Particle-size distribution effects on the energy levels of semiconductor quantum dots are investigated. By examining the low temperature photoluminescence spectra of microcrystals of the binary semiconductor CdSe embedded in a glass matrix, the distribution of energy levels due to three-dimensional confinement is determined. Calculations of the electron-hole pair ground state energy provide a relation between confinement energy and particle diameter. This allows conversion of the photoluminescence lineshape directly into a distribution of particle radii and facilitates analysis of the observed properties of the material. With extension to other systems the technique can become a valuable tool in the study of semiconductor microparticle composites.

Amorphous CoMnNiO film is doposited on oxidized Si substrate by RF sputtering equipment. Structure relaxation occurs in the amorphous CoMnNiO film when it is annealed below 550°C. Annealed in the range from 600°C to 1000°C, the amorphous film is converted into the polycrystal. After annealing in rich oxygen atmosphere, the amorphous film is transformed into spinel solid solution with stable structure and good electrical properties. The electrical conductivity will be reduced due to formation of low valence oxides when annealed without oxygen. As annealing temperature is higher than 1000°C, some spinel solid solutions will be resolved into low valence oxides CoO and NiO, reducing the conductivity of the CoMnNiO film.

We report the preparation and general, optical and resonant Raman scattering characterization of MoS2 platelets suspended in an insulating organic liquid. Structural results indicate that the platelets are predominantly 2H in structure and are about 500Å in diameter and 50–90 Å thick. The optical constants of the composite are close to those expected from the simple Maxwell-Garnett effective medium theory. We have observed resonant enhancement of the Raman cross-section for the MoS2 phonon mode at 408 cm−1 as the laser excitation energy is scanned through the “B” exciton.

We report and interpret two groups of experiments on the role that hydrogen plays in the formation of silicon microcrystals. We show that the growth of singlecrystal Si by molecular beam epitaxy at 475°C is disrupted by H2, which induces the formation of microcrystals. In crystallization experiments of non-hydrogenated a-Si and of hydrogenated a-Si:H on a hot stage in a transmission electron microscope, hydrogen facilitates the nucleation of crystallites. We explain our observations with a substantial reduction of the grain boundary energy by hydrogen.

The effects of deposition temperature, rf power and hydrogen dilution ratio on the growth, structure and transport of p-type microcrystal(μc-) Si films deposited by remote plasma CVD have been investigated. While low substrate temperature and low rf power yield small grain sizes, high temperature and high rf power tend to supress the growth of grains. The etching of Si by hydrogen radicals plays an important role to grow μc-Si, but excess etching supresses the growth of crystallites. We obtained 400 A of grain size and 3.5 S/cm of room temperature conductivity for p-type μ-Si.

In hydrogenated amorphous silicon NMR studies indicate a twophase structural inhomogenity. Hydrogenated microcrystalline films consist of small crystals with a typical size of 100 Å, embedded in an amorphous web. A hydrogen rf plasma is able to etch both type of films, but with different etch rates. The more crystalline parts of a film are etched more slowly, which makes hydrogen plasma etching a technique that can reveal structural inhomogenities and differences in structural disorder as present, both in amorphous and in microcrystalline silicon films.

Amorphous and microcrystalline films were etched and fractal-like structures were visible when using a SEM at a magnification of 20000 times. In microcrystalline films the fractals form a closed network. The number and typical size of the fractals present in amorphous films can be influenced by the conditions during the deposition.

The effects of fast-pulse excimer laser annealing of a-Si:H were investigated by measurements of electronic transport properties and impurity concentration depth profiles as a function of incident laser energy density. The dc dark conductivity of laser-annealed, highly-doped a-Si:H increases by a factor of ∼350 above a sharp laser energy density threshold whose magnitude increases with decreasing impurity concentration and which correlates with the onset of hydrogen evolution from and crystallization of the near-surface layer. The similarities between the preparation and properties of laser-crystallized a-Si:H and pc-Si:H are discussed.

The effect of hydrogen plasma treatment on the properties of undoped and doped microcrystalline silicon are investigated by Raman and infrared spectroscopy, conductivity measurements, hydrogen effusion, and subgap absorption. It is found that hydrogen causes a passivation of dopant atoms similar to that seen in crystalline silicon. However, the efficiency of the dopant passivation appears to be smaller in μc-Si, and the vibrational spectra of dopants and hydrogen show distinct broadening due to local disorder. It is suggested that intergrain regions may efficiently getter atomic hydrogen introduced from the plasma and also provide the origin for a weakly bound hydrogen phase observed in the effusion experiments.

A systematic study has been made on the formation of Si-network of amorphous(a-), microcrystalline(μc-) and epitaxial (epi)-Si prepared by Plasma-Enhaced (PE-) CVD under control of flow of atomic hydrogen. The control of the Si-network structures requires a deliberate selection of the precursor, i.e., SiHn (n≤53) and SiFnHm (n+m≤53), as well as an intentional acceleration of the chemical reactions for the propagation of Si-network in the vicinity of the growing surface by impinging of atomic hydrogen. A plausible interpretation was given to the growing mechanism of c-Si at low temperature.

Effects of hydrogen atoms bonded to silicon atoms on microcrystalline surfaces in a μc-Si:H and anodized porous silicon have been investigated using infrared spectroscopic technique and a semi-empirical molecular-orbital calculation (AM1 method). Experimental results on thermal stability of the Si-H bonds and oxidation of H-covered Si can be explained consistently in terms of system total energies and heats of formation of various clusters constructed by 13–18 Si and 18–24 H atoms (with an additional 0 atom). Possible role of H on the growth of μ c-Si:H is discussed in relation to stable Si-H bonds.

Both fully crystallized nanocrystalline as-deposited silicon layers with an average grain size ranging between 6 and 80 nm and mixed-phase hydrogenated doped and undoped silicon films are studied at room temperature by Photothermal Deflection Spectroscopy (PDS), Transmission Spectroscopy and Spectroscopic Ellipsometry. The differences with regard to similar data obtained on monocrystalline and hydrogenated amorphous silicon are discussed, with an emphasis on the low-energy part of the 0.6-5.6 eV explored range.

We report recent studies of the crystallization of ultrathin (< 10 nm ) amorphous silicon layers clad by silicon dioxide. We observe changes in Raman scattering spectra which indicate that nanocrystalline silicon layers formed by crystallization of amorphous silicon continue to evolve structurally with further annealing. There is evidence for significant strain in crystallized material.

We have extended our photomodulation studies of nc-Si:H to the picosecond time domain. We measured the decays of photoinduced reflectivity with 100fs temporal resolution as a function of light intensity. Comparison with the data obtained on a-Si:H and c-Si indicates that ultrafast trapping and recombination processes are mainly the properties of the amorphous phase. It has also been observed that nc-Si:H is unstable under high illumination.

Optical properties of undoped, microcrystalline silicon are investigated by photothermal deflection spectroscopy, spectroscopic ellipsometry and Raman scattering. Samples are prepared by recrystallization of hydrogenated amorphous silicon in the temperature range 680 – 900°C. The increase of grain sizes with increasing annealing temperature and the disappearance of amorphous tissue lead to noticeable changes in the observed spectra. It is argued that much of the pertinent structural information of μc-Si can be obtained by a suitable combination of optical measurements alone.

Undoped 500 nm-thick silicon layers with a crystalline fraction around 95% and an average grain size of 20 nm have been deposited at 350°C by 50 kHz triode PECVD in a H2/SiH4 mixture, in the presence of a magnetic field. Their room temperature (rt) dc conductivity μrt is 0.03 Δ−1cm−1 for a Hall mobility of 0.8 cm 2V−1s−1.

The study by SIMS, infrared absorption, grazing angle x-ray diffraction and Raman scattering spectroscopies of the doped samples shows how the crystalline fraction and the grain size drop as the B2H6/SiH4 and PH3/SiH4 volumic ratios increase from 10 ppm to 1%.

The rt dc conductivity reaches 2 Δ−1 cm−1 (Hall mobility: 15 cm2V−ls−1) for a solid phase density of 1019 cm−3 boron atoms, and 30 Δ−1cm−1 (Hall mobility: 55 cm2V−ls−1) at the maximum P incorporation of 8 × 1020cm−3.

Permeation of atomic hydrogen in p-type Si damaged with ion implantation or deposited with polycrystalline or amorphous Si has been studied. Following ion implantation or film deposition, atomic hydrogen was introduced by low energy H ion implantation or from an electron cyclotron resonance (ECR) plasma. Spreading resistance profiles indicate that deactivation of acceptor dopant boron atoms by atomic hydrogen is drastically reduced in silicon wafers with any of the above disordered surface layers, and secondary ion mass spectroscopy (SIMS) traces this reduction to the suppression of hydrogen movement into the crystalline Si substrate. Trapping of hydrogen or formation of molecular hydrogen at defect sites in the surface disordered regions apparently is responsible for this phenomenon.

Binary Si:H materials are prepared by means of the rf sputtering technique in pure hydrogen atmosphere on low temperature (about 100 K) and room temperature substrates. The physical properties of the obtained materials are very much affected by the rf power and substrate temperature during the deposition. The material prepared at a low substrate temperature with a low rf power has a wide optical gap, and shows a visible photoluminescence at room temperature. On the other hand, the material prepared at room temperature with a high rf power contains many Si microcrystals, whose diameters are relatively large, and its optical gap becomes very small. The latter condition causes the dependence of the crystalline direction of the material film on the substrate crystal even at the room temperature. An rf power-modulated multi-layered structure (superlattice) is also proposed, and an apparent diffraction peak can be observed in the low-angle X-ray scattering measurement.

Raman scattering is becoming a widely used tool for the characterization of semiconductor microcrystals due to its sensitivity to crystal sizes below a few hundred angstroms. Through detailed analysis of the first order Raman spectrum it is possible to determine the size and shape of microcrystalline grains. First order spectra must be examined with care however, since they are sensitive to other factors including: stress/strain, surface vibrations, mixed amorphous/microcrystalline phases and intragrain defects. Second order Raman spectra are more sensitive to microcrystalline effects than first order spectra. They offer the potential to measure crystal sizes greater than a few hundred angstroms but much work remains to be done to quantify the size dependence of the second order spectra.

Raman scattering measurements are used to characterize the components of microcrystalline Si and carbon films. A model is described which addresses the properties of Raman scattering from composites of materials of different optical absorption. The analysis shows that the observed spectra are dependent on both the percentage of the components and on the domain size of the more highly absorbing domains. Carbon films produced by different enhanced CVD techniques show both sp2 (graphite) and sp3 (diamond) regions. Silicon films prepared by excimer laser exposure of hydrogenated a-Si and by magnetron sputtering showed features due to both microcrystalline and amorphous regions. The experimental results reflect the length scales of the domains and vibrational excitations.

Size dependence of optical phonon frequencies and that of phonon dampings of SiC small particles have been studied by analysing their Raman data. The particle size ranges from 30 nm to 1000 nm. Decrease in the TO-phonon frequency as well as the LT-splitting (the splitting between the LO- and TO-phonon) with decrease in the particle size are much larger than that expected from the spatial correlation model or that from the phonon confinement model. The phonon damping for the small particle consists of the usual temperature-dependent term and an excess damping term, which is independent of temperature. These results suggest that the scattering of the phonon at the particle surface plays a major role in determining the phonon states of the small particle. Our experimental data suggest that the surface phonon-polariton mode at the interface between the crystallites plays a minor role in the Raman spectrum of particles consisting of a number of crystallites.