I.G. Austin

Photoluminescence properties of a-SiNx: H alloys

Abstract Photoluminescence (PL) studies are reported on a series of a-SiNx:H alloys prepared by glow discharge, with x up to around 1·1. As x increases, the main PL band broadens and moves to higher energies, and there is a marked reduction in the temperature dependence of the PL efficiency, linewidth and peak energy. The 0·9 eV defect band increases by a small factor and there is only a small reduction in the efficiency of the main band, strongly suggesting that nitrogen introduces few extra dangling-bond defects. Excitation studies show a strikingly large red-shift at low excitation energies up to 0·5eV or more in SiN1·1. This suggests a large increase in tail-state widths, probably due to compositional fluctuations, and this is consistent with most of the other changes in PL behaviour with alloying. We also compare our data briefly with PL from a-Si/SiNx multilayers.

Radiative and non-radiative tunnelling in glow-discharge and sputtered amorphous silicon

Abstract Photoluminescence decay measurements are reported for doped and undoped glow-discharge a-Si, and for a-Si prepared by sputtering in a hydrogenated atmo-sphere. It is concluded that a distribution of radiative lifetimes is present, due either to non-crystalline disorder or to a donor-acceptor pair mechanism. The main competitive mechanism is tunnelling to defects.

Photoluminescence excitation studies of a-SiNx:H alloys

Abstract Below gap excitation is shown to red shift the PL peak by >14% of the gap in SiNx alloys and produce a marked weakening of its temperature dependence.

Low energy excitation of photoluminescence in a-Si:H : Temperature and intensity effects

Abstract Photoluminescence (PL) spectra from both glow discharge and sputtered a-Si:H are reported, excited with photons of energies between 2.4eV and 1.55eV. Low energy excitation produces a red shifted PL spectrum, which responds quite differently to changes of temperature compared with PL excited by above-gap photons. With rising temperature, the peak moves more slowly to lower energies, the efficiency falls less rapidly, and the kinetics are bimolecular even at the lowest excitation intensities. We compare two possible models to explain these effects, one based on a thermalisation gap and the other on two centre emission.

Electrical, optical and luminescence properties of a-Si/SiN multilayers

Abstract Conductivity, absorption and photoluminescence measurements have been carried out on the above structures. The problem of interpreting the results in terms of quantum well effects will be discussed.

Recombination in a-Si:H Based Materials: Evidence for Two Slow Radiative Processes

New time resolved photoluminescence measurements show that two radiative processes contribute to the ~ 1.3 eV emission band seen in a-Si:H. These processes are distinguished by their different lifetimes. Very similar lifetime distributions are seen in a-SiNx:H alloys and also in a-Si:H based multilayers. Time resolved electroluminescence and photoconductivity also have similar lifetime distributions. The temperature and excitation intensity dependence of the lifetime distributions provides strong evidence for saturation effects. Together with spectral measurements, these data reveal a range of radiative slow processes below ~ 20 μs, and a predominantly non-radiative channel with a lifetime of about 8 μs.

Luminescence phenomena in a-Si:H p-i-n junctions

Abstract Injection electro-luminescence (EL) and photoluminescence (PL) have been studied in a range of a-Si p-i-n junctions on stainless steel and ITO glass substrates, in which the i layer thickness is varied. New data are presented on photoenhanced EL (or PEL) and emission and excitation spectra for this process.

A comparison of photo- and electroluminescence in a-Si p-i-n junctions

Abstract New measurements over an extended temperature range confirm the similarity between electro- and photoluminescence from a-Si:H junctions. The first lifetime studies show significant differences in the kinetics.

O.D.M.R. investigation of recombination in μc-Si:H

AbstractThe luminescence from μc-Si: H measured out to 0·54 eV shows a long low- energy tail with a broad maximum near 0·8 eV as well as bands at 0·95 and 1·3 eV. The O.D.M.R. shows that the long tail is associated with two enhancing signals with g= 1·999 and 2·006 implying donor-acceptor recombination in the microcrystallites. A weak quenching O.D.M.R. signal at g = 2·005 is associated with the 1·3 and 0·95 eV emission bands and, in particular, the results for the 1·3 eV band are consistent with it arising in the amorphous intercrystallite region. The 0·95 eV band is thought to arise from defects similar to those observed in crystalline material.

The 0·9 eV defect luminescence band in sputtered and other forms of plasma-deposited a-Si: H

Abstract The photoluminescence properties of a low-energy (0·9 eV) emission band are examined for a wide variety of samples of a-Si: H prepared in both glow-discharge and sputtering reactors, and are compared with those of similar bands seen in microcrystalline and crystalline silicon. We also report the first photoluminescence measurements on magnetron-sputtered films, which suggest that this material has defect densities as low as those found in good quality glow-discharge a-Si: H.