Optical Gain Spectroscopy of a Semipolar $\{20\bar{2}1\}$-Oriented Green InGaN Laser Diode

Optical gain is assessed for a green laser diode (LD) grown on a semipolar $\{20\bar{2}1\}$ GaN substrate. The estimated internal loss is $20\pm 5$/cm, and the maximum gain becomes saturated with the injection current, suggesting the existence of gain suppression mechanisms. The quantum-confined Stark effect due to the pn junction, state filling, and screening of polarization-induced electric fields can explain shifts in the gain and the emission peaks with the injection current. The tail states in $\{20\bar{2}1\}$ LDs are much smaller than those in (0001) LDs, and are not the major cause of the gain suppression in $\{20\bar{2}1\}$ LDs, in contrast to (0001) LDs.