Vitor Silva

New insights on large area flexible position sensitive detectors

Abstract In this paper we present an improved version of large area (5 mm ×80 mm ) flexible position sensitive detectors deposited on polyimide (Kapton ® VN) substrates with 75 μm thickness, produced by plasma enhanced chemical vapor deposition (PECVD). The structures presented by the sensors are Kapton/ZnO:Al/(pin)a-Si:H/Al and the heterostructure Kapton/Cr/(in)a-Si:H/ZnO:Al. These sensors were characterized by spectral response, photocurrent dependence as a function of light intensity and position detectability measurements. The set of data obtained on one-dimensional position sensitive detectors based on the heterostructure show excellent performances with a maximum spectral response of 0.12 A/W at 500 nm and a non-linearity of ±10%.

a-Si:H interface optimisation for thin film position sensitive detectors produced on polymeric substrates

Abstract In this paper we present results concerning the optimisation of the electronic and mechanical properties presented by amorphous silicon (a-Si:H) thin films produced on polyimide (Kapton® VN) substrates with different thicknesses (25, 50 and 75 μm ) by the plasma enhanced chemical vapour deposition (PECVD) technique. The purpose of this study is to obtain a low defect density as well as low residual stresses (specially at the interface) in order to provide good performances for large area (10 mm wide by 80 mm long) flexible position sensitive detectors. The electrical and optical properties presented by the films will be correlated to the sensor characteristics. The properties of samples have been measured by dark/photoconductivity, constant photocurrent measurements (CPM) and the results have been compared with films deposited on Corning 7059 glass substrates during the same run deposition. The residual stresses were measured using an active optical triangulation and angle resolved scattering. The preliminary results indicate that the thinner polymeric substrate with 25 μm presents the highest density of states, which is associated to the residual stresses and strains associated within the film.

32 linear array position sensitive detector based on NIP and hetero a-Si:H microdevices

Abstract In this paper we present results concerning the performance exhibited by an integrated array of 32 one-dimensional amorphous silicon thin film position sensitive detectors based on nip and hetero amorphous silicon structures, with a total active area size below 1 cm 2 . The main emphasis will be put on the devices linearity, its spatial resolution and response time, that make it one of the most interesting analog detector to be used in unmanned optical inspection control systems where a continuous detection process is required. This opens a wide range of applications for amorphous silicon devices in the area of image processing.

Performance of a-Six:C1−x:H Schottky barrier and pin diodes used as position sensitive detectors

Abstract Position sensitive detectors (PSD) using hydrogenated amorphous silicon as the active layer have been widely proposed either with the p–i–n or the Schottky structure. In this case, the devices are tailored to respond to light in the range 620–650 nm. Little is known about the use of silicon carbide active layers in such devices, which is important when the detected light is in the blue region of the light spectrum. In this paper we present for the first time the electro-optical properties of the a-Six:C1−x:H/Pd and p–ic–n PSD, using a-Six:C1−x:H layers deposited by plasma enhanced chemical vapour deposition (PECVD). These sensors are able to distinguish the wavelength of the impinging visible radiation (from red to blue light). In addition, the sensors respond to light intensities as lower as 1×10 −6 W cm −2 with a resolution better than 0.04 mm and a linearity between ±0.12% and ±0.8%.

Thin film position sensitive detectors based on pin amorphous silicon carbide structures

Abstract The aim of this paper is to present data concerning the performances of position sensitive detectors based on silicon carbide alloys, able to detect the green colour and to compare their performances with the ones exhibit by position sensitive detectors, optimised to detect the red colour. The data achieved show that the device linearity is quite high with spatial resolution errors below ±1%.

Dependence of the Strains and Residual Mechanical Stresses on the Performances Presented by a-Si:H Thin Film Position Sensors

The influence of residual stresses on the performances of large area position sensitive detectors produced on flexible substrates are presented here. For evaluating the residual stresses, two main techniques were used: An active optical triangulation and angle resolved scattering and the constant photocurrent method (CPM). From the results it was possible to correlate the stresses and the density of defects present in the films.

Role of ion bombardment and plasma impedance on the performances presented by undoped a-Si:H films

The aim of this paper was to present results of the role of the d.c. grid bias on the silane plasma impedance and its I-V characteristics to grow undoped amorphous silicon (a-Si:H) films by plasma enhanced chemical vapour deposition (PECVD) in conditions where some nanoparticles can be formed in the growth region of the deposition process, under proper ion bombardment. The results achieved show that the performances of the films produced are dependent on the self bias voltage that can present photosensitivities of approximately 10 7 (two orders of magnitude larger than the one exhibited by films grown under conventional conditions) with density of states determined by the constant photocurrent method below 4 × 10 15 cm -3 . Apart from that, the films grown are less affected by light soaking than the conventional films.

Characteristics of a linear array of a-Si:H thin film position sensitive detector

Abstract The increasing demand in automation processes in finishing techniques also calls for automatic measurement and inspection methods. These methods ought to be installed as close as possible to the production process and they ought to measure the values needed in a safe and fast way, without disturbing the process itself. Simultaneously they should be free of wear and insensitive against mechanical perturbations. This approach can be reached by proper combination of the laser triangulation technique with an array of linear position sensitive detectors, able to supply information about the surface finishing of an object. This is the aim of this paper that envisages to present experimental results of the performances exhibited by such an array constituting 128 elements. The analogue information supplied by this array is processed by an analogue/digital converter, directly coupled to the array and whose information is computer processed, concerning the recognition of patterns and the processing of information collected over the object to be inspected.

Mass spectroscopy analysis during the deposition of a-SiC:H and a-C:H films produced by hot wire and hot wire plasma-assisted techniques

Abstract This work analyse mainly the dissociation mechanism of the gas during the hot wire (HW) and hot wire plasma-assisted (HWPA) processes used to produce hydrogenated carbon films and silicon-carbide, using ethylene and silane as gas sources. The results show that ethylene is better decomposed by plasma-enhanced chemical vapour deposition (PECVD) than HW process. The data also show that the HWPA leads to a better carbon (C) incorporation than HW processes, when silicon carbide alloys are produced and, that the presence of atomic hydrogen (H) is beneficial for all processes. That is, the presence of the plasma and H lead to the formation of higher C radicals such as methylsilane (CH3SiH3), ethylsilane (C2H5SiH3) and silorane (C2H4SiH2), whose contributions are enhanced as the fraction of ethylene (Feth) in the gas mixture increases.

Role of the gas temperature and power to gas flow ratio on powder formation and properties of films grown by the PECVD technique

This paper deals with the study of the role of gas temperature and of the ratio of r.f. power to gas flow on the particles formation in amorphous silicon films grown by the plasma enhanced chemical vapour deposition technique, by monitoring the plasma impedance behaviour under different process conditions. The results achieved show the existence of two main boundary regions separating the so-called α-regime (no powder formed) from the γ-regime (powder formed). Those regions are reached either by heating the gas, changing the gas pressure or using high power to gas flow ratios, corresponding to the establishment of a balance between the plasma resistance and the plasma reactance. In the β-region the probability to incorporate nanoparticles in the films is low and the films exhibit photosensitivitys of about 10 5 with density of states determined by the constant photocurrent method below 6 × 10 15 cm -3 with Urbach energies below 50 meV. In the 0-region small nanoparticles can be incorporated leading to films with density of states below 3 x 10 15 cm - 3 , with Urbach energies above 50 meV and photosensitivitys above 10 6 , about two orders of magnitude larger than that of conventional amorphous silicon grown in the α-regime.