Concentration dependence of energy relaxation time in AlGaAs/GaAs heterojunctions: direct measurements

Abstract

We present measurements of the energy relaxation time, τ ε , of electrons in a single AlGaAs/GaAs heterojunction in a quasi-equilibrium state using microwave time-resolved spectroscopy at 4.2 K. We find the relaxation time has a power-law dependence on the carrier density of the two-dimensional electron gas, τ ε ∝ n γ s with γ = 0.40 ± 0.02 for values of the carrier density, n s , from 1.6 × 10 11 to 6.6 × 10 11 cm −2 . The results are in good agreement with predictions taking into account the scattering of the carriers by both piezoelectric and deformation potential acoustic phonons. We compare these results with indirect measurements of the energy relaxation time from energy loss measurements involving Joule heating of the electron gas.

Intrinsic limit to low-temperature mobility in semiconductor structures with two-dimensional electrons

“…Thus, the conclusion is confirmed about the dominant role of the piezoelectric scattering in the non-elastic scattering processes in a single GaAs/AlGaAs heterojunction in the temperature region T = 1.6-5 K given by authors of [11,13]. Moreover, once more the evidence of the piezoelectric scattering in these structures at T = 4.2 K is given in [24]. The authors identified piezoelectric scattering as the leading energy relaxation mechanism in the BG regime on the grounds of the excellent agreement between experimental and calculated concentration dependences on the energy relaxation time of electrons in a single GaAs/AlGaAs heterojunction.…”

“…Such dependence was observed experimentally in the range of the 2DEG concentration n s = (1.6-6.6) × 10 11 cm −2 . Additionally, the measured dependence of the energy relaxation time on the dissipated dc power allows the authors of [24] to identify unambiguously the leading mechanism of energy relaxation as piezoelectric scattering.…”

“…1.6, 2.5 and 4.2 K in figure 7. The experimental results from [11,24,30] are shown too. On the whole, we should stress good agreement between experimental data and our calculated concentration dependences of electron mobility.…”

“…The change of the mean electron energy is E = π 2 k 2 T T/3ε F under negligibly low-heating condition T T, T e , where the electron temperature is T e = T + T . Then, in [24], we obtained the following equations for the mean energy relaxation time due to the PA potential…”

“…The measured temperature dependence of the electron cooling rate Qe (T e ) allows identifying the mechanism of inelastic scattering in the temperature regions of interest. However, an adequate understanding of energy relaxation in those structures has not been achieved yet, and experimental data reveal substantial discrepancy, as mentioned in [24].…”