Thermal-noise temperature in GaAs-AlGaAs heterojunctions

The theory of hot-electron thermal noise in quasi-two-dimensional systems under a strong de electric field proposed by LEI et al.([4]) is extended to the case of multi-subband occupations. As an example, we use this extended method to calculate the thermal-noise temperature of GaAs-AlGaAs heterojunction systems at different de electric fields including the contributions of the lowest and next lowest subbands. We find that, in comparison with the results of the one-subband theory, the inclusion of a higher subband yields an electron density-dependent decrease 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 systems is a sufficiently good approximation in the case of sufficiently low electron densities not only for common transport problems but also for thermal noise.