The external differential quantum efficiency, defined as the ratio of number of photons emitted per unit time to number of carriers passing the laser diode junction, is known to be sensitive to laser diode’s operating temperature. In this paper, high-resolution spectral emissions of a commercially available GaN-based blue laser diode are measured and utilized to study the effect of temperature on the external differential quantum efficiency and over the operating temperature range of 270 – 330 °K. Upon studying the L-I curves and over the full range of laser diode’s operating current and temperature, three distinct temperature regimes of the quantum efficiency were identified with the regime of temperature range 285 -301 °K yielding the highest temperature stability. In addition to experimentally determining the characteristic temperature of the laser diode, the effect of non-radiative recombination and free carrier absorption processes on external differential quantum efficiency will be discussed.
Typical emission spectra of GaN-based blue laser diodes are known to have irregular shapes. Hence, well-resolved study of their spectra may help in understanding the origin of their spectral shapes irregularity. In this paper, the spectra of a commercial GaN-based blue laser diode are studied as a function of injection current and temperature using a spectrometer with highresolution of 0.003-nm over the spectral region 440 – 450 nm. The obtained laser spectra are used to track the longitudinal modes evolution as a function of operating currents and temperatures as well as to precisely map single mode operation. In addition, yielded laser spectra will be utilized to evaluate few parameters related to the laser diode, such as mode spacing, optical gain, slope efficiency and threshold current at certain temperature.