Superlattice period dependence on nonradiative recombination centers in the n-AlGaN layer of UV-B region revealed by below-gap excitation light

M Ismail Hossain,Shunsuke Kuwaba,Yuri Itokazu,Noritoshi Maeda,Norihiko Kamata,Hideki Hirayama

doi:10.1063/1.5134698

M Ismail Hossain, Shunsuke Kuwaba + Show 4 more

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https://doi.org/10.1063/1.5134698

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Journal: AIP Advances	Publication Date: Mar 1, 2020
Citations: 1	License type: cc-by

Affiliation: Saitama University, University of Rajshahi, RIKEN

Abstract

Nonradiative recombination (NRR) centers in n-AlGaN layers of UV-B AlGaN samples with different numbers of superlattice (SL) periods (SLPs), grown on the c-plane sapphire substrate at 1150 °C by the metalorganic chemical vapor deposition technique, have been studied by using below-gap-excitation (BGE) light in photoluminescence (PL) spectroscopy at 30 K. The SLP affects the lattice relaxation of the SL and n-AlGaN layer. The PL intensity decreased by the superposition of BGE light of energies from 0.93 eV to 1.46 eV over the above-gap-excitation light of energy 4.66 eV, which has been explained by a two-level model based on the Shockley–Read–Hall statistics. The degree of PL quenching from n-AlGaN layers of the sample with SLP 100 is lower than those of other samples with SLP 50, 150, and 200. By a qualitative simulation with the dominant BGE energy of 1.27 eV, the density ratio of NRR centers in n-AlGaN layers of 50:100:150:200 SLP samples is obtained as 1.7:1.0:6.5:3.4. This result implies that the number of SLP changes lattice relaxation and determines the density of NRR centers in the n-AlGaN layer, which affects the performance of LEDs.

Highlights

The demand of cheap, environmentally friendly, and smart AlGaN ultraviolet (UV) light emitters in the UV-B spectral range between 280 nm and 320 nm has arisen because of their legionary potential applications.[1,2,3,4,5,6,7,8] The conventional light sources in the aforesaid spectral ranges are bulky, have limited lifetime, and contain toxic substances.[9]
This result implies that the number of superlattice periods (SLPs) changes lattice relaxation and determines the density of Nonradiative recombination (NRR) centers in the n-AlGaN layer, which affects the performance of LEDs
In order to corroborate our qualitative interpretations, for the results shown in Figs. 6, 7, and 9 by the two-level model, a semiquantitative simulation of the two-wavelength excited PL (TWEPL) results was carried out for the most dominant PL quenching occurred by the 1.27 eV BGE energy

Summary

Introduction

The demand of cheap, environmentally friendly, and smart AlGaN ultraviolet (UV) light emitters in the UV-B spectral range between 280 nm and 320 nm has arisen because of their legionary potential applications.[1,2,3,4,5,6,7,8] The conventional light sources in the aforesaid spectral ranges are bulky, have limited lifetime, and contain toxic substances.[9] UV-B LEDs are promising devices, but their reliability still needs improvement.[10] One of the main reasons for the low efficiency of UV-B LEDs is the non-radiative recombination (NRR) losses [Shockley–Read–Hall (SRH) and Auger-related].9. One of the main reasons for the low efficiency of UV-B LEDs is the non-radiative recombination (NRR) losses [Shockley–Read–Hall (SRH) and Auger-related].9 Recent studies have indicated that the reduction in optical power with an increase in the temperature (thermal droop) may limit the performance of GaN-based

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