Masayuki Shono

AlGaInP strained multiple-quantum-well visible laser diodes ( lambda /sub L/<or=630 nm band) with a multiquantum barrier grown on misoriented substrates

Optimization of the misorientation angle of GaAs substrates to prepare multiple quantum wells (MQWS) and multiple quantum barriers (MQBs) with abrupt barrier-well interfaces is reported. The characteristics of AlGaInP strained MQW laser diodes incorporating an MQB grown on misoriented substrates are also investigated, with the aim of developing high-performance 630-nm laser diodes. MQW and MQB with homogeneous periodicity and abrupt barrier-well interfaces were obtained using

Operation at 700°C of 6H-SiC UV Sensor Fabricated Using N+ Implantation

We have realized, for the first time, a UV sensor that operates at temperatures up to 700°C by using N+ implantation into 6H-SiC. The photocurrent of the sensor increased with temperature, and at 400°C and 700°C, the photocurrent is approximately double and triple that at room temperature (RT), respectively. It was clarified that the temperature dependence of the photocurrent reveals the characteristics of absorption particular to indirect transition, and also the minority carrier diffusion length. Dark current increased rapidly at temperatures exceeding 450°C.

High-power 200 mW 660 nm AlGaInP laser diodes with low operating current

We have newly introduced a two-step-growth structure and a ridge stripe with steep sidewalls formed with a dry-etching process in the fabrication of a buried ridge stripe structure of a high-power 660 nm laser diode instead of a conventional three-step-growth structure and a ridge stripe with gentle sidewalls formed with a conventional wet-etching process in order to reduce the operating current. We have found that the two-step-growth structure provides better heat dissipation and the dry-etched ridge stripe structure offers higher characteristic temperature. The operating current under pulsed 200 mW at 70°C of the fabricated laser diode is 270 mA. This is the lowest value ever reported so far, to our knowledge. These laser diodes exhibit a kink level and a maximum light output power of 220 mW and higher than 300 mW, respectively. These laser diodes have also operated stably for 1500 h at 70°C with a light output power of 200 mW under the pulsed condition.

Reduction in Operating Current of High-Power 660 nm Laser Diodes Using a Transparent AlGaAs Cap Layer.

We have introduced a transparent AlGaAs cap layer instead of a conventional GaAs cap layer into high-power 660-nm-band-laser diodes with weaker optical confinement in the perpendicular direction, since this structure enables us to weaken the optical confinement without increasing the internal loss for a real index-guided structure. The fabricated laser diodes have demonstrated reduced operating current of 150 mA at 100 mW and increased maximum light output power of 200 mW under the pulsed condition. An aspect ratio of 1.5, which is the smallest of all 660-nm-band high-power laser diodes reported to date, has also been achieved. These laser diodes have been operating stably under the pulsed condition for nearly 2000 h at 60°C with a light output power of 100 mW, which is also the highest of all real index-guided 660-nm-band laser diodes reported to date.

High-Power 660-nm-Band AlGaInP Laser Diodes with a Small Aspect Ratio for Beam Divergence

High-power 660-nm-band AlGaInP laser diodes with a small aspect ratio have been successfully fabricated with a window-mirror structure. The relationship between optical confinement in the perpendicular direction and internal loss was investigated, and a real index-guided structure with an AlInP current blocking layer was applied on the basis of this investigation. A high-power laser diode with a small aspect ratio of 1.65 for beam divergences of 16.5° and 10° in the perpendicular and parallel directions, respectively, has shown a high kink level of 160 mW and a high maximum light output power of 180 mW under pulsed condition. These laser diodes have operated stably for more than 1500 h with a light output power of 90 mW at 60°C under pulsed condition. Stable pulsed operation at 60°C with a high power of 90 mW and small aspect ratio of 1.65 have been simultaneously achieved for the first time.

High-Power Blue-Violet Laser Diode Fabricated on a GaN Substrate

We have successfully fabricated blue-violet laser diodes, consisting of nitride-based semiconductors, with both high-power and low-noise characteristics on GaN substrates. These laser diodes have a ridge waveguide structure with a dielectric current blocking layer. By improving the crystal quality of the grown materials and optimizing the optical confinement in the device, a kink level as high as 250 mW has been achieved. Optimized optical confinement is also assumed to result in far field patterns without any additional peaks. In addition to this, since the threading dislocation density at the active layer below the ridge portion is reduced to less than 105cm-2, these laser diodes have been operating reliably for more than 1000 h with a light output power of 100 mW at 60°C under pulsed operation. We have also confirmed that these laser diodes have a noise level as low as -130 dB/Hz, which meets the requirement for practical use, for a light output power of 5 mW. These laser diodes are expected to enable dual layer recording in nextgeneration, large-capacity optical disc systems using blue-violet laser diodes.

AlGaInP visible laser diodes grown on misoriented substrates

AlGaInP laser diodes grown by metal organic chemical vaper deposition (MOCVD) with GaInP active layers have been practically applied in the lasing wavelength range of 667-680nm’) 2 , . However, the lasing wavelength of these devices is not as short as expected from the normal band-gap energy ( 1.92eV) of AlGaInP alloy systems because sublattice ordering is generated during crystal growth4) . In this paper, we report on AlGaInP laser diodes lasing at shorter wavelengths, ir, which the ordering in the active layer was controlled by using n( 1 0 0 ) GaAs substrates with a misorientation towards the ( 0 1 1) direction. Using ( 1 0 0 ) GaAs substrate with a misorientation of 5O off towards the (011) direction, highly reliable laser diodes lasing at 657nm were obtained for the first time without adding A1 to the active layer. Epitaxial growth was carried out by the threestep low pressure MOCVD method. Source materials were AsH3 , PH3 , TMGa, TMA1, and TMIn. The dopant sources were DMZn and SiH, for ptype and ntype layers, respectively. Substrates were n( 100) GaAs with a misorientation towards the ( 0 1 1) direction from 0 to 7O . Figure 1 shows a cross-sectional view of this laser. The stripe width at the bottom of the ridge was 5sm, the p-type cladding layer thickness under the blocking layer was O.Zam, and the active layer thickness was 0.07am. The cavity length was 400am. Figure 2 shows lasing wavelength dependence on the off-angle towards the (011) direction from ( 1 0 0 ) . With an increase in the off-angle, the lasing wavelength became shorter, approaching the band gap energy in GaInP grown by the LPE method” . We believe the shortened lasing wavelngth was achieved by suppressing the formation of the sublattice ordering structure by using the misoriented substrates5) ’ ) . Using (100) GaAs substrate with a misorientation of 7O off towards the (011) direction, device lasing at 655nm was obtained without adding A1 to the active layer. Fig.3 shows the typical I L curve for a laser diode whose wavelength was 657nm. The threshold current was 55mA. and the transverse mode was stable to 10mW. The maximum temperature (Tmax) for CW operation for this device lasing at 657nm was 85C, which was higher than devices lasing at 660nm with an ( Alo . o 5Gao . 9 ) InP active layer grown on a ( 100) substrate. Figure 4 shows the life test results for laser diodes lasing at 657nm under 3mW at 40T. Five devices have been operating without significant degradation for more than 3,000 hours. In summary, transverse-mode stabilized AlGaInP laser diodes were successfully fabricated by a low pressure MOCVD method on n( 100) GaAs substrates with a misorientation towards the ( 0 1 1 ) direction. Using (100) GaAs with a misorientation of 5-7O off towards ( 0 1 1) direction, the lasing wavelength was found to be about 2Onm shorter than those of ( 100) substrates. In the case of the 5O misorientation towards the (01 1) direction, the lasing wavelength was 657nm, the threshold

High-power blue-violet laser diodes for next-generation optical disc systems

High-power and low-noise characteristics are strongly required for blue-violet laser diodes in practical application to next generation optical disc systems. We have successfully fabricated blue-violet laser diodes meeting these requirements. These laser diodes have a ridge waveguide structure with a dielectric current blocking layer. Improving the crystal quality of the grown materials on a GaN substrate and optimizing the optical confinement in the emission layer have achieved a kink level as high as 250 mW. Optimized optical confinement is also assumed to result in a good beam profile with no fringe. In addition to this, since the threading dislocation density at the emission layer below the ridge portion is reduced to less than 10 5cm-2, these laser diodes have been operating reliably for more than 1000 h with a light output power of 100 mW at 60 °C under pulsed operation. This light output power makes it possible to realize dual layer recording systems. We have also confirmed that these laser diodes have a noise level as low as -130 dB/Hz for a light output power of 5 mW.

High-power 660-nm AlGaInP laser diodes with a small aspect ratio for the beam divergence

High-power 660-nm AlGaInP laser diodes with a small aspect ratio for beam divergence were successfully fabricated with a window mirror structure. The real index-guided structure was adopted from an investigation into internal loss dependence on the beam divergence in the perpendicular direction. A device with the aspect ration of 1.65 for the beam divergence of 10/spl deg/ and 16.5/spl deg/ in the parallel and perpendicular directions has demonstrated a kink level of 160 mW and maximum light output power of 180 mW, which was limited by thermal saturation. These laser diodes have operated reliably for more than 1500 h at 60/spl deg/C with a light output power of 90 mW under pulsed condition with a width of 100 ns and frequency of 5 MHz. High-power operation and a small aspect ratio were thus achieved, simultaneously.