MBE grown Si/SiGe undulating layer superlattices for infrared light detection

We have grown Si/Si0.61Ge0.39 and Si/Si0.55Ge0.45 superlattices by molecular beam epitaxy (MBE) and fabricated vertical metal-semiconductor–metal (MSM) detectors. Analysis by Rutherford backscattering yielded the actual Ge content of the layers. Transmission electron microscopy revealed undulating layers with vertically ordered Ge-rich regions. A MSM detector fabricated from the superlattice with the higher Ge content showed a quantum efficiency of 5.2% for the wavelength 1.3 μm, and 1% for 1.55 μm, while the material with lower Ge concentration did not absorb light at 1.55 μm.