Organometallic vapor phase epitaxial (OMVPE) growth of GaAs, GaP and InP on Si has been studied using the two-step growth method. Growth parameters for a heteroepitaxial film with a specular surface, a single-domain structure and high crystallinity are demonstrated and discussed. Residual strains in grown films are evaluated and analyzed by taking account of elastic lattice deformation due to lattice mismatch or thermally- induced strain accomodation by rearrangement of misfit dislocations. Thin film GaAs and InP solar cells are fabricated and their performances are discussed in relation to defect density in the films. For GaAs cells, an efficiency of 18 % (AM1.5, active area) is attained by reducing defect density to 2×106 >cm−2 . The defect density is ~. 5×107 cm−2 in the present InP films, and is needed to be less than 106 cm−2 to attain an efficiency of 18 %.

High quality GaAs and InP have been grown on silicon substrates, using low pressure metalorganic chemical vapor deposition technique. The growth temperature is 550ºC andthe growth rate 100 A/min.

Photoluminescence, X-ray diffraction and electrochemical profiling verified the high quality of these layers. The use of superlattices as buffer layers, (GaAs/GaInP) in the case of GaAs/Si and (GalnAsP/InP) in the case of InP/Si, decreased the amount of misfit dislocations in the epitaxial layer. Carrier concentrations as low as 5.1015 cm-3 have been measured by electrochemical profiling.

The heteroepitaxy of InP on Si substrates was investigated using MOCVD. A thin GaAs intermediate layer was used to alleviate the 8.4% lattice mismatch between InP and Si. With the use of this intermediate layer, four inch size, single domain InP epilayer with small residual stress was reproducibly grown on off-(100) oriented Si substrates. The etch pit density (EPD) of as-grown InP layer was 5x107~1x108 cm-2 . The post growth annealing of this epilayer at 800~850ºC in aPH3+H2 ambient reduced EPD to 1~2x107 cm-2

It is shown that GaP layers grown upon Si at a single temperature of 900ºC can have a crystalline quality superior to that exhibited by previous two—step and one—step growth methods. The layers are characterized by a planar network of misfit dislocations confined to the interface plane an a reduced density of threading dislocations (low 106 cm-2; previously >108). Very few threading defects were observed in areas devoid of amorphous oxide contamination, as shown by HREM examination of cross—sectional samples. A low growth rate during nucleation enhances crystalline perfection, since it decreases the tendency toward three—dimensional islanding.

GaP crystals are grown on Si substrates by MOCVD. Double crystal X-ray diffraction indicates that the crystal quality of GaP layers greatly improves when AsH3 is supplied before growth. The FWHM of (400) diffraction peak of the GaP layer decreases as the thickness increases and the best FWHM of 112.5 arcs is obtained at a thickness of 5 μm. The GaP/Si interface is characterized using secondary ion mass spectroscopy (SIMS) to demonstrate the effect of AsH3.

Single crystals of cubic(beta) SiC were heteroepitaxially grown on Si to ameliorate the large lattice mismatch of 20 %. The structure and the role of the carbonized layer used for crystal growth are discussed. Single crystals were successfully grown on Si(100) and(111). Antiphase domains on Si(100) were examined to obtain smooth surfaces. The use of Si(100) off-axis substrates oriented towards [011] allowed the successufulelimination of the antiphase domains. Anisotropy was found in the electrical properties of SiC on off-axis substrates. Possible applications are described.

High purity β—SiC films have been epitaxially grown on Si (100) and off-axis Si (100) substrates. Conventional chemical vapor deposition at 1633K and 1 atm using SiH4 and C2H4 reactants in an H2 carrier gas was employed for this growth. Large differences in lattice parameter and thermal coefficients of expansion between the film and the substrate were partially compensated for by growing aninitial “conversion layer.” Plan view and cross—sectional transmission electron microscopy were utilized to study the conversion layer and the defects present in the films. A high density of stacking faults and dislocations were present in allthe films grown on Si, however, antiphase boundaries were eliminated when certain off—axis Si (100) substrates were employed. The effects of misorientation angle and substrate preannealing were investigated. The electrical properties of the β-SiC films were also studied using differential capacitance—voltage and Hall effect measurements as well as the I—V characteristics of Au—β—SiC Schottky diodes. It was found that the elimination of antiphase boundaries reduced leakage current but did not significantly effect carrier concentration or Hall electron mobility. Finally, the I—V characteristics of a Metal—Semiconductor—Field—Effect—Transistor (MESFET) have been evaluated for a β—SiC filmon an on—axis Si (100) substrate.

Schottky barrier contacts have been made on CVD—grown β - SiC on Si substrates, and their C—V and I—V characteristics are measured. Dependence of the Schottky characteristics on Si substrate orientation ((n11),(n=1,3,4,5,6), and (100)) is examined. The Schottky diodes of the β-SiC films on Si (611), Si(411), and Si (111) show excellent characteristics compared with the conventional Schottky diodes using Si(100) substrates. That is, reverse leakage currents are small, ideality factors are close to unity, and barrier heights are larger.

We developed a heteroepitaxial growth technique for large-area β-SiC films on Si substrates without buffer layers at 850ºC and 1000ºC. The substrates were vicinal 4-inch (111) Si wafers. The β-SiC films had smooth surfaces and were crack-free. X-ray diffraction and electron diffraction analysis revealed that the films grown at 1000ºC were single crystals. Satisfactory characteristics were obtained in aMOSFET with a β-SiC/Si02/poly-Si substrate structure. Our evaluations indicate that the β-SiC films were high-quality crystals.

Zirconium dioxide (ZrO2) films are deposited on Si(100) and Si(lll) substrates at 800ºC by vacuum evaporation. Channeling spectrum of the Rutherford backscattering shows that ZrO2 films (tetragonal(200)) are epitaxially grown on the Si(100) substrate. The fluctuation of crystallite orientation in the epitaxial layer is estimated to be 0.32º, by analyzing the angular dependence of the aligned and random backscattering spectra. Energy dependence of dechanneling factors in 0.3—2.0 MeV 4He+ indicates that the dominant defect arises from the stackingfaults.

In—situ cleaning of Si surfaces in vacuum was successfully performed using excited hydrogen and it was applied to epitaxial growth of SrTiO3 films on Si(100) substrates. Epitaxial growth of SrTiO3 films was observed under optimum cleaning conditions, however, the epitaxial nature was found to be destroyed for films thicker than 50 nm, which is probably due to the non—stoichiometry of the films. The electrical properties of the initially epitaxial SrTiO3 films grown on the cleaned Si substrates were better than those of polycrystalline ones.

Heteroepitaxial A1203 thin films were grown successfully on Si(lO0) substrates by low—pressure chemical vapor deposition (LP—CVD). The growth was performed at a pressure of 30 Torr by pyrolysis of N2 bubbled AI(CH3)3 and N20 at substrate temperatures above 1000ºC.RHEED patterns indicated that the grown films were ɤ—Al203 single crystals with an orientation relationship of ɤ—Al203(l00)//Si(l00). The ɤ—A1203 films were stable and did not show phase transition after a 1140ºC heat—treatment for 2hr. MOS capacitors with 500—Å—thick A1203 films as a gate insulator showed highfrequency capacitance—voltage (C—V) curves without hysteresis. The A1203 interface state density determined from quasi—static C—V measurements was 1.7 X 1011cm-2eV-1. It can be seen that ɤ—Al203 film is a promising new insulator for Si on Insulator (SOI) structures.

The transformation of amorphous to crystal (a-c) structure of Si02 layers, thermally grown on both (100) and (111) Si substrates, was carried out by CO2 laser, flash-lamp, and furnace heat: treatments. All the treatments resulted in S102 crystallization according to two different mechanisms: normal and self-sustained growth processes. The kinetic characteristics of the S102 crystallization process such as incubation time, rates of nucleation and growth, and the microstructure of the Si-Si02 interface were investigated and are discussed from the point of view of growth theory. The a-c transformation in Si3N4 and SixOyNz films on Si substrates is also discussed.

We have continued our investigation1 of the effects of pre—deposition substrate annealing for the case of MBE grown silicon on sapphire. Three identical series of samples were grown with film thicknesses ranging between 65 and 1500 angstroms. Each series of samples was grown upon sapphire which had been annealed at either 1450ºC, 1300ºC, or 900ºC. The growth temperature and growth rate were the same for each series. The anneal time for each sample was 30 minutes.

An x-ray diffraction study is made of the effect of silicon film thickness on the peak broadening associated with the (024) sapphire Bragg reflection peak for MBE—grown SOS material. The predeposition treatment and growth parameters for the samples in the series were identical. The thicknesses ranged from 5500 to 40,000 angstroms and the growth rate was roughly I angstrom/second.

SOS films with silicon thicknesses below 5500A did not produce sapphire peak broadening when compared with the corresponding sapphire standard. With reference to standard sapphire reflection peaks, the 5500A film shows slight broadening while a I micron film broadened 14 seconds of arc when compared at FWHM with the sapphire standard. A possible explanation for this is that at overlayers less than 5500A, the film is not sufficiently massive to exert a uniform strain on the sapphire. At 5500A the film attains a critical thickness sufficient to strain the substrate and produce detectable broadening. For thickerfilms the strain would increase proportionally. Results from lattice parameter measurements on the silicon epilayer indicate that the perpendicular lattice parameter relaxes atgreater thicknesses but is still in tension when compared with bulk silicon. One would expect that the strain gradient suggested by these results would be greatest at the silicon/sapphire interface and that the defect concentration at the interface might beaffected by this strained condition.

By nature of their high degree of crystalline perfection, epitaxial insulators and metals on semiconductors are structurally characterizable to a considerably greater extent than are polycrystalline or amorphous materials. This offers the possibility of correlating the detailed structure of these thin epitaxial films and their interfaces with their electrical properties. We have recently found evidence for the influence of the atomic structure of the CaF2/Si(ll1) interface on its electrical properties. Wehave also studied the structural and electrical properties of ultrathin epitaxial cobaltsilicide layers on Si(111).

We report the first study on improvement in surface morphology and crystal quality of as—grown epitaxial CaF2 film on a (100) Si substrate grown through two MBE growth stages without any post-growth treatment. The degree of improvement in surfacemorphology and crystal quality depends not only on the thickness of an initial thin CaF2 film grown at the early growth stage of 550ºC but also on both the subsrate temperature and thickness of a sequential grown CaF2 film used for thesecond growth stage. Under optimum conditions, the CaF2 films exhibited high quality with an RBS/channeling minimum yield of 4%, together with a very smooth surface morphology without any other nuclel or cracks.

The growth of SrF2 on Si(111) is investigated using photoemission spectroscopy and compared to the growth of CaF2 on Si(l11). Both CaF2 and SrF2 have a fluorite lattice structure closely related to silicons diamond lattice structure. However, while the room temperature lattice constant of Si is only 0.6% smaller than that of CaF2, it is 6.8% smaller than that of SrF2. The photoemission results for thin films of SrF2 on Si(111) are very similar to previous measurements of the CaF2-on-Si(111) interface, reflective of strong silicon-cation bonding and the removal of fluorine from the interface. These results indicate that the chemical and electronic driving forces to dissociate the CaF2 or SrF2 molecule at the fluoride-silicon interface dominate over the structural constraints induced by the lattice mismatch.

Stacks of non lattice matched epitaxial CaF2, SrF2 and BaF2 layers have been grown by MBE onto Si(lll), and, for the first time, onto Si(l00). On CaF2 covered Si(lll) surfaces, BaF2 grows in a 2—d way after formation of the first monolayers despite a lattice mismatch of 14%. On Si(l00), BaF2 grows with the same (100)—lattice orientation as the underlying substrateif at least a thin (=100 Å) intermediate CaF2 layer is deposited first. Growth is 3—d on (100)—surfaces because of the large (100)—surface free energy of the group IIa—fluorides. By applying in situ short anneal cyclesat the first stages of growth, the crystallographic quality increases for (111)— as well as for (100)—orientation.

Growth techniques for very thin CoSi2 and Si layers for multilayer applications have been studied. CoSi2 layers without observable pinholes are grown by atechnique utilizing the room-temperature codeposition of Co and Si in stoichiometric ratio with a Si cap, followed by annealing. The crystallinity of the resulting CoSI2 layers annealed at various temperatures was studied by in-situ Rutherford backscattering channeling spectroscopy. The channeling minimum yield decreases with increasing annealing temperature, and drops sharply at ~ 570ºC. Si overgrowth was studied on CoSi2 by a Si template technique, which utilizes the deposition of a thin amorphous Si layer followed by annealing prior to the growth of the bulk of the Si layer. The effect of Si thickness and annealing temperature on Islanding of the Si overlayer was studied by Auger electron spectroscopy. Critical temperatures for a numberof Si thicknesses were identified, above which islanding of these layers occurs.