Investigation of heat transfer through interface germanium - AlN ceramics in heterostructure solar cells by laser thermal wave method

Heat transferring through the interfaces of multijunction solar cells to the heat removal ceramic heatsink are investigated by laser thermal wave methods. A theoretical model of thermal wave propagation in these structures is developed with allowance for a layer of solder present between the semiconductor and ceramics. It takes into account specific features of semiconductor structure surface processing, metallization and joining technology regimes. It is shown that the laser thermal wave methods can be successfully applied to the qualitative and quantitative characterization of thermal contacts between semiconductor elements and ceramics. It is also demonstrated that these methods make it possible to evaluate the homogeneity of thermal properties along the interfaces of soldered metal layers and to characterize their degradation under the action of working temperature variations. Examples of subsurface details imaging of various soldered metal layers in multijunction solar cells by the laser scanning thermal wave microscopy method are presented as well.