Structure and transport properties of Ga-doped semi- and polycrystalline Si/sub 1-x/Gex films

Abstract

Polycrystalline SiGe films have applications in solar cells, thermoelectrical devices and field-effect transistors for large area integration (liquid crystal displays etc.). Recently, a nanocrystalline state was detected by us in heavily B-doped SiGe films after vacuum annealing. Amorphous (a) Si/sub 1-x/Ge/sub x/ films with x=0.25-0.60, about 200-300 nm thick and heavily doped with Ga (1%), were deposited by molecular beam on SiO/sub 2//Si[001] substrates at room temperature. For crystallization, a-SiGe/SiO/sub 2//Si structures were annealed in vacuum of 10/sup -6/ Torr at 600 to 900/spl deg/C. X-ray diffraction and TEM observations in situ showed nanocrystalline (nc) structure in SiGe films with grain size of about 5-20 nm. The nc-Si/sub 1-x/Ge/sub x/ films demonstrated high hole mobility (1 to 100 cm/sup 2//Vs) and Seebeck coefficient values (5 to 110 /spl mu/V/K).