Evaluation of the concentration of point defects in GaN

M A Reshchikov,K Udwary,V Prozheeva,F Tuomisto,Yu Makarov,J H Leach,H Helava,I Makkonen,A Usikov

doi:10.1038/s41598-017-08570-1

Abstract

Photoluminescence (PL) was used to estimate the concentration of point defects in GaN. The results are compared with data from positron annihilation spectroscopy (PAS), secondary ion mass spectrometry (SIMS), and deep level transient spectroscopy (DLTS). Defect-related PL intensity in undoped GaN grown by hydride vapor phase epitaxy increases linearly with the concentration of related defects only up to 1016 cm−3. At higher concentrations, the PL intensity associated with individual defects tends to saturate, and accordingly, does not directly correlate with the concentration of defects. For this reason, SIMS analysis, with relatively high detection limits, may not be helpful for classifying unidentified point defects in GaN. Additionally, we highlight challenges in correlating defects identified by PL with those by PAS and DLTS methods.

Highlights

GaN is widely used in blue and white LEDs and lasers, as well as in other optical and electrical devices[1]
Attributions of PL bands to particular defects based on comparison of PL intensity with the concentration of defects obtained from other methods may be erroneous
We have found that the PL intensity is proportional to the concentration of related defects up to only 1016 cm−3, near the detection limit of secondary ion mass spectrometry (SIMS)

Summary

Introduction

GaN is widely used in blue and white LEDs and lasers, as well as in other optical and electrical devices[1]. Capacitance methods such as capacitance-voltage (C-V) measurements and deep-level transient spectroscopy (DLTS)[2] are routinely used for electrical characterization of semiconductors. A modification of the latter is optical DLTS (ODLTS)[3], which allows in particular the detection and analysis of hole traps in n-type semiconductors. The concentrations of impurities responsible for deep levels in undoped GaN are often below the detection limit. It is especially useful for analysis of defects in wide-bandgap, direct-bandgap semiconductors, including GaN, which has a bandgap of 3.50 eV at low temperature[6, 7]. Attributions of PL bands to particular defects based on comparison of PL intensity with the concentration of defects obtained from other methods may be erroneous. The calculated concentrations of radiative defects in selected samples are compared with values obtained from other methods

Objectives

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Results

Conclusion