THERMAL-NOISE TEMPERATURE IN GAAS-ALGAAS HETEROJUNCTIONS

The theory of hot-electron thermal noise in quasi-two-dimensional syst ems under a strong de electric held proposed by LEI et al.([4]) is ext ended to the case of multi-subband occupations. As an example, we use this extended method to calculate the thermal-noise temperature of GaA s-AlGaAs heterojunction systems at different de electric fields includ ing the contributions of the lowest and next lowest subbands. We find that, in comparison with the results of the one-subband theory, the in clusion of a higher subband yields an electron density-dependent decre ase of the electron temperature and the thermal-noise temperature and a reduction of the cooling effect. The numerical results also confirm the fact that considering only the lowest subband of heterojunction sy stems is a sufficiently good approximation in the case of sufficiently low electron densities not only for common transport problems but als o for thermal noise.