A thin highly doped layer at the surface of a semiconductor has been used to increase the surface field of a Schottky barrier and reduce the barrier height by an amount insensitive to applied bias. The effective barrier height of Ni–Si barriers of this type made using ion-implantation techniques has been reduced by an amount in the range 0–0.2 eV without significant degradation of the reverse characteristic.

Polycrystalline gallium nitride films, 100 nm to 1 m thick, were deposited under a range of conditions. Substrate electrode temperatures during sputtering were varied from room temperature to 450°C, the pressure from 0.15 to 6.0 Pa, the nitrogen fraction of the deposition atmosphere from 10% to 100% and the target bias from −400 to − 1800 V. The deposition rates as functions of these conditions are in the range 0.5-25 nm/ min. The growth rate is considered to be controlled respectively by the thermally activated desorption from the substrate, changes in the mean free path and concentration of gas particles, differences between the sputter yields of Ga and GaN in Ar and N 2 , and changes in the ion current and sputter yields. The films are generally columnar, with the grain size increasing with film thickness. The most crystalline films were grown at mid range temperatures, low N 2 concentrations, and low target biases, and the most disordered were grown at low pressures. The latter two cases suggest that decreasing the energy of particles incident on the film during deposition results in a more ordered film. The biaxial stress is compressive and shows an increasing trend with the target bias and N 2 concentration, reaching 4.7 GPa at 75% N 2 . Oxygen contamination of 3 -30 at. % has a major effect on the optical properties of the films, increasing the band gap values from 3.02 to Ͼ 4.0 eV and the Urbach tail energies from around 150 to 840 meV and decreasing the refractive index from 2.46 to 2.03. At a 40% N 2 deposition fraction, the N:Ga ratio is more or less constant at 1:1. Since the absolute oxygen incorporation rate changes very little, it is the relative film deposition rate which determines the final oxygen concentration. Excess Ga at low N 2 concentrations causes a decrease in the band gap and an increase in the Urbach tail energy.

The presence of a shallow n-type surface layer on a p-type substrate is shown to increase the effective height of a Schottky barrier to p-type material. The effective barrier height of Ni–Si diodes has been increased by an amount in the range 0–0.25 eV using surface layers formed by low-energy antimony implantation.

The holy-grail in terms of flat panel displays has been an inexpensive process for the production of large area 'hang on the wall' television that is based on an emissive technology. As such electron field emission displays, in principle, should be able to give high quality pictures, with good colour saturation, and, if suitable technologies for the production of the cathodes over large areas were to be made available, at low cost. This requires a process technology where temperatures must be maintained below 450 o C throughout the entire production cycle to be consistent with the softening temperature of display glass. In this paper we show three possible routes for nanoscale engineering of large area cathodes using low temperature processing that can be integrated into a display technology.The first process is based on carbon nanotube-polymer composites that can be screen printed over large areas and show electron field emission properties comparable with some of the best aligned nanotube arrays. The second process is based on the direct large area growth of carbon nanofibres directly on to substrates held at temperatures ranging from room temperature to 300 o C, thereby making it possible to use inexpensive substrates. The third process is based on the use of excimer laser processing of amorphous silicon for the production of lithography free large area three terminal nanocrystalline silicon substrates. Each route has its own advantages, and flexibility in terms of incorporation into an existing display technology. The harnessing of these synergies will be highlighted together, with the properties of the cathodes developed for the differing technologies.

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