Comparison of structural and optical properties of blue emitting In0.15Ga0.85N/GaN multi-quantum-well layers grown on sapphire and silicon substrates

Richard Liu,Can Bayram,Callan Mccormick

doi:10.1063/1.5078743

Abstract

Six periods of 2-nm-thick In0.15Ga0.85N/13-nm-thick GaN blue emitting multi-quantum-well (MQW) layers are grown on sapphire (Al2O3) and silicon (Si) substrates. X-ray diffraction, Raman spectroscopy, atomic force microscopy, temperature-dependent photoluminescence (PL), Micro-PL, and time-resolved PL are used to compare the structural and optical properties, and the carrier dynamics of the blue emitting active layers grown on Al2O3 and Si substrates. Indium clustering in the MQW layers is observed to be more pronounced on Al2O3 than those on Si as revealed through investigating band-filling effects of emission centers, S-shaped peak emission energy shifts with increasing temperature, and PL intensity-peak energy spatial nonuniformity correlations. The smaller indium clustering effects in MQW on Si are attributed to the residual tensile strain in the GaN buffer layer, which decreases the compressive strain and thus the piezoelectric polarization field in the InGaN quantum wells. Despite a 30% thinner total epitaxial thickness of 3.3 µm, MQW on Si exhibits a higher IQE than those on Al2O3 in terms of internal quantum efficiency (IQE) at temperatures below 250 K, and a similar IQE at 300 K (30% vs 33%). These results show that growth of blue emitting MQW layers on Si is a promising approach compared to those conventionally grown on Al2O3.

Highlights

Indium gallium nitride (InGaN)/gallium nitride (GaN) multiple quantum well (MQW)-based blue light emitting diodes (LEDs) and their white LED derivatives have transformed the lighting industry thanks to their superior power efficiency, longevity, and compactness
The difference of ∼41 meV in the main MQW emissions from the samples throughout the temperature range (Fig. 5d), despite the same physical structure shown by X-ray diffraction (XRD), is attributed to the reduced Quantum Confined Stark Effect (QCSE) in the InGaN active layers
It has been shown that the carrier dynamics are very different in MQW-Al2O3 and MQW-Si with the latter exhibiting less structural and optical characteristics that are associated with indium clustering

Summary

INTRODUCTION

LEDs on Al2O3 and Si substrates with identical blue emitting MQWs, inhibiting direct comparation of structural and optical properties of the blue emitting MQWs. The difference of ∼41 meV in the main MQW emissions from the samples throughout the temperature range (Fig. 5d), despite the same physical structure shown by XRD, is attributed to the reduced Quantum Confined Stark Effect (QCSE) in the InGaN active layers. The IQE of MQW-Si exceeds that of MQW-Al2O3 at all temperatures below 250 K This indicates that the activation energy of their respective carrier loss mechanism, either band filling or nonradiative recombination centers, are significantly different. The coincidence of a blue shift in the peak energy and an increase in the IQE of the MQW of the MQW-Al2O3 at 130 K suggests a change in the emission center as carriers gain enough thermal energy to freely move between the low energy minima and the higher energy minima as the temperature increases.. The net result of a reduced carrier escape probability and a lower crystal quality is a ∼ 40% longer nonradiative lifetime

Findings

DISCUSSION

CONCLUSION