GaN Doped with Neodymium by Plasma-Assisted Molecular Beam Epitaxy for Potential Lasing Applications
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1111-D02-04
GaN Doped with Neodymium by Plasma-Assisted Molecular Beam Epitaxy for Potential Lasing Applications Eric D. Readinger1, Grace D. Metcalfe1, Paul Hongen Shen1, Michael Wraback1, Naveen Jha2, Nathaniel Woodward2, Pavel Capek2, and Volkmar Dierolf2 1 U.S. Army Research Laboratory, 2800 Powder Mill Road, Adelphi, MD 20783, U.S.A. 2 Physics Department, Lehigh University, 16 Memorial Drive East, Bethlehem, PA 18015, U.S.A. ABSTRACT We provide an investigation of in situ doping of GaN with the RE element Nd by plasma assisted-molecular beam epitaxy (PA-MBE). GaN epilayers are grown on c-plane sapphire and free standing GaN substrates and the Nd doping is controlled by an effusion cell. The ideal growth conditions for Nd incorporation maintaining crystal quality in GaN were investigated. The optical absorption characteristics indicate that the GaN:Nd epilayer remains transparent at the Nd emission wavelength of interest. For the highest Nd effusion cell temperatures, Rutherford backscattering and secondary ion mass spectrometry data indicate ~5 at. % in epilayers grown on c-plane sapphire. X-ray diffraction found no evidence of phase segregation up to ~1 at. % Nd. The highest luminescence intensities correspond to a doping range 0.05-1 at. %, with the strongest emission occurring at 1.12 eV (1107 nm). We also present the Stark energy sublevels of Nd3+ ions in GaN as determined by luminescence spectra. Photoluminescence excitation spectra reveal an optimal excitation energy of 1.48 eV (836 nm). We correlate the photoluminescence spectra with transitions from the 4F3/2 excited state to the 4 I9/2, 4I11/2, and 4I13/2 multiplets of the Nd3+ ion for above (325nm) and below (836nm) bandgap excitation. Spectral correlation of the Nd emission multiplets in addition to site-selective spectroscopy studies using combined excitation-emission spectroscopy with confocal microscopy indicate enhanced substantial doping at the Ga site compared to other techniques (ion implantation and co-sputtering). INTRODUCTION Utilization of the rare-earth (RE) lanthanide series as dopants in a variety of ‘host’ materials may enable optoelectronic and photonic applications such as solid-state lasers, optical fiber telecommunications, and light-emitting displays [1]. After Favennec et al. [2] demonstrated a reduction in thermal quenching in Er-doped materials with increasing bandgap, interest in wide bandgap semiconductors as host materials expanded. In particular, wurtzite GaN has strong ionic bonds that can enhance the intra-4fn transition probability in the RE3+ ion with substitutional occupation of the Ga site; in addition, GaN has a high thermal conductivity (more than an order of magnitude larger than yittrium aluminum garnet, yittrium lithium fluoride, and other typical solid state laser hosts) [1,3], which may lead to improvement in heat extraction that could allow for major gains in solid state laser technology. Light emission from GaN doped with Eu, Er, Pr, Tm, Yb, Nd, and Dy has been demonstrated by photoluminescence (PL), electro
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