Estimation of the melting threshold of Ti supersaturated Si using time resolved reflectometry and haze measurements

Hyperdoped or supersaturated semiconductors are gathering the attention of industry and research institutions due to their sub-bandgap photon absorption properties. In this study, two fast and non-invasive techniques, time-resolved reflectometry (TRR) and Haze Measurements, are applied to infer the melt and solidification regimes of Ti supersaturated 300 mm silicon wafers, aiming to ease the characterization process towards high volume manufacturing of supersaturated materials. Ti supersaturation is attained by using an ion implantation process with a dose 3 x 10(15) cm(-2), which amorphizes the surface. Crystalline quality is then recovered by means of a XeCl UV nanosecond laser annealing process. TRR technique is used to determine two different melting and solidification processes of the laser annealed implanted surface. A first brief, low temperature peak (alpha peak) is associated with the melting process of the amorphized surface, followed by a longer peak/plateau (beta (1) peak/plateau), linked to the melting process of the crystalline phase below the amorphized layer, at sufficiently high laser fluences. Haze technique is used to indirectly measure the crystalline quality after the solidification process of the laser-annealed surface. Atomic force microscopy measurements are used to obtain the surface roughness value and cross-section high resolution transmission electron microscopy micrographs to check crystalline quality.Ministerio de Ciencia e Innovación (España)Comunidad de MadridMinisterio de Economia y Competitividad (España)Depto. de Estructura de la Materia, Física Térmica y ElectrónicaFac. de Ciencias FísicasTRUEpu

Fabrication of TiOx, by High Pressure Sputtering for Selective Contact in Photovoltaic Cells

Se deposita la versión postprint de la ponenciaIn this work we have studied the behavior of TiO x growth by the unconventional technique of High-Pressure Sputtering (HPS) as an electron selective contact (ESC). This technique shows promising aspects for low-damage and low-temperature deposition, which are relevant criteria for the fabrication of heterojunction solar cells. We explored the deposition of TiO x with a 2-step process. First a thin Ti film is deposited in an Ar atmosphere, immediately the film is oxidized with the aid of an Ar/O 2 plasma at a relatively low temperature (150°C or 200°C). We analyzed the deposited films with XPS, FTIR and TEM measurements. Finally, Cox & Strack (C&S) structures were fabricated to obtain the specific contact resistance of TiOx/c-Si, with this data we compared different deposition processesDepto. de Estructura de la Materia, Física Térmica y ElectrónicaFac. de Ciencias FísicasTRUEpu

Electronic transport properties of Ti-supersaturated Si processed by rapid thermal annealing or pulsed-laser melting

Se deposita la versión posprint del artículoIn the scope of supersaturated semiconductors for infrared detectors, we implanted Si samples with Ti at high doses and processed them by rapid thermal annealing (RTA) to recover the crystal quality. Also, for comparative purposes, some samples were processed by pulsed-laser melting. We measured the electronic transport properties at variable temperatures and analyzed the results. The results indicate that, for RTA samples, surface layers with a high Ti concentration have negligible conductivity due to defects. In contrast, the implantation tail region has measurable conductivity due to very high electron mobility. This region shows the activation of a very shallow donor and a deep donor level. While deep levels have been previously reported for Ti in Si, such a shallow level has never been measured, and we suggest that it originates from Ti-Si complexes. Finally, a decoupling effect between the implanted layer and the substrate seems to be present, and a bilayer model is applied to fit the measured properties. The fitted parameters follow the Meyer–Neldel rule. The role of the implantation tails in Si supersaturated with Ti is revealed in this work.Comunidad de MadridERDF Funds - MICINNEuropean Social Fund (ESF)Ministerio de Ciencia e Innovación (España)Mexican grants program CONACyTMinistry of Education in the Kingdom of Saudi ArabiaDepto. de Estructura de la Materia, Física Térmica y ElectrónicaFac. de Ciencias FísicasTRUEpu

Inversion charge study in TMO hole-selective contact based solar cells

In this article, we study the effect of the inversion charge ( Q _inv ) in a solar cell based on the hole-selective characteristic of substoichiometric molybdenum oxide (MoO_x ) and vanadium oxide (VO_x ) deposited directly on n-type silicon. We measure the capacitance–voltage ( C – V ) curves of the solar cells at different frequencies and explain the results taking into account the variation of the space charge and the existence of Q_inv in the c-Si inverted region. The high-frequency capacitance measurements follow the Schottky metal–semiconductor theory, pointing to a low inversion charge influence in these measurements. However, for frequencies lower than 20 kHz, an increase in the capacitance is observed, which we relate to the contribution of the inversion charge. In addition, applying the metal–semiconductor theory to the high-frequency measurements, we have obtained the built-in voltage potential and show new evidence about the nature of the conduction process in this structure. This article provides a better understanding of the transition metal oxide/n-type crystalline silicon heterocontact.Comunidad de MadridFondo Europeo de Desarrollo Regional (Unión Europea)Ministerio de Ciencia e Innovación (España)Agencia Estatal de Investigación (España)European Social Fund (Unión Europea)Depto. de Estructura de la Materia, Física Térmica y ElectrónicaFac. de Ciencias FísicasTRUEpu

Ti supersaturated Si by microwave annealing processes

Microwave annealing (MWA) processes were used for the first time to obtain Ti supersaturated Si. High Ti doses were ion implanted on Si substrates and subsequently MWA processed to recrystallize the amorphous layer. The resulting layers were monocrystalline with a high density of defects. Ti depth profiles indicate that diffusion is avoided once recrystallization is produced. Finally, the electronic transport properties measurements point to a decoupling effect between the Si:Ti layer and the substrate. The implanted layer present also a shallow donor and very high Hall mobility.Universidad Complutense de MadridEuropean Regional Development Fund (Unión Europea)Ministerio de Ciencia e Innovación (España)European Social Found (Unión Europea)Ministry of Education (Arabia Saudita)Consejo Nacional de Humanidades, Ciencias y Tecnologías (México)Depto. de Estructura de la Materia, Física Térmica y ElectrónicaFac. de Ciencias FísicasTRUEpu