Difference in the absorption coefficient profile of the amorphous and crystalline silicon is the key idea for the realization of a new visible/infrared tunable photodetector (VIP). The device consists on a n-doped a-Si:H/intrinsic a-Si:H/p-doped a-SiC:H multilayer grown by PECVD on a p-type crystalline silicon wafer doped by a phosphourus diffusion. A grid-shaped aluminum front contact with transparent conductive oxide coating is used as window for the incident light. Tunable sensitivity in the visible and near infrared spectral range can be achieved under different values of the external voltage, with excellent spectral separation between the two quantum efficiencies peaks at 480 nm and 800 nm.

A simple analytical model taking into account the absorption profile, diffusion and drift lengths, and layer thicknesses reproduces fairly well the experimental results.

A novel device based on a-Si:H p+-i-n−-i-p−-i-n+ structure, showing a hysteresis in its current-voltage curve is reported. A numerical device model allows to investigate in detail the fundamental role of the two lightly doped n− and p− layers, where charge trapping determines the bistable behavior of the device. The ON condition is mantained until the ambipolar charge injection overcomes the fixed charge. The transition OFF-ON starts when, increasing the applied voltage, one of the two lightly doped layers becomes completely depleted. The transition ON-OFF is, instead, mainly dependent on the recombination processes occurring in the central doped layers. Devices with hysteresis around 2 V and tum-on voltage around 12 are presented.

Hydrogenated amoiphous silicon photochemical sensors based on Pd-MIS structures were produced by Plasma Enhanced Chemical Vapor Deposition with two different oxidized surfaces (thermal and chemical oxidation). The behaviour of dark and illuminated current-voltage characteristics in air and in the presence of a hydrogen atmosphere is explained by the changes induced by the gases in the work function of the metal, modifying the electrical properties of the interface. The photochemical sensors produced present more than 2 orders of magnitude variation on the reverse dark current when in presence of 400 ppm hydrogen to which it corresponds a decrease of 45% on the open circuit voltage.

Amorphous SiNx:H thin film diodes (TFDs) can be used for pixel addressing in active matrix liquid crystal displays. They depend on the application of high electric fields to switch from the ‘off to the ‘on’ states. They prove to be remarkably rugged and can be made with high yield and tolerance. An important feature that contributes to this ruggedness is the ability of these switches to generate defect states at a rate dependent on current density. Current induced defect states trap electrons and cause a reduction in field at the cathode contact, which in turn causes a reduction in current density. Therefore, current will be transferred from regions of high current to regions of low current in the device, making the current flow more uniform. TFDs with thin regions will become effectively thicker during current stressing. In order to check this hypothesis, thin film diodes with nonuniform thickness a-SiNx:H layers were current stressed, and the I-V characteristics compared with those calculated using a defect generation model. The experimental data agreed well with our theoretical model.

A process to use a hydrogenated amorphous silicon (a-Si:H) film as a dry photoresist mask for plasma etching of HgCdTe has been demonstrated. The a-Si:H films were deposited using standard plasma enhanced chemical vapor deposition with pure silane as the source gas. X-ray photoelectron spectra show that virtually no oxide grows on the surface of an a-Si:H film after 3 hours in air, indicating that it is hydrogen passivated. Ultraviolet light frees hydrogen from the surface and enhances the oxide growth rate. A pattern of 60 micron square pixels was transferred from a contact mask to the surface of an a-Si:H film by ultraviolet enhanced oxidation in air. For the conditions used, the oxide thickness was 0.5–1.0 nm. Hydrogen plasmas were used to develop this pattern by removing the unexposed regions of the film. A hydrogen plasma etch selectivity between oxide and a-Si:H of greater than 500:1 allows patterns as thick as 700 nm to be generated with this very thin oxide. These patterns were transferred into HgCdTe by etching in an electron cyclotron resonance plasma. An etch selectivity between a-Si:H and HgCdTe of greater than 4:1 was observed after etching 2500 nm into the HgCdTe. All of the steps are compatible with processing in vacuum.