bluuebunny/crossref_metadata_2025 huggingface dataset:
Aging of InGaN/AlGaN/GaN Light-Emitting Diodes
Authors: Yunovich A. E. , Kovalev A. N. , Kudryashov V. E. , Imanyakin F. , Turkin A. N.
Published: April 2011

Changes in luminescent spectra, current-voltage, and capacitance-voltage characteristics were studied versus time of working at forward currents for light-emitting diodes based on InGaN/AlGaN/GaN heterostructures. The samples of blue and green LEDs with a single quantum well InGaN active layers were studied during 102-2.103 hours at currents 30–80 mA. An increase in efficiency at the first stage and a decrease one at the second stage were detected. The main changes were detected at low currents in blue diodes for tunnel components of current and radiation. Activation of acceptors Mg because of residual H atoms are going out of complexes Mg-H and creation of donor type defects are proposed as models for two stages. A model of injection stimulated (non-thermal) underthreshold creation of defects can explain the results.
InGaN Double-Heterostructures and Dh-Leds on Hvpe Gan-on-Sapphire Substrates
Authors: Boutros K. S. , Flynn J. S. , Phanse V. , Vaudo R. P. , Smith G. M. , Redwing J. M. , Tolliver T. R. , Anderson N. G.
Published: April 2011

We report on the growth of InGaN films, and the fabrication and characterization of GaN homojunction LEDs and InGaN double heterostructure (DH) LEDs on HVPE GaNon- sapphire substrates. The use of these substrates facilitates the III-nitrides growth process, as it avoids the use of complicated buffer layers. We have achieved InGaN films with strong and sharp band-to-band photoluminescence (PL) from 370 to 540 nm. Typical In 0.o9Ga0. g9N/GaN DH films had double-crystal XRD FWHM ∼ 300 arcsec, and 400 nm peak PL emission with FWHM ∼ 100 meV. DH-LEDs were fabricated with InGaN layers with various compositions, and produced strong electroluminescence (EL) in the blue and blue/green regions.
Dc and Microwave Characteristics of High Transconductance AlGaN/GaN Heterostructure Field Effect Transistors on Sic Substrates
Authors: Chen Q. , Yang J. W. , Khan M. A. , Ping A. T. , Adesida I.
Published: April 2011

High quality AJGaN/GaN heterostructures have been successfully deposited on both nand p-type SiC substrates. Heterostructure field effect transistors fabricated using these layers exhibited high channel current density (1.71 A/mm), well behaved pinch-off characteristics, and excellent extrinsic transconductance (Gm = 229 mS/mm). There is negligible channel current degradation up to a source to drain bias of 20 V as opposed to devices grown on sapphire substrates. The 0.25 μm gate-length devices fabricated on the heterostructures grown on p-type SiC has allowed us to extract a cutoff frequency of 53 GHz. The cutoff frequency showed little deterioration with increasing drain bias voltage. These results demonstrate for the first time the high frequency and high power operation potential of the heterostructure field effect transistors based on AlGaN grown on SiC.
Experimental Study of Sputter Deposited Contacts to Gallium Nitride
Authors: Piquette E. C. , Bandić Z. Z. , McGill T. C.
Published: April 2011

A variety of metal contacts to n-GaN is investigated, including Al, Au, Ce, Ti, Cr, Mg, Sb, W, and Mo, which were deposited using DC magnetron plasma sputtering onto MBE grown GaN. The contacts were characterized by current-voltage analysis and contact resistances were measured by the circular geometry transmission line method. The effects on contact resistance and Schottky barrier properties by surface sputtering treatments, GaN doping, and post-deposition annealing are reported.
Characteristics of GaN Schottky Diode Grown on Sapphire Substrate by Mocvd
Authors: Egawa T. , Ishikawa H. , Yamamoto K. , Jimbo T. , Umeno M.
Published: April 2011

We report here the characterization of metalorganic chemical vapor deposition grown GaN layer on sapphire substrate with (0001) orientation (c-face). The 2.4-μm-thick GaN layer on sapphire substrate showed the specular surface morphology. The full width at half-maximum of X-ray double crystal rocking curve was 214 arcsec. Photoluminescence measurement at 4.2 K showed the emissions from the two free excitons (FEA and FEB), acceptor and donor bound excitons (ABE and I2) and the first excited state of FEA. The etch pit density (EPD) was measured using molten KOH etching was 2∼4×108 cm-2 . The electron mobilities from Hall effect measurement were 585 cm2/V·s for the electron concentration 1.1×1017 cm-3 at 300 K, and 1217 cm2/V·s for 2.4×1016 cm-3 at 77 K, respectively. The measured mobility values are much higher than the previously reported values. The fabricated Pt/Ti/Au Schottky diode on GaN layer revealed the ideality factor 1.04 and the barrier height 0.9 eV which was calculated from forward current-voltage characteristics. The reverse current was as low as 1 mA for the reverse voltage 100 V. The barrier height was also determined to be 1.4 eV from the capacitance-voltage measurement. The electron-beam induced current observations were performed on the fabricated GaN Schottky diode. The dark spot was observed and the dark spot density was estimated to be 2×108 cm-2, which was comparable to the EPD measured using molten KOH etching. GaN metal semiconductor field effect transistors (MESFETs) with 3-μm gate-length and 15-μm gate-width have also been fabricated on high-quality GaN single crystalline layer. Maximum transconductance 25 mS/mm and the drain-source current 210 mA/mm have been achieved for the GaN MESFET.
Selection, Growth, and Characterization of Gate Insulators on Mocvd Gallium Nitride for the Use in High Power Field Effect Devices
Authors: Therrien R. J. , Nam O. H. , Bremser M. D. , Lithicum K. , Nimii H. , Carlson E. P. , Lucovsky G. , Davis R. F.
Published: April 2011

Metal-insulator-semiconductor (MIS) capacitors have been fabricated on n-type GaN (0001) films using thermally grown Ga2O3, remote plasma enhanced chemical vapor deposited (RPECVD) SiO2, and molecular beam epitaxy (MBE) AIN as the gate insulator and Al as the gate electrode. Each GaN epitaxial layer was grown by organometallic chemical vapor deposition (OMCVD) on a 6H-SiC(0001) substrate on which was previously deposited a 1000Å buffer layer of AIN. Nitrogen-free polycrystalline films of Ga2O3 were grown on the GaN. Capacitancevoltage measurements of capacitors fabricated from this oxide showed distinct depletion and accumulation regions with significant leakage. The AIN and SiO2 capacitors demonstrated better electrical characteristics than the Ga2O3 because of lower leakage. The RPECVD SiO2/GaN heterostructures, in particular, showed good agreement with the curves calculated for an ideal oxide and a small amount of hysteresis.
Analysis of Optical Gain of Strained Wurtzite InxGa1-xN/GaN Quantum Well Lasers
Authors: Chong T. C. , Yeo Y. C. , Li M. F. , Fan W. J.
Published: April 2011

The valence subband structures, density-of-states, and optical gain of (0001) wurtzite (WZ) InxGa1-xN/GaN quantum wells (QWs) are studied using a numerical approach without analytical approximations. We used the effective-mass parameters of GaN and InN derived using the Empirical Pseudopotential Method. By varying the well width and mole fraction of In in the well material, the effects of quantum confinement and compressive strain are studied. A narrower well width and a higher In mole fraction in the well lead to TE enhancement and TM suppression of the optical gain. From the relationship between the optical gain and the radiative current density, we obtain the transparent current density for a single QW to be 200 A/cm2. Further, we analyze the InxGa1-xN/GaN/AlGaN separate confinement heterostructure multiple-QW laser structure. It is shown that a suitable combination of well width and number of QWs should be selected in optimizing the threshold current density in such MQW lasers
Optical Gain in Bgan Lattice-Matched to (0001) 6H-SiC
Authors: Honda T. , Tsubamoto M. , Kuga Y. , Kawanishi H.
Published: April 2011

The optical gain of a BGaN ternary system lattice-matched to 6H-SiC was estimated. The parameters used in this estimation, such as effective mass and a bandgap energy, were estimated according to Harrison's theory. The optical gain was estimated using the density matrix theory with intraband relaxation broadening. The transparency carrier density of BGaN is slightly only smaller than that of GaN. It may be possible to fabricate a BGaN-based semiconductor laser operating in the UV spectral region.
Epitaxial Growth and Properties of Mg-Doped Gan Film Produced by Atmospheric Mocvd System With Three Layered Lammar Flow Gas Injection
Authors: Akutsu N. , Tokunaga H. , Waki I. , Yamaguchi A. , Matsumoto K.
Published: April 2011

Mg-doped GaN films with a variety of Mg concentrations were grown on sapphire (0001) by horizontal atmospheric metalorganic chemical vapor deposition (MOCVD) system with three layered laminar flow gas injection in an attempt to study the Mg doping effects on film quality. The increase of Mg concentration induced an increase of x-ray rocking curve full width at half maximum (FWHM) and degradation of surface morphology. Secondary ion mass spectroscopy (SIMS) analysis shows increase of Si and O, associated with Mg-doping concentration. Si and O concentrations of Mg-doped film are up to 5×1016cm−3 and 5×1017cm−3 at Mg concentration of 4.5×1019cm−3, respectively. Strong 380nm emission and weak 430nm emission were observed by photoluminescence (PL) measurement at room temperature for as-grown Mg-doped GaN films which shows p-type conductivity after thermal annealing. While, in highliy Mg-doped GaN films which do not show the p-type conduction after thermal annealing, 430nm and/or 450nm emission were dominating. The highest room temperature free hole concentration achieved was p=2.5× 1018cm−3 with mobility μp=l.9cm2/V s.
Gallium Nitride Multioperate Optoelectronic Devices
Authors: Sidorov V. G. , Drizhuk A. G. , Sidorov D. V.
Published: April 2011

Opportunity of creation of several optoelectronic devices such as optron, photoreceiver, switch device, IR-to-visible signal transformer and others based on i-n-GaN light emitting diodes (LED) is shown. Technology and properties of GaN LED in relation to the desired device properties are discussed. A discussion of issues relating to electrical and optical positive feed back between the device elements is also included.
Nitride Laser Diodes With InGaN Based Mqw Structures
Authors: Sugiura Lisa , Nishio Jobji , Onomura Masaaki , Nunoue Shin-Ya , Itaya Kazuhiko , Ishikawa Masayuki
Published: April 2011

Advantages of applying III-V nitride materials for short wavelength light-emitting devices despite their extremely high dislocation density are discussed from the viewpoint of dislocation motion. There are also difficulties proper to these materials, which make it difficult to fabricate laser diodes. We present recent works to realize high performance laser diodes. We introduce the nitrogen ambient metalorganic chemical vapor deposition (MOCVD) growth which realizes the highly p-typed GaN films without any post-treatments. Some of our results respecting the room temperature pulsed operation of the conventional laser diode and the advanced inner stripe (IS) laser diode with InGaN based multi-quantum-well (MQW) grown by MOCVD are reported.
Properties of Free-Standing GaN Bulk Crystals Grown by HVPE
Authors: Melnik YU. , Nikolaev A. , Nikitina I. , Vassilevski K. , Dmitriev V.
Published: April 2011

GaN wafers 200 μm thick and 30 mm diameter were fabricated. GaN was grown by hydride vapor phase epitaxy on SiC substrates and removed from the substrate by reactive ion etching. Lateral size of the GaN wafers was equal to the size of the initial SiC substrates. GaN wafers were cleaved in pieces and these pieces were characterised. It was found that after the fabrication, GaN crystals were slightly deformed and strained. An anneal at 830°C in nitrogen ambient eliminated the residual strains. The FWHM of ω-scan (0002) x-ray rocking curve for annealed crystals was less than 140 arcsec for both sides of the best GaN crystals. The lattice constants measured from both sides of the crystals were c =5.1853±0.0003 Å and a = 3.1889±0.0001 Å. The Nd– Naconcentration determined by a mercury probe was about 2×1017cm−3for as-grown GaN surface and about 2×1019cm−3for former interface surface. Photoluminescence spectrum taken at 17 K revealed an edge peak at 3.472 eV with the FWHM value of 2.3 meV. A ratio of the edge peak intensity to the intensity of yellow band was higher than 1000. Initial TEM experiments were performed.
Ultra-Smooth ZnO Buffer Layers on (001) Sapphire
Authors: Drehman A. J. , Wang S.-Q. , Yip P. W.
Published: April 2011

Using off-axis reactive rf sputtering, we have grown extremely smooth, nearly epitaxial, (001) oriented ZnO films on c-axis sapphire substrates. Atomic Force Microscopy was used to determine that these films are extremely smooth, having an rms roughness of only a few tenths of a nanometer. Based on high resolution x-ray diffraction (HXRD), the ZnO is highly oriented, with a rocking curve width of less than 400 arc seconds for the (006) diffraction peak, and only somewhat larger for the (112) reflection. HXRD Phi scans show that the ZnO (112) reflection is rotated in the a-b plane by 30 degrees from the sapphire (113) direction. These two measurements indicate excellent in-plane orientation. We are investigating the use of these buffer layers for subsequent GaN growth. Electrical resistivities of the films exceeded 100 kΩ-cm making ZnO a potential candidate as an insulating buffer layer.
Organometallic Vapor Phase Lateral Epitaxy of Low Defect Density GaN Layers
Authors: Nam O. H. , Zheleva T. S. , Bremser M. D. , Thomson D. B. , Davis R. F.
Published: April 2011

Lateral epitaxial overgrowth (LEO) of GaN layers has been achieved on 3 μm wide and 7 μm spaced stripe windows contained in SiO2 masks on GaN/AIN/6H-SiC(0001) substrates via organometallic vapor phase epitaxy (OMVPE). The extent and microstructural characteristics of lateral overgrowth were a complex function of stripe orientation, growth temperature and triethylgallium (TEG) flow rate. A high density of threading dislocations, originating from the interface of the underlying GaN with the AIN buffer layer, were contained in the GaN grown in the window regions. The overgrowth regions, by contrast, contained a very low density of dislocations. The second lateral epitaxial overgrowth layers were obtained on the first laterally grown layers by the repetition of SiO2 deposition, lithography and lateral epitaxy.
Photoluminescence Characteristics of GaN Layers Grown on Soi Substrates and Relation to Material Properties
Authors: Philippe A. , Bru-Chevallier C. , Guillot G. , Cao J. , Pavlidis D. , Eisenbach A.
Published: April 2011

GaN layers were grown by MOCVD on Silicon on Insulator (SOI) substrates in an effort to improve the material quality compared to more traditionally employed sapphire substrates. Their photoluminescence properties are reported and found to exhibit an intense and relatively large PL band around 3.47eV at low temperature (7K). This is about 10meV lower than the PL energy of samples grown on sapphire substrates and suggests the presence of lower strain in the layers which is expected for compliant growth on SOI substrates. The shape of the main PL peak appears to indicate that Silicon diffusion takes place from the substrate during growth. The behavior of the PL spectra is studied as a function of temperature. The GaN films show good overall electrical properties with Hall mobilities at room temperature in the range of 150 to 300cm2/Vs and background carrier concentration from 2.9 to 3.9×1019cm−3.The promising optical and electronic features of these layers could be of great interest for the development of high quality optical and electronic devices.
Energy Dependent Growth Rates of AIN using Pulsed Supersonic Jets
Authors: Ballarotto V. W. , Kordesch M. E.
Published: April 2011

AIN films were grown on Si< 100 >, using unskimmed pulsed supersonic jets of ammonia and trimethylaluminum (TMA). By seeding the ammonia gas in hydrogen or helium, several different energies of the N precursor were used to examine the effect of N kinetic energy on the growth rate of AIN. The energy of the Al precursor, TMA, was 130 meV in all cases. The highest growth rate (0.115 μm/hr) was achieved with the high energy ammonia jet. The role of number density on film growth is discussed.
Design and Characterization of a UHV Arcjet Nitrogen Source
Authors: Bicknell-Tassius R. N. , Deelman P. W. , Grunthaner P. J. , Grunthaner F. J. , Bryson C. E. , Snyder E. , Giuliani J. L. , AprUzes J. P. , Kepple P.
Published: April 2011

A UHV-compatible nitrogen arcjet suitable for the growth of III-nitrides by molecular beam epitaxy is described and characterized. The arcjet operates at powers between 10W and 300W (the highest power used for these studies); typical nitrogen flows range between 5sccm and 100sccm. Optical emission spectra show the presence of activated atomic (N*) and molecular (N2*) nitrogen. A collisional radiative equilibrium model has been employed to provide insight into the excitation state of the active nitrogen. These results indicate that the arcjet is capable of supplying atomic nitrogen fluxes consistent with growth rates on the order of several monolayers per second. Langmuir probe measurements conducted near the position of the sample holder in the MBE chamber show the charged particle flux density is very low. The arcjet operates over a large powerpressure parameter space, and properties of the arc can be systematically “tuned” to provide a source suitable for selected-energy-epitaxy.
Deposition Sequences for Atomic Layer Growth of AlN Thin Films on Si(100) Using Dimethylethylamine Alane and Ammonia
Authors: Kuo Jason S. , Rogers J. W.
Published: April 2011

Recent studies have demonstrated that dimethylethylamine alane (DMEAA) is a viable group III precursor for depositing high quality aluminum nitride thin films during atomic layer growth with ammonia as the group V source. However, a practical consideration that is questioned but seldom investigated is whether one should initiate the growth with the group III or the group V source. Clearly DMEAA interacts differently with silicon than does ammonia; hence, reversing the deposition sequence will lead to different interfacial composition. Earlier studies involving TMAA and ammonia indicate that direct interaction of group III precursor with the surface may lead to higher carbon contamination. In this work, adsorption of DMEAA on Si(100) and on ammonia-covered Si(100) are characterized with Temperature-Programmed Desorption (TPD), Secondary-Ion Mass Spectrometry (SIMS), and Temperature-Programmed Secondary-Ion Mass Spectrometry (TPSIMS). Preliminary results indicate that DMEAA adsorbs molecularly on both Si(100) and ammonia-covered Si(100), but to a much smaller coverage on the latter surface. Results from reversing the adsorption sequence, i.e. ammonia first then DMEAA, will be compared as a possibility for interfacial quality control.
Structure and Properties Of III-N Semiconductor Thin Films Grown at Low Temperatures by N-Radical-Assisted Pulsed Laser Deposition
Authors: Fernandez F. E. , Pumarol M. , Martinez A. , Pantojas V. , Garcia M.
Published: April 2011

Thin films of nitride semiconductors are usually grown by means requiring high substrate temperatures. Deposition techniques providing higher kinetic energies of incident species offer an alternative route which might allow growth of good quality films at lower temperatures. Pulsed Laser Deposition can provide higher kinetic energies than most thin film growth methods. However, III-nitride thin films grown by PLD are often nitrogen deficient. We have been able to obtain good stoichiometry for aluminum nitride films even at room temperature by providing atomic nitrogen at low (thermal) energies during growth. Very good orientation can be obtained on (001) sapphire substrates at moderate temperatures (∼ 500 C). AIN films were grown from either AIN or Al targets. We also report on preliminary work by the same method with GaN film growth from a liquid Ga target.
Role of Dopants and Impurities on Pinhole Formation; Defects Formed At Ingan/Gan And AlGaN/GaN Quantum Wells
Authors: Liliental-Weber Z. , Ruvimov S. , Swider W. , Kim Y. , Washburn J. , Nakamura S. , Kern R. S. , Chen Y. , Yang J. W.
Published: April 2011

Transmission electron microscopy has been applied to study defects in epitaxial doped and undoped GaN layers grown by MOCVD on sapphire and SiC substrates. Samples with InGaN/GaN and AlGaN/InGaN heterostructures have also been investigated. The results of this study show that incorporation of “foreign” atoms increases formation of nano-tubes and pinholes. The highest density of these defects was formed close to the interface with sapphire where oxygen outdiffusion might be expected, or in the subsurface area in the samples where oxygen was added deliberately. Addition of In (or Al) at QW's also leads to pinhole formation. Increased In fraction or a larger number of QW's results in a greater density of pinholes and more surface roughness. Many of the “hollow” nanotube defects are terminated during growth.
The Effect Of Si And Mg Doping In The Microstructure Of Epitaxially Grown Gan
Authors: Katsikini M. , Paloura E. C. , Fieber-Erdmann M. , Holub-Krappe E. , Moustakas T. D.
Published: April 2011

The effect of p- and n-type doping (using Mg and Si, respectively) in the microstructure of GaN, grown epitaxially on (0001)Al2O3 and (111)Si, is studied with X-ray absorption measurements at the N-K-edge. A distortion in the local microstructure around the N atom is detected in the undoped and the Mg doped samples. The N atom is 4-fold coordinated with n Ga atoms in the expected distance and 4-n atoms at a distance longer by 0.28Å, where 2.9 < n < 3.3. Such a distortion, which is attributed to the inward relaxation and the strong interaction between the Ga atoms surrounding the nitrogen vacancies (VN), does not exist in the Si doped sample (carrier concentration=1.57×1018cm−3) where the formation of VN is suppressed due to the n-type doping. However, in GaN:Si the N atom is undercoordinated with 3.3 nearest neighbors instead of 4. This undercoordination indicates the presence of VGa and/or NGa antisite defects. Finally, from the nearest neigbohr distances the lattice parameters were calculated and it is found that although the a and c vary by about 1.5%, the ratio of the lattice constants, c/a, remains constant and equal to 1.63.
Microstructure of InGaN Quantum Wells
Authors: Ponce F. A. , Cherns D. , Goetz W. , Kern R. S.
Published: April 2011

The microstructure of lnxGal-xN quantum wells with intermediate indium concentrations (x = 0.28 and 0.52) has been studied using transmission electron microscopy. High-resolution lattice images and dark-field images taken under high tilt conditions indicate that the quantum wells are inhomogeneous in character. Most of the area of the quantum wells is pseudomorphic with the GaN adjacent layer. However, misfit dislocations are sometimes observed, although with an inhomogeneous distribution. Strained cluster regions are observed in the high-indium concentration quantum wells, with dimensions ranging fi'om 3 to 10 nm in diameter. Evidence is presented suggesting the extent of clustering depends on the exact orientation of the growth surface which is related to the columnar nature of the GaN/sapphire epitaxy.
Localized Donors in Gan: Spectroscopy Using Large Pressures
Authors: Wetzel C. , Amano H. , Akasaki I. , Suski T. , Ager J. W. , Weber E. R. , Haller E. E. , Meyer B. K.
Published: April 2011

Properties of GaN and its alloys are strongly controlled by impurities and strain. Using large hydrostatic and biaxial pressure we identify the role of donor dopants and stress induced fields. The doping of Si and 0 as relevant representatives of group-IV and group-VI impurities are studied in Raman spectroscopy. For pressures above 20 GPa we find that oxygen induces a strongly localized gap state while Si continues to behave as a hydrogenic donor. Such a DX-like behavior of 0 indicates and corresponds to doping limitations in AIGaN alloys. The site specific (ON, SiGa) formation of a gap-state is attributed to bond strengths of the respective neighbors. In photoreflection of pseudomorphic GaInN we observe pronounced Franz-Keldysh oscillations corresponding to piezoelectric fields of 0.6 MV/cm. An observed redshift of the luminescence is found to originate in electric field induced tailstates. A reduced but similar effect is expected for GaN possibly explaining observations of persistent photoconductivity in a wide range of materials.
Electron Mobility of N-Type GaN Films
Authors: Ng H. M. , Doppalapudi D. , Singh R. , Moustakas T. D.
Published: April 2011

The lateral transport in GaN films produced by electron cyclotron resonance plasma-assisted molecular beam epitaxy (ECR-MBE) doped n-type with Si to the levels of 1015 − 1020 cm−3 was investigated. The room temperature electron mobility vs carrier concentration was found to follow a family of bell-shaped curves consistent with a recently proposed model in which dislocations with an edge component introduce acceptor centers along the dislocation lines which capture electrons from the conduction band in n-type GaN. The mechanism of scattering was investigated by studying the temperature dependence of the carrier concentration and electron mobility. We found that for the samples with high carrier concentration (> 1018cm−3), the scattering at low temperatures is dominated by impurities while for samples with low carrier concentration (<1017 cm−3), the scattering is dominated by charged dislocations.
Location Of Residual Donors In GaN Epitaxial Layers
Authors: Glaser E. R. , Kennedy T. A. , Wickenden A. E. , Koleske D. D. , Perry W. G. , Davis R. F.
Published: April 2011

Optically-detected electron-nuclear double resonance (ODENDOR) studies at 24 GHz on high-resistivity GaN films grown on Al2O3 have been combined with x-ray diffraction measurements to obtain information on the location of the residual shallow donors. Strong ODENDOR assigned to 69,71Ga lattice nuclei was detected on the g=1.951 effective-mass donor resonance found on the 2.2 eV emission bands. The x-ray studies reveal that the layers are under biaxial compression with high values of strain (∼ 2–3 × 10−3). The quadrupole splittings for 69Ga are smaller than those reported for strain-free samples by 15–25 %. The dominant sources of the local electric field gradient (EFG) responsible for the splittings are attributed to the wurtzite crystal structure and the strain fields that arise from the lattice constant mismatch and the difference in thermal expansion coefficients. An EFG/strain relationship of 3 × 1022 Vm−2 per unit strain at the 69,71Ga nuclei is deduced. The ODENDOR can be described with asymmetry parameter η=0. This provides evidence that the donors are in the crystallites rather than near grain boundaries.
Electron-Phonon Scattering in GaN/AlN and GaAs/AlAs Quantum Wells
Authors: Forbang T. F. , McIntyre C. R.
Published: April 2011

We have studied the effects on the phonon spectrum and on the electron-longitudinal optical phonon scattering in GaN/AlN and GaAs/AlAs quantum wells. Phonon modes and potentials have been calculated for both systems. Results for emission due to electroninterface phonons interactions are presented. We will discuss the implications for relaxation times and electron mobility due to modified LO-phonon scattering in both systems.
Photoluminescence Quenching Spectroscopy of Trapmediated Er3+ Excitation Mechanisms in Er-Implanted GaN
Authors: Rhee S. J. , Kim S. , Li X. , Coleman J. J. , Bishop S. G.
Published: April 2011

Two-source optical quenching spectroscopy demonstrates that the four site-selective Er3+ photoluminescence (PL) spectra observed in Er-implanted GaN contribute to the above-gap excited Er3+ PL spectrum, with relative efficiencies determined by the carrier capture cross sections and concentrations of the defects or traps which mediate the excitation of each Er site. The above-gap pumped PL spectrum is dominated by two of the trap-mediated Er3+ PL spectra, while the highest concentration Er site, which is efficiently pumped only by direct 4f absorption, contributes only weakly. These experiments indicate that the same defects and impurities are involved in the trapmediated processes responsible for both the above- and the below-gap excitations of the Er3+ PL.
Probing The Indium Mole Fraction In An Ingan Epilayer By Depth Resolved Cathodoluminescence
Authors: Trager-Cowan C. , Middleton P. G. , Mohammed A. , O'Donnell K. P. , Stricht W. Van der , Moerman I. , Demeester P.
Published: April 2011

Cathodoluminescence spectroscopy is used to depth profile the indium mole fraction of a 0.4 μm InGaN epilayer grown by metalorganic chemical vapour deposition, and to probe an underlying 1.0 μm GaN epilayer and the sapphire substrate beneath. Spectral information is obtained by using a variable energy electron beam as the excitation source. Calibration of beam penetration is achieved using Monte Carlo simulations of electron beam trajectories. The indium mole fraction is found to decrease from a mean value of 27% at the surface of the InGaN layer to ≈ 24% at its interface with the GaN layer.
The Effect Of The Nucleation Layer On The Low Temperature Growth Of Gan Using A Remote Plasma Enhanced – Ultrahigh Vacuum Chemical Vapor Deposition (RPE-UHVCVD)
Authors: Kim Kyoung-Kook , Kim Dong-Jun , Paek Jong-Sik , Jo Je-Hee , Kim Hyo-Gun , Seong Tae-Yeon , Park Seong-Ju
Published: April 2011

This study investigated the low temperature growth of GaN on a nucleation layer in a remote plasma enhanced-ultrahigh vacuum chemical vapor deposition (RPE-UHVCVD) system which is equipped with an rf plasma cell for a nitrogen source. It was found that the growth temperature and the film thickness of the nucleation layer and the nitrogen flow rate for GaN growth play important roles in the improvement of crystallinity of the GaN layer. The nitridation of sapphire was also found to enhance the formation of facet shaped nuclei on the nucleation layer. As the temperature of the nucleation layer increased, islands with hexagonal and other facet shapes were formed on the grown GaN surface. This facet formation was related with the surface morphology and crystallinity of GaN. The best crystallinity was measured in a GaN layer with hexagonal facets on the surface and such GaN layers could be grown on a nucleation layer grown at 375 °C. Nitridation of sapphire and the growth temperature of the nucleation layer were also found to change the island shapes which enhances the formation of columnar structures in the GaN layer, resulting in the growth of a high crystalline GaN layer at low temperature.
Nitridation Of Sapphire Substrate Using Remote Plasma Enhanced-Ultrahigh Vacuum Chemical Vapor Deposition At Low Temperature
Authors: Paek Jong-Sik , Kim Kyoung-Kook , Lee Ji-Myon , Kim Dong-Jun , Kim Hyo-Gun , Park Seong-Ju
Published: April 2011

A remote plasma enhanced-ultrahigh vacuum chemical vapor deposition (RPE-UHVCVD) system equipped with a radio frequency-inductively coupled plasma (RF-ICP) which produces the reactive nitrogen species was employed to study the nitridation process at low temperature. The sapphire surface nitridated under various conditions was investigated with x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The nitridation process seems to be mostly affected by the RF power even at low temperature since the intensity of the N1s, peak was not dependent on the substrate temperature but on the RF power. The AFM images showed that the protrusion density on the sapphire surface decreased rapidly when the nitridation temperature was decreased. This result suggests that the formation of the protrusions is closely related to the process temperature, indicating that the formation of such protrusions is caused by the change of an elastic strain energy due to the thermal stress. It was possible to nitridate the sapphire surface without protrusion at a very low temperature. The crystallinity of GaN grown at 450 °C was found to be much improved when the sapphire substrate was nitridated at low temperature prior to the GaN layer growth.
Constant Pressure First-Principles Molecular Dynamics Study On Bn, Ain, And Gan
Authors: Shimada K. , Sota T. , Suzuki K.
Published: April 2011

We have performed first-principles total energy calculations to obtain various physical parameters for both zinc-blende and wurtzite BN, AIN, and GaN. The calculation has been done within the local density approximation to the density functional theory together with plane wave expansion and norm-conserving pseudopotentials. Constant-pressure first-principles molecular dynamics method has been used to relax the unit cell shape and the atomic geometry. In calculating the elastic constants and the deformation potentials, the internal displacement of atoms in the strained crystal is simulated by moving atoms with first-principles molecular dynamics method. The optical phonon frequencies at the Brillouin zone center except for LO phonons are calculated within harmonic approximation by calculating the forces acting on atoms which are displaced from equilibrium positions according to the symmetry of each mode.
A Tem Study Of The Microstructural Evolution Of Mbe-Grown Gan
Authors: Tricker David M. , Brown Paul D. , Martin Graeme , Lu J. , Westwood D. I. , Hill P. , Haworth L. , Macdonald J. E. , Cheng T. S. , Foxon C. T. , Humphreys Colin J.
Published: April 2011

The evolution of the microstructure of GaN grown by molecular beam epitaxy on {001} and {111} oriented GaAs substrates has been followed using transmission electron microscopy and reflection high energy electron diffraction. A thin layer of GaN has been shown to form during the nitridation of the GaAs surface prior to growth. Growth of GaN then proceeds by an island mechanism. Faulting on the four {111} planes of the cubic zinc-blende phase which grows on the {001 } surface occurs at an early stage as a consequence of misfit strain. The distribution of the {111} microtwins is initially isotropic, but growth of one pair of {111} twins proceeds much faster than that of the other pair, leading to a final microstructure which has an anisotropic distribution of microtwins. Doping of GaN with Si hinders the growth of the zinc-blende phase, leading to a textured, columnar (0001) wurtzite microstructure. Evidence is presented to show that addition of Mg as a dopant may reduce the stacking fault energy of wurtzite GaN.
GaN Device Processing
Authors: Pearton S. J. , Ren F. , Zolper J. C. , Shul R. J.
Published: April 2011

Recent progress in the development of dry and wet etching techniques, implant doping and isolation, thermal processing, gate insulator technology and high reliability contacts is reviewed. Etch selectivities up to 10 for InN over AIN are possible in Inductively Coupled Plasmas using a Cl2/Ar chemistry, but in general selectivities for each binary nitride relative to each other are low (≤2)b ecause of the high ion energies needed to initiate etching. Improved ntype ohmic contact resistances are obtained by selective area Si+ implantation followed by very high temperature (>1300°C) anneals in which the thermal budget is minimized and AIN encapsulation prevents GaN surface decomposition. Implant isolation is effective in GaN, AlGaN and AlInN, but marginal in InGaN. Candidate gate insulators for GaN include AIN, A1ON and Ga(Gd)Ox, but interface state densities are still to high to realize state-of-the-art MIS devices.
Covalent Silicon Bonding At Room Temperature In Ultrahigh Vacuum
Authors: Plöbl Andreas , Stenzel Heinz , Tong Qin-Yi , Langenkamp Martin , Schmidthals Cord , Gösele Ulrich
Published: April 2011

One possibility of a low temperature joining techniques relies on the bonding of atomically clean surfaces. Results on the application of this method to silicon direct bonding are being presented. Clean surfaces for bonding were prepared by ex situ chemical cleaning with ensuing hydrogen passivation and their subsequent activation by thermal desorption of the hydrogen in ultrahigh vacuum (UHV). In UHV at room temperature, the wafers were gently brought into contact to initiate the bonding process. Without any subsequent heat treatment, the adhesive strength thus achieved was equivalent to the cohesion of bulk silicon: covalent bonds join the two crystals.
Icp Etching Of SiC
Authors: Wang J. J. , Lambers E. S. , Pearton S. J. , Ostling M. , Zetterling C.-M. , Grow J. M. , Ren F.
Published: April 2011

A number of different plasma chemistries, including NF3/O2, SF6/O2 , SF6/Ar, ICI, IBr, Cl2/Ar, BCl3/Ar and CH4/H2/Ar, have been investigated for dry etching of 6H and 3C-SiC in a Inductively Coupled Plasma tool. Rates above 2,000 Å·cm−1 are found with fluorine-based chemistries at high ion currents. Surprisingly, Cl2-based etching does not provide high rates, even though the potential etch products (SiCl4 and CCl4 ) are volatile. Photoresist masks have poor selectivity over SiC in F2 - based plasmas under normal conditions, and ITO or Ni are preferred.
4H-SiC Power Devices: Comparative Overview of UMOS, DMOS, and GTO Device Structures
Authors: Casady J. B. , Agarwal A. K. , Rowland L. B. , Seshadri S. , Siergiej R. R. , Mani S. S. , Sheridan D. C. , Sanger P. A. , Brandt C. D.
Published: April 2011

Silicon Carbide (SiC) is an emerging semiconductor material which has been widely predicted to be superior to both Si and GaAs in the area of power electronic switching devices [1]. This paper presents an overview of SiC power devices and concludes that MOS Turn-Off Thyristor (MTOTM) is one of the most promising near term SiC switching device given its high power potential, ease of turn-off, 500°C operation and resulting reduction in cooling requirements. It is further concluded that in order to take advantage of SiC power devices, high temperature packages and components with double sided attachment need to be developed along with the SiC power devices.
Optimization Of Technology And Design Parameters Of IGBT Using TWB
Authors: Fatemizadehl B. , Granik Y.
Published: April 2011

This paper presents a methodology to optimize the design of different types of IGBT using TWB (TMA WorkBench). Using RSM (Response Surface Modeling) and DOE (Design of Experiment) in TWB we have developed a methodology, which can be applied to explore the impact of design modifications on the speed improvement and study the trade-off between speed, on-resistance, and breakdown voltage of IGBT. This method is a rapid and cost-effective approach for studying design alternatives. Two-dimensional simulations were used to determine the influence of technology and design parameter on device characteristics.
Influence Of Silicon Defects On The Electrical Behavior Of Semiconductor Power Devices
Authors: Schulze H.-J. , Kolbesen B.O.
Published: April 2011

Since power devices require a thick electrically active n-type silicon layer with high resistivity and a large area, their electrical characteristics are extremely sensitive to contamination. If heavy metals diffuse into the silicon wafers during the high-temperature steps, an uncontrolled increase in the leakage current and the on-state voltage can be observed. Furthermore, current filamentation and instabilities of the electrical data can occur. It turned out that the optimization of the cleaning processes, high-temperature steps and gettering treatments alone is not sufficient to avoid such effects. It is also important to avoid silicon crystal defects by proper processing. A dramatic increase in the leakage current was correlated with the appearance of silicon defects decorated with heavy metals. As a consequence of the low doping level of the n-base, the blocking voltage and the failure rate due to cosmic radiation are sensitive to contaminating atoms acting as donors.
Thermo-Mechanical Simulation Of A Multichip Press-Packed Igbt
Authors: Pirondi A. , Nicoletto G. , Cova P. , Pasqualetti M. , Portesine M. , Zani P. E.
Published: April 2011

The reliability of press-packed integrated gate bipolar transistors (IGBT) depends on satisfactory contact conditions applied at assembly stage and mantained throughout the service life. The objective of this work is the simulation of the thermo-structural behavior of a multichip IGBT during initial assembly and subsequent uniform thermal cycling using the Finite Element method. A detailed axisymmetric FE model of the 3D-device is developed to assess multi-zone contact conditions. Elastic-plastic material behavior and Coulombian friction on contact surfaces are prescribed. The role of dimensional tolerances on contact conditions is discussed. The thermal cycling associated to accelerated testing is then introduced to determine the contact pressure evolution as well as local stick/slip conditions. The device sensitivity to potential damage initiation due to thermo-mechanical fatigue and/or fretting is addressed.
High Resistivity Oxygen-Doped AlGaAs For Power Devices
Authors: Sasajima Yuichj , Fukuhara Noboru , Hata Masahiko , Maeda Takayoshi , Okushi Hideyo
Published: April 2011

We have succeeded in making high resistive AlxGa1−xAs by oxygen doping (AlxGa1−xAs:O) and applying them to buffer layer for power metal-semiconductor field effect transistor (MESFET). Samples of Al0.3Ga0.7As:O were prepared by metalorganic vapor phase epitaxy (MOVPE). Oxygen-related levels in A10.3Ga0.7As:O were investigated by applying isothermal capacitance transient spectroscopy (107S) to MIS (Al/Al0.3Ga0.7As:O/n-GaAs) diodes. A breakdown voltage and a two terminal gate breakdown voltage of the MESFET with the Al0.3Ga0.7As:O buffer layer became higher as increasing in the intensity of oxygen related peak in the ICTS spectra. These results indicate that the electrically active oxygen in the Al1−xGa1−xAs:O is an important factor for the device characteristics.
Localized Lifetime Control In Silicon Bipolar Power Devices By Voids Induced By He Ion Implantation
Authors: Saggio M. , Raineri V. , Frisina F. , Rimini E.
Published: April 2011

Localized lifetime control in silicon bipolar devices is presented and discussed. It was achieved by formation of a void layer by He ion implantation. The void formation is reviewed and the void properties are described and carefully considered. Simulations demonstrate the advantages of using localized lifetime control, while the innovative method is applied to fabrication of high speed Insulated Gate Bipolar Transistors.
Power Limitation Due To Premature Breakdown In Algan/Gan Hfets
Authors: Gradinaru G. , Kao N. C. , Yang J. , Chen Q. , Khan M. A. , Sudarshan T. S.
Published: April 2011

A systematic investigation of high field prebreakdown and breakdown phenomena of AlGaN/GaN Heterojunction Field Effect Transistors (HFETs) is presented. The breakdown process was studied as a function of various parameters such as applied electric field, material layer structure, semiconductor surface conditions, ambient dielectric, and test conditions. Experimental evidence of a breakdown mechanism, distinct from the bulk/subsurface breakdown, namely on-surface breakdown or surface flashover is presented. A practical, unambiguous way of identifying device failure by surface flashover is proposed. Surface flashover between gate and drain contact edges is proposed as the main mechanism initiating premature breakdown in these devices leading to a significant reduction of their power capability.
Phase and Interface Stability Issues in Chalcopyrite-Based Thin Film Solar Cells
Authors: Guillemoles Jean-Francois , Haalboom Thomas , Gödecke Tilo , Ernst Frank , Cahen David
Published: April 2011

How stable are Cu(In,Ga)Se2 solar cells? CuInSe2 is known also as an ionic Cu conductor and the Cu-In-Se system has a rich phase diagram. Two stability-related problems are treated from a thermodynamic point of view: -a- Cu migration, -b- phase segregation. We show how Cu migration imparts self-stabilization on the system. Based on recently reported results on the room temperature phase diagram of CuInSe2, we explain why an overlayer of an ordered vacancy compound (OVC) is not to be expected to appear as a separate phase, even though the surface composition corresponds to that of the I-III3V5 OVC compound.
Na Impurity Chemistry in Photovoltaic Cigs thin-Films: An Investigation with Photo- and Auger Electron Spectroscopies
Authors: Niles D. W. , Ramanathan K. , Granata J. , Hasoon F. , Noufi R. , Tielsch B. J. , Fulghum J. E.
Published: April 2011

The incorporation of Na into Cu(Inl-xGax)Se2 thin-films is known to lead to an improvement in device performance. The authors use X-ray photoelectron and Auger electron spectroscopies to determine the chemical nature of Na in Cu(Inl-xGax)Se2 thin-films. The Na concentration is determined to be ∼ 0.1 atomic percent in the bulk of Cu(In1-xGax)Se2 thin-films. The Na is chemically bonded to Se. The authors propose a model invoking the replacement of column III elements by Na during the growth of Cu(Inl-xGax)Se2 thin-films. These Nain and NaGa defects act as acceptor states to increase the p-type conductivity of Cu(In1-xGax)Se2 thin-films.
Ultra Thin Indium Tin Oxide Films On Various Substrates By Pulsed Laser Deposition
Authors: Sun X. W. , Kim D. H. , Kwok H. S.
Published: April 2011

Indium Tin Oxide (ITO) thin films with low resistivities of 0.1 ∼0.2 mΩ-cm were deposited on various substrates such as YSZ, glass, and ZnO buffered glass by pulsed laser deposition (PLD). The X-ray rocking curve of crystalline (200) ITO films grown on (100) YSZ had a FWHM as narrow as 0.08°. ITO films grown on ZnO (0001) buffered glass had an single (222) orientation and the X-ray rocking curve had a FWHM of 2. 1°. Ultrathin ITO films of 3.6nm were fabricated on YSZ and their electrical properties were measured from 10K-300K. ITO films fabricated on ZnO buffered glass and bare glass were characterized by Hall effect measurements as a function of temperature. The results indicate that the resistivity of ITO films grown by PLD does not depend on the orientation or the structure of the thin film. The resistivity is dominated by impurity scattering in the range of 10K-300K. We show that ZnO/glass is a good alternative to bare glass for producing commercial ITO films.
The Characterization Of Chemical Bath Deposited Cds On Single Crystal InP Substrates
Authors: Riker G. M. , Al-Jassim M. M. , Hasoon F. S.
Published: April 2011

We have investigated CdS thin films as possible passivating window layers for InP. The films were deposited on single crystal InP by chemical bath deposition (CBD). The film thickness, as optically determined by ellipsometry, was varied from 500 to 840Å. The film morphology was investigated by high resolution scanning electron microscopy (SEM), whereas the film microstructure was studied by X-ray diffraction (XRD) and cross-sectional transmission electron microscopy (TEM). Most of the films were fine-grained polycrystalline CdS, with some deposition conditions resulting in epitaxial growth. Cross-sectional TEM examination revealed the presence of interface contaminants. The effect of such contaminants on the film morphology and microstructure was studied, and various approaches for InP surface cleaning/treatment were investigated. The epitaxial films were determined to be hexagonal on both the (111) and (100) InP substrates; however, they were heavily faulted.
Investigations of Oxidation Dependence on Type of Porous Silicon Near Room Temperature by Isothermal Microcalorimeter
Authors: Salonen J. , Lehto V-P. , Laine E.
Published: April 2011

Oxidation of porous silicon has been studied using thermal activity monitoring, i.e. isothermal microcalorimeter. It was found that, at room temperature (25 °C) the micro-calorimetric signal from the oxidation of the p+-type porous silicon (PS) reduces exponentially, while in the case of n-type PS, the signal starts to increase slowly, reaching its highest value after some hours. This kind of behaviour is typical of autocatalytic reactions. To clarify the origin of the difference, we varied the preparation parameters of the porous silicon. We determined the activation energy from the measurements near the room temperature (25–70 °C). The results of this research have been compared with the previous observations and the possible origin of the difference has been discussed.