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Full-Text Articles in Physics
Polariton And Free-Exciton-Like Photoluminescence In Zno, D. C. Reynolds, David C. Look, B. Jogai, T. C. Collins
Polariton And Free-Exciton-Like Photoluminescence In Zno, D. C. Reynolds, David C. Look, B. Jogai, T. C. Collins
Physics Faculty Publications
An unusual photoluminescence line X has been observed in ZnO at an energy between that of the common donor-bound excitons (DBEs) and the free excitons (FEs). In the presence of a high carrier concentration, induced by a second below-band gap laser, the DBEs decrease in intensity, due to screening, and both the FEs and X increase. Thus, X has free-exciton, rather than bound-exciton, character. However, its electric-field vector lies in the plane perpendicular to the c axis, as is also found for the DBEs. The appearance of X is discussed in terms of the polariton picture.
Thermal Stability Of Isolated And Complexed Ga Vacancies In Gan Bulk Crystals, K. Saarinen, T. Suski, I. Grzegory, David C. Look
Thermal Stability Of Isolated And Complexed Ga Vacancies In Gan Bulk Crystals, K. Saarinen, T. Suski, I. Grzegory, David C. Look
Physics Faculty Publications
We have applied positron annihilation spectroscopy to show that 2-MeV electron irradiation at 300 K creates primary Ga vacancies in GaN with an introduction rate of 1 cm-1. The Ga vacancies recover in long-range migration processes at 500–600 K with an estimated migration energy of 1.5 (2) eV. Since the native Ga vacancies in as-grown GaN survive up to much higher temperatures (1300–1500 K), we conclude that they are stabilized by forming complexes with oxygen impurities. The estimated binding energy of 2.2 (4) eV of such complexes is in good agreement with the results of theoretical calculations.
Electrical Characterization Of 1.8 Mev Proton-Bombarded Zno, F. D. Auret, S. A. Goodman, M. Hayes, M. J. Legodi, H. A. Van Laarhoven, David C. Look
Electrical Characterization Of 1.8 Mev Proton-Bombarded Zno, F. D. Auret, S. A. Goodman, M. Hayes, M. J. Legodi, H. A. Van Laarhoven, David C. Look
Physics Faculty Publications
We report on the electrical characterization of single-crystal ZnO and Au Schottky contacts formed thereon before and after bombarding them with 1.8 MeV protons. From capacitance–voltage measurements, we found that ZnO is remarkably resistant to high-energy proton bombardment and that each incident proton removes about two orders of magnitude less carriers than in GaN. Deep level transient spectroscopy indicates a similar effect: the two electron traps detected are introduced in extremely low rates. One possible interpretation of these results is that the primary radiation-induced defects in ZnO may be unstable at room temperature and anneal out without leaving harmful defects …
Solar Activity Variations Of The Venus Thermosphere/Ionosphere, Jane L. Fox, K. Y. Sung
Solar Activity Variations Of The Venus Thermosphere/Ionosphere, Jane L. Fox, K. Y. Sung
Physics Faculty Publications
We present models of the low and high solar activity thermospheres and ionospheres of Venus for a background atmosphere based largely on the VTS3 model of Hedin et al. [1983]. Our background model consists of 12 neutral species, and we compute the density profiles of 13 ions and 7 minor neutrals. We find that the peak production rates of some ions, such as CO2+ and N2+, vary approximately as the solar flux and that some, whose parent neutrals are photochemically produced, such as O+, N+, and C+, show variations …
Hot Carbon Densities In The Exosphere Of Mars, Andrew F. Nagy, Michael W. Liemohn, Jane L. Fox, Jhoon Kim
Hot Carbon Densities In The Exosphere Of Mars, Andrew F. Nagy, Michael W. Liemohn, Jane L. Fox, Jhoon Kim
Physics Faculty Publications
Theoretical results of hot carbon densities in the exosphere of Mars are presented. The calculation is a two-step process: First a two-stream transport code is used to solve for the distribution function at the exobase, and then these results are used in a Liouville equation solution above the exobase. It is found that photodissociation of carbon monoxide is the largest source of hot carbon atoms in the upper atmosphere of Mars, larger than dissociative recombination of CO+ and much larger than the creation of hot carbon through collisions with hot oxygen atoms. It is also found that the high …
Photochemical Escape Of Atomic Carbon From Mars, Jane L. Fox, F. M. Bakalian
Photochemical Escape Of Atomic Carbon From Mars, Jane L. Fox, F. M. Bakalian
Physics Faculty Publications
We have modeled the escape fluxes of atomic carbon from the Martian atmosphere for low and high solar activities due to various photochemical escape mechanisms, including photodissociation of CO, dissociative recombination of CO+, electron impact dissociation and dissociative ionization of CO, photodissociative ionization of CO, and dissociative charge transfer of O++ to CO. Only photodissociation of CO and dissociative recombination of CO+ are found to be important, and the time-averaged escape flux is predicted to be controlled by the high solar activity values. The computed global average escape fluxes of C due to photodissociation of CO …
Predicted Maximum Mobility In Bulk Gan, David C. Look, J. R. Sizelove
Predicted Maximum Mobility In Bulk Gan, David C. Look, J. R. Sizelove
Physics Faculty Publications
A 300 K bulk (three-dimensional) mobility of 1245 cm2/V s has been measured in free-standing GaN. Temperature-dependent Hall-effect data on this particular sample are fitted to obtain unknown lattice-scattering parameters, as well as shallow donor (ND) and acceptor (NA) concentrations, which are ND = 6.7×1015 and NA = 1.7×1015 cm−3. Realistic values of the maximum mobility attainable in bulk GaN are then obtained by assuming two-orders-of-magnitude lower values of ND and NA, leading to a maximum 300 K mobility of 1350 cm2 …
Characterization Of Near-Surface Traps In Semiconductors: Gan, David C. Look, Z-Q. Fang
Characterization Of Near-Surface Traps In Semiconductors: Gan, David C. Look, Z-Q. Fang
Physics Faculty Publications
We present a simple a criterion, based on deep-level transient spectroscopy peak heights S(Vr) at two or more values of reverse bias Vr, to unequivocally determine whether or not a particular semiconductor trap is of bulk or near-surface nature. Moreover, we present an expression for S(Vr) with fitting parameters ϕB, the Schottky barrier height; δ, the trap penetration depth; and NT, the trap density. Application of the method to a thick, high-quality, epitaxial GaN layer, reveals two common traps which penetrate only 2700±300 Å into the …
Evidence For Shallow Acceptors In Gan, D. C. Reynolds, David C. Look, B. Jogai, Richard J. Molnar
Evidence For Shallow Acceptors In Gan, D. C. Reynolds, David C. Look, B. Jogai, Richard J. Molnar
Physics Faculty Publications
Two low-temperature photoluminescence lines in GaN, in the region of energies commonly interpreted as longitudinal optical-phonon replicas of free excitons, donor-bound excitons, or acceptor-bound excitons, are reinterpreted as acceptor-bound excitons (A0X’s) collapsing to n=2 and n=3 excited states, respectively, of the acceptors involved. Application of this model to two sets of A0X-related lines in hydride-vapor-phase-grown GaN gives acceptor energies of 85±1, and 115±1 meV, respectively. The existence of such shallow acceptor states, if confirmed, is of great technological importance.
Fine Structure On The Green Band In Zno, D. C. Reynolds, David C. Look, B. Jogai
Fine Structure On The Green Band In Zno, D. C. Reynolds, David C. Look, B. Jogai
Physics Faculty Publications
An emission band at 2.4 eV, called the green band, is observed in most ZnO samples, no matter what growth technique is used. Sometimes this band includes fine structure, which consists mainly of doublets, repeated with a longitudinal-optical-phonon-energy spacing (72 meV). We have developed a vibronic model for the green band, based on transitions from two separate shallow donors to a deep acceptor. The donors, at energies 30 and 60 meV from the conduction-band edge, respectively, are also found from Hall-effect measurements.
Microcathodoluminescence Of Impurity Doping At Gallium Nitride/Sapphire Interfaces, S. H. Goss, X. L. Sun, A. P. Young, L. J. Brillson, David C. Look, Richard J. Molnar
Microcathodoluminescence Of Impurity Doping At Gallium Nitride/Sapphire Interfaces, S. H. Goss, X. L. Sun, A. P. Young, L. J. Brillson, David C. Look, Richard J. Molnar
Physics Faculty Publications
We have used low-temperature cathodoluminescence spectroscopy (CLS) to probe the spatial distribution and energies of electronic defects near GaN/Al2O3 interfaces grown by hydride vapor phase epitaxy (HVPE). Cross sectional secondary electron microscopy CLS shows systematic variations in impurity/defect emissions over a wide range of HVPE GaN/Sapphire electronic properties. These data, along with electrochemical capacitance–voltage profiling and secondary ion mass spectrometry, provide a consistent picture of near-interface doping by O diffusion from Al2O3 into GaN, over a range 100–1000 nm.
Deep Centers In A Free-Standing Gan Layer, Z-Q. Fang, David C. Look, P. Visconti, D. F. Wang, C. Z. Lu, F. Yun, H. Morkoç, Seong-Ju S. Park, K. Y. Lee
Deep Centers In A Free-Standing Gan Layer, Z-Q. Fang, David C. Look, P. Visconti, D. F. Wang, C. Z. Lu, F. Yun, H. Morkoç, Seong-Ju S. Park, K. Y. Lee
Physics Faculty Publications
Schottky barrier diodes, on both Ga and N faces of a ∼300-μm-thick free-standing GaN layer, grown by hydride vapor phase epitaxy (HVPE) on Al2O3 followed by laser separation, were studied by capacitance–voltage and deep level transient spectroscopy (DLTS) measurements. From a 1/C2 vs V analysis, the barrier heights of Ni/Au Schottky contacts were determined to be different for the two polar faces: 1.27 eV for the Ga face, and 0.75 eV for the N face. In addition to the four common DLTS traps observed previously in other epitaxial GaN including HVPE-grown GaN a new trap …
High Mobility In N-Type Gan Substrates, A. Saxler, David C. Look, S. Elhamri, J. R. Sizelove, William C. Mitchel, C. M. Sung, S. S. Park, K. Y. Lee
High Mobility In N-Type Gan Substrates, A. Saxler, David C. Look, S. Elhamri, J. R. Sizelove, William C. Mitchel, C. M. Sung, S. S. Park, K. Y. Lee
Physics Faculty Publications
No abstract provided.
Evolution Of Deep Centers In Gan Grown By Hydride Vapor Phase Epitaxy, Z-Q. Fang, David C. Look, J. Jasinski, M. Benamara, Z. Liliental-Weber, Richard J. Molnar
Evolution Of Deep Centers In Gan Grown By Hydride Vapor Phase Epitaxy, Z-Q. Fang, David C. Look, J. Jasinski, M. Benamara, Z. Liliental-Weber, Richard J. Molnar
Physics Faculty Publications
Deep centers and dislocation densities in undoped n GaN, grown by hydride vapor phase epitaxy (HVPE), were characterized as a function of the layer thickness by deep level transient spectroscopy and transmission electron microscopy, respectively. As the layer thickness decreases, the variety and concentration of deep centers increase, in conjunction with the increase of dislocation density. Based on comparison with electron-irradiation induced centers, some dominant centers in HVPE GaN are identified as possible point defects.