Identifying vacancy complexes in compound semiconductors with positron annihilation spectroscopy: a case study of InN

TL;DR

This study combines positron annihilation spectroscopy and ab-initio calculations to identify and characterize vacancy complexes in InN, revealing the nature of positron traps and their variation in different sample conditions.

Contribution

It provides a detailed analysis of vacancy and vacancy-impurity complexes in InN, identifying dominant positron traps and their characteristics through combined experimental and computational methods.

Findings

In vacancies and their complexes act as efficient positron traps.

Neutral or positively charged N vacancies do not trap positrons.

In vacancies are the dominant traps in irradiated InN.

Abstract

We present a comprehensive study of vacancy and vacancy-impurity complexes in InN combining positron annihilation spectroscopy and ab-initio calculations. Positron densities and annihilation characteristics of common vacancy-type defects are calculated using density functional theory and the feasibility of their experimental detection and distinction with positron annihilation methods is discussed. The computational results are compared to positron lifetime and conventional as well as coincidence Doppler broadening measurements of several representative InN samples. The particular dominant vacancy-type positron traps are identified and their characteristic positron lifetimes, Doppler ratio curves and lineshape parameters determined. We find that In vacancies and their complexes with N vacancies or impurities act as efficient positron traps, inducing distinct changes in the annihilation parameters compared to the InN lattice. Neutral or positively charged N vacancies and pure N vacancy complexes on the other hand do not trap positrons. The predominantly introduced positron trap in irradiated InN is identified as the isolated In vacancy, while in as-grown InN layers In vacancies do not occur isolated but complexed with one or more N vacancies. The number of N vacancies per In vacancy in these complexes is found to increase from the near surface region towards the layer-substrate interface.