Carrier Dynamics in MOVPE-Grown Bulk InGaAsNSb Materials and Epitaxial Lift-Off GaAs Double Heterostructures for Multi-j
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Carrier Dynamics in MOVPE-Grown Bulk InGaAsNSb Materials and Epitaxial Lift-Off GaAs Double Heterostructures for Multi-junction Solar Cells Yongkun Sina, Stephen LaLumondierea, Nathan Wellsa, Zachary Lingleya, Nathan Pressera, William Lotshawa, Steven C. Mossa, Tae Wan Kimb, Kamran Forghanib, Luke J. Mawstb, Thomas F. Kuechc, Rao Tatavartid, Andree Wibowod, and Noren Pand a Electronics and Photonics Lab, The Aerospace Corporation, El Segundo, CA 90245 b Electrical and Computer Engineering Dept., c Chemical and Biological Engineering Dept. University of Wisconsin – Madison, Madison, WI 53706 d MicroLink Devices Inc., Niles, IL 60714 ABSTRACT High performance and cost effective multi-junction III-V solar cells are attractive for satellite applications. High performance multi-junction solar cells are based on a triple-junction design that employs an InGaP top-junction, a GaAs middle-junction, and a bottom-junction consisting of a 1.0 – 1.25 eV-material. The most attractive 1.0 – 1.25 eV-material is the lattice-matched dilute nitride such as InGaAsN(Sb). A record efficiency of 43.5% was achieved from multijunction solar cells including dilute nitride materials [1]. In addition, cost effective manufacturing of III-V triple-junction solar cells can be achieved by employing full-wafer epitaxial lift-off (ELO) technology, which enables multiple substrate re-usages. We employed time-resolved photoluminescence (TR-PL) techniques to study carrier dynamics in both pre- and post-ELO processed GaAs double heterostructures (DHs) as well as in MOVPE-grown bulk dilute nitride layers lattice matched to GaAs substrates. INTRODUCTION Epitaxial layers grown on GaAs substrate can be separated from the host substrate via epitaxial lift-off. The ELO technique has been investigated since 1970s [2 4], but this technique has been recently accepted as a viable technology for low cost manufacturing of multi-junction solar cells because the process allows the host substrate to be reused [5 7]. We studied carrier dynamics in ELO samples consisting of GaAs DHs grown on top of a thin AlAs release layer, which allowed epitaxial layers grown on top of the release layer to be removed from the substrate. We report on our RT TR-PL results of the pre- and post-ELO processed GaAs DHs with different dopant types, doping densities, and thicknesses. Bulk dilute nitride materials with a 1 – 1.3 eV band-gap that are lattice matched to GaAs substrates are attractive for high efficiency multi-junction solar cells. However, issues related to performance including low internal quantum efficiencies (IQEs) and photocurrent mismatch between individual cells have been correlated to the small amount of N required to achieve a 1eV band-gap in InGaAsN materials [8]. Post-growth thermal annealing improves the IQEs [9 11], but high background carbon concentrations observed in MOVPE-grown materials have been correlated with short minority carrier diffusion lengths. One group has recently shown that the addition of dilute amounts of Sb to InGaAsN can increase the IQE o
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