Microstructures and strain relaxation in modulation-doped AlxGa1-xN/GaN heterostructures

摘要

Modulation-doped Al0.22Ga0.78N/GaN heterostructures with various thickness of Si-doped Al0.22Ga0.78N barrier (n-AlGaN) were deposited on (0001)-oriented sapphire (alpha-Al2O3) by atmosphere-pressure metal-organic chemical vapor deposition (MOCVD). The reciprocal space mappings (RSMs) of symmetric reflection (0002) and asymmetric reflection (10714) were measured by means of the high resolution X-ray diffraction (HRXRD). The results indicate that the microstructures and the strain status of the n-AlGaN barrier correlate to those of the underlying i-GaN layer. The strained n-AlGaN barrier starts to relax when its thickness is 75 nm. It is found that there exists an "abnormal" relaxation state (the strain parameter gamma > 1) in modulation-doped Al0.22Ga0.78N/GaN heterostructures, which maybe results from-the internal defects in Al0.22Ga0.78N barrier and the strain relaxation status at the i-GaN/alpha-Al2O3 interfaces.