Surface Diffusion and Islanding in Semiconductor Heterostructures

Molecular beam epitaxy (MBE) is an important technique for the creation of new, non-equilibrium semiconductor materials and structures exhibiting novel physical phenomena. Surface diffusion plays an important role in the growth of these structures, influencing such fundamental growth processes and constants as islanding, critical thickness and epitaxial temperatures. Two approaches to the general problem of surface diffusion and islanding, using the SiGe system as a prototypical semiconductor heterostructure, are discussed: The time evolution of patterned deposits, and kinetic studies of nucleation and growth. While disordered laminar growth occurs for deposition at 300 K, elevated temperatures lead to Stranski-Krastanow (SK) growth (uniform coverage SK with excess Ge in islands). Diffusion coefficients for Ge on Si(100) have been determined for coverages below SK and show a significant coverage dependence. They are extremely sensitive to contamination with carbon on the order of ≈0.05 ML, as well as to e-beam irradiation. In situ annealing experiments were performed to study the islanding process in real time. Provided the initial coverage exceeds the thickness of the SK layer, SK ≈3 ML on Si(100)2x1, the initially uniform but disordered layer begins to collapse into a SK-type morphology at about 250 °C. At a ramping rate of 0.1 °C/s this process is completed at ≈400 °C. A temperature dependence of the SK-layer thickness has been discovered for the first time. It is in excellent agreement with theoretical predictions

ENERGY TRANSFER IN F ATOM-RARE GAS COLLISIONS

Author Institution: Bell LaboratoriesResults of fully quantal close coupling calculations of F + He in a perturbed stationary state basis are presented using configuration interaction potentials. Comparison is made with experimental results for the temperature dependence of gas phase EPR generalized line broadening cross sections for the $^{2}P_{3/2}$ and $^{2}P_{1/2}$ lines. It is shown that these particular cross sections may be rewritten as a weighted sum of both inter- and intra-manifold population transfer cross sections. The major contribution to the small ($\sim 0.2$ {\AA}$^{2}) \ ^{2}P_{1/2}$ broadening cross section is shown to be due to the $^{2}P_{1/2} \rightarrow {^{2}P_{3/2}}$ fine structure transition cross section, while the $^{2}P_{3/2}$ lines are dominated by intramanifold transitions. The validity of the forbidden $m_{j} \not \to m_{j}^{\prime}$ transition selection rule is also discussed

LOCAL CRYSTAL ORIENTATION IN LASER ANNEALED SILICON USING A RAMAN MICROPROBE.

The authors discuss the application of polarization selective Raman microprobe spectroscopy to the detailed, non-destructive analysis of the local crystal orientation of a polysilicon sample grown over SiO//2 pads and laser annealed. Intensity measurements taken as a function of input polarization angle are fit to an expression derived from the Raman scattering selection rules to calculate the angles by which the crystal structure is twisted within the original substrate plane

MULTIPHOTON IONIZATION STUDIES OF THE DEUTEROACETALDEHYDES

$^{1}$ B. A. Heath M B. Robin, N. A. Kuebler, G. J. Fisanick and T. S. Eichelbergor, IV. J. Chem. Phys. (in press) $^{2}$ G. J. Fisanick, T. S. Eichelberger, IV, B. A. Heath and M. B. Tobin, J. Chem. Phys. (in press)Author Institution:Both parallel-plate and mass spectroscopic multiphoton ionization studies of $CD_{3}CDO, CD_{3}CHO^{1,2}$ and $CH_{3}CDO$ fragmentation have been carried out, extending previous work on CH,CHO. A $N_{2}$-pumped dye laser with $< 1cm^{-1}$ bandwidth, capable of providing a 7ns, $0.6^{3}$ mJ pulse at 363 nm was used as the ionization source. From the variation of total ion production with wavelength, the vibrational structure of the 2-Photon resonant $n\to 3s$ Rydberg st e is assigned. Variation of splitting patterns due to the $\nu_{15}$ methyl torsional barrier are discussed as a function of deuteration. Mass spectroscopic analysis of the fragments indicates that for the partially deuterated species, both $CDO^{+}$ and $CHO^{+}$ ions are formed at high flux, indicative of a hydrogen shift during the dissociative ionization. Extensive fragmentation is found for all species, with the fragmentation pattern highly flux dependent. Simple integer power law behavior for the fragment dependence on flux is not generally found. Total ion signals are compared in both the collision-free (mass spectrometer) and binary collision (parallel-plate) regime. Al though at low flux a $F^{3}$ dependence is found for both experiments, reflecting the lowest energy 2+1 photonionization at higher flux, ion signal variations differ. These differences, as well as the complex fragmentation behaviour, can be explained using a rate equation model for the fragmentation which properly includes the effect of spatial averaging over the ion collection region. Conditions for isotopically selective fragmentation are also discusse

Polarization sensitive raman microprobe studies of local crystal quality in laser annealed silicon

The technique of Raman microprobe spectroscopy has been extended to allow polarization sensitive characterization of local crystal quality with lateral mapping capability. Computer minimization algorithms have been utilized to invert Raman scattering intensity versus incident laser polarization information to local crystal orientation. This microprobe method has been applied to investigate the quality of laser annealed polysilicon over oxide films. During the course of laterally seeded epitaxial regrowth of silicon over the oxide film, it was found that the annealed crystal tends to develop large grains of varied size and orientation. Measurements of the local phonon frequency shift, which monitors strain in the material, show large variations across the structures. It is demonstrated that the strain inferred from phonon frequency shifts must be interpreted in terms of the local crystal orientation. © 1984 SPIE

Raman microprobe determination of local crystal orientation in laser annealed silicon

In this letter we discuss the application of polarization selective Raman microprobe spectroscopy to the detailed, nondestructive analysis of the local crystal orientation of a polycrystalline silicon sample grown over SiO 2 pads and laser annealed. Intensity measurements taken as a function of input polarization angle are fit to an expression derived from the Raman scattering selection rules to calculate the angles by which the crystal structure is twisted within the original substrate plane, as well as the degree of tipping of the crystal plane away from the plane of the Si substrate