Transcript Schottky diode I-V Characteristics

•Stavan Patel(140130117088)
•Vedant Patel(140130117089)
•Vidhi Patel(140130117090)
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The Schottky diode (named after German physicist
Walter H. Schottky; also known as hot carrier diode) is a
semiconductor diode with a low forward voltage drop
and a very fast switching action.
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When current flows through a diode there is a small
voltage drop across the diode terminals. A normal
silicon diode has a voltage drop between 0.6–1.7 volts,
while a Schottky diode voltage drop is between
approximately 0.15–0.45 volts. This lower voltage drop
can provide higher switching speed and better system
efficiency.
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A metal–semiconductor junction is formed
between a metal and a semiconductor, creating a
Schottky barrier (instead of a semiconductor–
semiconductor junction as in conventional diodes).
Typical metals used are molybdenum, platinum,
chromium or tungsten; and the semiconductor
would typically be N-type silicon.
The metal side acts as the anode and N-type
semiconductor acts as the cathode of the diode.
This Schottky barrier results in both very fast
switching and low forward voltage drop.
The most important difference between the p-n and
Schottky diode is reverse recovery time, when the diode
switches from conducting to non-conducting state.
Where in a p-n diode the reverse recovery time can be in
the order of hundreds of nanoseconds and less than
100 ns for fast diodes, Schottky diodes do not have a
recovery time, as there is nothing to recover from (i.e.
no charge carrier depletion region at the junction).
• The switching time is ~100 ps for the small signal diodes,
and up to tens of nanoseconds for special high-capacity
power diodes. With p-n junction switching, there is also
a reverse recovery current, which in high-power
semiconductors brings increased EMI noise. With
Schottky diodes switching essentially instantly with
only slight capacitive loading, this is much less of a
concern.
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Areas of Application
Very high frequency range
Lower noise figure
Low-voltage or high-current power supplies
AC-to-DC converters
Radar systems
Schottky TTL logic
Fig. Approximate equivalent circuit for
the Schottky diode
Schottky diode is a metal-semiconductor (MS) diode
Historically, Schottky diodes are the oldest diodes
MS diode electrostatics and the general shape of the
MS diode I-V characteristics are similar to p+n
diodes, but the details of current flow are
different.
Dominant currents in a p+n diode
– arise from recombination in the depletion layer under small
forward bias.
– arise from hole injection from p+ side under larger forward
bias.
Dominant currents in a MS Schottky diodes
– Electron injection from the semiconductor to the metal.
p+
M
n
n-Si
dominant
negligible
B
IR-G
Ir-g
negligible
dominant
 qVkTA

I  I s  e  1


where
I s  AA*T 2 e

B
kT
where B is Schottky barrier height, VA is applied voltage, A is
area, and A* is Richardson’s constant.
The reverse leakage current for a Schottky diode is generally
much larger than that for a p+n diode.
Since MS Schottky diode is a majority carrier devices, the
frequency response of the device is much higher than that of
equivalent p+ n diode.
Fig . Characteristics curves for Hewlett-Packard 5082-2300
series of general-purpose Schottky barrier diodes.
100
10
Forward current (mA)
IF
1
.1
0.1 0
Temperature Coeffiecient
10A
-2.3mV/ºC
100A
-1.8mV/ºC
1.0mA
-1.3mV/ºC
10mA
-0.7mV/ºC
100mA
-0.2mV/ºC
T = 100ºC
T = 25ºC
100
200
300
400
Forward voltage (mV)
500
600
700
T = -50ºC
I-V Curve Showing Typical Temperature Variation for 5082-2300 Series Schottky Diodes
(a)
1.2
Capacitance (pF)
1.0
0.8
0.6
2900
2303
0.3
0.2
2301
2302
2305
0
4
8
12
VR-Reverse voltage (V)
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5082-2300 Series Typical Capacitance vs. Reverse Voltage at TA = 25ºC
(c)
The most evident limitations of Schottky diodes are the
relatively low reverse voltage ratings for silicon-metal
Schottky diodes, typically 50 V and below, and a relatively
high reverse leakage current. Some higher-voltage designs
are available; 200V is considered a high reverse voltage.
• Reverse leakage current, because it increases with
temperature, leads to a thermal instability issue. This often
limits the useful reverse voltage to well below the actual
rating.
• While higher reverse voltages are achievable, they would be
accompanied by higher forward voltage drops, comparable
to other types; such a Schottky diode would have no
advantage.
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Thank You
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