Radiative recombination in GaAs/AlxGa1−xAs quantum wells

An experimental study at room temperature of the rate of radiative recombination in a range of p-type GaAs/${\mathrm{Al}}_{0.33}$ ${\mathrm{Ga}}_{0.67}$As quantum-well samples using both transient photoluminescence (PL) and photoconductivity (PC) techniques is reported. The PL measurements provided the small-signal time constant and the PC measurements probed the nonlinear excitation regime, providing quantitative evidence of excitonic involvement at hole densities less than about 3×${10}^{11}$ ${\mathrm{cm}}^{\mathrm{-}2}$. The intensity dependence of the PC gave the variation of effective mobility with excitation density. This mobility variation was used to successfully relate the PL and PC time constants. These time constants, corrected for photon recycling, had the same values as bulk material over a volume-hole-density range 8×${10}^{16}$ to 3×${10}^{18}$ ${\mathrm{cm}}^{\mathrm{-}3}$, described by a recombination coefficient B=1.8×${10}^{\mathrm{-}10}$ ${\mathrm{cm}}^3$ ${\mathrm{s}}^{\mathrm{-}1}$. A comparison with a theoretical model, which included excitonic effects, photon recycling, and reduced electron-hole overlap in the well, highlighted the importance of the magnitude of the effective density-of-states mass in the valence subbands. Experimental evidence suggests that the latter is 0.32 m, which is over twice the value of the heavy-hole mass at the band edge. For degenerate excited populations the time constant, corrected for photon recycling, was found to be 0.8 ns, which is in reasonable agreement with the theoretical prediction of 0.7 ns.