Low temperature metal induced crystallization of orientation-preferred polycrystalline germanium with n- and p-type doping for device applications

A metal-induced crystallization (MIC) doping method is proposed for the fabrication of n- and p-type doping polycrystalline germanium (poly-Ge). This method involves the use of amorphous- (α-) Ge/metal/α-Ge/crystal-Ge stacked structure to achieve orientation-preferred poly-Ge on Ge (100) substrate at a very low temperature of 240℃. Aluminum (Al) and bismuth (Bi) metal layers are selected for p- and n- type doping sources, respectively. The thickness ratio of metal to α-Ge is optimized to obtain dense poly-Ge. Raman spectrum, scanning electron microscopy and electron backscattered diffraction characterizations confirm that the crystallized α-Ge exhibits a preferred orientation along (100) with a smooth surface. The p- and n- type doping concentrations are evaluated to be 2.2×1021cm-3 and 2.7×1019cm-3, respectively, by Hall effect measurement. Furthermore, p-type poly-Ge/n-Ge and n-type poly-Ge/p-Ge junctions are formed with significant rectification ratios of 103 and 102@±2V, respectively. These findings indicate that the low-temperature MIC approach holds great potential for the fabrication of n- and p-type poly-Ge, enabling the development of Ge-based active devices at low temperature.