Infrared quenching of persistent photoconductivity in GaAs/${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As heterostructures

Carrier number density and conductance measurements on GaAs/${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As heterostructures for 2<T<77 K confirm there is an infrared-induced (ir, hν<0.7 eV) quenching of persistent photoconductivity (PPC) in samples with x=0.30, 0.23, and 0.21. This is observed in both ungated and gated heterostructures with small gate biases. Measurements of de Haas–Shubnikov (dHS) oscillations show a decrease (relative to the PPC state) of the two-dimensional electron number density from the ir illumination, accompanied by increases in the dHS oscillation amplitude and the carrier scattering lifetime when the ${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As layer is not fully depleted. Together with shifts of the transconductance peak gate voltage and threshold voltage during ir quenching, the data establish that the decay in PPC is dominated by the capture of ir-excited free electrons back to deep centers in the ${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As layer. The capture-cross-section value estimated from the data is about ${10}^{\mathrm{-}20}$ ${\mathrm{cm}}^2$, which agrees with a calculation based on the energy of the ir-excited free electrons and the deep-trap-capture barrier height and decay prefactor. Data from gated samples show a gate electric field effect, where ir quenching (low electric fields) changes to ir enhancement (strong electric fields). This is discussed in terms of an electric-field-induced decrease in the optical threshold of emission from DX centers.