III--V--N Materials for Super-High Efficiency Multi Junction Solar Cells

概要

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The majority and minority carrier traps in GaAsN grown by chemical beam epitaxy (CBE) and their relationships with the electrical properties of the materials and solar cells are presented. By adopting a new flow-rate modulation CBE (FM-CBE) method, a higher mobility and a longer minority-carrier lifetime than those obtained by other growth methods have been achieved. We have characterized deep levels in grown GaAsN films by deep-level transient spectroscopy (DLTS). As a result, we found that 1) a hole trap H2 center (E_{\text{v}} + 0.15 eV) in p-GaAsN acts as an acceptor state and correlates with N concentration, 2) an electron trap E2 (E_{\text{c}} - 0.33 eV) center in n-GaAsN and p-GaAsN is a non-radiative recombination center and 3) a hole trap H1 center (E_{\text{v}} + 0.052 eV) newly observed in p-GaAsN acts as an acceptor state and a radiative recombination center. Although further analyses are required, it is very important to reduce the E1 defect density in (In)GaAsN to understand the degradation mechanism of the CBE-grown (In)GaAsN solar cell property and realize a higher efficiency.
2013-08-25