Force free wafer bonding of lattice mismatched materials: Fabrication of extremely low dark current photodetectors

This dissertation describes the development of a new method for joining two materials of different lattice dimensions in a way which leads to the formation of a defect-free interface. This technique is unique in that one member of the bond pair is made compliant by removal of the film's substrate, and a permanent bond is then formed without the application of external pressure. This eliminates the strain of lattice and coefficient of thermal expansion mismatch between the two surfaces. The surface conditions required to achieve a strong bond and the optimization of epitaxially grown compound semiconductor surfaces during metalorganic chemical vapor deposition are compound semiconductor surfaces during metalorganic chemical vapor deposition are explored. The detection and removal of surface contaminants which prevent direct wafer bonding are investigated. Techniques for formation of van der Waals bonds between the two dissimilar surfaces are described, and the van der Waals bond formed negates the need for constraining and compressing the bond pair at high temperature. The thermal and lattice mismatch stress is therefore reduced, as is the interfacial energy which would force the nucleation of threading dislocations. Direct analysis of the bonded material by transmission electron microscopy and double crystal x-ray diffraction shows the superior nature of the interface produced as compared to previous techniques of wafer bonding. Novel photodetector devices were fabricated from the bonded material. Avalanche operation of these devices under 1.3 micron illumination resulted in gain (G) equal to 100, with a measured dark current (Idm) of 3 nano-amperes. This record low dark current further characterizes the interface as free of excitonic traps. This work makes a fundamental contribution to material science by making possible the monolithic integration of materials without necessary conscription to a single lattice parameter, thereby unlocking an infinite range of materials property combinations. This technique is demonstrated using InGaAs and Si, but is applicable to any material system, once appropriate surface treatments to achieve van der Waals bonding are determined, and with the development of techniques to mechanically manipulate the thin film to be bonded.