Connection between Carbon Incorporation and Growth Rate for GaN Epitaxial Layers Prepared by OMVPE.

Timothy Ciarkowski,Robert Mccarthy,Patrick Fay,Jinqiao Xie,Eric Carlson,Jingshan Wang,Noah Allen,Louis Guido,Chris Youtsey

doi:10.3390/ma12152455

Abstract

Carbon, a compensator in GaN, is an inherent part of the organometallic vapor phase epitaxy (OMVPE) environment due to the use of organometallic sources. In this study, the impact of growth conditions are explored on the incorporation of carbon in GaN prepared via OMVPE on pseudo-bulk GaN wafers (in several cases, identical growths were performed on GaN-on-Al2O3 templates for comparison purposes). Growth conditions with different growth efficiencies but identical ammonia molar flows, when normalized for growth rate, resulted in identical carbon incorporation. It is concluded that only trimethylgallium which contributes to growth of the GaN layer contributes to carbon incorporation. Carbon incorporation was found to decrease proportionally with increasing ammonia molar flow, when normalized for growth rate. Ammonia molar flow divided by growth rate is proposed as a reactor independent predictor of carbon incorporation as opposed to the often-reported input V/III ratio. A low carbon concentration of 7.3 × 1014 atoms/cm3 (prepared at a growth rate of 0.57 µm/h) was obtained by optimizing growth conditions for GaN grown on pseudo-bulk GaN substrates.

Highlights

Carbon has been shown by density functional theory to sit on the nitrogen sub-lattice and to behave as a compensator in n-type GaN [1,2]
TMGa flow was the chosen variable because ofthe its the “initial” source of both carbon and gallium and these two species do not compete for importance as the source of C→anion)
It was found that only TMGa contributing to the growth rate contributes to carbon incorporation

Summary

Introduction

Carbon has been shown by density functional theory to sit on the nitrogen sub-lattice and to behave as a compensator in n-type GaN [1,2]. Compensation in GaN epitaxial layers decreases electrical conductivity [3] which, in turn, increases on-resistance in high-power devices [4]. Drift layers in power devices with high blocking voltages require low n-type doping [6], (Nd −Na ) ≈ 1.5 × 1015 cm−3 for breakdown voltages approaching 20 kV. Carbon is part of the organometallic molecule used as the gallium source Ga(CH3 ) in GaN growth via organometallic vapor phase epitaxy (OMVPE). Regardless of source purity and possible reduction of contamination from reactor parts, carbon will always be part of the OMVPE environment

Methods

Results

Conclusion