Low frequency modulated photoconductivity in semiconductorshaving multiple species of traps

J. A. SCHMIDT; C. LONGEAUD; R.R. KOROPECKI; R.D. ARCE

JOURNAL OF APPLIED PHYSICS

AIP

Lugar: New York; Año: 2007 vol. 101 p. 103705 - 103715

0021-8979

Modulated photoconductivity has proved to be an excellent tool to probe the density of states of semiconductors. However, though a great deal of attention has been devoted to the high frequency regime for its simplicity of application, the modulated photoconductivity in the low frequency (LF-MPC) regime has been the object of researches only recently. In the case of a dominant species of states present in the forbidden gap, it was shown that LF-MPC is a good complementary technique to the high frequency method to extract different transport parameters. In this paper, we present a complete theoretical analysis of the LF-MPC experiment for the case when different species of traps are present. We solve the complete system of equations that describe the experiment, and we apply simplifying assumptions to deduce a simple formula relating the photocurrent phase shift to the density of states (DOS) at the majority carriers´ quasi-Fermi level. By means of numerical calculations, we discuss the accuracy of our development, and of previous approximate formulas, to reconstruct a given DOS. Finally, we present experimental and theoretical evidence that, under sensitization conditions, the sign of the phase shift of the modulated photocurrent reverses and the steady-state photoconductivity