The room-temperature continuous-wave operation of a 1.5λ-cavity GaN-based vertical-cavity surface-emitting laser with an n-type conducting AlInN/GaN distributed Bragg reflector (DBR) was achieved. A peak reflectivity of over 99.9% was obtained in the n-type conducting AlInN/GaN DBR so that the current was injected through the DBR for the operation. The threshold current was 2.6 mA, corresponding to the threshold current density of 5.2 kA/cm2, and the operating voltage was 4.7 V. A lasing spectrum with a peak wavelength of 405.1 nm and a full-width at half maximum of 0.08 nm was also observed.

We investigated MOVPE growth conditions for AlInN layers with high growth rates and obtained 0.5µm/h with smooth surfaces. We found that short gas mixing time, relatively high growth temperature, and very low In/Al supply ratio were key growth parameters in order to obtain the AlInN layers with high growth rate and smooth surface simultaneously. AlInN/GaN DBRs grown under such growth conditions showed smooth surfaces and a reflectivity of over 99%.

We demonstrated a room-temperature (RT) continuous-wave (CW) operation of a GaN-based vertical-cavity surface-emitting laser (VCSEL) using a thick GaInN quantum well (QW) active region and an AlInN/GaN distributed Bragg reflector. We first investigated the following two characteristics of a 6 nm GaInN 5 QWs active region in light-emitting diode (LED) structures. The light output power at a high current density (∼10 kA/cm2) from the 6 nm GaInN 5 QWs was the same or even higher than that from standard 3 nm 5 QWs. In addition, we found that hole injection into the farthest QW from a p-layer was sufficient. We then demonstrated a GaN-based VCSEL with the 6 nm 5 QWs, resulting in the optical confinement factor of 3.5%. The threshold current density under CW operation at RT was 7.5 kA/cm2 with a narrow (0.4 nm) emission spectrum of 413.5 nm peak wavelength.

We investigated electron and hole accumulations at GaN/AlInN/GaN interfaces by Hall effect measurement. The InN mole fraction and temperature dependences on the sheet carrier densities at the interfaces reveal that electrons and holes were induced by large positive and negative polarization charges to satisfy the charge neutrality conditions, respectively. On the basis of the above results, we then designed and demonstrated a low-resistity 10-pair Si-doped n-type AlInN/GaN distributed Bragg reflector (DBR) by using high Si doped and graded layers at the GaN/AlInN interfaces. The low-resistity n-type AlInN/GaN DBR will reduce the resistance and the internal loss in blue vertical-cavity surface emitting lasers.

We have achieved room-temperature CW operations of GaN-based vertical cavity surface emitting lasers (VCSELs) with periodic gain structures (PGSs). The PGS-VCSEL consisted of 4.5λ-thick optical cavity length and two GaInN 5-quantum-well (QW) active regions separated with a Mg-doped GaN intermediate layer. The uniform carrier injection into the two active regions was also investigated using light-emitting diodes (LEDs). It is found that the use of an optimum Mg concentration in the intermediate layers improves the uniform carrier injection in the two active regions. From these results, we realized the CW operation of VCSELs with PGSs grown on AlInN/GaN distributed Bragg reflectors (DBRs). The VCSEL under CW operation showed a threshold current density of 16.5 kA/cm2 and its operation wavelength was 409.9 nm.