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E11.45.1

Optical Properties of II-IV-N2 Semiconductors John Muth1, Ailing Cai1, Andrei Osinsky2, Henry Everitt3, Ben Cook4, and Ivan Avrutsky5 1

Department of Electrical and Computer Engineering, NC State University, Raleigh, NC 27695 SVT Associates, Eden Prairie, Minnesota, 55344 3 Physics Department, Duke University, Durham, NC 27708, and Army Research Office, RTP, NC 27709 4 Department of Mathematics, University of California - Los Angeles, Los Angeles, CA 90095 5 Department of Electrical and Computer Engineering, Wayne State University, Detroit, MI, 48202 2

ABSTRACT Recently, wide band gap II-IV-N2 semiconductors such as ZnSiN2, and ZnGeN2 and ZnSiGeN2 have been synthesized, but very little is known about their band structure, optical properties, or electronic properties. Bulk crystals are hard to synthesize because high temperatures and pressures are required. The success in growing II-IV-N2 films epitaxially by MOCVD creates interesting opportunities. The crystal structure of II-IV-N2 compounds is orthorhombic, and when grown on r-plane sapphire can provide a suitable template for GaN growth. Optical transmission studies of the band edge of ZnSiN2 and ZnSiGeN2 with varying Si and Ge percentages were conducted. The indirect nature of the band gap was investigated, and prism coupling was used to obtain the refractive indices in the visible and NIR portion of the spectrum. Although the crystal symmetry was orthorhombic, the refractive indices indicated uniaxial optical properties. Optical loss measurements indicate that the films are suitable for waveguides and novel devices based on birefringent optical effects. Introduction III-IV-N2 materials have an orthorhombic crystal structure with space group Pn21.1,2 Usually crystals with orthorhombic symmetry are considered for applications that require nonlinear optical effects or strong birefringence effects. However in the case of III-IV-N2 alloys such as ZnSiN2, ZnGeN2 and ZnSiGeN2 alloys the crystal structure is nearly lattice matched with GaN and SiC making it attractive as a template for low defect density optoelectronic devices.3,4 Furthermore, as wide band gap semiconductors they are optically transparent in the visible and near infrared portion of the spectrum. In thin film form this suggests that they may find uses in optical waveguide devices. It has also been suggested that these alloys may be useful for dilute magnetic semiconductors.5 At present, very little experimental work6,7,8 has been performed on these materials, and fundamental experimental information about the optical characteristics is needed. The fundamental properties of III-IV-N2 Semiconductors have previously been investigated theoretically using density functional theory to calculate the band structure, and optical properties.1,2 These studies revealed that ZnGeN2 is expected to have a direct gap, while

E11.45.2

ZnSiN2 is expected to have an indirect band gap. These simulations also indicated that by varying the alloy composition the lattice constants can be varied with the following