The formation mechanisms and properties of TiSi, on Si are investigated. The particular emphasis is in relating the nucleation, morphology, and phase stability of the films. TiSi, films were prepared by deposition of Ti on atomically clean silicon substrates in ultrahigh vacuum. The silicide formation was initiated either by in situ annealing or deposition onto heated substrates. The island formation of TiSi, and surface and interface morphologies of TiSi, were examined by scanning electron microscopy and transmission electron microscopy. The TiS& formation process was monitored with in situ Auger electron spectroscopy and low-energy electron diffraction to analyze the surface concentration and the surface structures, respectively. Raman spectroscopy was used for phase identification of the TiSi,. Titanium film thicknesses from 50 to 400 A were examined. For all thicknesses studied, the C49 TiSi, phase is observed to nucleate. Immediately after low-temperature deposition, the interface morphology was smooth, but after reaction and nucleation of the C49 TiSi, phase a rough interface was observed. After highertemperature annealing the transition to the C54 TiSi, phase was observed. For TiSi, on Si ( 1 1 1 ), the interface becomes smooth and flat. The temperature of the C49-to-C54 transition was observed to vary as a function of film thickness and substrate orientation. The films exhibited island formation after high-temperature annealing. For similar Ti thicknesses and annealing temperature, different area1 coverages and island morphologies of TiSi, on Si( 100) and Si ( 111) were observed. The island morphologies are modeled and analyzed based on a liquid-liquid model, and the surface and interface energies for different TiSiz island structures are deduced from contact angle measurements. The C49 nucleation, interface morphologies, surface morphologies, and the C49-to-C54 structural phase transition are discussed in terms of surface and bulk free-energy considerations. 4269

Epitaxial GaN films have been grown by plasma-enhanced chemical vapor deposition (PECVD). The growth procedure utilizes a He gas discharge combined with the down-stream introduction of trimethylgallium (TMGa) and nitrogen. Both cubic [1111 and wurtzitic [0001] GaN epitaxial films have been achieved on (0001) sapphire substrates. Differences in substrate growth temperatures are believed to account for the different observed phases. A comparative study pertaining to the microstructural, optical and electrical properties of the α-GaN and β-GaN heteroepitaxial films is presented. Also reported for the first time is the Raman spectroscopy data for cubic GaN.

The morphologies of ZrSi2 on Si(lll) and TiSi2 on Si(lll) and (100) have been investigated, and the results compared and contrasted. Films were prepared by UHV deposition of Ti or Zr onto clean, reconstructed Si(100) or (111) substrates, and reacted by in situ annealing. The sheet resistivity of the ZrSi2 was measured and found to be 33-42 yu,O-cm. The morphologies were examined by transmission and scanning electron microscopy. In particular, the islanding properties were studied; both the temperature of the onset of islanding and the island characteristics were measured. The surface and interface energies have been determined from the contact angles of the silicide islands, according to a solid-state capillarity model. The system of ZrSi2 on Si(lll) was found to have surface and interface energies lower than those of the system of TiSi2 on Si(100), but higher than those of the system TiSi2 on Si(lll). ZrSi2 on Si(lll) was found to island at a higher temperature than TiSi2 on either substrate, a result attributed to kinetic effects. Areal coverage of the islands was measured, and the results were consistent with the solid-state capillarity model. For both TiSi2 and ZrSi2, increasing faceted structure was observed with increasing anneal temperature. Preferred faceting planes were found to be of Si(lll) and (100) type for TiSi2 islands and of Si(lll) type for ZrSi2. Faceted islands were apparently epitaxial. As the solid-state capillarity model does not directly apply to islands with a faceted structure, an observation of the percentage of faceted islands produced by different annealing temperatures was used to suggest the processing conditions in which the model is applicable.

This study explores the nucleation and surface and interface morphology of TiSi2 films formed on Si (100) and (111) surfaces. Titanium suicide films were formed on atomically clean Si(111) and (100) surfaces by UHV deposition of Ti followed by in situ anneals. The TiSi2 formation process was characterized is itu using AES and LEED, and the interface structure was determined post preparation by HRTEM. The metastable C49 and stable C54 TiSi2 phases have been identified from Raman spectroscopy measurements. The islands were partially recessed into the substrate, and the shape and degree of recession was different for the islands on (111) and (100) substrates. On (111) substrates epitaxial islands were observed which exhibited different interface structures and epitaxial alignments. The contact angles of the islands were measured and the surface and interface energies of the different configurations were deduced. The mechanisms pertaining to island formation and interface morphology are described in terms of the wetting properties of a liquid-liquid system, with the effects of interface structures causing deviations from the model.

A comparative study pertaining to the molecular beam epitaxial growth of GaAs directly on silicon-on-sapphire and (101̄2) sapphire substrates has been made. Thermal strain is significantly reduced in these heteroepitaxial GaAs films as compared with GaAs on silicon; however, the (111) GaAs epitaxy on nominal (101̄2) sapphire contains double-position boundaries. Hall effect measurements and current-voltage characteristics from metal-semiconductor contacts show that GaAs grown on silicon-on-sapphire is superior to GaAs grown on (101̄2) sapphire under the experimental conditions employed.