Incorporation of Silicon in Low Temperature Molecular Beam Epitaxial GaAs
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INCORPORATION OF MOLECULAR
SILICON IN LOW TEMPERATURE BEAM EPITAXIAL GaAs
M. 0. MANASREH*, K. R. EVANS*, C. E. STUTZ*, D.C.LOOK**, and J. HEMSKY** *Solid State Electronics Directorate (WL/ELRA), Wright Laboratory, Wright-Patterson Air Force Base, OH 45433-6543. **Department of Physics, Wright State University, Dayton,OH 45435. ABSTRACT of silicon donor The localized vibrational mode (LVM) (SiGa) in molecular beam epitaxial GaAs layers grown at various temperatures is studied using the infrared absorption technique. It is found that the total integrated absorption of this LVM is decreased as the growth temperature decreases. This finding suggests a nonsubstitutional incorporation of Si in GaAs layers grown at - 200 *C. On the other hand, an almost complete substitutional incorporation is obtained in GaAs layers grown at temperatures higher that 350 'C. Thermal annealing does not cause any recovery of the SiGa LVMs in present GaAs layers grown at -200 *C. INTRODUCTION
AND
EXPERIMENTAL
TECHNIQUE
It has been shown recently1 that the arsenic-rich molecular beam-epitaxial (MBE) GaAs layers grown at low temperature contain a large density (_1019 cm- 3 ) of deep defects that are related to the arsenic antisite (AsGa) defect. 2' 3 This material when used as buffer layers in field-effect transistor devices can substantially reduces backgating and sidegating. 4 For device applications and kinetic limitations 5 of low temperature MBE GaAs, it is desired to dope this materials with n- or p-type dopants. One method of studying the incorporation of dopants in this class of materials is to measure their localized vibrational mode frequencies (LVMs) . The optical absorption technique has the advantage of evaluating the LVMs of isolated 6 shallow impurities in GaAs regardless of their charge states. ,7 In this letter, we report on the optical absorption measurements of the SiGa LVMs in MBE GaAs layers grown at temperatures ranging between 200 and 580 'C. It is observed that the total integrated absorption of these LVMs is reduced as the growth temperature decreases suggesting a nonsubstitutional incorporation in layers grown at low temperatures. The effect of the thermal annealing on the SiGa LVM in layers grown at 200 'C will be presented. The MBE layers were grown in Varian systems under normal, As-stabilized conditions, at a growth rate of 0.8 pim/h. The beam equivalent As-to-Ga pressure ratio was about 20. The substrate was semi-insulating GaAs grown by the liquid-encapsulated Czochralski technique. The substrate temperature (T) was varied between 200 and 580 'C. The thickness was 20 pm for layers doped with Si. Infrared absorption measurements were made at 77 K with a BOMEM spectrometer. Silicon doped GaAs layers grown at T > 350 "C were electron irradiated at room temperature by Mat. Res. Soc. Symp. Proc. Vol. 241. ©1992 Materials Research Society
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using a 2.1 MeV electron beam from a van de Graaff accelerator in order to reduce the free carrier absorption. A conventional Hall effect technique is used to measure the
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