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In situ attenuated total reflection Fourier transform infrared spectroscopy was used to study the H bonding on the surfaces of a-Si:H and nc-Si:H during plasma enhanced chemical vapor deposition from SiH4/H2/Ar containing discharges. Well-resolved SiHx (1⩽x⩽3) absorption lines that correspond to the vibrational frequencies commonly associated with surface silicon hydrides were detected. During deposition of a-Si:H films using SiH4 without H2 dilution, the surface coverage was primarily di- and trihydrides, and there are very few dangling bonds on the surface. In contrast, during deposition of nc-Si:H using SiH4 diluted with H2, the amount of di- and trihydrides on the surface is drastically reduced and monohydrides dominate the surface. Furthermore, the vibrational frequencies of the monohydrides on nc-Si:H film surfaces match well with the resonant frequencies of monohydrides on H terminated Si (111) and Si (100) surfaces. The decrease of higher hydrides on the surface upon H2 dilution is attributed to increased dissociation rate of tri- and dihydrides on the surface through reaction with dangling bonds created by increased rate of H abstraction from the surface. Results presented are consistent with SiH3 being at least one of the precursors of a-Si:H deposition.

The lateral oxidation rate of AlAs layers decreases dramatically for layers thinner than about 500 Å, because the activation energies for the rate constant of the reaction at the oxidation front increases by an amount inversely proportional to the layer thickness. We derive a model for the thickness dependence of the lateral oxidation rate of AlAs based on the surface energy of the curvature observed at the oxide tip. From the model, we show that the linear oxidation rate has an exp(−θ0/θ) dependence on the AlAs layer thickness θ, and we can predict the slowing of oxidation when the AlAs layer is cladded with AlGaAs barriers. Also, we estimate the surface energy of the AlAs/oxide interface to be 50 eV/nm2.

We report the observation of room-temperature and low-temperature visible photoluminescence from nanocrystalline silicon (nc-Si) thin films produced by plasma-enhanced chemical vapor deposition (PECVD) through a gas discharge containing SiH4 diluted in Ar and H2. The nanocrystalline silicon films were characterized using transmission electron microscopy, spectroscopic ellipsometry, infrared and Raman spectroscopy, and were examined for photoluminescence. Luminescent films consisted of dense silicon nanocrystals that grew in a columnar structure with approximately 20%–30% void space dispersed inside the film. Aside from having small crystalline silicon regions, the structure of the nc-Si films is different than that of porous Si, another luminescent Si material generally produced by electrochemical anodization. Yet, the photoluminescence spectra of the thin nc-Si films were found to be similar to those observed from porous silicon. This similarity suggests that the same mechanism responsible for light emission from porous silicon may also be responsible for emission from nc-Si. The photoluminescence spectra are analyzed in terms of a simple quantum confinement model. Although the mechanism of visible luminescence from porous Si is still a point of controversy, our results support the hypothesis that some of the luminescence from porous silicon and nc-Si films is due to quantum confinement of electrons and holes in crystals with dimensions 2–15 nm.

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Quantum-dot (QD) lasers have fallen short of their promise of ultralow threshold and high characteristic temperature. Here, we report that QDs show great promise for controlling lateral carrier leakage. While oxide apertures continue to enable improved performance in vertical cavity surface emitting lasers (VCSELs) by reducing optical losses and current spreading, lateral carrier losses remain uncontrolled. We investigate QD active material in which lateral diffusion is intentionally reduced. Cathodoluminescence results demonstrate reduced lateral diffusion in the material with which we expect >50% reduction in the threshold current for 1-μm-wide edge emitters or 5-μm-diam VCSELs. However, initial edge-emitter results demonstrated 10% reduction due to unintended current spreading and lasing from higher states.

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