Excitation Mechanisms of Er Optical Centers in GaN Epilayers

TL;DR

This study identifies two excitation mechanisms for Er3+ ions in GaN epilayers, revealing their different behaviors and implications for optical amplification and lasing at room temperature.

Contribution

It provides direct evidence of two excitation mechanisms for Er3+ in GaN and characterizes their distinct properties, aiding future optical device development.

Findings

Isolated Er centers can be excited by both mechanisms with high cross-section.

Defect-related Er centers are only excited by band-to-band with the largest cross-section.

Differences in spectra, decay, and excitation explain challenges in achieving gain.

Abstract

We report direct evidence of two mechanisms responsible for the excitation of optically active Er3+ ions in GaN epilayers grown by metal-organic chemical vapor deposition. These mechanisms, resonant excitation via the higher-lying inner 4f shell transitions and band-to-band excitation of the semiconductor host, lead to narrow emission lines from isolated and the defect-related Er centers. However, these centers have different photoluminescence spectra, decay dynamics, and excitation cross sections. The isolated Er optical center, which can be excited by either mechanism, has the same decay dynamics, but possesses a much higher cross-section under band-to-band excitation. In contrast, the defect-related Er center can only be excited through band-to-band excitation but has the largest cross-section. These results explain the difficulty in achieving gain in Er doped GaN and indicate new approaches for realization of optical amplification, and possibly lasing, at room temperature.