Above-band-gap dielectric functions of ZnGeAs2: Ellipsometric measurements and quasiparticle self-consistentGWcalculations

Abstract

We report the above-bandgap dielectric function spectra ε a = ε a1 + iε a2 of single-crystal ZnGeAs 2 grown epitaxially on (001)GaAs, and study it theoretically. After surface overlayers were removed chemically to minimize artifacts, pseudodielectric-function spectra <ε> = <ε 1 > + i<ε 2 > were acquired ellipsometically from 1.5 to 6.0 eV with the sample at room temperature. The ε a spectra were then extracted by the multilayer analysis. The procedure ensures that the result is a close approximation to the a-axis component of the dielectric-function tensor ε = ε 1 + iε 2 of ZnGeAs 2 . The data exhibit numerous spectral features associated with critical points. The energies of these critical points are determined accurately by fitting standard lineshapes to second energy derivatives of the data obtained by a combined method of spectral analysis. We compare our results to the predictions of quasiparticle self-consistent GW calculations. Good agreement is achieved for the major critical-point features, and their probable origins are identified. a)Author to whom correspondence should be addressed; electronic mail: Sukgeun.Choi@nrel.gov b)Present affiliation: eQED, LLC., Mayfield Village, Ohio 44143, USA.2

Dielectric function spectra and critical-point energies of Cu2ZnSnSe4 from 0.5 to 9.0 eV

“…In addition, significant enhancement of the CP structures at $ 4 and $ 5 eV in the < e 2 > spectra, which is further improved by AmH treatment, indicates the successful reduction of surface overlayers in accordance with previous SE studies. 8,16,18 Large oscillations below $ 1.3 eV are the thickness fringes from the transparent characteristic of the film below its fundamental absorption edge. 18,19 A VUV-SE measurement was carried out over an extended photon energy range from 0.5 to 9.0 eV to acquire the < e > spectra of CZTSe after the CMP procedures and AmH treatment of the surface.…”

“…8,16,18 Large oscillations below $ 1.3 eV are the thickness fringes from the transparent characteristic of the film below its fundamental absorption edge. 18,19 A VUV-SE measurement was carried out over an extended photon energy range from 0.5 to 9.0 eV to acquire the < e > spectra of CZTSe after the CMP procedures and AmH treatment of the surface. To obtain the e of CZTSe with the mathematical corrections for the presence of residual surface overlayers and thickness fringes, the < e > data were analyzed by a multilayer model consisting of the ambient, a surface-roughness layer, the CZTSe layer, and the Mo buffer layer.…”

Ellipsometric characterization and density-functional theory analysis of anisotropic optical properties of single-crystal α-SnS

“…[11][12][13] Complex refractive index N ¼ n þ ik and relevant properties, such as normal-incidence reflectivity R and absorption coefficient a, are used to characterize the device performance. 14,15 The complex dielectric function e ¼ e 1 þ ie 2 provides great insight into the electronic structure of materials and can be used to compare experimental data to theoretical predictions, [16][17][18][19] which in turn further enhances the performance and functionality of solar cells through band gap-and defect-engineering.…”

Pseudodielectric function and critical-point energies of iron pyrite

“…2 In addition, the vast abundance and low procurement cost of the constituent elements may make pyrite PV a practical solution for terawatt-scale solar electricity generation. 3 The complex dielectric function ε = ε 1 + iε 2 and complex refractive index N = n + ik are important for understanding the electronic structure of materials 4 and developing PV device structures. 5 However, only a limited number of ε and N spectra are available for pyrite from electronic structure calculations [6][7][8][9] or optical reflectance measurements.…”