Data are presented on strain compensation in InGaN-based multiple quantum wells (MQW) using AlGaN interlayers (ILs). The MQWs consist of five periods of InxGa1-xN/AlyGa1-yN/GaN emitting in the green (λ ∼ 535 nm ± 15 nm), and the AlyGa1-yN IL has an Al composition of y = 0.42. The IL is varied from 0 - 2.1 nm, and the relaxation of the MQW with respect to the GaN template layer varies with IL thickness as determined by reciprocal space mapping about the (202¯5) reflection. The minimum in the relaxation occurs at an interlayer thickness of 1 nm, and the MQW is nearly pseudomorphic to GaN. Both thinner and thicker ILs display increased relaxation. Photoluminescence data shows enhanced spectral intensity and narrower full width at half maximum for the MQW with 1 nm thick ILs, which is a product of pseudomorphic layers with lower defect density and non-radiative recombination.
Significant enhancement in green emission by integrating a thin AlInN barrier layer, or interlayer (IL), in an InGaN/GaN multiple quantum well (MQW) is demonstrated. The MQWs investigated here contains 5 periods of an InGaN QW, a 1 nm thick AlInN IL, and a 10 nm thick GaN barrier grown by metalorganic chemical vapor deposition. To accommodate the optimum low-pressure (20 Torr) growth of the AlInN layer a growth flow sequence with changing pressure is devised. The AlInN IL MQWs are compared to InGaN/AlGaN/GaN MQWs (AlGaN IL MQWs) and conventional InGaN/GaN MQWs. The AlInN IL MQWs provide benefits that are similar to AlGaN ILs, by aiding in the formation of abrupt heterointerfaces as indicated by X-ray diffraction omega-2theta (x-2h) scans, and also efficiency improvements due to high temperature annealing schedules during barrier growth. Room temperature photoluminescence of the MQW with AlInN ILs shows similar performance to MQWs with AlGaN ILs, and $4-7 times larger radiative efficiency (pump intensity dependent) at green wavelengths than conventional InGaN/GaN MQWs. This study shows the InGaN-based MQWs with AlInN ILs are capable of achieving superior performance to conventional InGaN MQWs emitting at green wavelengths.
The recombination rates in InGaN/AlGaN/GaN multiple quantum wells (MQWs) emitting in the green-yellow and grown with different Al compositions in the AlGaN interlayer (IL) are shown. By transforming measurements on radiative efficiency, absorption, and differential carrier lifetime, the radiative and nonradiative rates are determined. The IL Al composition controls lattice relaxation of the MQWs, as determined by X-ray reciprocal space mapping, and, therefore, defect formation. For the most pseudomorphic MQWs, the Shockley-Read-Hall (SRH) A coefficient is minimized and is similar to reports at shorter (blue and green) wavelengths. It is an order of magnitude smaller than a conventional InGaN/GaN MQW and is the most significant factor behind the improvement in radiative efficiency using the IL. The radiative B coefficient is also reduced and a minimum for the most pseudomorphic MQWs due to a reduction in the electron-hole wavefunction overlap. However, the decrease in A is more significant and leads to an overall improvement in the radiative efficiency. These recombination rate measurements confirm that if the SRH recombination is controlled, then the severe reduction of radiative recombination with an increased emitting wavelength is one of the main challenges in realizing high efficiency, long-wavelength InGaN-based MQW emitters operating at low to moderate current densities.
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