Resonance Raman Spectroscopy of Mn-Mgk Cation Complexes in GaN

Andrii Nikolenko,Viktor Strelchuk,Alberta Bonanni,Dmytro Kysylychyn,Giulia Capuzzo,Bogdan Tsykaniuk

doi:10.3390/cryst9050235

Abstract

Resonance Raman analysis is performed in order to gain insight into the nature of impurity-induced Raman features in GaN:(Mn,Mg) hosting Mn-Mgk cation complexes and representing a prospective strategic material for the realization of full-nitride photonic devices emitting in the infra-red. It is found that in contrast to the case of GaN:Mn, the resonance enhancement of Mn-induced modes at sub-band excitation in Mg co-doped samples is not observed at an excitation of 2.4 eV, but shifts to lower energies, an effect explained by a resonance process involving photoionization of a hole from the donor level of Mn to the valence band of GaN. Selective excitation within the resonance Raman conditions allows the structure of the main Mn-induced phonon band at ~670 cm−1 to be resolved into two distinct components, whose relative intensity varies with the Mg/Mn ratio and correlates with the concentration of different Mn-Mgk cation complexes. Moreover, from the relative intensity of the 2LO and 1LO Raman resonances at inter-band excitation energy, the Huang-Rhys parameter has been estimated and, consequently, the strength of the electron-phonon interaction, which is found to increase linearly with the Mg/Mn ratio. Selective temperature-dependent enhancement of the high-order multiphonon peaks is due to variation in resonance conditions of exciton-mediated outgoing resonance Raman scattering by detuning the band gap.

Highlights

Gallium nitride (GaN)-based semiconductors, due to their remarkable properties such as wide tunability of direct band-gap, the availability of both n- and p-type material, high thermal stability, large heat conductivity, high electric field strength, and electron mobility, are key materials for state-of-the-art high-efficiency optoelectronic devices, such as blue, ultra-violet, and white light emitting diodes (LEDs) [1], laser diodes [2], and high-power and high-frequency electronic devices, like e.g., electron mobility transistors (HEMTs) [3]
Resonance Raman studies at room temperature of GaN:(Mn,Mg) have shown that in contrast to the case of GaN:Mn, the resonance enhancement of the Mn-induced modes in Mg co-doped samples is not observed at an excitation of 2.4 eV, but shifts to lower energies
This effect is explained by the resonance Raman process of photoionization of a hole from the donor level of Mn to the valence band of GaN, followed by the recombination with an ionized Mn5+ donor with the emission of LO

Summary

Introduction

Gallium nitride (GaN)-based semiconductors, due to their remarkable properties such as wide tunability of direct band-gap, the availability of both n- and p-type material, high thermal stability, large heat conductivity, high electric field strength, and electron mobility, are key materials for state-of-the-art high-efficiency optoelectronic devices, such as blue, ultra-violet, and white light emitting diodes (LEDs) [1], laser diodes [2], and high-power and high-frequency electronic devices, like e.g., electron mobility transistors (HEMTs) [3]. Doping of GaN with Mg and Mn leads to a rich set of impurity-related Raman bands. The most prominent feature related to the incorporation of Mn is the phonon band detected at 667 cm−1 [8,9]. This mode was shown to have a strong polarization dependence similar to the one of the A1 (LO) mode of GaN [9], a resonance enhancement at an excitation of 2.4 eV and a linear-like dependence on the Mn concentration [8]

Methods

Results

Conclusion