Growth and Properties of Lattice Matched GaAsSbN Epilayer on GaAs for Solar Cell Applications
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Growth and Properties of Lattice Matched GaAsSbN Epilayer on GaAs for Solar Cell Applications Sudhakar Bharatan1, Shanthi Iyer1, Kevin Matney2, Ward J. Collis1, Kalyan Nunna1, Jia Li1, Liangjin Wu1, Kristopher McGuire3,*, Laurie E. McNeil3. 1 Department of Electrical and Computer Engineering, North Carolina A&T State University, Greensboro, NC 27411 2 Bede Scientific Inc, Englewood, CO 3 Department of Physics and Astronomy, University of North Carolina, Chapel Hill, NC ABSTRACT In this work, the growth and characterization of GaAsSbN epilayers nearly lattice matched to GaAs, grown in an elemental solid source molecular beam epitaxy (MBE) system with a RF plasma nitrogen source, are discussed. The Sb and N compositions of the nearly lattice matched layers are 2.6% and 6.8%, respectively, as determined by high resolution x-ray diffraction (HRXRD) and secondary ion mass spectroscopy (SIMS) analysis. The layers are found to be fully strained as evidenced by the presence of Pendellosung fringes on the x-ray diffraction spectra. Effects of in-situ and ex-situ annealing on the low temperature photoluminescence (PL) characteristics are discussed. The 10 K PL peak energy of 1 eV with a FWHM of 18 meV has been achieved on ex-situ annealed samples in N ambient. The temperature dependence of PL peak energy exhibits “S-shaped” behavior in the low temperature regime, indicative of the presence of localized excitons. Raman spectroscopy analysis has been carried out to determine the local structural changes on annealing. INTRODUCTION The III-V semiconductor alloys such as GaInP and GaInAsN have received considerable attention in the recent past due to their unique optoelectronic properties and potential applications in solar cells [1-4]. Addition of a 1 eV junction of GaInP or GaInAsN to the tandem solar cell could greatly enhance the efficiency of multijunction solar cells [4]. The quaternary GaInAsN system lattice matched to GaAs has been extensively studied for solar cell applications [4]. A comparison between InGaAs and GaAsSb shows that GaAsSb has lower compressive strain relative to InGaAs [5]. Addition of relatively smaller amounts of N would drop the band gap close to 1 eV. Hence, the GaAsSbN system is a potential alternative to InGaAsN, to enhance the efficiency of a multi-layer GaAs based solar cells. Bian et al. [6] have achieved photoluminescence (PL) peak energy of 1 eV on GaAsSbN thick layers lattice matched to GaAs for tandem solar cell applications. The lowest lattice mismatch of 700 ppm has been reported by Wicaksono et al [7]. To realize high efficiency solar cells, it is important to investigate and improve the quality of the GaAsSbN layers lattice matched to GaAs. In this work, we present a detailed and a systematic study of the structural and optical properties of lattice matched GaAsSbN/GaAs structures. The effects of N and Sb concentrations on the lattice mismatch are investigated. The variation in the PL characteristics of the layers due to in-situ and ex-situ annealing are examined with a vi
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