ZnO/p-Si hetero-structure photodiodes have been fabricated by ion beam sputtering technique. The sputtered ZnO films
were identified to be polycrystalline nature with wurtzite structure of ZnO and n-type electrical conductivity. Several
single and bi-layer metal contacts were produced on both sides of hetero-junction and IV characteristics were measured.
It was found that Ni-Au bi-layer contacts were ohmic and best for the diode measurements, having high linearity and low
resistivity on both p-Si and ZnO. The IV curve of the hetero-junction indicate that all of the samples have low forward
resistance, around 30 ohms and a leakage current around 1 milliamp at 4 volts reverse bias. The photo response of these
diodes was tested by shining an 8mW, 780-nm diode laser on to the diodes and measuring the resulting photo current.
The responsivity of the hetero-junction was measured as 0.3A/W. This is a quantum efficiency of 48% at 780-nm.
Measurement of the ZnO absorption at 780-nm and estimates of the first surface reflectivity of these samples suggests
that quantum efficiencies up to 85% are achievable. This is comparable with the best silicon diodes reported in the
literature to date which has quantum efficiencies up to 32% and responsivities up to 0.18A/W.
The bandgap of indium nitride has long been accepted to be 1.9 eV. However, recent results have cast doubt over this as modern epitaxy techniques have allowed experimental studies of high quality material. Single crystalline and polycrystalline indium nitride films have been grown on (0001) sapphire and silica glass using plasma assisted molecular beam epitaxy (PAMBE). Optical measurements on the films revealed a luminescence feature in the vicinity of 0.8 eV for all films, both on sapphire and glass. No feature around 1.9 eV could be identified above the background noise. To our knowledge this is the first report of polycrystalline InN exhibiting the 0.8 eV feature. Ion beam analysis of the material could find no measurable oxygen contamination in the bulk of the films. These results along with recent reports of blue shifting of the absorption onset of InN films with increasing oxygen content appear to point towards oxygen contamination as being the source of the previously reported higher bandgap. Like other groups we observed a small anomalous blue shifting of the luminescence with increasing temperature when using a germanium detector. We have verified that this is a real feature by measuring the temperature dependent PL with a lead sulphide detector. Two distinct growth regimes were identified. High In:N flux ratios lead to spotty RHEED accompanied by a morphology of flat plateaus separated by narrow valleys. Low In:N flux ratios lead to rough films consisting of facets largely disjoint from each other. Surprisingly, this regime gave streaky RHEED, suggesting high levels of crystal alignment between facets and high crystal quality within facets.
This paper discusses the growth of silicon nanostructures on silicon (100), (110) and (111) substrates by electron beam annealing. The nanofabrication procedure involves annealing of the untreated Si substrates in the temperature range 750°C - 1200°C using a raster scanned 20 keV electron beam. Nanostructuring occurs as a result of kinetic amplification of the surface disorder induced by thermal decomposition of the native oxide. Pyramidal and truncated pyramidal nanocrystals were observed on Si(100) surfaces. The nanostructures are randomly distributed over the entire surface and square-based, reflecting the two-fold symmetry of the substrate surface. Similar square-based pyramidal structures with four equivalent facets are observed following nanostructuring of Si(110). With Si(111), nanostructure growth occurs preferentially along step-edges formed on the vicinal surfaces. Significant differences in nanostructure shapes formed on step-edges and terraces are related to the different growth mechanisms on the unreconstructed and 7x7 reconstructed domains respectively.