Element III Segregation During Mocvd Growth on Structured Substrates
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ELEMENT III SEGREGATION DURING MOCVD GROWTH ON STRUCTURED SUBSTRATES ERIC P. MENU, KENNETH M. DZURKO AND P. DANIEL DAPKUS Department of Electrical Engineering and Center for Photonic Technology, University of Southern California, Los Angeles CA. 90089-0483 ABSTRACT The crystal habits of GaAs and GaAlAs grown on structured substrates by Metalorganic Chemical Vapor Deposition (MOCVD) have been investigated. The growth behavior was delineated by depositing alternating thin layers of AlGaAs and GaAs over grooves and mesas. A strong temperature dependence of facet growth rate and an anisotropy of Al composition with facet orientation are observed. This latter effect so far undocumented in MOCVD has been analysed by Auger Electron Spectroscopy performed on cleaved cross-sections. BCF theory has been used to extract quantitative microscopic data. These observations demonstrate the importance of surface effects and provide an insight into MOCVD growth mechanisms. INTRODUCTION MOCVD growth of III-V compounds on non-planar substrates has become a very active and successful area [1-4], adding a new dimension to the already recognized versatility of MOCVD. Overgrowth of patterned features provides lateral control of dielectric as well as electronic material properties for the fabrication of waveguides [5] and semiconductor lasers [4,6,7]. As an application, we have fabricated very low threshold GaAs/GaAlAs quantum well lasers for which the unique property of temperature dependent growth rate of facets allows us to isolate and tailor the sizes of the active and cladding layers in a single step process [6]. Such a technique can also be applied to the fabrication of reduced dimension structures (quantum wires and boxes) which are expected to yield remarkable properties [8]. Finally, non planar growth is also attractive as a potential tool to study growth mechanisms in MOCVD, the least understood of all epitaxial techniques. However, little work has been done in this direction because MOCVD is most often considered as a non-equilibrium diffusionlimited process. In this paper we present results on the element III segregation on side facets of mesas and grooves and the temperature dependence of growth rates. These observations strongly suggest surface kinetics effects. A step layered growth model based on Burton, Cabrera and Frank theory [9] (hereafter BCF) is used to interpret our results.
EXPERIMENTALS AND GENERAL RESULTS Experimental details regarding patterning and wet etching are described elsewhere [1]. Cross sections were observed with a Scanning Electron Microscope (SEM) equipped with a backscatter detector. Compared to the secondary electron signal, the backscattered electron signal is much more sensitive to and increases with the atomic number of the element (Z-contrast) [10]. No composition sensitive etch was thus needed to reveal layers of different compositions. Mat. Res. Soc. Symp. Proc. Vol. 145. @1989 Materials Research Society
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Auger Electron Spectroscopy AES was chosen to analyse the composition of the
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