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

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 diodesID
Hot
carrier
diode
p-n
junction
diode VD
p-n
junction
diode
Hot
carrier
diode

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

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

17. IO Average rectified forward current (amperes)
Fig 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 60
Metal
257
(DO-4)
(DO-5)
430-2
(DO-21) 20
MBR020
IN5817
MBR120P
IN5820
MBR320P
MBR320M
IN5823
IN5826
MBR1520
IN5829
MBR2520
IN5832
MBR4020
MBR4020PF 30
MBR030
IN5818
MBR130P
IN5821
MBR330P
MBR330M
IN5824
IN5827
MBR1530
IN5830
MBR2530
IN5833
MBR4030
MBR4030PF 35
MBR135P
MBR335P
MBR335M
MBR1535
MBR2535
MBR4035
MBR4035PF 40
IN5819
MBR140P
IN5822
MBR340P
MBR340M
IN5825
IN5828
MBR1540
IN5831
MBR2534
IN5834
MBR4040
IFSM (Amps)
5.0
100 50
250
200
500
800
Rated IO (ºC) 85 80 75 70
TJ Max
125ºC
Max IFM = IO

18. IF Temperature Coeffiecient
Fig 20.6 Characteristics curves for Hewlett-Packard series of general-purpose Schottky barrier diodes.
100 10
Forward current (mA)
IF Temperature Coeffiecient
10A mV/ºC
100A mV/ºC
1.0mA mV/ºC
10mA mV/ºC
100mA mV/ºC 1 .1
T = 100ºC
T = 25ºC
T = -50ºC
0.1
100
200
300
400
500
600
700
Forward voltage (mV)
I-V Curve Showing Typical Temperature Variation for Series Schottky Diodes
(a)

19. (b) 2301 2302 2305 100 500 Reverse current (nA) 2900 2303 100 50 10 55 10 15
Reverse voltage (V)
Series Typical Reverse Current vs. Reverse Voltage at TA = 25ºC
(b)

20. 1.2
1.0
0.8
Capacitance (pF)
0.6
2900
2303
0.3
2301
2302
2305
0.2 4 8 12 16 20
VR-Reverse voltage (V)
Series Typical Capacitance vs. Reverse Voltage at TA = 25ºC
(c)

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
M n-Si p+ n
dominant
negligible B
Ir-g
IR-G
negligible
dominant

23. I-V characteristics
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.