|Advisor:||Paul R. Berger|
|Students:||Al-Sameen Khan (graduated with Ph.D. in October 1996)|
|Xiaoping Shao (graduated with Ph.D. in September 1997)|
|Hao Feng (graduated with Master's thesis in March 1998)|
|Sean L. Rommel (graduated with Bachelor's in May 1996)|
|Collaborators:||James Kolodzey (University of Delaware, Elec. Engin.)|
|S. S. Iyer (Sibond/IBM)|
|F. Guarin (IBM)|
|S. Ismat Shah (Dupont)|
|K. M. Unruh (University of Delaware, Physics)|
Importance of the Problem:
The predominance of Si-based circuits in the
marketplace is due to the easy maufacturability of silicon. Consumers
expect the semiconductor industry to continue marching along Moore's Law
which is outlined in the Semiconductor Roadmap as reaching 0.18 m
gate lengths by 2001 and 0.07 m gate lengths by 2010.
However, as device dimensions shrink, the cost of
further miniaturization to improve performance is becoming prohibitive.
Current estimates are that a new fabrication line for a microprocessor
based chip is 1 billion dollars. It will be difficult to achieve these
expected results using Si only without a major breakthrough.
SiGeCSn would open the door to a wide
variety of Si-based heterostructure devices commonly reserved for III-V
compounds. The SiGe material system has already pushed Si devices in this
direction and clearly demonstrates improved performance.
However, SiGe is not lattice-matched. By additions of Ge and C in an
8:1 ratio an alloy would maintain Si lattice matching.
However, the SiGeCSn material system is in its infancy. Unlike Si and Ge
which mix well, the GeC binary system does not occur under equilibrium
conditions, and SiC alloys want to precipitate out as a carbide. Carbon,
which has a much smaller lattice constant and atomic
radius is difficult to get incorporated into the crystal lattice
substitutionally. Much of the carbon goes interstitially. We are in the
process of investigating the SiGeCSn material system using molecular beam
epitaxy which is a far-from-equilibrium growth technique. We are
investigating the fundamental material properties using transmission
electron microscopy (TEM) and photoluminescence (PL).
The first application of these materials will be for electronic devices
but further refinement could lead to photonic devices as well.
III-V compounds are the leading semiconductor materials for light
emission and detection due to their inherent direct bandgap. Their direct
bandgap dramatically improves the quantum efficiency of optical transistions.
However, Si-based opto-electronics, which have an indirect bandgap, have
very poor optical emission efficiency. Si-based materials are also
poor optical detectors due to their indirect bandgap. But, since Si is cheap
and plentiful, it is utilized for simple commercial photodetectors. On the
other hand, Si-based electronics have matured rapidly and impacts us in
virtually every aspect of our lives. The relative maturity of
Si-based electronics compared to III-V electronics make it very attractive
to be able to incorporate Si-based optical devices (emitters and detectors)
with Si-based electronics on the same chip.
The union of both electronic and optical devices would make a very
powerful combination for optoelectronic integrated circuits (OEIC). We
are investigating Group IV-based photodetectors as well as ways to improve
Si-based opto-electronics efficiency by making materials which are
It has been proposed that Brillioun Zone folding by growing short
period superlattices could convert the SiGeC indirect bandgap to a
quasi-direct bandgap. This new binary superlattice is viewed as a new
crystal with a different Bravais lattice. Within the material, a new energy
state is created at the zone center by which efficient optical transistions
could occur. Also, by tailoring the ternary alloy or buffer
composition, strain can be independently controlled about the lattice
matching condition for Si substrates. Strain can act to modify the band
structure as well.
Brief Description of Work and Results:
We have been investigating the Si
1-x-y-zGexCySnzmaterial system focusing on the constituent ternary alloy
Si1-x-yGexCy and binary alloys Ge1-xCx,
Si1-xSnx and Si1-xCx. The layers studied to date
have been grown by molecular beam epitaxy (MBE).
Initial work focused on the materials charaterization of the
epilayers. The specimens are studied structurally for defect structure
and physical manifestation by transmission electron microscopy (TEM).
Also, the optical quality of the epilayers is characterized by
photoluminescence (PL), and the electrical quality by Hall measurements.
Current work is branching off to investigate the etching and contact
resistance of these new materials. Work is commencing to develop these
materials into infrared photodetectors and electronic devices, such as
heterojunction bipolar transitors (HBT), field effect
transitors (FET), and resonant tunneling diodes (RTD).
The goal of these projects is to develop Si
cubic alloys and heterostructures for infrared light detection and emission
as well as enhanced electronic devices. An ultimate realization would be
monolithically integrated optoelectronic devices such as
detectors and emitters in the Si
system which would be compatible with existing Si-based or SiGeCSn-based
For further information contact:
Nanofabrication and Materials Processing Center (NanoMPC)
Nanoscale Patterning Laboratory
Nanoelectronics and Optoelectronics Laboratory (NOEL)
Polymer Device Laboratory (PDL)
201 Caldwell Laboratory
Department of Electrical and Computer Engineering
The Ohio State University
205 Dreese Laboratory
2015 Neil Avenue
Columbus, OH 43210 USA
Direct phone: (614) 247-6235
EE Dept. FAX: (614) 292-7596
|Supported By:||Defense Advanced Research Projects Agency (DARPA)|
|National Science Foundation (NSF)|
|University of Delaware Research Foundation (UDRF)|
Recent Publication Activity:
Recent Conference Activity: