Temperature dependent band-gap energy for Cu2ZnSnSe4: A spectroscopic ellipsometric study

Abstract

Spectroscopic ellipsometry (SE) is used to study the dependence of the band-gap energy for Cu2ZnSnSe4 (CZTSe) on temperature ranging from 50 to 350 K. A CZTSe thin film prepared by the pseudo-bulk approach allows direct observation of the fundamental band-gap E0(A,B) in the SE data without need for multi-layer modeling. We obtain accurate energy values for E0(A,B) and its spin-orbit splitting component E0(C) from standard lineshape analysis of the secondenergy-derivative spectra. The E0(A,B) and E0(C) energies for CZTSe decrease with increasing temperature, as for many semiconductors, but their temperature dependencies are relatively weak. Our experimental observation can be explained in terms of relatively small change in bond-length and strong p-d states coupling at the valence band maximum.

Optical properties of Cu2ZnSn(SxSe1-x)4 solar absorbers: Spectroscopic ellipsometry and ab initio calculations

“…The dimensional assignments are related to details in joint density of states and band structure; 25 however, previous CP studies did not always agree regarding such assignments. [6][7][8]26,27 In this work, the purpose of CP analysis was to pin-point the threshold energy in a systematic and reproducible way; therefore, excitonic line shape was chosen since it gave the best fit at E 0 and E 1 for all samples. An example fit is shown in Fig.…”

Temperature dependent electroreflectance study of Cu2ZnSnSe4 solar cells

“…This deviation could be an indication of a second critical point at higher energy. For example, in [15] the room temperature E 0 (C) bandgap of CZTSe due to spin-orbit splitting of valence band was found at 1.272 eV. However, our ER signal was too low near this energy and therefore we fitted only the main peak.…”

“…The dashed curve represents the temperature dependence of bandgap energy of CZTSe according to data from ref. [15].…”

“…al. [15] published their spectroscopic ellipsometry study of the dependence of the band-gap energy for CZTSe on temperature ranging from 50 to 350 K. Their thin film samples showed a room temperature bandgap energy of E g ¼0.97 eV and according to [9], this low E g must be related to high degree of Cu-Zn disordering. It was found that E g of CZTSe decreases with increasing temperature, but the variation seems to be relatively small.…”

Photoluminescence studies in epitaxial CZTSe thin films

“…The red-shift starting from 160 K can be explained by thermal narrowing of the band gap. 20 Type 2 samples show only a BB transition at all temperatures. This conclusion is drawn from the fact that c remains virtually constant, indicating that the underlying DOS does not change with temperature.…”