Raman Spectroscopic Analysis of p-doped Bridged InP Nanowire
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1080-O07-10
Raman Spectroscopic Analysis of p-doped Bridged InP Nanowire Ataur Sarkar1, M. Saif Islam1, Sungsoo Yi2, and A. Alec Talin3 1 Electrical and Computer Engineering, University of California, One Shields Avenue, Davis, CA, 95616 2 Molecular Technology Laboratory, Agilent Technologies, Currently at Advanced Labroratories, Philips Lumileds Lighting Company, San Jose, CA, 95131 3 Sandia National Laboratories, P.O. Box 969, Livermore, CA, 94551 ABSTRACT Raman spectroscopy was performed on magnesium (Mg) doped InP nanowires bridged between single crystal vertical silicon electrodes using a green laser (λ~ 532 nm). First order TOphonon and LO phonon-plasmon peaks observed at 305 cm-1 and 345 cm-1, respectively, are consistent with those for bulk single crystal InP. Misorientation of the nanowires is found to influence the TO and LO peak intensities. Bottom broadening up to ~20 cm-1 of the TO peak is observed in the shifted Stokes spectrum due to the energy dispersion and residual strain in long (~6 µm) nanowires. Raman measurements indicated a trace of uncatalyzed InP on the insulating silicon oxide substrate and was verified through the electrical measurements of leakage currents before and after the nanowire growth. Initial investigation reveals that Raman spectroscopy can be a very useful in the study of nanowire heterostructures. INTRODUCTION Raman spectroscopy is a noninvasive characterization technique based on the material’s interaction with light and was first demonstrated by the great mind, C. V. Raman, in 1928 using sun light, blue and ultraviolet filters, and organic vapors [1-3]. When incident photons interact with a material at the atomic level, the resultant transverse-optical (TO) and longitudinal-optical (LO) phonon-plasmon-coupled modes bear unique information characteristic to the particular material [3-6]. The unique signature, a shift in the frequency of the incident photons and usually expressed as a wave number, is the key yardstick in differentiating materials using Raman spectroscopy. Raman spectroscopy has been extensively used in material study ranging from crystallographic investigation to charge density estimation [7]. This is an easy and noninvasive technique to characterize the surface profiles compared to chemical technique, a fast and simple way of estimating carrier concentrations compared to electrical Hall measurements, and an efficient means to determine crystallographic pattern compared to the transmission electron microscopic investigation. Raman spectroscopy can be a very useful tool to study nanostructures. There have been reports on the Raman study of vibrational properties of ZnO nanostructures fabricated by femtosecond pulses [4], size dependent material properties of CdS nanostructures [6], charge carrier concentration estimation for n-type bulk InP [7], terahertz radiation from LO phonon-plasmon coupling modes in InSb film [8], phonon confinement of silicon nanowire [9], surface optical phonons in crystalline GaP nanowires [10], impact of laser power density on the Ra
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