Hybrid waveguide brings photonic integrated circuits closer

31 May 2007

A photodetector utilizing a silicon waveguide could be incorporated into power monitors or preamplified receivers.

A team from the University of California and Intel has developed a hybrid silicon evanescent waveguide photodetector with an internal quantum efficiency of 90% over the 1.5 µm range (Optics Express 15 6044).

"This is the first demonstration of photodiodes using a silicon evanescent device platform," Hyundai Park of the University of California, Santa Barbara, told optics.org. "It's an important step towards photonic integration."

Cross section

The hybrid photodetector comprises AlGaInAs quantum wells bonded to silicon waveguides. The team reported an internal chip responsivity of 1.1 A/W, a quantum efficiency of 90% covering a wavelength range up to 1.6 µm, and a dark current of less than 100 nA at a reverse bias of 2 V.

Constructing the hybrid device posed some technical challenges. "Silicon and III-V material processing are quite different and use different chemistry, noted Park. "As a result it was difficult to protect the exposed silicon material during the III-V formation. The device design was also a challenge, since coupling loss at the junction of the input silicon waveguide and the detector can degrade the responsivity."

Top view

The responsivity and dark current of the hybrid device are the same or slightly better than those of Ge or SiGe detectors. However, the device's relatively large size gave it a high capacitance value, and as a result the bandwidth was found to be only 0.5 GHz.

"The next step is to increase bandwidth by optimizing the device's size, or employing the travelling wave electrode design that we have already demonstrated with III-V detectors," said Park. "Another path will be a demonstration of preamplified receivers integrated with silicon evanescent amplifiers, to increase the sensitivity of the receivers."

SEM image

The team has already developed lasers and amplifiers based on this platform, and the new photodetector is part of their continuing plan to demonstrate all the components of a photonic device using silicon evanescent technology, including lasers, amplifiers, detectors and modulators.