Characterization of Ge Photodiodes Fabricated on Vicinal Si Substrate

概要

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We have fabricated a series of Ge n+np photodiodes on Si(100) substrates with different off azimuths. Ge films were epitaxially grown on three types of substrate: (a) a Si just (100) ($\pm 1$°) substrate, (b) a Si(100) substrate 4° off toward the $\langle 001\rangle$ azimuth, and (c) a Si(100) substrate 4° off toward the $\langle 011\rangle$ azimuth. Two-step low-pressure chemical vapor deposition (LPCVD) was used for the epitaxial growth of Ge, which consists of first low-temperature (300 °C) deposition followed by high-temperature (580 °C) growth by the thermal deposition of GeH4. The films were evaluated by X-ray diffraction (XRD), atomic force microscopy (AFM), and secondary ion mass spectroscopy (SIMS). As a result, the Ge film grown on the Si(100) substrate 4° off toward the $\langle 011\rangle$ azimuth has the best quality. The photodiode fabricated with the Ge film has the lowest dark current and the highest photosensitivity for the Si(100) substrate 4° off toward the $\langle 011\rangle$ azimuth presumably because it has the lowest dislocation density at the Ge/Si interface.
2009-04-25