Correlation of Morphology Evolution with Carrier Dynamics in InN Films Heteroepitaxially Grown by MOMBE

Fang‐I Lai ,Woei-Tyng Lin,Jui‐Fu Yang ,Wei Chun Chen ,Yu‐Chao Hsu ,Shou‐Yi Kuo

doi:10.3390/catal11080886

Abstract

In this study, we report the catalyst-free growth of n-type wurtzite InN, along with its optical properties and carrier dynamics of different surface dimensionalities. The self-catalyzed epitaxial growth of InN nanorods grown by metal–organic molecular-beam epitaxy on GaN/Al2O3(0001) substrates has been demonstrated. The substrate temperature is dominant in controlling the growth of nanorods. A dramatic morphological change from 2D-like to 1D nanorods occurs with decreasing growth temperature. The InN nanorods have a low dislocation density and good crystalline quality, compared with InN films. In terms of optical properties, the nanorod structure exhibits strong recombination of Mahan excitons in luminescence, and an obvious spatial correlation effect in phonon dispersion. The downward band structure at the nanorod surface leads to the photon energy-dependent lifetime being upshifted to the high-energy side.

Highlights

Since Davydov et al discovered the narrow band gap phenomenon of InN (Eg~0.7 eV), InN has attracted a wide range of research interest [1]
As can be seen from our experimental results, the two-dimensional InN layer tends to form at higher growth temperatures, while 1D nanorods form at lower growth temperatures
This research reports the preparation of InN samples grown at different growth temperatures by MOMBE, including nanorods and films

Summary

Introduction

Since Davydov et al discovered the narrow band gap phenomenon of InN (Eg~0.7 eV), InN has attracted a wide range of research interest [1]. We expect InN to have the highest electron mobility among III-nitrides (approximately 4400 cm2/V·S). Many research teams have recently discussed the origin of the high emission peaks above the theoretical bandgap (~0.65 eV) in degenerate InN samples [11,12]. This high-energy peak has been ascribed to Mahan excitons and inspected by PL spectra and reflectivity measurement [12]. FFiigguurree11..SSccaannnniinnggeelleeccttrroonnmmiiccrroossccooppyyiimmaaggeessooffIInnNNssaammpplleess:: ((aa)) ttoopp--vviieeww iimmaaggeess aanndd ((bb)) ccrroossss-sseeccttiioonnaall iimmaaggeess

Films and Nanorods

Conclusions