bluuebunny/crossref_metadata_2025_split huggingface dataset:
Properties and Effects of Hydrogen in GaN
Authors: Pearton S.J. , Cho H. , Ren F. , Chyi J.-I. , Han J. , Wilson R.G. 
Published: September 2012

AbstractThe status of understanding of the behavior of hydrogen in GaN and related materials is reviewed. In particular, we discuss the amount of residual hydrogen in MOCVD-grown device structures such as heterojunction bipolar transistors, thyristors and p-i-n diodes intended for high power, high temperature applications. In these structures, the residual hydrogen originating from the growth precursors decorates Mgdoped layers and AlGaN/GaN interfaces. There is a significant difference in the diffusion characteristics and thermal stability of implanted hydrogen between n- and p-GaN, due to the stronger affinity of hydrogen to pair with acceptor dopants and possibly to the difference in H2 formation probability.
A Comparative Study Of GaN Diodes Grown by MBE on Sapphire and HVPE-GaN /Sapphire Substrates
Authors: Sampath Anand V. , Misra Mira , Seth Kshitij , Fedyunin Yuri. , Ng Hock M. , Iliopoulos Eleftherios , Feit Zeev , Moustakas Theodore.D. 
Published: September 2012

AbstractIn this paper we report on the fabrication and characterization of GaN diodes (Schottky and p-n junctions) grown by plasma assisted MBE. We observed that Schottky diodes improve both in reverse as well as forward bias when deposited on 5 μm thick HVPE n+-GaN/sapphire instead of bare sapphire substrates. These improvements are attributed to the reduction of disloctions in the MBE homoepitaxially grown GaN. Similar benefits are observed in the reverse bias of the p-n junctions which according to EBIC measurements are attributed to the reduction of etch pits in the MBE grown p-GaN.
Full Band Monte Carlo Comparison of Wurtzite and Zincblende Phase GaN MESFETs
Authors: Farahmand Maziar , Brennan Kevin F. 
Published: September 2012

AbstractThe output characteristics, cutoff frequency, breakdown voltage and the transconductance of wurtzite and zincblende phase GaN MESFETs have been calculated using a self-consistent, full band Monte Carlo simulation. It is found that the calculated breakdown voltage for the wurtzite device is considerably higher than that calculated for a comparable GaN zincblende phase device. The zincblende device is calculated to have a higher transconductance and cutoff frequency than the wurtzite device. The higher breakdown voltage of the wurtzite phase device is attributed to the higher density of electronic states for this phase compared to the zincblende phase. The higher cutoff frequency and transconductance of the zincblende phase GaN device is attributed to more appreciable electron velocity overshoot for this phase compared to that for the wurtzite phase. The maximum cutoff frequency and transconductance of a 0.1 μm gate-length zincblende GaN MESFET are calculated to be 220GHz and 210 mS/mm, respectively. The corresponding quantities for the wurtzite GaN device are calculated to be 160GHz and 158 mS/mm.
High-Gain, High-Speed ZnO MSM Ultraviolet Photodetectors
Authors: Shen H. , Wraback M. , Gorla C. R. , Liang S. , Emanetoglu N. , Liu Y. , Lu Y. 
Published: September 2012

AbstractHigh quality zinc oxide (ZnO) films were epitaxially grown on R-plane sapphire substrates by metalorganic chemical vapor deposition at temperatures in the range 350-600°C. In-situ nitrogen compensation doping was performed using NH3. The metalsemiconductor-metal ultraviolet-sensitive photodetectors were fabricated on nitrogencompensation-doped epitaxial ZnO films. The photoresponsivity of these devices exhibits a linear dependence upon bias voltage up to 10 V, with a photoresponsivity of 400 A/W at 5 V. The rise and fall times are 1 and 1.5 μs, respectively.
Electron Beam Pumping in Nitride Vertical Cavities with GaN/ Al0.25 Ga0.75 N Bragg Reflectors
Authors: Klausing H. , Aderhold J. , Fedler F. , Mistele D. , Stemmer J. , Semchinova O. , Graul J. , Dänhardt J. , Panzer S. 
Published: September 2012

AbstractElectron beam pumped surface emitting lasers are of great interest for a variety of applications, such as Laser Cathode Ray Tubes (LCRT) in projection display technology or high power UV light sources for photolithography.Two distributed Bragg reflector (DBR) samples were grown by plasma assisted molecular beam epitaxy (PAMBE). The active regions of the samples are a GaN:Si bulk layer and a multihetero (MH) structure, respectively.Also, a separately grown single DBR stack was studied to find optical transmission and reflection properties which were compared to transfer matrix simulations.Scanning electron beam pumping at 80 K with an excitation energy of 40 keV at varying beam currents revealed luminescence emission maxima located at about 3.45 eV for the sample with the MH structure active region. Optical modes appeared for excitation powers greater than 0.85 MW/ cm2. Further increasing the excitation power density the number of modes increased and a broadening and redshift of the luminescence spectrum could be observed.Based on our experimental results, we discuss the dependence of optical parameters of the nitride vertical cavity and sample surface reactions on primary electron beam power.
Microstructure-Based Lasing in GaN/AlGaN Separate Confinement Heterostructures
Authors: Bidnyk S. , Lam J. B. , Little B. D. , Gainer G. H. , Kwon Y. H. , Song J. J. , Bulman G. E. , Kong H. S. 
Published: September 2012

AbstractWe report on an experimental study of microstructure-based lasing in an optically pumped GaN/AlGaN separate confinement heterostructure (SCH). We achieved low-threshold ultra-violet lasing in optically pumped GaN/AlGaN separate confinement heterostructures over a wide temperature range. The spacing, directionality, and far-field patterns of the lasing modes are shown to be the result of microcavities that were naturally formed in the structures due to strain relaxation. The temperature sensitivity of the lasing wavelength was found to be twice as low as that of bulk-like GaN films. Based on these results, we discuss possibilities for the development of ultra-violet laser diodes with increased temperature stability of the emission wavelength.
Sign of the Piezoelectric Field in Asymmetric GaInN/AlGaN/GaN Single and Double Quantum Wells on SiC
Authors: Im Jin Seo , Hangleiter A. , Off J. , Scholz F. 
Published: September 2012

AbstractWe study both GaInN/GaN/AlGaN quantum wells with an asymmetric barrier structure grown on SiC substrate and GaN/AlGaN asymmetric double quantum well (ADQW) structures. In the first case, a time-resolved study reveals an enhanced oscillator strength when the AlGaN barrier is on top of the GaInN quantum well. In comparison to our previous study of the same structure grown on sapphire, we find that the sign of the field is the same in both cases: the field points towards the substrate. In the case of ADQW, we observed not only intrawell transitions of both a 4 nm and a 2 nm QW separated by a 2.5 nm AlGaN barrier but also an interwell transition between the two QWs in the photoluminescence. The lifetimes and emission energies of the transitions can be well explained by the existence of the piezoelectric field built in the QWs.
Pulsed-Laser-Deposited AlN Films for High-Temperature SiC MIS Devices
Authors: Vispute R. D. , Patel A. , Baynes K. , Ming B. , Sharma R. P. , Venkatesan T. , Scozzie C. J. , Lelis A. , Zheleva T. , Jones K. A. 
Published: September 2012

AbstractWe report on the fabrication of device-quality AlN heterostructures grown on SiC for high-temperature electronic devices. The AlN films were grown by pulsed laser deposition (PLD) at substrate temperatures ranging from 25 °C (room temperature) to 1000 °C. The as-grown films were investigated using x-ray diffraction, Rutherford backscattering specttroscopy, ion channeling, atomic force microscopy, and transmission electron microscopy. The AlN films grown above 700 °C were highly c-axis oriented with rocking curve FWHM of 5 to 6 arc-min. The ion channeling minimum yields near the surface region for the AlN films were ∼2 to 4%, indicating their high degree of crystallinity. TEM studies indicated that AlN films were epitaxial and single crystalline in nature with a large number of stacking faults as a results of lattice mismatch and growth induced defects. The surface roughness for the films was about 0.5 nm, which is close to the unit cell height of the AlN. Epitaxial TiN ohmic contacts were also developed on SiC, GaN, and AlN by in-situ PLD. Epitaxial TiN/AlN/SiC MIS capacitors with gate areas of 4 * 10-4 cm2 were fabricated, and high-temperature current-voltage (I-V) characteristics were studied up to 450 °C. We have measured leakage current densities of low 10-8 A/cm2 at room temperature, and have mid 10-3 A/cm2 at 450°C under a field of 2 MV/cm.
The Formation of In-Rich Regions at the Perphery of the Inverted Hexahonal Pits of Ingan Thin-Films Grown by Metalorganic Vapor Phase Epitaxy
Authors: Li P. , Chua S. J. , Hao M. , Wang W. , Zhang X. , Sugahara T. , Sakai S. 
Published: September 2012

AbstractInGaN thin films were grown by low-pressure metalorganic-vapor-phase-epitaxy (MOVPE) and characterized by cathodoluminescence (CL) and scanning electron microscopy (SEM). SEM images showed that InGaN samples have inverted hexagonal pits which are formed by the In segregation on the (1011) surfaces. Room temperature CL at the wavelengths corresponding to the GaN band edge, the In-poor and In-rich regions showed that the In–rich regions formed at the periphery of the hexagonal pits.
Emission Enhancement of GaN/AlGaN Single-Quantum-Wells Due to Screening of Piezoelectric Field
Authors: Kinoshita A. , Hirayama H. , Riblet P. , Ainoya M. , Hirata A. , Aoyagi Y. 
Published: September 2012

AbstractPhotoluminescence (PL) enhancement due to the screening of piezoelectric field induced by Si-doping is systematically studied in GaN/AlGaN quantum wells (QWs) fabricated by metal organic vapor-phase-epitaxy (MOVPE). The PL enhancement ratio of QWs for Si-doped directly into the wells was much larger than that for doped only into the barrier layers. This result shows that the crystal quality of the quantum well is not so damaged by heavy Si-doping, which is different from the cases of GaAs or InP material systems. The PL intensity enhancement ratio was especially large for thick wells. The typical value of the enhancement ratio was 30 times for a 5 nm-thick single QW. The optimum Si-doping concentration was approximately 4×1018 cm-3. From the well width dependence of the PL enhancement ratio and PL peak shift under high excitation conditions, we determined that the dominant effect inducing the PL enhancement is screening of piezoelectric field in the QWs. These results indicate that Si-doping is very effective for the application of GaN/AlGaN QWs to optical devices.
Correlation between Structural Properties and Optical Amplification in InGaN/GaN Heterostructures Grown by Molecular Beam Epitaxy
Authors: Kaschner A. , Holst J. , von Gfug U. , Hoffmann A. , Bertram F. , Riemann T. , Rudloff D. , Fischer P. , Christen J. , Averbeck R. , Riechert H. 
Published: September 2012

AbstractWe comprehensively studied InGaN/GaN heterostructures grown by molecular beam epitaxy (MBE) using a variety of methods of optical spectroscopy, such as cathodoluminescence microscopy (CL), time-integrated and time-resolved photoluminescence. To correlate the fluctuations in emission wavelength with values for the optical amplification we performed gain measurements in edge-stripe geometry. The lateral homogeneity can be drastically improved using a template of GaN grown on the sapphire substrate by metal-organic vapor phase epitaxy (MOVPE). Gain values up to 62 cm-1 were found in samples with low indium fluctuations, which is comparable to values for high-quality InGaN/GaN heterostructures grown by MOVPE.
Optical Properties of AlGaN Quantum Well Structures
Authors: Hirayama Hideki , Enomoto Yasushi , Kinoshita Atsuhiro , Hirata Akira , Aoyagi Yoshinobu 
Published: September 2012

AbstractWe demonstrate 230-250 nm efficient ultraviolet (UV) photoluminescence (PL) from AlN(AlGaN)/AlGaN multi-quantum-wells (MQWs) fabricated by metalorganic vapor-phase-epitaxy (MOVPE). Firstly, we show the PL properties of high Al content AlGaN bulk (Al content: 85-95%) emitting from near band-edge. We systematically investigated the PL properties of AlGaN-MQWs consisting of wide bandgap AlGaN (Al content: 53-100%) barrier. We obtained efficient PL emission of 234 and 245 nm from AlN/Al0.18Ga0.82N and Al0.8Ga0.2N/Al0.18Ga0.82N MQWs, respectively, at 77 K. The optimum value of well thickness was approximately 1.5 nm. The emission from the AlGaN MQWs were several tens of times stronger than that of bulk AlGaN. We found that the most efficient PL is obtained at around 240 nm from AlGaN MQWs with Al0.8Ga0.2N barriers. Also, we found that the PL from AlGaN MQW is as efficient as that of InGaN QWs at 77 K.
Characterization of InGaN Quantum Wells Grown by Molecular Beam Epitaxy (MBE) Using Ammonia as the Nitrogen Source
Authors: Semendy F. , Li L.K. , Jurkovic M.J. , Wang W.I. 
Published: September 2012

AbstractSingle quantum well InGaN was grown by molecular beam epitaxy with ammonia as the nitrogen source. The samples were grown on (0001) sapphire substrates. The photoluminescence (PL) intensity of InGaN quantum wells showed band-edge emissions at 2.71eV at low temperature (10 K). PL was investigated as a function of excitation intensity and temperature. The relationship between PL intensity and excitation intensity, as well as the relationship between PL intensity and lattice temperature was studied. Also studied was the combined effect of temperature and intensity variation. Detailed results are reported here.
Comparative Study of Structural Properties and Photoluminescence in InGaN Layers with a High in Content
Authors: Vantomme A. , Wu M.F. , Hogg S. , Langouche G. , Jacobs K. , Moerman I. , White M.E. , O'Donnell K.P. , Nistor L. , Landuyt J. Van , Bender H. 
Published: September 2012

AbstractRutherford backscattering and channeling spectrometry (RBS), photoluminescence (PL) spectroscopy and transmission electron microscopy (TEM) have been used to investigate macroscopic and microscopic segregation in MOCVD grown InGaN layers. The PL peak energy and In content (measured by RBS) were mapped at a large numberof distinct points on the samples. An indium concentration of 40%, the highest measured in this work, corresponds to a PL peak of 710 nm, strongly suggesting that the lightemitting regions of the sample are very indium-rich compared to the average measured by RBS. Cross-sectional TEM observations show distinctive layering of the InGaN films. The TEM study further reveals that these layers consist of amorphous pyramidal contrast features with sizes of order 10 nm. The composition of these specific contrast features is shown to be In-rich compared to the nitride matrix.
Optical Spectroscopy of Ingan Epilayers in the Low Indium Composition Regime
Authors: Crawford M. H. , Han J. , Banas M. A. , Myers S. M. , Petersen G. A. , Figiel J. J. 
Published: September 2012

AbstractPhotoluminescence (PL) spectroscopy was carried out on a series of Si-doped bulk InGaN films in the low indium (In) composition regime. Room temperature PL showed a factor of 25 increase in integrated intensity as the In composition was increased from 0 to 0.07. Temperature dependent PL data was fit to an Arrhenius equation to reveal an increasing activation energy for thermal quenching of the PL intensity as the In composition is increased. Time resolved PL measurements revealed that only the sample with highest In ( x=0.07) showed a strong spectral variation in decay time across the T=4K PL resonance, indicative of recombination from localized states at low temperatures. The decay times at room temperature were non-radiatively dominated for all films, and the room temperature (non-radiative) decay times increased with increasing In, from 50-230 psec for x=0-0.07. Our data demonstrate that non-radiative recombination is less effective with increasing In composition.
The Use of Micro-Raman Spectroscopy to Monitor High-Pressure High-Temperature Annealing of Ion-Implanted GaN Films
Authors: Kuball M. , Hayes J.M. , Suski T. , Jun J. , Tan H.H. , Williams J.S. , Jagadish C. 
Published: September 2012

AbstractWe have investigated the high-pressure high-temperature annealing of Mg/P-implanted GaN films using visible and ultraviolet (UV) micro-Raman spectroscopy. The results illustrate the use of Raman spectroscopy to monitor processing of GaN where fast feedback is required. The structural quality and the stress in ion-implanted GaN films was monitored in a 40nm-thin surface layer of the sample as well as averaged over the sample layer thickness. We find the nearly full recovery of the crystalline quality of ion-implanted GaN films after annealing at 1400-1500°C under nitrogen overpressures of 1.5GPa. No significant degradation effects occurred in the GaN surface layer during the annealing. The high nitrogen overpressures proved very effective in preventing the nitrogen out-diffusion from the GaN surface. Stress introduced during the annealing was monitored. Raman spectra of ion-implanted GaN films were investigated at different temperatures and excitation wavelengths to study the GaN phonon density of states.
A Study of Annealed GaN Grown by Molecular Beam Epitaxy Using Photoluminescence Spectroscopy.
Authors: Bell Abigail , Harrison Ian , Korakakis Dimitris , Larkins Eric C. , Hayes J. M. , Kuball M. 
Published: September 2012

AbstractPhotoluminescence (PL) spectroscopy has been used to investigate the effect annealing has on molecular beam epitaxially grown GaN in different ambients. By observing the changes in the PL spectra as a function of ambient temperature and atmosphere used, important information concerning the origin of defects within GaN has been found. Samples were annealed in different atmospheres, (including oxygen, oxygen and water vapour, nitrogen and argon), different temperatures. In the 2.0eV-2.8eV region of the PL spectra, two peaks appeared at approximately 2.3eV and 2.6eV, somewhat higher than the usual yellow luminescence peak. We find that the 2.6eV peak is dominant for high annealing temperatures and the 2.3eV peak dominates at low annealing temperatures for the samples annealed in oxygen. When annealed in argon and nitrogen the 2.6eV peak dominates at all annealing temperatures. Changes in the PL spectra between anneals were also seen in the 3.42eV region. The 3.42eV peak is often assigned to excitons bound to stacking faults. Power resolved measurements indicate that in our sample the cause is a donor acceptor pair transition.
Nonlinear Optical Characterization of GaN Layers Grown by MOCVD on Sapphire
Authors: Tiginyanu Ivan M. , Kravetsky Igor V. , Pavlidis Dimitris , Eisenbach Andreas , Hildebrandt Ralf , Marowsky Gerd , Hartnagel Hans L. 
Published: September 2012

AbstractOptical second and third harmonic generation measurements were carried out on GaN layers grown by metalorganic chemical vapor deposition (MOCVD) on sapphire substrates. The measured d33 is 33 times the d11 of quartz. The angular dependence of second-harmonic intensity as well as the measured ratios d33/d15= -2.02 and d33/d31 = -2.03 confirm the wurzite structure of the studied GaN layers with the optical c-axis oriented perpendicular to the sample surface. Fine oscillations were observed in the measured second and third harmonic angular dependencies. A simple model based on the interference of the fundamental beam in the sample was used to explain these oscillations.
Picosecond Photoinduced Reflectivity Studies of GaN Prepared by Lateral Epitaxial Overgrowth
Authors: Wraback M. , Shen H. , Eiting C.J. , Carrano J.C. , Dupuis R.D. 
Published: September 2012

AbstractThe pump-probe technique has been used to perform room temperature studies of the photoinduced changes in the reflectivity ΔR associated with exciton and carrier dynamics in GaN prepared by lateral epitaxial overgrowth. For resonant excitation of cold excitons, the ΔR decay possesses a 720 ps component attributed to the free exciton lifetime in this high quality material. For electrons with small excess energy (< 50 meV), the strong increase in the ΔR decay rate with decreasing excitation density suggests that screening of the Coulomb interaction may play an important role in the processes of carrier relaxation and exciton formation. The faster decay times at a given carrier density observed for hot (> 100 meV) electron relaxation are attributed to electron-hole scattering in conjunction with the screened electron-LO phonon interaction.
Photoluminescence Enhancement and Morphological Properties of Carbon Codoped GaN:Er
Authors: Overberg M.E , Abernathy C.R. , Pearton S. J. , Wilson R. G. , Zavada J. M. 
Published: September 2012

AbstractThe surface morphology and the room temperature 1.54 µm photoluminescence (PL) intensity from GaN:Er grown by gas source molecular beam epitaxy have been investigated as a function of C concentration as introduced by CBr4. Similar to previous results with increasing Er level, increasing the C concentration initially improved the surface smoothness as measured by atomic force microscopy (AFM) and scanning electron microscopy (SEM), with RMS roughness improving by a factor of seven over undoped GaN. The PL also improved dramatically. However, the highest amounts of C investigated produced a decrease in the PL as well as a roughening of the film surface. These effects indicate that the GaN:Er had reached its C solubility limit, producing an increased amount of defect induced nonradiative recombination.
Comparison of the Optical Properties of Er3+ Doped Gallium Nitride Prepared by Metalorganic Molecular Beam Epitaxy (MOMBE) and Solid Source Molecular Beam Epitaxy (SSMBE)
Authors: Hömmerich U. , Seo J. T. , MacKenzie J. D. , Abernathy C. R. , Birkhahn R. , Steckl A. J. , Zavada J. M. 
Published: September 2012

AbstractWe report on the luminescence properties of Er doped GaN grown prepared by metalorganic molecular beam epitaxy (MOMBE) and solid-source molecular beam epitaxy (SSMBE) on Si substrates. Both types of samples emitted characteristic 1.54 µm PL resulting from the intra-4f Er3+ transition 4I13/2→4I15/2. Under below-gap excitation the samples exhibited very similar 1.54 µm PL intensities. On the contrary, under above-gap excitation GaN: Er (SSMBE) showed ∼80 times more intense 1.54 µm PL than GaN: Er (MOMBE). In addition, GaN: Er (SSMBE) also emitted intense green luminescence at 537 nm and 558 nm, which was not observed from GaN: Er (MOMBE). The average lifetime of the green PL was determined to be 10.8 µs at 15 K and 5.5 µs at room temperature. A preliminary lifetime analysis suggests that the decrease in lifetime is mainly due to the strong thermalization between the 2H11/2 and 4S3/2 excited states. Nonradiative decay processes are expected to only weakly affect the green luminescence.
Comparison of Implant Isolation Species for GaN Field-Effect Transistor Structures
Authors: Dang G. , Cao X. A. , Ren F. , Pearton S. J. , Han J. , Baca A. G. , Shul R. J. , Wilson R. G. 
Published: September 2012

AbstractDifferent ions (Ti+, O+, Fe+, Cr+) were implanted at multiple energies into GaN field effect transistor structures (n and p-type). The implantation was found to create deep states with energy levels in the range EC –0.20 to 0.49 eV in n-GaN and at EV +0.44 eV in p-GaN after annealing at 450-650 oC. The sheet resistance of the GaN was at a maximum after annealing at these temperatures, reaching values of ∼4×1012 Ω/⊏ in n-GaN and ∼1010 Ω/⊏ in p-GaN. The mechanism for the implant isolation was damage-related trap formation for all of the ions investigated, and there was no evidence of chemically induced isolation.