Effects of Surfactants N and Br on Ordering in GaInP
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Effects of Surfactants N and Br on Ordering in GaInP D.C. Chapman, A.D. Howard, L. Rieth, R.R. Wixom, and G.B Stringfellow Department of Materials Science and Engineering, University of Utah, Salt Lake City, Utah 84112 ABSTRACT Formation of the CuPt ordered structure during the organometallic vapor phase epitaxial (OMVPE) growth of GaInP has significant effects on the electrical and optical properties, necessitating control of ordering. Formation of the CuPt structure is thermodynamically driven by the surface structure during growth. This has led to the study of the use of surfactants as a way of controlling ordering. To date, these studies have centered on the group V elements isoelectronic with P. Sb and Bi are both larger than P. This leads to less ordering. N, on the other hand, is smaller than P, which makes it potentially interesting. The other disordering mechanism, observed for Te as a surfactant in GaInP, is kinetic. Rapid step propagation leads to a reduction in ordering. This suggests another potentially interesting class of surfactants, the group VII elements, such as Br, that have been reported to increase the step velocity during OMVPE growth. This paper describes the results of the addition of the surfactants N and Br during the OMVPE growth of GaInP. Addition of N (DMHy) results in a clear reduction in order parameter, due to thermodynamic effects. The addition of Br (CBr4) is also observed to systematically decrease the amount of CuPt ordering and is found to correspond to a significant roughening of the surface, which is postulated to be the origin of the reduction in order parameter. INTRODUCTION Semiconducting alloys are of immense value for the fabrication of photonic and electronic devices and circuits. However, the optical and electronic properties are complex, because they depend explicitly on the arrangement of the atoms in the solid, i.e., the properties, for a fixed solid composition, are dependent on the growth conditions[1]. For example the bandgap of GaInP is postulated to differ by more than 500 meV between an alloy lattice matched to GaAs (xIn of approximately 50%) that is completely random and one that is completely ordered in the CuPt structure[2,3]. Of course, phase separation and clustering can also occur in alloys having a large positive enthalpy of mixing[4]. This also has major consequences for the materials properties. Phase separation is particularly a problem for the newly important dilute N alloys such as GaInAsN[5]. Thus, for alloy semiconductors, the microstructure, and hence the optical and electrical properties are dependent on growth parameters [6]. More significantly, recent work has demonstrated that surfactants, added in minute quantities during OMVPE growth, can also strongly affect the microstructure. Surfactants are elements that “float” on the surface during growth. They are largely rejected from the solid, although, as the concentration builds up on the surface, dopant quantities may be incorporated. These surfactants can change the thermodynamic prop
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