Effects of the Cu off-stoichiometry on transport properties of wide gap p-type semiconductor, layered oxysulfide LaCuSO

TL;DR

This study investigates how copper off-stoichiometry affects the electrical and optical properties of LaCuSO, revealing that Cu deficiency significantly enhances electrical conductivity and introduces in-gap states, impacting its potential as a p-type transparent semiconductor.

Contribution

It provides new insights into the role of Cu off-stoichiometry in tuning the transport and optical properties of LaCuSO, a wide-gap p-type layered oxysulfide.

Findings

Electrical resistivity decreases by four orders of magnitude with Cu deficiency.

Broad optical absorption at ~2.1 eV is observed in Cu-deficient samples.

Density functional theory links in-gap states to sulfur vacancies caused by Cu off-stoichiometry.

Abstract

Layered oxysulfide LaCuSO (x = 0-0.03) was prepared to elucidate the effect of Cu off-stoichiometry on their electrical and thermal transport properties. Electrical resistivity drastically decreases down from ~10^5 ohmcm to ~10^-1 ohmcm as a result of Cu deficiency (x = 0.01) at 300 K. Thermal conductivity of the samples at 300 K, which is dominated by lattice components, is estimated to be 2.3(3) Wm^-1K^-1. Stoichiometric LaCuSO has an optical band gap of 3.1 eV, while broad optical absorption at photon energies of approximately 2.1 eV was observed for Cu-deficient samples. Density functional theory calculation suggests that these broad absorption structures probably originate from the in-gap states generated by the sulfur vacancies created to compensate the charge imbalance due to Cu off-stoichiometry. These results clearly demonstrate that Cu deficiency plays a crucial role in determining the electrical transport properties of Cu-based p-type transparent semiconductors.