bluuebunny/crossref_metadata_2025 huggingface dataset:
Breakdown Behavior of Aigan Msm uv Photodetectors
Authors: Liang S. , Liu Y. , Lu Y. , Schurman M. , Tran C. A. , Ferguson I.
Published: April 2011

GaN is an attractive wide bandgap semiconductor material for optoelectronic device applications at blue and UV wavelengths. The breakdown behavior of interdigital MSM type of AlGaN UV photodetectors (PDs) are reported here. The A1GaN was deposited using MOCVD technique. The MSM devices were fabricated using undoped AlGaN (Al composition is 0.13) epitaxial layer on sapphire substrate. Au/Ti metallization was patterned as metal electrodes on AlGaN. Very high UV responsivity of the devices was achieved at DC bias voltage in the range of 60–140V depending on the device dimensions. The breakdown voltage exhibits a negative temperature coefficient. The relationship between the breakdown voltage and device dimensions has been investigated using both of I-V, C-V characteristics. It has been found that annealing of the contact modifies the device characteristics, in particular, the breakdown behaviors.
Wide Gan Stripes by Lateral Growth in Metalorganic Vapor Phase Epitaxy
Authors: Kimura A. , Sasaoka C. , Sakai A. , Usui A.
Published: April 2011

We investigated the growth conditions for enhancing epitaxial lateral overgrowth (ELO) of GaN stripes selectively grown by low-pressure metalorganic vapor phase epitaxy. The ELO was enhanced for GaN <1100> stripes and with a small trimethylgallium flow-rate. This tendency did not depend on mask materials. The cross-sectional shape of the GaN <1100> stripes was trapezoidal for SiO2 masks, and rectangular for silicon nitride (SiN2) masks in a certain growth condition. A low dislocation density in the ELO region was obtained not only for the SiO2 masks but also for the SiN2 masks.
Application of Blue Diode Lasers to Printing
Authors: Bringans R. D.
Published: April 2011

The availability of blue diode lasers would have a significant impact on several printing applications. The laser printing market is moving towards higher resolutions and higher print speeds. The optical systems for polygon scanner laser printers are diffraction limited and therefore to improve the optical resolution it is very advantageous to reduce the wavelength of the scanning laser beam from that of the IR or red lasers currently being used. The other printing application of blue lasers is exposure of film, an area where argon ion lasers are currently being used. Replacement of these by diode lasers would potentially lower system costs. In this paper, the applications of blue lasers to printing will be outlined and the technical requirements that the lasers will need to satisfy will be discussed.
MOVPE Growth of GaPAsN Quaternary Alloys Lattice-Matched to GaP
Authors: Biwa Goshi , Yaguchi Hiroyuki , Onabe Kentaro , Shiraki Yasuhiro
Published: April 2011

GaP1-x-yAsyNx. (x ∼,2.3%, 0< y <19%) quaternary alloy semiconductor films on GaP substrates have been successfully grown by metalorganic vapor phase epitaxy (MOVPE). With the fixed supplies of trimethylgallium(TMG), AsH3 and dimethylhydrazine(DMHy) during the growth, the As concentration in the solid increased with increasing AsH3 supply, while the N concentration was almost unaffected. It has been demonstrated that the crystalline quality of the alloy films is much improved with the close lattice-matching to the GaP substrate, giving a superior surface morphology without any cross-hatches, a much narrower x-ray diffraction linewidth, and a significantly higher photoluminescence(PL) intensity.
Si and Mg Doped Gan Layers Grown by Gas Source Molecular Beam Epitaxy Using Ammonia
Authors: Grandjean N. , Massies J. , Leroux M.
Published: April 2011

The growth of GaN layers was carried out on c-plane sapphire substrates by molecular beam epitaxy (MBE) using NH3. Undoped GaN layers were grown at 830°C with growth rates larger than 1 μm/h. Optical properties are characteristics of high quality GaN material and the linewidth of x-ray diffraction (0002) rocking curve is less than 350 arcsec. N- and p-type doping were achieved by using solid sources of Si and Mg. No post-growth annealing was needed to activate the Mg acceptors. As-grown GaN:Mg layers exhibit hole concentrations of 3×1017 cm−3and mobilities of 8 cm2/Vs at 300 K. Light emitting diodes (LEDs) based on GaN p-n homojunction have been processed. The turn on voltage is 3 V and the forward voltage is 3.7 V at 20 mA. The 300 K electroluminescence (EL) peaks at 390 nm.
Effect Of Atomic-Hydrogen Treatment Of (001) Gaas Substrate At “High Temperatures” On Rf Plasma-Assisted Molecular Beam Epitaxy Of Cubic Gan
Authors: Yoshikawah A. , Nagano H. , Qiny Z. X. , Sugure Y. , Jia A. W. , Kobayashi M. , Shimotomai M. , Kato Y. , Takahashi K.
Published: April 2011

Abstracts

Growth of high quality c-GaN on atomic-H treated (001) GaAs was examined by rf plasma-assisted MBE. First the initial growth stages (atomic-H treatment of GaAs, nitridation/deposition of a thin GaN buffer layer, the post deposition annealing of the buffer layer, and epitaxy of c-GaN) were studied by RHEED and AFM observations. It was found that atomically flat GaAs surface with one monolayer-height steps and ragged step edges could be obtained by the atomic-H treatment at high temperatures. It was found that the atomic-H treated GaAs surface was preferable to grow high quality c-GaN; the FWHM of the X-ray rocking curve for the (002) c-GaN was as small as 70 – 90 arcsec.
GaN PN-Structures Grown by Hydride Vapor Phase Epitaxy
Authors: Nikolaev A. E. , Melnik YU. V. , Kuznetsov N. I. , Strelchuk A. M. , Kovarsky A. P. , Vassilevski K. V. , Dmitriev V. A.
Published: April 2011

For the first time, GaN pn-junctions were fabricated by hydride vapor phase epitaxy. GaN pn-structures were grown directly on 6H-SiC substrates without any buffer layer. Undoped GaN layers were n-type with Nd-Naconcentration ranged from 1×1017to 5×1018cm−3. Magnesium was used as an acceptor to grow p-type GaN layers. Mg atomic concentration determined by secondary ion mass spectroscopy ranged from 5×1019to 5×1020cm−3. As-grown GaN layers doped with Mg were p-type, and p-type conductivity was improved by post-growth anneal. Mesa diodes with a vertical current flow geometry were formed by reactive ion etching. The position of the GaN pn-junction was determined by the electron beam induced current method. The electrical characteristics of the pn diodes were studied. Electroluminescence from the pn diodes was measured.
Homoepitaxial Growth of GaN Using Seeded Supersonic Molecular Beams
Authors: Chen E. , Zhang S. , Michel A. , Davis R. F. , Lamb H. H.
Published: April 2011

Homoepitaxial growth of GaN on MOCVD-grown GaN/AlN/6H-SiC substrates was investigated using NH3-seeded supersonic molecular beams and an effusive Ga source. Ga-limited growth is observed at 730 and 770°C for incident Ga fluxes ≤ 1.2×1015 cm−2 s−1 using a 0.25 eV NH3 beam. A Ga incorporation efficiency of 20–25% is observed under these conditions. Increasing NH3 kinetic energy in the 0.25 to 0.61 eV range results in a modest increase in the GaN growth rate which we ascribe to an enhancement in NH3 reactivity. A concomitant increase in surface roughness is observed with increasing GaN growth rate.
Pulsed Laser Deposition of Highly Crystalline Gan Films on Sapphire
Authors: Vispute R. D. , Talyansky V. , Chupoon S. , Enck R. , Dahmas T. , Ogale S. B. , Sharma R. P. , Venkatesan T. , Li Y. X. , Salamanca-Riba L. G. , Iliadis A. A. , He M. , Tang X. , Halpern J. B. , Spencer M. G. , Khan M. A. , Jones K. A. , Bel'kov V. , Botnaryuk V. , Diakonu I. , Fedorov L. , Zhilyaev Y.
Published: April 2011

We report high quality epitaxial growth of GaN film by pulsed laser deposition technique. In this method, a KrF pulsed excimer laser was used for ablation of a polycrystalline, stoichiometric GaN target. The ablated material was deposited on a substrate kept at a distance of ∼ 7 cm from the target surface and in an NH3 background pressure of 10−5 Torr and temperature of 750°C. The films (∼0.5 μm thick) grown on AIN buffered sapphire showed a x-ray diffraction rocking curve FWHM of 4–6 arc minutes. The ion channeling minimum yield in the surface region was ∼3% indicating a high degree of crystallinity. The optical band gap was found to be 3.4 eV. The epitaxial films were shiny, and the surface RMS roughness was ∼ 5–15 nm. The electrical resistivity of these films was in the range of 10−2–102 Ω-cm with a mobility in excess of 60 cm2V-1s−1 and carrier concentration of 1017–1019cm−3.
Lateral Epitaxy Formation Mechanism And Microstructure Of Selectively Grown Gan Structures
Authors: Zheleva Tsvetanka , Nam Ok-Hyun , Griffin Jason D. , Bremser Michael D. , Davis Robert F.
Published: April 2011

The microstructure and the lateral epitaxy mechanism of formation of homoepitaxially and selectively grown GaN structures within windows in SiO2 masks have been investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Three types of samples and each of their microstructures as a function of the geometry of the mask pattern and the selective growth parameters have been studied: GaN pyramids, GaN stripes oriented along [1100] and [1120] directions, and GaN continuous layers. Observations via TEM showed in all three types of samples that the laterally overgrown GaN exhibit four-to-six orders of magnitude reduction in the dislocation density compared to the vertically grown GaN films. Owing to the lateral epitaxy, the threading dislocations bend when the growth front changes from vertical to lateral, thus changing their character from being mostly threading dislocations of mixed or edge character, to being basal plane dislocations with lines parallel to the interfacial planes. The underlying GaN provided the crystallographic template for the initial vertical selective growth through the openings (windows) in the SiO2 mask. The GaN structures in these areas had a threading dislocations density of 108-1010 cm−2. Lateral growth of the GaN films over the amorphous SiO2 mask, resulted in a reduction of the dislocation density to <106 cm−2. The primary materials source for both the vertical and lateral growth of the structures was the vapor phase. Essentially no GaN deposited on the SiO2 because of the very low sticking coefficients of Ga and N species on SiO2. Thermal stress relaxation is responsible for the final morphology and microstructure in these selectively grown structures.
Crystal Defects In Gan On (0001) Sapphire
Authors: Johnson Matthew T. , Mao Zhigang , Carter C. Barry
Published: April 2011

Defect structures in GaN thin films grown on (0001) sapphire have been studied using a combination of different transmission electron microscopy (TEM) techniques. Two fundamentally different types of defects are found in these films. Planar defects which lie on planes perpendicular to the growth surface are common. In some regions of the films, other planar defects are present which run parallel to the surface of the substrate. The terminology used to describe these different defects varies quite widely in the literature and includes combinations of antiphase (inversion) domain boundaries and stacking faults. The second type of defect is generally referred to as a threading dislocation since many thread through the whole thickness of the film. Dislocations with different Burgers vectors have been identified in this work and in previous studies; these dislocations usually have a component of their Burgers vector lying normal to the (0001) plane. The overall defect structures in these films have been characterized using conventional bright-field and dark-field imaging. The detailed structure of the individual defects have been examined using weak-beam microscopy both in plan view and in cross section. This paper illustrates the different types of defects, both planar and linear, compares them to defects which have been characterized more thoroughly in related materials, and discuss the nomenclature of the different defect configurations.
Transmission Electron Microscopy Study of Room Temperature Lasing Epitaxial ZnO Films on Sapphire
Authors: Wang N. , Fung K. K. , Yu P. , Tang Z. K. , Wong G. K. L. , Kawasaki M. , Ohtomo A. , Koinuma H. , Segawa Y.
Published: April 2011

We have studied the microstructures of lasing and non-lasing ZnO films on sapphire in plan-view and cross-section by transmission electron microscopy (TEM). While ZnO films in general are made up of cloumnar close-packed c-axis misoriented nanocrystals, the misorientation in nonlasing film, typically 5°, is considerably larger than lasing film, typically less than 1°. A rather high density of pinholes or nanotubes is associated with the highly misoriented films. The misorientation between adjacent grains is taken up by grain boundary dislocations. Room temperature lasing films contain a high density of threading boundary edge dislocations, in excess of 1010 cm−2. But faceting in the columnar nanocrystals is not well developed so that the grain boundaries are not clearly visible. Tilting of (0001) lattice planes between grains originating from substrate surface step and growth fault step, however, has been observed in high resolution electron microscopy (HREM) images.
Amorphous Domains in GaN Layers Grown on 6H-SiC by MBE
Authors: Vermaut P. , Potin V. , Ruterana P. , Hairme A. , Nouet G. , Salvador A. , Morkoç H.
Published: April 2011

Using N-rich growth conditions, amorphous domains were formed in the initial stage of a cyclotron assisted MBE of GaN grown over 6H-SiC (0001) without any buffer layer. These domains are facetted along {1010} prismatic planes. Their density is about 1010cm-2 and they are mainly located in a 50 nm layer close to the substrate surface.
Low-Angle and High-Angle Grain Boundaries in AIN/GaN Layers Grown on (0001) Sapphire by MBE
Authors: Potin V. , Ruterana P. , Hairie A. , Nouet G.
Published: April 2011

AIN buffer and GaN layers grown on (0001) sapphire substrate by molecular beam epitaxy have been analysed by high resolution electron microscopy. They are found to be made of mosaic grains rotated around the c-axis by angles in the range of 0-20°. According to the value of the rotation angle, these boundaries can be classified as low-angle and high-angle grain boundaries. Some of these high-angle grain boundaries correspond to special misorientations which can be described in terms of coincidence site lattice. For one of these grains, the rotated angle is equal to 18.94° that is very close to the coincidence orientation, sigma = 31 with a rotation angle equal to 17.89°. This leads to a new epitaxial relationship (0001)sap// (0001)AIN and [1120]sap//[2130]AIN.
Tem Study of Interfaces And Defects in Mocvd-Grown Gan on Sic on Simox
Authors: Zhou W. L. , Pirouz P. , Namavar F. , Colter P. C. , Yoganathan M. , Leksono M. W. , Pankove J. I.
Published: April 2011

SiC was grown on the top Si layer of SIMOX by carbonization followed by chemical vapor deposition (CVD). Subsequently, GaN was deposited on the SiC by metalorganic (MO)CVD to produce a GaN/SiC/Si/SiO2/Si multilayer structure. This multilayer film was investigated by conventional transmission electron microscopy (TEM) and high resolution (HR)TEM using cross-sectional thin foils. The GaN layer was found to consist of predominately hexagonal gallium nitride (h-GaN), and a smaller fraction of cubic GaN (c-GaN) crystallites. The orientation relationship between most of the h-GaN grains and cubic SiC (3C-SiC) was found to be (0001)GaN//(1I1)sic; [1120]GaN//[110]SiC, while most of the c-GaN grains had an orientation relationship (001)GaN//(001)SiC; [110]GaN//[110]SiC with respect to the 3C-SiC substrate. The hexagonal grains of GaN were found to grow as two variants. In this paper, the defects in both h-GaN and c-GaN are characterized and discussed.
Effect of Nitridation and Buffer in GaN Films Grown on A-Plane (11-20) Sapphire
Authors: Doppalapudi D. , Iliopoulos E. , Basu S. N. , Moustakas T. D.
Published: April 2011

In this paper, we report on a systematic study of GaN growth on the A-plane sapphire by plasma-assisted MBE. The effects of plasma nitridation of the substrate and the growth of a low temperature GaN buffer on the structure and optoelectronic properties of the films are addressed. TEM studies indicate that films grown on substrates which were not nitridated prior to growth have a significant fraction of zinc-blende domains and poor orientational relation with the substrate. On the contrary, nitridation leads to films with superior structural and optoelectronic properties. The low temperature GaN buffer, grown on nitridated substrates, was found to also have a pronounced effect on the optoelectronic properties of the GaN films, especially in those with low carrier concentrations. The correlation between TEM and photoluminescence studies suggest that the transition at 3.27 eV can be attributed to the cubic domains in the films.
Magnetoluminescence and Resonant Electronic Raman Scattering Investigation of Donors and Excitons in Hydride Vpe and Mocvd GaN
Authors: Skromme B. J. , Jayapalan J. , Wang D. , Sankey O. F.
Published: April 2011

The donor and exciton states in ultra high-quality heteroepitaxial GaN grown by hydride vapor phase epitaxy (HVPE) and metalorganic chemical vapor deposition (MOCVD) on sapphire substrates are investigated using low temperature photoluminescence (PL), reflectance, magnetospectroscopy in fields up to 12 T, and resonant electronic Raman scattering (RERS). The A free exciton is confirmed to have a binding energy of about 26.4 meV, independent of strain in the material. Bound n=2 exciton peaks are distinguished in the PL spectrum by their thermalization and sample dependence. The Si donor is shown to have a binding energy of about 21 meV using Si-doped HVPE samples grown at Epitronics. Up to five additional residual donor species are observed when comparing various HVPE and MOCVD samples. Pronounced temperaturedependence of the two-electron satellites is observed, suggesting the existence of unresolved excited rotator states of the neutral donor-bound exciton. Highly resolved magnetic splitting patterns are observed in the two-electron satellites. A nonperturbative theory of these donor splittings is developed, including anisotropy. Resonant electronic Raman scattering from residual donors is reported, and yields improved linewidths compared to PL.
Characterization Of Bulk, Polycrystalline Indium Nitride Grown At Sub-Atmospheric Pressures
Authors: Dycka Jeffrey S. , Kash Kathleen , Kim Kwiseon , Lambrecht Walter R. L , Hayman Cliff C. , Argoitia Alberto , Grossner Michael T. , Zhouc Weilie L. , Angus John C.
Published: April 2011

Polycrystalline, wurtzitic indium nitride was synthesized by saturating indium metal with atomic nitrogen from a microwave plasma source. Plasma synthesis avoids the high equilibrium pressures required when molecular nitrogen is used as the nitrogen source. Two types of growth were observed: 1) small amounts of indium nitride crystallized from the melt during cooling and 2) hexagonal platelets formed adjacent to the In metal source on the crucible sides. The mechanism of this latter growth is not established, but may involve transport of indium as a liquid film. The crystals were characterized by electron diffraction, X-ray diffraction, elemental analysis, scanning electron microscopy, and Raman spectroscopy. Lattice parameter and Raman active phonon modes are reported and compared with calculations based on the full-potential linear muffin-tin orbital method (FP-LMTO).
GaN Room Temperature exciton Spectra by Photovoltaic Measurement
Authors: Liu W. , Li M. F. , Chua S. J. , Zhang Y. H. , Uchida K.
Published: April 2011

Exciton absorption peak has been clearly observed at room temperature by photovoltaic spectra, on a GaN layer grown on (0001)-plane Sapphire by metalorganic chemical vapor deposition. From the spectra, we obtained A and B exciton transition energies to be 3.401 eV, 3.408 eV, and the energy gap to be 3.426 eV in wurztite GaN, respectively. We have also performed photovoltaic measurements with various incidence angles of light, and observed the polarization behavior of exciton absorption in GaN. Finally, we used UV-polarizer to further confirm the polarization properties of GaN. In conjuction with previous room temperature photoreflectance measurements, this work provide direct and reliable assessment of the excitonic properties and crystal quality of GaN semiconductor layers.
Photoluminescence Properties Of Gan/AlGaN Multiple Quantum Well Microdisks
Authors: Mair R. A. , Zeng K. C. , Lin J. Y. , Jiang H. X. , Zhang B. , Dai L. , Tang H. , Botchkarev A. , Kim W. , Morkoc H.
Published: April 2011

An array of microdisks with diameter of about 9 μm and spacing of 50 μm has been fabricated by dry etching from a 50 Å/50 Å GaN/AlxGa1-xN (x∼ 0.07) multiple quantum well (MQW) structure grown by reactive molecular beam epitaxy. The as-grown MQWs and the microdisk structures have been studied by picosecond time-resolved photoluminescence (PL) spectroscopy. PL emission spectra and decay dynamics were measured at various temperatures and pump intensities. With respect to the original MQWs, we observe strong enhancement of the transition intensity and lifetime for both the intrinsic and barrier transitions. The intrinsic transition is excitonic at low temperatures and exhibits an approximate 10 fold increase in both lifetime and PL intensity upon formation of the microdisks. The exciton transition magnitude diminishes rapidly with increased temperature however, while the enhanced lifetime shows little change. At room temperature the dominant GaN well transition is found to be band-to-band in nature as evidenced by effective band gap shrinkage and band-filling effects seen within the PL spectrum. The implications of our results to III-Nitride microdisk lasers are discussed.
Isoelectronic Trap Like Luminescence Centers Of Ingan
Authors: Kanie H. , Koami H. , Kawano T. , Totsuka T.
Published: April 2011

This paper describes the characteristics of the luminescence centers observed in the various photoluminescence (PL) and photoluminescence excitation (PLE) spectra of hexagonal InxGa1−xN microcrystals, synthesized by the nitridation of sulfide in the In concentration range of 2%<x<6%. The grown crystals showed macroscopic and microscopic inhomogeneity. A series of component bands expressed by Gaussian functions with discrete peak energies selected from the frequently observed peaks in the PL spectra and full width at half maximum obtained from the narrowest PL bands were fitted well to observed broad emission bands. As some of the peak energies of the component bands coincide with those of the bands that are attributed to the decay of excitons at the localized states caused by the In content fluctuation in the literature, we concluded the luminescence center for the component bands also originates from the fluctuation of the In contents. Although the In contents of the samples determined by the X ray diffraction method were compatible the gap energies from the PLE measurements were different. The PLE spectra showed that the Stokes shifts were large and the gap energies were irrelevant to the emission band peaks. The excitation bands for the emission bands in the range of 2.8 to 2.48 eV were located at 3.36, 3.26, and 3.21 eV. These results indicate that the states of the luminescence center are localized and the energy levels are discrete. To obtain the microscopic structure of the localized states in InxGa1−xN, we propose the isoelectronic atom cluster model comparable with Te clusters in ZnSeTe.
Ingan Quantum Dots Fabricated On Aigan Surfaces -Growth Mechanism And Optical Propertiesh-
Authors: Hirayama H. , Tanaka S. , Ramvall P. , Aoyagi Y.
Published: April 2011

We demonstrate photoluminescence from self- assembling InGaN quantum dots (QDs), which are artificially fabricated on AlGaN surfaces via metal- organic chemical vapor deposition. InGaN QDs are successfully fabricated by the growth mode transition from step- flow to three dimensional island formation by using anti-surfactant silicon on AlGaN surface. The diameter and height of the fabricated InGaN QDs are estimated to be ˜10nm and ˜5nm, respectively, by an atomic- force- microscope (AFM). Indium mole fraction of InxGal−x N QDs is controlled from x=˜0.22 to ˜0.52 by varying the growth temperature of QDs. Intense photoluminescence is observed even at room temperature from InGaN QDs embedded with the GaN capping layers. In addition, the temperature- dependent energy shift of the photoluminescence peak- energy shows a localization behavior.
Elemental Analysis On Group-Hi Nitrides Using Heavy Ion Erd
Authors: Dollinger G. , Karsch S. , Ambacher O. , Angerer H. , Bergmaier A. , Schmelmer O. , Stutzmann M.
Published: April 2011

Elastic recoil detection (ERD) using energetic heavy ion beams (e.g. 170 MeV 127I) is a suitable method to measure depth profiles of light and medium heavy elements in thin films. The main advantages of ERD, which makes it favorable over many other techniques for elemental analysis, is the possibility to obtain reliable and quantitative results, a sensitivity in the ppm region or a depth resolution even better than 1 nm.

ERD analysis was employed to obtain quantitative information about the aluminium content x in MBE grown AlxGa1−xN layers on Al2O3 substrates. Using this stoichiometry information and the lattice constants obtained from high resolution X-ray diffraction, Vegard's law could be confirmed with high accuracy. Secondly, nitridation of heated Al2O3 substrates in NH3 atmosphere was investigated using high resolution ERD. A substantial nitrogen content on the surface of the substrate was detected which means a nearly complete AIN layer grown on the Al2O3 surface by a heat treatment only. Such a nitridation layer can be the base for further growth of nitrides on Al2O3 surfaces. As a third, the impurity content of group III nitrides was investigated in dependence on deposition conditions for both, MBE and MOCVD grown samples. In all samples investigated an oxygen concentration larger than 100 ppm was detected which is much higher than the intrinsic charge carrier density of these samples. In addition it is shown that the efficiency of p-doping by Mg may not only be hindered by hydrogen but also by carbon impurities.
Direct Observations Of Atomic Structures Of Defects In Gan By High Resolution Z-Contrast Stem
Authors: Xin Y. , Pennycook S.J. , Browning N.D. , Nellist P. D. , Sivananthan S. , Beaumont B. , Fauriel J-P , Gibart P.
Published: April 2011

GaN/(0001)Sapphire grown by low pressure MOVPE is studied by high resolution Z-contrast imaging using STEM. First direct observation of the threading dislocation with edge character shows the atomic core structure, which appears to have a similar configuration to the {10–10} surface. The surfaces of the nanopipe walls are on {10–10} with the terminating layer between the atoms with one bond per pair. In addition, the high resolution Z-contrast image of the prismatic stacking fault confirms the results by conventional HRTEM.
Monte Carlo Calculation Of High- And Low-Field AlxGa1−xN Electron Transport Characteristics
Authors: Albrecht J.D. , Wang R. , Ruden P.P. , Farahmand M. , Bellotti E. , Brennan K.F.
Published: April 2011

The Monte Carlo technique is used to simulate electron transport in bulk, wurtzite phase AlxGa1−xN. A multi-valley analytical band model consisting of five spherical, non-parabolic conduction band valleys at the Γ, U, M, and K symmetry points of the Brillouin zone is matched to band structures of GaN and AlN. Parameters for the AlxGa1−xN alloy are obtained by linear interpolation. The Monte Carlo simulations are performed for ambient temperatures in the range of 300K to 600K. Scattering mechanisms taken into account include ionized impurity scattering and alloy scattering, in addition to deformation potential scattering (intra- and inter-valley), and polar optical phonon scattering. We present results for the electron steady-state drift velocity and the valley occupancy for electric fields up to 500 kV/cm. Low-field drift mobilities are extracted from the Monte Carlo calculations as functions of the electron concentration, of the ambient temperature, and of the alloy composition.
Interband Radiative Recombination Calculations In Ternary Nitride Solid Solutions
Authors: Dmitriev A. V. , Oruzheinikov A. L.
Published: April 2011

We calculated for the first time the interband radiative recombination rate R in the wide-gap semiconductors GaN, InN and AIN crystallizing in the hexagonal wurtzite structure, and in ternary InxGayAl1−x−yN alloys including also binary solid solutions GaxAl1−xN, InxAl1−xN and GaxIn1−xN. All our calculations were based on experimental data on energy band structures and optical absorption spectra of the nitride materials. The radiative recombination coefficient B defined according to the equation R = B np, n and p being the carrier densities, is higher in InN and lower in GaN, taking intermediate values in AlN. For example, B=(2.7, 0.4 and 0.15) × 10−10cm3/s for InN, AIN and GaN, correspondingly. The carrier lifetime in GaN equals 60ns at 300K and n=1 × 1017cm−3. The radiative recombination coefficient increases with the concentration of indium nitride in the ternary alloys.
Electron Irradiation Induced Trap In N-Type Gan
Authors: Fang Z-Q. , Hemsky J. W. , Look D. C. , Mack M. P. , Molnar R. J. , Via G. D.
Published: April 2011

A 1-MeV-electron-irradiation (EI) induced trap at Ec-0.18 eV is found in n-type GaN by deep level transient spectroscopy (DLTS) measurements on Schottky barrier diodes, fabricated on both metal-organic-chemical-vapor-deposition and hydride-vapor-phase-epitaxy material grown on sapphire. The 300-K carrier concentrations of the two materials are 2.3 × 1016 cm−3 and 1.3 × 1017 cm−3, respectively. Up to an irradiation dose of 1 × 1015 cm−2, the electron concentrations and pre-existing traps in the GaN layers are not significantly affected, while the EI-induced trap is produced at a rate of at least 0.2 cm−1. The DLTS peaks in the two materials are shifted slightly, possibly due to electric-field effects. Comparison with theory suggests that the defect is most likely associated with the N vacancy or Ga interstitial.
Theoretical Study of Native Point Defects in Aln and InN
Authors: Stampfl C. , Walle Chris G. Van De
Published: April 2011

We have studied native point defects in AlN and InN using density-functional calculations employing both the local-density and generalized gradient approximations for the exchange-correlation functional. For both materials we find that the nitrogen vacancy acts as a compensating center in p-type material. For AIN in the zinc-blende structure, the aluminum interstitial has an equally low formation energy as the nitrogen vacancy. For n-type material the aluminum vacancy is the dominant compensating center in AlN. For n-type InN, all defect formation energies are high.
New Method of Computing Band Offsets and Its Application to AlGaN/GaN Heterostructures
Authors: Webster Richard T. , Anwar A. F. M.
Published: April 2011

Calculated sheet carrier concentration as a function of Al mole fraction in the quantum well (QW) formed at the GaN/AlGaN heterointerface is calculated and compared to experimental data. Close agreement between experiment and theory is observed. The calculated sheet carrier concentration reflects the maximum carrier concentration possible in the GaN QW for a given Al mole fraction and can not be used to argue in favor of either interface charge or piezoelectric effect as giving rise to the carriers. Based on experimental data the charge density in the AlGaN layer is estimated to be 4 × 1012cm-2

The calculations are based upon a simple technique to determine valence band alignments. Calculated values are compared to experimental data showing excellent agreement. A calculated valence band discontinuity of 0.42eV for AlN/GaN is well within the experimental bounds.
Investigation Of Nucleation And Initial Stage Of Gan Growth By Atomic Force Microscopy And X-Ray Diffraction
Authors: Yip P. W. , Wang S.-Q. , Drehman A. J. , Zhu L. D. , Norris P. E.
Published: April 2011

The nucleation and initial stage of GaN growth on sapphire was investigated by atomic force microscopy, X-ray diffraction and photoluminescence. A 15 to 30 nm thick GaN buffer layer deposited at proper conditions was extremely smooth and nearly amorphous. Proper post deposition annealing resulted in the buffer crystallized. The buffer layer deposition temperature, thickness and annealing time and temperature must be coordinated. Low deposition temperature and/or insufficient annealing of the buffer results in a GaN wafer which has fine spiking surface morphology with an RMS of 3.4 nm for 1.4 μm wafer, strong yellow luminescence and wide xray rocking curve FWHM. High deposition temperature, longer crystallization time, and a low growth rate results in a wafer which exhibits strong band edge luminescence without noticeable yellow luminescence, and a narrow (002) diffraction rocking curve. However, the surface morphology exhibits well developed hexagonal feature with RMS roughness of 14.3 nm for a 570 nm thick layer. X-ray rocking curve analysis revealed buffer crystallization, domain coalescence and alignment process. The FWHM of the ω–scan of GaN (101) diffraction was 1700–2000 arc seconds for 200–1400 nm wafers which indicates that the twist of the domains is not changing much with the growth.
Laser-Processing for Patterned and Free-Standing Nitride Films
Authors: Kelly M. K. , Ambacher O. , Dimitrov R. , Angerer H. , Handschuh R. , Stutzmann M.
Published: April 2011

Films of GaN and related materials can be processed by methods that invoke thermal decomposition, induced by intense illumination with a pulsed laser. At elevated temperatures, the nitride semiconductors undergo decomposition, with the effusion of nitrogen gas. We exploit this mechanism as an alternative to etching for the patterning of nitride films and for the opening of buried interfaces. Films of GaN have been etched to a depth of 1 μm in less than three seconds. This interface decomposition allows in particular the separation of nitride films from transparent growth substrates such as sapphire.
Recent Progress in Implantation and Annealing of Gan and Aigan
Authors: Zolper J. C. , Han J. , Deusen S. B. Van , Crawford M. H. , Biefeld R. M. , Jun J. , Suski T. , Baranowski J. M. , Pearton S. J.
Published: April 2011

Heterostructure modulation doped transistors (MODFETs) based on AlGaN/GaN structures have demonstrated impressive DC and microwave performance often despite high transistor access resistance. One approach to reducing the access resistance is to use selective area Si-implantation. While several reports exist on Si-implantation in GaN, little work has been done on implantation in AlGaN. In addition, more information on the annealing of implantation damage in GaN is needed to optimize its use in FETs and thyristors.

We report the electrical and structural properties of Si-implanted Al0.15Ga0.85N based on Hall measurements and Rutherford Backscattering (RBS) spectra, respectively. Al0.15Ga0.85N shows less damage accumulation than GaN for a room temperature Si-implant dose of 5×1015 cm-2 based on the minimum channeling yield (26% for AlGaN as compared to 34% for GaN), however, as with GaN, this damage is difficult to remove by thermal annealing at °C.
Formation Mechanism Of Negative Fixed Charge In Glass At Lead Glass/Silicon Interface
Authors: Murakami Susumu , Matsuzaki Hitoshi , Matsuzaki Mitsuyuki , Tsuruoka Masao , Kanno Minoru
Published: April 2011

The physical origins of negative fixed charges at the lead glass/silicon interface have been studied. It was found that a thin p-type region is present on the n-type substrate in the PbO-SiO2-Al2O3 glass/silicon system from the punch-through voltage, pinch-off voltage, and SIMS analysis. A new model of the negative fixed charge was proposed from the MIS structure with the surface pn junction.
Low-Temperature PECVD SiO2 On Si And SiC
Authors: Teng L. , Anderson W. A.
Published: April 2011

The deposition of SiO2 films by plasma-enhanced-chemical-vapor-deposition (PECVD) using tetraethylorthosilicate (TEOS) was studied. MOS capacitors were fabricated on both Si and SiC for this study. Several different sets of experiments were conducted for PECVD deposition according to different growth parameters and the results compared. For Si samples with SiO2 deposited at a substrate temperature 300°C, the C∼V curve gave a flat-band voltage of 1V and a transition slope of 112 pF/V. The dielectric constant of the deposited SiO2 film was 4.2 and the Si/SiO2 interface trap density was calculated to be 1.8×1010 cm−2. The I-V curve showed a leakage current density of l.2×10−9 A/cm2 and dielectric breakdown field strength of 9.2 MV/cm. For SiC samples, the PECVD deposition gave a uniform SiO2 film with a controllable deposition rate of 0.3nm/sec. The refractive index and dielectric constant of the as-deposited SiO2 film were 1.46 and 3.84 respectively. The I∼V curve showed a leakage current density of 2×10−9 A/cm2 and a breakdown field of 4.7 MV/cm.
Etching And Hydrogen Incorporation In ScAlMgO4
Authors: Brandlel C. D. , Ren F. , Wilson R. G. , Lee J. W. , Pearton S. J. , Zavada J. M.
Published: April 2011

ScAlMgO4 is a potential substrate for GaN epitaxy. We have compared three different plasma chemistries for dry patterning of ScAlMgO4, namely Cl2−, F2− or CH4/H2-based. Significant etch rates (>1000Å.min−1) were obtained only with Cl2 (and BCl3), and the rates were directly proportional to both ion energy and ion density in the plasma. Since the etching is ionassisted under all conditions, extremely anisotropic sidewalls are produced on patterned features. Of the wet chemistries investigated at 300K, only HF wet chemical solutions were found to etch ScAlMgO4, although HNO3 can be used at ≤150°C for removal of substrate polishing damage. Hydrogen as 2H has been incorporated into ScAlMgO4 by both ion implantation and by exposure to a plasma at 250°C. In the implanted material diffusion begins at ˜500°C and most of the hydrogen is lost by ≤ 750°C. This thermal stability for hydrogen retention is considerably lower than for other substrate materials for GaN epilayer growth, such as Al2O3 and SiC. There is minimal permeation of 2H from a plasma at 250°C (DH ˜5×10−16 cm2·s−1) in ScAlMgO4, and thus unintentional hydrogen incorporation into GaN overlayers should be minimal at typical growth temperatures.
Optical Characterization Of Silicon Oxycarbide Thin Films
Authors: Wolfe D. M. , Wang F. , Hinds B. J. , Lucovsky G.
Published: April 2011

The local bonding environments in silicon oxycarbide thin films with different amounts of carbon were analyzed using the complementary optical techniques of Fourier transform infrared (FTIR) and Raman spectroscopies. Film formation was accomplished by low-temperature (250°C), plasma-enhanced CVD using SiH4, CH4 and O2 as the source gases. Control samples were also deposited using only SiH4 and CH4, and SiH4 and O2 source gases. The films were then subjected to rapid thermal annealing at 800, 900 and 1100 °C for 90 seconds. Results showed that carbon incorporation into the oxide hinders stoichiometric SiO2 formation upon annealing at 800 and 900 °C. Annealing at 1100 °C produced films which showed stoichiometric SiO2 formation. Phase separation into nano-crystalline silicon (<5 nm) and a mixture of amorphous silicon carbide and silicon oxide was also observed upon annealing, with crystallite size decreasing as the carbon content of the films was increased.
Influence Of Open-Tube Ga Diffusion On The Characteristics For Thyristor
Authors: Ruimei Wen , Suhua Pei
Published: April 2011

Open-tube Ga diffusion into a SiO2/Si structure was used for fabrication of the high speed thyristor. The advantages of open-tube Ga diffusion are as follows; it is easier to operate and easier to control the profile of the Ga concentration during processing, a clean surface, which is free from alloy spots can be obtained, this technique ensures to improve the on-state characteristics and dynamic characteristics.
Microraman Characterization Of Microdefects In Bulk Sic
Authors: Martín E. , Chafai M. , Jiménez J.
Published: April 2011

MicroRaman spectroscopy is used for characterizing defects in large SiC crystals with micrometer spatial resolution. The ability to identify microscopic inclusions of polytypes different than the crystal matrix is demonstrated; silicon and carbon inclusions and disorder effects are found in micropipes. A study of the Longitudinal Optic Phonon Plasmon Coupled (LOPC) Raman modes allowed to obtain local fluctuations of the net donor concentration, ND-NA, and the electron mobility around defects, which allowed impurity gettering effects to be observed.
A Novel Bi-Layer Photoresist T-Gate Technique To Reduce Gate Resistance.
Authors: Lothian J. R. , Ren F.
Published: April 2011

As the gate dimensions of FET's continue to shrink, the gate resistance increases. This increased gate resistance is undesirable for power applications. In order to reduce this problem short gate length features are covered with a larger length feature to reduce the gate resistance (T-gate)1. Generally this is done using bi-layer PMMA and E-beam writing for the upper and lower features, but this technique is very expensive and time consuming2,3. It is desirable to find a technique using conventional photoresist that would replace e-beam to produce T-gates.

We demonstrate a novel technique that utilizes conventional photoresist and optical stepper to create T-gate features4. The bottom feature is exposed and developed creating the lower part of the T. A short exposure of the photoresist pattern to an argon plasma hardens the resist just enough to allow a second layer to be put on without mixing of the two layers. This second layer is then exposed and developed forming the T. Plasma exposure allows us to create the second resist layer pattern without distorting or changing the bottom layer pattern. This technique is very robust, fast and much cheaper than e-beam technology.
Breakdown Degradation Associated With Elementary Screw Dislocations In 4H-SiC P+N Junction Rectifiers
Authors: Neudeck P. G. , Huang W. , Dudley M.
Published: April 2011

It is well-known that SiC wafer quality deficiencies are delaying the realization of outstandingly superior 4H-SiC power electronics. While efforts to date have centered on eradicating micropipes (i.e., hollow core super-screw dislocations with Burgers vector > 2c), 4H-SiC wafers and epilayers also contain elementary screw dislocations (i.e., Burgers vector = Ic with no hollow core) in densities on the order of thousands per cm2, nearly 100-fold micropipe densities. This paper describes an initial study into the impact of elementary screw dislocations on the reverse-bias current-voltage (I-V) characteristics of 4H-SiC p+n diodes. First, Synchrotron White Beam X-ray Topography (SWBXT) was employed to map the exact locations of elementary screw dislocations within small-area 4H-SiC p+n mesa diodes. Then the high-field reverse leakage and breakdown properties of these diodes were subsequently characterized on a probing station outfitted with a dark box and video camera. Most devices without screw dislocations exhibited excellent characteristics, with no detectable leakage current prior to breakdown, a sharp breakdown I-V knee, and no visible concentration of breakdown current. In contrast devices that contained at least one elementary screw dislocation exhibited a 5% to 35% reduction in breakdown voltage, a softer breakdown I-V knee, and visible microplasmas in which highly localized breakdown current was concentrated. The locations of observed breakdown microplasmas corresponded exactly to the locations of elementary screw dislocations identified by SWBXT mapping. While not as detrimental to SiC device performance as micropipes, the undesirable breakdown characteristics of elementary screw dislocations could nevertheless adversely affect the performance and reliability of 4H-SiC power devices.
Introduction Of Ions Into Wide Band Gap Semiconductors
Authors: Maruska H. Paul , Lioubtchenko Mike , Tetreault Thomas G. , Osinskif Marek , Pearton Stephen J. , Schurmant Matthew , Vaudo Robert , Sakap Shiro , Chen Qisheng , Shult Randy J.
Published: April 2011

With great attention now being given to the wide band gap materials for electronic and optoelectronic device applications, there is interest in using ion implantation to introduce dopants into selected regions of devices. Work on ion implantation into SiC and the III-V nitrides is reviewed, new device concepts are given, and recent results are presented. These include SiC implantations at elevated temperatures, a GaN sample implanted with Si having an electron mobility after annealing of 106 cm2/V-s, and a novel GaN np junction diode created by implantation.
Material Requirements For High Voltage, High Power Igbt Devices
Authors: Zehringer R. , Stuck A. , Lang T.
Published: April 2011

The two basic package types of current IGBT modules, which evolved from opposing requirements of traction and power transmission applications, are presented. It is shown that reliability and lifetime aspects given by traction puts most stringent limitations on the choice of materials at given cost targets. The materials used today for high power packaging and the future developments of high power IGBT-packages are discussed.
A New Methodology For Designing Floating Ring Termination Technique In High Voltage Structure
Authors: Stefanov E. , Charitat G. , Bailon L. , Barbolla J.
Published: April 2011

A new methodology to optimise the design of Floating Ring (FR) termination technique for high voltage device is presented. The basic idea is to simulate the blocking capability of the structure with only one guard ring and then extend the results to a multiple FR system. A second advantage of our method is to include the ring width in the optimisation process. The effectiveness and efficiency of our methodology is illustrated by optimising a FR structure with a junction depth xj=5 μm and Si substrate doping 2.1014cm−3 A seven rings structure is optimized giving 90 % efficiency in respect to the ideal plane parallel junction breakdown voltage VBD =840 V. Moreover the 2D simulation program POWER2D has been extended by an efficient numerical algorithm to reduce drastically the number of iterations when adjusting the quasi-Fermi potential of the rings.
Morphology Of Silicon Oxides On Silicon Carbide
Authors: O‘Brien M. L. , Pejdo S. , Nemanich R. J.
Published: April 2011

The development of high power devices based on silicon carbide requires a more complete understanding of the oxide formation process and interface characteristics. By using an integrated UHV system, samples were cleaned and oxides deposited in situ. The approach of the oxide formation process was to form the initial insulator, a few angstroms thick, and then deposit an oxide. Various deposition techniques are used in the oxide growth process; both thermal and plasma enhanced chemical vapor deposition were employed with two different precursors (oxygen and nitrous oxide), and the results were compared with thermal oxidation. The morphology of each of the deposited oxides was compared to the bare substrate and the thermal oxide wafers. This study focuses on the morphology of the different deposition processes using AFM. Examination of the morphology of the initial insulator growth process and the oxide deposition process gives insight into the physical characteristics of the silicon dioxide deposited on silicon carbide. The RMS values of the initial insulator formation and the control wafers are 0.93 and 0.95 nm respectively. Meanwhile, the RMS values for PECVD (200–400°C) and thermal CVD (400–600°C for oxygen-silane and 800–1000°C for nitrous oxide-silane) range from 1.43 to 1.93 nm.