Local Vibrational Modes of Carbon-Hydrogen Complexes in Proton Irradiated AlGaN
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LOCAL VIBRATIONAL MODES OF CARBON-HYDROGEN COMPLEXES IN PROTON IRRADIATED AlGaN M. O. Manasreh*, and B.D. Weaver** * Department of Electrical and Computer Engineering, University of New Mexico, Albuquerque, New Mexico 87131 ** Naval Research Lab, 4555 Overlook Ave, SW, Washington, DC 20375 ABSTRACT Local vibrational modes (LVMs) of carbon-hydrogen (C-H) complexes in proton implanted AlGaN grown on sapphire by metalorganic chemical vapor deposition (MOCVD) were investigated using Fourier transform infrared (FTIR) spectroscopy. The LVMs exhibit five distinctive peaks in the spectral region of 2846~2963 cm-1, which are due to the symmetric and asymmetric stretching modes of C-Hn (n=1-3). The LVMs intensities in doped AlGaN are increased as irradiation dose is increased in the entire irradiation dose range used without reaching the saturation stage. On the other hand, undoped samples show that LVMs intensity increase then either decreased or saturated as the irradiation dose is increased above 5x1016 cm-2. Proton irradiation causes a drastic increase in the CH3 LVM while electron irradiation causes the opposite effect suggesting strongly that the observed LVMs are truly due to CH complexes. INTRODUCTION Optoelectronic devices based on III-nitrides and their ternary alloys have a broad range of application due to their wide direct band-gaps covering the spectral range from visible to ultraviolet. GaN has unique applications in blue, green and ultraviolet-blue light-emitting diodes, detectors and laser diodes [1-4]. III-nitride material system also shows tremendous potential in the field of high-temperature and high-power electronics because of their superior materials parameters [5]. Omnipresent impurities such as C, H and O play detrimental and beneficial roles in fabrication processes. For example, hydrogen can passivate the acceptor Mg [6-8] in GaN. Hydrogen can be easily incorporated into III-nitride during or after the growth of the materials [8]. Therefore, dopant incorporation remains the subject of various investigations. Ion irradiation is a very attractive tool for several steps in III-nitride based devices’ fabrication. The performance of devices such as fast switches [9] and detector [10] has been improved by subjecting them to well-controlled dose of particle irradiation. Compare to the understanding of ion beam process in mature semiconductors (i.e. Si and GaAs), the understanding of the complex ion beam process in III-nitrides is still at its infancy. Much more work is essentially needed to understand the irradiation effect on III-nitride material and device behaviors. LVMs spectroscopy is a powerful tool in identifying impurities and dopant incorporation in semiconductors. LVMS give rise to sharp peaks in IR absorption spectra. With this method, one can identify the lattice site of the impurity atoms due to the fact that LVMs of impurities are sensitively affected by the atomic structure surrounding the dopant or impurity atom [11]. One typical example is that isotopic composition of the impurity and the
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