Modulated photocurrents in a sandwich-cell structure

Abstract

Approximate formulae describing modulated photocurrents in a sandwich configuration of sample electrodes are derived. The carrier transport is described in terms of the multiple-trapping model. The formulae refer to arbitrary spatial distribution of generated carriers. The case of exponential light absorption in the sample is considered in detail. It is shown that for limiting low and high modulation frequencies, both the amplitude and the phase shift of the photocurrent are almost independent of the light absorption coefficient. In the intermediate-frequency range, for the case of surface carrier generation, the phase shift of the photocurrent usually shows oscillations. This makes it possible to obtain the energetic density of states from a simple formula. Examples of calculated frequency dependencies of the photocurrent phase shift and amplitude are given for exponential and Gaussian trap distributions as well as for a single trap level.

The role of the recombination centers on the modulated photocurrent: Determination of the gap state parameters of semiconductors

“…This formula provides by means of the i ac and φ data the r-DOS at the probe energy level E ω for which the thermal emission rate of the majority carriers equals the modulation frequency ω. Thus by scanning ω [8,[16][17][18]] the DOS at different E ω levels can be obtained. This method is applicable exclusively for the MPC data in the HF regime.…”

Modulated photocurrents in a sandwich-cell structure: II. Influence of bias illumination intensity and carrier diffusion

“…In the present work we examine the influence of trap saturation, depending on the intensity of the bias illumination component, as well as the influence of the carrier diffusion on the MPCs, measured in the sandwich sample configuration. This paper constitutes a continuation of the investigations reported in [19], hereafter referred to as I. The corresponding multipletrapping (MT) transport equations are similar to those of I and are presented here in an abbreviated manner.…”

“…In the papers [11,13,15] the modified Oheda theory has been utilized. The more rigorous theoretical descriptions have been published by Tomaszewicz [17] and Hattori et al [18] for the case of surface carrier photogeneration and by Grygiel and Tomaszewicz [19] for finite absorption depth of the light, generating the carriers.…”

Subgap modulated photocurrent spectroscopy and its application to the study of the solar cell absorber defect distributions

“…6 However, in polycrystalline materials with columnar structure of the grains, the electronic transport, which is parallel to the substrate in coplanar configuration, differs from that in sandwich structure of the solar cell where the transport path of the photogenerated carriers is essentially perpendicular to the substrate. For such materials, it is then interesting to study the modulated photocurrent in sandwich configuration but so far, only few studies have been devoted to this point, [7][8][9][10][11] essentially in the framework of multiple-trapping model and for the case where the light excitation energy is higher than the semiconductor band gap, except works of Abe et al 8 and Mencaraglia et al, 9 where subgap light excitation has been considered.…”