Águas, H., Cabrita Tonello Nunes Fortunato Martins A. P. P. "
Two step process for the growth of a thin layer of silicon dioxide for tunnelling effect applications."
Materials Research Society Symposium - Proceedings. Vol. 619. 2000. 179-184.
AbstractIn today's main crystalline silicon (c-Si) applications in MOS (metal-oxide-silicon), MIS (metal-insulator-semiconductor) or SIS (Semiconductor-Insulator-Semiconductor), the growing of the oxide layer plays the main role, dictating the device performances, in particular if it has to be grown by a low temperature process. Of fundamental importance is the SiO2 interface with the c-Si. A very low defect density interface is desirable so that the number of trapping states can be reduced and the devices performance optimised. A two step low temperature oxidation process is proposed. The process consists of growing first a layer of oxide by a wet process and then treating the grown oxide with an oxygen plasma. The oxygen ions from the plasma bombard the oxide causing compaction of the oxide and a decrease in the interface roughness and defect density. Infrared spectroscopy and spectroscopic ellipsometry measurements were performed on the samples to determine the oxide thickness, optical and structural properties. SIS structures were built and capacitance measurements were performed under dark and illuminated conditions from which were inferred the interface defect density and correlated with the oxide growth process.
Águas, H.a, Pereira Ferreira Ramos Viana Andreu Vilarinho Fortunato Martins L. a I. a. "
Effect of an interfacial oxide layer in the annealing behaviour of Au/a-Si:H MIS photodiodes."
Journal of Non-Crystalline Solids. 338-340 (2004): 810-813.
AbstractThis work presents a study on the effect of an interfacial silicon oxide layer placed between Au and a-Si:H MIS (metal-insulator-semiconductor) photodiodes in their performances, by stopping the Au diffusion towards the a-Si:H. The results show that the Au diffuses very easily to the oxide free a-Si:H surface, even at room temperature, degrading the photodiode performance. On the other hand, the MIS photodiodes with the interfacial oxide show an improvement of their characteristics after annealing, function of its thickness, and degree of film's compactness. This effect is associated with the presence of oxide of thicknesses ≥5 Å at the Au/a-Si:H interface that prevents the Au diffusion and improves the photodiode characteristics, which does not happen when the interfacial oxide is absent. © 2004 Elsevier B.V. All rights reserved.
Águas, H., Martins Fortunato R. E. "
Influence of the plasma regime on the structural, optical and transport properties of a-Si:H thin films."
Key Engineering Materials. 230-232 (2002): 583-586.
AbstractIn this work we show that it is possible to control the plasma species present near the substrate surface, from what is usually associated with an α regime (a plasma free of particles) to a γ' regime (a plasma where particles are present) and simultaneously control the energy of the ions striking the substrate during a-Si:H deposition from a silane glow discharge in a modified triode (MT) type PECVD reactor, where a DC mesh electrode biased with Vpol is located in front of the r.f electrode. The presence of large particles in the plasma leads to the deposition of the films with the poorest optoelectronic properties. When the particle size in the plasma decrease the film properties improve, but, when particles are no longer present in the plasma region close to the substrate, like in a α like regime, the properties of the films deteriorate again. The results show that the best transport properties are achieved for the films deposited in the α-γ' transition regime corresponding to 0V<Vpol<51V. Under this condition the films present a dark conductivity, σ d ≈ 10-11 (Ωcm)-1, photosensitivity, S ≈ 107, activation energy, ΔE ≈ 0.9 eV, hydrogen content, CH ≈ 10%, factor of microstructure, R ≈ 0.085 and an optical gap, Eop ≈ 1.77 eV.
Águas, H., Pereira Raniero Fortunato Martins L. L. E. "
Effect of the load resistance in the linearity and sensitivity of MIS position sensitive detectors."
Materials Research Society Symposium Proceedings. Vol. 862. 2005. 691-696.
AbstractIt is experimentally known that the linearity and sensitivity of the position sensitive detectors (PSD) are dependent on the resistance of the collecting layer and of the load resistance, mainly if the detection is based on the measurement of the photo-lateral voltage. To determine the value of the load resistance to be used in metal - insulator - semiconductor (MIS) PSDs structures that lead to the maximum value of sensitivity and linearity, we propose an electrical model through which it is able to simulate the proper sensor response and how the load resistance influence the results obtained. This model is valid for PSDs where the resistance of the collecting resistive layer is quite low (≤ 500 Ω), leading to a low output impedance. Under these conditions we conclude that the value of the load resistance should be of about 1 kΩ in order to achieve a good compromise between the linearity and the sensitivity of the PSD. This result is in agreement with the set of experiments performed. © 2005 Materials Research Society.
Águas, H.a, Pereira Goullet Silva Fortunato Martins L. a A. b. "
Correlation between the Tunnelling Oxide and I-V Curves of MIS Photodiodes."
Materials Research Society Symposium - Proceedings. Vol. 762. 2003. 217-222.
AbstractIn this work we present results of a study performed on MIS diodes with the following structure: substrate (glass) / Cr (2000Å) / a-Si:H n + (400Å) / a-Si:H i (5500Å) / oxide (0-40Å) / Au (100Å) to determine the influence of the oxide passivation layer grown by different techniques on the electrical performance of MIS devices. The results achieved show that the diodes with oxides grown using hydrogen peroxide present higher rectification factor (2×106) and signal to noise (S/N) ratio (1×107 at -1V) than the diodes with oxides obtained by the evaporation of SiO2, or by the chemical deposition of SiO 2 by plasma of HMDSO (hexamethyldisiloxane), but in the case of deposited oxides, the breakdown voltage is higher, 30V instead of 3-10 V for grown oxides. The ideal oxide thickness, determined by spectroscopic ellipsometry, is dependent on the method used to grow the oxide layer and is in the range between 6 and 20 Å. The reason for this variation is related to the degree of compactation of the oxide produced, which is not relevant for applications of the diodes in the range of ± 1V, but is relevant when high breakdown voltages are required.