Deep center characterization by photo-induced transient spectroscopy

Abstract

We show that photo-induced current transients in semi-insulating GaAs are well fitted by a unique sum of exponentials including the anomalous case, in which one of the exponentials has a negative amplitude. This fitting procedure is proposed as a more reliable method to be used in obtaining the trap emission constant. We also present an analytic solution for the kinetic equations of carriers taking into account the background current and the carrier recapture processes, which have been neglected in the previous approaches. This solution contains a very simple and physically coherent explanation for the appearance of negative peaks in the spectra of photo-induced transient current spectroscopy.

Compensating defect centres in semi-insulating 6H-SiC

“…This seems to be the case when a donor or accep− tor centres influencing the material conductivity are in ex− cess filled with majority charge carriers. For example, the negative amplitude of the photocurrent relaxation waveform is observed when the deep donor EL2 level is filled with the electrons of n−type high−purity semi−insulating GaAs [14]. So, similarly as in the capacitance spectroscopy, the ampli− tude of the photocurrent relaxation waveform can be posi− tive when the deep traps are filled with the minority carriers, or negative when the traps are filled with the majority carri− ers.…”

“…When the retrapping of the carriers by the centres is ne− glected and the time constant of the relaxation waveform is much longer than the carrier lifetime (ô rel » ô n ), the recipro− cal of the relaxation waveform time constant is equal to the thermal emission rate of charge carriers [14]. So, the param− eters of defect centres can be determined directly from the temperature dependence of the emission rate fitted with the Arrhenius formula.…”

“…The mechanism responsible for the occurrence of the negative amplitude of the photocurrent relaxation waveforms has not been until now fully understood. However, there are some results allowing for explanation of this phenomenon [13,14]. They indicate that the negative amplitude of the re− laxation waveform can result from the specific change in the occupancy of a defect level involved in the material com− pensation.…”

Photocurrent Transients in Presence of a Double Impurity in Semi-Insulating Semiconductors

“…However, in some cases reported in the literature [12, Photocurrent Transients in Presence of a Double Impurity in Semiconductors 13,18], the photocurrent was found to increase after a short decay following the cut-off of the light. In our case, we have observed a peak in the current transient curve at constant temperature for Mg x Zn 1Àx Te crystals with x 0:10.…”

“…By studying the shift with temperature of this peak, it is possible to determine the second ionization energy of the double acceptor as follows: The peak occurs at the value t p where dp=dt 0, p being given by eqn. (13) and t is the time after the cut-off of the light: dp dt À p0 t p exp Àt p =t p À Á À p t1 0 t p e 1 2 exp Àe 1 t p À Á At p e 1 e 2 exp Àe 1 e 2 t p À Á 0:…”