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Sun, Sicong

Publications and source records attributed to Sun, Sicong.

4 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

From Salt to Electronics: Heteroepitaxy and GaAs Solar Cells

This paper presents work on the heteroepitaxy of salts, specifically fluorides, on semiconductor and heteroepitaxy of semiconductor on salts. Fluorides layers are deposited on commercial Gallium Arsenide (GaAs) wafers followed by the heteroepitaxial growth of GaAs using metal organic chemical vapor deposition (MOCVD). The fluoride layers consist of 2 lattice-engineered layers of alkaline-earth compounds to match with GaAs, and are used to sandwich another alkaline-earth compound with higher water-solubility as sacrificial layer. The triple fluoride layers enable liftoff of free-standing semiconductor films which can be further transferred to desirable substrates. 2D-X-ray Diffraction (2D-XRD) measurements confirm epitaxial growth of both the fluorides and the subsequently grown GaAs films. Single junction (SJ) solar cell devices based on thus prepared films show a power conversion efficiency (PCE) of 10.3% under 1 sun illumination. After the completion of device fabrications, the GaAs film is lifted off from the substrate by a novel water-assisted epitaxial liftoff (H 2 O-ELO) technique and transferred to a cheaper substrate. The original GaAs wafer is recycled and reused twice. Devices based on reused substrates show no significant degradation in performance. Lastly, the semiconductor-salt-semiconductor scheme has great implications in high performance, flexible, and large area electronics.

14 SOLAR ENERGY↗
DOE OSTI2020

High-efficiency single-junction p-i-n GaAs solar cell on roll-to-roll epi-ready flexible metal foils for low-cost photovoltaics

We demonstrate the fabrication and characterization of high-efficiency, single-junction p-i-n GaAs solar cells, on flexible metal foil with epi-ready buffer via roll-to-roll fabrication. Single-junction p-i-n GaAs solar cells were fabricated using metal–organic chemical vapor deposition (MOCVD). Furthermore, an efficiency greater than 13% was obtained at 1 sun, which is the highest reported efficiency on GaAs photovoltaics directly deposited on metal tapes. This exceeds our previously reported study showcasing 11.5% efficiency on single-junction p-n solar cell structure. Improved morphology of p-i-n structure compared with p-n is explained by atomic force microscopy (AFM), scanning electron microscopy (SEM), and helium ion microscopy (HIM) measurements. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis showed reduced Zn diffusion in p-i-n cell compared with the p-n cell. We attribute the improvement in efficiency of p-i-n cells on flexible metal tapes to the quality of the junction, surface morphology, controlled diffusion of species within the active layers, and increase in absorption due to the optimized intrinsic layer thickness.

14 SOLAR ENERGY↗
DOE OSTI2020

Directly Linking Low-Angle Grain Boundary Misorientation to Device Functionality for GaAs Grown on Flexible Metal Substrates

A new growth method to make highly oriented GaAs thin films on flexible metal substrates has been developed, enabling roll-to-roll manufacturing of flexible semiconductor devices. The grains are oriented in the <001> direction with <1 degree misorientations between them, and they have a comparable mobility to single-crystalline GaAs at high doping concentrations. At the moment, the role of low-angle grain boundaries (LAGBs) on device performance is unknown. A series of electron backscatter diffraction (EBSD) and cathodoluminesence (CL) studies reveal that increased doping concentrations decrease the grain size and increase the LAGB misorientation. Cross-sectional scanning transmission electron microscopy (STEM) reveals the complex dislocation structures within LAGBs. Most importantly, a correlative EBSD/electron beam-induced current (EBIC) experiment reveals that LAGBs are carrier recombination centers and that the magnitude of recombination is dependent on the degree of misorientation. The presented results directly link increased LAGB misorientation to degraded device performance, and therefore, strategies to reduce LAGB misorientations and densities would improve highly oriented semiconductor devices.

36 MATERIALS SCIENCE↗