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.
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.
The oxidation of semiconductors is a fundamental building block of many modern electronic devices. The prime example is the oxidation of silicon into silicon dioxide, which is used as a gate dielectric, waveguides, masking layer, and a device isolation layer. The ability to form an analogous stable and insulating oxide in III-nitride semiconductors would enable a new generation of III-nitride-based electronic and optoelectronic devices. Here we present data on the conversion of thick (>100 nm) AlInN epitaxial layers into oxides with H 2 O vapor in an N 2 carrier gas (wet oxidation) at elevated temperatures (900 °C). The Al x In 1−x N layers are grown on and latticed-matched (x = 0.82) to GaN layers. The oxide can be formed over its entirety or selectively by patterning the surface. The conversion to an oxide is confirmed and characterized by atomic force microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, spectroscopic ellipsometry, and electrical measurements. The oxide is smooth and crystalline, has a low index of refraction of ∼1.8 in the visible, and exhibits very high resistivity of >10 14 Ω•cm.
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