Monolithic integration of near infrared (NIR) photodetectors on existing silicon CMOS technology platform is highly desirable and is currently actively pursued for low cost optical communication applications. In this context, germanium-on-silicon-on-insulator (Ge-on-SOI) metal-semiconductor-metal (MSM) photodetector has been identified as a promising option for its ease of device fabrication, low capacitance and faster speed response. However, high dark current observed in these MSM photodetectors due to low hole Schottky barrier height has resulted in undesirable poor signal-to-noise ratio. In order to circumvent this issue, various approaches have been explored for effective dark current suppression which include the adoption of silicon oxide (SiO2) passivation, armorphous-Si or Ge thin films between the Schottky contact and the semiconductor interface for modulating the Schottky barrier height.

For the first time, using an established silicon photonics technology platform, IME researchers have successfully demonstrated high performance evanescent coupled Ge-on-SOI metal-semiconductor-metal (MSM) photodetector with novel silicon-carbon (Si:C) Schottky barrier enhancement layer.

Significant suppression of dark current (Idark) by ~4 orders of magnitude was achieved over a conventional MSM photodetector due to an enhanced hole Schottky barrier height of 0.52 eV. At an applied bias VA of 1.0 V, a -3dB bandwidth of ~12 GHz at an incident wavelength of 1550 nm was demonstrated. Optical measurements performed at photon wavelengths λ of 1520-1570 nm reveal a uniform spectral response and internal quantum efficiency of ~760 mA/W and ~60% respectively, demonstrating an effective photo-detection for the entire C-band spectrum range. Good spectral response and speed performance achieved in such novel photodetector makes it a promising option for optical communication applications.

(a) Dark current characteristics of the Ge-on-SOI MSM photodetectors with increasing applied bias. Significant reduction of dark current performance was achieved for devices with Si:C Schottky barrier enhancement layer as compared to the conventional devices without Schottky barrier modification. (b) Normalised frequency response measured at a photon wavelength of 1550 nm. A -3dB bandwidth of ~12 GHz was achieved at a VA=1.0 V.