Sputtered Ge-on-Si heteroepitaxial pn junctions: Nanostructure, interface morphology and photoelectrical properties

Ge thin films are epitaxially grown onto (1 0 0) Si substrates by DC-Pulsed Magnetron Sputtering. Relaxed single crystalline layers, with slightly misoriented domains are identified by XRD, TEM and HREM. Planar defects and threading dislocations are the relevant lattice imperfections. As-deposited Ge films are p-type without the need for intentional doping, even in the absence of grain boundaries. A pronounced flatness in the near IR absorption spectra is evident, in the absence of strong interfacial strain. This could be traced to a bandgap narrowing effect due to intragap states related to defects in the interfacial region. Photoconductive response around λ = 1.5 μm is flat and an equivalent responsivity Reff|Vbias = −1V = 1.0088 A/W at λ = 1.5 μm has been estimated.DC-Pulsed Magnetron Sputtering is therefore an attractive solution, deserving further development, to build near-infrared C-MOS compatible photodetectors, particularly suitable for low-speed applications.