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Cite this article as: MRS Internet J. Nitride Semicond. Res. 4S1, G3.44(1999) ABSTRACT Arsenic-doped GaN films and GaNAs films have been synthesized by MOCVD. Samples were grown on sapphire, GaN-coated sapphire, and GaAs substrates. Composition, structure, and phase distribution were characterized by EPMA, SIMS, XRD, and TEM. The arsenic content increases demonstrably as the growth temperature descreases from 1030 to 700 'C. In the high temperature limit, high quality arsenic-doped GaN forms on GaN-coated sapphire. In the low temperature regime, nitrogen-rich GaNAs forms under some growth conditions, with a maximum arsenic mole fraction of 3%, and phase segregation in the form of GaAs precipitates occurs with an increase in arsine pressure, Preferential formation of the nitrogen-rich phase on GaN-coated sapphire suggests the presence of substrate-induced "composition pulling". I.

INTRODUCTION

Group III nitride semiconductor alloys with mixing on the anion sublattice are of considerable interest because of their potential application to a wide range of optoelectronic devices. The large difference in bond lengths between group III nitrides and arsenides results in an enormous miscibility gap in the pseudo-binary phase diagram, making it difficult to synthesize alloys in the intermediate composition range. While arsenic-rich alloys have been studied by a number of research groups, there are only a few reports on the synthesis of nitrogen-rich compounds. 1-3 In the present work, nitrogen-rich GaNAs alloys and arsenic-doped GaN have been synthesized by metalorganic chemical vapor deposition (MOCVD). Emphasis was placed on determining the influence of growth parameters, and the choice of substrate material, on the composition, phase distribution, and structural properties of these materials. II.

EXPERIMENTAL PROCEDURE

All of the samples described herein were grown in a conventional, horizontal-flow MOCVD reactor held at a pressure of 100 torr. Palladium-purified hydrogen was used as the carrier gas with a total flow rate of 8 slm. Trimethylgallium, ammonia, and arsine precursors were employed during growth, with the ammonia and trimethylgallium flows kept constant at 4 slm and 50 pmol/min, for all samples, while the arsine flow was varied between 4 and 400 sccm. Growths were performed on bare sapphire and GaAs substrates, as well as on GaN 4 pseudo-substrates. for the purpose of studying the relationship between gas phase chemistry and arsenic incorporation in the solid. In addition, a two-step growth method was employed in some cases to optimize 5 electronic properties. Film composition was determined using quantitative electron probe microanalysis (EPMA), by measuring the nitrogen Ka line and gallium and arsenic Lee line intensities, with the electron beam energy ranging from 6 to 13 keV. Substrate and surface contamination effects were eliminated as sources of error by performing variable-energy measurements. The arsenic mole fraction (x) and Ill-V stoichiometry ratio (s) were derived as follows [As atomic %] [As