We demonstrate electrically driven InGaN based laser diodes (LDs), with a simple AlGaN-cladding-free epitaxial structure, grown on semipolar (2021) GaN substrates. The devices employed In0.06Ga0.94N waveguiding layers to provide transverse optical mode confinement. A maximum lasing wavelength of 506.4 nm was observed under pulsed operation, which is the longest reported for AlGaN-cladding-free III-nitride LDs. The threshold current density (Jth) for index-guided LDs with uncoated etched facets was 23 kA/cm2, and 19 kA/cm2 after application of high-reflectivity (HR) coatings. A characteristic temperature (T0) value of ∼130 K and wavelength red-shift of ∼0.05 nm/K were confirmed.

We demonstrate continuous-wave (CW) operation of nonpolar m-plane InGaN/GaN laser diodes without Al-containing waveguide cladding layers. Thick InGaN quantum wells (QWs) are used to generate effective transverse optical mode confinement, eliminating the need for Al-containing waveguide cladding layers. Peak output powers of more than 25 mW are demonstrated with threshold current densities and voltages of 6.8 kA/cm 2 and 5.6 V, respectively. The unpackaged and uncoated laser diodes operated under CW conditions for more than 15 h.

We demonstrate the first electrically-injected InGaN/GaN laser diodes (LDs) grown on semipolar (3031) free-standing GaN substrates. The lowest threshold current density (Jth) was 5.6 kA/cm2 with a clear lasing peak at 444.7 nm. The peak electroluminescence (EL) wavelength blue-shifted 4 nm below threshold and the characteristic temperature was ∼135 K. These results suggest that the semipolar (3031) plane may be a potential candidate for growing high performance nitride-based LDs.

We demonstrate AlGaN-cladding-free m-plane InGaN/GaN laser diodes with threshold current densities that are comparable to state-of-the-art c-plane InGaN/GaN laser diodes. Thick InGaN waveguiding layers and a relatively wide active region with three 8 nm quantum wells were used to provide adequate refractive index contrast with the GaN cladding layers, thus eliminating the need for AlGaN cladding layers. Despite the large active region volume, lasing was achieved at a threshold current density of 1.54 kA/cm2, suggesting that the realization of even lower threshold current densities should be possible by reducing the number of quantum wells in the active region.

Nonpolar blue-green (481 nm) InGaN/GaN laser diodes (LDs) were realized by using m-plane GaN substrates with a misorientation angle of approximately 1° toward [0001] direction. The laser diode structures grown on miscut m-plane GaN substrates showed significantly smoother surface morphology compared to structures grown on nominally on-axis m-plane GaN substrates. It is contributed to lower threshold current densities, longer lasing wavelength, and higher lasing yield than those on on-axis substrates grown by the same growth condition. Material improvement based on the control of substrate misorientation is essential to achieve high performance LDs beyond the blue spectral range.