Visible and Infrared Emission from Er-doped III-N Light Emitting Diodes
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Visible and Infrared Emission from Er-doped III-N Light Emitting Diodes John M. Zavada1*, Ei Ei Nyein2, Uwe Hömmerich2, J. Li3, J. Y. Lin3, H. X. Jiang3, P. Chow4 and Jian-Wei Dong4 1 U.S. Army Research Office, Durham, NC 27709 2 Department of Physics, Hampton University, Hampton, VA 23668 3 Department of Physics, Kansas State University, Manhattan, KS 66506 4 SVT Associates, Inc., Eden Prairie, MN 55344 *E-mail: [email protected] ABSTRACT We report on the visible and infrared emission characteristics of Er-doped III-N lightemitting diodes (LEDs). Quantum well-like device structures were grown through a combination of metal-organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) on cplane sapphire substrates. The dual stage growth process was used to take advantage of the high quality of AlGaN layers produced by MOCVD and in situ doping of Er during MBE growth. The multilayer structures were processed into devices and LEDs with different sizes and geometric shapes were produced. Electroluminescence (EL) was observed under either forward or reverse bias conditions. Visible and infrared spectra displayed narrow emission lines representative of the Er3+ system. The temperature dependence of the spectra, which were measured from 100K to 300K, showed a stability in the visible emission intensity but a sharp decrease in the infrared intensity at room temperature. Based on light output vs current measurements, estimates of the excitation cross-section were obtained for visible EL emission. INTRODUCTION In recent years, the optical properties of semiconductors doped with rare earth (RE) elements have received considerable attention [1, 2]. Due to the importance of the infrared (IR) region for optical communications, erbium (Er) has been the main RE element to be investigated. Semiconductors doped with REs offer the prospect of temperature-stable, electrically-pumped optical amplifiers and light emitters. Since a strong temperature quenching of the intensity of the light emission occurs in narrow bandgap semiconductors, such as Si, the wide bandgap semiconductors, such as III-N, appear to be superior host materials for room-temperature device applications [3]. In addition, RE-doped wide gap III-N semiconductors allow light emission at visible wavelengths for full-color display applications [4]. Light emitting diodes (LEDs) based on Er-doped III-N represent a new class of optical sources that produce electroluminescence (EL) from the intra-4f transitions of the Er3+ ions by means of electrical injection [5]. Under forward bias, energy can be transferred from electronhole pairs to the Er3+ ions leading to excitation of the 4f electrons. This process likely involves an intermediate defect level in the GaN host to which the exciton pair is efficiently coupled. The Er3+ ions can also be excited directly under reverse bias through impact of hot carriers. In both cases, the intra-4f transitions of Er3+ ions give rise to sharp emission lines whose wavelengths are largely independent of the host mater
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