The role of gaseous species in group-III nitride growth
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Internet Journal o f
Nitride S emiconductor Research
Volume 2, Article 45
The role of gaseous species in group-III nitride growth S. Yu. Karpov Advanced Technology Center Yu. N. Makarov Lehrstuhl für Strömungsmechanik, University of Erlangen-Nürnberg M. S. Ramm Ioffe Physical-Technical Institute This article was received on June 30, 1997 and accepted on October 15, 1997.
Abstract A quasi-thermodynamic model accounting for kinetics of molecular nitrogen evaporation is applied to simulate the growth of binary and ternary group-III nitrides using atomic group-III elements and molecular ammonia as the sources. The values of the molecular nitrogen evaporation coefficients from the surface of GaN and AlN necessary for the simulation are extracted from experiments on free evaporation of the crystals in vacuum, while for InN only estimates are available. The growth process of AlN and InN is studied by analyzing the composition of the desorbed vapor species that are thought to influence the native defect formation in group-III nitrides. Different channels of desorption from the surfaces of group-III nitrides (related either to group-III atoms or to their hydrides) are compared. Specific features of the growth processes under the metal-rich and N-rich conditions are analyzed. The developed approach is extended to study the growth of the ternary compounds GaInN and AlGaN. The growth rate of ternary compounds versus temperature shows a two-drop behavior corresponding to the rapid increase of the respective group-III atom desorption. The effect is accompanied by a corresponding stepwise change in the solid phase composition. Factors retarding the growth of ternary compounds — the miscibility gap related to internal strain accumulated in the solid phase due to the lattice mismatch of binary constituents, and the extra liquid phase formation during growth — are discussed with respect to GaInN.
1. Introduction Group-III nitrides have attracted considerable interest in recent years due to their potential application to blue/green light emitters (including lasers), high-temperature electronic devices, and UV photodetectors [1]. During the early stage, high-quality epitaxial layers were obtained mainly by using the Metal Organic Chemical Vapor Deposition (MOCVD) technique [2] [3] [4]. Now, Molecular Beam Epitaxy (MBE) also plays an important role in growth of nitrides. This is due, in part, to the possibility of detailed studies of the growth process with standard MBE tools – Reflection High Energy Electron Diffraction (RHEED) and Desorption Mass Spectrometry (DMS) [5] [6] [7] [8] [9]. Additional progress has been achieved in the last few years by implementation in MBE of gaseous ammonia as the source of reactive nitrogen [10] [11] [12] [13]. The ammonia source provides relatively high growth rates, comparable with those of MOCVD, and produces high-quality epitaxial layers [11] [12] [13] [14] without having the effects of accelerated ions on material properties (as takes place in MBE based on plasma activated molecular nitrogen
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