Single stage thin film coolers based on thermoelectric and thermionic cooling in p-type InGaAsP superlattice structures have been fabricated. Devices with different sizes and at various ambient temperatures have been characterized. Experimental results showed 0.5 degree centigrade cooling below the ambient temperature at 25C. This cooling over 1 4mu2m thick superlattice barrier corresponds to cooling power densities on the order of 200 W/cm2. The device cools by a factor of two better at higher temperatures (70C). This is due to the reduction of the superlattice thermal conductivity and the broadening of the electronic distribution function at higher temperatures. 150x150 micrometers 2 devices provide largest cooling at room temperature while the optimum device size shrinks as the temperature increases. Simulations results that take into account finite thermal resistance of the InP substrate, the effect of the contact resistance, heat generation in the wire-bonds and metallic pads on top of the device predict accurately the optimum cooling of these micro refrigerators. By eliminating the major parasitic sources of heating (Joule heating in the substrate, heat conduction through the side contact and reducing the contact resistance to 5x7-7 ohm-cm2) simulations show that, ultimately, one can achieve 15 degree(s)C cooling (10's of kW/cm2 cooling power) with single stage p-InGaAsP thin film coolers.
Active refrigeration of optoelectronic components through the use of thin film solid state coolers based on III-V materials is proposed and investigated. Enhanced cooling power comparing to the thermoelectric effect of the bulk material is achieved through thermionic emission of hot electrons over a heterostructure barrier layer. It is shown that these heterostructures can be monolithically integrated with other devices made from similar materials. Experimental analysis of an InP p-i-n diode monolithically integrated with a heterostructure thermionic cooler is performed. Cooling performance is investigated for various device sizes and ambient temperatures. Several important non-ideal effects are determined such as contact resistance, heat generation in the wire bonds, and the finite thermal resistance of the substrate. These non-ideal effects are studied both experimentally and analytically, and the limitations induced on performance are considered. The experimental results are then used to predict the improved performance of better designed coolers. These micro- refrigerators can provide control over threshold current, power output, wavelength, and maximum operating temperature in diode lasers. Heterostructure integrated thermionic cooling is demonstrated to provide cooling power densities of several 100's W/cm2.
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