Molecular-beam mass spectrometry has been used to study plasma-enhanced chemical vapor deposition (PECVD) of diamondlike carbon films. A threshold-ionization technique was used to identify and quantify species in the plasma. Mole fractions of H, H2, CH4, C2H2, C2H6 and Ar were measured in an 83.3% CH4/Ar mixture at a pressure of 0.1 torr and a total flow of 30 sccm. Comparisons were made between mole fractions measured at plasma powers of 25W and 50W. These results were compared to measured concentration profiles and to film growth rates.

Diamond growth experiments were carried out by a microwave plasma assisted CVD technique in various gas mixtures of CH4(0–100%)/02/H2. The phase diagram obtained by this study shows that a diamond growth region exists. With addition of more than 5% O2 in reactant gases, diamond particles could be included in amorphous or graphitic carbon films even using CH4/O2 gas mixtures. Faceted diamond films were obtained if the oxygen gas concentration [O2] was approximately more than half the methane gas concentration [CH4] ([O2]>[CH4]/2). However, no films were grown when [O2] exceeded half of [CH4] plus 7% ([O2]>[CH4]/2+7%). These results corresponded to the observations by plasma emission spectroscopy. Though oxygen etches carbon films and decomposes methane by forming carbon monoxide, oxygen rarely reacts with hydrogen in a film growth region.

Determination of the gas phase composition at or near a substrate surface during plasma assisted chemical vapor deposition presents a challenging problem. The species located at a growing surface include highly reactive radicals which are difficult to detect in atmospheric plasma conditions. A system has been designed which consists of an inductively coupled rf plasma reactor linked to a quadrupole mass spectrometer (QMS) via a supersonic convergent-divergent nozzle. Differential pumping in the transient stages allows the plasma chamber to be operated at or near atmospheric pressures, while facilitating the detection of reactant species present in the growth boundary layer with the QMS.

Polycrystalline diamond thin films have been selectively grown on mirror-polished silicon substrates using bias-enhanced microwave plasma chemical vapour deposition (MPCVD) to increase diamond nucleation density. A slight etching of Si02 mask was employed after the nucleation treatment to remove the diamond nuclei on the mask. Perfect diamond patterns with smooth surface (particle size <0.5µm) and sharp boundaries were obtained. The diamond film gears with 400µm in diameter and 5µm in thickness were first fabricated by this technique.

Reflectance anisotropy spectroscopy (RAS) is presented as real time analytical tool for metalorganic vapourphase epitaxy (MOVPE) of III-V-semiconductors. This optical method derives its surface sensitivity from the anisotropy of surface structures. It is shown that it is possible to monitor with RAS the oxide desorption from the substrate and that the substrate surface conditions thereafter, still in the pregrowth stage, can be correlated with certain reconstructions of the (001)-surfaces of InP and GaAs. The latter is possible through simultaneous RAS and RHEED measurements during MBE (molecular beam epitaxy) or MOMBE (metalorganic molecular beam epitaxy). Characteristic spectral features are also observed for other binary or ternary III-V-semiconductors. Time resolved measurements during growth give monolayer resolution for the growth rate in the case of GaAs. In the study of heterointerface growth exchange reactions between As and P together with their corresponding reaction time constants can be monitored and conclusions for the epitaxial growth procedure can be drawn.

Gas phase and surface decomposition reactions of a novel arsenic precursor tris- (dimethylamino) arsenic (DMAAs) have been studied. Optical fiber-based Fourier transform infrared spectroscopy was used to monitor, in situ, the gas-phase pyrolysis of DMAAs. Homolysis of the arsenic-nitrogen bond with formation of dimethylamine radicals was identified as the key gas-phase reaction pathway. Formation of methylmethyleneimine from reactions with the decomposition products was directly observed. Surface decomposition of DMAAs on GaAs(100) was investigated by low energy electron diffraction and temperature-programmed reaction under ultra-high vacuum conditions. DMAAs adsorbed onto GaAs(100)-(4x6) was found to decompose with 100% efficiency and two surface reaction pathways were identified. The first reaction channel was homolysis of the arsenic-nitrogen bond with formation of dimethylamine radicals, whereas the second pathway involved a β-hydrogen transfer.

The growth of undoped GaAs films from Ga(C2H5)3 (TEG) and AsH3 by Metalorganic Chemical Vapor Deposition (MOCVD) has been studied in a low-pressure reactor operating at 3 Torr. This precursor combination is known to produce GaAs films with very low carbon incorporation when compared to films grown from Ga(CH3)3 (TMG) and AsH3. A kinetic model of the growth process has been developed that includes both gas-phase and surface reactions based on reported decomposition mechanisms of TEG and AsH3. The kinetic model was coupled to a transport model describing flow, heat and mass transfer. Finite element simulations were performed to determine the rate constants of the growth reactions that provide the best fit between predicted and observed growth rates. Under typical operating conditions the surface reactions were found to dominate the growth process and a reduced surface kinetic model was identified by sensitivity analysis. The proposed reaction-transport models can successfully predict observed growth rates of GaAs films and they can be used for identifying optimal operating conditions in MOCVD reactors.

We have grown GaAs epilayers by ultrahigh vacuum chemical vapor deposition(UHVCVD) using adsorbed hydrides and metalorganic compounds via a surface decomposition process. This result indicates that unprecracked arsine(AsH3) can be used in chemical beam epitaxy(CBE) and that a new hydride source with a low decomposition temperature, monoethylarsine(MEAs) can replace the precracked AsH3 source in CBE. The impurity concentrations in GaAs grown with trimethylgallium(TMG) and triethylgallium(TEG) were found to be very sensitve to growth temperature. It was also found that the uptake of carbon impurity is significantly reduced when TMG is replaced with TEG. The carbon concentrations in epilayers grown using TMG and TEG with unprecracked AsH3 and MEAs were reduced by 2-3 orders of magnitude compared to those by CBE process employing TMG and arsenics from precracked hydrides. We have also found that the hydrogen atoms play an important role in the reduction of carbon content in GaAs epilayer. Intermediates like dihydrides from MEAs decomposed on the surface are considered to supply hydrogen atoms and hydrides during growth, which may remove other carbon containing species.

We present here an overview of recent studies of the influence of oxygen doping on the electrical and structural properties of semiconductors grown through the metal organic vapor phase epitaxy (MOVPE) technique. In particular, we have measured the impact of oxygen introduction on several of the principal aspects of the growth process: incorporation, activation, and influence on the growing surface structure. The gas phase chemistry and dopant incorporation was investigated for two different precursors: dimethyl aluminum methoxide and diethyl aluminum ethoxide. The simple change in the structure of the oxygen source leads to significant changes in the oxygen incorporation behavior. Complementary studies of the gas phase decomposition of these oxygen sources have indicated that the decomposition mechanism is substantially different for these two sources leading to the change in incorporation behavior. The impact of the selective incorporation of oxygen at heterointerfaces has been studied here through the growth of superlattice structures. Glancing angle X-ray diffraction and atomic force microscopy measurements have shown that the incorporation of oxygen at the GaAs-to-AlxGaI-x As interface leads to modest increases in the average roughness of the heterointerface with more significant changes in the interfacial structure. The structure of this interfacial roughness was also studied through measurements of the diffuse X-ray scattering about a Bragg peak. Measurements of the component of the roughness which is correlated between the superlattice layers show significant changes with oxygen addition.

MOVPE growth experiments have been used to evaluate the role of gas phase and surface chemistry in the silicon doping of GaAs films grown using SiH4 and Si2H6 dopant sources and tertiarybutylarsine (t-C4H9AsH2 or TBAs) as the Group V source. The use of TBAs with SiH4 results in a greater Si doping efficiency and weaker dependence on growth temperature than is typically observed with AsH3. Gas phase pyrolysis studies combined with reactor residence time experiments indicate that heterogeneous chemistry is responsible for this enhanced Si doping process. TBAs has much less of an effect on Si incorporation from Si2H6, a doping process controlled by homogeneous Si2H6 chemistry. Increased Si doping from Si2H6 with TBAs can be attributed to contributions from the enhanced doping efficiency of SiH4, a product of Si2H6 decomposition. The influence of TBAs on SiH4 doping chemistry was found to improve the doping uniformity of GaAs films grown in our reactor, from +/-12% for films grown with AsH3to +/-5% for TBAs-based material.

Rare earth elements are important as dopants in the preparation of semiconductors, particularly for temperature-independent optical devices. The compound Er{N\Si(CH3)3]2}3 has been demonstrated to be a suitable source compound for erbium doping of semiconducting materials. Further investigations of this and related compounds have been carried out. New compounds have been characterized by 1H NMR, FTIR, TGA and elemental analysis techniques. Vapor pressures and decomposition profiles have been examined for these compounds.

Tetrakis(iso-propyl)diarsine was synthesized by the reaction of (i-Pr)2AsLi with (i-Pr)2AsI. The lithium salt of the secondary arsine was produced following deprotonation of (i-Pr)2AsH, obtained by reduction of (i-Pr)2AsI, which was prepared by the thermolysis of (i-Pr)3Asl2. The X-ray crystal structure of \(i-Pr)3AsI]\I] has been determined on the product of the reaction of (i-Pr)3As and 12. Compounds of the general form E=As(i-Pr)3 (E = O, S, Se) have been prepared.

In earlier work, the effective utilization of Zn {N\Si(CH3)3]2}2 as a site-selective dopant for the production of p-type ZnSe by OMVPE was demonstrated. Several new zinc-bis(dialkylamides) of the general form (R)(R′)NZnN(R″)(R‴) now have been prepared. They have been characterized by 1H- and 13C-NMR, GC/MS and elemental analysis. Vapor pressures and gas phase decompositior profiles have been examined. Correlations of vapor pressure and structure are discussed for this series of compounds. A mechanism for the site-selectivity observed in the incorporation of nitrogen is proposed.

Atomic layer epitaxy (ALE) of InAs has been developed using trimethylindium-dimethylethylamine adduct (TMIDMEA) as a novel In source. Distinct self-limiting growth of InAs was successfully carried out over a wide temperature range from 350°C to 500°C because of the high thermal stability of TMIDMEA. The possible growth temperature range for ALE-InAs was extended by using TM1DMEA. These results lead us to conclude that the use of TMIDMEA enables us to grow InAs/GaAs heterostructures at a single growth temperature. Using this technique, (InAs)1(GaAs)l short period superlattice (12 periods) quantum-well structures were grown on a GaAs(100) substrate at 460°C. A photoluminescence peak at 1.3 µm was observed in these structures at room temperature.

ZnSe epitaxial films have been grown on (100) GaAs by reduced pressure organometallic chemical vapor deposition (OMCVD) from tertiary-butyl(allyl)selenium (tBASe) and dimethylzinc triethylamine adduct (DMZnNEt3) at temperatures of 325-450ΰC. Good surface morphology, film crystallinity and interface quality have been found with scanning electron microscopy (SEM), double crystal X-ray diffraction (DCD) and Rutherford back scattering spectroscopy (RBS). Secondary ion mass spectrometry (SIMS) shows negligible carbon concentration (below 5x1017atoms/cm3). Low temperature photoluminescence (PL) exhibits a strong near band-edge emission with a dominant donor-bound peak. Gas-phase pyrolysis of tBASe has been probed at reduced pressure in a molecular beam mass spectrometric system in hydrogen and deuterium carrier gases. The precursor decomposes above 200ΰC by β-hydrogen elimination and by homolysis of the Se-C bonds. High isobutene vs. isobutane ratios (50-100) indicate a predominance of β-hydrogen elimination over homolysis at temperatures below 400ΰC. Diallylselenium is present in the gasphase in low concentrations at temperatures of 200-350ΰC. Diallylselenium, methylallylselenium and dimethyl-selenium have been observed as minor by-products during pyrolysis of co-dosed tBASe and DMZnNEt3. The effect of the retro-ene decomposition pathway of allylselenium reagents on carbon incorporation into ZnSe films is further probed by growth experiments with in situ generated 2-methylpropaneselenal.

Temperature programmed desorption (TPD) studies in ultra high vacuum revealed that diethyltellurium (DETe) and dimethylcadmium (DMCd) adsorb weakly on clean Si(100) and desorb upon heating without decomposing. These precursors adsorb both weakly and strongly on CdTe(111)A, with DMCd exhibiting the stronger interaction with the surface than DETe. Dimethylcadmium partially decomposes to produce Cd adatoms; a large fraction of the excess Cd atoms desorb upon heating. In contrast, DETe desorbs without decomposing, suggesting that the rate limiting step in CdTe MOCVD on CdTe(111)A is surface decomposition of the tellurium alkyl.

Angularly resolved time-of-flight (TOF) measurements have been used to probe the velocity and angular distributions of Cd atoms and Te2 molecules ejected from CdTe (100) substrates under irradiation by 248 nm nanosecond and sub-picosecond laser pulses. These experiments employ a dye laser TOF mass spectrometer with resonance enhanced multiphoton ionization for sensitive, high resolution detection of the desorbed products. The velocity distributions are well described by Maxwell-Boltzmann distributions for low fluence nanosecond (<60 mJ/cm2) and sub-picosecond (<3.3 mJ/cm2) pulses. Angular flux distributions for nanosecond irradiation are observed to be highly forward peaked about the surface normal, whereas, for sub-picosecond irradiation the distribution approaches cos3θ.

Time resolved surface second harmonic generation has been used to probe the photoreduction kinetics of malachite green adsorbed onto single crystal cadmium sulfide. A detailed analysis is presented of how the adsorbates and the noncentrosymmetric substrate contribute separately to the total second harmonic signal. Conditions under which the adsorbates can be cleanly detected are described. To complement kinetic measurements of adsorbate reduction, the time evolution of conduction band carriers was determined using sum frequency up conversion of the recombination luminescence. In addition, the formation and decay of surface trapped carriers was monitored using near infrared transient absorption. Comparing the time scale for photoreduction with the relaxation kinetics of mobile and trapped charge carriers indicates that short lived mobile carriers rather than longer lived surface trapped carriers dominate interfacial charge transfer in this system.

The patterned Zn nucleation and the ZnS growth onto the Zn seeds on a thermal oxidized silicon substrate was demonstrated at room temperature with the excimer laser chemical vapor deposition method.

The formation of ZnS films was realized by the method based on the two—step process consisting of the nucleation and the subsequent ZnS growth. In the nucleation, a gaseous dimethylzinc was sealed in a reaction chamber and was then evacuated immediately. Then, the substrate surface which was uniformly adsorbed by dimethylzinc molecules was exposed with a single shot irradiation of a patterned KrF laser; Zn seeds were created only on the irradiated parts by a photodecomposition. And the subsequent growth of ZnS was performed by the parallel or perpendicular irradiation methods. As a result, in the perpendicular irradiation method, the high selectivity and crystallinity of the film were performed by irradiating the whole substrate surface with very low fluence of the KrF laser such as 3 mJ/cm2.

Ag2S as a narrow band gap semiconductor is appropriate for photoimaging in the infrared (IR) region. Co-evaporation of Ag and S from two separate sources was used for preparing of thin Ag2S films with different Ag/S ratio. Gelatine subbed glass plates were used as substrates. The structure of the films obtained was examined by transmission electron microscopy and electron diffraction. The effects of chemical composition, film thickness and processing conditions on the photographic parameters were studied.

It is shown that after appropriate processing thin Ag2S films with stoichiometric composition can. be successfully used as high resolution (1600 lines/mm) photographic materials in the IR region.