Electrical current, voltage, resistance, capacitance, and inductance are a few of the basic elements of electronics and radio. Apart from current, voltage, resistance, capacitance, and inductance, there are many other interesting elements to electronic technology. ... Use Electronics Notes to learn electronics online.

1. SCHOTTKY BARRIER DIODE
•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.
•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.

2. CONSTRUCTION
• 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.

3. Reverse recovery time
• 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.

4. CONSTRUCTION AND APPLICATIONS
• It is often said that the Schottky diode is a "majority
carrier" semiconductor device. This means that if the
semiconductor body is doped n-type, only the n-type
carriers (mobile electrons) play a significant role in normal
operation of the device. The majority carriers are quickly
injected into the conduction band of the metal contact on
the other side of the diode to become free moving
electrons. Therefore no slow, random recombination of n-
and p- type carriers is involved, so that this diode can cease
conduction faster than an ordinary p-n rectifier diode. This
property in turn allows a smaller device area, which also
makes for a faster transition.

5. • This is another reason why Schottky diodes are useful in
switch-mode power converters; the high speed of the diode
means that the circuit can operate at frequencies in the
range 200 kHz to 2 MHz, allowing the use of small
inductors and capacitors with greater efficiency than would
be possible with other diode types. Small-area Schottky
diodes are the heart of RF detectors and mixers, which
often operate up to 50 GHz.

6. Limitations
• 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

7. Applications
• Voltage clamping
• Reverse current and discharge protection
• Power supply
7

8. *Other Two-Terminal Devices
*Schottky Barrier Diodes

9. Two-Terminal Devices Having A
Single p-n Junction
Schottky
Tunnel
Varactor
Photodiode
Solar Cell

10. Other Two-Terminal Devices
Of A Different Construction
Photoconductive Cell
LCD (Liquid-Crystal Display)
Thermistor

11. Schottky-Barrier Diode
*Surface-Barrier/Hot-Carrier Diode

12. Schottky-Barrier Diode
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

13. Fig. 20.1 Passivated hot-carrier diode
Gold leaf metal contact
Anode (+)
Metal
Silicon dioxide screen
Metal semiconductor junction
Metal contact
Cathode (-)

14. Fig. 20.2 Comparison of characteristics
of hot-carrier and p-n junction diodes
ID
VD
p-n
junction
diode
Hot
carrier
diode
Hot
carrier
diode
p-n
junction
diode

15. Fig. 20.3 Schottky (hot-carrier) diode:
(a) equivalent circuit; (b) symbol
(a)

16. Fig. 20.4 Approximate equivalent
circuit for the Schottky diode

17. Fig. 20.5 Motorola Schottky barrier devices.
(Courtesy Motorola Semiconductor Products, Incorporated
IO Average rectified forward current (amperes)
VRRM
(Volts)
Case
Anode
Cathode
51-02
(DO-7)
Glass
59-04
Plastic
267
Plastic
60
Metal
257
(DO-4)
Metal
257
(DO-5)
Metal
430-2
(DO-21)
Metal
20
MBR020
IN5817
MBR120P
IN5820
MBR320P
MBR320M
IN5823
IN5826
MBR1520
IN5829
MBR2520
IN5832
MBR4020
MBR4020P
F
30
MBR030
IN5818
MBR130P
IN5821
MBR330P
MBR330M
IN5824
IN5827
MBR1530
IN5830
MBR2530
IN5833
MBR4030
MBR4030P
F
35
MBR135P
MBR335P
MBR335M
MBR1535
MBR2535
MBR4035
MBR4035P
F
40
IN5819
MBR140P
IN5822
MBR340P
MBR340M
IN5825
IN5828
MBR1540
IN5831
MBR2534
IN5834
MBR4040
IFSM (Amps) 5.0 100 50 250 200 500 500 500 500 800 800 800 800 800
TC @ Rated IO (ºC) 85 80 85 80 75 70 50
TJ Max 125ºC
Max VF @ IFM = IO

18. Fig 20.6 Characteristics curves for Hewlett-Packard 5082-
2300 series of general-purpose Schottky barrier diodes.
.1
0.1
1
10
100
T = 100ºC
T = 25ºC
T = -50ºC0 100 200 300 400 700600500
IF 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
Forward voltage (mV)
Forwardcurrent(mA)
I-V Curve Showing Typical Temperature Variation for 5082-2300 Series Schottky Diodes
(a)

19. 50
10
100
500
100
0 5 1510
Reverse voltage (V)
Reversecurrent(nA)
5082-2300 Series Typical Reverse Current vs. Reverse Voltage at TA = 25ºC
(b)
2900
2303
2301
2302
2305

20. Capacitance(pF)
VR-Reverse voltage (V)
5082-2300 Series Typical Capacitance vs. Reverse Voltage at TA = 25ºC
(c)
0 8 16124 20
0.2
0.3
0.6
0.8
1.0
1.2
2900
2303
2301
2302
2305

21. Schottky diode I-V characteristics
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.

22. Current components in a p+n and MS Schottky diodes
IR-G
negligible
dominant
p+ n
B
dominant
Ir-g
negligible
M n-Si

23. I-V characteristics
kT*kT
qV
TAIII
BA
ewhere1e 2
ss













 A
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.