Research achievements
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Achievements in FY 2016
Surface-emitting laser
1 device: 3 mW （highest power output in the world）
Ultraviolet sensor
High-performance photosensor with high photosensitivity and low dark current density
The level of light sensitivity is equivalent to that of photo-electron multipliers.
→Response speed is relatively high.
Vertical-cavity surface-emitting laser (VCSEL)
VCSEL design structure
Electric field distribution and refractive index distribution in an active layer
- Vertical current injection structure penetrating through lower DBR
- 1.5 λ resonator length is close to that of infrared VCSEL
Vertical-cavity surface-emitting laser (VCSEL)
Current – Voltage – Optical output characteristics
Laser oscillation
- Threshold current: 2.6 mA (5.2 kA/cm2)
- Threshold drive voltage: 5.0 V
- Series resistance: 135 Ω (when high current is injected)
First nitride surface-emitting laser to achieve continuous oscillation at room temperature by vertical drive current injection penetrating through lower DBR
Using the combination of vertical conducting DBR and tunnel junction
Purpose: To lower the threshold level and improve the slope efficiency of blue surface-emitting laser (VCSEL)
→Application of current constriction structure through buried tunnel junction
Present status
- Drive voltage: 6.16 V @ 5 kA/cm2
- Clear current constriction
- Relatively favorable surface shape
Future
- Application to surface-emitting lasers
- Application to other optical devices
- Solutions in physics
Electron beam excitation GaN-based ultraviolet semiconductor laser
Optical intensity – Injection power – Density dependence
Sample structure
Spectrum
Polarization property