HOT-ELECTRON NOISE AND DIFFUSION IN ALGAAS/GAAS

The electric field dependence of the microwave noise temperature and the diffusion coefficient are found to be significantly different for two sets of AlGaAs/GaAs structures with different spacer thickness and aluminium mole fraction. In the samples with a 'wide' quantum well (QW), one maximum of the diffusion coefficient is observed at fields below the threshold for the intervalley diffusion, but two maxima are characteristic of a 'narrow' QW with an intersubband gap wider than the k(B)T0. A microscopic explanation of the observed noise spectra of AlGaAs//GaAs is given and used to determine kinetic parameters of the heterostructures.