Cathodoluminescence Study of Orientation Patterned GaAs Crystals for Nonlinear Optical Frequency Conversion by Quasi-Pha
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1108-A11-07
Cathodoluminescence Study of Orientation Patterned GaAs Crystals for Nonlinear Optical Frequency Conversion by Quasi-Phase-Matching H. Angulo1, M. Avella1, O. Martínez1, J. Jiménez1, C. Lynch2, and D. Bliss2 1 GdS Optronlab, Edificio I+D, Paseo de Belén 1, 47011 Valladolid, Spain 2 Air Force Research Laboratory, Sensors Directorate, Hanscom AFB, MA 01731, USA ABSTRACT Orientation patterned (OP)-GaAs crystals show promise for use in tunable coherent light sources in the infrared (IR) and terahertz (THz). These structures consist of an alternating array of [001]/[00-1] oriented domains grown by hydride vapor phase epitaxy (HVPE). Material characteristics concerning the propagation losses, the crystal dimensions, and the grating size must be taken into account to implement optical devices for specific wavelength ranges and operating modes (CW or pulsed). The analysis of the main factors contributing to optical loss in the OP crystals is a crucial step toward their use in many promising applications. We present a cathodoluminescence study, where the main defects and their distribution over the OP-GaAs crystals are revealed, with special emphasis paid to the properties of the domain walls. INTRODUCTION Compact and efficient laser sources in the IR and THz are desired for applications such as infrared countermeasures, remote gas sensing, infrared spectroscopy, and terahertz imaging. An attractive approach to producing such laser sources involves nonlinear optical frequency conversion in GaAs. GaAs is a semiconductor with a large nonlinear susceptibility, but it is isotropic, therefore birefringent phase matching is not possible. Instead, IR and THz laser sources have been produced using quasi-phasematched (QPM) GaAs, with a grating of alternating crystallographic orientation (1, 2). Along with the choice of pump laser wavelength, the period of these structures determines the signal wavelength range. This allows the possibility of laser sources with wavelengths ranging from 2 µm to the THz range, enabling a large number of applications. To accommodate the pump and signal beams the OP crystal must typically be grown to thickness 500 µm – 1 mm. To meet this requirement, it is desirable to have very fast growth rates during production of the periodic [001] and [00-1] oriented columns (3, 4). Hydride Vapor Phase Epitaxy (HVPE) is the technique of choice for the growth of these thick layers suitable for QPM. In order to attain high conversion efficiencies, one needs high quality crystals with a very low concentration of defects and the preservation of the grating duty cycle all along the crystal. We present herein a cathodoluminescence (CL) study of the main extended and point defects and their distribution across the OP-crystals. EXPERIMENTAL DETAILS Epitaxial growth of orientation-patterned semiconductor layers useful for bulk quasiphasematched nonlinear optics requires templates with crystallographic orientation modulation (1-4). Typically, orientation-patterned templates are created epitaxially using molecular
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