Microstrain in Al0.22Ga0.78N/GaN heterostructure studied by X-ray diffraction and scattering

Modulation-doped Al0.22Ga0.78N/GaN heterostructure with 1000 Å Si-doped n-Al0.22Ga0.78N barrier (n-AlGaN) were deposited on (0 0 0 1)-oriented sapphire (α-Al2O3) by means of atmosphere-pressure metal-organic chemical vapor deposition. The reciprocal space mappings of symmetric reflection (0 0 0 2) and asymmetric reflection (1 0 1¯ 4) were measured with high resolution X-ray diffraction. The results indicate that the microstructure and strain status of barrier correlate to that of the underlying i-GaN layer. The barrier holds an “abnormal” strain-relaxation status, which probably results from the internal defects of n-AlGaN and the strain relaxation status at the i-GaN/α-Al2O3 interfaces. The results from grazing incidence X-ray diffraction show that the strain in barrier is nonuniform, which is consistent with the results from the reciprocal space mappings.