Investigation and comparison of optical gain spectra of (Al,In)GaN laser diodes emitting in the 375 nm to 470 nm spectral range

We measure gain spectra for commercial (Al,In)GaN laser diodes with peak gain wavelengths of 470 nm, 440 nm, 405 nm, and 375 nm, covering the spectral range accessible with electrical pumping. For this systematic study we employ the Hakki-Paoli method, i.e. the laser diodes are electrically driven and gain is measured below threshold current densities, The measured gain spectra are reasonable for a 2D carrier system and understandable when we take into account homogeneous and inhomogeneous broadening. While inhomogeneous broadening is almost negligible for the near UV laser diode, it becomes the dominant broadening mechanism for the longer wavelength laser diodes. We compare the gain spectra with two models describing the inhomogeneous broadening. The first model assumes a constant carrier density, while the second model assumes a constant quasi Fermi level. Both are in agreement with the experimental gain spectra, but predict very different carrier densities. We see our measurements as providing a set of standard gain spectra for similar laser diodes covering a wide spectral range which can be used to develop and calibrate theoretical manybody gain simulations.