Critical discussion of the determination of internal losses in state-of-the-art (Al,In)GaN laser diodes

Abstract

Green laser diodes are being used for many applications, especially for laser projection. An important parameter for laser diodes are the internal losses. The internal losses of blue and green (Al,In)GaN laser diodes have been decreased to values significantly below αint = 10 cm-1, such enabling laser diodes with low threshold, high efficiency, and high output power. However, it is difficult to measure such low internal losses. From the slope efficiency and from Hakki-Paoli gain spectra, we derive an upper and lower limit for the internal losses of 5.4 cm-1 and 3.7 cm-1, respectively, for a specific green laser diode. Furthermore, we perform transfer matrix method simulations of the waveguide modes to simulate the dispersion of the internal losses in the wavelength range where the quantum wells are transparent. Comparing simulated and measured dependency of the internal losses on wavelength, we argue that the leakage of the waveguide mode to the p-contact and into the substrate are the main contributions to the dispersion of the internal losses.