The sublimation of GaN is a powerful alternative etching technique to avoid the electrical traps usually induced by dry etching. It is selective towards Al containing alloys such as AlGaN and towards dielectric materials like silicon oxide or silicon nitride so that patterns can be defined to fabricate devices based on GaN/AlGaN heterostructures. In the present work, we report on the fabrication of enhancement mode p-GaN/Al(Ga)N/GaN high electron mobility transistors (HEMTs) with selective area sublimation under vacuum of the p-GaN cap layer used to define the gate. Furthermore, we show that sublimation can be combined with the regrowth of AlGaN, which is a key to increase the maximum drain current in the transistors and enables the co-integration of enhancement mode devices with depletion mode ones.
Deep ultra-violet (DUV) light emitting diodes (LED) are expected to be the next generation of UV sources, offering significant advantages such as compactness, low consumption and long lifetimes. Yet, improvements of their performances are still required and the potential of AlyGa1-yN quantum dots as DUV emitters is investigated in this study. Using a stress induced growth mode transition, quantum dots (QD) are spontaneously formed on Al0.7Ga0.3N/AlN heterostructures grown on sapphire substrates by molecular beam epitaxy. By increasing the QD Al composition, a large shift of the QD photoluminescence in the UV range is observed, going from an emission in the near UV for GaN QD down to the UVC region for Al0.4Ga0.6N QD. A similar behavior is observed for electroluminescence (EL) measurements performed on LED structures and an emission ranging from the UVA (320-340 nm) down to the UVC (265-280 nm) has been obtained. The main performances of Al0.7Ga0.3N based QD LED are presented in terms of electrical and optical characteristics. In particular, the emission dependence on the input current density, including the emitted wavelength, the optical power and the external quantum efficiency are shown and discussed.
The optical performance of red-light emitters grown along polar orientation InGaN/(In)GaN multiple quantum well (MQW) with semi-polar structure are examined and compared.
Given a colour of the emitted light, time-resolved photoluminescence (TRPL) measurements show a large difference of decay times between polar and semi-polar structures, when temperature varies in 8 K to 300 K range. The TRPL results evidence a weak internal electric field for the semi-polar structure as the decay time in this structure is slightly wavelength-dependent and is, at a given wavelength, two orders of magnitude smaller than for the polar sample.
The Auger non-radiative recombination is probed by the evolution of the PL intensity with changing photo-excitation power density. In the semi-polar structure, the Auger non-radiative recombination is observed at a threshold PT of photo-excitation density 200 times smaller than in the polar oriented sample. This observation is linked to the difference in efficiency of the localization effect ( different indium compositions) and impact of the quantum confined Stark effect (QCSE) for polar and semi-polar samples. Both localization effect and the QCSE facilitate the establishment of carrier-carrier repulsions before the radiative recombination of electrons and holes occurs. This favor Auger non-radiative recombination process and hence leads to the decrease of the IQE. The smaller threshold PT of the semi-polar oriented structure indicates that the QCSE dominates the reduction of the IQE at high injection level rather than the localization. The semi-polar oriented structure is one promising structure for growth red-light emitters with strong luminescence.
Despite an already existing abundant literature dedicated to report of lot of experimental investigations towards the understanting of the mechanisms that rule the limitation of intense light emission in nitride-based heterostructures, there are still some issues that are not fully elucidated. This is probably related to the lack of investigations away from the blue and aquamarine light regions. In this communication we cover the 480 nm to 620 nm range by using a series of samples with different designs: single and multiple GaInN-GaN quantum wells. This paper is limited to heterostructures grown along the polar orientation. By changing the well width, and the indium content we could tune in the one hand the Quantum Confined Stark Effect that is to say the intrinsic radiative recombination rate while we could tune the crystalline quality by using strain-compensated GaInN-GaN-AlGaN designs. Finally, by changing our optical pump density we modified the intrinsic non radiative Auger. Given an emission wavelength, we find that the photoexcitation density P for the onset of substantial Auger effect to increase with the number of wells. Using an ABC-type modelling we find a clear 3/2 power law correlation between parameters B and C. This behavior is discussed in terms of electron-hole coulomb interaction and electron-electron repulsion in photo-excited samples. In condition of efficient Auger recombination, the variation of the internal quantum efficiency with photoexcitation density is ruled by a universal power law independent of the design: IQE = IQE0 – a log10 P with a =16 %cm2/Watt.
We present an investigation of optical properties of yellow light emitting (Ga,In) N-based devices grown by metalorganic vapor phase epitaxy (MOVPE) on c-plane sapphire with different designs: well width, indium composition up to 23 percent in the well layer. Using time-resolved photoluminescence measurements collected in range of 8-300K, temperature – dependent photoluminescence decays are determined, they exhibit similar behaviors for all samples. These quantum devices always display a two-mode exponential decay with a long decay time and a short one in a ratio about four to five. The photoluminescence intensities measured from low temperature to room temperature give large values of activation temperature that indicate the increasing of the non-radiative recombination rate when the temperature increases. The average decay times are found by a procedure using fitting sigmoidal functions. These decay times increase exponentially with the indium concentration and the well width due to influence of quantum confined Stark effect on these devices. Finally, in order to estimate the performances of our samples, we plotted the decay times obtained versus product of the indium content and the well width together with others published decay times.
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