Electrical and Optical Properties of Vanadium in OMVPE-Grown GaAs
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ELECTRICAL AND OPTICAL PROPERTIES OF VANADIUM IN OMVPE-GROWN GaAs
W. S. HOBSON*, S. J. PEARTON*, V. SWAMINATHAN*, A. S. JORDAN*, Y. J. KAO**, N. MKHAEGEL**, and H. KANBER*** * AT&T Bell Laboratories, Murray Hill, N.J. 07974 ** UCLA, Los Angeles, CA 90024 *** Hughes Aircraft Company, Torrance, CA 90505
ABSTRACT The electrical and photoluminescent properties of vanadium incorporated into GaAs epitaxial layers from a VO(OC 2 H5)3 source during organometallic vapor phase epitaxy were examined. The vanadium concentration in the GaAs was controllably varied from 1016 to 1018 atoms cm-3. Deep level transient spectroscopy showed the presence of an electron trap at Ec - 0.15 eV which increased in concentration with vanadium content of the epitaxial layers. A maximum value of 8 x 1015 cm-3 for this trap was obtained. There were no midgap electron traps associated with vanadium. In intentionally Si-doped epitaxial layers, co-doping with vanadium was observed to have no effect in reducing the carrier density when the Si concentration was > 4 x 1016 cm-3. The net carrier concentration profiles resulting from 29 5i implantation into GaAs containing 1018 cm-3 of total V had sharper tails than for similar implantation into undoped material, indicating the presence of less than 1016 cm-3 V-related acceptors. Photoluminescent spectra exhibited the characteristic V÷3 intracenter emission at 0.65-0.75 eV. No other deep level photoluminescence was detected. For a V concentration of 1016 cm- 3 only 2.5 x 1013 cm- 3 was electrically active. Over the entire V concentration investigated this impurity was predominantly (_>99%) inactive. INTRODUCTION There has been an exceptional amount of interest in the properties of vanadium in GaAs(- 15 ). To a large extent this has been prompted by the possible application of vanadium as a compensating impurity in order to produce high resistivity material. However, the role of vanadium in semi-insulating GaAs has been the subject of much uncertainty. A number of authors have reported that vanadium gives rise to a level at Ec - 0.15 eV and rule out the possibility of a midgap vanadium or vanadium-related center(6' 7',10,11). Rather, it is suggested that melt grown 6semi-insulating GaAs doped with vanadium depends solely upon EL2 for its high resistivity(6,1"0 ". On the other hand, Barrau et al.,(4) based on photoconductivity measurements, have postulated the existence of isolated vanadium as a double acceptor with energy levels at E, - 0.65 ± 0.03 eV and Ec - 0.16 ± 0.01 eV. Other levels associated with vanadium-related complexes have also been proposed 8 9,' 14,15). Finally, Terao et al.(1 3) have demonstrated the need for the presence of oxygen in order to obtain vanadium-doped semiinsulating GaAs by chloride vapor phase epitaxy, while workers at OKI Electric have utilized an oxygen-containing organometallic vanadium source to obtain semi-insulating GaAs:V by organometallic vapor phase epitaxy (OMVPE)1 2'3" 2 ). Due to the importance of obtaining semi-insulating GaAs epitaxial layers for a number of
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