Photoluminescence studies of 〈100〉 and 〈111〉 In x Ga 1 − x A s / G a A s single quantum wells under hydrostatic pressure

We report the results of a pressure study of strained ${\mathrm{In}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ thin single quantum wells (QW's) grown along [100] and [111] directions. The 〈100〉-grown QW exhibits the expected two-slope behavior with a pressure coefficient of $\ensuremath{\partial}E/\ensuremath{\partial}P=10.3\ifmmode\pm\else\textpm\fi{}0.1\mathrm{m}\mathrm{e}\mathrm{V}/\mathrm{k}\mathrm{b}\mathrm{a}\mathrm{r}$ for the direct emission. The observation of a type-II crossover yields a valence-band offset for the [100] of 0.060 eV. In contrast, the 〈111〉-grown quantum well exhibits an unusual three-slope pressure behavior. We find a pressure coefficient of $\ensuremath{\partial}{E}_{111}/\ensuremath{\partial}P=10.1\ifmmode\pm\else\textpm\fi{}0.3\mathrm{m}\mathrm{e}\mathrm{V}/\mathrm{k}\mathrm{b}\mathrm{a}\mathrm{r}$ for the direct emission. Excitation intensity studies assist in the identification of above crossover emissions which imply a large valence-band discontinuity for the 〈111〉 QW of $\ensuremath{\approx}100\mathrm{meV}.$