We have measured the capacitance of a-SiGe:H p-i-n solar cells as functions of temperature, frequency and bias. The density of states at the Fermi level g(EF) has been determined from two methods. We find that g(EF) increases from 1–2×1016 to 5–10×1017/(cm3eV) as the Ge content increases from 0 to 63%.

Small microvoids having a radius of gyration between 3.3Å-4.6Å are found by the Small Angle X-Ray Scattering (SAXS) technique to exist in both glow discharge a-Si1−xCx:H (O<x<0.3) and a-Si:H (40°C<Ts<250°C) films. Included in these results are the first observation of microvoids, as detected by SAXS, in device quality a-Si:H. The volume fraction of microvoids (vf) is found to increase from 0.01 in device quality a-Si:H to greater than 0.20 for both the a-SiC:H(x=.30) and a-Si:H(Ts=40°C) films. Tilting experiments indicate that the microvoids are non-oriented (spherical) in a-SiC:H and are oriented (columnar) in non-device quality a-Si:H. The normalized coplanar photoconductivities of all samples decrease with increasing vf, but for a given vf the photoconductivity is larger in a-SiC:H than in a-Si:H. We discuss reasons for this behavior.

The behaviour of DC dark conductivity of amorphous silicon alloys versus modifier concentration is investigated. By increasing the modifier concentration, the conductivity decreases, reaches

This paper presents the results of a comparison of the electron trapping in plasma-enhanced chemical vapor deposited nitrides (PECVD) to low pressure CVD (LPCVD) nitrides. The electron trapping was investigated using avalanche injection of electrons from the c-Si substrate over a thermal Si02 barrier into the various nitrides. The average trapping distance was 3–20nm in the various nitrides and the density of the traps was found to be around 2X1018 cm−3 for the PECVD nitrides while the density for LPCVD nitride was about 4X1018traps cm−3.

The effect of using the 13C isotope on the ESR signal in a-Si1−x Cx:H is investigated. The ESR linewidth increases with increasing the C content for a-Si1−x Cx.:H with 12C, while it is almost unchanged for a-Si1−x Cx:H with 12C. However, a doublet line which is expected for a C dangling bond having the hyperfine interaction with the 13C nucleus was not detected. In the range of a small x, it is possible that Si dangling bonds with 13C at the back bonds are the origin of the wide ESR signal. In the range of a large x, 13C dangling bonds should exist, but they are in a clustered form, being observed as an exchange narrowed single line instead of the hyperfine split line.

Large simultaneous changes in ambipolar diffusion length and d.c. photoconductivity are observed with boron doping below 5ppm. We show that the observation can be explained successfully with a model for the doping effect, which is also consistent with earlier studies. The μτ products for both carriers as a function of doping are determined. The light intensity dependence of diffusion length and photoconductivity is also discussed.

This paper investigates the application of the dispersive hydrogen diffusion defect kinetic equation for the generation of light-induced defects. Self-limited monomolecular carrier defect generation by dispersive motion can explain the observed t1/3 and the G0.6 dependence where t is the illumination time and G is the illumination intensity as well as the equilibrium defect density as a function of temperature. However, the temperature dependence of the creation rate and compatibility with current degradation experiments remain unresolved problems.

The changes in the absorption spectra of a-SiC films of varying bandgap were monitored as a function of light-soaking time. It was found that the greatest change in absorption occurred at an energy which was 0.55eV less than the energy of the bandgap. It is demonstrated that this could result from a band of states which remain fixed in energy with respect to one of the band edges as the bandgap changes.

Light-induced degradation of a-Si solar cells is dependent on their design. The degradation rate for single cells increases with i-layer thickness. Very thin i-layer devices (d < 100 nm) exhibit a delayed onset of degradation which is accompanied by a severe loss of open circuit voltage at prolonged exposure times. By extrapolating i-layer thickness to zero and therefore separating bulk and interface effects, the latter may account for a substantial loss of stability. The introduction of a SiC buffer layer at the p/i interface results in a considerable higher degradation mainly caused by a loss in fill factor.

Double stacked cells, as compared to single cells having similar initial efficiences, show higher stability. The instability at extended exposure times of very thin single cells as used in a tandem configuration did not influence the stacked device.

Using an exponential distribution of activation barriers, annealing data for metastable effects in hydrogenated amorphous silicon, a-Si:H, are quantitatively explained. This includes the stretched exponential time dependence of annealing and a Meyer-Neldel rule for the annealing time constant. An exponential distribution of annealing energies arises because defects are frozen in during growth at high temperature. Mechanisms that lead to an exponential distribution of annealing energies are weak bond-breaking and charge trapping.

Secondary ion mass spectrometry (SIMS) and IR measurements of long range deuterium motion in rf sputter deposited (rf sp) p-doped a-Si:H and undoped a-Ge:H are compared to recently published results on undoped rf sp a-Si:H, which exhibited strongly power-law time dependent diffusion constants (exponent α= 0.75±0.1) in films of as-deposited content of di-H and tri-H bonds (usually associated with microvoids) Ndo –4–5 at.%. In pdoped a-Si:H samples where Ndo-l.8–3.8at.%, the diffusion is much faster, but the exponent is similar. In undoped a-Ge:H exhibiting a stretch vibration band indicative of mono-H bonding only, the diffusion is about one order of magnitude faster than in undoped a-Si:H, and α = 0.23. The results are discussed in relation to both the multiple trapping (dispersive) and defect mediated diffusion models.

We report on kinetics of photo-induced degradation in a-Si:H films and devices. We find that in device-quality films, the degradation kinetics do not follow either the time or the intensity behavior predicted by the bondbreaking model. Instead, there is a strong tendency towards saturation, as predicted by Redfield's equilibration model. We also find that increased SiH2 bonding in the film leads to increased degradation. The initial degradation kinetics follow the intensity behavior predicted by the trap-todangling bond conversion model of Adler. Trace levels of impurities such as O and P significantly increase the initial degradation, also in accord with the predictions of the trap conversion model.

The relationship between the optical degradation and the morphology of hydrogenated amorphous silicon (a-Si:H) films was studied through the analysis of the annealing processes. The annealing of optically induced metastable dangling bonds can be explained in terms of the first and the second order reactions with dispersive hydrogen diffusion for the films deposited at lower and higher temperature, respectively. The activation energy of the annealing was estimated to be 0.8 eV with a small distribution in both cases. Optically enhanced annealing was first observed. It was found by DLTS and CT measurements that the density of hole trap located at Ev+0.6 eV was remarkably decreased by the light soaking, accompanied by the simultaneous increase of electron trap at Ec-0.7 ∼ Ec-0.9 eV due to the dangling bonds. These experimental facts support the view that the hole trap corresponds to the weak bonds, which convert to the metastable dangling bonds by light soaking.

We light-soaked two a-Si:H, F films up to 1,300 hours at a generation rate of 5×1020 cm−3s− 1. The films differ in fluorine content (1 vs. 5 at.%) and in hydrogen content (8 vs. 15 at.%). At each step, we measured the subgap absorption with the constant photocurrent method, the dark- and the photoconductivity. The magnitude and rate of light-induced defect production is similar to that of a-Si:H films.

We outline the characteristics of thick hydrogdenated amorphous silicon layers which are optimized for the detection of charged particles, x-rays and γ-rays. Signal amplitude as a function of the linear energy transfer of various particles are given. Noise sources generated by the detector material and by the thin film electronics - a-Si:H or polysilicon proposed for pixel position sensitive detectors readout are described, and their relative amplitudes are calculated. Temperature and neutron radiation effects on leakage currents and the corresponding noise changes are presented.

Two types of position sensitive device (PSD) using a-Si:H thin films have been developed. One has been produced by large area plasma CVD, with usual metal deposition techniques. The other is the application of a linear image sensor as a one dimensional position sensor. There are some advantages and disadvantages in these two types of position sensitive device. Resolution of the linear image sensor is limited by the size of the elements and the pitch; in contrast, uniformity of the electrodes on the p-i-n diode and thickness of the a-Si thin film are the key factors for the resolution of one and two dimensional analogue PSDs.

The analogue PSD is applicable to a digitizer which takes the role of a man-machine (computer) interface. The large area two dimensional digitizer was fabricated using the same technique as large area solar cell production, and was shown to be useful as a drawing tool on a CRT or other display devices with the aid of a micro-computer.

New multilayered photoreceptor consisting of all layers of a-Si1−xCx:H (x=0.1−0.8) has been developed on the basis of a high rate deposition process established using a glow discharge in a mixture of SiH4 and C2H2. This SiC photoreceptor is for negative charging and shows the excellent spectral sensitivity that is high in a short wavelength region and is reduced at the wavelengths longer than 600nm, suitable for the plain paper copier. The charge acceptance more than 40V/μn is achieved for the thickness less than 20μm. The charging characteristics are discussed in terms of deep emission states in the a-SiC:H.

Transient photoconductivity and ESR measurements were done to relate the ionized dangling bond density and the spin density of thick hydrogenated amorphous silicon (a-Si:H) detectors. We found that only a fraction (∼30–35%) of the total defect density as measured by ESR is ionized when the detector is biased into deep depletion. The measurements on annealed samples also show that this fraction is about 0.3. An explanation based on the shift of the Fermi energy is given. The measurements show that the time dependence of relaxation is a stretched exponential.

Thin film amorphous silicon diodes are being examined as a possible high energy particle detector for use in the superconducting super collider. One of the key requirements for any such detector is the ability to withstand relatively high doses of high energy particles without degradation of performance. We report here results of degradation studies of amorphous silicon p-i-n diodes to protons and neutrons with energies in excess of 100 keV.

The signal produced by protons in a-Si:H detectors has been measured. The charge collected from a 5.8 μm p-i-n diode is studied as a function of the reverse bias and the energy deposited in the detector. The charge collection process is discussed. Limits on the pair-creation energy, Ep, are obtained (3.4 eV<Ep< 4.5 eV).