Theoretical study of time-resolved luminescence in semiconductors. I. Decay from the steady state

Abstract

Time-resolved luminescence (TRL) is a non-destructive, non-invasive, and contactless characterization method. We studied TRL decay on semiconductor layers and thin film homostructures after a steady state illumination by simulation with Synopsys TCAD® and by analytical approximate solution of the appropriate equations. First, we show that the luminescence decay time in general equals the minority carrier lifetime only for a homogeneous and time-independent carrier lifetime. Then, we investigate the influence of photon recycling, injection level, charge carrier diffusion, defects in the bulk and at the surfaces, as well as space charge on the TRL decay separately by quasi one-dimensional simulations of semiconductor layers and semiconductor homostructures. We further study the influence of sample non-homogeneity as may be found in polycrystalline semiconductors. We show how carrier lifetime can be extracted from the TRL transients and how the samples can be characterized by excitation dependent measurements in the open circuit case. We can explain some effects found in luminescence experiments, like a decrease of the decay time with an increasing excitation, a maximum in the decay time due to saturated bulk-defects and curved luminescence transients due to high injections or sample inhomogeneities. Furthermore, we are focussing on the question, how single layers within a semiconductor stack can be characterized.

Identifying the Real Minority Carrier Lifetime in Nonideal Semiconductors: A Case Study of Kesterite Materials

“…This behavior rules out radiative and Auger recombination limits for Δn(t), where τ varies as a function of Δn. [3,44] Additionally, Shockley-Read-Hall (SRH) recombination is expected to be dependent upon the injection level, with the decay time τ ≈ τ n0 in low injection and τ ≈ τ n0 + τ p0 in high injection, [1,26] where τ n0 and τ p0 are the SRH minority and majority carrier lifetimes, respectively; an intensity-independent decay time would only be expected for τ p0 ≪ τ n0 . Intensity-dependent minority carrier lifetimes consistent with SRH recombination have been reported for CIGSe.…”

“…Detailed theoretical and experimental discussion regarding the role of various absorber properties and measurement conditions on the PL decay signal are reported by Maiberg et al, [2,26,27] Ahrenkiel, [1,28] and Kuciauskas et al [4] First, carrier redistribution processes can dominate the early decay signal, as illustrated in Figure 1a. As generation follows a Beer-Lambert absorption profile, carrier diffusion will occur during initial times following the excitation pulse; this process may include energetic relaxation of carriers due to gradients in the absorber or due to potential (i.e., electrostatic or band gap) fluctuations, as illustrated.…”

Photovoltaic Performance of Perovskite Solar Cells with Different Grain Sizes

“…Here, B SRH is given by:where C n and C p are the capture coefficients for electrons and holes at trapped sites, respectively, N t is the density of trap states with an energy E t in the bandgap, and n 1 and p 1 are given by:where n 1 and p 1 are the density of electrons and that of holes, respectively, when the Fermi levels of electron and hole are equal to the trap level . In Figure , the energy diagram of the SRH recombination is summarized.…”

Defects characterization in thin films photovoltaics materials by correlated high-frequency modulated and time resolved photoluminescence: An application to Cu(In,Ga)Se2

“…Time Resolved Photoluminescence (TRPL) is, for its part, a wellestablished technique for probing fast recombination mechanisms in thin film semiconductors. However, the temporal decays might be difficult to interpret as they can strongly deviate from single exponential behavior associated with a simple notion of lifetime [4][5][6]. In fact several mechanisms play a role in the temporal decay of photoluminescence signals, including bulk, interfaces, and grain boundaries recombination, carrier trapping, and transport (thermionic emission at the heterojunction, diffusion and drift)… This is for instance the case in Cu(In,Ga)Se 2 (CIGS) materials, a promising thin films photovoltaic absorber we investigate in this study to illustrate the method we propose.…”