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- ( alpha-) Ge/metal/ alpha-Ge/crystal- Ge stacked structure to achieve orientation -preferred poly-Ge on Ge (100) substrate at a very low temperature of 240 degrees C. Aluminum (Al) and bismuth (Bi) metal layers are selected for p- and n- type doping sources, respectively. The thickness ratio of metal to alpha-Ge is optimized to obtain dense poly-Ge. Raman spectrum, scanning electron microscopy and electron backscattered diffraction characterizations confirm that the crystallized alpha-Ge exhibits a preferred orientation along (100) with a smooth surface. The p- and n- type doping concentrations are evaluated to be 2.2x10 21 cm -3 and 2.7x10 19 cm -3 , respectively, by Hall effect measurement. Furthermore, p -type polyGe/n-Ge and n -type poly-Ge/p-Ge junctions are formed with significant rectification ratios of 10 3 and 10 2 @ +/- 2 V, 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.