Norimichi Noguchi

231–261nm AlGaN deep-ultraviolet light-emitting diodes fabricated on AlN multilayer buffers grown by ammonia pulse-flow method on sapphire

The authors demonstrated AlGaN multiquantum-well (MQW) deep-ultraviolet light-emitting diodes (LEDs) with wavelengths in the range of 231–261nm, fabricated on low threading dislocation density AlN buffers formed through an ammonia (NH3) pulse-flow multilayer growth technique. The authors obtained a single-peaked operation of the AlGaN-MQW LED with a wavelength of 231nm, which is the shortest wavelength of AlGaN-based LED on sapphire. The maximum output power and external quantum efficiency of the 261 and 231nm LEDs were 1.65mW and 0.23% under room-temperature (RT) continuous-wave (cw) operation, and approximately 5μW and 0.001% under RT pulsed operation, respectively.

227 nm AlGaN Light-Emitting Diode with 0.15 mW Output Power Realized using a Thin Quantum Well and AlN Buffer with Reduced Threading Dislocation Density

AlGaN multi-quantum-well (MQW) deep-ultraviolet (DUV) light-emitting diodes (LEDs) fabricated on sapphire substrates with emission at 227 nm are demonstrated. A remarkable enhancement in the DUV LED output power was achieved by using a thin AlGaN quantum well only 1.3 nm in thickness, with atomically flat hetero-interfaces, together with an AlN buffer layer of reduced threading dislocation density. The AlGaN-MQW DUV LEDs exhibited single emission peaks. The output power was 0.15 mW with injection current of 30 mA and the maximum external quantum efficiency was 0.2%, under room temperature pulsed operation.

222 nm Deep-Ultraviolet AlGaN Quantum Well Light-Emitting Diode with Vertical Emission Properties

We demonstrated a 222 nm deep-ultraviolet (DUV) AlGaN multi-quantum well (MQW) light-emitting diode (LED) fabricated on a high-quality AlN buffer layer grown on a sapphire substrate, which is the shortest wavelength AlGaN LED ever reported. The maximum output power and the external quantum efficiency of the 222 nm AlGaN LED were 14 µW and 0.003%, respectively, under pulsed current injection. We also investigated the radiation angle dependence of a series of 222–253 nm AlGaN QW DUV LEDs, and demonstrated that vertical c-axis emission can be obtained even when the Al composition of the AlGaN QW is as high as 83%.

222-282 nm AlGaN and InAlGaN based deep-UV LEDs fabricated on high-quality AlN template

We demonstrate 222-282 nm AlGaN and InAlGaN-based deep ultraviolet (DUV) light-emitting diodes (LEDs) fabricated on low threading dislocation density (TDD) AlN template. Low TDD AlN templates were realized by using ammonia (NH3) pulse-flow multilayer (ML) growth technique. The edge- and screw-type dislocation densities of AlN layer were reduced to 7.5×108 and 3.8×107, respectively. We obtained significant increase of an AlGaN quantum well (QW) emission (by more than 50 times) by fabricating them on a low TDD ML-AlN template. We fabricated AlGaN multi (M)QW DUV-LEDs with emission range of 222-273 nm on ML-AlN templates. Single-peaked electroluminescence (EL) was obtained for AlGaN DUV-LEDs. We obtained the maximum output power of 1.1, 2.4 and 3.3 mW for the AlGaN LEDs with wavelengths of 241, 253 and 273 nm, respectively, under RT CW operation. The maximum output power of 227 and 222 nm AlGaN-QW were 0.15mW and 0.014mW, respectively, under RT pulsed operation. The maximum external quantum efficiency (EQE) of the 227 and 250 nm AlGaN LEDs were 0.2% and 0.43 %, respectively. We also fabricated 280 nm-band quaternary InAlGaN-MQW DUV-LEDs with p-type InAlGaN layers on low TDD ML-AlN templates. We obtained significant increase of photoluminescence (PL) intensity by introducing Si-doped InAlGaN buffer and barrier layers and undoped InAlGaN interlayer. We then demonstrated high internal quantum efficiency (IQE) of 284 nm InAlGaN-QW emission, which was confirmed by the fact that the ratio of the integrated intensity of the RT-PL against the 77K-PL was 86%. The maximum output power and EQE of the 282 nm InAlGaN LED were 10.6 mW and 1.2%, respectively, under RT CW operation.