A method to calculate the reflectivity of the coated cavity facet was proposed, and the distribution of the optical power near the two coated cavity facets was calculated for GaN-based laser diodes. A new design method for reducing the optical power at the two cavity facets without changing the output power of laser diodes was discussed, which is helpful to optimize the cavity facet coating and raise the threshold current at which catastrophic optical damage occurs.
We have fabricated InGaN-based superluminescent diodes(SLDs)with one-sided oblique facet.The characteristics of the SLDs and laser diodes with the same cavity length(800 lm)were compared.The typical peak wavelength and the full width at half maximum of the spectrum in superluminescence regime are 445.3 and 7.7 nm for the SLDs with 800 lm cavity length.The characteristics of the SLDs with different cavity length were also demonstrated in a comparative way.It is found that the gain of the InGaN multi-quantum wells in blue spectral range is a linear function of the current density below gain saturation region.The lasing threshold current turns out to be higher for the shorter SLD(S-SLD)(400 lm),but the output light intensity of the longer SLD(800 lm)is higher than that of the S-SLD under the same current density.The gain saturation phenomenon was observed in S-SLD when it was biased at a current density larger than 27.5 kA/cm2.The increase of junction temperature was identified as the main reason for gain saturation through spectra analysis.
Using the finite-element method,the thermal resistances of GaN laser diode devices in a TO 56 package for both epi-up configuration and epi-down configuration are calculated.The effects of various parameters on the thermal characteristics are analysed,and the thicknesses of the AlN submount for both epi-up configuration and epi-down configuration are optimized.The obtained result provides a reference for the parameter selection of the package materials.
The epitaxial growths of GaN films and GaN-based LEDs on various patterned sapphire substrates(PSSes) with different values of fill factor(f) and slanted angle(θ) are investigated in detail.The threading dislocation(TD) density is lower in the film grown on the PSS with a smaller fill factor,resulting in a higher internal quantum efficiency(IQE).Also the ability of the LED to withstand the electrostatic discharge(ESD) increases as the fill factor decreases.The illumination output power of the LED is affected by both θ and f.It is found that the illumination output power of the LED grown on the PSS with a lower production of tan θ and f is higher than that with a higher production of tan θ and f.
