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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]

Terahertz quantum cascade lasers (THz-QCLs) are compact THz laser source with narrow emission linewidth and high output power. Currently, a maximum operation temperature ( Tmax) of 199.5 K is reported by using a state-of-the-art longitudinal optical (LO) phonon depopulation scheme AlGaAs/GaAs structure. We propose an effective method to obtain higher operating temperature for AlGaAs/GaAs THz-QCL by increasing LO-phonon scattering energy by utilizing high Al composition AlGaAs barrier. We have successfully fabricated an LO phonon depopulation scheme AlGaAs/GaAs THz-QCL with double metal waveguide, and obtained 3.7 THz lasing. We obtained the Tmax of 150 K. We observed an increase of Tmax by about 7 K by increasing the Al composition of AlGaAs barrier from 15% to 30%. The characteristic temperature ( T0) was also improved from 44.7 K to 69.9 K by changing the Al composition of AlGaAs barriers. The increase of Al composition in AlGaAs-based THz-QCL was shown to be promising way for obtaining higher operating temperature of THz-QCL. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

The terahertz quantum cascade laser (THz-QCL) is a promising compact THz laser source with high output power and narrow emission line width, and could be put to use in a variety of applications. However, the operating temperature of lower frequency (< 2 THz) QCLs is particularly low, and is limited by the kBT line. This paper demonstrates a 1.9 THz GaAs/Al0.175Ga0.825As QCL operating at temperatures much higher than the kBT line. A selective injection scheme (using a four-level design) with high-Al composition barrier was used to build the low-frequency QCL with high operating temperature. We succeeded in surpassing the kBT line limit for a 1.9 THz QCL that operates up to 160 K (∼1.8 ħw/kB). The selective injection 1.9 THz QCL shows one-frequency lasing operation over the entire injection bias voltage range. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [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]