Formation of CuIn_(1–x)Ga_xS₂ Thin Films through a Solution Approach: Nonlinear Variation of Fermi Energy and Band Gap Bowing

Abstract

We report the formation of CuIn (1−x) Ga x S 2 (CIGS) thin films through a solution approach, namely, successive ionic layer adsorption and reaction (SILAR) technique. The obtained films possessed a high degree of crystallinity indicating the efficacy of the deposition process in forming CIGS films. A series of alloys have evidenced band gap bowing, that is, the optical band gap does not follow a linear relationship with the composition; the band gap of an intermediate compound is higher than that is interpolated from a linear relationship or Vegard's law. The composition-dependent band gap followed a quadratic relationship evidencing reverse band gap bowing, manifesting an upward convex behavior. With scanning tunneling spectroscopy (STS) and thereby the density of states of the disordered semiconductors, we have observed a bowing behavior in the transport gap as well and identified the roles of the conduction and valence bands in yielding the bowing phenomenon. The results are explained in terms of the anionic and cationic orbitals involved in forming the two bands. The STS studies have been analyzed further to derive the Urbach energy of the disordered semiconductors. When STS studies are combined with Kelvin probe force microscopy, which in effect provides the Fermi energy of the alloyed semiconductors, we could derive the band edges and the Fermi energy of the whole series in an absolute energy scale during the manifestation of the bowing phenomenon.

Pyro-Phototronic Effect in All-Inorganic Two-Dimensional Ruddlesden–Popper Ferroelectric Perovskite Thin-films and Photodetection

“…The FWHM of the V CPD distribution (Figure 3c) refers to intrinsic defects present in the perovskite thinfilm. 48 The results from STS and KPFM studies were then used to derive the band-energies of the Cs 2 PbI 2 Cl 2 thin-film with respect to the vacuum level (E Vac = 0 eV), so that the absolute energies of the material can be obtained. The band-edges of the HTL, RP, and ETL were accordingly obtained from dI/dV and V CPD plots (Figure S5 in the Supporting Information) and collated in Table S1 in the Supporting Information.…”

“…It should be stated that the surface work function is an important parameter in semiconductor-based optoelectronic devices, since it influences the electronic transport in a large manner. The FWHM of the V CPD distribution (Figure c) refers to intrinsic defects present in the perovskite thin-film …”

Effect of ambient argon pressure on the structural, optical and electrical properties of non-crystalline Se85Te3Bi12 nano-thin films

“…The observed value of the DC conductivity and activation energy points that the thermally assisted charge carrier tunneling in the localized states of band tails were responsible for the conduction mechanism in the Se 85 Te 3 Bi 12 nanothin films [80]. The trivial rise in the DC conductivity and activation energy with increase in the ambient pressure can be associated with the shift of Fermi level [81] or the increasing amount of hopping conduction by defect states [82].…”