EL-2 Defect Formation and Carbon Incorporation in GaAs grown by Organometallic Vapor Phase Epitaxy
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EL-2 DEFECT FORMATION AND CARBON INCORPORATION GaAs GROWN BY ORGANOMETALLIC VAPOR PHASE EPITAXY
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R. Venkatasubramanian, Research Triangle Institute, Research Triangle Park, NC 27709; .T.M. Borrego and S.K. Ghandhi, Electrical Computer and Systms Engineering Dept., Rensselaer Polytechnic Institute, Troy, NY 12180.
ABSTRACT The anti-site defect AsCa, EL-2, is used to understand the nature of arsenic surface species during the Organometallic Vapor Phase Epitaxy(OMVPE) of GaAs. The concentration of EL-2 in unintentionally doped n-GaAs, measured by Deep Level Transient Spectroscopy, is presented as a function of AsH 3 partial pressure, TMGa partial pressure and the growth temperature. Based on this data, a model for EL-2 incorporation in OMV•PE GaAs is developed in which all surface species As-H, are converted to As 2 at around 765 *C. Under the same set of growth conditions, relative carbon levels measured by 4K Photoluminescence, suggest that the increase in carbon levels with growth temperature is due to the gas-phase loss of H radical from the As-H species.
Introduction EL-2 is a deep donor located at E.-O.82 eV, with a relatively high electron capture cross-section of about 4 x 10-15 cm 2 [1]. Although its exact electronic nature is far from clear, it is known that the anti-site defect (AsGa) is involved. Although this level is regularly observed in OMVPE n-GaAs, there has been no discussion of the EL-2 defect formation mechanism in the OMVPE process, along the lines of the probable nature of the growth mechanism [2]. There have been a number of studies on the concentration of this level as a function of arsine (AsH3 ) and trimethylgallium (TMG) partial pressure ratio, but the results vary considerably [3,41. Analysis of these results is complicated by the fact that the electron concentration depends on the AsH 3 /TMG ratio, and thermodymanically can affect the EL-2 concentration since the EL-2 is a donor-like specie. Further, an oxygen-related level is expected to be close to the energy position of EL-2, possibly affecting interpretation [5]. We have addressed these issues by studying arsine partial pressure dependencies at growth temperatures where intrinsic carrier levels exist, to isolate the EL-2 concentration dependence on AsH3 /TMG ratio. Oxygen-related levels were minimized by incorporating molecular-sieves on the AsH3 source. The concentration of EL-2 was measured by Deep-Level Transient Spectroscopy (DLTS) as a function of AsH 3 partial pressure (PA-, 3 ) TMG partial pressure (PTMG) and growth temperature. A model for
Mat. Res. Soc. Symp. Proc. Vol. 163. ©1990 Materials Research Society
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the nature of arsenic species and EL-2 formation in OMVPE GaAs, is developed, based on these results. Since carbon incorporation in OMPVE GaAs is closely tied to the nature of arsenic species, either on the growing GaAs surface or in its vicinity, we have also studied the carbon incorporation in the same set of samples. Carbon levels were evaluated by 4K photoluminescence (PL).
Experimental The GaAs layers w
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