Effect of Substrate Orientation on the Growth Rate and Surface Morphology on GaSb Grown by Metal-Organic Vapor Phase Epi
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Effect of Substrate Orientation on the Growth Rate and Surface Morphology on GaSb Grown by Metal-Organic Vapor Phase Epitaxy Jian Yu and Ishwara B. Bhat Department of Electrical, Computer and Systems Engineering Rensselaer Polytechnic Institute, Troy, NY 12180 ABSTRACT MOVPE of GaSb grown on (100), (111)A and (111)B GaSb substrates were investigated to study the effect of substrate orientation on the growth rate and surface morphology. Besides growth temperature and V/III ratio, the GaSb growth rate strongly depends on the crystallographic orientation. As the V/III ratio rises, the growth rate on the (111)B oriented substrate decreases, whereas that on the (111)A oriented substrate increases. The surface morphology on different substrates was studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). On (111)A substrates, triangular hillocks are the dominant defects, while on (111)B planes, three distinct types of hexagonal hillocks are observed, namely, non-flat top hexagonal structure with spiral growth features (Type I), flat top structure with lateral growth features (Type II), and non-flat top hexagonal structure with multiple islands (Type III). For all types, the basal edges of each hillock are preferentially aligned along directions. A closer look reveals that the top surface of Type II feature consists of many levels of small hexagonal shaped terraces, with each step height in the monolayer range, indicating a step flow growth involved. INTRODUCTION Semiconductor materials based on GaSb are promising for mid-infrared optoelectronics and thermophotovoltaic (TPV) devices [1-6]. One of the many factors that should be considered during GaSb epitaxial growth is the effect of substrate orientation on the defect formation and dopant incorporation. To the best of our knowledge, very little has been explored in the epitaxial growth of GaSb on different substrate orientations. In this paper, we present a detailed study of the effect of substrate orientation on the growth rate and surface morphology on GaSb grown by MOVPE. Orientation dependence of growth rate was studied as a function of temperature and V/III ratio. Morphology of epitaxial layers grown on (100), (111)B and (111)A substrates was studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Three distinct growth features on (111)B substrates were observed. Evidence of layer-by-layer step flow growth was identified using AFM. EXPERIMENTAL CONDITIONS GaSb epitaxial layers were grown by low pressure MOVPE in a horizontal quartz reactor with an RF-heated graphite susceptor. The organo-metallic sources were trimethylgallium (TMGa) kept at –7 °C and trimethylantimony (TMSb) at 4 °C. Experiments were performed under a total hydrogen flow of 5 standard liter per minute (slm), with V/III (i.e., TMSb/TMGa) ratios in the range from 0.8 to 1.6, at temperatures in the range from 550 to 620°C. Unintentionally doped, p-type (100), (111)A and (111)B oriented GaSb substrates were used in this study. Before loading into
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