Investigation of the degradation modes in GaN-based blue laser diodes grown by metal organic chemical vapor deposition (MOCVD) is carried out. Early failure of the LDs happened at the initial stage of the aging. After analysis of the electrical and thermal characteristics, local degradation of the active region is observed. Further investigation on the microstructures of the local regions shows that the early failure of the LDs is due to the local structure damage with the formation of gallium metal.

•A high accuracy thermal resistance measurement method is presented.•Measurement time delay is shortened to 300 ns.•The measured results are revised based on the simulation results.•Real-time monitoring of the sensor current further improves the accuracy.•The thermal resistance of TO56 packaged GaN/InGaN LD is 30.2 ± 0.3 K/W.A thermal resistance measurement method of high accuracy for GaN/InGaN laser diodes (LDs) is presented based on the forward-voltage method. Three items are optimized in order to improve the accuracy of the measurement. (i) Measurement time delay is shortened to 300 ns by using the single trigger function of a MDO4104-3 Mixed Domain Oscilloscope. (ii) The measured results are revised based on the simulation result. (iii) The accuracy of the measurement is further improved by the real-time monitoring of the sensor current. Thermal resistance of the LD operating under different injection current is measured by using this method. The thermal resistance of TO56 packaged GaN/InGaN LD is 30.2 ± 0.3 K/W.

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 μm) 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 μm 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 μm), but the output light intensity of the longer SLD (800 μm) 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.