An investigation into the temperature sensitivity of strained and unstrained multiple quantum-well, long wavelength lasers: new insight and methods of characterization

The magnitude of the temperature rate of change of the threshold current density (J_th) is examined with respect to J_th , for a variety of unstrained and strained, long wavelength multiple quantum-well (MQW) lasers. A strong correlation is found between these parameters, and a new relationship describing the J_th -T relationship for these lasers is arrived at in terms of two new essentially temperature and length independent constants. A third constant, T_max, also appears which estimates the theoretical maximum operating temperature of the laser. It is proposed that these constants may prove to be more useful in characterizing the temperature sensitivity of semiconductor lasers than the conventional parameters T ₀ and I₀ which exhibit both a length and temperature dependence. Furthermore, an expression is found which relates the magnitude of T_max to adjustable device structural and material parameters, such as: the cavity length, L; facet reflectivity, R; transparency current density, J_tr; and, the modal gain coefficient, β. It is revealed that a close examination of this relationship may provide new insight into the physics of semiconductor lasers as well as a means for optimizing device design to obtain a high maximum operating temperature in order to eliminate the need for thermoelectric coolers in device packaging. Finally, the measured T_max, versus L characteristics of six different strained and unstrained MQW laser structures are presented