Localized Vibrational Modes of Carbon-Hydrogen Complexes in MOCVD Grown GaN and AlGaN thin films
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Localized Vibrational Modes of Carbon-Hydrogen Complexes in MOCVD Grown GaN and AlGaN thin films J. Chen1, Q. Zhou1, Y. Berhane1, M. O. Manasreh1, C. A. Tran2, M. Pophristic2, and I. T. Ferguson2 1 Department of Electrical and Computer Engineering, University of New Mexico, Albuquerque, NM 87131. E-Mail: [email protected] 2 EMCORE Corporation, 394 Elizabeth Ave, Somerset, NJ 08873 ABSTRACT Localized vibrational modes of carbon-hydrogen complexes in metalorganic chemical vapor deposition grown GaN on sapphire were studied using a Fourier-transform infrared spectroscopy technique. Three distinctive localized vibrational modes were observed around 2850, 2922, and 2959 cm-1 for undoped, Si- and Mg-doped samples. These peaks are related to CH, CH2, and CH3 defect complexes, respectively. It is also observed that the frequencies and intensities of the localized vibrational modes are sample dependent. INTRODUCTION: The development of III-V nitride semiconductors and the emerging advances in a broad range of nitride-based electronic and optoelectronic devices have witnessed dramatic successes in recent years. One of the most important aspects of recent investigations of IIIV nitrides is the ability to produce and fairly control n- and p-type doped materials. Massive research efforts on devices have been launched after Amano et al.1 observed cathodoluminescence results from Mg-doped GaN. However, the dopant incorporation remains the subject of various investigations. The localized vibrational modes (LVMs) spectroscopy is a very powerful tool in identifying impurities and dopant incorporation in semiconductors. This is due to the fact that the LVMs spectroscopy is very sensitive to the atomic structure surrounding a dopant atom, the dopant location, dislocation density, and strain. As a typical example, the high resolution LVMs spectrum of a substitutional acceptor carbon in GaAs exhibits a fine structure due to the Ga isotopic effect2. The LVMs spectroscopy has not been employed aggressively in studying dopants incorporation and impurities in GaN and related compounds. One of the major problems associated with the study of the LVMs in GaN is that the substrate used to grow GaN is sapphire, which has a very strong infrared absorption band in the spectral region of 450 1500 cm-1. This band obscured many LVMs of simple substitutional impurities and dopants such as Mg, C, and Si. Hydrogen related defect complexes usually possess LVMs at frequencies higher than 1500 cm-1. Hence, it is possible to study dopants incorporation in GaN by monitoring the dopant-H complexes related LVMs. As an example, hydrogen can passivate Mg, which is an important acceptor in GaN. Hydrogen can be easily incorporated into III-V nitrides during or after the growth of the materials3. Additionally, atomic hydrogen can easily diffuse into the III-V nitrides during device processing, since most of the chemicals that come into contact with the surface contain hydrogen.
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In this article, we report on the LVMs of carbon-hydrogen complexes in dope
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