Graphene-Assisted Quasi-van der Waals Epitaxy of AlN Film on Nano-Patterned Sapphire Substrate for Ultraviolet Light Emitting Diodes

Summary

A protocol for graphene-assisted growth of high-quality AlN films on nano-patterned sapphire substrate is presented.

Abstract

This protocol demonstrates a method for graphene-assisted quick growth and coalescence of AlN on nano-pattened sapphire substrate (NPSS). Graphene layers are directly grown on NPSS using catalyst-free atmospheric-pressure chemical vapor deposition (APCVD). By applying nitrogen reactive ion etching (RIE) plasma treatment, defects are introduced into the graphene film to enhance chemical reactivity. During metal-organic chemical vapor deposition (MOCVD) growth of AlN, this N-plasma treated graphene buffer enables AlN quick growth, and coalescence on NPSS is confirmed by cross-sectional scanning electron microscopy (SEM). The high quality of AlN on graphene-NPSS is then evaluated by X-ray rocking curves (XRCs) with narrow (0002) and (10-12) full width at half-maximum (FWHM) as 267.2 arcsec and 503.4 arcsec, respectively. Compared to bare NPSS, AlN growth on graphene-NPSS shows significant reduction of residual stress from 0.87 GPa to 0.25 Gpa, based on Raman measurements. Followed by AlGaN multiple quantum wells (MQWS) growth on graphene-NPSS, AlGaN-based deep ultraviolet light-emitting-diodes (DUV LEDs) are fabricated. The fabricated DUV-LEDs also demonstrate obvious, enhanced luminescence performance. This work provides a new solution for the growth of high quality AlN and fabrication of high performance DUV-LEDs using a shorter process and less costs.

Introduction

AlN and AlGaN are the most essential materials in DUV-LEDs^1,2, which have been widely used in various fields such as sterilization, polymer curing, biochemical detection, non-line-of-sight communication, and special lighting³. Due to the lack of intrinsic substrates, AlN heteroepitaxy on sapphire substrates by MOCVD has become the most common technical route⁴. However, the large lattice mismatch between AlN and sapphire substrate leads to stress accumulation^5,6, high density dislocations, and stacking fau....

Protocol

CAUTION: Several of the chemicals used in these methods are acutely toxic and carcinogenic. Please consult all relevant material safety data sheets (MSDS) before use.

1. Preparation of NPSS by nanoimprint lithography (NIL)

1. Deposition of SiO₂ film
   1. Wash the 2" c-plane flat sapphire substrate with ethanol followed by deionized water three times.
   2. Dry the substrate with a nitrogen gun.
   3. Deposit 200 nm SiO₂ film on the flat sapphire substrate by plasma-enhanced chemical vapor deposition (PECVD) under 300 °C. The deposition rate is 100 nm/min.
2. ....

Results

Scanning electron microscopy (SEM) images, X-ray diffraction rocking curves (XRC), Raman spectra, transmission electron microscopy (TEM) images, and electroluminescence (EL) spectrum were collected for the epitaxial AlN film (Figure 1, Figure 2) and AlGaN-based DUV-LEDs (Figure 3). The SEM and TEM are used to determine the morphology of the AlN on graphene-NPSS. XRD and Raman are used to calculate the dislocation densities and the r.......

Discussion

As shown in Figure 1A, the NPSS prepared by the NIL technique illustrates the nano-concave cone patterns with 400 nm depth, 1 μm period of pattern, and 300 nm width of the unetched regions. After the APCVD growth of graphene layer, the graphene-NPSS is shown in Figure 1B. The significant increased D peak of N-plasma treated graphene in Raman spectra Figure 1C demonstrates the i.......

Materials

Name	Company	Catalog Number	Comments
Acetone,99.5%	Bei Jing Tong Guang Fine Chemicals company	1090
APCVD	Linderberg	Blue M
EB	AST	Peva-600E
Ethonal,99.7%	Bei Jing Tong Guang Fine Chemicals company	1170
HF,40%	Beijing Chemical Works	1789
ICP-RIE	AST	Cirie-200
MOCVD	VEECO	P125
PECVD	Oerlikon	790+
Phosphate,85%	Beijing Chemical Works	1805
Sulfuric acid,98%	Beijing Chemical Works	10343