Electronic properties of ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$Sb/InAs quantum wells

We have studied the electronic properties of ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$Sb/InAs quantum wells, including the negative persistent photoconductivity effect, the magnetic-field-induced semimetal-to-semiconductor transition, and the sources of electron accumulation. We have also demonstrated that the negative persistent photoconductivity effect observed in these quantum wells can be used as a tool to investigate not only the electron-density dependence of the semimetal-to-semiconductor transition but also the alloy dependence of ionized deep donors in the ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$Sb barrier layers. We found that negative persistent photoconductivity is a general property in this quantum-well system and the saturated reduction of the electron density due to the negative persistent photoconductivity effect increases with Al composition. From the alloy dependence of the electron density, we believe that the electrons removed from the InAs well after the illumination are captured by the ionized deep donors in the ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$Sb layer, and that the deep donor level is not the only source of electron accumulation in the InAs well.