In this article, we show the structural, optical, and electrical characterization of TiOx deposited by the unconventional technique of High-Pressure Sputtering (HPS). This technique has the potential to reduce the plasma-induced damage of the samples. To fabricate the TiOx, a 2-step process was used. Firstly, a thin Ti film was deposited in an Ar atmosphere. Secondly, O-2 was introduced into the HPS chamber to create an Ar/O-2 plasma that, along with low temperatures (150 degrees C or 200 degrees C), induces the oxidation of the deposited Ti film. With this approach, the Ti film is expected to behave as a capping layer that will reduce the oxidation of the Si substrate. This study aims to obtain a TiOx layer with low specific contact resistivity (rho(c)) and high minority carrier lifetime. These are crucial characteristics for obtaining high-quality selective contact. It was found that the 2-step process can oxidize the Ti layer. These HPS TiOx layers show a resistivity in the order of 0.3-10 Omega cm and a ratio Ti/O of similar to 1.9. Moreover, the SiOx regrowth is minimal since this is comparable to the native oxide. This was confirmed by transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). The samples fabricated with a Ti layer (similar to 4 nm) plus an oxidation temperature of 200 degrees C (duration of less than 2 h) show a low rho(c) of 0.02 Omega cm(2), an excellent transmittance (>87 %) in the visible region and an optical bandgap of 2.8 eV. These TiOx layers are amorphous, although some anatase phase crystalline clusters appear for the 200 degrees C processes. However, the minority carrier lifetime results of Si passivated by TiOx were inadequate for fabricating efficient solar cells. We also found that using the RCA oxide improved lifetime. This indicates that introducing alternative low-temperature passivating layers can solve this issue.

In this work, we demonstrate that ultrafast laser processing (1030 nm, 290 fs) of silicon in ambient air strongly improves the material's performance in terms of absorption, both in the visible and near infrared spectral range, which paves the way for further studies on increasing the sub-bandgap absorption after texturing, suggesting the material developed as a sustainable substitute for black silicon processed in greenhouse gases atmospheres. Our approach is based on the fabrication of spike-like morphologies in ambient air and the subsequent annealing of the material by pulsed laser melting or rapid thermal annealing to recover its crystalline phase. In particular, the influence of three main processing parameters (fluence, pulse number and repetition rate) on the properties of the spike-like structures has been investigated, each of them revealing the possibility of a direct control on the size, shape and period of the spikes, and achieving a total tuning range of the period from 4 mu m to 14 mu m for a single laser wavelength. Macroscopic areas have been fabricated using short processing times, yielding absorption values A > 94% over the UV-VIS-NIR spectral range (250 nm - 1100 nm) without hyperdoping, and A >= 20% for longer wavelengths up to 2500 nm, while preserving the electrical performance of pristine silicon.

Supersaturated GaP is of interest for the photovoltaic field since optical transitions at energies below the bandgap (2.26 eV) could enhance the overall device efficiency up to theoretically 60%. We have previously demonstrated that Ti supersaturated GaP can be obtained by means of ion implantation and pulsed-laser melting with high structural quality and measured its below-bandgap photoconductivity. In this work we report the first results of a GaP:Ti based photovoltaic device. We have fabricated and measured photovoltaic devices with a GaP:Ti absorber layer showing enhanced external quantum efficiency at wavelengths above 550 nm. Also, we have measured the absorption coefficient (around 104 cm-1 ) and refractive index of this absorber layer. Finally, current-voltage curves in darkness were measured and analyzed using a two-diodes model, showing improvable characteristics. Ideas to enhance the properties of the devices are suggested.

Herein, the structural properties and chemical composition of Ge samples implanted with tellurium at cryogenic temperatures are analyzed, focusing on the role of the native oxide. For germanium, cryogenic‐temperature implantation is a requirement to achieve hyperdoped impurity concentrations while simultaneously preventing surface porosity. In this work, the critical role of the thin native germanium oxide is demonstrated when performing ion implantations at temperatures close to the liquid nitrogen temperature. The structural and chemical composition of tellurium‐implanted samples as a function of the implanted dose from 5 × 10 14 to 5 × 10 15 cm −2 is analyzed. After a laser melting process, the incorporated oxygen is diffused to the surface forming again a GeO x layer which retains a large fraction of the total implanted dose. These detrimental effects can be eliminated by a selective etching of the native oxide layer prior to the ion implantation process. These effects have been also observed when implanting on Si substrates. This work identifies key aspects for conducting implantations at cryogenic temperatures, that are otherwise negligible for ion implanting at room temperature.

Herein, a detailed investigation on the properties of supersaturated gallium arsenide (GaAs) using Ti + implantation followed by nanosecond pulsed laser melting (PLM) is presented. The supersaturated samples are analyzed by means of electrical, optical, and optoelectronic characterization. The sheet resistance results obtained using van der Pauw configuration measurements do not show activation of the implanted Ti + in semi‐insulating GaAs after PLM. Absorptance measurements show a sub‐bandgap absorption (up to 6.5% for λ = 1000 nm) of the supersaturated GaAs:Ti and the just PLM‐processed GaAs, with the same laser melting fluence used (0.50 J/cm −2 ). The origin of this sub‐bandgap absorption is analyzed. Optoelectronic measurements show a similar sub‐bandgap photo‐response related to the absorption analyzed. The photo‐response measured below the bandgap originates from point defects introduced by the PLM process.

In 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 processes.

According to intermediate band (IB) theory, it is possible to increase the efficiency of a solar cell by boosting its ability to absorb low-energy photons. In this study, we used a hyperdoped semiconductor approach for this theory to create a proof of concept of different silicon-based IB solar cells. Preliminary results show an increase in the external quantum efficiency (EQE) in the silicon sub-bandgap region. This result points to sub-bandgap absorption in silicon having not only a direct application in solar cells but also in other areas such as infrared photodetectors. To establish the transport mechanisms in the hyperdoped semiconductors within a solar cell, we measured the J – V characteristic at different temperatures. We carried out the measurements in both dark and illuminated conditions. To explain the behavior of the measurements, we proposed a new model with three elements for the IB solar cell. This model is similar to the classic two-diodes solar cell model but it is necessary to include a new limiting current element in series with one of the diodes. The proposed model is also compatible with an impurity band formation within silicon bandgap. At high temperatures, the distance between the IB and the n-type amorphous silicon conduction band is close enough and both bands are contacted. As the temperature decreases, the distance between the bands increases and therefore this process becomes more limiting.

We have deposited thin films of MoO x using high-pressure sputtering (HPS) and Ar/O 2 /H 2 atmospheres aiming at the compositional and interface control. We found that H2 impacts plasma composition, which in turn produces a reduction of the oxygen content and a change in the refractive index of the films. However, the presence of hydrogen in the plasma atmosphere enhances interfacial SiO x regrowth, as FTIR shows. TEM measurements show that this regrowth is not critical for thin films. Also, increasing the hydrogen ratio produces a change from amorphous to an amorphous/polycrystalline mixture. Lifetime measurements show that these films are adequate for their integration into test HIT -like structures, but require more work to produce competitive iVoc values.

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 × 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 ( α peak) is associated with the melting process of the amorphized surface, followed by a longer peak/plateau ( β 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.

In 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.

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.

We present a detailed investigation on the formation of supersaturated GaAs using Ti+ implantation followed by nanosecond Pulsed Laser Melting (PLM). We have synthesized high-crystal quality supersaturated GaAs layers with concentrations of Ti above the insulator to metal transition (Mott limit). The Ti-implanted concentration depth profiles after PLM obtained by Time-of-Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) show a redistribution of Ti impurities within the first hundred nanometers and superficial concentration up to 1 x 1021 cm-3. Raman spectroscopy of these Ti supersaturated, and regrown GaAs samples shows a sharp crystalline peak and tensile strain due to the Ti lattice incorporation. Scanning Transmission Electron Microscopy (STEM) and high-resolution Transmission Electron Microscopy (TEM) images show a good GaAs crystallinity after the PLM process. Energy-Dispersive X-ray Spectroscopy (EDS) reveals an enhanced Ti signal inside bubble-like structures and an appearance of interface oxide layer with all processed samples.

This article studies the physical and electrical behavior of indium tin oxide layers (ITO) grown by an unconventional technique: High Pressure Sputtering (HPS), from a ceramic ITO target in a pure Ar atmosphere. This technique has the potential to reduce plasma induced damage to the samples. The aim is to obtain, at low temperature via HPS, good quality transparent conductive oxide layers for experimental photovoltaic cells with emerging selective contacts such as transition metal oxides, alkaline metal fluorides, etc. We found that the resistivity of the films was strongly dependent on Ar pressure. To obtain device-quality resistivity without intentional heating during deposition a pressure higher than 1.0 mbar was needed. These films deposited on glass were amorphous, presented a high electron mobility (up to 45 cm2V- 1s- 1) and a high carrier density (2.9 x 1020 cm-3 for the sample with the highest mobility). The optimum Ar pressure range was found at 1.5-2.3 mbar. However, the resistivity degraded with a moderate annealing temperature in air. Finally, the feasibility of the integration with photovoltaic cells was assessed by depositing on Si substrates passivated by a-Si:H. The film deposited at 1.5 mbar was uniform and amorphous, and the carrier lifetime obtained was 1.22 ms with an implied open circuit voltage of 719 mV after a 215 degrees C air anneal. The antireflective properties of HPS ITO were also demonstrated. These results show that ITO deposited by HPS is adequate for the research of solar cells with emerging selective contacts.

This work deepens the understanding of the optoelectronic mechanisms ruling hyperdoped‐based photodevices and shows the potential of Ti hyperdoped‐Si as a fully complementary metal‐oxide semiconductor compatible material for room‐temperature infrared photodetection technologies. By the combination of ion implantation and laser‐based methods, ≈20 nm thin hyperdoped single‐crystal Si layers with a Ti concentration as high as 1020 cm−3 are obtained. The Ti hyperdoped Si/p‐Si photodiode shows a room temperature rectification factor at ±1 V of 509. Analysis of the temperature‐dependent current–voltage characteristics shows that the transport is dominated by two mechanisms: a tunnel mechanism at low bias and a recombination process in the space charge region at high bias. A room‐temperature sub‐bandgap external quantum efficiency (EQE) extending to 2.5 µm wavelength is obtained. Temperature‐dependent spectral photoresponse behavior reveals an increase of the EQE as the temperature decreases, showing a low‐energy photoresponse edge at 0.45 eV and a high‐energy photoresponse edge at 0.67 eV. Temperature behavior of the open‐circuit voltage correlates with the high‐energy photoresponse edge. A model is proposed to relate the optoelectronic mechanisms to sub‐bandgap optical transitions involving an impurity band. This model is supported by numerical semiconductor device simulations using the SCAPS software.

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.

In this work we have successfully hyperdoped germanium with tellurium with a concentration peak of 10(21) cm(-3). The resulting hyperdoped layers show good crystallinity and sub-bandgap absorption at room temperature which makes the material a good candidate for a new era of complementary metal-oxide-semiconductor-compatible short-wavelength-infrared photodetectors. We obtained absorption coefficients ci higher than 4.1 x 10(3) cm(-1) at least up to 3 mu m. In this study we report the temperature-dependency electrical properties of the hyperdoped layer measured in van der Pauw configuration. The electrical behaviour of this hyperdoped material can be explained with an electrical bilayer coupling/decoupling model and the values for the isolated hyperdoped layer are a resistivity of 4.25 x 10(-3) Omega.cm with an electron-mobility around -100 cm(2) V-1 s(-1).

Germanium hyperdoped with deep level donors, such as tellurium, would lead to dopant-mediated sub-band gap mid-infrared photoresponse at room temperature. We use a combination of non-equilibrium techniques to supersaturate Ge with Te via ion implantation followed by pulsed laser melting (PLM). Typically, liquid N 2 (77K) temperatures are used to avoid implantation-induced Ge surface porosity. In this work, alternatively, we report on the use of slightly higher implantation temperatures (143 K) together with an amorphous Si (a-Si) capping layer. We demonstrate that the solid solubility limit of Te in Ge is overcome upon recovering the crystallinity of the material after laser processing.

In this work we have explored the growth by high pressure sputtering (HPS) of materials intended for novel selective contacts for photovoltaic cells. This technique shows promise for the low-damage low-temperature deposition of PV materials. We studied the deposition of ITO, MoOx and TiOx using pure Ar and mixed Ar/O-2 atmospheres as well as ceramic or metallic targets. We show that HPS deposition of these materials is feasible. The growth rate is greatly reduced when oxygen is added to the argon sputtering atmosphere. The best sputtering RF power was 20-45 W for the pressure range studied. Finally, as-deposited films present high surface recombination, but a mild hot plate anneal at 200 degrees C recovers long effective lifetimes.

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