We have fabricated accumulation mode MOSFETS in poly-silicon thin films and studied the effect of passivation of the leakage currents in these devices. We have used C-V measurements ot determine the effective doping concentration and depletion layer widths in the passivated and unpassivated devices. We find that passivation reduces the effective doping concentration and therefore increases the depletion layer width. Although this change in effective doping concentration is small (less thean a factor of 2), the increase in depletion layer width is sufficient to pinch off the passivated device but not the unpassivated one. This leads to the dramatic reduction in leakage currents after passivation.

An analytical model is developed to describe quantitatively the increase in the threshold voltage of n-channel polysilicon (poly-Si) MOSFET's. The model takes into account charge-coupling between the gate and grain boundary traps. This charge-coupling appears in Poisson's equation and a charge neutrality equation. A drift-diffusion mode of conduction is used to describe the turn-on characteristics that occur beyond the strong inversion threshold.

The performance of MOSFET's fabricated in LPCVD polysilicon thin films and operating in accumulation mode is modeled analytically. The model quantitatively explains reported device characteristics. Specifically, measured temperature coefficient of current, drive and leakage current, transconductance, drain admittance and ON/OFF current ratio are described in terms of inherent structural and electronic properties of polysilicon. The role of grain boundary hydrogenation in effectino the device performance is highliohted and ouantified.

Amorphous silicon TFTs have been realized using several plasma-CVD systems which differ in the conception of the reactor: hot or cold walls, and from the frequency used: 400 kHz and 13.56 MHz. Silicon nitride has been used as insulator. Inverted and direct staggered structures with different channel dimensions (0.5 ≤ W/L ≥ 20) are compared. High performance TFTs with mobility from 0.5 to 0.7 cm2V−1s−1 for inverted and from 0.1 to 0.4 cm2V−1s−l for direct staggered TFTs have been optimized by a full study of the insulator semiconductor and source/drain contact properties.

A series of low temperature CVD films of oxide (VAPOX and LTO) and nitride (PECVD ∝-SixNy:H) have been compared and optimised for use as gate dielectrics for TFT on insulator technology. The method of investigation involves the fabrication of MIS capacitor structures using the deposited insulator on single crystal n+ Si. I-V and C-V analyses yield information of the interested electronic stability parameters which are compared for the various insulators.

It has been previously reported that intense illumination on a-Si:H induces luminescence fatigue. The effect of light soaking on the photoconductivity of this material is also known. In this work, studies of photoluminescence (PL) at 10°K shows that the intensity of the main peak at 1.3eV can be correlated with the decrease in the photoconductivity (PC) of the sample. Similar to the PC, the effects of light soaking on the PL spectrum are reversible; annealing at 200°C fully restore the PL spectrum. Our results indicate that the light-induced radiative defects are also involved in the carrier recombination mechanism. By measuring the PL spectrum at temperatures in the range from 10 to 120°K, the activation energy for the non-radiative process has been determined in both light-soaked and heat-dried states.