The amorphous/crystalline silicon technology has demonstrated its potentiality leading to high efficiency solar cells. We propose the use of surface photovoltage technique as a contact-less tool for the evaluation of the energetic distribution of the state density at amorphous/crystalline silicon interface. We investigate the effect hydrogen plasma treatments performed on thin amorphous silicon buffer layer deposited over crystalline silicon surface and we compare its effect with that of thermal annealing on the interface. The surface photovoltage technique results to be very sensitive to the different experimental treatments, and therefore it can be considered a precious tool to monitor and improve the interface electronic quality.
In this paper, we present the first integration of an amorphous silicon balanced photosensor with a microfluidic network to perform on-chip detection for biomedical applications, where rejection of large background light intensity is needed. This solution allows to achieve high resolution readout without the need of high dynamic range electronics. The balanced photodiode is constituted by two series-connected a-Si:H/a-SiC:H n-i-p stacked junctions, deposited on a glass substrate. The structure is a three terminal device where two electrodes bias the two diodes in reverse conditions while the third electrode (i.e. the connection point of the two diodes) provides the output signal given by the differential current. The microfluidic network is composed of two channels made in PolyDimetilSiloxane (PDMS) positioned over the glass substrate on the photodiode-side aligning each channel with a diode. This configuration guarantees an optimal optical coupling between luminescence events occurring in the channels and the photosensors. The experiments have been carried out measuring the differential current in identical and different conditions for the two channels. We have found that: the measurement dynamic range can be increased by at least an order of magnitude with respect to conventional photodiodes; the balanced photodiode is able to detect the presence or absence of water in the channel; the presence of fluorescent molecules in the channel can be successful detected by our device without any need of optical filter for the excitation light. These preliminary results demonstrate the successful integration of a microfluidic network with a-Si:H photosensor for on-chip detection in biomedical applications.
A detailed characterization of the performances of amorphous silicon photodiodes in the detection of chemiluminescent signal is carried out. Comparison with commercial CCD acquisition system has been done as benchmark. The underlying idea is the development of stand-alone and compact micro-total-analysys-systems (μ-TAS) that do not need bulky and expensive equipment for their operation as external focusing optics and excitation sources. The photosensor is p-i-n structures deposited by Plasma Enhanced Chemical Vapour Deposition on a glass substrate covered with a transparent conductive oxide that acts as bottom electrode and window layer for the light impinging through the glass. A PDMS layer with wells has been fabricated using an aluminum mold and bonded on the glass substrate with a well aligned with a photosensor. The experiments have been performed by filling a well with solutions containing different quantities of horseradish peroxidase. A good linearity of the photosensor response is observed across the entire measurement range that spans over three orders of magnitude. The system detection limit is 70 fg/μL. A very good agreement between results achieved with conventional off-chip CCD detection and the on-chip photodiode has been observed. Experiments with target molecules immobilized on a functionalized glass surface have been also performed in microfluidic regime, confirming the validity of the proposed integrated approach based on a-Si:H technology.
In this work we present a system for the detection of labeled DNA by means of a two-color amorphous silicon photosensor. The device is a p-i-n-i-p structure, whose spectral response is controlled by tuning the voltage applied to its electrodes. The thicknesses of the different layers has been optimized to match the emission spectra of the two utilized fluorochromes. Minima detectable concentrations range in the order of few nmol/l. Very good linearity in the photosensor responses, comparable with those of commercial equipment, has been achieved.
In this work we investigate, for the first time, the performances of a system based on hydrogenated amorphous silicon
photosensors for the detection of Ochratoxin A. The sensor is a n-type/intrinsic/p-type amorphous silicon stacked
structure deposited on a glass substrate. The mycotoxin is deposited on a thin layer chromatographic plate and aligned
with the sensor. An ultraviolet radiation excites the ochratoxin A, whose fluorescence produces a photocurrent in the
sensor. The photocurrent value is proportional to the deposited mycotoxin quantity. An excellent linearity of the detector
response over more than two orders of magnitude of ochratoxin A amount is observed. The minimum detected
mycotoxin quantity is equal to 0.1ng, suggesting that the presented detection system could be a good candidate to
perform rapid and analytical ochratoxin A analysis in different kind of samples.