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Non-polar m-plane GaN terahertz quantum cascade laser (THz-QCL) structures have been studied. One is traditional three-well resonant-phonon (RP) design scheme. The other is two-well phonon scattering injection (PSI) design scheme. The peak gains of 41.8 and 44.2 cm−1 have been obtained at 8.2 and 7.7 THz respectively at 300 K according to the self-consistent non-equilibrium Green's function calculation. Different from the usual GaAs two-well design, the upper and lower lasing levels are both ground states in the GaN quantum wells for the PSI scheme, mitigating the severe broadening effect for the excited states in GaN. To guide the fabrication of such devices, the doping effect on the peak gain has been analyzed. The two designs have demonstrated distinct doping density dependence and it is mainly attributed to the very different doping dependent broadening behaviors. The results reveal the possibility of GaN based THz-QCL lasing at room temperature. [ABSTRACT FROM AUTHOR]

The influence of residual impurities in quaternary InAlGaN active layers on the emission efficiency of 350 nm band ultraviolet light-emitting diodes on GaN substrates has been investigated. Secondary ion mass spectrometry and capacitance-voltage measurements have revealed that a large amount of oxygen is incorporated into the InAlGaN active layers owing to relatively low growth temperatures for Al-content epitaxial films. The increase of the InAlGaN growth temperature from 780 to 830 °C results in both the residual oxygen level decrease from 1×1018 to 4×1017 cm-3 and the output power improvement from 0.6 to 2.6 mW at 100 mA. It is also found that devices containing lower oxygen concentration in the InAlGaN active layers demonstrate a higher electroluminescence intensity ratio of the band-edge emission from the well layers to the donor-acceptor-pair emission from the p-type layers at low temperatures. These experimental results, in conjunction with numerical calculations, suggest that the reduction in the oxygen impurity level in the InAlGaN active layers has an effect on suppressing the electron leakage current into the p-type layers, and thus improving the internal quantum efficiency of InAlGaN-based ultraviolet light-emitting diodes. [ABSTRACT FROM AUTHOR]

In order to realize 250–350-nm-band high-efficiency deep ultraviolet (UV) emitting devices using group-III-nitride materials, it is necessary to obtain high-efficiency UV emission from wide-band-gap (In)AlGaN. The use of the In-segregation effect, which has already been used for InGaN blue emitting devices, is quite effective for achieving high-efficiency deep UV emission. We have demonstrated high-efficiency UV emission from quaternary InAlGaN-based quantum wells in the wavelength range between 290 and 375 nm at room temperature (RT) using the In-segregation effect. Emission fluctuations in the submicron region due to In segregation were clearly observed for quaternary InAlGaN epitaxial layers. An internal quantum efficiency as high as 15% was estimated for a quaternary InAlGaN-based single quantum well at RT. Such high-efficiency UV emission can even be obtained on high threading-dislocation density buffer layers. A comparison of electroluminescence is made between light-emitting diodes (LEDs) with InAlGaN, AlGaN, and GaN active regions fabricated on SiC substrates with emission wavelengths between 340 and 360 nm. The emission intensity from the quaternary InAlGaN UV-LED was more than one order of magnitude higher than that from the AlGaN or GaN UV-LEDs under RT cw operation. We therefore fabricated 310–350-nm-band deep UV-LEDs with quaternary InAlGaN active regions. We achieved submilliwatt output power under RT pulsed operation for 308–314-nm LEDs. We also demonstrated a high output power of 7.4 mW from a 352-nm quaternary InAlGaN-based LED fabricated on a GaN substrate under RT cw operation. The maximum external quantum efficiency (EQE) of the 352-nm InAlGaN-based LED was higher than that obtained for an AlGaN-based LED with the same geometry. From these results, the advantages of the use of quaternary InAlGaN in 350-nm-band UV emitters were revealed. [ABSTRACT FROM AUTHOR]

Semipolar III-nitrides have attracted increasing attention because of the reduced piezoelectric field in the active layer. In particular, (11-22) plane is promising due to the small polarization field along the growth axis and the epitaxial matching on m-plane sapphire. The aim of this study was to assess the effect of growth conditions on the structural and electrical properties of Si-doped (11-22) AlGaN. Semipolar AlGaN/AlN layers were grown on m-plane sapphire by metal-organic chemical vapor deposition at different temperatures, V/III ratios, and tetraethylesilane flows. Surface morphology, crystalline quality, and electrical properties of the AlGaN layers were investigated with AFM, XRD, and by Hall measurements, respectively. [ABSTRACT FROM AUTHOR]

We demonstrated high-efficiency deep-ultraviolet light-emitting diodes (DUV-LEDs) by improving light-extraction efficiency (LEE) by using a transparent p-AlGaN contact layer and a highly-reflective p-type electrode. We fabricated DUV-LEDs with emission wavelengths between 265-288 nm using p-AlGaN contact layers with compositional wavelength at around 275 nm. The reflectivity of p-type electrode was increased to be approximately 70% by introducing Ni(1nm)/Al layers. The external quantum efficiency (EQE) of the 287 nm LED was increased from 2% to 5.5% by replacing conventional p-GaN contact layer by transparent p-AlGaN contact layer. The increase of LEE was estimated to be by approximately more than 1.7 times. The use of transparent p-AlGaN contact layer is considered to be basic and quite important technique in order to obtain high LEE in DUV LEDs. The EQE of DUV-LED would be much increased by optimizing the device structure and by combining with other approaches to improve LEE. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

This paper describes the fabrication of quantum dots of GaN, a typical III-V nitride group semiconductor. On investigating GaN growth on the AlGaN mixed crystal surface to be used as a optical and electron confinement layer for device applications, it is found that two-dimensional step flow growth mode can be changed to three-dimensional growth mode by Si supply. This phenomenon is proposed to be effective for fabrication of GaN quantum dots. From the growth kinetics or the energy point of view, Si functions to prevent GaN step flow growth on the AlGaN surface. Furthermore, the free energy on the AlGaN surface is varied by additions of Si. The optical characteristics of GaN quantum dots are evaluated by the photoluminescence method. The dependence of the emission energy from GaN quantum dots on the dot size is confirmed. A laser structure was fabricated and stimulated emission was observed by optical pumping. © 1998 Scripta Technica, electron Comm Jpn Pt 2, 81(6): 20–26, 1998 [ABSTRACT FROM AUTHOR]

GaN quantum dots were formed on an AlGaN/SiC substrate by gas-source molecular beam epitaxy using a self-assembling technique with Ga droplets. The photoluminescence properties of the quantum dots obtained at several crystallization temperatures were investigated. High photoluminescence intensity was observed from GaN quantum dots formed without a wetting layer at a crystallization temperature of 700 °C. Single-electron transistors formed using GaN quantum-dot islands exhibited Coulomb blockade phenomena with negative conductance at 2.7 K and a clear Coulomb staircase at 200 K. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Examines the stimulated emission from optically pumped gallium nitride quantum dots in a heterostructure. Application of chemical vapor deposition in the fabrication of heterostructures; Importance of the simulated emission in understanding lasing mechanism; Effect of insufficient laser light absorption in barrier layers on threshold value.

Influence of Undoped-AlGaN Final Barrier of MQWs on the Performance of Lateral-Type UVB LEDs 17 mW semiconducting aluminium gallium nitride (AlGaN)-based ultraviolet-B (UVB) light-emitting diodes (LEDs) at 300 nm emission grown on AlN template are expected to be useful for production of vitamin D3 in the human body as well as for killing of tomato mosaic virus (ToMV) in tomato. UV-light power is improved in AlGaN UVB LED using optimized undoped-AlGaN final barrier of the quantum well. [Extracted from the article]

Highlights • GaN-based THz-QCL active region was grown by MOCVD on Si substrate. • A GaN/AlGaN QC active layer consisting of two-QW for one-period was grown. • Samples were evaluated by HR-XRD and cross-sectional TEM. • FWHM of the XRD satellite peaks became narrower when growth temperature decreased. Abstract GaN/AlGaN THz quantum-cascade laser (QCL) structures were grown on AlGaN/Si templates by a metal-organic chemical vapor deposition (MOCVD). We aim to fabricate a double metal waveguide (DMW) based GaN THz QCL through removing the Si substrate by wet etching. The DMW is essential for realizing low cavity loss and a very high optical confinement factor (99%). We grew 100 periods of GaN/Al 0.21 Ga 0.79 N two quantum wells (QW) type active region on Al 0.08 Ga 0.92 N/Si templates. Samples were evaluated by cross-sectional transmission-electron microscopy (TEM) and high-resolution X-ray diffraction (HR-XRD). We found that the full width at half maximum (FWHM) of the XRD satellite peaks became narrower when the growth temperature decreased, and the steepness of the QC layer hetero-interfaces has been improved. [ABSTRACT FROM AUTHOR]