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Articles 271 - 300 of 488

Full-Text Articles in Physics

Frequency Scanned Interferometer Demonstration System, Tim Blass, Jason A. Deibel, Sven Nyberg, Keith Riles, Haijun Yang Jul 2003

Frequency Scanned Interferometer Demonstration System, Tim Blass, Jason A. Deibel, Sven Nyberg, Keith Riles, Haijun Yang

Physics Faculty Publications

No abstract provided.

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Effect Of H-2 On The Martian Ionosphere: Implications For Atmospheric Evolution, Jane L. Fox Jun 2003

Effect Of H-2 On The Martian Ionosphere: Implications For Atmospheric Evolution, Jane L. Fox

Physics Faculty Publications

Because H2 reacts efficiently with O+, CO2 +, CO+, and N2 +, the molecular hydrogen abundance assumed in models of the Martian ionosphere greatly affects the high altitude density profiles of these ions. We have found that models of the low solar activity Martian ionosphere exhibit much smaller O+ densities than the measured values if the adopted H2 abundance is of the order of 40 ppm, the value proposed in a 1998 model of the Martian atmosphere. For a model based on the recently measured H2 abundance of …

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Ga Vacancies As Dominant Intrinsic Acceptors In Gan Grown By Hydride Vapor Phase Epitaxy, J. Oila, J. Kivioja, V. Ranki, K. Saarinen, David C. Look, Richard J. Molnar, S. S. Park, S. K. Lee, J. Y. Han May 2003

Ga Vacancies As Dominant Intrinsic Acceptors In Gan Grown By Hydride Vapor Phase Epitaxy, J. Oila, J. Kivioja, V. Ranki, K. Saarinen, David C. Look, Richard J. Molnar, S. S. Park, S. K. Lee, J. Y. Han

Physics Faculty Publications

Positron annihilation measurements show that negative Ga vacancies are the dominant acceptors in n-type gallium nitride grown by hydride vapor phase epitaxy. The concentration of Ga vacancies decreases, from more than 1019 to below 1016 cm−3, as the distance from the interface region increases from 1 to 300 μm. These concentrations are the same as the total acceptor densities determined in Hall experiments. The depth profile of O is similar to that of VGa, suggesting that the Ga vacancies are complexed with the oxygen impurities.

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Plasma-Etching-Enhanced Deep Centers In N-Gan Grown By Metalorganic Chemical-Vapor Deposition, Z-Q. Fang, David C. Look, X. L. Wang, J. Han, F. A. Khan, I. Adesida Mar 2003

Plasma-Etching-Enhanced Deep Centers In N-Gan Grown By Metalorganic Chemical-Vapor Deposition, Z-Q. Fang, David C. Look, X. L. Wang, J. Han, F. A. Khan, I. Adesida

Physics Faculty Publications

By using deep-level transient spectroscopy (DLTS), deep centers have been characterized in unintentionally doped n-GaN samples grown by metalorganic chemical-vapor deposition and subjected to inductively coupled plasma reactive ion etching. At least six DLTS traps exist in the control sample: A1 (∼0.90 eV), Ax (∼0.72 eV), B (0.61 eV), C1 (0.44 eV), D (0.25 eV), and E1 (0.17 eV), with B dominant. Then, as the etching bias-voltage increases from −50 to −150 V, trap D increases strongly and becomes dominant, while traps A1, C (0.34 eV), and E1 increase at a slower …

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Hydrogen Incorporation And Diffusivity In Plasma-Exposed Bulk Zno, K. Ip, M. E. Overberg, Y. W. Heo, D. P. Norton, S. J. Pearton, C. E. Stutz, B. Luo, F. Ren, David C. Look, J. M. Zavada Jan 2003

Hydrogen Incorporation And Diffusivity In Plasma-Exposed Bulk Zno, K. Ip, M. E. Overberg, Y. W. Heo, D. P. Norton, S. J. Pearton, C. E. Stutz, B. Luo, F. Ren, David C. Look, J. M. Zavada

Physics Faculty Publications

Hydrogen incorporation depths of >25 μm were obtained in bulk, single-crystal ZnO during exposure to 2H plasmas for 0.5 h at 300 °C, producing an estimated diffusivity of ∼ 8×10−10 cm2/V⋅s at this temperature. The activation energy for diffusion was 0.17±0.12 eV, indicating an interstitial mechanism. Subsequent annealing at 500–600 °C was sufficient to evolve all of the hydrogen out of the ZnO, at least to the sensitivity of secondary ion mass spectrometry (<5×1015 cm−3). The thermal stability of hydrogen retention is slightly greater when the hydrogen is incorporated by direct implantation …

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Si Doping Of High-Al-Mole Fraction Alxga1-Xn Alloys With Rf Plasma-Induced Molecular-Beam-Epitaxy, Jeonghyun Hwang, William J. Schaff, Lester F. Eastman, Shawn T. Bradley, Leonard J. Brillson, David C. Look, J. Wu, Wladek Walukiewicz, Madalina Furis, Alexander N. Cartwright Dec 2002

Si Doping Of High-Al-Mole Fraction Alxga1-Xn Alloys With Rf Plasma-Induced Molecular-Beam-Epitaxy, Jeonghyun Hwang, William J. Schaff, Lester F. Eastman, Shawn T. Bradley, Leonard J. Brillson, David C. Look, J. Wu, Wladek Walukiewicz, Madalina Furis, Alexander N. Cartwright

Physics Faculty Publications

Very high levels of n-type doping of AlxGa1−xN alloys were recently achieved by rf plasma-induced molecular-beam epitaxy on sapphire substrates and Si as a dopant. Electron concentrations were obtained up to 1.25×1020 cm−3 when the Al mole fraction was 50%, and 8.5×1019 cm−3 electrons were measured even when the Al mole fraction was 80%. Other material properties were determined by optical absorption, photoluminescence, cathodoluminescence, x-ray diffraction, and atomic force microscopy measurements and high optical and morphological qualities were shown.

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Recombination Of Excitons Bound To Oxygen And Silicon Donors In Freestanding Gan, A. Wysmolek, K. P. Korona, R. Stepniewski, J. M. Baranowsky, J. Bloniarz, M. Potemski, R. L. Jones, David C. Look, J. Kuhl, S. S. Park, S. K. Lee Dec 2002

Recombination Of Excitons Bound To Oxygen And Silicon Donors In Freestanding Gan, A. Wysmolek, K. P. Korona, R. Stepniewski, J. M. Baranowsky, J. Bloniarz, M. Potemski, R. L. Jones, David C. Look, J. Kuhl, S. S. Park, S. K. Lee

Physics Faculty Publications

The neutral donor bound exciton recombination processes in freestanding GaN have been studied. The photoluminescence spectrum shows emission lines related to silicon and oxygen donors. Time-resolved luminescence allows us to correlate the principal donor bound exciton lines with their two-electron satellites. The magnetic field splitting of the two-electron lines is well described by the theory of the hydrogen atom in a magnetic field. For the oxygen donor a 1.5 meV chemical shift and a 30.8 meV effective Rydberg have been evaluated. Two-electron satellites involving excitations to the 2p and 2s donor states are separated by an energy of 1.0 and …

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Microcathodoluminescence And Electron Beam Induced Current Observation Of Dislocations In Freestanding Thick N-Gan Sample Grown By Hydride Vapor Phase Epitaxy, A. Y. Polyakov, A. V. Govorkov, N. B. Smirnov, Z-Q. Fang, David C. Look, Seong-Ju S. Park, J. H. Han Nov 2002

Microcathodoluminescence And Electron Beam Induced Current Observation Of Dislocations In Freestanding Thick N-Gan Sample Grown By Hydride Vapor Phase Epitaxy, A. Y. Polyakov, A. V. Govorkov, N. B. Smirnov, Z-Q. Fang, David C. Look, Seong-Ju S. Park, J. H. Han

Physics Faculty Publications

Microcathodolumunescence (MCL) spectra measurements, MCL and electron beam induced current (EBIC) imaging of the freestanding n-GaN samples grown by hydride vapor phase epitaxy were made. Dark-spot defects in plan-view EBIC and MCL images and dark line defects in MCL images taken on the cleaved surface of the samples could be associated with dislocations. MCL spectra measurements in the vicinity of dislocations and in the matrix do not reveal specific luminescence bands that could be attributed to dislocations but rather suggest that dislocation regions have higher density of deep nonradiative traps.

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Deep Electron And Hole Traps In Freestanding N-Gan Grown By Hydride Vapor Phase Epitaxy, A. Y. Polyakov, N. B. Smirnov, A. V. Govorkov, Z-Q. Fang, David C. Look, Seong-Ju S. Park, J. H. Han Nov 2002

Deep Electron And Hole Traps In Freestanding N-Gan Grown By Hydride Vapor Phase Epitaxy, A. Y. Polyakov, N. B. Smirnov, A. V. Govorkov, Z-Q. Fang, David C. Look, Seong-Ju S. Park, J. H. Han

Physics Faculty Publications

Deep level electron and hole traps were studied by means of deep level transient spectroscopy with electrical and optical injection on a freestanding thick n-GaN sample with low dislocation density. It is shown that at both the upper and the lower surface of the sample there exists a thin, ∼0.5 μm layer of damaged material with lowered concentration of electrons and enhanced density of deep centers. Deep in the bulk of the film the densities of the majority of the electron and hole traps are shown to be very low, but measurably higher on the lower face (N face), …

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Thermoelectric Effect Spectroscopy Of Deep Levels In Semi-Insulating Gan, U. V. Desnica, M. Pavlovic, Z-Q. Fang, David C. Look Oct 2002

Thermoelectric Effect Spectroscopy Of Deep Levels In Semi-Insulating Gan, U. V. Desnica, M. Pavlovic, Z-Q. Fang, David C. Look

Physics Faculty Publications

The report of thermoelectric effect spectroscopy (TEES) applied on semi-insulating GaN was presented. The type of TEES setup, especially suitable for film-on-substrate samples, was devised. TEES enabled determination of sign of observed deep traps. Using TEES and thermally stimulated current spectroscopy measurements in combination with the simultaneous multiple peak analysis formalism all important trap parameters were determined. The shallowest identified electron and hole traps had activation energies Ec−0.09 eV and Ev+0.167 eV, respectively. Results indicate that both these traps, oppositely charged are present in the studied material in relatively high concentrations causing the electrical compensation and …

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Characterization Of Homoepitaxial P-Type Zno Grown By Molecular Beam Epitaxy, David C. Look, D. C. Reynolds, C. W. Litton, R. L. Jones, D. B. Eason, G. Cantwell Sep 2002

Characterization Of Homoepitaxial P-Type Zno Grown By Molecular Beam Epitaxy, David C. Look, D. C. Reynolds, C. W. Litton, R. L. Jones, D. B. Eason, G. Cantwell

Physics Faculty Publications

An N-doped, p-type ZnO layer has been grown by molecular beam epitaxy on an Li-diffused, bulk, semi-insulating ZnO substrate. Hall-effect and conductivity measurements on the layer give: resistivity = 4×101 Ω cm; hole mobility = 2 cm2/V s; and hole concentration = 9×1016 cm−3. Photoluminescence measurements in this N-doped layer show a much stronger peak near 3.32 eV (probably due to neutral acceptor bound excitons), than at 3.36 eV (neutral donor bound excitons), whereas the opposite is true in undoped ZnO. Calibrated, secondary-ion mass spectroscopy measurements show an N surface concentration of about …

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Representation Of A Quantum Ensemble As A Minimal Set Of Pure States, Thomas E. Skinner, Steffen J. Glaser Sep 2002

Representation Of A Quantum Ensemble As A Minimal Set Of Pure States, Thomas E. Skinner, Steffen J. Glaser

Physics Faculty Publications

The density matrix ρ for an n-level system is decomposed into the minimum number of pure states necessary to calculate physical observables. The corresponding physical system is first represented by a set B of n pure states |βi〉, together with their statistical weights. The time evolution of the system is therefore calculated as B(t)=UB(t0), with the propagator U operating on each member of the set, in contrast to the more laborious ρ(t)=Uρ(t0)U†. At least one of the states can be eliminated from the set by reducing its weight to zero via a …

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Deep Hole Traps In N-Gan Films Grown By Hydride Vapor Phase Epitaxy, A. Y. Polyakov, N. B. Smirnov, A. V. Govorkov, Z-Q. Fang, David C. Look, Richard J. Molnar, A. V. Osinsky May 2002

Deep Hole Traps In N-Gan Films Grown By Hydride Vapor Phase Epitaxy, A. Y. Polyakov, N. B. Smirnov, A. V. Govorkov, Z-Q. Fang, David C. Look, Richard J. Molnar, A. V. Osinsky

Physics Faculty Publications

Concentrations of deep hole traps were measured in a set of hydride vapor phase epitaxy grown samples with thicknesses varying from 2.6 to 68 μm. Results were obtained from low temperature capacitance–voltage measurements before and after illumination and from deep level transient spectroscopy measurements with optical injection (ODLTS). The former revealed the presence of high densities (∼1015 to 1016 cm−3) of hole traps whose concentration decreased with sample thickness in a manner similar to that found for the dislocation density. Capacitance versus temperature measurements in the dark and after illumination suggested that these traps form a …

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Depth-Dependent Investigation Of Defects And Impurity Doping In Gan/Sapphire Using Scanning Electron Microscopy And Cathodoluminescence Spectroscopy, X. L. Sun, S. H. Goss, L. J. Brillson, David C. Look, Richard J. Molnar May 2002

Depth-Dependent Investigation Of Defects And Impurity Doping In Gan/Sapphire Using Scanning Electron Microscopy And Cathodoluminescence Spectroscopy, X. L. Sun, S. H. Goss, L. J. Brillson, David C. Look, Richard J. Molnar

Physics Faculty Publications

Cathodoluminescence (CL) imaging and temperature-dependent cathodoluminescence spectroscopy (CLS) have been used 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 imaging, CLS, and CL imaging show systematic variations in defect emissions with 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 out-diffusion from Al2O3 into GaN over hundreds of nanometers. Low-temperature CL spectra exhibit a new donor level …

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Production Of Nitrogen Acceptors In Zno By Thermal Annealing, N. Y. Garces, N. C. Giles, L. E. Halliburton, G. Cantwell, D. B. Eason, D. C. Reynolds, David C. Look Feb 2002

Production Of Nitrogen Acceptors In Zno By Thermal Annealing, N. Y. Garces, N. C. Giles, L. E. Halliburton, G. Cantwell, D. B. Eason, D. C. Reynolds, David C. Look

Physics Faculty Publications

Nitrogen acceptors are formed when undoped single crystals of zinc oxide (ZnO) grown by the chemical-vapor transport method are annealed in air or nitrogen atmosphere at temperatures between 600 and 900 °C. After an anneal, an induced near-edge absorption band causes the crystals to appear yellow. Also, the concentration of neutral shallow donors, as monitored by electron paramagnetic resonance (EPR), is significantly reduced. A photoinduced EPR signal due to neutral nitrogen acceptors is observed when the annealed crystals are exposed to laser light (e.g., 364, 442, 458, or 514 nm) at low temperature. The nitrogens are initially in the nonparamagnetic …

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Electrical Characterization Of Vapor-Phase-Grown Single-Crystal Zno, F. D. Auret, S. A. Goodman, M. J. Legodi, W. E. Meyer, David C. Look Feb 2002

Electrical Characterization Of Vapor-Phase-Grown Single-Crystal Zno, F. D. Auret, S. A. Goodman, M. J. Legodi, W. E. Meyer, David C. Look

Physics Faculty Publications

Gold Schottky-barrier diodes (SBDs) were fabricated on vapor-phase-grown single-crystal ZnO. Deep-level transient spectroscopy, using these SBDs, revealed the presence of four electron traps, the major two having levels at 0.12 eV and 0.57 below the conduction band. Comparison with temperature-dependent Hall measurements suggests that the 0.12 eV level has a temperature activated capture cross section with a capture barrier of about 0.06 eV and that it may significantly contribute to the free-carrier density. Based on the concentrations of defects other than this shallow donor, we conclude that the quality of the vapor-phase-grown ZnO studied here supercedes that of other single-crystal …

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Donor And Acceptor Concentrations In Degenerate Inn, David C. Look, H. Lu, William J. Schaff, J. Jasinski, Z. Liliental-Weber Jan 2002

Donor And Acceptor Concentrations In Degenerate Inn, David C. Look, H. Lu, William J. Schaff, J. Jasinski, Z. Liliental-Weber

Physics Faculty Publications

A formalism is presented to determine donor (ND) and acceptor (NA) concentrations in wurtzitic InN characterized by degenerate carrier concentration (n) and mobility (μ). The theory includes scattering not only by charged point defects and impurities, but also by charged threading dislocations, of concentration Ndis. For a 0.45-μm-thick InN layer grown on Al2O3 by molecular beam epitaxy, having Ndis = 5×1010 cm−2, determined by transmission electron microscopy, n(20 K) = 3.5×1018 cm−3 and μ(20 K) = 1055 cm2 …

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High Spatial Resolution Thermal Conductivity Of Bulk Zno (0001), Diana I. Florescu, L. G. Mourokh, Fred H. Pollak, David C. Look, G. Cantwell, X. Li Jan 2002

High Spatial Resolution Thermal Conductivity Of Bulk Zno (0001), Diana I. Florescu, L. G. Mourokh, Fred H. Pollak, David C. Look, G. Cantwell, X. Li

Physics Faculty Publications

We measured high spatial/depth resolution 300 K thermal conductivity κ of the Zn and O surfaces of two bulk n-type ZnO (0001) samples, grown by a vapor-phase transport method, using scanning thermal microscopy (SThM). The thermal investigation was performed in both point-by-point (∼2 μm resolution) and area-scan modes. On the first sample κ=1.16±0.08 (Zn face)/1.10±0.09 (O face) W/cm K while for the second material κ=1.02±0.07 (Zn face)/0.98±0.08 (O face) W/cm K. These are the highest κ values reported on ZnO. A correlation between SThM area-scan readings and surface topography was established by simultaneously performing atomic force microscopy scans. The …

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Polariton And Free-Exciton-Like Photoluminescence In Zno, D. C. Reynolds, David C. Look, B. Jogai, T. C. Collins Dec 2001

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.

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Thermal Stability Of Isolated And Complexed Ga Vacancies In Gan Bulk Crystals, K. Saarinen, T. Suski, I. Grzegory, David C. Look Nov 2001

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.

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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 Nov 2001

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 …

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Hot Carbon Densities In The Exosphere Of Mars, Andrew F. Nagy, Michael W. Liemohn, Jane L. Fox, Jhoon Kim Oct 2001

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 …

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Photochemical Escape Of Atomic Carbon From Mars, Jane L. Fox, F. M. Bakalian Oct 2001

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 …

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Solar Activity Variations Of The Venus Thermosphere/Ionosphere, Jane L. Fox, K. Y. Sung Oct 2001

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 …

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Predicted Maximum Mobility In Bulk Gan, David C. Look, J. R. Sizelove Aug 2001

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 …

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Characterization Of Near-Surface Traps In Semiconductors: Gan, David C. Look, Z-Q. Fang Jul 2001

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 …

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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 Jun 2001

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.

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Fine Structure On The Green Band In Zno, D. C. Reynolds, David C. Look, B. Jogai Jun 2001

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.

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Evidence For Shallow Acceptors In Gan, D. C. Reynolds, David C. Look, B. Jogai, Richard J. Molnar Jun 2001

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.

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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 Apr 2001

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 …

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