Role of Arsenic Hexagonal Growth-Suppression on a Cubic GaNAs Growth Using Metalorganic Chemical Vapor Deposition
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ABSTRACT The hexagonal domain suppression-effects in cubic-GaNAs grown by metalorganic chemical-vapor deposition (MOCVD) is reported. A thin buffer layer (20 nm) was first grown on a substrate at 853 K using trimethylgallium and dimethylhydrazine (DMHy), and GaNAs samples were grown at different AsH3 flow rates (0 ~ 450 µmol/min) at 1193 K. As a result, three types of surface morphologies were obtained: the first was a smooth surface (AsH3 = 0 µmol/min); the second was a mirrorlike surface having small and isotropic grains (AsH3 : 45 ~ 225 µmol/min ); and the third involved threedimensional surface morphologies (above 450 µ mol/min of AsH3 flow rate). Furthermore, it was confirmed using X-ray diffraction that the mixing ratio of hexagonal GaNAs in cubic GaNAs decreased with an increase of the AsH3 flow rate. We could obtain GaNAs having a cubic component of above 85% at AsH3 flow rates above 20 µ mol/min. Therefore, the MOCVD growth method using AsH3 and DMHy was mostly effective for suppressing hexagonal GaNAs. It was observed that the photoluminescence intensity of GaNAs was decreased with increase of arsine flow rate.
INTRODUCTION III-N-V materials, such as GaNP and GaNAs, have a very large band-gap bowing and are very promising for light-emitting devices with a very wide wavelength region from ultraviolet to infrared [1,2]. They are expected to realize a wider range of bandgaps with a smaller lattice mismatch to GaN. However, III-N-V type alloys can be hardly grown under an equilibrium condition, since they have a very large miscibility gap [3,4]. The gas-source molecular-beam epitaxy (GSMBE) growth of nitrogen (N) rich hexagonal (h) GaNAs [5] and GaNP [6,7] alloys on sapphire substrates and their optical properties have been recently reported. The maximum As and P concentrations of these alloys with a hexagonal structure are so far limited to 0.26% [6] and 8.3% [7], respectively. However, there has been no report on a metalorganic chemical vapor deposition (MOCVD) growth of cubic-GaNAs using
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the dimethylhydrazine (DMHy). In this paper, the As effect for hexagonal growthsuppression on cubic GaNAs growth is reported in MOCVD.
EXPERIMENTAL GaNAs was grown on a GaAs (001) substrate using a horizontal MOCVD apparatus. The pressure in the reactor was 160 Torr. Trimethylgallium (TMG), DMHy [(CH3)2NNH2] and arsine (AsH3) were used as precursors of Ga, N, and As, respectively. A GaN buffer layer of about 20 nm in thickness was grown on the substrate using TMG and DMHy at 853 K. After that, a GaNAs layer was grown on the GaN buffer layer at 1193 K under the conditions of different AsH3 flows. The growth temperature was constant at 1193 K, since when the growth temperatures were lower than 1193 K and also higher than 1223 K, the grown surface became rough. The surface morphologies of the samples were observed by scanning electron microscopy (SEM), and the surface roughness was measured by atomic force microscopy (AFM). The crystal structure was investigated by an X-ray diffraction (XRD) measurement. Seconda
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