Electron and proton irradiation effect on the minority carrier lifetime in SiC passivated p-doped Ge wafers for space photovoltaics

Abstract

We report on the effect of electron and proton irradiation on effective minority carrier lifetimes (τeff) in p-type Ge wafers. Minority carrier lifetimes are assessed using the microwave-detected photoconductance decay (µW-PCD) method. We examine the dependence of τeff on the p-type doping level and on electron and proton radiation fluences at 1 MeV. The measured τeff before and after irradiation are used to estimate the minority carriers' diffusion lengths, which is an important parameter for solar cell operation. We observe τeff ranging from ≈ 50 to 230 µs for Ge doping levels between 1x10 17 and 1x10 16 at.cm -3 , corresponding to diffusion lengths of ≈ 500-1400 µm. A separation of τeff in Ge bulk lifetime and surface recombination velocity is conducted by irradiating Ge lifetime samples of different thicknesses. The possible radiation-induced defects are discussed on the basis of literature.

Passivated, Highly Reflecting, Laser Contacted Ge Rear Side for III-V Multi-Junction Solar Cells

“…The simulation of V OC,sim allows for access to the passivation quality of the Ge rear side via the SRV. From our simulations, an SRV of 900 ± 180 cm/s was derived, which corresponds to a moderate passivation quality compared to lifetime samples, which reach SRV in the low tens cm/s range [10], [11]. This suggests that the solar cell process affects the Ge rear side passivation quality and that there is room for improvement, for example by protecting the unpassivated Ge rear side during the MOVPE process.…”

“…For the in-depth analysis of the implemented mirror and surface passivation at the Ge rear side, a 2-D optoelectrical model for a Ge solar cell was implemented in Sentaurus Device [9], [18]. The two cells above the Ge cell are optically modeled, whereas the Ge cell itself is modeled optically and electrically using measured Ge bulk lifetimes [9], [10]. The input parameters for the cell simulation are given in Table I.…”

“…Thus, our simulation corresponds to an infinitely small contact distance (pitch). In the electrical simulations we use the measured e − lifetime for Ge from [9] and [10]. For the standard Ge cell, we assume no surface passivation at the rear side, i.e., a recombination velocity of 10 7 cm/s.…”

Modeling of Solar Cells and Environmental Conditions for Space Microgrids

“…The modeling of the degradation due to particle radiation of PV cells has been widely supported by numerical solvers like SRIM [36,[56][57][58][59] and SPENVIS/MULASSIS [22,35,60]. While these software have shown a good accuracy to represent the damage profiles of particle-radiated PV cells, they are usually too slow given that the trajectory is computed particle by particle.…”

“…Also the profile of degradation depends on the distribution of the particle spectrum. For instance, low energetic particles impacting PV cells normal to the surface can get trap inside of the wafers to form a region with the largest damage, usually called Bragg peak [35,58], see Fig However, with the new and more challenging proposed missions for the coming future, many more issues will be faced. In this regard, the review studies are useful tools to identify the challenges to address.…”