The document discusses research on rare earth (RE)-doped gallium nitride (GaN) films grown via diffusion doping with neodymium (Nd) and erbium (Er). Key findings include: 1) Nd-doped and Er-doped GaN samples exhibited room temperature ferromagnetism and near-infrared luminescence. Emission wavelengths matched telecommunications applications. 2) Increasing silicon doping decreased the ferromagnetic properties, as silicon competes with rare earths for gallium sites. Luminescence intensity was less affected by silicon doping. 3) Annealing time affected luminescence intensity, which increased then decreased with longer annealing, suggesting

1. Ferromagnetism and near-infrared luminescence in RE-GaN via diffusion M. O. Luen 1 , N. Nepal 1 , P. Frajtag 2 , J. M. Zavada 1 , E. Brown 3 , U. Hommerich 3 , S. M. Bedair 1 , and N. A. El-Masry 2 1 Electrical and Computer Engineering, North Carolina State University, Raleigh, NC 27695 USA 2 Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695 USA 3 Department of Physics, Hampton University, Hampton, VA 23668 USA Ferromagnetic RE-GaN films via MBE Ferromagnetism vs. Annealing & Doping Effects of GaN Growth Parameters Emission Intensity vs. Si-doping Ferromagnetism vs. Si-doping Emission Intensity vs. Annealing Time Ferromagnetism vs. Annealing Time Ms “saturates” beyond 9 hours of annealing * We have shown that n-type GaN:Si grown by MOCVD and ex-situ doped with Nd and Er via diffusion exhibits room temperature ferromagnetism and near-infrared and infrared luminescence as well. All Nd-doped samples showed emission in the near-infrared (~1060nm and ~1350nm) while the Er-doped samples’ emission was weak at ~1546 nm. * Substrate conditions play a role in magnetic behavior as both Si and RE atoms compete for gallium sites, and increased Si-doping leads to decreased saturation magnetization. Luminescent intensity varies slightly over the Si doping range, and emission intensity also varies with annealing time. * To the best of our knowledge, this is the first demonstration of above room temperature ferromagnetism and emission in GaNdN via diffusion. Rare earth doped semiconductor based devices that utilize both the ferromagnetic properties (through electron spin) and atomic-like emission of RE-GaN to store and transmit information can have reduced size and more efficient transmission across optical fiber. Most recent studies on dilute magnetic semiconductor (DMS) materials have been focused on GaMnAs and InMnAs Motivation Summary Nd Er This work is supported by the U. S. Army Research Office Grant No. W911NF-07-1-0603. Rare Earth Properties SIMS Profile for RE-Diffused GaN RE-GaN films via Diffusion We are unsure of the cause of Ms saturation for annealing beyond 9 hours. One explanation: localized high Er concentration (due to shallow diffusion) causing anti-ferromagnetic/ ferromagnetic competition between additional, nearby RE ions. This competition proposed to occur between substitutional and interstitial RE ions T. Dietl, Physica E, 35 (2006) 293-299 NC STATE UNIVERSITY Low-dispersion wavelength Low-loss wavelength Nd Er Nd 3+ Er 3+ * Nd emits at ~1.3μm : the low-dispersion regime for optical fiber communications. Low dispersion = faster transmission. * Er emits at ~1.5 μ m : the low-loss regime for optical fiber communications. Low loss = fewer amplifiers. * Similar outer e - config. mean similar chemical behavior: Nd: atomic no.=60; e - config.=[Xe]4f 4 ,6s 2 ; 3µ β per trivalent ionic state Er : atomic no.=68; e- config.=[Xe]4f 12 ,6s 2 ; 3µ β per trivalent ionic state 3sccm silane flow favors FM in Nd-diffused GaN:Si 1.5sccm silane flow is favored For FM in Er-diffused GaN:Si * FM coupling saturates at Longer anneal times. * Ms levels-off for +9hr Anneal times. * 16nm diffusion depth @ 15hr anneal. * 50% reduction in silane: 3X improvement in Ms(Er) while Ms(Nd) appears unaffected. * 32nm diffusion depth @ 15hr anneal. Nd-doped GaN:Si (2hr anneal) * Increased Si-doping has little effect on emission intensity, but decreases saturation magnetization of GaN:Nd. * Nd does not have to be substitutional for emission. * ~1um emission has application in future optical fiber telecommunication windows. Er-doped GaN:Si (Si: 3sccm) * Increased diffusion time increases emission to a point and then intensity decreases. * Emission intensity very weak so fluctuations are insignificant. * ~ +9hr anneal is best for Er-IR emission. Ref: S. Dhar, PHYSICAL REVIEW B 72, 245203 (2005) MBE–grown GaGdN shows average colossal magnetic moment (4000 μ β ) compared to atomic magnetic moment of 8 μ β . Gd concentration: 7x10 15 /cm 3 to 2x10 19 /cm 3 . Ref: M. Hashimoto, Jpn. J. Appl. Phys. Vol. 42 (2003) Pt. 2, No. 10A MBE-grown GaEuN with 2 at.% Eu with 0.1 μ β per Eu ion at 300K and 200mT applied magnetic field. Conventional approach to ferromagnetic RE-GaN Computed Values of the Curie Temperature (using the Zener model description) for various p-type semiconductors. Ref: T. Dietl, et. al., Science, Vol. 287, 2000, p. 1019. * T c (GaMnAs) = 140 K and T c (InMnAs) = 90 K * T c (GaMnN) > 300 K T c (GaN:RE) > 300 K * According to Zener model, predicted T c for GaMnN is above room temperature Ref. National Laboratory for Advanced Tecnology and nano Science, Nottingham Univ. Curie Temperature of GaMnAs NC State University reported RT-FM in GaMnN (2000), press release. Sources Ga: TMGa, N: NH3 Si: SiH4 RE-GaN layer: T dif = 800  C P base = ~ 2x10 -9 Torr Laser: KrF @ 248nm RE film: 10nm < t < 40nm Sapphire (Al 2 O 3 ) GaN (1µm) RE-GaN * The magnetic film shows a strong saturation magnetization of 5.7 µ emu. * Blue curve is representative of pre-diffusion saturation magnetization of samples. RE-doped GaN achieved via diffusion has benefits of ease of “growth” and low cost. Technique demonstrates both optical and magnetic response in samples. Layer structure * Similar outer e - configuration means similar chemical behavior, therefore Er diffusion profile approximates Nd diffusion profile. * Ting et al. and Chen et al. calculated diffusion constant and coefficient for GaErN via diffusion at 800 ° C for 7.5 and 21 hours to be D 0 = 1.8x10 -12 cm 2 /s, D(800 ° C) = 2x10 -17 cm 2 /s. * We estimate a smaller D Nd (800 ° C) ~ 1x10 -17 cm 2 /s due to larger atomic size of Nd. Ref: Y-S Ting et al. Optical Materials, 24, 515- 518 ( 2003 ) ‏ Ref: C-C Chen et al. Solid-State Electronics, 47, 529-531 (2003) ‏ 1x10 18 /cm 3 2x10 17 /cm 3 * Vacancy and/or Defect-mediated Diffusion. * Increased silane means more Si competing with RE for Gallium Vacancies. * H diminishes Ms via: H-complex passivation of V Ga or e - donation which compensates V Ga . D (Nd in GaN) ~ 1x10 -17 cm 2 /s @ 800°C D (Si in GaN) ~ 6.5x10 -11 cm 2 /s @ ~900°C Si occupies V Ga and stays Ref: R. Jakiela et al. Phys. Stat. Sol. (c) , vol. 3, issue 6, 1416-1419 ( 2006 ) ‏ Ref: A. F. Wright et al., J. Appl. Phys. ,vol. 90, 1164 ( 2001 ) ‏ Ms decreases with increased Si-doping Nd Er