PECULIARITIES OF ACOUSTIC INDUCED CHANGES OF ELECTROPHYSICAL CHARACTERISTICS IN GaN/Al0,2Ga0,8N/GaN/AlN HETEROSTRUCTURES

Abstract

We studied temperature, amplitude and time dependencies of electrophysical parameters in GaN/Al0,2Ga0,8N/GaN/AlN structures when the ultrasound (US) was switched on/off (fUS = 9 MHz). We found out the charge carriers concentration n(Т) increases and the mobility μH(Т) decreases under the ultrasonic loading. With decreasing the temperature, the effect of acoustic induced changes increases. When US switches on/off, long-term (up to ~ 500 s) relaxation of the acoustic conductivity US(t) is observed, with increasing the amplitude of the ultrasound at low temperatures the acoustic conductivity increases exponentially, and at high ones decreases exponentially. It is established that the main mechanisms of charge carrier scattering at low temperatures (T ≤ 150 K) are ionized centers scattering and dislocations scattering; at high temperatures (T > 200 K) the charge carriers mobility is limited by polar optical phonons scattering. An acoustic deformation mechanism of charge carrier redistribution as a result of acoustic lattice deformation and corresponding additional structure piezopolarization is proposed. In our opinion, the determining factor that contributes to these effects, is the high density of boundary dislocations, as well as the change in the linear charge density on the dislocations in the process of their forced oscillations in the field of an external ultrasonic deformation. We have also considered an alternative mechanism that related with an acoustic induced (AI) transformation of metastable DX centers and can occur simultaneously. The mechanism of AI concentration n(Т) increase in this model is associated with a decrease of the barrier for an electron capture in DX0-state as a result of a periodic change distance between possible positions of the donor atoms (at the lattice node and non-central DX¯-state). To study the effect allows to obtain information both about such defect structure of the material and about the nature of changes in its macroscopic characteristics under the ultrasonic loading influence. From a practical point of view, it leads to the search for new opportunities for using of ultrasound for control the physical parameters kinetics of semiconductor structures.