Gain of blue and cyan InGaN laser diodes

Experimental gain spectra of 450 and 490 nm laser diodes on c-plane GaN are analyzed by detailed comparison with the results of a fully microscopic theory. The gain calculation shows the importance of electron LO-phonon coupling. The whole spectral gain shape, not only the low energy tail, is strongly influenced by the LO-phonon contribution. The inhomogeneous broadening parameter increases by a factor of about two for the cyan laser diode in comparison with the blue laser structure. This indicates an increase in alloy and thickness fluctuations for the longer wavelength material.