Optical control of the two-dimensional electron-gas density in single asymmetric quantum wells: Magnetic-field effect

The effect of a magnetic field on the optical-assisted charge-transfer mechanism in a ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}}_{1-x}{\mathrm{Al}}_x\mathrm{As}$ single asymmetric quantum well (SAQW) is investigated. In a 150-Å-thick asymmetric quantum well the maximum photoluminescence blueshift observed at low temperature (2 K) was 10.3 meV at zero field (9.0 meV at 2.53 T). The flat-band condition of the SAQW under zero field is achieved at 0.1 ${\mathrm{W}/\mathrm{c}\mathrm{m}}^2$ while 1 ${\mathrm{W}/\mathrm{c}\mathrm{m}}^2$ is required to reduce the two-dimensional electron-gas (2DEG) density from $4\times {10}^{11}{\mathrm{cm}}^{\mathrm{-}2}$ down to zero at 2.53 T. The difference in the maximum blueshift is discussed in terms of the field dependence of the 2DEG density, while the difference in the optical excitation required for the saturation condition is explained in terms of inter-Landau-level transition mediated by acoustic phonons.