Intrinsic Silicon Properties
Intrinsic Silicon Properties
? Read textbook, section 3.2.1, 3.2.2, 3.2.3
? Intrinsic Semiconductors
? undoped (i.e., not n+ or p+) silicon has intrinsic charge
carriers ? electron-hole pairs are created by thermal energy ? intrinsic carrier concentration ni = 1.45x1010 cm-3,
at room temp. ? function of temperature: increase or decrease with temp? ? n = p = ni, in intrinsic (undoped) material
? n number of electrons, p number of holes
? mass-action law, np = ni2
? applies to undoped and doped material
ECE 410, Prof. A. Mason
Lecture Notes 6.1
Extrinsic Silicon Properties
? doping, adding dopants to modify material properties
? n-type = n+, add elements with extra an electron
? (arsenic, As, or phosphorus, P), Group V elements
? nn concentration of electrons in n-type material ? nn = Nd cm-3, Nd concentration of donor atoms
n-type Donor
+
P P+ electron
group V element
ion
free carrier
? pn concentration of holes in n-type material ? Nd pn = ni2, using mass-action law
n+/p+ defines region as heavily doped,
? always a lot more n than p in n-type material
typically 1016-1018 cm-3
? p-type = p+, add elements with an extra hole
less highly doped regions generally labeled n/p
? (boron, B)
(without the +)
? pp concentration of holes in p-type material ? pp = Na cm-3, Na concentration of acceptor atoms ? np concentration of electrons in p-type material ? Na np = ni2, using mass-action law
p-type Acceptor
-
B
B+ +
hole
group III element
ion
free carrier
? always a lot more p than n in p-type material
? if both Nd and Na present, nn = Nd-Na, pp=Na-Nd
do example on board
ni2 = 2.1x1020
ECE 410, Prof. A. Mason
Lecture Notes 6.2
Conduction in Semiconductors
? doping provides free charge carriers, alters conductivity
? conductivity, , in semic. w/ carrier densities n and p
? = q(nn + pp), q electron charge, q = 1.6x10-19 [Coulombs]
? mobility [cm2/V-sec], n 1360, p 480 (typical values)
? in n-type region, nn >> pn
? qnnn
? in p-type region, pp >> np
? qpnp
mobility = average velocity per Mobility often
unit electric field
assumed constant
n > p
electrons more mobile than holes conductivity of n+ > p+
but is a function of Temperature and Doping
Concentration
? resistivity, = 1/
t
? resistance of an n+ or p+ region
? R = l , A = wt
A
w
l
? drift current (flow of charge carriers in presence of an electric field, Ex)
? n/p drift current density: Jxn = n Ex = qnnnEx, Jxp = p Ex = qpppEx
? total drift current density in x direction Jx = q(nn + pp) Ex = Ex
ECE 410, Prof. A. Mason
Lecture Notes 6.3
pn Junctions: Intro
? What is a pn Junction?
contact to p-side
contact to n-side
? interface of p-type and
depletion region boundaries
p+
n+
n-type semiconductor
pn diode junction
n "well"
? junction of two materials forms a diode
p-type Si wafer
dielectric insulator (oxide)
p-type
n-type
? In the Beginning...
p-type -+ -+ - + -+ +- +- +- n-type
? ionization of dopants at material interface
-+ -+ -+ -+ -+ -+ 3
+-
+-
+-
-
+3
N acceptors/cm A
N donors/cm D
hole diffusion hole current
-
+ donor ion and electron free carrier
electron diffusion electron current
-+ acceptor ion and hole free carrier
? Diffusion -movement of charge to regions of lower concentration
? free carries diffuse out ? leave behind immobile ions ? region become depleted of
free carriers ? ions establish an electric field
? acts against diffusion
depletion region
E electric field
p-type
3
N acceptors/cm A
immobile acceptor ions (negative-charge)
-
-
++ +
++ +
++
x
x
p
n
W
n-type
3
N donors/cm D
immobile donor ions (positive-charge)
ECE 410, Prof. A. Mason
Lecture Notes 6.4
pn Junctions: Equilibrium Conditions
? Depletion Region
depletion region
E electric field
? area at pn interface void of free charges
? charge neutrality
p-type
NA 3
N acceptors/cm A
-
-
++ +
++ +
++
n-type
ND 3 N donors/cm D
?
must have equal charge on both sides
immobile acceptor ions (negative-charge)
x p
x n
immobile donor ions (positive-charge)
W
? q A xp NA = q A xn ND , A=junction area; xp, xn depth into p/n side
? xp NA = xn ND
? depletion region will extend further into the more lightly doped side
of the junction
? Built-in Potential
? diffusion of carriers leaves behind immobile charged ions
? ions create an electric field which generates a built-in potential
0
= VT
ln
NAND ni 2
? where VT = kT/q = 26mV at room temperature
ECE 410, Prof. A. Mason
Lecture Notes 6.5
................
................
In order to avoid copyright disputes, this page is only a partial summary.
To fulfill the demand for quickly locating and searching documents.
It is intelligent file search solution for home and business.
Related download
- e5 mechanical effect of current and electro magnetic induction
- intrinsic silicon properties
- high voltage dc dc converter
- atomic units a u
- si and cgs units in electromagnetism
- units in mass spectrometry home chemistry
- ohm s law
- voltage current and resistance mit opencourseware
- relativity 4 relativistic momentum
- the photoelectric effect
Related searches
- crm properties lexington ky
- properties of radioisotopes
- intrinsic myocardial disease
- intrinsic kidney disease
- describe the intrinsic conduction system
- 5g startups silicon valley
- startup companies in silicon valley
- silicon valley startups 2020
- silicon valley ai companies list
- top silicon valley startups 2020
- how does cognitive dissonance effect intrinsic motivation
- silicon valley staffing group