Self-compensation in arsenic doping of CdTe

Area of Science:

• Semiconductor Physics
• Materials Science
• Solid-State Chemistry

Background:

• Efficient p-type doping in Cadmium Telluride (CdTe) is crucial for semiconductor device performance but remains a persistent challenge.
• Arsenic (As) is a potential p-type dopant for CdTe, yet achieving reproducible high concentrations and long carrier lifetimes is difficult.

Purpose of the Study:

• To systematically investigate the defect structures in Arsenic-doped CdTe (As-CdTe) single crystals.
• To identify the mechanisms limiting efficient p-type doping and carrier lifetime in As-CdTe.

Main Methods:

• Growth of As-doped and undoped CdTe single crystals in controlled Cd-rich and Te-rich environments.
• Characterization of defect structures using thermoelectric-effect spectroscopy (TEES).
• Identification and assignment of experimentally observed defects through first-principles calculations.

Main Results:

• Low Arsenic activation and very short carrier lifetimes were observed in As-CdTe samples, indicating significant compensation and carrier trapping defects.
• TEES and calculations revealed two acceptor levels (~88 meV, ~293 meV) and one donor level (~377 meV) introduced by As doping.
• A prominent peak at ~162 K in TEES spectra, attributed to AX-center donors, was observed in both As-doped samples.

Conclusions:

• AX-center donors, due to their low formation energy and high TEES signal, are identified as the primary cause of compensation in As-CdTe.
• Understanding and mitigating these AX-center defects are critical for advancing p-type doping in CdTe for improved device applications.