Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session K7: Dopants and Defects in Semiconductors: NitridesFocus Industry
|
Hide Abstracts |
Sponsoring Units: DMP FIAP Chair: Christopher Van de Walle, UCSB Room: 303 |
Wednesday, March 16, 2016 8:00AM - 8:36AM |
K7.00001: Point and Extended Defects in GaN-based Materials Invited Speaker: James Speck In this presentation, the origin and evolution of threading dislocations in GaN heteroepitaxy are reviewed. For heteroepitaxial of GaN on most substrates (e.g., sapphire, MgAl$_{\mathrm{2}}$O$_{\mathrm{4}}$, SiC, \textellipsis ) high temperature GaN grows in a Volmer-Weber mode. Threading dislocations result from island coalescence. The evolution of threading dislocations has been extensively modeled. Tensile stress generation via threading dislocation inclination is a major ongoing issue in GaN growth. We review older and more recent work on the impact of threading dislocations in GaN materials properties and device performance. Finally, we review recent work from our group on stress relaxation in nonpolar and semipolar GaN. We demonstrate the first GaN-based laser diodes grown on intentionally stress-relaxed buffer layers and we demonstrate control of relaxation in semipolar laser diodes by selective area growth. [Preview Abstract] |
Wednesday, March 16, 2016 8:36AM - 9:12AM |
K7.00002: Impact of defects on efficiency of nitride devices Invited Speaker: Chris Van de Walle Nitride semiconductors are the key materials for solid-state lighting and also increasingly for power electronics. In both bulk crystals and epitaxial layers, point defects may act as compensating centers, charge traps, or radiative or nonradiative recombination centers. Unintentional impurities often play an equally important role; for instance, carbon that is unavoidably incorporated during metal-organic chemical vapor deposition (MOCVD) acts as a source of yellow luminescence [1]. Theoretical advances now enable us to calculate the energetics as well as electronic and optical properties of point defects with unprecedented accuracy [2]. In AlN, we have identified the defects that lead to characteristic luminescence and absorption lines [3]. Both point defects and impurities can affect the radiative efficiency of light emitters. We have developed a first-principles methodology [4] to determine nonradiative carrier capture coefficients. Accurate calculations of electron-phonon coupling, combined with results for defect formation energies and charge-state transition levels [5], enable the calculation of nonradiative capture rates for electrons and holes and the evaluation of Shockley-Read-Hall coefficients. This approach allows us to identify specific defects that play a key role in limiting the efficiency of nitride semiconductor devices. \\ \\ 1. J. L. Lyons, A. Janotti, and C. G. Van de Walle, Phys. Rev. B \textbf{89}, 035204 (2014).\\ 2. C. Freysoldt \textit{et al.}, Rev. Mod. Phys. \textbf{86}, 253 (2014).\\ 3. Q. Yan, A. Janotti, M. Scheffler, and C. G. Van de Walle, Appl. Phys. Lett. \textbf{105}, 111104 (2014).\\ 4. A. Alkauskas, Q. Yan, and C. G. Van de Walle, Phys. Rev. B \textbf{90}, 075202 (2014).\\ 5. J. L. Lyons, A. Alkauskas, A. Janotti, and C. G. Van de Walle, Phys. Stat. Sol. B \textbf{252}, 900 (2015). [Preview Abstract] |
Wednesday, March 16, 2016 9:12AM - 9:24AM |
K7.00003: Saturation Behavior of Eu ion emission in GaN Natalie Hernandez, Brandon Mitchell, Yasufumi Fujiwara, Volkmar Dierolf Europium doped Gallium Nitride (GaN:Eu) has been recognized as a candidate for the red-emitting active layer in nitride-based light emitting diodes. To better comprehend the excitation energy transfer from the excited GaN host to the Eu ion, we performed an extensive analysis of GaN:Eu and GaN co-doped with Eu and other dopants (Silicon and Magnesium). We determined how various growth parameters manipulated site formations and measured the optical accessibility of the Eu ions within the GaN host and the excitation efficiency of the energy transfer between the host material and the Eu ions. Furthermore, we derived a model for the saturation behavior of the emission of Eu ions within GaN. Our results suggest that the saturation behavior is strongly influenced by different crystal growth specifications and co-dopants. [Preview Abstract] |
Wednesday, March 16, 2016 9:24AM - 9:36AM |
K7.00004: Hydrogen-carbon complexes and the blue luminescence band in GaN. Denis Demchenko, Ibrahima Diallo, Michael Reshchikov The blue luminescence band with a maximum at 3.0 eV and the zero-phonon line at 3.33 eV (labeled BL2) is observed in high-resistivity GaN. Under prolonged ultraviolet (UV) light exposure, the BL2 band transforms into the yellow luminescence (YL) band with a maximum at 2.2 eV. Our calculations using hybrid functionals suggest that the BL2 band is related to a hydrogen-carbon defect complex, most likely C$_{N}$O$_{N}$-H$_{i}$. The complex creates defect transition level close to the valence band, which is responsible for the BL2 band. Under UV illumination the complex dissociates, leaving as byproduct the source of the YL band (C$_{N}$O$_{N}$ or C$_{N})$ and interstitial hydrogen. [Preview Abstract] |
Wednesday, March 16, 2016 9:36AM - 9:48AM |
K7.00005: Impact of point defects on III-nitride tunnel devices. Darshana Wickramaratne, John Lyons, Chris G. Van de Walle Heterostructures using GaN and InGaN are being pursued in designs of tunnel field-effect-transistors (TFETs) to enable low-power switching devices. Point defects and impurities in these heterostructures can adversely affect the performance of these devices through Shockley-Read-Hall (SRH) and Trap-Assisted-Tunneling (TAT) processes. Using first-principles calculations based on a hybrid functional, we calculate the thermodynamic and charge-state switching levels as well as nonradiative recombination rates of point defects and impurities in GaN and InGaN. Gallium vacancies and their complexes, in particular, are found to be potentially detrimental centers. We then investigate how these defects can contribute to SRH and TAT processes in a nitride TFET device. [Preview Abstract] |
Wednesday, March 16, 2016 9:48AM - 10:00AM |
K7.00006: Density Functional Theory Calculations of Activation Energies for Carrier Capture by Defects in Semiconductors N. A. Modine, A. F. Wright, S. R. Lee The rate of defect-induced carrier recombination is determined by both defect levels and carrier capture cross-sections. Density functional theory (DFT) has been widely and successfully used to predict defect levels, but only recently has work begun to focus on using DFT to determine carrier capture cross-sections. Lang and Henry developed the theory of carrier-capture by multiphonon emission in the 1970s and showed that carrier-capture cross-sections differ between defects primarily due to differences in their carrier capture activation energies. We present an approach to using DFT to calculate carrier capture activation energies that does not depend on an assumed configuration coordinate and that fully accounts for anharmonic effects, which can substantially modify carrier activation energies. We demonstrate our approach for intrinisic defects in GaAs and GaN and discuss how our results depend on the choice of exchange-correlation functional and the treatment of spin polarization. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Wednesday, March 16, 2016 10:00AM - 10:12AM |
K7.00007: First-principles identification of optically active Er$^{3+}$ centers in GaN Khang Hoang Rare-earth (RE) doped III-nitrides are of great interest for optoelectronic and spintronic applications. The identification of optically active RE centers in these materials has however been challenging, both in experimental and theoretical/computational studies. In this talk, we present a hybrid density functional study of the interaction between the erbium (Er) dopant and wurtzite GaN, including intrinsic point defects and other impurities that may be present in the host material. Particularly, we investigate the structure, energetics, and transition levels of the Er impurity and its complexes with N and Ga vacancies, substitutional C and O impurities, and H interstitials. In light of our results, we identify possible luminescent Er$^{3+}$ centers in Er-doped GaN and discuss the role of these centers in the excitation of the Er 4\textit{f}-electron core. [Preview Abstract] |
Wednesday, March 16, 2016 10:12AM - 10:24AM |
K7.00008: Native defects in GaN: a hybrid functional study Ibrahima Castillo Diallo, Denis Demchenko Intrinsic defects play an important role in the performance of GaN-based devices. We present hybrid density functional calculations of the electronic and possible optical properties of interstitial N (N$_{\mathrm{i}}$-N$_{\mathrm{i}})$, N antisite (N$_{\mathrm{Ga}})$, interstitial Ga (Ga$_{\mathrm{i}})$, Ga antisite (Ga$_{\mathrm{N}})$, Ga vacancy (V$_{\mathrm{Ga}})$, N vacancy (V$_{\mathrm{N}})$ and Ga-N divacancies (V$_{\mathrm{Ga}}$V$_{\mathrm{N}})$ in GaN. Our results show that the vacancies display relatively low formation energies in certain samples, whereas antisites and interstitials are energetically less favorable. However, interstitials can be created by electron irradiation. For instance, in 2.5 MeV electron-irradiated GaN samples, a strong correlation between the frequently observed photoluminescence (PL) band centered around 0.85 eV accompanied with a rich phonon sideband of \textasciitilde 0.88 eV and the theoretical optical behavior of interstitial Ga is discussed. N vacancies are found to likely contribute to the experimentally obtained green luminescence band (GL2) peaking at 2.24 eV in high-resistivity undoped and Mg-doped GaN. [Preview Abstract] |
Wednesday, March 16, 2016 10:24AM - 10:36AM |
K7.00009: Native point defects and doping in ZnGeN$_2$ Dmitry Skachkov, Walter Lambrecht A computational study within the framework of density functional theory is presented for native defects and doping in ZnGeN$_2$. We study the three types of vacancies $V_{\rm Zn}$, $V_{\rm Ge}$, $V_{\rm N}$, cation antisite defects Zn$_{\rm Ge}$, Ge$_{\rm Zn}$, and potential n-type (O$_{\rm N}$, Ga$_{\rm Zn}$) and p-type Ga$_{\rm Ge}$ dopants. The cation antisite defects are found to have significantly lower formation energy than the cation vacancies. The charge neutrality condition pins the Fermi level close to the the crossing of the ${\rm Zn}_{\rm Ge}^{-1}$ acceptor with the ${\rm Ge}_{\rm Zn}^{2+}$ donor, and intrinsic $p$-type doping would result. The $V_{\rm N}$ is found to be a rather deep donor. ${\rm Ge}_{\rm Zn}$ is found to behave as a shallow donor. Oxygen impurities are found to strongly prefer the ${\rm O}_{\rm N}$ subsitutional site and are found to be shallow donors with a very low energy of formation. Energies of formation of ${\rm Ga}_{\rm Zn}$ and ${\rm Ga}_{\rm Ge}$ are lower than those of the cation antisites. Thus good solubility is expected and these impurities can hence pin the Fermi level at the crossing of the donor ${\rm Ga}_{\rm Zn}^{+1}$ with the acceptor ${\rm Ga}_{\rm Ge}^{-1}$, and efficient $p$-type doping should result. [Preview Abstract] |
Wednesday, March 16, 2016 10:36AM - 10:48AM |
K7.00010: Fluorescent Defects in Hexagonal Boron Nitride Annemarie L. Exarhos, Kameron Oser, David A. Hopper, Richard R. Grote, Lee C. Bassett Mono- and few-layer hexagonal boron nitride (h-BN) can host defects whose electronic states lie deep within the bandgap, similar to the nitrogen-vacancy color center in bulk diamond. Here, we study defect creation in h-BN through irradiation and thermal annealing. We employ confocal photoluminescence (PL) imaging and spectroscopy under various excitation energies on both supported and suspended h-BN to identify and characterize the emission of isolated defect centers. Polarization- and temperature-dependent measurements of the observed PL are used to map out the electronic structure of the defects, enabling optical control of fluorescent defects in h-BN. This knowledge, coupled with the spatial confinement to 2D and the unique electrical, optical, and mechanical properties of h-BN, will enable the use of these defects for quantum sensing and other applications in quantum information processing. [Preview Abstract] |
Wednesday, March 16, 2016 10:48AM - 11:00AM |
K7.00011: Unique stability of neutral interstitial hydrogen in cubic BN and diamond John L. Lyons, Chris G. Van de Walle In virtually all semiconductors and insulators, hydrogen interstitial impurities act as negative-U centers, implying that hydrogen is never stable in the neutral charge state. Using hybrid density functional calculations, which are crucial for obtaining accurate properties of defects in semiconductors, we find a different behavior for hydrogen interstitials in diamond and cubic BN. In diamond, we find that hydrogen is a very strong positive-U center, and the neutral charge state of the interstitial is stable over a Fermi-level range of more than 2 eV. In cubic BN, a III-V compound semiconductor with properties similar to diamond, we also find positive-U behavior, though over a much smaller Fermi-level range. We will discuss the electronic-structure origins of this negative-U behavior, and compare with the properties of hydrogen in other materials. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700