Temperature dependence of Stokes shift in InxGa1−xN epitaxial layers

Optical properties of ${\mathrm{In}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}$ epitaxial layers with various indium compositions $\text{(x=0.02}\mathrm{,\hspace{0.17em}}\text{0.03}\mathrm{,\hspace{0.17em}}\text{0.05}\mathrm{,\hspace{0.17em}}\text{0.06}\mathrm{,\hspace{0.17em}and}\text{\hspace{0.05em}0.09)}$ have been studied by means of temperature-dependent optical absorption and photoluminescence spectroscopy. A clear peak due to the absorption of ${\mathrm{In}}_x{\mathrm{Ga}}_{\text{1−x}}\mathrm{N}$ ternary alloys was observed up to 300 K, which enabled us to investigate the temperature dependence of the Stokes shift. The Stokes shift at 4 K increased with an increase in the indium composition, and was estimated to be 22 and 45 meV for the samples with $\text{x=0.02}$ and 0.09, respectively. With an increase in temperature up to about 50 K, the Stokes shift increased slightly. With a further increase in temperature from 50 to 100 K, the Stokes shift decreased. Above 100 K, the Stokes shift was independent of the temperature and showed an almost constant value up to 300 K. The Stokes shift at 300 K was estimated to be 19 and 34 meV for the samples with $\text{x=0.02}$ and 0.09, respectively. This temperature dependence of the Stokes shift was characteristically common to all of the samples used in the present work, and was observed to be more prominent for the samples with higher indium compositions.