Download Introduction - NUS Physics

Graduate Attributes
(Southern Cross University, Australia)
The graduates of the University are expected to develop the following
during their programmes:
 Intellectual rigour
 Creativity
 Ethical understanding, sensitivity, commitment
 Command an area of knowledge
 Lifelong learning --- ability of independent & self-directed learning
 Effective communication and social skills
 Cultural awareness
(From: S. Yeo, CDTLink, NUS, July 2004)
Importance of Materials Processing
 All electronic devices & systems are made of materials in
various combinations
 Raw materials are far from the final electronic products
 Semiconductor materials (e.g., Si, Ge, GaAs, GaN...) used for
devices must be of extremely high purity and crystalline order
Desirable Device Qualities
 Strong functionality
 Reliable, long lifetime
 Low cost, high energy efficiency
 Small volume, light weight...
 Examples: your notebook PC, mobile phone…
All these require high precision and efficient
materials processing technologies
Real Materials and their Processing
 Particles, lines and rigid bodies vs. real materials
 Material-specific properties determine the function
and processing details of a material
 Comprehensive knowledge of materials processing
requires ~ 5-10 years of learning and practice
 Advantage and role of physics students
Insulators, Conductors, Semiconductors
from energy band structures
E
E
conduction band
empty
Band
gap
Forbidden
region
Eg > 5eV
valence band
filled
Insulator
SiO2: Eg = 9 eV
E
conduction
band
Band
gap Eg <
valence
band
electron
hole
5eV
partially-filled
band
+
Semiconductor
Si: Eg = 1.1 eV
Ge: Eg = 0.75 eV
GaAs: Eg = 1.42 eV
Conductor
Electrons and Holes in Semiconductor
N type
P type
Intrinsic semiconductor
Carriers come from valence
electron excitation
Key: Effective control
of charge carriers
Doped semiconductor
Carrier type, density & mobility
determined in Hall measurements
B
Longitudinal conductance:
Jx = Ex = e(ne + ph)Ex
Longitudinal resistivity:  = 1/
Jx
VH
Ey
The Hall coefficient:
p h2  ne2
RH 

J x B e( p h  ne )
Ey
If electron is the dominant carrier in the material, then we have:
 = 1/ = (ene)-1, and RH   1
ne
Carrier density: n = -(eRH)-1, and the mobility: e = - RH/
Light Emission in Semiconductors
E
conduction electron
band
-
h
Band
gap
valence
band
Electron-hole
recombination
+
hole
Si:
Eg = 1.1 eV,  = 1100 nm
GaAs: Eg = 1.4 eV,  = 873 nm
AlAs: Eg = 2.23 eV,  = 556 nm
Si: indirect bandgap, ineffective
GaAs: direct bandgap, effective
Basic semiconductor devices
p
E
n
Diode
p
n
p
C
B
Bipolar transistor
Metal-semiconductor
contacts
G
G
p+
S
S
n+
D
n
p+
G
Junction field-effect
transistor (JFET)
Depletion
region
p
SiO2
D
n+
Inversion
region
Metal-oxide-semiconductor
FET (MOSFET)
Real Device Structures in IC
metal contacts
n+
p
n
Diode
Bipolar transistor
MOSFET