Anomalous Temperature dependence of Fermi-edge Singularity in Modulation-doped AlGaAs/InGaAs/GaAs hetero-structures

Abstract

The temperature and power dependence of Fermi-edge singularity (FES) in highdensity two-dimensional electron gas, specific to pseudomorphic Al x Ga 1-x As/In y Ga 1y As/GaAs heterostructures is studied by photoluminescence (PL). In all these structures, there are two prominent transitions E 11 and E 21 considered to be the result of electronhole recombination from first and second electron sub-bands with that of first heavy-hole sub-band. FES is observed approximately 5 -10 meV below the E 21 transition. At 4.2 K, FES appears as a lower energy shoulder to the E 21 transition. The PL intensity of all the three transitions E 11 , FES and E 21 grows linearly with excitation power. However, we observe anomalous behavior of FES with temperature. While PL intensity of E 11 and E 21 decrease with increasing temperature, FES transition becomes stronger initially and then quenches-off slowly (till 40K). Though it appears as a distinct peak at about 20 K, its maximum is around 7 -13 K.