Si doping effect on strain reduction in compressively strained Al0.49Ga0.51N thin films

Evaluation of the structural properties of 200-nm-thick Si-doped ${\mathrm{Al}}_{\text{0.49}}{\mathrm{Ga}}_{\text{0.51}}\mathrm{N}$ films, grown on nominally relaxed 1-μm-thick ${\mathrm{Al}}_{\text{0.62}}{\mathrm{Ga}}_{\text{0.38}}\mathrm{N}$ buffer layers on sapphire, revealed that increased Si doping promoted the relaxation of the compressively strained layers. The degree of strain relaxation $R$ of the ${\mathrm{Al}}_{\text{0.49}}{\mathrm{Ga}}_{\text{0.51}}\mathrm{N}$ films, as determined by x-ray diffraction (XRD), increased from $\text{R=0.55}$ to $\text{R=0.94}$ with an increase in disilane injection from 1.25 nmol/min to 8.57 nmol/min. Transmission electron microscopy analysis showed that the edge threading dislocations (TDs) in the ${\mathrm{Al}}_{\text{0.49}}{\mathrm{Ga}}_{\text{0.51}}\mathrm{N}$ layers were inclined, such that the redirected TD lines had a misfit dislocation component. The calculated strain relaxation due to the inclined TDs was in close agreement with the values determined from XRD. We propose that the TD line redirection was promoted by the Si-induced surface roughness.