Three dimensional heteroepitaxy: A new path for monolithically integrating mismatched materials with silicon

In the quest for a Ge x-ray detector mono-lithically integrated onto a Si-CMOS chip we developed a novel method for combining dissimilar materials that may provide a solution to the main problems of heteroepitaxy, e.g. high threading dislocation densities, wafer bowing and cracks. It consists of replacing the conventional continuous layers by space-filling arrays of strain- and defect-free Ge crystals, the width, height and shape of which are controlled by tuning epitaxial growth onto micrometer-sized features deeply etched into Si-substrates. Heterojunctions formed between the Ge-crystals and the Si-substrate exhibit the required rectifying diode behavior with low dark currents (<;1 mA/cm2).