Room-Temperature Stimulated Emission from AlN at 214 nm (original) (raw)
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physica status solidi (a), 2020
Ammonia and plasma-assisted (PA) molecular beam epitaxy modes are used to grow AlN and AlGaN epitaxial layers on sapphire substrates. It is determined that the increase of thickness of AlN buffer layer grown by ammonia-MBE from 0.32 μm to 1.25 μm results in the narrowing of 101 X-Ray rocking curves whereas no clear effect on 002 X-Ray rocking curve width is observed. It is shown that strong GaN decomposition during growth by ammonia-MBE causes AlGaN surface roughening and compositional inhomogeneity, which leads to deterioration of its lasing properties. AlGaN layers grown by ammonia-MBE at optimized temperature demonstrate stimulated emission (SE) peaked at λ = 330 nm, 323 nm, 303 nm and 297 nm with the SE threshold values of 0.7 MW cm-2 , 1.1 MW cm-2 , 1.4 MW cm-2 and 1.4 MW cm-2 , respectively. In comparison to these, AlGaN layer grown using PA-MBE pulsed modes (migration-enhanced epitaxy, metal-modulated
Excitonic recombination in epitaxial lateral overgrown AlN on sapphire
Applied Physics Letters, 2013
Excitonic emission in heteroepitaxially grown aluminum nitride (AlN) with reduced defect density due to the epitaxial lateral overgrowth (ELO) of patterned AlN/sapphire templates has been investigated by photoluminescence spectroscopy and compared to AlN/sapphire and homoepitaxially grown AlN. The ELO sample exhibits small linewidths of the free exciton and two different bound exciton emission bands. The free exciton emission energy is shifted by 58.5 meV with respect to unstrained homoepitaxially grown AlN attributed to compressive strain. A donor bound exciton D 0 X with an exciton localization energy of 13.0-13.5 meV is dominating in the photoluminescence spectra of ELO AlN/sapphire. This D 0 X does not show strong phonon replica and is dominant at elevated temperatures in ELO AlN/sapphire. The optical quality of heteroepitaxial AlN is significantly improved using the ELO technique and therefore suitable for high efficiency ultraviolet light emitters. V C 2013 AIP Publishing LLC.
Growth of high quality AlN on sapphire by using a low-temperature AlN interlayer
SPIE Proceedings, 2009
Aluminum nitride is a material of great potential for high power electronic devices, UV photonic devices as well as acoustic devices. However, the lack of a good crystal growth technology for bulk material and substrate hinders the development of these AlN-based devices. While AlN has been successfully grown on sapphire substrate for some time, the presence of a large number of dislocations in the material is still a major barrier to overcome [1]. In this work, we demonstrate a low-dislocation-density AlN template on sapphire by inserting an AlN interlayer by metal-organic chemical vapor deposition. The main idea of our approach is to change the growth mode in the course of the epitaxial growth by decreasing growth temperature and changing V/III ratio. As the growth mode changes, dislocations tend to be redirected and/or form dipole half loops via annihilation processes [2]. The etch-pit-density of the AlN templates is reduced from 3.6×10 9 cm-2 to 1.7×10 9 cm-2. Accordingly, the full width at half maximum of the (0002) x-ray rocking curve is reduced from 37 arcsec to 12 arcsec. The result indicates that the AlN template has low screw and mixed type dislocations. AlGaN/GaN Schottky diodes fabricated on this high quality AlN template exhibit very high breakdown voltage (> 2000 V), which sets a record-high figure of merit of 1.37 GW/cm 2 .
Journal of Crystal Growth, 2019
We present overgrowth of nano-patterned sapphire with different offcut angles by metalorganic vapor phase epitaxy. Hexagonal arrays of nano-pillars were prepared via Displacement Talbot Lithography and dry-etching. 6.6 µm crack-free and fully coalesced AlN was grown on such substrates. Extended defect analysis comparing Xray diffraction, electron channeling contrast imaging and selective defect etching revealed a threading dislocation density of about 10 9 cm-2. However, for c-plane sapphire offcut of 0.2° towards m direction the AlN surface shows step bunches with a height of 10 nm. The detrimental impact of these step bunches on subsequently grown AlGaN multi-quantum-wells is investigated by cathodoluminescence and transmission electron microscopy. By reducing the sapphire offcut to 0.1° the formation of step bunches is successfully suppressed. On top of such a sample an AlGaN-based UVC LED heterostructure is realized emitting at 265 nm and showing an emission power of 0.81 mW at 20 mA (corresponds to an external quantum efficiency of 0.86 %).
Applied Physics Letters, 2014
Optically-pumped deep-ultraviolet (DUV) lasing with low threshold was demonstrated from AlGaN-based multiple-quantum-well (MQW) heterostructures grown on sapphire substrates. The epitaxial layers were grown pseudomorphically by metalorganic chemical vapor deposition (MOCVD) on (0001) sapphire substrates. Stimulated emission was observed at wavelengths of 256 nm and 249 nm with thresholds of 61 kW/cm 2 and 95 kW/cm 2 at room temperature, respectively. The thresholds are comparable to the reported state-of-the-art AlGaN-based MQW DUV lasers grown on bulk AlN substrates emitting at 266 nm. These low thresholds are attributed to the optimization of active region and waveguide layer as well as the use of high-quality AlN/sapphire templates. The stimulated emission above threshold was dominated by transverse-electric (TE) polarization. This work demonstrates the potential candidacy of sapphire substrates for DUV diode lasers.
Very high quality AlN grown on (0001) sapphire by metal-organic vapor phase epitaxy
Applied Physics Letters, 2006
Very high quality AlN epitaxially grown on ͑0001͒ sapphire by metal-organic vapor phase epitaxy is investigated by atomic force microscopy, x-ray diffraction, and photospectrometry. A clear and continuously linear step-flow pattern with sawtooth shaped terrace edges is observed in atomic force microscopic images. Triple-axis x-ray rocking curves show a full width at half maximum of 11.5 and 14.5 arc sec for the ͑002͒ and ͑004͒ reflections, respectively. KOH etching reveals an etch-pit density of 2 ϫ 10 7 cm −2 , as deduced from atomic force microscopy measurements. The optical transmission spectrum shows a sharp absorption edge with a band gap energy of 6.10 eV.
Structural and optical characterization of AlN films grown by pulsed laser deposition
Applied Surface Science, 2005
High quality Al x Ga 1À x N layers have been grown on c-plane sapphire substrate by Metal Organic Vapor Phase Epitaxy. The aluminum (Al) composition was varied from 15% to 51%. When the flow rate of trimethylaluminum was increased, the growth rate was found to be decreased. The crystalline quality of AlGaN layers has been evaluated using High Resolution X-ray Diffraction rocking curves. Reciprocal Space Mapping results confirmed that at low Al composition (x¼ 0.15), AlGaN layers are found to be fully strained. At high Al composition (x¼ 0.33, 0.51), AlGaN layers are relaxed by generation of cracks due to lattice mismatch. The optical properties of AlGaN/GaN layers have been investigated by room temperature photoluminescence. With increasing Al content, the AlGaN emission peak has been found to shift towards higher energies. The surface morphology and roughness of AlGaN have been studied by Atomic Force Microscopy. Root Mean Square roughness values have been found to increase with the increase of Al.
Diamond and Related Materials, 2010
We investigated influences of a repetition frequency of laser pulses on growth of AlN crystalline films by pulsed laser deposition. The structural and morphological properties of the films were studied by X-ray diffraction and scanning electron microscopy. Employment of high frequency laser pulses not only enhanced the growth of AlN crystallites, but also afforded the crystal growth at higher nitrogen pressures. Growth of α-AlN was dramatically enhanced with an increase in the laser pulse frequency, while β-AlN was grown at the high frequency of laser pulses and high nitrogen pressures.
Growth of high quality AlN on sapphire by using a low-temperature AlN interlayer
Gallium Nitride Materials and Devices IV, 2009
Aluminum nitride is a material of great potential for high power electronic devices, UV photonic devices as well as acoustic devices. However, the lack of a good crystal growth technology for bulk material and substrate hinders the development of these AlN-based devices. While AlN has been successfully grown on sapphire substrate for some time, the presence of a large number of dislocations in the material is still a major barrier to overcome [1]. In this work, we demonstrate a low-dislocation-density AlN template on sapphire by inserting an AlN interlayer by metal-organic chemical vapor deposition. The main idea of our approach is to change the growth mode in the course of the epitaxial growth by decreasing growth temperature and changing V/III ratio. As the growth mode changes, dislocations tend to be redirected and/or form dipole half loops via annihilation processes [2]. The etch-pit-density of the AlN templates is reduced from 3.6×10 9 cm-2 to 1.7×10 9 cm-2. Accordingly, the full width at half maximum of the (0002) x-ray rocking curve is reduced from 37 arcsec to 12 arcsec. The result indicates that the AlN template has low screw and mixed type dislocations. AlGaN/GaN Schottky diodes fabricated on this high quality AlN template exhibit very high breakdown voltage (> 2000 V), which sets a record-high figure of merit of 1.37 GW/cm 2 .