DETERMINATION OF THE LIMITING MOBILITY OF A 2-DIMENSIONAL ELECTRON-GAS IN ALXGA1-XAS GAAS HETEROSTRUCTURES AND DIRECT MEASUREMENT OF THE ENERGY RELAXATION-TIME/

We present results for a method to measure directly the energy relaxat ion time (tau(e)) for electrons in a single AlxGa1-xAs/GaAs heterojunc tion; measurements were performed from 1.6 to 15 K under quasiequilibr ium conditions. We find tau(e) alpha T-1 below 4 K, and tau(e) indepen dent of T above 4 K. We have also measured the energy-loss rate, [Q], by the Shubnikov-de Haas technique, and find [Q]alpha(T-e(3)-T-3) for T less than or equal to 4.2 K; T-e is the electron temperature. The va lues and temperature dependence of tau(e) and [Q] for T<4 K agree with calculations based on piezoelectric and deformation potential acousti c phonon scattering. At 4.2 K, we can also estimate the momentum relax ation time, tau(m), from OUT measured tau(e). This leads to a prelimin ary estimate of the phonon-limited mobility at 4.2 K of mu=3 x 10(7) c m(2)/V s (n(s)=4.2X10(11) cm(-2)), which agrees well with published nu merical calculations, as well as with an earlier indirect estimate bas ed on measurements on a sample with much higher mobility.