Lowly Doped Silicon Research Articles

Adaption of Basic Metal–Insulator–Semiconductor (MIS) Theory for Passivating Contacts Within Numerical Solar Cell Modeling

The main goal of a solar cell's contact is to simultaneously minimize the contact resistivity ρ cont and the effective recombination, the latter often expressed via J0, cont. To model the resulting solar cell characteristics, the simplest approach is to use those two measurable quantities as an effective boundary condition. Within crystalline silicon solar cell modeling, this “lumped” modeling approach is well valid for classical contacts, which feature high doping near the surface. Contacts to lowly doped silicon in contrast require a suitable stack of materials deposited onto the absorber surface to simultaneously induce band bending via an electrical barrier (field-effect passivation), provide chemical passivation, and efficiently extract majority carriers. Such “passivating contacts” often show effects not reproducible by the lumped modeling approach, e.g., non-ohmic contact resistivity, injection-dependent recombination, and voltage drops independent of current extraction. In this paper, we explore the suitability of the basic metal–insulator–semiconductor theory, employed as a boundary condition to a numerical model of the semiconductor transport in the absorber, to represent such effects of passivating contacts. We show that with only very few input parameters, several relevant experimental observations can be quantitatively replicated: temperature dependence of the fill factor of solar cells featuring tunnel-oxide passivating contacts, as well as implied versus external open-circuit voltage losses for heterojunction solar cells. While being the focus of this paper, the presented approach is well applicable also beyond crystalline silicon cells.

Continuous electrowetting at the low concentration electrolyte-insulator-semiconductor junction

Electrowetting (EW) has applications including displays, microactuation, miniaturized chemistry, adaptive optics, and energy harvesting—understanding the physics of EW junctions is of key importance. Here, the roles of semiconductor space-charge and electric double layer in continuous EW at an electrolyte-insulator-semiconductor junction are considered. A model is formulated in terms of experimental parameters—applied voltage, zero-bias wetting contact angle, semiconductor type and doping, insulator thickness and dielectric constant, and electrolyte concentration and dielectric constant. The model predicts, and experiments indicate, that the EW behavior is diminished for low concentration solutions (∼1–10 nM) and lowly doped silicon (1014–1015 cm−3).

The Charge Plasma P-N Diode

A simulation study on a new rectifier concept is presented. This device basically consists of two gates with different workfunctions on top of a thin intrinsic or lowly doped silicon body. The workfunctions and layer thicknesses are chosen such that an electron plasma is formed on one side of the silicon body and a hole plasma on the other, i.e., a charge plasma p-n diode is formed in which no doping is required. Simulation results reveal a good rectifying behavior for well-chosen gate workfunctions and device dimensions. This concept could be applied for other semiconductor devices and materials as well in which doping is an issue.

Characterisation of oxygen and oxygen-related defects in highly- and lowly-doped silicon

In this paper, an overview will be given about analytical techniques which are suitable for the study of oxygen and oxygen precipitation in highly- and lowly-doped silicon. It will be shown that in the case of highly-doped silicon, the application of Fourier Transform Infrared (FT-IR) absorption spectroscopy requires the use of ultra-thinned or high-fluence irradiated samples and a dedicated data analysis. This sample preparation is necessary to reduce the free carrier absorption in the mid-IR region. It is shown that besides the interstitial oxygen concentration [O i] and the amount of precipitated oxygen, it is possible to determine the stoichiometry of oxygen precipitates from the study of the corresponding absorption bands. Oxygen precipitation in p + silicon can also be investigated by the D1–D2 lines in photoluminescence (PL) on as-grown or heat–treated material without special sample preparation. In oxygen-doped high-resistivity float-zone silicon, standard FT-IR analysis can be applied to determine [O i]. The presence of oxygen-related shallow donors can be probed by a combination of electrical (spreading resistance probe, SRP; capacitance–voltage, C– V) and (quasi-)spectroscopic techniques (deep-level transient spectroscopy, DLTS).