Defects in Mg-Doped InP and GaInAs Grown by Omvpe
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DEFECTS IN Mg-DOPED InP AND GaInAs GROWN BY OMVPE
FRED R.
BACHER,
H. CHOLAN, AND WALLACE B. LEIGH
Oregon Graduate Center, Department of Applied Physics and Electrical Engineering, 19600 N.W. Von Neumann Drive, Beaverton, Oregon 97006-1999, USA ABSTRACT We report on the defects present in doped InP and GaInAs grown by The material was grown in an organometallic vapor phase epitaxy (OMVPE). atmospheric pressure system using group III trimethyl sources, arsine and phosphine. Bis(cyclopentadienyl) magnesium (Cp2Mg) was present as a p-type source of magnesium. Defects in as-grown material were characterized using photoluminescence (PL), Hall-effect, and deep level transient spectroscopy (DLTS). Various levels of Mg doping were investigated, ranging from 5 x 1015 to 1 X 1019 cm- 3 . Radiative defects were observed at 77 K corresponding to PL emission from conduction band/shallow donor to acceptor
levels including emission at 1.37 eV identified as the shallow hydrogenic acceptor, and emission lines at 1.3 eV and 1.0 eV in heavily doped material. Corresponding hole traps in InP:Mg were observed by DLTS having thermal activation energies of 0.20 and 0.40 eV, the 0.40 eV trap being the dominant defect in p-type InP. In GaInAs grown near lattice-matched to InP, radiative emission is also observed from deep centers 100 meV from band edge emission. This emission is observed to be related to lattice-mismatch of the ternary with the InP, and is found to be accentuated and broadened in GaInAs doped with Mg. INTRODUCTION A great majority of the present and proposed near-infrared optical and optoelectronic devices require p-type epitaxial layers of InP, GaInAs, and/or GaInAsP. Emission devices such as light emitting diodes or solid state lasers require heavily doped p+ material to insure recombination is maintained in the active region. Heavily doped p-type material is also desirable in such applications as photocathodes. A final p+ layer on a multi-layer epitaxial device insures good ohmic contact as well as lower series resistance. P-type doping of III-V compounds can often be difficult: doping during growth from the melt is complicated by unfavorable dopant distribution coefficients and high vapor pressures. Doping using diffusion sources requires precise control of diffusion times and temperatures to insure the proper junction depth. Cadmium and zinc impurities have a tendency to re-diffuse during any further high temperature processing. P-type doping during growth via organometallic vapor phase epitaxy (OMVPE) has the capability to alleviate some of these effects. At the same time that heavy p doping is needed, it is important that the p-type layer be relatively free of defects [1]. Frequently, the p+ layer is used as a window for optical transmission, and any stray absorption by defects is undesirable. Also, deep levels tend to limit diffusion lengths of carriers, and promote non-radiative recombination. In this study, defects in Mg-doped InP and GaInAs grown by OMVPE using Trimethyl group III sources and bis(cyclopentadi
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