 Science and technology in nano-meter scale is now receiving feverish
attention due to both a desire to explore the new science in
this small dimension and development of novel device applications
expected
in this area. Particularly, demands in developing new systems
in communication, computing, storage, and transportation
require fabrication
of better electronic and photonic devices. The recent development
of materials, electronics, and opto-electronics in this nano-dimension
area, would help to fulfill these goals. However, these new nano-technologies
would be made possible when the related nano-science is understood.
In nano electronic devices, surfaces and interfaces of semiconductors
with dielectric insulators such as oxides always play critical
roles in determining properties of materials and performance
of devices.
 In the past few years, we have discovered new oxides, containing
a rare earth oxide of Gd2O3, which unpin the Fermi level
on GaAs surfaces. We have then solved
a problem in the field of compound semiconductors, which has puzzled researchers
over 35 years. Subsequently, demonstration of forming inversion and accumulation
channels on GaAs surfaces, with a Dit of mid-1010 cm-2eV-1 has been made. Inversion-channel
GaAs and InGaAs MOSFETs and GaAs CMOS circuits, have now been achieved. A depletion-mode
GaAs MOSFET has exhibited negligible drain current drift and hysteresis, an
important technological advance for the manufacturing of
this class of devices. Interestingly
and unexpectedly, Gd2O3 was found to grow epitaxially on GaAs in a cubic structure.
More remarkably, single crystal Gd2O3 on GaAs showed excellent electrical properties
such as very low gate leakage current. When grown on GaN, Gd2O3 was found to
be epitaxial, but with an hcp structure, which has also unpinned the Fermi
level in GaN. This then leads to the possibility of fabricating
a high-power GaN-based
MOSFET, which can be operated at high temperatures.
Advanced nano-materials, new science, and high-performance devices
through novel epitaxy
The Si MOS technology is entering the age of nano-meters,
with the gate length of 90 nm in production and devices of
50 nm or
smaller in research and development. Is the good old Si/SiO2
technology coming to an end? Is there any new technology in horizon?
It is known that electrons move much faster in GaAs (and
other compound semiconductors) than those in Si, an important
aspect
for building high-speed devices. Furthermore, semiinsulating
substrates, not available in Si, will reduce cross talks between
high-speed signal lines in dense circuits. A mature compound
semiconductor technology (particularly III-V MOS devices) with
electron mobilities at least 10 times higher than that in Si
and with dielectrics having k several times higher that that
of SiO2 would certainly enable the electronic industry to continue
pushing its new frontiers for a few more decades. Is it possible
to develop these new compound devices into a feasible technology
in the next few years?
 
Low interfacial density of states in oxide-GaAs through novel
nano-epitaxy
How to passivate GaAs surface? Previous efforts over thirty
five years !
Previous Efforts
─ Anodic, thermal, and plasma oxidation of GaAs
─ Wet or dry GaAs surface cleaning followed by deposition of various dielectrics
Our Breakthrough Growth using multiple chambers
─ Novel gate oxides Ga2O3(Gd2O3) and Gd2O3 in-situ deposited by e-beam evaporation
with low Dit
─ Have applied to GaAs, InGaAs, AlGaAs, InP, GaN, and Si
THE KEY is to clean GaAs surface and to identify a dielectric
being thermodynamically and electronically stable, and showing
low Dit with GaAs. 
Effective Passivation of GaAs and other compound semiconductors
GaAs MOSFET
─ Advantages
inherent higher electron mobility and semi-insulating GaAs substrates, comparing
with Si-based MOSFET
─ Rich band gap engineering in compound semiconductors
low power consumption and circuit simplicity of CMOS, comparing with GaAs
MESFET, HEMT
─ Applications
new generation of digital GaAs IC's of high speed and low power for communication
and computer industries
Other electronic applications
─ High power devices in MESFET,
HEMT, and high speed devices in HBT
Laser facet coatings and other photonic applications
 
High performance and novel devices through new advanced thin
film materials
The epitaxy of two dissimilar materials is always fascinating
because of the challenge in the material growth. Recent notable
examples of semiconductor/oxide structures were found in the
growth of single crystal GaN on sapphire, which find its application
in blue and green LEDs, lasers, and high power electronic devices.
GaN surfaces are not as robust and inert as generally thought
when exposed to atmosphere such as room air. Research efforts
of depositing or growing insulators (and methods to prepare them)
on GaN to give a low Dit at the insulator/GaN interface have
shown that appropriate insulators and proper steps for cleaning
GaN surfaces are critical to achieve a low Dit.
Not only single crystal rare earth oxide films (Gd2O3) were
grown epitaxially on single crystal GaN films, but also single
crystal GaN films were shown to overgrow epitaxially on these
rare earth oxide films. Thin single crystal Gd2O3 was used as
a gate dielectric for GaN-based MOSFET's. The rare earth oxide
film was unexpectedly found to have an hcp structure.
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