Shigetoshi Ito

Blue Laser Diodes Fabricated on m-Plane GaN Substrates

Blue laser diodes (LDs) were fabricated on m-plane oriented GaN substrates by atmospheric-pressure metalorganic chemical vapor deposition. Typical threshold current for stimulated emission at a wavelength λ of 463 nm was 69 mA. Blueshift of the spontaneous emission peak with increasing injection current was examined in LDs fabricated on m- and c-plane GaN substrates. Blueshifts for the m-plane LD (λ=463 nm) and the c-plane LD (λ=454 nm) with an injection current density just below threshold were about 10 and 26 nm, respectively. These results confirm that the blueshift in quantum-wells fabricated on m-plane oriented substrates is smaller than on c-plane oriented substrates due to the absence of polarization-induced electric fields.

Self-pulsation in InGaN laser diodes with saturable absorber layers

Self-pulsating InGaN laser diodes with a p-type InGaN saturable absorber (SA) layer are demonstrated. The SA layer consists of a 1-nm-thick p-type InGaN well surrounded by 2-nm-thick p-type In0.02Ga0.98N barriers. The lower barrier of the SA is located on the 18-nm-thick p-type Al0.3Ga0.7N evaporation-prevention layer of the active region. Self-pulsation is demonstrated for output powers in the range 4 to 22 mW with corresponding self-pulsation frequencies in the range 1.6 to 2.9 GHz. Results indicate that the position of the SA layer in the structure has a strong influence on the carrier lifetime and is responsible for the observation of self-pulsation in these devices.

Highly reliable 500 mW laser diodes with epitaxially grown AlON coating for high-density optical storage

Highly reliable operation of 405 nm laser diodes for high-density optical storage was demonstrated. Introduction of epitaxially grown AlON layer between the front facet and normal coating layer was shown to be effective to suppress catastrophic optical damage at the laser facet. Stable operation in excess of 1000 h was confirmed at an output power of 500 mW in a pulsed-mode at a case temperature of 80 °C.Highly reliable operation of 405 nm laser diodes for high-density optical storage was demonstrated. Introduction of epitaxially grown AlON layer between the front facet and normal coating layer was shown to be effective to suppress catastrophic optical damage at the laser facet. Stable operation in excess of 1000 h was confirmed at an output power of 500 mW in a pulsed-mode at a case temperature of 80 °C.

AlGaInN Violet Laser Diodes Grown on GaN Substrates with Low Aspect Ratio

AlGaInN violet laser diodes grown on GaN substrates have been studied. Waveguide simulations have been performed and perpendicular radiation angles have been investigated. A peculiar layer structure has been proposed to reduce the perpendicular radiation angle and compared with a conventional laser. The laser structure has an n-cladding layer consisting of three AlGaN films, the middle film of which has relatively high Al composition. A laser diode with an optimized structure has been fabricated. The threshold current density and slope efficiency have been 2.9 kA/cm2 and 1.4 W/A, respectively. The perpendicular radiation angle has been as small as 16.2°. The AlGaInN violet laser diode with a low aspect ratio of 1.6 and a small threshold current of 29 mA has been realized.

Self-pulsation in an InGaN laser-theory and experiment

Room-temperature operation of self-pulsating InGaN lasers was obtained at a wavelength of 395 nm. The laser structure consists of a multiquantum-well InGaN active layer and a p-type InGaN single-quantum-well saturable absorber. The frequency range of the self-pulsation was from 1.6 to 2.9 GHz. The experimental results were well explained with our theoretical analysis. We found that features of the saturable absorber strongly affect the self-pulsation. Influence of device and material parameters on the laser dynamics was also investigated.

Electric Field Induced Carrier Sweep-Out in Tandem InGaN Multi-Quantum-Well Self-Pulsating Laser Diodes

Mechanisms of carrier sweep-out in tandem InGaN multiple-quantum-well self-pulsating laser diodes were investigated. Laser diodes showed self-pulsating characteristics without significant change in the light output–current (I–L) characteristics when an electric field high enough was established in the saturable absorber by the applied reverse bias. Improvements in the design of the band-energy profile allowed a substantial reduction in the bias required for self-pulsating operation. These results indicate that carrier lifetime can be controlled by the electric field in the saturable absorber and that band-energy profile engineering is effective for the reduction of carrier lifetime.