Ph. D. Oral Examination - Ali Kemal Okyay Fri 8:45AM

Ali Kemal Okyay aokyay at
Tue Feb 27 14:05:32 PST 2007

Ph. D. Oral Examination




Ali K. Okyay

Department of Electrical Engineering

Adviser: Professor Krishna C. Saraswat


Date: Friday, March 2nd, 2007

Time: 8:45am (Refreshments at 8:30am)

Location: CIS-X Auditorium




The communications bottleneck is identified as one of the grand challenges
in the progress of silicon computation. While individual logic elements have
become significantly faster, computational speed is limited by the
communication between different parts of a processor. Traditional copper
wires are efficient at short distances, but they suffer excessive power
dissipation and delay in global lines, and cannot cope with the ever growing
bandwidth demand. Moreover, with the chip architectures evolving towards a
modular design, the requirements for increased bandwidth density further
strain the electrical interconnects. Optical interconnects (OIs) can provide
a solution to the communication bottleneck by alleviating  significant power
dissipation and delay problems faced by copper wires. Monolithically
integrated photodetectors with very low capacitance are sought after for the
receiver end of high performance OIs.


In the first part of the talk, we will discuss Ge based
metal-semiconductor-metal (MSM) optical detectors integrated on Silicon. The
Ge layer is grown by a novel multi-step Ge-on-Si direct epitaxial growth
technique. An important byproduct of this growth technique is tensile strain
within the Ge film, resulting in enhanced absorption around 1550 nm. We will
present experimental results of electrical and optical characterization of
Ge detectors. We have report very high responsivity of 0.84 A/W at 1550 nm.
We have investigated the origin of strain in the Ge layers, and report a
significant red shift in the absorption edge of Ge in these films.


In the second part of the talk, we will discuss a novel CMOS compatible
optoelectronic switch. The proposed device is a Si MOSFET with Ge gate. We
have investigated the basic operation of the proposed device. The gate
photocurrent is amplified by the MOSFET current gain at the drain terminal.
We will present experimental proof-of-principle demonstration of device
operation. We will discuss complementary function in the proposed device by


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