Monolithic integration of solid state thermionic coolers with semiconductor lasers

Many types of semiconductor lasers such as vertical cavity surface emitting lasers (VCSELs) or distributed feedback (DFB) lasers can generate large heat power densities on the order of kW/cm² over areas as small as 100 μm². It is desirable in many applications to control the operating temperature in order to tune the operating characteristics such as emission wavelength or to enhance the performance such as increasing the output power. Conventionally, thermoelectric (TE) coolers are used to manage temperature, however since they are not easily integrated with semiconductor devices, the packaging can be costly. Moreover, the TE device usually determines the reliability and lifetime of a packaged laser module. An alternative to traditional TE coolers is heterostructure integrated thermionic coolers. These thin film coolers use the selective emission of hot electrons over a heterostructure barrier layer from emitter to collector resulting in an evaporative cooling of the electron gas beyond what is possible with the Peltier effect. Thermionic coolers fabricated in the InGaAsP material system have demonstrated cooling on the order of several degrees over one-to-two micron thick barriers and cooling power densities of over 100 W/cm₂. This cooling power density is approximately an order of magnitude greater than what is possible with TE coolers. The InGaAsP material system is important for long wavelength semiconductor lasers used in long haul and other high-speed optical communication systems. By using the same material system for the laser and cooler growth, monolithic integration is possible