Silicon cross doping and its effect on the Si or Be implantation doping of gallium arsenide grown on (100) silicon by me
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P. Chi and D. Simons National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (Received 2 May 1991; accepted 29 April 1992)
A study of the cross doping of GaAs layers grown by a two-step metalorganic chemical vapor deposition on Si substrates is reported. All as-grown, unintentionally doped layers of GaAs were n-type, and the carrier profiles tracked the Si atomic profiles. Furnace annealing at 850 °C for 30 min in an arsine overpressure, which is used to improve the crystalline quality of the GaAs near the heterointerface, caused additional Si to diffuse into the GaAs layer. Comparison of the Si concentration at the interface with the carrier concentration suggested the presence of compensating acceptors. Resonance Raman scattering by the SiAs local vibrational mode near the interface shows that a fraction of the Si atoms are localized at the As sites. The furnace annealing increased the Si concentration in the 1.7-1.8 /mm thick initially grown GaAs layer. This, in turn, influenced the electrical profiles created with Si or Be implantation on a 2.3 /x,m thick GaAs layer.
I. INTRODUCTION Recently, there has been a considerable effort to grow GaAs on a Si substrate to combine the capabilities of Si for very large-scale integration with the optoelectronic advantages of GaAs in the same monolithic structure. 1 ^ The main obstacle to the use of the GaAson-Si technology seems to be the crystalline imperfections in the GaAs films. Post-growth annealing is one of the most effective ways to reduce these defects.4"6 The electrical integrity of the heteroepitaxial structure and the determination of the background n-type dopant have been a primary concern. The cause of «-type doping in nominally undoped GaAs grown on Si has not been conclusively established. Some results indicate that this n-type carrier concentration is an intrinsic property of the large number of dislocations resulting from the substantial lattice mismatch.7'8 For the case of GaAs on Si grown by molecular beam epitaxy (MBE), the Si substrate has been suggested as the source of the electrons.3 In a GaAs/Si heterostructure, the substrate Si could act as an n-type dopant in the epilayer and the As could also act as an n-type dopant in the substrate. Cross doping with Si has been observed in GaP layers grown on Si.9 While one study of MBE-grown GaAs on Si by secondary ion mass spectrometry (SIMS) did not reveal any cross doping in samples, even when subjected to anneals up to 900 °C for 30 min,10 another SIMS investigation clearly indicated Si transport into the GaAs.11 The Si uptake near the GaAs/Si interface has also shown orientation dependence. Less uptake has 2186 http://journals.cambridge.org
J. Mater. Res., Vol. 7, No. 8, Aug 1992 Downloaded: 26 Mar 2015
been seen on (321) GaAs than on (100) GaAs.12 Where metalorganic chemical vapor deposition (MOCVD) was used to grow GaAs on Si, SIMS indicated some tailing of Si into the GaAs.13"16 At a growth temperature of 630 °C, the "ordinary" diffusion of Si into the GaAs and As into the Si
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