Kunihiro Takatani

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.

Laser Diode Active Height Control for Near Field Optical Storage

The use of commercial laser diodes as near field, nano-scale position sensors for feedback control systems was experimentally investigated. A static experimental setup was constructed to measure and characterize the laser diode feedback mechanism. Experiments show that the lasers, which act as miniature interferometers, provide a high accuracy, high signal-to-noise ratio (SNR) signal both in the near and far field. The laser diodes were then mounted in commercial digital versatile disc (DVD) actuators and a control system was constructed. The control system can operate both in the near and far field, and a controlled approach from the far to near field is demonstrated using a fringe jump controller. Finally, using the experimentally gathered feedback data, the residual control error of ±1 nm was estimated for this system.

Ohmic Contact Formation on p-type GaN Using Pd/Mo Electrode without Alloying Process

Ohmic contact formation on a p-GaN layer with a specific contact resistance of ρc=5×10-4 Ωcm2 has been achieved using a Pd/Mo electrode without the use of an alloying process. ρc was reduced to 2×10-4 Ωcm2 by annealing in vacuum at 500°C. The Pd/Mo electrode showed much improved ohmic-contact characteristics than the Ni/Mo electrode. Characterization by micro-Raman scattering revealed that the hole concentration increased in the p-GaN layer just under the Pd/Mo electrode with increasing annealing temperature. This cannot be explained by the removal of hydrogen. A decrease in the density of hole traps and an increase in the density of active acceptors, such as Ga vacancies, are considered to be the most significant contributing factors.