Photoluminescence study of potential fluctuations in thin layers of Cu(In0.75Ga0.25)(SySe1−y)2

Abstract

Thin layers of the pentenary material Cu(In,Ga)(S,Se)2 (CIGSSe) are studied using photoluminescence (PL) spectroscopy. The layers were produced by a two-stage deposition process, which produces thin chalcopyrite films with a high degree of compositional uniformity throughout the thickness of the layer. It is shown that potential fluctuations, caused by compensation and high concentrations of defects, dominate the PL behavior of the investigated layers. This is inferred from a number of PL studies such as variable temperature and excitation power measurements. It is deduced that the average amplitude of fluctuations increases with increasing sulfur mole fraction S∕(Se+S). Thus, sulfur incorporation increases the degree of compensation (and hence the charged defect concentration). From the strong asymmetry and the observed weak shift of the low energy tails in the PL spectra with increasing sulfur content, it is also concluded that a significant fraction of defect states associated with the quaternary CIGSSe is still present in the pentenary layers.

Influence of an Sb doping layer in CIGS thin-film solar cells: a photoluminescence study

“…Hence it is expected to exhibit a high concentration of copper vacancies, providing the p-type conductivity of the material. It has been shown previously that Cu-poor CIGS is highly compensated [11,12], having comparable and high density of donors and acceptors [13]. Most of the defects are charged without generating free carriers.…”

“…This is a result of the decrease in the average distance between the donor and acceptor involved in the recombination as excitation power increases. However, for CIGS a maximal shift of 1-2 meV/decade excitation power is expected for this effect [11].…”

“…The average depth of potential fluctuations is dependent on the total charged impurity concentration and the screening by the free carriers. Peaks in the PL spectra of a highly compensated semiconductor are usually assigned to donor-acceptor pair DAP recombination [11]. The tunneling of carriers between spatially separated donors and acceptors, at different local potential, can considerably reduce the transition energy.…”

“…The theory developed for DAP recombination in a highly compensated semiconductor also predicts distinctive excitation power and temperature dependencies of the PL as a result of potential fluctuations [11,13,14] which are examined in the following subsections.…”

Characterization of radiative recombination in Ag(In,Ga)Se2 thin films by photoluminescence

“…For Cu-poor CuInSe 2 thin films, potential fluctuations play a main role in influencing the optical properties of the PL spectra. [18][19][20] We assume that this is the same for AIGS films. Figure 6(a) shows logarithmic plots of the dominant peak intensity of AIGS films with different compositions as a function of excitation intensity.…”