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.

Abstract:In this work we present, for the first time, a rapid, compact and innovative method for detection of Ochratoxin A (OTA) based on hydrogenated amorphous silicon (aSi:H) sensors. 2 µl of acidified toluene containing OTA at different concentrations were spotted on the silica side of a High Performance Thin Layer Cromatography plate and aligned with a a-Si:H p-i-n photodiode deposited by Plasma Enhanced Chemical Vapor Deposition on a different glass substrate. As an UV radiation excites the mycotoxin, the reemitted light is detected by the a-Si:H sensor. Results show a very good linearity between OTA concentration and the sensor photocurrent over almost three orders of magnitude. The minimum detected OTA concentration is equal to 0.1ng, showing that the presented system has the potential for a low cost system suitable for the early detection of toxins in foods.

We present a novel family of photodetectors based on hydrogenated amorphous Si/SiC p-in-i-p heterostructures. Front p-i-n and rear n-i-p diodes work one as a detector and the other as a load impedance, depending on the polarity of the applied voltage. Due to different absorption at different wavelengths, the devices operate as bias-controlled light detectors in either the blue or the red regions. The energy gap and the thickness of the two intrinsic layers have been optimized to obtain a sharp wavelength selection (centered at 430 and 630 nm) with high rejection-ratios and good quantum efficiencies. The I-V characteristics and the device time response are investigated and simulated by SPICE.

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Indium Tin Oxide (ITO) is widely used in solar cell devices for its excellent electrical and optical characteristics, such as high transparency in the Ultraviolet-Visible range and good conductivity (around 10 4 -1 cm-1). In this work we have compared thin (70-150 nm) ITO layers deposited by Direct Current or Radio Frequency sputtering. We have used different substrate temperatures during film growth and have afterwards thermally annealed the samples at different temperatures up to 300°C to investigate the effects on the electrical and optical properties of the material. We have found out that the different growth/annealing conditions induce changes in the optical properties of the samples as well as in the conductivity and carrier concentration.