I. H. Campbell

The effects of microcrystal size and shape on the one phonon Raman spectra of crystalline semiconductors

Abstract Small physical dimensions of the scattering crystals lead to a downshift and broadening of the first order Raman line through a relaxation of the q = 0 selection rule. We consider the effect of the exact shape of the microcrystal and show that there are significant differences between spherical, columnar and thin slab microcrystals. The relationship between the width, shift and asymmetry of the Raman line is calculated and is in good agreement with available experimental data.

Raman spectroscopy of low-dimensional semiconductors

Abstract Raman spectroscopy is widely used to study the vibrational and structural properties of single crystals. More recently, in the fields of chemistry, physics, and engineering, interest in the properties of small objects has arisen. Small objects include microcrystalline materials, artificially layered semiconductor structures, and colloidal suspensions. The reason for this recent interest is that these objects often display unique electronic properties which may find applications in devices. Since Raman spectroscopy is a convenient nondestructive tool, it is not surprising that it has been used to characterize such objects. In this review, we consider almost exclusively results obtained with semiconductors.

Properties of p+ microcrystalline films of SiC:H deposited by conventional rf glow discharge

Using a conventional rf glow discharge, we have grown microcrystalline p+ SiC:H films having conductivities 2–2×10−3 (Ω cm)−1 and activation energies 0.05–0.1 eV with carbon concentrations 0–6 at. %, respectively. Increasing the carbon content suppresses the microcrystallinity. The choice of substrate is crucial to initiating the immediate onset of microcrystalline growth in thin (∼200–400 A) films.

Long range material relaxation after localized laser damage

We observe, for the first time, structural modifications that extend many microns beyond the area where laser‐induced damage is visible by high resolution optical microscopy. These modifications are recorded by a Raman microprobe, which is sensitive to stress and microcrystallinity.

cw laser irradiation of GaAs: Arsenic formation and photoluminescence degradation

Low‐power, cw laser irradiation of GaAs leads to the formation of solid arsenic at the sample surface and to the degradation of band‐gap photoluminescence (PL) efficiency. In situ Raman scattering and PL are used to measure the lattice and carrier temperature in addition to monitoring the arsenic formation and PL efficiency. Both effects are athermal, do not involve surface oxidation, and occur in n,p and semi‐insulating GaAs prepared by different growth techniques. These observations suggest that arsenic formation and PL decrease may both be the result of a nonradiative recombination process.

Mechanism of the growth of amorphous and microcrystalline silicon from silicon tetrafluoride and hydrogen

We study the growth of amorphous (a‐Si:H,F) and of microcrystalline (μc‐Si) silicon over trench patterns in crystalline silicon substrates. We vary the conditions of the SiF4‐H2 glow discharge from deposition to etching. All deposited films form lips at the trench mouth and are uniformly thick on the trench walls. Therefore, surface diffusion is not important. The results of a Monte Carlo simulation suggest that film growth is governed by a single growth species with a low (∼0.2) sticking coefficient, in combination with a highly reactive etching species.

Trapping time in processed polycrystalline silicon measured by picosecond time-resolved reflectivity

We have used the methods of picosecond time‐resolved reflectivity to measure the carrier lifetime in fine grain polycrystalline silicon films grown by low pressure chemical vapor deposition at 625 °C. After monatomic hydrogen diffusion or implantation with phosphorus ions followed by high temperature annealing (1150 °C), the trapping time τ increased from 40 to 150 ps, consistent with passivation of the grain boundaries or an increase in grain size, respectively. If implantation was not followed by annealing, τ decreased to less than 10 ps, while if it was followed by low temperature annealing (900 °C), which approximately restored the original grain size, τ recovered to 50 ps, very close to the trapping time measured in the as‐grown samples. In all cases, we found indications that trapping of carriers was much faster than their subsequent recombination.

Temperature dependence of H radical etching in the deposition of microcrystalline silicon alloy thin films by HG-sensitized photo-CVD

Abstract The etching of a-Si:H by H radicals in Hg-sensitized photo-CVD is studied as a function of deposition temperature, etch temperature and film hydrogen content. For films deposited at the same temperature, etch rates increased as etch temperature decreased from 230°C to 100°C and were temperature independent for temperatures between 100°C and 40°C. Etch rate increased with decreasing deposition temperature, but did not change when hydrogen content was varied by changing pressure and dilution. Under conditions producing high etch rates, microcrystalline films of Si:B:H and SiGe:H were prepared at temperatures as low as 100°C.

Mechanism of microcrystalline silicon growth from silicon tetrafluoride and hydrogen

Abstract We studied the growth of amorphous (a-Si:H,F) and of microcrystalline (μc-Si) silicon over trench patterns in crystalline silicon substrates. All deposited films show elbows at the trench mouth and are uniformly thick on the trench walls. Therefore, surface diffusion is not important. The results of a Monte-Carlo simulation suggest that film growth is controlled by a single growth species with a low sticking coefficient plus a highly reactive etching species.

Critical Review of Raman Spectroscopy as a Diagnostic Tool for Semiconductor Microcrystals

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.