Kimon C. Palinginis

Saturated defect densities of hydrogenated amorphous silicon grown by hot-wire chemical vapor deposition at rates up to 150 Å/s

Hydrogenated amorphous-silicon (a-Si:H) is grown by hot-wire chemical vapor deposition (HWCVD) at deposition rates (Rd) exceeding 140 A/s (∼0.8 μm/min). These high rates are achieved by using multiple filaments and deposition conditions different than those used to produce our standard 20 A/s material. With proper deposition parameter optimization, an AM1.5 photo-to-dark-conductivity ratio of 105 is maintained at an Rd up to 130 A/s, beyond which it decreases. In addition, the first saturated defect densities of high Rd a-Si:H films are presented. These saturated defected densities are similar to those of the best HWCVD films deposited at 5–8 A/s, and are invariant with Rd up to 130 A/s.

Defect bands in a-Si–Ge:H alloys with low Ge content

Abstract We have studied a series of optimized glow discharge a-Si1−xGex:H films with Ge content 0.02⩽x⩽0.2. The drive level capacitance profiling method indicated defect densities 5×10 15 cm −3 in these samples. Modulated photocurrent measurements detected two defect bands at 0.68±0.05 and 0.79±0.05 eV, compared to the single band normally observed in pure a-Si:H. The magnitudes of these bands vary with Ge content and with the state of light-induced degradation. Based on electron spin resonance (ESR) measurements on matched samples we have identified these defect bands as Si and Ge neutral dangling bonds. The Ge dangling bond concentration was found to be larger in the annealed state for all samples, even at 2 at.% Ge. However, in the light-induced degraded state the density of Si dangling bonds was larger for all the alloys in this series.

Defect densities in tetrahedrally bonded amorphous carbon deduced by junction capacitance techniques

Junction capacitance measurements performed on tetrahedrally bonded amorphous carbon (ta-C)/crystalline-Si (c-Si) heterostructures are used to deduce the defect density in thin ta-C films. Using the drive level capacitance profiling technique, we determine a homogeneous defect density of 6±1.5×1017 cm−3 in the undoped (p-type) ta-C films and one order of magnitude larger in the nitrogen-doped (n-type) films. Admittance measurements reveal defect states at the ta-C/c-Si interface with a density exceeding 2×1012 cm−2.

Insights into the mechanisms of light-induced degradation from studies of defects in low Ge fraction a-Si,Ge:H alloys

Abstract The modulated photocurrent (MPC) method was used to study deep defect creation and annealing in low Ge fraction a-Si,Ge:H alloys (2–10 at.% Ge). These measurements reveal two distinct bands of deep defects in these samples which are identified as neutral Si and neutral Ge dangling bonds. Upon thermal annealing in the dark from a strongly light degraded state, these two defects are found to decrease in a manner which indicates a direct competition between the annealing of the Si and Ge dangling bonds, and therefore implies a global reconfiguration mechanism. Comparing purely thermal annealing with light-induced annealing indicates that the relative anneal rate for the two types of defects is different. This therefore tends to rule out models in which the rate limiting step in the annealing process comes from the release of the mediating entity (hydrogen? strain?) from a remote site.

Defect band distributions in hydrogenated tetrahedral amorphous carbon/crystalline silicon heterostructures

Junction capacitance measurements and voltage-pulse stimulated capacitance transient measurements have been applied to undoped hydrogenated tetrahedral amorphous carbon (ta-C:H)/crystalline-Si (c-Si) heterostructures to deduce the defect densities in as-grown and post-annealed ta-C:H films. Transient capacitance measurements reveal a component corresponding to the emission of carriers out of defect states at the ta-C:H/c-Si interface, and a slower component corresponding to the carrier emission from defect states of interior ta-C:H. The interior defect density of as-grown films was estimated at 1×1018±2×1017cm−3, decreasing to (6.5±2)×1017cm−3 for films annealed at 300°C. A Gaussian defect band was identified with activated hole emission with a 0.35 eV activation energy. Steady state admittance measurements indicate two thermal activation processes and have allowed us to determine a defect density of 1×109±2×108cm−2 at the ta-C:H/c-Si interface.

Light-induced Annealing of Deep Defects in Low Ge Fraction a-Si,Ge:H Alloys: Further Insights into the Fundamentals of Light-induced Degradation

Modulated photocurrent (MPC) was employed to study metastable deep defect creation and annealing in low Ge fraction a-Si,Ge:H alloys (Ge fractions below 10at.%). These MPC spectra reveal two distinct bands of deep defects identified as neutral Si and neutral Ge dangling bonds. Upon heating in the dark from a strongly light degraded state, these are reduced in direct competition to each other, therefore implying a global reconfiguration mechanism. We have extended our studies to compare purely thermal annealing with light-induced annealing in these alloys. We have found that the relative anneal rate for the two types of defects differs from the case of purely thermal annealing. This therefore tends to rule out models in which the rate limiting step during annealing comes from the release of the mediating entity from a remote site.