Electrical properties of undoped ${\mathrm{Ga}}_{\mathit{x}}$${\mathrm{In}}_{1\mathrm{-}\mathit{x}}$P/GaAs quantum wells

We report a study of ${\mathrm{Ga}}_{\mathit{x}}$${\mathrm{In}}_{1\mathrm{-}\mathit{x}}$P/GaAs in very thin quantum wells. Our samples are not intentionally doped; nevertheless, we observed that exposing this structure to red light induces a photocurrent which is persistent at low temperatures. This is accompanied by an increase in the carrier concentration, the Hall mobility, and the quantum scattering time. Since the shallow donor concentration in the ${\mathrm{Ga}}_{\mathit{x}}$${\mathrm{In}}_{1\mathrm{-}\mathit{x}}$P layers is too low to produce the observed concentration, the persistent photocarriers cannot be produced by DX-like defects. We suggest that the persistent carriers are produced by photoionization of deep intrinsic donors in the ${\mathrm{Ga}}_{\mathit{x}}$${\mathrm{In}}_{1\mathrm{-}\mathit{x}}$P barrier layer. Extended illumination also induces a parallel conduction path. In the case of an infinite barrier height, theoretical studies predict that in thin quantum wells such as ours, interface roughness is the dominant low-temperature scattering mechanism and that the mobility in these wells should vary as ${\mathit{L}}^6$ where L is the well width. In the case of a finite barrier height, theoretical studies predict that the mobility will not depend as strongly on L. Our measured mobilities follow an ${\mathit{L}}^{1.3}$ dependence, resulting in higher mobilities and supporting what is predicted theoretically. As predicted, we believe that this dependence is due to the finite barrier height of the quantum well. The barrier height affects how much of the electron wave function penetrates into the barrier and hence influences how interface roughness scattering affects the mobility. © 1996 The American Physical Society.