Effects of Al and N2 Flow Sequences on the Interface Formation of AlN on Sapphire by EVPE

Katsuhiro Kishimoto,Mitsuru Funato,Yoichi Kawakami

doi:10.3390/cryst7050123

Abstract

The interface formation mechanisms of AlN films on sapphire substrates grown by the elementary source vapor phase epitaxy (EVPE) method, which is a new AlN bulk fabrication method using Al and N2 as precursors, are investigated. Supplying N2 after the substrate temperature reaches the growth temperature [Process N2(GT)] causes the interface to become rough due to the thermal decomposition of sapphire. Self-separation occasionally occurs with the Process N2(GT), suggesting that the rough interface generates self-separating films with little strain. On the other hand, supplying N2 beginning at room temperature forms a relatively smooth interface with voids, which can be realized by the reaction between a nitrided sapphire surface and an Al source.

Highlights

AlN bulk crystals are promising as substrates of AlGaN-based deep ultraviolet light emitters and high-frequency electronic devices with high-breakdown voltages
We have proposed a new growth method of AlN substrates: elementary source vapor phase epitaxy (EVPE) [11,12]
The dependence of the c lattice parameter on thickness indicates that the strain derived from the thermal stress remains in crack-free films on sapphire substrates, but is almost completely relaxed in self-separated films

Summary

Introduction

AlN bulk crystals are promising as substrates of AlGaN-based deep ultraviolet light emitters and high-frequency electronic devices with high-breakdown voltages. AlN substrates are fabricated mainly by the physical vapor transport method [1,2,3,4,5] and hydride vapor phase epitaxy method [6,7,8,9,10]. Increase the diameter, and improve the crystalline qualities, these methods must be refined. To this end, we have proposed a new growth method of AlN substrates: elementary source vapor phase epitaxy (EVPE) [11,12]. EVPE can fabricate AlN with a maximum growth rate of 18 μm/h and a minimum dislocation density of 5 × 108 cm−2 [11,12]

Methods

Discussion

Conclusion