b Vieira, M.a, Fantoni Koynov Cruz Maçarico Martins A. a S. a. "
Amorphous and microcrystalline silicon p-i-n optical speed sensors based on the flying spot technique."
Journal of Non-Crystalline Solids. 198-200 (1996): 1193-1197.
AbstractFrom the flying spot technique (FST) the ambipolar diffusion length and the effective-lifetime of the carriers photogenerated by a moving light spot that strikes a p-i-n junction can be inferred. In this paper, those properties of a p-i-n junction are used together with an optical triangulation principle to determine the velocity of an object that is moving in the direction of a light source. The light reflected back from the object is analysed through an amorphous or a microcrystalline p-i-n structure. Its transient transverse photovoltage is dependent on the velocity of the object. A comparison between the performances of both kinds of devices is presented.
Vieira, M., Martins Fortunato Soares Guimarães R. E. F. "
A-Si:H ambipolar diffusion length and effective lifetime measured by flying spot (FST) and spectral photovoltage (SPT) techniques."
Journal of Non-Crystalline Solids. 137-138 (1991): 479-482.
AbstractOn this paper we report the physical model that supports the theory of the Flying Spot Technique (FST). Through this technique it is possible to determine separately the ambipolar diffusion length (L*) and the effective lifetime (τ*) of the generated carriers, using either Schottky diodes or quasi-ohmic sandwich structures. We also report a new static method based on the Spectral Photovoltage (SPT) that allows to infer the ambipolar diffusion length and to estimate the surface recombination velocity. © 1991 Elsevier Science Publishers B.V. All rights reserved.
Vieira, M., Fantoni Fortunato Lavareda Martins A. E. G. "
AD-layer for spatial control of light induced degradation on pin devices."
Materials Research Society Symposium Proceedings. Vol. 336. 1994. 741-746.
AbstractIn this work we report experimental results on light induced metastability of a-Si: H p.i.n. devices with different microscopic/macroscopic structures and we discuss them in terms of improved stability through spatial control of charged defects grown during light exposure. By placing a thin (few A) intrinsic layer (i) between both p/i and i/n a-Si: H interfaces we are able to reduce the effective degradation rate through spatial modification of the electric field profile in the device. The electronic transport and the stability changes that accompany the change in microstructure (R) and hydrogen content (CH) of the i- and i′-layer, were monitored throughout the entire light induced degradation process and compared with the corresponding μT product (for both carriers) inferred through steady state photoconductivity and Flying Spot Technique (FST) measurements. Results show that the degradation rate is a function of CH and R of both layers and can be correlated with the density of microvoids and di-hydride bonding. Since the i′-layers have a higher CH bonded mainly as SiF2 radicals (R≈0.4), they act as an hindrance to the growth of the defect, in the active region, generating "gettering centers" whose localisation and density are tailored in such a way that they will control spatially the electric field profile during light exposure. Preliminary results show improvements in film's stability when the interfacial layer is included. So future progress toward more stable and efficient a-Si: H solar cells will depend on a careful engineering design of the devices. © 1994 Materials Research Society.