P‐Type Transparent Cu‐Alloyed ZnS Deposited at Room Temperature

Abstract

All transparent conducting materials (TCMs) of technological practicality are n‐type; the inferior conductivity of p‐type TCMs has limited their adoption. In addition, many relatively high‐performing p‐type TCMs require synthesis temperatures >400 °C. Here, room‐temperature pulsed laser deposition of copper‐alloyed zinc sulfide (CuxZn1‐xS) thin films (0 ≤ x ≤ 0.75) is reported. For 0.09 ≤ x ≤ 0.35, CuxZn1‐xS has high p‐type conductivity, up to 42 S cm−1 at x = 0.30, with an optical band gap tunable from ≈3.0–3.3 eV and transparency, averaged over the visible, of 50%–71% for 200–250 nm thick films. In this range, synchrotron X‐ray and electron diffraction reveal a nanocrystalline ZnS structure. Secondary crystalline CuyS phases are not observed, and at higher Cu concentrations, x > 0.45, films are amorphous and poorly conducting. Within the TCM regime, the conductivity is temperature independent, indicating degenerate hole conduction. A decrease in lattice parameter with Cu content suggests that the hole conduction is due to substitutional incorporation of Cu onto Zn sites. This hole‐conducting phase is embedded in a less conducting amorphous CuyS, which dominates at higher Cu concentrations. The combination of high hole conductivity and optical transparency for the peak conductivity CuxZn1‐xS films is among the best reported to date for a room temperature deposited p‐type TCM.