Extraordinary Changes in the Electronic Structure and Properties of CdS and ZnS by Anionic Substitution: Cosubstitution of P and Cl in Place of S

Abstract

Unlike cation substitution, anion substitution in inorganic materials such as metal oxides and sulfides would be expected to bring about major changes in the electronic structure and properties. In order to explore this important aspect, we have carried out first-principles DFT calculations to determine the effects of substitution of P and Cl on the properties of CdS and ZnS in hexagonal and cubic structures and show that a sub-band of the trivalent phosphorus with strong bonding with the cation appears in the gap just above the valence band, causing a reduction in the gap and enhancement of dielectric properties. Experimentally, it has been possible to substitute P and Cl in hexagonal CdS and ZnS. The doping reduces the band gap significantly as predicted by theory. A similar decrease in the band gap is observed in N and F co-substituted in cubic ZnS. Such anionic substitution helps to improve hydrogen evolution from CdS semiconductor structures and may give rise to other applications as well.

Effects of Aliovalent Anion Substitution on the Electronic Structures and Properties of ZnO and CdS

“…A reduction in the band gap of P,Cl‐codoped ZnS was found to be 0.7 eV, relative to that of undoped ZnS (Figure a). Substitution of N and F in place of S results in a similar decrease in the band gap, whereas ZnS 0.7 N 0.15 F 0.17 shows a band gap of 2.7 eV, which presents a good correlation with the theoretically predicted band gap (Figure b) …”

“…Similar results were found in the case of P,Cl‐cosubstituted ZnS, where a decrease in the band gap by 0.67 and 0.19 eV was observed for the hexagonal and cubic Zn 8 S 6 PCl, respectively. Cosubstitution of N,F in CdS and ZnS also results in the lowering of their optical band gaps …”

“…Aliovalent substitution of P,Cl in place of S in CdS was achieved by a solid‐state reaction in an N 2 atmosphere, wherein Cd 3 P 2 or red‐P was used as the P precursor, whereas NH 4 Cl was used as the Cl precursor . P,Cl‐cosubstituted CdS show marked effect on its optical absorption, wherein a 0.5 eV lowering of the band gap was observed (Figure ).…”

“…There have been reports of the effect of substitution of Cl or P alone in CdS on its electronic properties . However, cosubstitution of P and Cl in CdS or ZnS gives rise to extraordinary changes in the optical and electronic properties, since S 2− , P 3− , and Cl − are isoelectronic and of nearly the same size . A complete substitution of S by P and Cl in CdS would give a compound of formula Cd 2 PCl.…”

“…The structure and properties of this compound are unknown, because this compound has not been prepared. However, a compound of formula Cd 2 PCl 1.5 or Cd 4 P 2 Cl 3 is known ,…”