Characteristics of thick ZnSe films on quasi-phase-matched (QPM) GaAs substrates N.B. Singh a , G.S. Kanner b,n , A. Berghmans a , D. Kahler a , A. Lin c , B. Wagner a , S.P. Kelley b , D.J. Knuteson a , R. Holmstrom b , K.L. Schepler e , R. Peterson e , M.M. Fejer d , J.S. Harris c a Northrop Grumman Electronic Systems, 1212 Winterson Road, Linthicum, MD 21090, USA b Northrop Grumman Electronic Systems, 600 Hicks Road, Rolling Meadows, IL 60008, USA c Solid State Photonics Laboratory, Stanford University, Stanford, CA 94305, USA d E.L. Gintzon Laboratory, Stanford University, Stanford, CA 94305, USA e Air Force Research Laboratory/RYJW, Wright-Patterson AFB, OH 45433, USA article info Available online 29 December 2009 Keywords: A3. Physical vapor transport (PVT) B1. Zinc selenide B3. Optical parametric amplification (OPA) B3. Quasi-phase-matching (QPM) B3. Second harmonic generation (SHG) abstract We have grown and characterized thick zinc selenide (ZnSe) films up to millimeter thickness on unpatterned gallium arsenide (GaAs) wafers and orientation-patterned substrates by physical vapor transport. The patterns were designed to achieve alternating [0 0 1] and [0 0 1 ¯ ] orientations. The quality of the films was evaluated by X-ray diffraction, scanning electron microscopy (SEM), and anisotropic etching to determine the morphology and crystallinity. ZnSe films grew epitaxially on the templates and X-ray rocking curves showed full widths at half maximum (FWHM) less than 0.21. Orientation- patterning up to hundreds of microns film thickness was verified by SEM and etching profiles. & 2010 Elsevier B.V. All rights reserved. 1. Introduction A large amount of research has been performed on wavelength conversion for second harmonic generation (SHG) and optical parametric oscillation (OPO) devices. Most earlier research focused on bulk crystals such as silver gallium selenide [1], thallium arsenic selenide [2], gallium selenide [3], zinc germa- nium phosphide [4], silver gallium germanium selenide [5], and many other materials. We have chosen ZnSe, which has transparency spanning from visible through LWIR. ZnSe is closely lattice-matched to GaAs, and GaAs orientation-patterned tem- plates have been well developed [6]. For these reasons we chose ZnSe to grow on GaAs in a quasi-phase-matched (QPM) structure. We report preliminary growth results and structural character- istics of the PVT-grown thick ZnSe films. 2. Experimental method We purified as-supplied materials by transporting them under a thermal gradient in a vacuum-sealed quartz tube. In order to achieve orientation-patterning, the GaAs substrates consisted of epitaxially grown templates from Stanford University [7]. Orientation reversal of alternating domains was fostered by use of (0 0 1) GaAs wafers misoriented by 41 toward [1 1 1]B. ZnSe films were grown by physical vapor transport (PVT) growth in a vertical geometry. The morphology of the film was studied by scanning electron microscopy (SEM) and anisotropic etching. X-ray diffrac- tion and rocking curves were used to determine the crystallinity of the film. We used chemical etching to distinguish between the orientation-patterned domains. 3. Results and discussion Fig. 1 shows the X-ray 2y–o curve for a 300 mm thick film grown on a GaAs template. We observed a peak for (0 0 4) reflections, along with a weaker (0 0 2), in accordance with the selections rules for zincblende crystals. The crystal quality of the films was evaluated by rocking curves; an example is shown in the inset of Fig. 1. We observed only a single peak indicating a single crystalline film. Also, the FWHM of 320 arcsec is quite good for a film of this thickness. With no lattice matching (i.e., by doping), the narrowest rocking curve of ZnSe epitaxially grown on GaAs is 70–90 arcsec [8]. As film thickness increases the rocking curve width increases. We attribute the trend in thickness to stress associated with mismatch in the coefficients of thermal expansion (CTE) of the film and substrate, which causes bowing of the film–substrate composite. However, films often exhibit cracking along (1 1 0) planes. In thicker samples optical ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jcrysgro Journal of Crystal Growth 0022-0248/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jcrysgro.2009.12.054 n Corresponding author. E-mail addresses: nb.singh@ngc.com (N.B. Singh), gary.kanner@ngc.com (G.S. Kanner). Journal of Crystal Growth 312 (2010) 1142–1145