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 demonstrated low-resistivity GaInN-based tunnel junctions using graded GaInN layers. A systematic investigation of the samples grown by metalorganic vapor phase epitaxy revealed that a tunnel junction consisting of a 4 nm both-sides graded GaInN layer (Mg: 1 × 1020 cm−3) and a 2 nm GaN layer (Si: 7 × 1020 cm−3) showed the lowest specific series resistance of 2.3 × 10−4 Ω cm2 at 3 kA/cm2 in our experiment. The InN mole fraction in the 4 nm both-sides graded GaInN layer was changed from 0 through 0.4 to 0. The obtained resistance is comparable to those of standard p-contacts with Ni/Au and MBE-grown tunnel junctions.

We have systematically investigated acceptor (Mg) and donor (Si) profiles at GaN tunnel junction interfaces with the aim of a low resistivity under reverse bias. We found that an overlap between Mg and Si at the tunnel junction interface was effective in helping to obtain a lower resistivity of the GaN tunnel junctions, which contradicts the typical picture of conventional semiconductor-based tunnel junctions. We demonstrated a LED with the GaN tunnel junction prepared in a single growth run by metalorganic vapor phase epitaxy, showing a differential resistivity of 2.4 × 10−4 Ω cm2 at 5 kA cm−2.

A 4.0λ-cavity GaN-based vertical-cavity surface-emitting laser (VCSEL) using an n-type conductive AlInN/GaN bottom distributed Bragg reflector (DBR) showed a light output power of 1.8 mW with a low differential resistance of 90 Ω. In order to obtain low resistive AlInN/GaN DBRs, 5 nm AlGaInN graded interfaces were introduced. A 40-pair AlInN/GaN DBR with the graded interfaces showed a peak reflectivity over 99.8% and a series resistance of 17 Ω. At the same time, the maximum light output power of a 1.5λ-cavity GaN-based VCSEL with the conductive DBR was only 0.03 mW due to a high thermal resistance of 2700 K W−1 caused by a high thermal resistivity of AlInN. We also conclude that a short cavity typically used in GaAs-based VCSELs is not appropriate in GaN-based VCSELs.