WARM-ELECTRON POWER LOSS IN GAAS GA1-XALXAS MULTIPLE-QUANTUM WELLS - WELL-WIDTH DEPENDENCE/

We report the observation of the well-width dependence of the two-dime nsional (2D) warm-electron power loss in GaAs/Ga1-xAlxAs quantum wells . Electron-energy-loss rates via the emission of acoustic phonons are determined from the measurements of the amplitudes of Shubnikov-de Haa s oscillations as a function of both lattice temperature and the appli ed electric field. The samples studied have quantum well widths rangin g between L=50 and 145 Angstrom. However, the 2D electron density in a ll the samples studied is kept constant to within 10%. Experimental re sults are compared with the existing theoretical models including a re cent numerical model developed by one of us. All the models include pi ezoelectric and deformation-potential scattering. It is shown that the theoretical models predict a dependence of power loss on electron tem perature and well width which is similar to that observed experimental ly. However, all the models considered fail to estimate the magnitude of the power loss correctly, especially in narrower quantum wells. Thi s suggests that with decreasing confinement length, acoustic phonons b ecome less efficient in cooling electrons than those predicted by the theoretical models. It is argued that this discrepancy may be associat ed with the overestimated piezoelectric component and with the simplif ying assumptions made in the theoretical calculations regarding both t he 2D nature of phonons and the ideal quantum-well approximation in th e extreme quantum limit.