Álvaro del Prado

Sub-Bandgap External Quantum Efficiency in Ti Implanted Si Heterojunction with Intrinsic Thin Layer Cells

In this work we present the manufacturing processes and results obtained from the characterization of heterojunction with intrinsic thin layer solar cells that include a heavily Ti ion implanted Si absorbing layer. The cells exhibit external circuit photocurrent at photon energies well below the Si bandgap. We discuss the origin of this below-bandgap photocurrent and the modifications in the hydrogenated amorphous intrinsic Si layer thickness to increase the open-circuit voltage.

Interfacial state density and conductance-transient three-dimensional profiling of disordered-induced gap states on metal insulator semiconductor capacitors fabricated from electron-cyclotron resonance plasma-enhanced chemical vapor deposited SiOxNyHz films

An electrical characterization of Al/SiOxNyHz/Si metal–insulator–semiconductor (MIS) structures has been carried out. SiOxNyHz films of different compositions have been obtained from these structures by varying gas flow in the electron-cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) system. The presence of nitrogen in the films increases the dielectric constant value and degrades the interface quality, as our measurements demonstrate. The effect of thermal annealing has also been determined. Capacitance–voltage (C–V) results show that unannealed samples exhibit positive flat-band voltages, whereas annealed ones exhibit negative values. On the other hand, from deep-level transient spectroscopy (DLTS) measurements we can conclude that interfacial state density diminishes when thermal treatments are applied. Moreover, conductance transient analysis provides the energetic and spatial distribution of defects in the films and demonstrates that thermal improvement affects not only the interface, but also the insulator bulk.

Meyer Neldel rule application to silicon supersaturated with transition metals

This paper presents the results for the transverse conductance across a bilayer formed by supersaturating with diverse transition metals a thin layer of a silicon wafer. The layer is formed by ion implantation and annealed by pulsed laser melting. The transverse conductance is exponentially activated, obtaining values ranging from 0.018 to 0.7 eV for the activation energy and pre-exponential factors of 10^-2-10^12 S depending on the annealing energy density. A semi-logarithmic plot of the pre-exponential factor versus activation energy shows an almost perfect linear behavior as stated by the Meyer Neldel rule. The Meyer Neldel energy obtained for implantation with different transition metals and also annealed in different conditions is 22meV, which is within the range of silicon phonons, thus confirming the hypothesis of the Multi Excitation Entropy theory.

High pressure sputtering as a viable technique for future high permittivity dielectric on III-V integration: GdOx on InP demonstration

The electrical properties of metal–oxide–semiconductor devices based on GdOx obtained by high pressure sputtering on InP substrates are studied. In order to prevent damage of the semiconductor substrate, an optimized two-step sputtering procedure has been used for the high permittivity dielectric deposition. First, a thin metallic Gd film was sputtered using a metallic Gd target and a pure Ar plasma. Then, without extracting the sample from the system, the GdOx films were obtained by plasma oxidation using an Ar/O2 mixed atmosphere and reducing plasma power to minimize damage and interfacial regrowth. The resulting devices show fully functional capacitance curves. After forming gas annealing, the capacitors do not show interface regrowth up to a temperature of 500 °C and the gate leakage stays within reasonable limits, below 2 × 10−4 Acm−2 at a gate voltage of 1.5 V. In addition, the interface trap density remains roughly constant with annealing temperature up to 400 °C, in the low 1013 eV−1cm−2 range, de...

Deposition of Intrinsic a-Si:H by ECR-CVD to Passivate the Crystalline Silicon Heterointerface in HIT Solar Cells

We have deposited intrinsic amorphous silicon (a-Si:H) using the electron cyclotron resonance (ECR) chemical vapor deposition technique in order to analyze the a-Si:H/c-Si heterointerface and assess the possible application in heterojunction with intrinsic thin layer (HIT) solar cells. Physical characterization of the deposited films shows that the hydrogen content is in the 15-30% range, depending on deposition temperature. The optical bandgap value is always comprised within the range 1.9- 2.2 eV. Minority carrier lifetime measurements performed on the heterostructures reach high values up to 1.3 ms, indicating a well-passivated a-Si:H/c-Si heterointerface for deposition temperatures as low as 100°C. In addition, we prove that the metal-oxide- semiconductor conductance method to obtain interface trap distribution can be applied to the a-Si:H/c-Si heterointerface, since the intrinsic a-Si:H layer behaves as an insulator at low or negative bias. Values for the minimum of Dit as low as 8 × 1010 cm-2 · eV-1 were obtained for our samples, pointing to good surface passivation properties of ECR-deposited a-Si:H for HIT solar cell applications.

Conductance Transient Comparative Analysis of Electron-Cyclotron Resonance Plasma-Enhanced Chemical Vapor Deposited SiNx, SiO2/SiNx and SiOxNy Dielectric Films on Silicon Substrates

An interface quality comparative study of metal-insulator-semiconductor (MIS) structures based on SiNx, SiO2/SiNx and SiOxNy dielectric films deposited on silicon substrates by electron-cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) has been carried out. Overall interpretation of deep-level transient spectroscopy (DLTS) and conductance transient (G-t) measurements enables us to conclude that the interface quality of Al/SiOxNy/Si MIS structures is superior to those of Al/SiNx/Si devices. Moreover, we have proved that thermal treatments applied to Al/SiOxNy/Si capacitors induce defect passivation, possibly related to the presence of hydrogen in the films, and disorder-induced gap-state (DIGS) density maxima can decrease to values even lower than those corresponding to Al/SiNx/SiO2/Si devices.