Abstract
The optical gain properties of InGaN-based green (512 nm) laser diodes fabricated on (0001) GaN substrates are investigated. Fitting simulations to the experimental gain spectra provides a Gaussian inhomogeneous broadening of 95 meV, an optical confinement factor of 0.006, and an internal loss as low as ∼10/cm. The remarkable suppression of inhomogeneous broadening and internal loss compensate for the low optical confinement, leading to a low threshold current density of 2.75 kA/cm2. The suppressed inhomogeneity contributes to the highly linear gain increase with the injection carrier, while the low optical confinement results in a relatively low differential mode gain.