Gen-ichi Hatakoshi

Room Temperature Pulsed Operation of Nitride Based Multi-Quantum-Well Laser Diodes with Cleaved Facets on Conventional C-Face Sapphire Substrates

We demonstrate room temperature pulsed operation of nitride based multi-quantum-well (MQW) laser diodes with cleaved mirror facets grown on a conventional C-face sapphire substrate. Cleavage was performed along the direction of the sapphire substrate, and the resultant facet was analyzed using an atomic force microscope (AFM) and theoretical calculation. A single peak emisson, at a wavelength of 417.5 nm, with a full width at half-maximum of 0.15 nm, was obtained. The threshold current density of the laser was 50 kA/cm2 and a voltage for the threshold current was 20 V.

High‐efficiency InGaAlP/GaAs visible light‐emitting diodes

High‐efficiency InGaAlP surface emission light emitting diodes (LEDs) have been successfully fabricated. Newly designed double‐heterostructure LEDs with a GaAlAs current spreading layer were employed to expand the light emission area, which is necessary to take out the light efficiently. The external quantum efficiency was 1.5% at 620 nm orange light for an In0.5 (Ga0.8Al0.2)0.5P active layer LED. This LED is five times more efficient at 620 nm than that of the GaAlAs and GaAsP LEDs. 563 nm green electroluminescence, which is the shortest wavelength ever reported for InGaAlP LEDs, was also achieved with an In0.5(Ga0.5Al0.5)0.5P active layer.

Short-wavelength InGaAlP visible laser diodes

Results achieved on the operation of short-wavelength InGaAlP visible-light laser diodes are described. It is found that there is a strong correlation between operation temperature and oscillation wavelength. The deterioration of favorable temperature characteristics in the short-wavelength region is attributed to an increase in the leakage current, which originates in a small conduction-band discontinuity inherent in the InGaAlP material system. The introduction of a highly doped p-cladding layer improves these temperature characteristics. Short-wavelength oscillation at 630-nm-band wavelength was achieved for transverse-mode stabilized InGaAlP lasers. >

High‐brightness InGaAlP green light‐emitting diodes

Candela class InGaAlP surface‐emission green light‐emitting diodes (LEDs) have been successfully fabricated. The growth of InGaAlP on an intentionally misoriented substrate improved emission properties, as confirmed by a quantitative estimation of the diffusion length in the active material. A Bragg reflector using InGaAlP was realized for the first time. A new device structure, including this Bragg reflector, drastically improved the light extraction efficiency. An external quantum efficiency of 0.7% at 573 nm green light was obtained, corresponding to a luminous intensity of 2 cd.

Highly reliable InGaP/InGaAlP visible light emitting inner stripe lasers with 667 nm lasing wavelength

To obtain highly reliable InGaP/InGaAlP inner stripe (IS) lasers, the relation between the maximum CW operation temperature and other laser characteristics has been determined. The Al composition of the cladding layer, the carrier concentration of the p-cladding layer, and the thicknesses of the active layer and cladding layer have been optimized. It was found that an Al composition of 0.7 was the most suitable for the cladding layer, and the optimized carrier concentration was 4*10/sup 17/ cm/sup -3/. A maximum temperature of 90 degrees C was obtained for a 0.1- mu m active layer thickness and a 0.6- mu m cladding layer thickness. This is the highest value for InGaP/InGaAlP IS lasers. In the case of a 0.06- mu m active layer thickness and a 0.8- mu m cladding layer thickness, a maximum temperature of 75 degrees C was obtained. IS lasers with facet coating have been operating stably for more than 8000 h at 40 degrees C and 3 mW and for more than 4000 h at 50 degrees C and 3 mW. >

Characteristics of a distributed Bragg reflector for the visible‐light spectral region using InGaAlP and GaAs: Comparison of transparent‐ and loss‐type structures

Distributed Bragg reflectors (DBRs) for the visible‐light spectral region constructed by InAlP/InGaAlP pairs and InAlP/GaAs pairs, grown by metalorganic chemical‐vapor deposition, have been investigated with the point of comparing optical and structural properties. In the case of the InAlP/InGaAlP stacked type, a reflectivity above 80% has been realized; however, the bandwidth decreased by shortening the peak wavelength. The reflection spectrum of the InAlP/GaAs DBR showed a wide‐band characteristic and provided a relatively high reflectivity to the green region in spite of the absorption loss of the GaAs layers. These results were in good agreement with theoretical calculations considering the absorption loss and refractive index of individual stacked layers. These DBRs have also been confirmed to have good uniformity and periodicity through cross‐sectional transmission electron microscopy and x‐ray rocking curve analysis. Good electrical conductivity through these DBRs has been obtained for the n‐type s...

Waveguide grating lenses for optical couplers

New waveguide grating lenses for coupling a guided wave to a spherical wave, focusing in the air, have been designed. The lenses have the advantages. of high efficiency and high practicability for fabrication. Chirped and curved grating lenses were fabricated on PMMA waveguides by an electron beam exposure system.

New window-structure InGaAlP visible light laser diodes by self-selective Zn diffusion-induced disordering

The behavior of Zn diffusion in InGaAlP double heterostructures during a second metalorganic chemical vapor deposition (MOCVD) growth was investigated, and it found that the behavior of Zn diffusion strongly depends on the presence of an n-GaAs capping layer. A process for InGaAlP window-structure InGaAlP laser diodes was designed using this unique diffusion behavior and disordering of a natural superlattice. A window structure realizing a high power operation was successfully fabricated. A maximum output power above 80 mW was obtained for continuous wave (CW) operation, and 400 mW for pulsed operation. >

Emission Properties of InGaAlP Visible Light-Emitting Diodes Employing a Multiquantum-Well Active Layer

Visible InGaAlP light-emitting diodes (LEDs) employing a multiquantum-well (MQW) active layer have been investigated. Photo luminescence measurements showed that growth on a GaAs substrate, with an intentional surface misorientation from the (100) plane towards the [011] direction, resulted in a marked improvement in the quality of the MQW compared with growth on a just (100) substrate. The emission properties of the LED strongly depended on the various parameters of the MQW structure, in particular the number of wells. The external quantum efficiency of a 600 nm LED with a 20-well MQW active layer was found to be 1.6%. The emission wavelength could be further reduced by 10 nm without any significant decrease in the external quantum efficiency.

High-Power InGaAlP Laser Diodes for High-Density Optical Recording

Theoretical investigation has been carried out for high-power InGaAlP visible-light laser diodes. The thin active layer, essential for preventing catastrophic optical damage of the laser facet, enhances carrier overflow and causes a deterioration in temperature characteristics. Increase in the bandgap energy difference between the active layer and the cladding layer is required in order to maintain sufficient heterobarrier height. High acceptor concentration for a p-cladding layer has a great effect on the prevention of the carrier overflow and, as a result, on the improvement of the temperature characteristics. High-power transverse-mode stabilized InGaAlP lasers, operating at high temperature, were realized by employing a composition-shifted thin active layer and a highly doped p-cladding layer. High-power operation, at over 100 mW, was achieved.