Defect identification based on first-principles calculations for deep level transient spectroscopy

TL;DR

This paper demonstrates how first-principles calculations can improve the interpretation of DLTS measurements by accurately determining defect activation energies, considering temperature effects and capture barriers, with applications to GaN defects.

Contribution

It introduces a methodology combining first-principles calculations with DLTS data to accurately identify defect activation energies and their microscopic origins.

Findings

DLTS activation energies include temperature-dependent capture barriers.

First-principles calculations can distinguish ionization energies from capture barriers.

Application to GaN defects shows improved defect identification.

Abstract

Deep level transient spectroscopy (DLTS) is used extensively to study defects in semiconductors. We demonstrate that great care should be exercised in interpreting activation energies extracted from DLTS as ionization energies. We show how first-principles calculations of thermodynamic transition levels, temperature effects of ionization energies, and nonradiative capture coefficients can be used to accurately determine actual activation energies that can be directly compared with DLTS. Our analysis is illustrated with hybrid functional calculations for two important defects in GaN that have similar thermodynamic transition levels, and shows that the activation energy extracted from DLTS includes a capture barrier that is temperature dependent, unique to each defect, and in some cases large in comparison to the ionization energy. By calculating quantities that can be directly compared with experiment, first-principles calculations thus offer powerful leverage in identifying the microscopic origin of defects detected in DLTS.