Abstract
The knowledge of minority carrier lifetime of a semiconductor is important for the assessment of its quality and design of electronic devices. Time-resolved photoluminescence (TRPL) measurements offer the possibility to extract effective lifetimes in the nanosecond range. However, it is difficult to discriminate between surface and bulk recombination and consequently the bulk properties of the semiconductor cannot be estimated reliably. Here we present an approach to constrain systematically the bulk and surface recombination parameters in semiconducting layers and reduces to finding the roots of a mathematical function. This method disentangles the bulk and surface recombination based on TRPL decay times of samples with different surface preparations. The technique is exemplarily applied to a CuInSe2 and a back-graded Cu(In,Ga)Se2 compound semiconductor, and upper and lower bounds for the recombination parameters and the mobility are obtained. Sets of calculated parameters are extracted and used as input for simulations of photoluminescence transients, yielding a good match to experimental data and validating the effectiveness of the methodology. A script for the simulation of TRPL transients is provided.
Highlights
Minority carrier lifetime τ is generally evaluated by using time-resolved photoluminescence (TRPL) in thin film semiconductors, such as Cu(In,Ga)Se2 (CIGS)[1,2,3,4,5], CdTe6 or perovskite[7,8,9,10]
An interpretation of the Time-resolved photoluminescence (TRPL) decay time as the bulk lifetime leads in turn to an underestimation, which might result in incorrect conclusions
In this regime it is assumed that the system can be described by low injection conditions and that the photo luminescence (PL) decay time can be described by Eqn (11), i.e. by a single exponential decay with effective lifetime τeff
Summary
Minority carrier lifetime τ is generally evaluated by using time-resolved photoluminescence (TRPL) in thin film semiconductors, such as Cu(In,Ga)Se2 (CIGS)[1,2,3,4,5], CdTe6 or perovskite[7,8,9,10]. The drift of charge carriers[13] due to a built-in electric field was not taken into account, leading to an underestimated bulk lifetime and an overestimated diffusion coefficient Another method was proposed by Barnard et al.[14] and Kuciauskas et al.[15] that is based on two-photon excited TRPL. Staub et al determined an upper limit of the surface recombination velocity assuming that the non-radiative lifetime is solely caused by interface recombination[7] This approach might be useful for high PL decay times observed for instance in high quality perovskite layers[7], might not yield reasonable limits for other thin film technologies with lower effective lifetimes
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