Effects of the non equilibrium phonons and the band non parabolicity on the small signal high frequency AC mobility in narrow gap semiconductors in the extreme quantum limit at low temperatures

摘要

The small signal high frequency ac mobility of the hot electrons in n-HgCdTe and n-InSb has been calculated in the extreme quantum limit at low temperatures considering the non equilibrium phonon distribution as well as the thermal phonon distribution. The energy and the momentum losses of the carriers have been considered due to acoustic phonon scattering via deformation potential and piezoelectric coupling. The ac mobility is found to remain constant up to about 110 GHz for n-HgCdTe and up to about 100 GHz for n-InSb and then it decreases at higher frequencies. The ac mobility for the non equilibrium phonon distribution at lower frequency is found to be higher compared to the thermal phonon distribution and the variation at higher frequency is faster for the thermal phonons. The inclusion of the non equilibrium phonons increases the cut off frequency i.e. the cut off frequency is higher for the non equilibrium phonon distribution. The phase lag of drift velocity is found to increase with the frequency both for the nonequilibrium and the thermal phonon distribution respectively. The influence of the band non parabolicity based on simplified Kane's model for the extreme quantum limit has also been investigated on the ac mobility of hot electrons and the phase angle. It is observed that at lower frequencies the normalized ac mobility is same both for the parabolic and the non parabolic band but at higher frequencies it is higher for the non parabolic than that of the parabolic band structure. The phase angle increases with frequency and is found to be higher for the parabolic band compared to the non parabolic band. These results can be explained by the Drude theory for ac conductivity.