Ultrafast carrier relaxation in GaN, In_(0.05)Ga_(0.95)N and an In_(0.05)Ga_(0.95)/In_(0.15)Ga_(0.85)N Multiple Quantum Well

TL;DR

This study investigates ultrafast carrier relaxation in GaN, InGaN, and MQW structures using pump/probe measurements, revealing wavelength-dependent relaxation dynamics and the emergence of stimulated emission at high excitation intensities.

Contribution

It provides new insights into the wavelength and intensity dependence of carrier relaxation and stimulated emission in GaN-based materials at room temperature.

Findings

Spectrally-resolved sub-picosecond relaxation varies with pump wavelength.

Stimulated emission appears above 100 μJ/cm², accelerating relaxation.

Carrier recombination times are up to 1 ns for epilayers and 660 ps for MQW.

Abstract

Room temperature, wavelength non-degenerate ultrafast pump/probe measurements were performed on GaN and InGaN epilayers and an InGaN multiple quantum well structure. Carrier relaxation dynamics were investigated as a function of excitation wavelength and intensity. Spectrally-resolved sub-picosecond relaxation due to carrier redistribution and QW capture was found to depend sensitively on the wavelength of pump excitation. Moreover, for pump intensities above a threshold of 100 microJ/cm2, all samples demonstrated an additional emission feature arising from stimulated emission (SE). SE is evidenced as accelerated relaxation (< 10 ps) in the pump-probe data, fundamentally altering the re-distribution of carriers. Once SE and carrier redistribution is completed, a slower relaxation of up to 1 ns for GaN and InGaN epilayers, and 660 ps for the MQW sample, indicates carrier recombination through spontaneous emission.