Effect of traps on steadily travelling domains in semiconductors

Abstract

This paper deals with the effect of traps on the domain velocity (u0) and total current ()s) in the presenee of steadily travelling high field domains. The treatment is applieable both for the Watkins--Gunn effect and recombination instability. The calculations are earried out without linearization of the related equations, using the method proposed in [9] for the trapfree case. The assumptions used are: (i) Only transitions leading to negative differential conductivity depend on the electrie fie]d; (ii) The relaxation times of transitions between high and low mobility states ate shorter than the other characteristic times of the problem; (iii) The mobilities and diffusion coefficients are field independent; (iv) The electron concentration in the band is much lower than those of empty and filled centres.The effect of traps on the Watkins --Gunn effeet is discussed in detail and expressions for possible domain-velocity are derived. In contrast to the trap-free case the domain velocity is sensitive to the domain shape. For quadratic domains, the peak field dependente of possible domain modes is discussed.A simple analysis shows that the applicability of the model for slowly moving domains in semi-insulating GaAs cannot be definitely deeided without a knowledge of the relaxation time from low-mobility states to the traps.