Shinji Terao

UV Light-Emitting Diode Fabricated on Hetero-ELO-Grown Al0.22Ga0.78N with Low Dislocation Density

Using a hetero-epitaxial lateral overgrowth (ELO) technology with low-temperature deposited AlN interlayer, high-quality crack-free Al 0.22 Ga 0.78 N with low dislocation density is realized. The dislocation density in the Al 0.22 Ga 0.78 N was reduced to as low as the order of 10 7 cm -2 over the whole wafer. Applying the high-quality AlGaN layer to a UV light-emitting diode (LED), high output power of more than 0.1 mW at a forward current of 50 mA has been demonstrated with the emission peak wavelengths from 323 to 352 nm. The highest output power of 0.6 mW is obtained for the 352 nm LED with GaN/AlGaN multiple quantum well active layer. The emission efficiency was dependent on the wavelength, and the 323 nm LED has the lowest output power of 0.18 mW at 50 mA bias. One of the factors determining the external quantum efficiency is thought to be an inferior hole spread in highly resistive p-type layers.

High-Efficiency GaN/AlxGa1—xN Multi-Quantum-Well Light Emitter Grown on Low-Dislocation Density AlxGa1—xN

Crack-free and low-dislocation-density Al x Ga 1-x N was achieved by low-temperature-deposited interlayer technique in combination with a lateral seeding epitaxy. We found that there was a strong correlation between the threading dislocation density and the PL intensity in the GaN/AIGaN MQWs. This new UV light emitting diode exhibits strong UV light output, having peak wavelength of 352 nm, a full width at half maximum as narrow as 6 nm and output power of 0.6 mW at 50 mA dc current injection.

Realization of crack-free and high-quality thick AlxGa1−xN for UV optoelectronics using low-temperature interlayer

Crack-free and high-quality thick AlxGa1−xN, with x ranging from 0 to 1, has been grown on sapphire, using a low-temperature interlayer. The low-temperature AlN interlayer reduces tensile stress during the growth of AlxGa1−xN, while simultaneously improving the crystalline quality. The AlxGa1−xN film was characterized by high-resolution X-ray diffraction (XRD) and transmission electron microscopy (TEM).

Fracture of AlxGa1-xN/GaN Heterostructure –Compositional and Impurity Dependence–

Grown-in stress and subsequent fracture in AlxGa1-xN/GaN heterostructures with or without impurity doping were studied in situ. It was found that the critical thickness of AlxGa1-xN depends not only on its composition but also on the concentration of impurities such as Si or Mg. Increase in tensile stress during growth at a constant AlN molar fraction can be explained by the increase in the biaxial modulus of AlxGa1-xN due to impurity doping.

Annihilation of Threading Dislocations in GaN/AlGaN

Cross-sectional transmission electron microscopy (TEM) was performed to observe the behavior of threading dislocations (TDs) in a heterostructure of a GaN/AIGaN layer grown on IL-AlN/ GaN/LT-GaN/α-Al 2 O 3 (0001), where IL-AlN and LT-GaN are an intermediate layer of AlN and a low-temperature buffer layer of GaN, respectively. TDs of (a + c)-type, or TDs with a Burgers vector a + c, are formed at the LT-GaN layer and propagate upwards as far as the top surface, penetrating the AlGaN layer. A number of a-type TDs are generated at the IL, and many of these are annihilated within about 100 nm above the GaN/AIGaN interface. Quick stress relief in the GaN layer on AlGaN is due to the annihilation of a-type TDs.

Relaxation of misfit-induced stress in nitride-based heterostructures

Abstract Relaxation processes of misfit-induced stress in GaN/Al y Ga 1− y N and Al x Ga 1− x N/Al y Ga 1− y N structures ( x > y ) were studied. In case of GaN on relaxed Al y Ga 1− y N, relaxation of compressive-stress occurs in a very early stage of the GaN growth, while in case of Al y Ga 1− y N on Al x Ga 1− x N ( x > y ), tensile-stress relaxation does not occur until the catastrophic relaxation by fracture formation. Surface roughness of the GaN grown on Al y Ga 1− y N can be suppressed by doping with Mg.

Defect and Stress Control of Algan and Fabrication of High-Efficiency Uv-Led

Defects and stress are the most serious issues for growth of AlGaN. Low-temperature deposited (LT -) AlN interlayer between AlGaN and GaN is found to reduce tensile stress during growth, and at the same time suppress the propagation of dislocations having screw components, by which UV-photodetector showing very-low-dark current has been successfully fabricated. However, additional pure-edge dislocations are generated at the LT -interlayer, which resulted in the poor emission property. In addition to the LT -interlayer, lateral growth at the trenched structure was used, thereby achieving crack-free AlGaN and reduction of the density of all types of dislocations in the AlGaN layer. UV light emitting diodes having AlGaN/GaN multi-quantum well active layer was fabricated on the low dislocation density AlGaN. The LED shows strong and sharp UV-emission from GaN-wells.

Transverse-mode control in GaN-based laser diodes

Transverse mode in GaN-based violet laser diodes for both vertical and horizontal directions was investigated. In order to achieve stable fundamental mode operation in vertical direction, thick AlGaN contact layer is found to be effective. For the stabilization of a transverse-mode in horizontal direction of the conventional ridge-waveguide structure, it is necessary to precisely control the remaining thickness of p-AlGaN cladding layer. In comparison, inner stripe structure using AlGaN current blocking layer has wide feasibility of the device parameter, excellent stability of large optical confinement, and small aspect ratio of beam divergence, under the condition of the precise control of the AlN molar fraction in AlGaN current blocking layer.

High Efficiency Uv Emitter Using High Quality GaN/Al x Ga 1−x N Multi-Quantum Well Active Layer

We investigated temperature dependence of the photoluminescence (PL) efficiency of GaN/Al 0.08 Ga 0.92 N multi-quantum wells (MQWs) with variations of Si-doping condition and threading dislocation density. Si-doping in the GaN/Al 0.08 Ga 0.92 N MQWs, especially in the barrier layer improves the PL efficiency. In addition, reduction of threading dislocation density also improves the PL intensity. The PL intensity of the GaN/Al 0.08 Ga 0.92 N MQW is drastically increased at least by a factor of 40, by a combination of the Si-doping and reduction of threading dislocation density. We fabricated a light emitting diode (LED) emitting at 357 nm using such a GaN/Al 0.08 Ga 0.92 N MQWs. Electro-luminescence intensity from the region with threading dislocation density of less than 10 8 cm −2 was much larger than that from the region with threading dislocation density of 6×10 9 cm −2 .

High-Quality Al xGa 1−xN Using Low Temperature-Interlayer and its Application to UV Detector

Low-temperature (LT-) AlN interlayer reduces tensile stress during growth of Al x Ga 1−x N, while simultaneously acts as the dislocation filter, especially for dislocations of which Burgers vector contains [0001] components. UV photodetectors using thus-grown high quality Al x Ga 1−x N layers were fabricated. The dark current bellow 50 fA at 10 V bias for 10 [.mu]m strip allowing a photocurrent to dark current ratio greater than one even at 40 nW/cm 2 have been achieved.