We report a significant increase in electroluminescence from GaSb based mid-wave infrared
inter band cascade (IC) LED device through coupling with localized surface plasmon layer. Thin
Au Plasmon layer of 20 nm thickness is deposited on top anode electrode by e-beam evaporation
technique. Surface Plasmon enhancement effects result is 100% increase in light output for 50
μm square mesa device. We fabricated an IC LED device with nine cascade active/injection
layers with InAs/Ga1-xInxSb/InAs quantum well (QW) active region.
We report here the electroluminescence in the range of 3-4.5 μm and 6-10 μm from
Sb-based type II interband quantum cascade structure LED devices. We measured the light
emission from the top surface of the device with different grating structures. We used
different etch depths for the grating formation. The light-current-voltage (LIV)
characteristics measured at both room and cryogenic temperatures show that the device
with 45 degree angle grating and 1.0 μm deep etch onto the GaSb surface has the highest
emission power.
Authors report the demonstration of the emission wavelength tuning of InAs quantum-dashes within InAlGaAs
quantum-wells grown on InP substrate, that gives the initial wavelength emission at ~1.65 &mgr;m. The impurity-free
dielectric cap annealing and the nitrogen ion-implantation induced intermixing techniques have been implemented to
spatially control the group-III intermixing in the structure, which produces differential bandgap shift of 80 nm and 112
nm, respectively. Transmission electron microscopy, optical and electrical characterizations have been performed to
evaluate the quality of the intermixed QD material and bandgap tuned devices. Compared to the control (nonintermixed)
lasers, the light-current characteristics for the over 125 nm wavelength shifted QD lasers are not
significantly changed suggesting that the quality of the intermixed material is well-preserved. The intermixed lasers
exhibit the narrow linewidth as compared to the as-grown due to the improved QD homogeneity. The integrity of the QD
material is retained after intermixing suggesting the potential application for the planar integration of multiple
active/passive QD-based devices on a single InP chip.
High Speed Multi-Channel Fiber-Optic Transmitter (Tx) and Receiver (Rx) modules are needed for communication Applications. The fiber optic network should take advantage of the high speeds (10 Gbps/channel) and have the ability to connect multiple systems using fiber-optic network capable of working with 100’s of Gigabits of information. In addition, the network should provide redundant links between nodes so that in case one node goes out of service, the remainder of the network remains operational. In this paper we will present design, development and performance results for 1x12 Tx and Rx module operating at 10Gbps/channel. Each of the 1x12 modules is capable of providing 120 Gbps/Module operations for Military and Commercial Applications. Experimental results on 1x12 channel modules will include performance characteristics at 10 Gbps and will demonstrate high performance fiber-optical Tx and Rx Modules. We will also present architecture and simulation for a Fiber-Optic Network Card that has the capability to transmit and receive data, add and drop data at each node, and provide dual network redundancy. This network card includes Tx, Rx modules, serializer and de-serializer (SERDES) and a cross bar switch. This architecture can be used as a building block for high-speed local area network applications and also applicable to optical backplanes for distributed microprocessor communication.
Two-dimensional (2-D) multi-channel 8x8 optical interconnect and processor system were designed and developed using complementary metal-oxide-semiconductor (CMOS) driven 850-nm vertical-cavity surface-emitting laser (VCSEL) arrays and the photodetector (PD) arrays with corresponding wavelengths. We performed operation and bit-error-rate (BER) analysis on this free-space integrated 8x8 VCSEL optical interconnects driven by silicon-on-sapphire (SOS) circuits. Pseudo-random bit stream (PRBS) data sequence was used in operation of the interconnects. Eye diagrams were measured from individual channels and analyzed using a digital oscilloscope at data rates from 155 Mb/s to 1.5 Gb/s. Using a statistical model of Gaussian distribution for the random noise in the transmission, we developed a method to compute the BER instantaneously with the digital eye-diagrams. Direct measurements on this interconnects were also taken on a standard BER tester for verification. We found that the results of two methods were in the same order and within 50% accuracy. The integrated interconnects were investigated in an optoelectronic processing architecture of digital halftoning image processor. Error diffusion networks implemented by the inherently parallel nature of photonics promise to provide high quality digital halftoned images.
8×8 parallel-channeled optical interconnect systems operating at 1 Gbits/s per channel were designed and developed using complimentary metal-oxide-semiconductor (CMOS) circuits driven 850-nm vertical-cavity surface-emitting laser (VCSEL) arrays and the corresponding photodetector arrays. Low operating threshold and voltage were adapted and facilitated in the design and fabrication of VCSELs and photodetectors in order to achieve the low-power consumption for the entire system. The driver and receiver circuits were fabricated on transparent sapphire substrates using 0.5-μm ultra-thin silicon-on-sapphire (SOS) technology and subsequently flip-chip bonded with corresponding VCSEL and photodetector arrays. The VCSEL transmitter and photoreceiver arrays were biased at 3.3 V and optically coupled in a free-space configuration using compound lens systems. Data communications at bandwidth up to 1.0 Gb/s for each single channel were characterized. Bit-error-rate (BER) was measured to be better than 10-9 from the eye diagrams. Such interconnect systems were also demonstrated for optical data processing using diffractive optical elements.
Finite difference analysis was used to determine the thermal characteristics of continuous wave (CW) 850 nm AlGaAs/GaAs implant-apertured vertical-cavity surface-emitting lasers. A novel flip-chip design was used to enhance the heat dissipation. The temperature rise in the active region can be maintained below 40 °C at 4 mW output power with 10 mA current bias. In contrast, the temperature rise reaches above 60 °C without flip-chip bonding. The transient-temperature during turn-on of a VCSEL was also investigated. The time needed for the device to reach the steady-state temperature was in the range of a few tenths of a milli-second, which is orders of magnitude larger than the electrical or optical switch time. Flip-chip bonding will reduce the shift of the wavelength, peak power, threshold current and slope efficiency during VCSEL operations.
The design of the next generation of vertical-cavity surface-emitting lasers (VCSELs) will greatly depend on the availability of accurate modeling tools. Comprehensive models of semiconductor lasers are needed to predict realistic behavior of various laser devices, such as the spatially nonuniform gain that results from current crowding. Advanced physics models for VCSELs require benchmark quality experimental data for model validation. This paper presents preliminary results of a collaborative effort at ARL to fabricate and experimentally characterize test optoelectronic structures and VCSEL devices, and at CFDRC to develop comprehensive multiphysics modeling, design and optimization tools for semiconductor lasers and photodetectors. Experimental characterization procedure and measurements of optical and electrical data for oxide-confined intracavity VCSELs are presented. A comprehensive multiphysics modeling tools CFD-ACE+ O’SEMI has been developed. The modeling tool integrates electronic, optical, thermal, and material gain data models for the design of VCSELs and edge emitting lasers (EELs). This paper presents multidimensional simulation analysis of current crowding in oxide-confined intracavity VCSELs. Computational results helped design the test structures and devices and are used as a guide for experimental measurements performed at ARL.
A high-bandwidth, free-space integrated optoelectronic interconnect system was built for high-density, parallel data transmission and processing. Substrate-emitting 980 nm vertical-cavity surface-emitting laser (VCSEL) arrays and photodetector arrays, both driven by complimentary metal- oxide-semiconductor (CMOS) circuitry, were employed as a transmitter and receiver. We designed, fabricated, hybridized, and packaged the VCSEL transmitter and photoreceiver arrays. Data rates above 1 Gbs for each channel on the VCSEL/CMOS emitter and 500 MHz for each channel on photoreceiver were measured, respectively. We integrated the optical interconnects using free-space optical alignment and demonstrated serial and parallel transmissions of digital data and video images.
A free-space integrated optoelectronic interconnect was built to explore parallel data transmission and processing. This interconnect comprises an 8 X 8 substrate-emitting 980-nm InGaAs/GaAs quantum-well vertical-cavity surface- emitting laser (VCSEL) array and an 8 X 8 InGaAs/InP P-I- N photodetector array. Both VCSEL and detector arrays were flip-chip bonded onto the complimentary metal-oxide- semiconductor (CMOS) circuitry, packaged in pin-grid array packages, and mounted on customized printed circuit boards. Individual data rates as high as 1.2 Gb/s on the VCSEL/CMOS transmitter array were measured. After the optical alignment, we carried out serial and parallel transmissions of digital data and live video scenes through this interconnect between two computers. Images captured by CCD camera were digitized to 8-bit data signals and transferred in serial bit-stream through multiple channels in this parallel VCSEL-detector optical interconnect. A data processing algorithm of edge detection was attempted during the data transfer. Final images were reconstructed back from optically transmitted and processed digital data. Although the transmitter and detector offered much higher data rates, we found that the overall image transfer rate was limited by the CMOS receiver circuits. A new design for the receiver circuitry was accomplished and submitted for fabrication.
The presentation gives an overview of the ongoing Army Research Laboratory (ARL)/University of Maryland research effort on vertical-cavity-surface-emitting-laser (VCSEL) interconnects and OE processing and why this technology is of interest. ARL is conducting a research and development effort to develop VCSELs, VCSEL arrays, and their hybridization with complimentary metal-oxide-semiconductor (CMOS) electronics and microwave monolithic integrated circuits (MMICs). ARL is also very active in the design, modeling, and development of diffractive optical elements (DOEs). VCSEL-CMOS flip-chip optoelectronic circuits and DOEs are of interest together with detector-CMOS flip-chip circuits to provide digital and analog optoelectronic interconnects in optoelectronic processing architectures. Such optoelectronic architectures show promise of relieving some of the information flow bottlenecks that are emerging in conventional digital electronic processing as the electronic state of the art advances at a rapid pace and the electronic interconnects become a significant limitation. Such optoelectronic interconnects are also of interest in the development of analog optoelectronic processing architectures that are very difficult to implement in conventional electronic circuitry due to the incorporation of dense arrays of interconnects between electronic elements. VCSEL-MMIC- detector flip-chip circuits are of interest for the incorporation of optoelectronic interconnects into analog RF systems where the optoelectronic interconnect offers advantages of size, weight, bandwidth, and power consumption. VCSEL-MMIC interconnects may also play a role in future high- speed digital optoelectronic processing.
KEYWORDS: Vertical cavity surface emitting lasers, Sensors, Photodetectors, Signal detection, Optoelectronics, Optical interconnects, Modulation, Signal attenuation, Detector arrays, Chemical elements
We demonstrate an optoelectronic interconnect based on an 8 by 8 array of vertical-cavity surface-emitting lasers, an 8 by 8 array of photodetectors, and a single compound lens. The substrate-emitting VCSEL array and back-illuminated photodetector array were flip-chip bonded to a CMOS driver circuit and a Si fan-out pad array, respectively. The CMOS driver provides laser addressing, signal conditioning and modulation current.In this paper we will describe the interconnect configuration, device structures and characteristics, and CMOS driver circuits. We then discuss the system operation and performance.
Corrugated quantum well infrared photodetectors (C-QWIPs) use total internal reflection to couple normal incident light into the detectors. In this work, we report the performance of C- QWIPs at different wavelengths. Compared with 45 degrees edge coupling, a C-QWIP increases the background photocurrent to dark current ratio rI by a factor between 2.4 and 4.4, thereby increasing the background-limited temperature by 3 to 5 K. The detectivity D* is increased by a factor of 2.4. We applied the C-QWIP to two-color detection and obtained precision thermometric measurements. We have also fabricated and characterized a 256 X 256 C-QWIP array with cutoff wavelength at 11.2 micrometer. The uncorrected nonuniformity ((sigma) /mean) in the central 128 X 128 subarray is 2.3%. The NE(Delta) T at 63 K is estimated to be 23 mK. Furthermore, we have shown that rI can be further increased by fabrication of the C-QWIP into the corrugated hot-electron transistor structure. The enhanced performance of the corrugated structure, combined with its simple processing steps, greatly improves the QWIP technology.
A new light coupling geometry for quantum well infrared photodetectors (QWIP), which is referred as the corrugated- QWIP or the C-QWIP, has been demonstrated. The coupling scheme is based on the total internal reflection at a number of slanted sidewalls created within a detector pixel. The structure was found to be able to couple normal incident light efficiently into the detector with concomitant reduction in the dark current. For a C-QWIP with thinned substrate, the background photocurrent to the dark current ratio is improved by a factor of 4.9 compared with the edge coupling. The coupling scheme does not show significant wavelength and size dependence, and is therefore suitable for multi-color or high resolution thermal imaging. With these characteristics, a C- QWIP behaves as a detector with normal incident absorption. Because of its simple fabrication procedures, the manufacturability of the detector arrays can be greatly improved.
New I-line resists are claimed to be usable at 0.35 micrometers design rules. We have examined the suitability of several such materials (JSR IX750, Sumitomo PFi-38a, OCG RX64I) for this purpose and compared them with our production 0.5 micrometers resist, JSR IX700. A variety of criteria have been used, including the measured focus exposure windows at e-min and e-max, DOF vs. CD for grouped and isolated lines as well as contacts, linearity, and proximity response as a function of pitch. A limited study has been done on the impact of embedded phase shift reticles on printing small geometry contacts. We report upon the process improvements observed with two different reticle transmissions, their impact on isofocal bias, as well as the issue of sidelobe formation. Proponents of DUV claim that modern DUV materials exhibit significant advantages in terms of process window and more over are applicable to smaller geometries without the need for supplementary techniques such as phase shifting or modified illumination. In this study, we have examined the performance of a number of DUV materials (BASF ST3.5, OCG ARCH, JSR KRFL2 and an as yet experimental JSR resists) on ASM-L and Nikon excimer laser steppers. Limited results were also obtained using Shipley 2408 and dyed XP-9444 (0.8) on the SVG Micrascan II. Our studies conclude with a comparison of the CD swing observed over a variety of chemically mechanically planarized steps. This has been done for selected I-line and DUV resists with the aid of a TAR or BARC or as in the case of the broad band SVG system either a BARC or a dyed resist.
The physics and application of the intersubband transitions in GaAs/AlGaAs quantum well superlattice structures have been under intense investigation in recent years. In this report, theoretical design and experiment of three GaAs/AlGaAs quantum well superlattice samples are given in detail. The samples are grown by MBE technique on semi-insulating GaAs substrate. The three samples have different growth parameters and therefore different energy band structures. The transitions have bound to bound and bound to continuum states. Fourier Transform Infrared (FTIR) spectra and the infrared photoelectron tunneling (IPET) spectra are measured and the results agree well with each other and with the calculations.
We present a systematic theoretical and experimental study on wavelength tuning and absorption lineshape of single bound state quantum well infrared photodetectors. We found that the absorption energy is determined by the energy level structure above the barriers as well as the shape of the quantum well ground state wave function. We calculated the absorption lineshape and show that it depends sensitively on the position of the final state relative to the global band structure of the detector. Using a quantum barrier as an electron energy high pass filter to discriminate against the lower energy dark current, we are able to increase the detectivity of the detector. The new device is referred as an IR hot-electron transistor. Its potential advantages in focal plane array applications will be discussed.
We report the first photoreflectance measurement of strain-induced piezoelectric field in a (111)B InGaAs/GaAs structure. The InGaAs quantum well was pseudomorphically grown in the undoped regions of a GaAs undoped-heavily doped structure. Four structures, two each with the same layer structures but different orientation, (111)B and (100), were used in this study. The electric fields in the undoped GaAs region were measured by Franz-Keldysh oscillations in photoreflectance. All the samples have a surface barrier height of about 0.7 eV. However, the measured electric field is 30% stronger in the (111)B sample compared to the (100) sample. We attribute this difference to the strain induced electric field in the (111)B sample. The piezoelectric field in (111)B strained In0.15Ga0.85As obtained in this measurement is 2.2 +/- 0.5 X 105 V/cm, which agrees very well with theory.
A process was developed for the fabrication of high power GaAs
photoconductive switches with ohmic Ni/Ge/Au contact metallization in a lateral NIN switch configuration. The main features of the process
were ion implanted silicon in the contact regions and rapid thermal
processing for annealing the implants and alloying the metallization.
A 50 mill dia. process wafer included 28 photolithographically defined
switches of four different types to comparatively investigate the
effects of ohmic contacts and switch dimensions on switch lifetime,
together with monitors to characterize the ohmic contact process.
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