Research on II–VI semiconducting compounds during the last two decades has been motivated by possible device applications such as thin film transistors, photodetectors and solar energy converters. In particular, the direct gap n-type semiconductor CdSe, has remained the subject of studies aimed at developing efficient photovoltaic and photoelectrochemical cells. For the low-cost production of polycrystalline CdSe layers, many noteworthy methods have been employed, such as: vacuum deposition, spray pyrolysis, chemical bath deposition and electrodeposition [1–5]. The best reported performances of photoelectro-chemical cells using CdSe films obtained by these methods, in contact with an aqueous polysulfide electrolyte and under solar or simulated solar radiation, have varied between 5 and 7% [6,7].

We apply scanning tunneling microscopy (STM) and spectroscopy (STS) to study the reaction of NH3 with Si(111)-(7×7), and the epitaxial growth of CaF2 on Si(11). By a combination of topographs and atom-resolved spectra we can follow the spatial distribution of the reaction and changes in electronic structure with atomic resolution. We find that there are strong site-selectivities for the NH3 reaction on the 7×7 surface. We also observe the initial stages of the CaF2 deposition and even are able to image insulating multi-layer CaF2 films.

The kinetics of the initial oxidation of silicon surfaces by O2 were studied using laser-induced thermal desorption (LITD), temperature programmed desorption (TPD) and Fourier Transform Infrared (FTIR) spectroscopy. The LITD results showed that the oxidation of Si(111)7×7 by O2 was characterized by two kinetic processes: an initial rapid oxygen uptake followed by a slower growth that asymptotically approached an apparent saturation oxygen coverage. The initial reactive sticking coefficient of O2 on Si(111)7×7 decreased with surface temperature. In contrast, TPD experiments on Si(111)7×7 and FTIR studies on porous silicon demonstrated that the apparent saturation oxygen coverage increased as a function of surface temperature. Experiments with preadsorbed hydrogen also revealed that silicon oxidation was inhibited as a function of increasing hydrogen coverage on the Si(111)7×7 surface.

The reactive sticking coefficient, SR, of SiH4 on the Si(111)-(7×7) surface has been studied as a function of hydrogen coverage (ΘH) in the surface temperature (TS) range 80–500°C. At 400°C, evidence is seen for two adsorption regimes which are proposed to correspond to minority and majority surface sites. On the minority sites (ΘH = 0 to 0.08), SR is approximately independent of TS. On the majority sites (ΘH > 0.08), SR is a complicated function of TS and ΘH. After SiH4 exposure, surface SiH is the dominant stable decomposition intermediate from 80 to 500°C, with detectable populations of SiH2 and SiH3 present at the lowest temperatures.

We have investigated the interaction of gaseous hydrofluoric acid (HF) with single crystal silicon surfaces using soft x-ray photoemission spectroscopy and Electron Stimulated Desorption Ion Angular Distributions (ESDIAD). Examination of the Si(2p) core level for surfaces saturated with HF shows the formation of silicon-fluoride bonds indicating the dissociative chemisorption of HF on both Si(111) and Si(100) surfaces. Inspection of the F(2s) and F(2p) valence levels at saturation coverage indicate that only one-half monolayer of fluorine bonds to the silicon. The primary ion desorbed by electron bombardment of these surfaces is F+ with only a minor contribution from H+. ESDIAD images from a saturation coverage of HF on stepped Si(100) surfaces reveal F+ desorption primarily along the direction of the terrace dimers. The ESDIAD patterns from HF adsorbed on Si(111) are characterized by strong normal F+ emission with a weak background component of off-normal emission. These results are consistent with the dissociative chemisorption of HF where the ion emission direction is determined by the Si-F bond directions.

The methodology for extracting structural information from surface infrared spectra is exemplified by considering the silicon-hydrogen stretching modes of flat and vicinal Si(111) and Si(100) surfaces obtained after HF treatment.

The kinetics of SiCl4 adsorption on Si(lll) 7×7 were studied using laser induced thermal desorption (LITD) and temperature programmed desorption (TPD) techniques. The initial reactive sticking coefficient of SiCl4 on Si(lll) 7×7 was observed to decrease with increasing surface temperature. This decrease was consistent with a precursor-mediated adsorption model. Both LITD and TPD experiments monitored SiCl2 as the main desorption product. These results suggest that SiC12 may be the stable chlorine species on the Si(lll) 7×7 surface.

We present a detailed study of the growth of a-Si:H,F from SiF4 and H4. The growth surface appears to have a high density of surface states. These surface states can be thermally relaxed by keeping the films at growth temperature after the termination of growth, suggesting that the states were created during film growth. When frozen in, the surface state density is found to depend on the conditions during film growth. The density is related to the sharpness of the valence band tail as measured by the Urbach Energy. We believe that a reaction on the growth surface resulting in fluorine elimination creates these surface states and also affects the formation of the Si-network.

The adsorption, thermoreactions, and photoreactions of NO coadsorbed with K on Si(111)7×7 at 90 K have been studied and compared with the results obtained from the Kfree surface. The experiments were performed under ultra-high vacuum conditions using high resolution electron energy loss spectroscopy, work function change measurements, and mass spectrometry. NO adsorbs both molecularly and dissociatively on the K-free surface. Two molecular N–O stretching modes are observed at 188 and 225 meV. The concentration of these NO molecules on the surface decreases as the K exposure increases and vanishes at high K exposures. A new N–O stretching mode, attributed to adsorption of NO molecules on K clusters, is observed at 157 meV. After thermal heating or photon irradiation, the surface is covered with atomic O and N. The surface is more oxidized in the presence of K. A steady decrease in the photodesorption cross section is observed as the K exposure increases and is attributed to K-induced band structure changes.

The thermal nitridation of Si(100) by NH3 and N2H4 has been studied by X-ray photoelectron (XPS) and Auger electron (AES) spectroscopies. The pressure dependence of the rates as a function of reaction time has been measured. It has been found that the growth of the first monolayer (ML) of nitride is mediated by a surface reaction step. For subsequent growth, diffusion of one or more of the reacting species becomes an important process in determining the rate of reaction. Such species may be substrate Si diffusing to the vacuum/Si3N4 interface, or possibly network nitrogen diffusing into the Si substrate. The independence of the reaction rate on NH3 or N2H4 pressure at long reaction times rules out a mechanism involving molecular diffusion of the nitriding gas to the Si3N4/Si interface in a manner similar to the oxidation of Si by O2 or H2O. Careful analysis of the Si(2p) XPS spectra reveals the presence of a unique Si species with a Si(2p) binding energy intermediate between elemental Si and Si in Si3N4. Further, the relative intensity of the Si(2p) features due to this species, and the angular dependence of the XPS peaks indicate that they result from a ML of Si at the outermost surface layer, on top of the growing Si3N4 film.

Thin silicon nitride films on a Si(100) substrate have been oxidized using potassium in a low thermal budget process. The presence of potassium on the SisN4 surface greatly lowers the temperature-time requirements for oxidation as compared with direct thermal oxidation.

Reactions of C2H4, C3H8, and CH4 on Si(111) and C2H4 on Si(100) have been investigated for surface temperatures in the range of 1062 K to 1495 K. These studies used x-ray photoelectron spectroscopy to identify the reaction products, characterize the solid state transport process, determine the nucleation mechanism and growth kinetics, and assess orienta-tion effects. The results are used to provide insight into the mechanisms of SiC CVD processes.

This paper presents a new method for studying the interaction of radicals with the surface of a depositing film using a combination of laser spectroscopy and molecular beam techniques. The reactivity of SiH molecules with the surface of a depositing a-Si:H film is measured to be at least 0.95, with no strong dependence on rotational state.

Scattering and desorption of In from Si(100) is investigated. Laser induced fluorescence is used to probe the desorbing and or scattered species. Auger Electron Spectroscopy is used to study the composition on the surface. The results show that at surface temperatures below 820 K a two dimensional layer of In desorbs by a half order mechanism. This is explained by assuming two dimensional In islands on the surface. Above 820 K, desorption takes place by a first order mechanism. The desorption para-meters appear to be spin-orbit state specific. The desorption energy for In 2P3/2 is 2.8 ± 0.4 eV and for In 2P½ 2.5 ± 0.2 eV. The difference is equal to the difference in the spin-orbit energy. So far no specular scattering of In is observed, suggesting that the sticking coefficients are unity.

The adsorption and reaction of atomic oxygen on the Si(100) surface has been examined by employing supersonic beam techniques, X-ray photoelectron spectroscopy and mass spectrometry. Atomic oxygen adsorbs with a unit probability of adsorption on the clean Si(100) surface. The probability of adsorption decreases monotonically with increasing coverage. At surface temperatures above approximately 1000 K. the adsorption of atomic oxygen results in the gasification of the substrate, producing SiO(g). In comparison to molecular oxygen for this reaction, where two surface intermediates were implicated, only one surface intermediate is formed from the reaction of atomic oxygen with the Si surface.

Sticking coefficients γ of neutral transient species at ambient temperature were measured using in situ Resonance Enhanced Multiphoton Ionization (REMPI) of the transients in a Knudsen cell. γ for I and CF3I‡ on a stainless steel surface were 0.16 and >0.5, respectively, whereas γ for CF3 on the same surface was measured to <0.01; γof SiH2 on a growing carbon containing amorphous silicon surface was 0.11; this value increased to 0.15 for interaction of SiH2 with a “pure” growing silicon-hydrogen surface, and γ of SiH2‡ on both types of surfaces was found to be >0.5.

The deposition of diamond, a metastable crystalline form of carbon, from low pressure gases poses intriguing questions about the mechanisms of growth. Tunable IR Diode Laser Absorption Spectroscopy, Laser Multi-Photon Ionization Spectroscopy, and Laser Induced Fluorescence were used to characterize the gaseous environment in the Chemical Vapor Deposition growth of diamond films. The quality of the deposited material was examined by optical and SEM microscopies, and Raman, Auger, and XPS spectroscopies. When a reactant mixture of 0.5% methane in hydrogen, was passed across a hot Tungsten filament (2000 C), C2H2, C2H4, H and CH3 were detected above the growing diamond surface, and concentration limits for undetected species were determined. These results are discussed in terms of simple models for species formation and consumption, as well as the implications for the diamond growth mechanism.

We have grown thin films of a-Si:H alloys by Remote Plasma Enhanced CVD (Remote PECVD) and have studied the deposition process by mass spectrometry. We find that the concentration of silane fragments (SiHx x=0 to 3) and higher silanes (e.g. disilane Si2H6) in the gas phase is below our detection limit of =0.5%. Bias experiments and a comparison of the a-Si:H deposition rate with the known concentration of silane in the gas phase suggest that in Remote PECVD, silane molecules, SiH4*, vibrationally excited in the gas phase or on the deposition surface may lead dirtectly to a-Si:H film deposition.

The growth of thin Si films by RF glow discharge undergoes a transition from amorphous to microcrystalline as power density is increased. This results in a substantial change in the film's electrical conductivity and activation energy for electrical conduction. The RF glow discharge has been characterized in terms of plasma density, plasma potential and electron temperature with emissive Langmuir Probe measurements. The structural transition has been observed with a transmission electron microscope.

In-situ analysis of low temperature Plasma Enhanced Chemical Vapor Deposition (PECVD) SiO2 films deposited on HgCdTe, Silicon, and Aluminum substrates was performed by double modulation Fourier Transform Infrared Reflection Absorption spectroscopy (FT-IRRAS). The sensitivity and selectivity of this technique are sufficient for an in-situ assessment of the film quality and reaction conditions at any stage of film growth. An oblique angle of incidence of ca. 557deg; was chosen to yield maximum sensitivity for the 1260 cm−1 LO mode of SiO2 on Si. The peak frequency and shape of the LO mode absorption band varied with the quality of the SiO2 films. This diagnostic technique can be applied readily to in-situ analysis of dielectric thin films formed under a variety of reaction conditions as long as the gaseous ambient is partially transmissive to the IR radiation.