Anomalous Temperature dependence of Fermi-edge Singularity in Modulation-doped AlGaAs/InGaAs/GaAs hetero-structures
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Anomalous Temperature dependence of Fermi-edge singularity in modulationdoped AlGaAs/InGaAs/GaAs hetero-structures K. Gopalakrishna Naik, K.S.R.K. Rao1 , T. Srinivasan2 , R. Muralidharan2 and S. K. Mehta2 Department of physics, Indian Institute of Science, Bangalore 560 012, India. 1 Email address of corresponding author: [email protected] 2 Solid State Physics Laboratory, Lucknow Road, Delhi-110 054, India. ABSTRACT The temperature and power dependence of Fermi-edge singularity (FES) in highdensity two-dimensional electron gas, specific to pseudomorphic Alx Ga1-x As/Iny Ga1y As/GaAs heterostructures is studied by photoluminescence (PL). In all these structures, there are two prominent transitions E11 and E21 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 E21 transition. At 4.2 K, FES appears as a lower energy shoulder to the E21 transition. The PL intensity of all the three transitions E11 , FES and E21 grows linearly with excitation power. However, we observe anomalous behavior of FES with temperature. While PL intensity of E11 and E21 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. INTRODUCTION The FES is a many-body enhancement of optical spectra that originates from the response of a degenerate two-dimensional electron gas (2DEG) to the photogeneration or annihilation of a localized hole. This interaction results in an enhanced oscillator strength for electrons near the Fermi surface recombining with photogenerated hole. Skolnick et al. [1] were the first to report FES in the optical spectra from the two-dimensional semiconductor system in photoluminescence (PL) from modulation-doped InGaAs/InP quantum wells (QWs). Since then FES has been widely investigated in modulation-doped Alx Ga1-x As/GaAs [2] and Alx Ga1-x As/Iny Ga1-y As/GaAs [3-5] QWs by PL. It has been shown theoretically that for the observation of FES in optical spectra requires an abrupt Fermi-surface and a strong overlap of both the wave functions of spatially separated electrons and holes to ensure effective electron-hole interaction [6-14]. The existing theoretical models predict that FES can be largely suppressed by any broadening mechanisms, such as temperature. There are several experimental results that are not fully understood within the existing theoretical framework [2,6]. In this paper, we present the PL measurements on two sets of silicon delta-doped Alx Ga1-x As/Iny Ga1-y As/GaAs pseudomorphic hetero-structures having different densities
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of 2DEG. In all these samples, there are two prominent transitions E11 and E21 (considered to be the result of electron-hole recombination from first and second electron sub-bands with that of first heavy-hole sub-band) indicating that both first and second electron sub-bands
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