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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Sr(GaAs)2 by Materials Project

Sr(GaAs)2 crystallizes in the monoclinic P2/m space group. The structure is three-dimensional. there are three inequivalent Sr2+ sites. In the first Sr2+ site, Sr2+ is bonded to six As3- atoms to form edge-sharing SrAs6 octahedra. There are two shorter (3.09 Å) and four longer (3.15 Å) Sr–As bond lengths. In the second Sr2+ site, Sr2+ is bonded to six As3- atoms to form edge-sharing SrAs6 octahedra. There are four shorter (3.11 Å) and two longer (3.15 Å) Sr–As bond lengths. In the third Sr2+ site, Sr2+ is bonded to six As3- atoms to form edge-sharing SrAs6 octahedra. There are a spread of Sr–As bond distances ranging from 3.17–3.26 Å. There are four inequivalent Ga2+ sites. In the first Ga2+ site, Ga2+ is bonded in a trigonal non-coplanar geometry to three As3- atoms. There are one shorter (2.54 Å) and two longer (2.58 Å) Ga–As bond lengths. In the second Ga2+ site, Ga2+ is bonded in a trigonal non-coplanar geometry to three As3- atoms. There are one shorter (2.54 Å) and two longer (2.56 Å) Ga–As bond lengths. In the third Ga2+ site, Ga2+ is bonded in a trigonal non-coplanar geometry to three As3- atoms. There are two shorter (2.56 Å) and one longer (2.58 Å) Ga–As bond lengths. In the fourth Ga2+ site, Ga2+ is bonded in a trigonal non-coplanar geometry to three As3- atoms. All Ga–As bond lengths are 2.58 Å. There are four inequivalent As3- sites. In the first As3- site, As3- is bonded to three Sr2+ and three Ga2+ atoms to form a mixture of corner and edge-sharing AsSr3Ga3 octahedra. The corner-sharing octahedra tilt angles range from 0–78°. In the second As3- site, As3- is bonded to three Sr2+ and three Ga2+ atoms to form a mixture of corner and edge-sharing AsSr3Ga3 octahedra. The corner-sharing octahedra tilt angles range from 0–13°. In the third As3- site, As3- is bonded to three Sr2+ and three Ga2+ atoms to form a mixture of corner and edge-sharing AsSr3Ga3 octahedra. The corner-sharing octahedra tilt angles range from 0–18°. In the fourth As3- site, As3- is bonded to three Sr2+ and three Ga2+ atoms to form a mixture of corner and edge-sharing AsSr3Ga3 octahedra. The corner-sharing octahedra tilt angles range from 0–78°.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Conversion efficiency improvement of ELO GaAs solar cell, deposited on water soluble sacrificial buffer

Here, we demonstrate the improvement of power conversion efficiency of an epitaxially-lifted-off single junction GaAs solar cell deposited on a water-soluble sacrificial buffer architecture by introducing an additional germanium (Ge) interlayer between GaAs and the fluoride buffer. The epitaxial lift-off (ELO) technique has been extensively used to separate III-V device layers from their single crystal GaAs substrates. However, conventional ELO requires the use of concentrated hydrofluoric acid (HF) for extended times to etch out the sacrificial layer, subsequently degrading the surface roughness of the parent wafer. As a result, the wafer has to undergo expensive and intensive chemical mechanical polishing (CMP) processes, costing about 25% of a pristine 6-inch GaAs substrate. In our previous work, we demonstrated a method to eliminating the need for CMP post-processing by using water-assisted ELO (H 2 O-ELO). A water-soluble, 3-layer buffer architecture was developed using alkaline earth compounds. However, devices suffered low performance due to a high defect density in the GaAs active layers. A Ge interlayer was introduced to provide a more favorable surface energy for GaAs growth, which leads to an improvement of GaAs crystal quality. The Ge deposition conditions were optimized to achieve a high-quality Ge layer on triple-layer fluoride buffer. Single junction GaAs devices fabricated on Ge/(Ca,Sr)F 2 /BaF 2 /(Ca,Sr)F 2 showed improvement of solar cell performance parameters featuring increases in V oc by 23.7%, and fill factor (F.F.) by 4.9%, which results in an overall improvement of power conversion efficiency from 10.3% to 12.69%.

14 SOLAR ENERGY↗