Basic limitations of single-junction and tandem p-n and p-in diodes are established from thermodynamical considerations on radiative recombination and semi-empirical considerations on the classical diode equations. These limits are compared to actual values of short-circuit current, open-circuit voltage, fill factor and efficiency for amorphous (a-Si:H) and microcrystalline (mc-Si:H) silicon solar cells. For single-junction cells, major efficiency gains should be achievable by increasing the short-circuit current density by better light trapping. The limitations of p-in junctions are estimated from recombination effects in the intrinsic layer. The efficiency of double-junction cells is presented as a function of the energy gap of top and bottom cells, confirming the 'micromorph' tandem (a-Si:H/mc-Si:H) as an optimum combination of tandem solar cells.

Radiation tests of 32 lm thick hydrogenated amorphous silicon n-i-p diodes have been performed using a high-energy 24 GeV proton beam up to fluences of 2 · 10 16 protons/cm 2 . The results are compared to irradiation of similar 1 lm and 32 lm thick n-i-p diodes using a proton beam of 405 keV at a fluence of 3 · 10 13 protons/cm 2 . All samples exhibited a drop of the photoconductivity and an increase in the dark leakage current under both high-and low-energy proton irradiation. An almost full recovery of the device performance was observed after a subsequent thermal annealing.

PACS 29.40 Wk, 81.05 Gc, 85.60 Bt, Integrated particle sensors have been developed using thin-film on ASIC technology. For this purpose, hydrogenated amorphous silicon diodes, in various configurations, have been optimized for particle detection. These devices were first deposited on glass substrates to optimize the material properties and the dark current of very thick diodes (with thickness up to 50 µm). Corresponding diodes were later directly deposited on CMOS readout chips. These integrated particle sensors have been characterized using light pulse illumination and beta particle irradiation from 63 Ni and 90 Sr sources. Direct detection of single lowand high-energy beta particles have been demonstrated. The application of this new integrated particle sensor concept for medical imaging is also discussed.

Image sensors based on thin-film on CMOS technology (TFC) have been developed. In this approach, amorphous silicon (a-Si:H) detectors are vertically integrated on top of a CMOS readout chip so as to form monolithic image sensors. In order to reduce as far as possible the dark current density (J dark ) of the TFC sensors, we have focused on analyzing and understanding the behavior of J dark in this type of detectors. Edge effects along the periphery and at the corners of the pixel, due to the non planar configuration of the vertically integrated photodiodes, are found to be responsible for an increase of the dark current. A new and adapted solution for the minimization of J dark is proposed, which combines the use of a metal-i-p a-Si:H diode configuration with a deposition on top of an unpassivated CMOS chip. Values of J dark as low as 12 pA/cm 2 at a reverse polarization of V = -1 V are measured on such TFC sensors.

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