To achieve high concentrations and electrical activation of As in Si without subsequent annealing, 500-3000 eV As + ions were implanted during MBE growth of Si at 450-840°C. The epitaxial layers were characterized by Rutherford backscattering/channeling, transmission electron microscopy, secondary ion mald spectroscopy, and electrical measurements. Samples containing 1.2×1020 As cm-3 grown at 700°C showed little damage, high As substitutionality and high electrical activation. However, similarly doped layers grown at 460°C showed lower As activation and varying amounts of structural damage. In one case, a band of damage near the Si substrate was observed which persisted even after rapid thermal annealing at 1120°C (10 s); the damage was characterized by a dechanneling step, non-substitutional As atoms and dislocation loops. A sample grown at 460°C with a high implantation energy (3 keV) was highly defected.

Growth of epitaxial single crystal nickel and cobalt disilicide films on silicon is performed under UHV conditions by deposition of Co or Ni on silicon followed by a high temperature reaction to form the silicide. The uniformity and perfection of ultrathin epitaxial layers has been studied using transmission electron microscopy. Mechanisms controlling island growth are discussed. Island nucleation observed in pseudomorphic films of NiSi2 /Si(100) (∼60Å thick) is shown to be the result of the difference in symmetry between the NiSi2 and Si. Islands related by a translation vector a/4<111> show an equilibrium island separation of 15±1.5Å. The boundary between islands is described as a coreless defect. In comparison,, pseudomorphic layers of CoSi2 /Si(111) are observed up to thicknesses ∼30Å. Pinholes are commonly observed in CoSi2 /Si(111) thin films. Finite contact angles (∼50) between substrate and deposit suggest a desire for three-dimensional growth under equilibrium conditions.

Single crystal epitaxial films of CoSi2 were grown by MBE on various (111)Si single crystal substrates, whose surfaces were purposely tilted towards the < 110>>g, direction by small angles ϕg,†, 0°, ≤ϕg, ≤, 4° measured between the surface normal and the < 111>>g, direction of Si. The actual offset angle, .ϕ8,, was determined by back Laue reflection method. The average perpendicular strain of the CoSi2 epilayer, ε┵, and the < 111 >f orientation of the epitaxial CoSi2 film were determined by double crystal diffractometry. We find that the misorientation angle, a, measured between the Si < 111>g, and CoSi2 < 111>f directions, increases linearly with the offset angle, ϕg, up to ϕg, = 4°. A simple geometrical model is developed which predicts that α = ε┵ × tan ϕg,. The model agrees quantitatively with the experimental data. The equivalent strain energy associated with the misorientation is approximated by that of a low angle tilt boundary. The misorientation angle α of the equilibrium state, determined by minimizing the total strain energy of the epitaxial film, is nonzero in general.

The growth of ultrathin epitaxial CoSi2 layers on Si by molecular beam epitaxy has been studied. This paper briefly outlines recent progress in the growth on Si(111) substrates. New results on the growth of epitaxial CoSi2 on Si(100) are also presented.

600∼4000Å thick Ag films grown on 3∼4· misoriented Si(111) substrates by molecular beam epitaxy (MBE) technique have been studied by using x-ray pole-figure analysis and MeV He+ Rutherford Backscattering Spectrometry (RBS)/channeling technique. X-ray pole-figure measurements revealed that despite the large lattice mismatch (∼25%) between Ag and Si, Ag films with epitaxial relationship Ag(111)//Si(111):Ag[011]//Si[011] were grown with a small quantity (15∼20%) of twin structure. The <111> axial channeling minimum yield (Xmin) is reduced at the Ag surface as the Ag film thickness increases. These films were thermally stable up to 500°C annealing but the twinning disappeared after annealing

We have deposited thin Ge films on GaAs(111) crystals over a temperature range of 250-400° C by Remote Plasma Enhanced Chemical Vapor Deposition (RPECVD). Rutherford Backscattering (RBS)/channelinf analysis of these heteroepitaxial films were carried out using 2.07 MeV He ions channeled along the <111> axis. RBS/channeling analysis showed that the best Ce films were grown at a substrate temperature of 300° C. The minimum yield for <111> channeling on films deposited at 300° C was 0.08, slightly greater than that of the GaAs crystal. Films grown at temperatures below 300° C showed poor epitaxy. No channeling was observed for the film grown at 250° C. Films grown at substrate temperatures above 350° C showed high dechanneling near the interface and poor epitaxy indicating films are highly defective. The RBS/channeling results are correlated with microstructural characterization using transmission electron microscopy of these films.

A simple and easily expandable atmospheric pressure MOCVD (metal organic chemical vapor deposition) reactor for the growth of germanium films is proposed and implemented. It employs a resistively heated horizontal quartz reaction chamber. The organometallic compound tetramethylgermanium (TMGe) is used as the germanium source, and hydrogen as the carrier gas. Using this reactor, epitaxial films of germanium on <111> germanium substrates were grown at 550-650°C. The growth rate was found to increase with temperature. The single crystallinity of these films was evaluated by x-ray rocking curves, and the interface strain between the film and substrate was found to be less than 1%. These Ge/Ge samples have the same morphology as the bare substrate and their sheet resistance is 30% higher than the bare substrate value.

X-ray absorption fine structure, Auger electron spectroscopy and low energy electron diffraction have been used to study the evolution of the lattice constant and the degree of intermixing of thin (∼5 Å) silicon films grown on the germanium(111) surface by solid phase epitaxy. Our results indicate that as the system is annealed, the silicon intermixes with the germanium at elevated temperatures to form a pseudomorphic Si-Ge alloy with the germanium bulk lattice constant. We further observe a splitting of the ‘white line’ Is absorption edge in crystalling Si, SiGe and dilute (<10% silicon) SiGe. The measured splittings agree with band structure calculations for Si, SiGe, and Ge, respectively, indicating that the density of conduction band states of SiGe behaves as the interpolation between the states of Si and Ge. Qualitatively, our spectra may be interpreted in terms of a one electron picture without invoking many body excitonic effects. The absorption edge of amorphous silicon is also presented and the features of the density of states due to long versus short range order are extracted.

Si-Si(B) doping superlattices (pipi structures) were grown by MBE and studied using double crystal x-ray diffraction and SIMS. Detailed analysis of the complex x-ray rocking curves required comparison of experimental data with theoretically simulated data. It is demonstrated that this technique is sensitive to irregularities in the dopant composition, dopant distribution and superlattice period. The B concentration profile is shown to spread well into the intrinsic layers and the extent and magnitude of the dopant distribution has been quantified. A comparison of this data with SIMS showed good agreement for the distribution of B and reasonable agreement for the peak values of B concentration.

The oxidation of strained SiGe alloy layers grown by Molecular Beam Epitaxy (MBE) was studied. An initial fast growth regime was identified for 800°C steam oxidations, where the growth rate is 2.5 times that of silicon. The oxides formed on SiGe were found to be essentially Ge-free: Ge present in the material is rejected by the oxide, resulting in the formation of a Ge-rich epitaxial layer at the oxide/substrate interface.

Atomic positions near interfaces and defects are required to assess their physical properties. Their electronic properties can be calculated only after fixing the positions of atoms. The determination of atomic positions consists of three parts: (1) Theoretical calculations of atomic positions with appropriate interatomic potentials, (2) simulation of positions of atoms in the electron microscope, and (3) comparison of experimental results with the calculations. We have performed these three operations to determine atomic structures of coherent and semicoherent interfaces in Si/Ge systems. A coherent Si/Ge interface is simulated using a computer program. An edge dislocation is introduced at this interface with the help of elasticity theory. Energy minimization calculations are then carried out using interatomic potentials for germanium and silicon. The positions of atoms at the interface are thus determined. Critical phenomena in coherent and semicoherent interfaces are examined in relation to the strain energy of the system. For semicoherent interface containing dislocations, we can determine the critical thickness at which dislocations are generated. Energy minimization computations are found to play a major role in establishing critical phenomena. A model is also developed for the distribution of boron atoms near this dislocation. Isotropic elasticity theory is used for boron-dislocation interaction with correction factors inside the core to avoid singularities. Occupation probabilities of the atomic sites in the computational cell are calculated using the Fermi-Dirac distribution function. Interaction between boron atoms is neglected in the present analysis. Two configurations: 1. Si/Ge interface with a impurity free dislocation, and 2. the dislocation with boron impurities are then used to simulate high resolution images using the SHRLI computer program.

High quality, low defect density, single crystalline silicon/germanium alloys have been grown on Si(100) substrate wafers in a low temperature UHV-CVD reactor. Using a silane/germane gaseous source, the growth rate of the epitaxial layer increases from 4 angstroms/minute with no germane present to 82 angstroms/minute with 12.7% germane present in the reaction gas mixture at 550C. The germanium/silicon ratio in the deposited alloy is a factor of two greater than the germane/silane ratio in the reaction gas mixture. The kinetics of this effect are studied and correlation to UHV hydrogen thermal desorption from single crystal silicon-germanium alloys are made.

The dislocation density in undoped Si-MBE layers grown on wafers without any chemical pre-cleaning has been studied. The oxide layer was removed using a low silicon flux. Factors influencing the dislocation density have been studied, including substrate type, growth temperature and the temperature at which oxide is removed. Dislocation densities below 10-3 cm-2 have been obtained. The defect density in p-type silicon doped with boron oxide has also been studied. The influence of boron oxide on dislocation density has been found to be negligible, even though incorporation of oxygen is large at growth temperatures ≤650°C. Boron oxide doped Si.88Ge.12 layers have also been grown and a similar level of dislocations has been found.

The selfconsistent electronic properties of the epitaxial Si(111)-NiSi2 interface are computed for the experimentally observed type-A and type-B growth orientations. The densities of states projected on the various sites provide a detailed analysis of the siliconsilicide interface electronic states. The measured Schottky barrier heights may be interpreted by assuming that deviations from epitaxy must be taken into account.

We have demonstrated low temperature (300°C) Ge epitaxy on Ge(111) and on Si(100) substrates. Critical to this epitaxy has been the use of wet chemistry to produce controlled, thin oxides on the substrates prior to loading into the reactor and an in-situ 300°C hydrogen plasma treatment to remove those oxides from the semiconductor surfaces. Reflection high energy electron diffraction shows the plasma treatments to be effective in producing clean, well-ordered surfaces. This represents a new approach for in-situ cleaning of Ge(111) and Si(100) surfaces.

We demonstrate the fabrication of high quality GexSi1−x heteroepitaxial alloy layers on Si(100) substrates by pulsed laser melting of a-Ge/Si(100) layered structures. First, 50–200Å of germanium are evaporated onto a chemically cleaned silicon wafer. Next, an excimer laser pulse is used to melt the sample surface to a depth of 200–2500Å. Finally, the melt solidifies in 20–100ns producing a heteroepitaxial alloy layer. By varying the thickness of the evaporated Ge film and the laser energy, alloys of 500–1500Å thickness and Ge fraction x=3–20% are obtained. The crystallinity of the layer and interface are found to be excellent as evaluated by Rutherford Backscattering Spectrometry (RBS), ion channeling, and high resolution cross sectional TEM. This technique for producing GexSi1−x alloy layers is insensitive to minor levels of contamination because the original Ge/Si interface is melted through during the laser processing

We present low-temperature photoluminescence (PL) spectra of MBE and MOCVD ZnTe layers deposited on (100) GaAs substrates under different growth conditions. Strong bands associated with Zn vacancies are observed in the MBE materials, while the MOCVD spectra are dominated by sharp impurity-related lines. Stress levels less than 0.1 kbar are determined for both the MBE and MOCVD layers. A study of the effects of the Zn:Te ratio in the MBE growth chamber reveals an optimal value of −2.2 for a growth temperature of 325°C.

CdTe is a very important semiconductor with versatile applications extending from solar energy conversion to optoelectronics. In addition, both the close lattice match between CdTe and HgCdTe and the immunity of CdTe to autodoping of the HgCdTe make CdTe the substrate of choice for the growth of HgCdTe. However, CdTe is extremely difficult to grow and the nonavailability of good quality, large area, inexpensive, single crystal CdTe has slowed the development of HgCdTe detectors. Infrared device processing requires large areas of single crystal material and the problems associated with CdTe have called for alternative substrates for growing HgCdTe.

Electron diffraction and high resolution electron microscopy were used for analysis of Cd1−xMnxTe films grown on (100)2°[011] GaAs substrates by metal organic chemical vapor deposition (MOCVD) at 420°C (x=O.3) and 450°C (x=0.5). It has been found that these two conditions produce dramatically different microstructures. Two orientation relationships of the epilayers with respect to the substrate were observed. It is suggested that this phenomenon may be related to GaAs substrate surface morphology.

Recent progress in the heteroepitaxial growth of layered structures of Si, Ge, GaAs, and alkaline earth fluorides is reviewed. Effectiveness of the predeposition technique, in which a thin Si layer is deposited on the CaF2 surface at room temperature prior to the growth of a thick Si film at 800°C, is shown for the growth of Si films on CaF2/Si structures. In case of the overgrowth of Ge and GaAs films on (111) substrates, modification of the fluoride surface by electron beam exposure is effective to increase the wettability between fluoride and semiconductor films and to improve the crystallinity and surface morphology of the films. Finally, antiphase disorder in the GaAs(l00) films grown on fluorides is experimentally studied and the generation mechanisms are discussed.