The impact of deep levels on the photocurrent transients in semi-insulating GaAs

Abstract

The photocurrent transients, I PC (t), were studied in semi-insulating (SI) GaAs during a low-temperature (low-T) illumination. Unusual transients were explained by the model, relating I PC (t) to the deep levels/traps and their occupancy. Such traps were actually detected and characterized by the independent measurements of the thermally stimulated currents (TSCs). The processes of the generation, recombination, and capture were described by a set of coupled differential equations and solved numerically. The I PC (t), calculated without any free parameter, well reproduced (through eight orders of magnitude) the experimental transients over a wide range of the photon energies and intensities. The best-fit parameters agreed well with those determined from the TSC measurements.

Dipolar‐Modulated Charge‐Doped Trilayer Organic Semiconductor n–n Heterojunction

“…It can be seen in Figure 1c that the initial macroscopic transient delay to constant photocurrent density I takes several tens of seconds (time t ) after the laser is switched on under ‐ V . In fact, the time scale of the transient delay is closely related to the structures of the different materials, for example poly(phenylene vinylene) (microseconds),27 pentacene (several tens of seconds)28 and semi‐insulator GaAs at low temperature (a few hundreds of seconds) 29. This is thought to be mainly due to the impact of deep‐level trapping on the free‐carriers.…”

Explanation of positive and negative PICTS peaks in SI-GaAs

“…So the system starts at and relaxes back into thermal equilibrium for every given temperature. In contrast to low temperature studies of GaAs [11,13] (e.g. simulations of the EL2 photoquenching effect), where equilibrium occupations of the bands are practically zero and can be neglected, they are important for the simulation of negative peaks for temperatures above 300 K, where transients are known to show a drop below equilibrium values [6].…”

“…the Fermi level in the samples). The model assumes an additional recombination center (RC), which has been suggested several times [9][10][11]. It will be shown that such a center is an important precondition for the formation of negative EL2 peaks.…”