Nucleation and Defect Structures of GaAs Films Grown on Reactive Ion Etched Si Substrates
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NUCLEATION AND DEFECT STRUCTURES OF GaAs FILMS GROWN ON REACTIVE ION ETCHED Si SUBSTRATES
Henry P. Leea), Thomas George, Hyunchul Sohn, Jay Tu, Eicke R. Weber and Shyh Wang University of California,Berkeley, CA. 94720
ABSTRACT The nucleation and interfacial defect structure of thin GaAs films grown on reactive ion etched Si substrates by normal molecular beam epitaxy (MBE) and modulated molecular beam epitaxy (MMBE) at 300'C were studied by plan view and high resolution cross-sectional electron microscopy (TEM). Plan view TEM micrographs show a pronounced three-dimensional (3-d) island type nucleation for the MBE grown sample. A high density of microtwins is also found in these nucleated islands from high resolution cross-sectional TEM micrographs. The 3-d nucleation and the interfacial twinning is suppressed however in the MMBE grown samples. The FWHM of the (400) Bragg peak for 3 pan thick GaAs on Si films shows a reduction of 60 arcseconds when the initial buffer layer is grown by MMBE as compared to normal MBE.
INTRODUCTION The opportunity to combine optoelectronic and high speed GaAs-based devices with highly developed Si integrated circuit is the most rewarding long-term objective of GaAs on Si (GaAs/Si) technology[l]. In realizing such circuitry, GaAs films have to be grown on designated areas of the Si substrates on which Si devices have already been fabricated. A dielectric layer such as SiN is deposited over Si devices to prevent the diffusion of Ga and As during the epitaxial growth of GaAs[1]. The definition of opened vias exposing the Si substrate for GaAs growth requires the etching of Si 3N4. Although wet etching can be used for such a purpose, reactive ion etching (RIE) is preferred since it is more compatible with VLSI technology. Frequently, the RIE process of the Si 3N4 results in a slight etching of the Si substrate. While MBE grown GaAs/AlGaAs double-heterostructure lasers have been demonstrated on Si 3N4-
a)Present address: Bellcore 331 Newman Spring Rd. Red Bank NJ.07701.
Mat. Res. Soc. Symp. Proc. Vol. 198. @1990 Materials Research Society
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patterned Si substrates defined by RIE process with threshold current densities comparable or superior to similar lasers grown on a planar Si substrates[2], the effect of RIE process on the crystalline quality of the subsequently grown GaAs films is not clear. In this paper, the effect of RIE treatment on the nucleation and defect structure of thin GaAs/Si films grown by molecular beam epitaxy (MBE) and modulated MBE is investigated. EXPERIMENTAL PROCEDURES Heavily doped n-type (100) Si substrates tilted 3.50 towards the [011] axis have been used in all experiments described here. A 800
A
thick Si 3N4 is first deposited by thermal
chemical vapor deposition. The substrates (without any lithographic patterning) are then etched by RIE using a mixture of CHF 3(90%) and 02(10%) and a 20% over etching time in the same way as a lithographically patterned sample would be processed. Etching of the Si substrate was calibrated in a separate experiment
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