The effect of pressure and temperature on AlGaInP and AlGaAs laser diodes

Two InGaP/AlGaInP lasers (emitting at 660 nm and at 690 nm) and one GaAs/AlGaAs laser (emitting at 780 nm) have been studied under hydrostatic pressure up to 20 kbar and at temperatures from 240 K to 300 K. The power-current characteristics and the spectra have been measured in the specially designed pressure cell. The emission spectra shifted in agreement with the pressure/temperature variation of the bandgaps in active layers of the lasers. Since at high pressure the F-X separation in the conduction band is strongly reduced (both in AlGaInP and in AlGaAs) the dominant loss mechanism of the lasers is the carrier leakage to X minima in the claddings. This, in turn, leads to high sensitivity of threshold currents to temperature. The dependence of threshold currents on pressure and on temperature is in good agreement with the simple phenomenological analysis taking into account the carrier leakage and the radiative and nonradiative recombination. Good description of the pressure and temperature variation of the threshold currents is obtained using three adjustable parameters. Our fits indicate that the dominant contribution to electronic leakage is drift rather than diffusion. These results are important for the application of pressure/temperature tuning of laser diodes in the 600-800 nm range. In particular, we were able to turn red laser diodes into yellow (emitting below 600 nm) and infrared 780 nm lasers into bright red. By simultanous control of pressure and temperature it is possible to obtain constant emission power of the lasers in the full tuning range (at a fixed operating current).