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GaN Substrates (gan + substrate)
Kinds of GaN Substrates Selected AbstractsStrain Mapping at the Atomic Scale in Highly Mismatched Heterointerfaces,ADVANCED FUNCTIONAL MATERIALS, Issue 14 2007M. Sánchez Abstract A complete characterization of dislocation network in a highly mismatched interface with high spatial resolution has been performed. The interface between InN quantum dots and a (0001) GaN substrate contains three noninteracting sets of regularly-spaced misfit dislocations lying along <110> directions. The network has a "Star of David" form, with each star bounding a hexagonal region which is pseudomorphic. These misfit dislocations form a threading dislocation network at the island edges due to free surface forces. [source] Various misfit dislocations in green and yellow GaInN/GaN light emitting diodesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2010Mingwei Zhu Abstract We report the growth and structural characteristics of green and yellow (529,576,nm) GaInN/GaN light emitting diodes (LEDs) grown on two types of c -plane substrates , bulk GaN and sapphire. In this longer wavelength range, depending on the substrate, we find different strain relaxation mechanisms within the GaInN/GaN quantum well (QW) region. In optimized epitaxy, structures on sapphire that contain a low density of threading dislocations (TDs) within the n -GaN show virtually no generation of additional misfit dislocations (MDs) (<108,cm,2) or V -defects within the QW region for emission wavelengths up to 571,nm. On bulk GaN substrate, however, where much fewer TDs reach the QWs, strain relaxation is observed by inclined dislocation pairs in green emitters and a high density of edge-type MDs in yellow emitters. The electroluminescence line width, as well as the efficiency droop, was found to increase with dislocation density in the QWs. [source] InGaN-based 518 and 488,nm laser diodes on c -plane GaN substratePHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2010Takashi Miyoshi Abstract We succeeded in fabricating InGaN-based laser diodes (LDs) with a wavelength of 518 and 488,nm under continuous wave (cw) operation. The both LDs structures were grown on conventional c -plane GaN substrates by metal organic chemical vapor deposition (MOCVD). The threshold current and threshold voltage were 45,mA and 5.5,V at 518,nm, 30,mA and 4.5,V at 488,nm, respectively. The lifetime test of these LDs was carried out under high driving temperature up to 80,°C in cw operation. Lifetime was estimated to be over 5000,h with an optical output power of 5,mW at 80,°C in 515,518,nm LDs from 1000,h operation, and was estimated to be over 10,000,h with an output power of 60,mW at 60,°C in 488,nm LDs from 2000,h operation. [source] AlGaN/GaN HFETs on Fe-doped GaN substratesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010Yoshinori Oshimura Abstract AlGaN/GaN HFETs with different undoped GaN thicknesses were grown on Fe-doped freestanding GaN substrates by conventional MOVPE. To realize a high drain current, thick undoped GaN is found to be necessary. SIMS measurement shows that Fe is redistributed into the epilayer, by which the scattering center is generated at the channel when the thickness of the undoped GaN is insufficient. We also observed a similar Fe profile in the GaN/sapphire template placed on the side of the Fe-doped GaN substrate during growth. Therefore, Fe in the Fe-doped GaN substrate is redistributed not only through a solid but also through vapor. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Cathodoluminescence evaluation of subsurface damage in GaN substrate after polishingPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009K. Y. Lai Abstract The surface of HVPE grown GaN substrates were treated with two different polishing procedures. Both procedures were successful in producing highly smooth and featureless surfaces. However, subsurface damage was observed in the sample treated by one of the procedures. The subsurface damage was revealed by cathodoluminescence (CL) spectroscopy imaging but was not visible by scanning electron microscopy (SEM) or Atomic force microscopy (AFM). Thermal annealing at 950 °C with different gases was performed in an attempt to remove subsurface damages. Annealing in gas mixtures containing H2 increased both the presence of surface scratches and overall surface roughness. On the other hand, annealing in mixtures of NH3 and N2 (with no H2) led to the surfaces with significantly reduced subsurface damage. The surface roughness and optical properties of the sample after the annealing with such gas mixtures were slightly sacrificed. In order to evaluate subsurface damage depth, CL images were taken from the annealed surface for different acceleration voltages. The results suggest that the observed subsurface damages were within 1.48 ,m of the surface. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Blue light emitting diode fabricated on a-plane GaN film over r-sapphire substrate and on a-plane bulk GaN substratePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007Y. Naoi Abstract We studied the growth technique for the dislocation reduction in a-plane GaN grown by metal organic chemical vapour deposition (MOCVD) using AlInN buffer layer, high temperature atomic layer epitaxy, and trenched r-sapphire technique. By using these techniques, the crystal quality was much improved. We also fabricated blue light emitting diodes (LEDs) on a-plane GaN film over r-sapphire substrate and on a-plane bulk GaN substrate. The electroluminescence (EL) characteristics of the LED samples were examined, and we found that the EL near field pattern from homo-epitaxially grown a-GaN based LED was spatially uniform, although the pattern from the LED on r-sapphire substrate was not uniform. The output power at the wavelength of 430nm was 0.72mW at the 20mA injection current for the sample on a-plane bulk GaN. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optical properties of InGaN/GaN quantum wells on sapphire and bulk GaN substratePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006M. Dworzak Abstract We investigated the recombination dynamics in InGaN quantum well (QW) structures, grown by metal organic chemical vapour deposition on sapphire and bulk GaN crystals. We present the results of time-integrated and time-resolved photoluminescence (PL) spectroscopy performed on single QWs with widths of 4.5 nm and 9.5 nm. The recombination mechanisms were studied at 5 K and elevated temperatures up to room temperature. Radiative and nonradiative life-times were determined. The luminescence properties are strongly influenced by the localization of excitons in a complex potential landscape with localization sites of varying depth. Redistribution of charges from shallow to deeper localization sites were observed. The band profile fluctuations influence the thermal stability of the luminescence. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Defect density dependence of carrier dynamics in AlGaN multiple quantum wells grown on GaN substrates and templatesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005G. A. Garrett Abstract Subpicosecond time-resolved photoluminescence (TRPL) has been used to compare the room temperature carrier dynamics in Al0.1Ga0.9N/Al0.3Ga0.7N multiple quantum well (MQW) structures simultaneously deposited on a high quality free standing HVPE GaN substrate (dislocation density ,1 × 107cm,2) and 1 µm MOCVD GaN template on sapphire. The PL lifetime of ,500 ps in the MQW on GaN substrate is about 5 times longer than that for the MQW on GaN template, with a concomitant increase in CW PL intensity. This behavior is attributed primarily to an increase in nonradiative lifetime associated with a 100 times reduction in dislocation density in the GaN substrate. The observation that the PL lifetime in the MQW falls short of the ,900 ps dominant decay time in the GaN substrate may be indicative of generation of additional defects and dislocations due to substrate surface preparation, strain relaxation, and nonoptimal growth temperature associated with the difference in heating of the thin GaN template on sapphire and the thick GaN substrate. An extended PL rise time of greater than 20 ps for the MQW emission when above barrier pumping is employed implies that both wells and barriers are of high quality. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Improvements in crystalline quality of thick GaN layers on GaAs (111)A by periodic insertion of low-temperature GaN buffer layersPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003H. Murakami Abstract Thick and high quality GaN layer growth using periodic insertion of low-temperature (LT)-grown GaN buffer layers was investigated by metalorganic hydrogen chloride vapor phase epitaxy (MOHVPE). Both morphological and optical properties of GaN epitaxial layers were drastically improved by inserting a second LT-GaN buffer layer. Also, the thickness of the second buffer layer was found to affect the quality of subsequently grown epitaxial layers. The full-width at half maximum (FWHM) value of X-ray diffraction for () plane (, scan) of the GaN layer with double buffer layer structure decreased to 608 arcsec whereas that with single buffer structure was 3600 arcsec. These results indicate that the free-standing GaN substrate with low dislocation density can be possible by reiterating the growth sequence of buffer layer and epitaxial layer. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Spatially resolved X-ray diffraction as a tool for strain analysis in laterally modulated epitaxial structuresCRYSTAL RESEARCH AND TECHNOLOGY, Issue 10 2009A. Wierzbicka Abstract Spatially resolved X-ray diffraction (SRXRD) is applied for micro-imaging of strain in laterally modulated epitaxial structures. In GaAs layers grown by liquid phase epitaxial lateral overgrowth (ELO) on SiO2 -masked GaAs substrates a downward tilt of ELO wings caused by their interaction with the mask is observed. The distribution of the tilt magnitude across the wings width is determined with ,m-scale spatial resolution. This allows measuring of the shape of the lattice planes in individual ELO stripes. If a large area of the sample is studied the X-ray imaging provides precise information on the tilt of an individual wing and its distribution. In heteroepitaxial GaSb/GaAs ELO layers local mosaicity in the wing area is found. By the SRXRD the size of microblocks and their relative misorientation were analyzed. Finally, the SRXRD technique was applied to study distribution of localized strain in AlGaN epilayers grown by MOVPE on bulk GaN substrates with AlN mask. X-ray mapping proves that by mask patterning strain in AlGaN layer can be easily engineered, which opens a way to produce thicker, crack-free AlGaN layers with a higher Al content needed in GaN-based laser diodes. All these examples show that high spatial and angular resolutions offered by SRXRD makes the technique a powerful tool to study local lattice distortions in semiconductor microstructures. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Patterned Growth and Transfer of ZnO Micro and Nanocrystals with Size and Location Control,ADVANCED MATERIALS, Issue 8 2008Jesse J. Cole A method to fabricate and transfer crystalline ZnO with control over location, orientation, size, and shape is reported. The process uses an oxygen plasma treatment in combination with a photoresist pattern on magnesium-doped GaN substrates to define narrow nucleation regions and attachment points with 100 nanometer scale dimensions. Lateral epitaxial overgrowth follows nucleation to produce single-crystalline ZnO shown in the figure. [source] Tilt of InGaN layers on miscut GaN substratesPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 7 2010M. Kry Abstract We report on the crystallographic orientation of InGaN layers grown on GaN substrates with a miscut with respect to c -planes up to 2.5°. The samples were examined using high-resolution X-ray diffraction (HRXRD) and atomic force microscopy (AFM). Because of the large (up to about 2% in this study) lattice mismatch between InGaN and GaN, an additional tilt between the c lattice planes of InGaN and GaN was observed and explained by using the Nagai model [J. Appl. Phys. 45, 3789 (1974)]. We observed that for part of the samples, this tilt is about 10% smaller compared to the one predicted by the model. The experimental data are important for understanding the microstructure of InGaN layers grown on substrates of non-perfect morphology. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optimization of homoepitaxially grown AlGaN/GaN heterostructuresPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 10 2010J. A. Grenko Abstract We report on the growth of Al0.25Ga0.75N/GaN heterostructures on low dislocation density semi-insulating c -axis GaN substrates by metalorganic vapor phase epitaxy (MOVPE). A room temperature (RT) Hall mobility (µRT) up to 2065,cm2,V,1,s,1 at sheet density (ns) of 8.25,×,1012,cm,2 has been measured. This work compliments prior studies in which we observed a buffer-induced modulation of the RT two-dimensional electron gas (2DEG) ns and µRT by varying the GaN buffer layer thickness. Here, we focus on the optimization of the heterostructure 2DEG properties by elimination of silicon doping in the Al0.25Ga0.75N barrier and unintentional Al in the not-intentionally doped (n.i.d.) GaN buffer layer. The 15% improvement in µRT and ns relative to previous results is consistent with those predicted by Poisson solver calculations. Use of thick GaN buffers has minimized the theoretical mobility reduction based on intersubband scattering and has enabled us to determine the 2DEG sheet density associated with the polarization field () to be ,5,×,1012,cm,2. [source] InGaN-based 518 and 488,nm laser diodes on c -plane GaN substratePHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2010Takashi Miyoshi Abstract We succeeded in fabricating InGaN-based laser diodes (LDs) with a wavelength of 518 and 488,nm under continuous wave (cw) operation. The both LDs structures were grown on conventional c -plane GaN substrates by metal organic chemical vapor deposition (MOCVD). The threshold current and threshold voltage were 45,mA and 5.5,V at 518,nm, 30,mA and 4.5,V at 488,nm, respectively. The lifetime test of these LDs was carried out under high driving temperature up to 80,°C in cw operation. Lifetime was estimated to be over 5000,h with an optical output power of 5,mW at 80,°C in 515,518,nm LDs from 1000,h operation, and was estimated to be over 10,000,h with an output power of 60,mW at 60,°C in 488,nm LDs from 2000,h operation. [source] Optical anisotropy of A - and M -plane InN grown on free-standing GaN substratesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 5 2010P. Schley Abstract Wurtzite A - and M -plane InN films were grown by molecular beam epitaxy (MBE) on free-standing GaN substrates. Spectroscopic ellipsometry (SE) in the photon energy range from 0.56 up to 15,eV was applied in order to determine the ordinary and extraordinary complex dielectric function (DF) of InN. A distinct optical anisotropy was found over the whole energy range. The extraordinary absorption edge in comparison to the ordinary one is shifted to higher energies confirming previous studies. The investigations in the upper vacuum-ultraviolet (VUV) spectral range (9.5,15,eV) yielded transition energies for four critical points (CPs) of the band structure (BS) which have not been observed so far. [source] Nitride-based quantum structures and devices on modified GaN substratesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2009Piotr Perlin Abstract We have studied the properties of InGaN layers and quantum wells grown on gallium nitride substrates with intentional surface misorientation with respect to its crystalline c -axis. Misorientation varied in the range from 0 up to 2 degree. The indium content was changed by using the different growth temperature (between 750 °C and 820 °C) during metalorganic vapor phase epitaxy. With increasing misorientation angle the average indium content decreased significantly. This effect was accompanied by the strong increase of the emission line bandwidth suggesting more pronounced indium segregation. The results of cathodoluminescence measurements show that these effects correspond to different number of atomic steps/terraces existing on the surface of gallium nitride substrate. Very interesting result is also demonstrated concerning p-type GaN layers. With increasing misorientation, the free hole density drastically increases above 1018 cm,3. This improvement in p-type doping is not related to the increased Mg concentration but to the reduction in the compensating donor density. Using this advantage we demonstrate nitride light emitters with improved electrical properties. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Growth optimisation of the GaN layers and GaN/AlGaN heterojunctions on bulk GaN substrates using plasma-assisted molecular beam epitaxyPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2004C. Skierbiszewski Abstract Influence of growth conditions in plasma assisted molecular beam epitaxy on quality of GaN layers and GaN/AlGaN heterojunctions is studied. The growth diagram for step-flow growth mode and different nitrogen flux is presented. The low defect density of bulk GaN substrates together with very low impurity background concentrations resulted in high electron mobility for GaN/AlGaN heterojunctions: 109,000 cm2/Vs at 1.5 K, and 2500 cm2/Vs at 295 K. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] HVPE GaN substrates: growth and characterizationPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010D. Gogova Abstract GaN substrates with low dislocation densities were prepared by halide vapor-phase epitaxy (HVPE) on c-plane sapphire and by means of a post-growth laser-induced lift-off or natural stress-induced (self-) separation process. The HVPE growth on InGaN/GaN buffer layers and subsequent self-separation method was seen as advantageous, in comparison with the laser-induced lift-off one, in terms of lower cost and better crystalline quality of the GaN material obtained. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] AlGaN/GaN HFETs on Fe-doped GaN substratesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010Yoshinori Oshimura Abstract AlGaN/GaN HFETs with different undoped GaN thicknesses were grown on Fe-doped freestanding GaN substrates by conventional MOVPE. To realize a high drain current, thick undoped GaN is found to be necessary. SIMS measurement shows that Fe is redistributed into the epilayer, by which the scattering center is generated at the channel when the thickness of the undoped GaN is insufficient. We also observed a similar Fe profile in the GaN/sapphire template placed on the side of the Fe-doped GaN substrate during growth. Therefore, Fe in the Fe-doped GaN substrate is redistributed not only through a solid but also through vapor. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Fabrication of light emitting diodes transferred onto different substrates by GaN substrate separation techniquePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010Y. Kunoh Abstract We have successfully transferred GaN films grown on high crystalline quality GaN substrates onto different substrates, where we have developed a laser lift-off technique with a green laser and an absorption-enhanced InGaN layer as a sacrificial layer (a layer to absorb laser beams). We have also achieved an output power of 13.0 mW at 20 mA with a wavelength of approximately 410 nm and an external quantum efficiency of 21.6% for light emitting diodes transferred on Si substrates by using this method (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Cathodoluminescence evaluation of subsurface damage in GaN substrate after polishingPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009K. Y. Lai Abstract The surface of HVPE grown GaN substrates were treated with two different polishing procedures. Both procedures were successful in producing highly smooth and featureless surfaces. However, subsurface damage was observed in the sample treated by one of the procedures. The subsurface damage was revealed by cathodoluminescence (CL) spectroscopy imaging but was not visible by scanning electron microscopy (SEM) or Atomic force microscopy (AFM). Thermal annealing at 950 °C with different gases was performed in an attempt to remove subsurface damages. Annealing in gas mixtures containing H2 increased both the presence of surface scratches and overall surface roughness. On the other hand, annealing in mixtures of NH3 and N2 (with no H2) led to the surfaces with significantly reduced subsurface damage. The surface roughness and optical properties of the sample after the annealing with such gas mixtures were slightly sacrificed. In order to evaluate subsurface damage depth, CL images were taken from the annealed surface for different acceleration voltages. The results suggest that the observed subsurface damages were within 1.48 ,m of the surface. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Investigation of polarity dependent InN{0001} decomposition in N2 and H2 ambientPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009R. Togashi Abstract The polarity dependence of decomposition of the (0001) In- and (000) N-polarity InN layers grown by hydride vapor phase epitaxy (HVPE) on freestanding GaN substrates was investigated. In flowing N2, In- and N-polarity InN layers start to decompose over 550 and 610 °C, respectively. Therefore, the N-polarity InN layer is more stable than the In-polarity InN layer. On the other hand, in flowing H2, InN layers of both polarities start to react with H2 at a low temperature of 350 °C leaving In droplets on the surfaces. Further more, the decomposition rate of the N-polarity InN layer is larger than that of the In-polarity InN layer below approximately 450 °C, while the decomposition rate of the In-polarity InN layer is larger than that of the N-polarity InN above 450 °C. An Arrhenius plot of the decomposition rates revealed that the activation energies, EA, for the decomposition reactions of In- and N- polarity InN layers are 168 and 107 kJ/mol, respectively, which are much smaller than that for GaN and AlN decomposition. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Optical characterization of bulk GaN substrates with c -, a -, and m -plane surfacesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009P. P. Paskov Abstract Thick free-standing GaN grown by hydride vapour phase epitaxy and epi-ready substrates with c -, a -, m -plane surfaces are examined by variable-temperature photoluminescence (PL), polarized PL and spatially resolved micro-PL. Both as-grown samples and polished substrates exhibit linewidth of the donor-bound exciton emission below 0.7 meV at 2 K indicative of a high structural quality of the material. For as-grown samples the relative intensity of green (2.4 eV) and red (1.8 eV) deep-level-defect emissions are found to decrease with increasing sample thickness. Based on plentiful two-electron-transition spectra measured in the samples the electronic fine structure of the donors and their bound-exciton complexes was examined and discussed. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Modulation of mobility in homoepitaxially-grown AlGaN/GaN heterostructuresPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S2 2009J. A. Grenko Abstract We report on the growth of Al0.25Ga0.75N/GaN heterostructures on low dislocation density semi-insulating c-axis GaN substrates. Room temperature Hall mobilities up to 1805 cm2/Vs at sheet carrier densities of 0.77x1013 cm,2 have been measured. By varying the GaN buffer layer thickness in these homoepitaxially-grown Al0.25Ga0.75N/GaN heterostructures, we observed a buffer-induced modulation of the room temperature 2DEG sheet carrier densities and Hall mobilities. The increase in sheet carrier density and corresponding decrease in mobility as the GaN buffer layer thickness is reduced below 0.75 ,m is related to the presence of Si impurities at the bulk GaN substrate/epitaxial interface. Capacitance-voltage measurements and SIMS analysis confirm the presence of Si impurities at the surface prior to and after epitaxial growth. The factor of 2 reduction in the room temperature mobility is consistent with a predicted theoretical mobility reduction based on intersubband scattering. We have also been able to separate the contributions to the 2DEG carrier density from the ionized donors and the polarization field; the magnitude of each is ,5x1012 cm,2. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Barrier-to-well carrier dynamics of InGaN/GaN multi-quantum-wells grown by plasma assisted MBE on bulk GaN substratesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006K. P. Korona Abstract We present study of carrier dynamics in GaInN/GaN multi quantum wells (MQWs) with screened electric fields. The PL emission showed clearly resolved peaks emitted from the Ga0.9In0.1N QWs (at about 3.1 eV, FWHM 30-50 meV). Two samples with 2.5-nm-QWs and 4-nm-QWs showed decay-times of 1.1 ns and 2.3 ns. The decay-rates in the barriers were thermally activated, activation energies were 21 meV and 46 meV, for the 2.5-nm-QWs and 4-nm-QWs structures, respectively. Analysis of correlation between rising-rates of the MQW PL and the decay-rates of the barriers PL confirmed increase of transport through barrier. The MQW PL energy changed with time. The phenomenon was due to trapping of excitons on donors or localization in potential minima. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Defect density dependence of carrier dynamics in AlGaN multiple quantum wells grown on GaN substrates and templatesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005G. A. Garrett Abstract Subpicosecond time-resolved photoluminescence (TRPL) has been used to compare the room temperature carrier dynamics in Al0.1Ga0.9N/Al0.3Ga0.7N multiple quantum well (MQW) structures simultaneously deposited on a high quality free standing HVPE GaN substrate (dislocation density ,1 × 107cm,2) and 1 µm MOCVD GaN template on sapphire. The PL lifetime of ,500 ps in the MQW on GaN substrate is about 5 times longer than that for the MQW on GaN template, with a concomitant increase in CW PL intensity. This behavior is attributed primarily to an increase in nonradiative lifetime associated with a 100 times reduction in dislocation density in the GaN substrate. The observation that the PL lifetime in the MQW falls short of the ,900 ps dominant decay time in the GaN substrate may be indicative of generation of additional defects and dislocations due to substrate surface preparation, strain relaxation, and nonoptimal growth temperature associated with the difference in heating of the thin GaN template on sapphire and the thick GaN substrate. An extended PL rise time of greater than 20 ps for the MQW emission when above barrier pumping is employed implies that both wells and barriers are of high quality. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] GaN based light emitters fabricated on bulk GaN substrates.PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2004New class of low dislocation density devices Abstract In this work we demonstrate the quality of laser diodes fabricated on bulk GaN substrates. These substrates were obtained via high-temperature, high-pressure synthesis and are characterized by a dislocation density as low as 102 cm,2. The epitaxial structure was deposited using a combination of MOVPE and MBE methods. Thanks to such a low and uniform density of dislocations it was possible to realize high power, pulsed current laser diodes with a total output power exceeding 2.5 W. Interestingly enough, the MBE growth method can produce very satisfying results once the growth is resumed on bulk GaN substrates. This contradicts the common believe concerning the poor applicability of the MBE method for the growth of nitride violet laser structures. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||