Nobuyuki Otake

High-Power Vertical-Cavity Surface-Emitting Laser under a Short Pulsed Operation

We report on the lasing characteristics of a single vertical-cavity surface-emitting laser (VCSEL) with InGaAs/GaAs multiple-quantum-wells under high-power pulsed operations. External quantum efficiency was improved by decreasing carrier overflow in the active region, and it was found that increasing the number of quantum wells suppressed carrier overflow. The highest peak pulsed power of over 12.5 W at an injection current of 20 A was achieved by a single VCSEL with five InGaAs quantum wells (QWs) in the active region.

High-Pulsed-Power (49W) Vertical-Cavity Surface-Emitting Laser with Five Quantum Wells by Uniform Current Injection into Large Emitting Area

We report on the high-power lasing characteristics of a large area bottom-emitting vertical-cavity surface-emitting laser (VCSEL). There have been difficulties in uniform current injection for large area VCSELs, which are caused by the band discontinuity at the interface between AlAs and GaAs of the n-type Distributed Bragg Reflector (DBR). We have reported the n-type DBR using a graded composition interface of 20nm thick suppresses the crowding of current to the edge of emitting area and improves external efficiency [1]. The highest peak pulsed power of over 49W was achieved by a five-quantum-well VCSEL with a current aperture diameter of 200µm.

Highly reliable GaN MOS-HFET with high short-circuit capability

A new MOS-HFET structure of a GaN power device for highly reliable GaN MOS gates has been designed. A normally-on JFET structure is fabricated between the gate and drain of the GaN MOS-HFET. By using this technology, the reliability of the gate insulator is greatly improved under the high drain voltage of the blocking-state. The new GaN MOS-HFET also reduces saturation current in the short-circuit condition by about 30%. It is expected that this new device improves the tolerance characteristics in the short-circuit condition without the on-resistance penalty associated with conventional structures.

High-power vertical-cavity surface-emitting laser under pulsed operation

We have investigated InGaAs multiple-quantum-wells vertical-cavity surface-emitting laser (VCSEL) under high-power pulsed operation. The peak pulsed power of over 12.5 W has been achieved with the single VCSEL device which has five InGaAs quantum wells.