVPE layers on foreign substrates, or using direct methods of crystallization as ammonothermal one or high
pressure growth from the nitrogen solution in gallium. This paper shows some of the most most important issues
concerning application of such substrates. The first issue is the choice of the substrate thickness influencing the
accommodation of strain, cracking and bowing of the samples. In this point, a new way of prestressing the
substrate by lateral patterning will be presented. The second issue is the surface preparation either by mechanical
polishing and reactive ion etching, or mechano-chemical polishing, in particular, a distribution of defects
revealed by chemical etching will be discussed. Finally, the problem of substrate misorientation influencing the
further morphology and indium incorporation into InGaN quantum wells will be shown. For higher
misorientation of the substrates, the incorporation of indium decreases , but at the same time, the fluctuations of
indium increase giving blue-shifted, weaker and broader photoluminescence peaks.
Growth of GaN under pressure from solution in gallium results in almost dislocation free plate-like crystals but with size limited to app. 1-2 cm (lateral) and 100 μm (thickness) or up to about 1cm long needles. Deposition of GaN by HVPE on the pressure grown seeds allows stable crystallization (in terms of flatness of the crystallization front and uniformity of the new grown material) at a rate of about 100 μm/h on both types of seed crystals. However, in the thick GaN crystals grown on almost dislocation free plate-like substrates quite a high number of dislocations appears if the crystal thickness exceeds certain critical value. Since the critical thickness for defect generation is of the order of 100 μm, almost dislocation free layers (density below 104 cm-2) thinner than 100 μm can be grown. The most obvious further step is removing the substrate and continuation of the HVPE deposition on the free standing low dislocation density layer of sub-critical thickness. The pressure grown substrates were removed by mechanical polishing or conductivity sensitive electrochemical etching (for strongly n-type substrates). Then the HVPE low dislocation density GaN 1platelets were used as substrates for the growth of a few mm thick bulk GaN crystals. The crystals were characterized by defect selective etching of both polar (0001) and non-polar (10 -10) surfaces to check presence and distribution of structural defects. The X-ray measurements allowed concluding about character of strain and deformation in high pressure GaN-HVPE GaN system.
In this work the results of high pressure solution growth of GaN on various patterned substrates are presented. The growth on GaN/sapphire substrates patterned in GaN parallel stripes and with SixNy and Mo masks between stripes is studied and analyzed. The results are compared with the growth on patterned substrates without any mask, thus with a bare sapphire between stripes. The usefulness of tungsten and iridium for masking is also determined. The HVPE free standing GaN substrates with high stripes, up to 10 mm, are examined in details. The stripes growth modes are shown and described.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.