The effects of composition and doping on the response of GeC-Si photodiodes

The spectral responses of a series of heterojunction diodes of p-type Ge1-y Cy on n-type Si (100) substrates were measured by Fourier transform infrare d (IR) spectroscopy, Alloy layers 0.5 mu m thick were grown by molecular be am epitaxy at a substrate temperature of 400 degrees C and were doped p-typ e with different B concentrations. With increasing C content, the diode dar k current decreased, and the optical absorption band edge shifted toward hi gher energy by 70 meV for 0.12 atomic persent of C, The increase in energy was attributed to the composition dependence of the bandgap rather than to strain relaxation, because the GeC layers were nearly relaxed with the same strain, The photoresponsivity was 0.07 A/W at a wavelength of 1.55 mu m, a nd 0.2 A/W at a wavelength of 1.3 mu m, These measurements show that GeC ph otodetectors have good properties and reasonable response at technologicall y important near-IR wavelengths and can be fabricated by heteroepitaxy for compatibility with Si integrated circuits.