Detailed photoluminescence study of vapor deposited films of different surface morphology

Abstract

authorenWe present a temperature‐ and intensity‐dependent photoluminescence (PL) study of the binary semiconductor Bi2S3 on the mm‐scale and a laterally resolved PL measurement with a resolution of x≈900nm. The films can show a rather rough surface with needles and flakes of Bi2S3 with different orientations as well as very flat and smooth surface morphology. Despite a band gap of Eg≈1.3eV the films show a splitting of quasi‐Fermi levels (QFL) of μ≈700meV at room temperature. By means of temperature‐dependent PL we have located several radiative and non‐radiative defect states in the band gap. For a better understanding of this thin film semiconductor a full analysis of the laterally resolved PL measurement including the integrated PL yield, energetic position of the PL maximum, optical band gap, splitting of quasi‐Fermi levels and defect absorption of both sample morphologies is presented to avoid misinterpretation of experimental data.

PARPLE: Detailed automatized and parallel evaluation of luminescence mappings

“…The mean temperature is about 40 K above room temperature, what is most likely an effect of the local heating due to the excitation laser and limited heat conduction. Similar heat depositions have been reported before [22,23]. The optical band gap is about 1.50 eV and coincides with the reported band gaps for this material.…”

“…Due to the non-perfect quantitative calibration the exact value of the QFL-splitting of 1.255 eV might be not precise and is probably overestimated. Nevertheless, as shown in a recent publication, the standard deviation of 24 meV is within an error of 1 meV [23]. The Urbach energy E U evaluated in the sub-gap regime is about 20 meV and is in the range of observed Urbach energies in CuInS 2 [24,25].…”

Avoiding arbitrarily wrong microluminescence statistics due to a non-quantitatively calibrated setup

“…For example, a varying band structure of the semiconductor or defect absorption may lead to a larger heat deposition, or the grain boundary can transport the heat differently depending from the illuminated spot to the surrounding material. A similar observation of a lateral temperature distribution has been made by Delamarre et al for a thin film and inhomogeneous temperatures along the film have also been observed for the binary semiconductors Cu 2 S and Bi 2 S 3 .…”

“…The reason for the lateral temperature distribution most probably results from different chemical compositions, opto-electronical properties, and heat conductivities of the grains forming the film. For example, a varying band structure of the semiconductor or defect absorption may lead to a larger heat deposition, or the grain boundary can [18]. We now consider a set of N different PL spectra recorded under the same experimental conditions.…”

Absorption Coefficient of a Semiconductor Thin Film from Photoluminescence

“…For thin-film investigation with a calibrated PL, the spectral variation of Θ is often disregarded by simply setting Θ ¼ 1 in Eq. (13) [26,[29][30][31]. Here, we compare two approximations for Θ from the perspectives of QFLS and absorption coefficient measurement.…”