A possibility of the Atomic Layer Epitaxy, ALE, for InN was demonstrated by using InC13/N2 and NH3/N2. The InCl3 is a solid at room temperature and can be supplied in the reactor by heating with N2 carrier gas. When the solid InCl3 is heated in an inert gas, InCl, InCl3 and In2Cl3 gases are formed. It was clear that the In2Cl5 which is the largest molecule of the three results in solid structural defects. The ALE growth temperature was from 440°C to 505°C. The fact that the ALE was performed at the temperature range from 440°C to 505°C indicates that In was supplied as InC13, suggesting the possibility of InN ALE by using InCl3 and NH3.

Single-crystal Si films have been grown on Si(001)2×1 substrates by UVphotostimulated atomic-layer epitaxy (ALE) from Si2H6. The ALE deposition rate R per growth cycle remains constant at 0.4 monolayers (ML) over a wide range of deposition parameters: growth temperature (Ts= 180–400 °C), Si2H6 exposure (peak pressure during gas pulse = 0.1−5 mTorr), laser energy density ( = 250–450 mJ cm−2 where is determined by Ts), and number of UV laser pulses per cycle. A film growth mocrel, based upon the results of the present deposition experiments and Monte Carlo simulations, together with our previous adsorption/desorption measurements, Is used to describe the reaction pathway for the process. The Hterminated silylene-saturated surface formed by adsorption and desorption of disilene is thermally stable and passive to further Si2H6 exposure. ArF or KrF laser pulses (≅20 ns) are used to desorb H, following a Si2H6 exposure, and the growth cycle is repeated until the desired film thickness is obtained. At Ts < 180 °C, the growth process becomes rate limited by the surface dissociation step and R decreases exponentially as a function of 1/Ts with an activation energy of ≅0.5 eV. At Ts > 400 °C, H is thermally desorbed and pyrolytic growth competes with ALE. Transmission electron micrographs together with selected-area electron diffraction patterns show that the ALE films are epitaxial layers with no observed extended defects or strain.

The adsorption and decomposition behavior of disilane and digermane are quite similar on the Ge(111) surface. Both precursors are weakly bound at low temperatures, but dissociatively adsorb at temperatures above 150K. Trihydride species are produced and stable at low temperatures, but decompose to di- and monohydride species at slightly higher temperatures. The desorption of hydrogen from the resulting layer is strongly dependent on the Si and Ge composition of the layer.

Digital etching was carried out by repeating the fundamental reaction cycles of adsorption, reaction and desorption for fluorine(F) or chlorine(Cl)/Si systems. In the F/Si case, atomic layer etching of Si(100) was achieved by adsorption of F atoms produced by a remote discharge of F2/99.8%He on the cooled Si surface and subsequent Ar* ion (≅20eV) irradiation. The digital method revealed that the cryogenic etching occurred by ion bombardment on physiosorbed F atoms on the cooled Si surface. Adsorption of Cl atoms on Si at room temperature allowed self-limiting reaction with etch rate of 0.4 Å/cycle. The etching increased rapidly over 40 V of substrate voltage. Secondly, reaction of TES (triethylsilane) with hydrogen(H) atoms was also found to lead to conformal CVD (Chemical Vapor Deposition) of Si film involving organic species. Then Si oxide and nitride films were formed by digital CVD which repeated a cycle of first deposition of this film and subsequent its oxidation and nitridation. The electrically excellent multilayer stacked oxide and nitride film was filled in to deep trench. Insitu FTIR-ATR spectroscopy demonstrated that the surface reaction was predominant for the TES/H process.

A novel mechanism of atomic level control in crystal growth utilizing reconstruction of surface superstructures is proposed. We have found a distinguished feature of surface reconstruction during crystal growth of 3C-SiC using an alternate gas molecular beam supply of Si2H6 and C2H2. When Si2H6 is supplied, S atoms generated by thermal decomposition adsorb on the surface constructing superstructures. A fixed number of Si atoms forming surface superstructures can react with C2H2 yielding single crystalline 3C-SiC growth in the subsequent period, which realizes atomic level control in epitaxy of 3C-SiC. The reconstruction sequence is analyzed based on RHEED observations, and the obtained crystal quality is discussed.

Fourier transform infrared (FTIR) transmission spectroscopy was used to monitor the decomposition of alkylsilanes such as diethylsilane (DES) [(CH3 CH2)2SiH2], di-t-butylsilane (DTBS) [((CH3)3C)2SiH2] and ethylsilane (ES) [CH3CH2SiH3 on high-surface-area porous silicon samples. The FTIR spectra revealed that tKe akylsilanes dissociatively adsorb on porous silicon at 300 K to form SiH and Si-alkyl species. As the silicon surface was progressively annealed, the Si-alkyl species decomposed and produced gas phase ethylene (DES,ES) or isobutylene (DTBS). The decomposition of the alkyl group was accompanied by the growth of additional SiH surface species. These reaction products were consistent with a [β-hydride elimination reaction. Above 700 K, the SiH surface species decreased concurrently with the desorption of H2 from the porous silicon surface. The uptake of surface species was also monitored at various adsorption temperatures to determine the optimal exposure temperatures for carbon-free silicon deposition. Carbon contamination was not detected at adsorption temperatures below 640 K prior to H2 desorption. Because the alkylsilane adsorption process is self-limiting at temperatures below 640 K, alkylsilanes may be useful molecular precursors for the atomic layer epitaxy (ALE) of silicon.

We describe observations made in situ in a modified UHV transmission electron microscope of the process of etching of the Si (111) surface by oxygen. Etching occurs by the motion of individual bilayer steps across the surface and by analysing the step motion we discuss the etching mechanism in the context of macroscopic parameters.

Growth kinetics of native oxide on HF-treated Si surfaces terminated with Si-H bonds has been studied by angle-resolved x-ray photoelectron spectroscopy. The oxide growth rate in pure water for an n+ Si(100) surface is significantly high compared to that of p+, and the n or p type Si oxidation rate is in between. This is explained by the formation of ions through electron transfer from Si to adsorbed O2 molecules and the resulting enhancement of the oxidation rate. The oxide growth on Si(100) is faster than (110) and (111) as interpreted in terms of the steric hindrance for molecular oxygen adsorption on the hydrogen terminated silicon 1×1 surface structures.

Recent advances in understanding the ALE (atomic layer epitaxy) growth of ZnSe, ZnS and ZnTe are reviewed. The Ideal ALE growth is obtained in the substrate temperature range of 250–350°C for ZnSe. In the ALE growth of ZnSe and ZnTe, a unique self-limiting mechanism is observed, in which the deposition rate saturates at 0.5 monolayer per cycle. Furthermore, applications of ALE of II–VI compounds to the growth of strained layer superlattices are also reviewed.

The detailed observation of dynamical behaviors of reflection high energy electron diffraction (RHEED) patterns during the adsorption processes of Li, Se and Zn is carried out. It is found that the RHEED intensity variation reflects the Li surface coverage during Li adsorption process on a Secovered surface. This fact enables one to control quantitatively the doping of Li “in situ”. A new method for atomic-layer controlled substitutional doping of ZnSe layers with lithium is proposed based on the RHEED investigations. The method allows the incorporation of Li dopants on Zn-sites of ZnSe by monitoring the RHEED patterns and intensities, and is expected to suppress the compensation by Li interstitials. Photoluminescence spectrum shows the growth of high quality p-type layers.

We have obtained p-type zinc selenide films by nitrogen doping combined with a post growth anneal. These films were grown on <100> gallium arsenide substrates using a low-pressure MOCVD process. Ammonia gas was used as the source for nitrogen. The as-grown films were annealed and then studied by photoluminescence (PL) and capacitance-voltage (CV) techniques. The PL data is dominated by the acceptor-bound exciton peak and donor-acceptor pair spectrum associated with the nitrogen acceptor. The C-V data shows that the films are p-type, with the highest measured net acceptor concentration of 3×1016/cm3.

High quality ZnSe films were successfully grown on GaAs(100) at low temperatures, 200 °C or lower by Hydrogen Radical-enhanced Chemical Vapor Deposition (HRCVD). Defects were makedly eliminated by the following factors: selection of source materials; avoidance of ion bombardment; and suppression of formation of adducts by alternate gas supply. Strained-layer superlattice (SLS) consisting of ZnSe as the well and ZnS0. 1Se0.9 as the barrier was made by this technique. Emission line attributed to the free exciton was dominantly observed in the SLS.

Polycrystalline cadmium sulphide (CdS) thin films were grown by Atomic Layer Epitaxy (ALE) using indium tin oxide and tin oxide coated glass substrates. Some of the experiments were made using elemental reactants, and others with inorganic compounds as reactants. Films were characterized using various techniques such as XRD, SEM and optical transmission spectroscopy. Growth rate of CdS films was observed to be 1/4 - 1/3 monolayer per cycle with elemental reactants. A full monolayer/cycle coverage was obtained when using CdCl2 and H2S as reactants. The crystalline structure of the CdS films wis β-cubic (111) when using elemental reactants. The mixed structure was observed when inorganic compounds were used as reactants. Only the hexagonal phase was observed, when substrate surface was pretreated before CdS deposition.

Polycrystalline CdTe films up to 2 μm thick were grown by Atomic Layer Epitaxy (ALE) at 350–450°C. The growth was carried out in a lateral flow reactor, using the elements as source materials and 25 cm2 glass/ITO and glass/ITO/SnO2 as substrates. A growth of CdS film by ALE preceded the growth of CdTe.

Profilometry, X-ray diffraction analysis and scanning electron microscopy were used to characterize the films.

The relatively high vapor pressure of CdTe determined the upper limit of the processing window, while the small vapor pressure of Te2 set a practical lower limit of 390–400°C.

The CdTe films were smooth up to 100–500 nm depending on the temperature and the substrate surface. Development of surface roughness was detected as the growth process proceeded. At the same time there was an increase of the effective surface area of the film, observed as a significant increase in the macroscopic growth rate. The greater surface roughness was also evident in the reduced degree of (111) orientation.

The CdS/CdTe structure was investigated for its potential in solar cell applications.

A pressure controlled vapor source was developed for the gas source doping of (Hg,Cd)Te alloys. The dopant source has been subjected to extensive tests, and the flow characteristics determined. The dopant source was used to control the flow rates of ethyliodide for the n-type doping of CdTe. Highly conductive CdTe:l films were grown by molecular beam epitaxy.

The principles of Atomic Layer Epitaxy (ALE) have been applied to the formation of compound semiconductors by an electrochemical technique, referred to as Electrochemical Atomic Layer Epitaxy (ECALE). Atomic layers of the component elements are alternately electrodeposited at underpotential (UPD) from separate solutions and at separate potentials. Results are presented concerning the structures of both CdTe and GaAs deposits formed by ECALE. Studies were performed using singlecrystalline Au electrodes in a UHV surface analysis instrument coupled directly with an electrochemical cell. This instrument was used in order to prevent corruption by contact with air during transfer to the surface analysis environment.

Molecular beam epitaxy of ultra thin films of Bi2Sr2CuO8-(2201 phase) is realized on the surface of SrTiO3 (100) and LaAlO3 (100) at the substrate temperature of 573 K, using 10-5Pa of NO2 as an oxidant. The film epitaxially grown from the surface of the substrate has identical in-plane lattice constant to the substrate itself. Such a growth can only be obtained on the substrate with similar lattice constant to those of the material to be formed. The crystallinity of the film strongly depended on the sequence of the metal depositions and the oxidation process. In the case of the Bi system, the elementary unit of the epitaxial growth has proved to be the subunit of the perovskite structure (Sr-Cu-Sr). The structure of the film grown on a substrate with large mismatch (MgO) is also discussed.

We report the results of a pulsed organo-metallic beam epitaxy (POMBE) process for growing complex oxide films at low background gas pressure (10-4 -10-2 torr) and low substrate temperature (600 to 700 C) using organo-metallic precursors in an oxygen plasma environment. Our results show that POMBE can extend the capability of organo-metallic chemical vapor deposition to growing complex oxide films with high precision both in composition and structure without the need for post-deposition oxidation and heat treatments. The growth of phase-pure, highly oriented Y-Ba-Cu-O superconducting oxide films ([Tc (R=0)=90.5K] and Jc (77K, 50K gauss)=l.l×105 A/cm2) is given as an example. Similar to the pulsed laser deposition process, the POMBE method has the potential for in-situ processing of multilayer structures (e.g. junctions).

Thin films of (Ca,Sr)CuO2 and Bi2Sr2Can-1CunO2n+4 are formed by laser molecular beam epitaxy with in-situ reflection high energy electron diffraction observation. The diffraction pattern shows that these materials are formed with layer-by-layer growth. The change of the diffraction intensity as well as the analysis of the total diffraction pattern makes It possible to control the grown of the atomic layer or the unit-cell layer.

The growth of strontium sulfide thin films in a flow-type Atomic Layer Epitaxy reactor from Sr(thd)2 (thd = 2,2,6,6-tetramethyl-3,5-heptanedione) and H2S has been studied. The growth is independent on flow rate and duration of the purge gas (N2) pulse and it does not depend on the Sr(thd)2 and H2S pulses either provided their amounts are sufficient to saturate the surface. The variables significantly affecting the growth rate are the substrate temperature and source temperature for Sr(thd)2. The observed lower than one monolayer growth rate is mainly due to the large size of the Sr(thd)2 molecule.