Comparison of the Optical Properties of Er 3+ Doped Gallium Nitride Prepared by Metalorganic Molecular Beam Epitaxy (MOM
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U. Hömmerich*,+, J. T. Seo*, J. D. MacKenzie**, C. R. Abernathy**, R. Birkhahn†, A. J. Steckl†, and J. M. Zavada‡ *Hampton University, Department of Physics, Hampton, VA 23668 **University of Florida, Dept. of Materials Science and Eng., Gainesville, FL 32611 †University of Cincinnati, Nanoelectronics Laboratory, Cincinnati, OH 45221 ‡U.S. Army European Research Office, London, UK, NW1 5 TH + E-mail: [email protected] ABSTRACT We report on the luminescence properties of Er doped GaN grown prepared by metalorganic molecular beam epitaxy (MOMBE) and solid-source molecular beam epitaxy (SSMBE) on Si substrates. Both types of samples emitted characteristic 1.54 µm PL resulting from the intra-4f Er3+ transition 4I13/2→4I15/2. Under below-gap excitation the samples exhibited very similar 1.54 µm PL intensities. On the contrary, under above-gap excitation GaN: Er (SSMBE) showed ~80 times more intense 1.54 µm PL than GaN: Er (MOMBE). In addition, GaN: Er (SSMBE) also emitted intense green luminescence at 537 nm and 558 nm, which was not observed from GaN: Er (MOMBE). The average lifetime of the green PL was determined to be 10.8 µs at 15 K and 5.5 µs at room temperature. A preliminary lifetime analysis suggests that the decrease in lifetime is mainly due to the strong thermalization between the 2H11/2 and 4S3/2 excited states. Nonradiative decay processes are expected to only weakly affect the green luminescence. INTRODUCTION The luminescence from rare earth doped III-nitrides is of significant current interest for potential applications in optical communications and full color displays.[1] Visible and infrared electroluminescence (EL) has been reported from a number of rare earth doped GaN systems: GaN: Er (green, IR)[2,3,4], GaN: Pr (red, IR) [5], GaN: Eu (red) [6,7] and GaN: Tm (blue) [1] The incorporation, optical activation, and luminescence efficiency of rare earth ions in III-nitrides, however, is not yet fully understood. In this paper, we present a comparison of the PL properties of Er doped GaN grown by MOMBE and SSMBE. Excitation wavelength and temperature dependent PL studies were performed and analyzed in view of optoelectronic applications of Er doped GaN. EXPERIMENTAL PROCEDURES The GaN: Er (MOMBE) sample was grown in an INTEVAC Gas Source Gen II on In-mounted (100) Si substrate as described in reference [8]. The GaN: Er (SSMBE)
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sample was grown on Si by solid source and RF-assisted molecular beam epitaxy (MBE). Details of the Riber MBE32 system used for growth have been discussed previously [3]. PL studies were performed using a HeCd laser operating at either 325 nm or 442 nm. Infrared PL spectra were recorded using a 1-m monochromator equipped with a liquidnitrogen cooled Ge detector. In visible PL studies a thermo-electric cooled PMT was employed for detection. The signal was processed using lock-in techniques. IR lifetime studies employed the 355 nm line of a Nd: YAG laser for excitation. Visible lifetime data were taken by pumping into the 4F7/2 Er3+ transition at ~495 nm. RESULTS AND DISCU
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