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{{Short description|Semiconductor diode}}
The '''Schottky diode''' (named after German physicist ]) is a ] ] with a low forward voltage drop and a very fast switching action. A typical application is discharge-protection for ]s connected to ]. While standard silicon diodes have a forward voltage drop of about 0.6 ]s, Schottky diodes voltage drop at forward biases of around 1 mA is in the range 0.15V to 0.45 V, which makes them useful in voltage ] and prevention of transistor saturation. This is due to the higher current density in the Schottky diode.
{{Distinguish|Shockley diode}}


{{Infobox electronic component
A Schottky diode uses a metal-semiconductor junction as a ] (instead of a ] as in conventional diodes). This Schottky barrier results in both very fast switching times and low forward voltage drop.
|name = Schottky diode
|image = Image:schottky.jpg
|image_size =
|caption = Various Schottky-barrier diodes: Small-signal RF devices (left), medium- and high-power Schottky rectifying diodes (middle and right)
|type = ]
|working_principle =
|invented = ]
|first_produced =
|symbol = ]
|pins = ] and ]
}}


The '''Schottky diode''' (named after the German physicist ]), also known as '''Schottky barrier diode''' or '''hot-carrier diode''', is a semiconductor ] formed by the ]. It has a low ] drop and a very fast switching action. The ]s used in the early days of ] and ]s used in early power applications can be considered primitive Schottky diodes.
It is often said that the Schottky diode is a "]" semiconductor device. This means that if the semiconductor body is doped N-type, only the N-type carriers (mobile ]s) play a significant role in normal operation of the device. No slow, random ] of N- and P- type carriers is involved, so this diode can cease conduction faster than an ordinary PN rectifier ]. This property in turn allows a smaller device area, which also makes for a faster transition. Therefore broad-area Schottky diodes are useful in switch-mode ]s which operate at frequencies approaching 1 MHz. Small-area Schottky diodes are the heart of RF ]s and ], which often operate up to 5 GHz.


When sufficient forward voltage is applied, a current flows in the forward direction. A silicon ] has a typical forward voltage of 600–700 mV, while the Schottky's forward voltage is 150–450 mV. This lower forward voltage requirement allows higher switching speeds and better system efficiency.
The most evident limitation of the Schottky diode is difficulty reaching high reverse-bias voltage ratings, and relatively high ] ] when high voltage ratings are attempted. Relatively high reverse leakage current may present an issue in some applications.


== Construction ==
Commonly encountered Schottky diodes include the 1N5817, and Schottky metal-semiconductor junctions are featured in ] logic devices because of their higher switching speeds and lower voltage drops.
{{more citations needed section|date=July 2015}}
] against one metal electrode (providing rectifying action) and an ] with the other electrode.]]
]
A ] is formed between a metal and a semiconductor, creating a ] (instead of a ] as in conventional diodes). Typical metals used are molybdenum, platinum, chromium or tungsten, and certain ]s (e.g., ] and ]), whereas the semiconductor would typically be n-type silicon.<ref>‘’{{cite book | last1 = Laughton | first1 = M. A. | title = Electrical engineer's reference book | chapter = 17. Power Semiconductor Devices | publisher = Newnes | year = 2003 | pages = 25–27 | chapter-url = https://books.google.com/books?id=5jOblzV5eZ8C&pg=SA17-PA25 | access-date = 2011-05-16 | isbn = 978-0-7506-4637-6}}</ref> The metal side acts as the ], and n-type semiconductor acts as the ] of the diode; meaning ] can flow from the metal side to the semiconductor side, but not in the opposite direction. This Schottky barrier results in both very fast switching and low forward voltage drop.


The choice of the combination of the metal and semiconductor determines the forward voltage of the diode. Both n- and p-type semiconductors can develop Schottky barriers. However, the p-type typically has a much lower forward voltage. As the reverse leakage current increases dramatically with lowering the forward voltage, it cannot be too low, so the usually employed range is about 0.15–0.45&nbsp;V, and p-type semiconductors are employed only rarely. ] and other refractory silicides, which are able to withstand the temperatures needed for source/drain annealing in CMOS processes, usually have too low a forward voltage to be useful, so processes using these silicides therefore usually do not offer Schottky diodes.{{clarify|date=August 2015}}
==External references==
*
* Free IC DataSheet Search Site : http://www.Datasheet4U.com


With increased doping of the semiconductor, the width of the depletion region drops. Below a certain width, the charge carriers can tunnel through the depletion region. At very high doping levels, the junction does not behave as a rectifier any more and becomes an ohmic contact. This can be used for the simultaneous formation of ohmic contacts and diodes, as a diode will form between the silicide and lightly doped n-type region, and an ohmic contact will form between the silicide and the heavily doped n- or p-type region. Lightly doped p-type regions pose a problem, as the resulting contact has too high a resistance for a good ohmic contact, but too low a forward voltage and too high a reverse leakage to make a good diode.
{{electro-stub}}


As the edges of the Schottky contact are fairly sharp, a high electric field occurs around them, which limits how large the reverse breakdown voltage threshold can be. Various strategies are used, from guard rings to overlaps of metallisation to reduce the field. The guard rings consume valuable die area and are used primarily for larger higher-voltage diodes, while overlapping metallization is employed primarily with smaller low-voltage diodes.
]


Schottky diodes are often used as antisaturation clamps in ]s. Schottky diodes made from palladium silicide (PdSi){{clarify|reason=PtSi is Platinum Silicide – Pd or Pt?|date=July 2015}} are excellent due to their lower forward voltage (which has to be lower than the forward voltage of the base-collector junction). The Schottky temperature coefficient is lower than the coefficient of the B–C junction, which limits the use of PdSi at higher temperatures.
]

]
For power Schottky diodes, the parasitic resistances of the buried n+ layer and the epitaxial n-type layer become important. The resistance of the epitaxial layer is more important than it is for a transistor, as the current must cross its entire thickness. However, it serves as a distributed ballasting resistor over the entire area of the junction and, under usual conditions, prevents localized thermal runaway.
]

]
In comparison with the power p–n diodes, the Schottky diodes are less rugged. The junction is in direct contact with the thermally sensitive metallization; a Schottky diode can therefore dissipate less power than an equivalent-size p–n counterpart with a deep-buried junction before failing (especially during reverse breakdown). The relative advantage of the lower forward voltage of Schottky diodes is diminished at higher forward currents, where the voltage drop is dominated by the series resistance.<ref>{{cite book|first=Alan|last=Hastings|title=The Art of Analog Layout|edition=2nd |year=2005|publisher=Prentice Hall|isbn=0-13-146410-8}}</ref>
]

]
== Reverse recovery time ==
]
The most important difference between the ] diode and the Schottky diode is the reverse recovery time (t<sub>rr</sub>) when the diode switches from the conducting to the non-conducting state. In a p–n diode, the reverse recovery time can be in the order of several microseconds to less than 100&nbsp;ns for fast diodes, and it is mainly limited by the ] caused by minority carriers accumulated in the diffusion region during the conducting state.<ref name="Pierret96">{{cite book |first1=Robert F. |last1=Pierret|title=Semiconductor Device Fundamentals |url=https://books.google.com/books?id=GMZFHwAACAAJ |date=1996 |publisher=Addison-Wesley |isbn= 978-0-131-78459-8}}</ref> Schottky diodes are significantly faster since they are unipolar devices and their speed is only limited by the junction capacitance. The switching time is ~100 ] 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 ] noise. With Schottky diodes, switching is essentially "instantaneous" with only a slight capacitive loading, which is much less of a concern.
]

]
This "instantaneous" switching is not always the case. In higher voltage Schottky devices, in particular, the guard ring structure needed to control breakdown field geometry creates a parasitic p–n diode with the usual recovery time attributes. As long as this guard ring diode is not forward biased, it adds only capacitance. If the Schottky junction is driven hard enough however, the forward voltage eventually will bias both diodes forward and actual {{abbr|t<sub>rr</sub>|time to turn its status OFF}} will be greatly impacted.
]

]
It is often said that the Schottky diode is a "]" semiconductor device. This means that if the semiconductor body is a ] n-type, only the n-type carriers (mobile ]s) play a significant role in the 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 ]. Therefore, no slow random ] of n and p-type carriers is involved, so that this diode can cease conduction faster than an ordinary p–n rectifier ]. This property, in turn, allows a smaller device area, which also makes for a faster transition. This is another reason why Schottky diodes are useful in switch-mode ]: the high speed of the diode means that the circuit can operate at frequencies in the range 200&nbsp;kHz to 2&nbsp;MHz, allowing the use of small ]s and ]s with greater efficiency than would be possible with other diode types. Small-area Schottky diodes are the heart of RF ] and ], which often operate at frequencies up to 50&nbsp;GHz.
]

== Limitations ==
The most evident limitations of Schottky diodes are their relatively low reverse voltage ratings, and their relatively high ]. For silicon-metal Schottky diodes, the reverse voltage is typically 50 V or less. Some higher-voltage designs are available (200 V is considered a high reverse voltage).
Reverse leakage current, since it increases with temperature, leads to a ] issue. This often limits the useful reverse voltage to well below the actual rating.

While higher reverse voltages are achievable, they would present a higher forward voltage, comparable to other types of standard diodes. Such Schottky diodes would have no advantage <ref>{{cite magazine|url=http://www.microsemi.com/sites/default/files/micnotes/401.pdf|title=Introduction to Schottky Rectifiers|magazine=MicroNotes|series=401|quote=Schottky rectifiers seldom exceed 100 volts in their working peak reverse voltage since devices moderately above this rating level will result in forward voltages equal to or greater than equivalent pn junction rectifiers.}}</ref> unless great switching speed is required.

== Silicon carbide Schottky diode ==
Schottky diodes constructed from ] have a much lower reverse leakage current than ] Schottky diodes, as well as higher forward voltage (about 1.4–1.8&nbsp;V at 25&nbsp;°C) and reverse voltage. {{As of|2011}} they were available from manufacturers in variants up to 1700 V of reverse voltage.<ref name="SiC">{{cite web|url=https://www.electronicdesign.com/technologies/discrete-power-semis/article/21193085/schottky-diodes-the-old-ones-are-good-the-new-ones-are-better|title=Schottky Diodes: the Old Ones Are Good, the New Ones Are Better|date=March 1, 2011|website=Electronic Design}}</ref>

Silicon carbide has a high thermal conductivity, and temperature has little influence on its switching and thermal characteristics. With special packaging, silicon carbide Schottky diodes can operate at junction temperatures of over 500&nbsp;] (about 200&nbsp;°C), which allows passive ] cooling in ] applications.<ref name=SiC />

== Applications ==

=== Voltage clamping ===
While standard silicon diodes have a forward voltage drop of about 0.7 V and germanium diodes 0.3 V, Schottky diodes' voltage drop at forward biases of around 1 ] is in the range of 0.15 V to 0.46 V (see the 1N5817<ref name=1N5817>{{cite web|url=http://www.datasheetcatalog.com/datasheets_pdf/1/N/5/8/1N5817.shtml |title=1N5817 Datasheets (PDF) |publisher=Datasheetcatalog.com |access-date=2013-01-14}}</ref> and 1N5711<ref name=1N5711>{{cite web|url=http://www.datasheetcatalog.com/datasheets_pdf/1/N/5/7/1N5711.shtml |title=1N5711 Datasheets (PDF) |publisher=Datasheetcatalog.com |access-date=2013-01-14}}</ref>), which makes them useful in voltage ] and prevention of ]. This is due to the higher ] in the Schottky diode.

=== Reverse current and discharge protection ===
The Schottky diode's low forward voltage drop is good for energy-efficient applications, because little energy is wasted to heat. This makes them useful as ''blocking diodes'' in stand-alone ("off-grid") ] (PV) systems which prevent ] from discharging through the solar panels at night. They are also used in grid-connected systems with multiple ] connected in parallel, in order to prevent reverse current flowing from adjacent strings through shaded strings if the bypass diodes have failed.

=== Switched-mode power supplies ===
Schottky diodes are also used as ] in ]. The low forward voltage and fast recovery time leads to increased efficiency.

They can also be used in power supply "]"ing circuits in products that have both an internal ] and a ] input, or similar. However, the high reverse leakage current presents a problem in this case, as any high-impedance voltage sensing circuit (e.g., monitoring the battery voltage or detecting whether a mains adapter is present) will see the voltage from the other power source through the diode leakage.

=== Sample-and-hold circuits ===
Schottky diodes can be used in diode-bridge based ] circuits. When compared to regular ] based diode bridges, Schottky diodes can offer advantages. A forward-biased Schottky diode does not have any minority carrier charge storage. This allows them to switch more quickly than regular diodes, resulting in lower transition time from the sample to the hold step.
The absence of minority carrier charge storage also results in a lower hold step or sampling error, resulting in a more accurate sample at the output.<ref>Johns, David A. and Martin, Ken. ''Analog Integrated Circuit Design'' (1997), Wiley. Page 351. {{ISBN|0-471-14448-7}}</ref>

=== Charge control ===
Due to its efficient electric field control, Schottky diodes can be used to accurately load or unload single electrons in semiconductor nanostructures such as quantum wells or quantum dots.<ref>{{cite journal | last1=Couto | first1=O. D. D. | last2=Puebla | first2=J. | last3=Chekhovich | first3=E. A. | last4=Luxmoore | first4=I. J. | last5=Elliott | first5=C. J. | last6=Babazadeh | first6=N. | last7=Skolnick | first7=M. S. | last8=Tartakovskii | first8=A. I. | last9=Krysa | first9=A. B. | title=Charge control in InP/(Ga,In)P single quantum dots embedded in Schottky diodes | journal=Physical Review B | publisher=American Physical Society (APS) | volume=84 | issue=12 | date=2011-09-01 | issn=1098-0121 | doi=10.1103/physrevb.84.125301 | page=125301| arxiv=1107.2522 | bibcode=2011PhRvB..84l5301C | s2cid=119215237 }}</ref>

== Designation ==
]AC (SMA) package <br/>(surface mount version of ])<ref name=SS14/>]]

Commonly encountered Schottky diodes include the ] series rectifiers, such as the 1N581x (1 ]) and 1N582x (3 A) through-hole parts,<ref name=1N5817 /><ref name=1N5820>{{cite web|url=http://www.datasheetcatalog.com/datasheets_pdf/1/N/5/8/1N5820.shtml |title=1N5820 Datasheets (PDF) |publisher=Datasheetcatalog.com |access-date=2013-11-23}}</ref> and the SS1x (1 A) and SS3x (3 A) surface-mount parts.<ref name=SS14>{{cite web|url=http://www.datasheetcatalog.com/datasheets_pdf/S/S/1/4/SS14.shtml |title=SS14 Datasheets (PDF)|publisher=Datasheetcatalog.com |access-date=2013-11-23}}</ref><ref name=SS34>{{cite web|url=http://www.datasheetcatalog.com/datasheets_pdf/S/S/3/4/SS34.shtml |title=SS34 Datasheets (PDF)|publisher=Datasheetcatalog.com |access-date=2013-11-23}}</ref> Schottky rectifiers are available in numerous ] styles.<ref></ref><ref></ref>

Small-signal Schottky diodes such as the 1N5711,<ref name=1N5711 /> 1N6263,<ref>{{cite web|url=http://www.datasheetcatalog.com/datasheets_pdf/1/N/6/2/1N6263.shtml |title=1N6263 Datasheets (PDF) |publisher=Datasheetcatalog.com |access-date=2013-01-14}}</ref> 1SS106,<ref>{{cite web|url=http://www.datasheetcatalog.com/datasheets_pdf/1/S/S/1/1SS106.shtml |title=1SS106 Datasheets (PDF) |publisher=Datasheetcatalog.com |access-date=2013-01-14}}</ref> 1SS108,<ref>{{cite web|url=http://www.datasheetcatalog.com/datasheets_pdf/1/S/S/1/1SS108.shtml |title=1SS108 Datasheets (PDF) |publisher=Datasheetcatalog.com |access-date=2013-01-14}}</ref> and the BAT41–43, 45–49 series<ref>{{cite web|url=http://www.datasheetcatalog.com/datasheets_pdf/B/A/T/4/ |title=BAT4 Datasheets (PDF) |publisher=Datasheetcatalog.com |access-date=2013-01-14}}</ref> are widely used in high-frequency applications as detectors, mixers and nonlinear elements, and have superseded germanium diodes.<ref></ref> They are also suitable for ] (ESD) protection of sensitive devices such as ] devices, ]s and, to a lesser extent, exposed lines of ] circuitry.

Schottky metal–semiconductor junctions are featured in the successors to the ] ] family of ]s, the 74S, 74LS and 74ALS series, where they are employed as ]s in parallel with the collector-base junctions of the ]s to prevent their saturation, thereby greatly reducing their turn-off delays.

== Alternatives ==
When less power dissipation is desired, a ] and a control circuit can be used instead, in an operation mode known as ].

A ], consisting of a pn-diode or Schottky diode and an ], provides an almost perfect diode characteristic due to the effect of negative feedback, although its use is restricted to frequencies the operational amplifier used can handle.

==Electrowetting==
] can be observed when a Schottky diode is formed using a ] of liquid metal, e.g. ], in contact with a semiconductor, e.g. ]. Depending on the ] type and density in the semiconductor, the droplet spreading depends on the magnitude and sign of the voltage applied to the mercury droplet.<ref>{{cite journal | last1=Arscott | first1=Steve | last2=Gaudet | first2=Matthieu | title=Electrowetting at a liquid metal-semiconductor junction | journal=Applied Physics Letters | publisher=AIP Publishing | volume=103 | issue=7 | date=2013-08-12 | issn=0003-6951 | doi=10.1063/1.4818715 | page=074104| bibcode=2013ApPhL.103g4104A | url=https://hal.archives-ouvertes.fr/hal-02345658/file/Arscott_2013_1.4818715.pdf }}</ref> This effect has been termed ‘Schottky electrowetting’.<ref>{{cite journal | last=Arscott | first=Steve | title=Electrowetting and semiconductors | journal=RSC Advances | publisher=Royal Society of Chemistry (RSC) | volume=4 | issue=55 | date=2014-07-04 | issn=2046-2069 | doi=10.1039/c4ra04187a | page=29223| bibcode=2014RSCAd...429223A }}</ref>

== See also ==

* {{annotated link|Heterostructure barrier varactor}}
* {{annotated link|List of 1N58xx Schottky diodes}}
* {{annotated link|Schottky effect}}

== References ==
{{Reflist|2}}

== External links ==
{{Commons category|Schottky diodes}}
* {{Webarchive|url=https://web.archive.org/web/20130321043335/http://www.powerguru.org/characteristics-of-schottky-diodes/ |date=2013-03-21 }} – PowerGuru
*
* {{Webarchive|url=https://web.archive.org/web/20120308045744/http://www.ixyspower.com/images/technical_support/Application%20Notes%20By%20Topic/FREDs,%20Schottky%20and%20GaAS%20Diodes/IXAN0042.pdf |date=2012-03-08 }} Technical application, ].
*

{{Electronic components}}

{{Authority control}}

]

Latest revision as of 10:08, 30 October 2024

Semiconductor diode Not to be confused with Shockley diode.
Schottky diode
Various Schottky-barrier diodes: Small-signal RF devices (left), medium- and high-power Schottky rectifying diodes (middle and right)
TypePassive
InventorWalter H. Schottky
Pin namesanode and cathode
Electronic symbol

The Schottky diode (named after the German physicist Walter H. Schottky), also known as Schottky barrier diode or hot-carrier diode, is a semiconductor diode formed by the junction of a semiconductor with a metal. It has a low forward voltage drop and a very fast switching action. The cat's-whisker detectors used in the early days of wireless and metal rectifiers used in early power applications can be considered primitive Schottky diodes.

When sufficient forward voltage is applied, a current flows in the forward direction. A silicon p–n diode has a typical forward voltage of 600–700 mV, while the Schottky's forward voltage is 150–450 mV. This lower forward voltage requirement allows higher switching speeds and better system efficiency.

Construction

This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources in this section. Unsourced material may be challenged and removed. (July 2015) (Learn how and when to remove this message)
1N5822 Schottky diode with cut-open packaging. The semiconductor in the center makes a Schottky barrier against one metal electrode (providing rectifying action) and an ohmic contact with the other electrode.
HP 5082-2800 Schottky Barrier Diodes for General Purpose Applications

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 certain silicides (e.g., palladium silicide and platinum silicide), whereas 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; meaning conventional current can flow from the metal side to the semiconductor side, but not in the opposite direction. This Schottky barrier results in both very fast switching and low forward voltage drop.

The choice of the combination of the metal and semiconductor determines the forward voltage of the diode. Both n- and p-type semiconductors can develop Schottky barriers. However, the p-type typically has a much lower forward voltage. As the reverse leakage current increases dramatically with lowering the forward voltage, it cannot be too low, so the usually employed range is about 0.15–0.45 V, and p-type semiconductors are employed only rarely. Titanium silicide and other refractory silicides, which are able to withstand the temperatures needed for source/drain annealing in CMOS processes, usually have too low a forward voltage to be useful, so processes using these silicides therefore usually do not offer Schottky diodes.

With increased doping of the semiconductor, the width of the depletion region drops. Below a certain width, the charge carriers can tunnel through the depletion region. At very high doping levels, the junction does not behave as a rectifier any more and becomes an ohmic contact. This can be used for the simultaneous formation of ohmic contacts and diodes, as a diode will form between the silicide and lightly doped n-type region, and an ohmic contact will form between the silicide and the heavily doped n- or p-type region. Lightly doped p-type regions pose a problem, as the resulting contact has too high a resistance for a good ohmic contact, but too low a forward voltage and too high a reverse leakage to make a good diode.

As the edges of the Schottky contact are fairly sharp, a high electric field occurs around them, which limits how large the reverse breakdown voltage threshold can be. Various strategies are used, from guard rings to overlaps of metallisation to reduce the field. The guard rings consume valuable die area and are used primarily for larger higher-voltage diodes, while overlapping metallization is employed primarily with smaller low-voltage diodes.

Schottky diodes are often used as antisaturation clamps in Schottky transistors. Schottky diodes made from palladium silicide (PdSi) are excellent due to their lower forward voltage (which has to be lower than the forward voltage of the base-collector junction). The Schottky temperature coefficient is lower than the coefficient of the B–C junction, which limits the use of PdSi at higher temperatures.

For power Schottky diodes, the parasitic resistances of the buried n+ layer and the epitaxial n-type layer become important. The resistance of the epitaxial layer is more important than it is for a transistor, as the current must cross its entire thickness. However, it serves as a distributed ballasting resistor over the entire area of the junction and, under usual conditions, prevents localized thermal runaway.

In comparison with the power p–n diodes, the Schottky diodes are less rugged. The junction is in direct contact with the thermally sensitive metallization; a Schottky diode can therefore dissipate less power than an equivalent-size p–n counterpart with a deep-buried junction before failing (especially during reverse breakdown). The relative advantage of the lower forward voltage of Schottky diodes is diminished at higher forward currents, where the voltage drop is dominated by the series resistance.

Reverse recovery time

The most important difference between the p–n diode and the Schottky diode is the reverse recovery time (trr) when the diode switches from the conducting to the non-conducting state. In a p–n diode, the reverse recovery time can be in the order of several microseconds to less than 100 ns for fast diodes, and it is mainly limited by the diffusion capacitance caused by minority carriers accumulated in the diffusion region during the conducting state. Schottky diodes are significantly faster since they are unipolar devices and their speed is only limited by the junction capacitance. 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 is essentially "instantaneous" with only a slight capacitive loading, which is much less of a concern.

This "instantaneous" switching is not always the case. In higher voltage Schottky devices, in particular, the guard ring structure needed to control breakdown field geometry creates a parasitic p–n diode with the usual recovery time attributes. As long as this guard ring diode is not forward biased, it adds only capacitance. If the Schottky junction is driven hard enough however, the forward voltage eventually will bias both diodes forward and actual trr will be greatly impacted.

It is often said that the Schottky diode is a "majority carrier" semiconductor device. This means that if the semiconductor body is a doped n-type, only the n-type carriers (mobile electrons) play a significant role in the 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. 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 at frequencies up to 50 GHz.

Limitations

The most evident limitations of Schottky diodes are their relatively low reverse voltage ratings, and their relatively high reverse leakage current. For silicon-metal Schottky diodes, the reverse voltage is typically 50 V or less. Some higher-voltage designs are available (200 V is considered a high reverse voltage). Reverse leakage current, since 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 present a higher forward voltage, comparable to other types of standard diodes. Such Schottky diodes would have no advantage unless great switching speed is required.

Silicon carbide Schottky diode

Schottky diodes constructed from silicon carbide have a much lower reverse leakage current than silicon Schottky diodes, as well as higher forward voltage (about 1.4–1.8 V at 25 °C) and reverse voltage. As of 2011 they were available from manufacturers in variants up to 1700 V of reverse voltage.

Silicon carbide has a high thermal conductivity, and temperature has little influence on its switching and thermal characteristics. With special packaging, silicon carbide Schottky diodes can operate at junction temperatures of over 500 K (about 200 °C), which allows passive radiative cooling in aerospace applications.

Applications

Voltage clamping

While standard silicon diodes have a forward voltage drop of about 0.7 V and germanium diodes 0.3 V, Schottky diodes' voltage drop at forward biases of around 1 mA is in the range of 0.15 V to 0.46 V (see the 1N5817 and 1N5711), which makes them useful in voltage clamping applications and prevention of transistor saturation. This is due to the higher current density in the Schottky diode.

Reverse current and discharge protection

The Schottky diode's low forward voltage drop is good for energy-efficient applications, because little energy is wasted to heat. This makes them useful as blocking diodes in stand-alone ("off-grid") photovoltaic (PV) systems which prevent batteries from discharging through the solar panels at night. They are also used in grid-connected systems with multiple strings connected in parallel, in order to prevent reverse current flowing from adjacent strings through shaded strings if the bypass diodes have failed.

Switched-mode power supplies

Schottky diodes are also used as rectifiers in switched-mode power supplies. The low forward voltage and fast recovery time leads to increased efficiency.

They can also be used in power supply "OR"ing circuits in products that have both an internal battery and a mains adapter input, or similar. However, the high reverse leakage current presents a problem in this case, as any high-impedance voltage sensing circuit (e.g., monitoring the battery voltage or detecting whether a mains adapter is present) will see the voltage from the other power source through the diode leakage.

Sample-and-hold circuits

Schottky diodes can be used in diode-bridge based sample and hold circuits. When compared to regular p–n junction based diode bridges, Schottky diodes can offer advantages. A forward-biased Schottky diode does not have any minority carrier charge storage. This allows them to switch more quickly than regular diodes, resulting in lower transition time from the sample to the hold step. The absence of minority carrier charge storage also results in a lower hold step or sampling error, resulting in a more accurate sample at the output.

Charge control

Due to its efficient electric field control, Schottky diodes can be used to accurately load or unload single electrons in semiconductor nanostructures such as quantum wells or quantum dots.

Designation

SS14 Schottky diode in a
DO-214AC (SMA) package
(surface mount version of 1N5819)

Commonly encountered Schottky diodes include the 1N58xx series rectifiers, such as the 1N581x (1 A) and 1N582x (3 A) through-hole parts, and the SS1x (1 A) and SS3x (3 A) surface-mount parts. Schottky rectifiers are available in numerous surface-mount package styles.

Small-signal Schottky diodes such as the 1N5711, 1N6263, 1SS106, 1SS108, and the BAT41–43, 45–49 series are widely used in high-frequency applications as detectors, mixers and nonlinear elements, and have superseded germanium diodes. They are also suitable for electrostatic discharge (ESD) protection of sensitive devices such as III-V-semiconductor devices, laser diodes and, to a lesser extent, exposed lines of CMOS circuitry.

Schottky metal–semiconductor junctions are featured in the successors to the 7400 TTL family of logic devices, the 74S, 74LS and 74ALS series, where they are employed as Baker clamps in parallel with the collector-base junctions of the bipolar transistors to prevent their saturation, thereby greatly reducing their turn-off delays.

Alternatives

When less power dissipation is desired, a MOSFET and a control circuit can be used instead, in an operation mode known as active rectification.

A super diode, consisting of a pn-diode or Schottky diode and an operational amplifier, provides an almost perfect diode characteristic due to the effect of negative feedback, although its use is restricted to frequencies the operational amplifier used can handle.

Electrowetting

Electrowetting can be observed when a Schottky diode is formed using a droplet of liquid metal, e.g. mercury, in contact with a semiconductor, e.g. silicon. Depending on the doping type and density in the semiconductor, the droplet spreading depends on the magnitude and sign of the voltage applied to the mercury droplet. This effect has been termed ‘Schottky electrowetting’.

See also

References

  1. ‘’Laughton, M. A. (2003). "17. Power Semiconductor Devices". Electrical engineer's reference book. Newnes. pp. 25–27. ISBN 978-0-7506-4637-6. Retrieved 2011-05-16.
  2. Hastings, Alan (2005). The Art of Analog Layout (2nd ed.). Prentice Hall. ISBN 0-13-146410-8.
  3. Pierret, Robert F. (1996). Semiconductor Device Fundamentals. Addison-Wesley. ISBN 978-0-131-78459-8.
  4. "Introduction to Schottky Rectifiers" (PDF). MicroNotes. 401. Schottky rectifiers seldom exceed 100 volts in their working peak reverse voltage since devices moderately above this rating level will result in forward voltages equal to or greater than equivalent pn junction rectifiers.
  5. ^ "Schottky Diodes: the Old Ones Are Good, the New Ones Are Better". Electronic Design. March 1, 2011.
  6. ^ "1N5817 Datasheets (PDF)". Datasheetcatalog.com. Retrieved 2013-01-14.
  7. ^ "1N5711 Datasheets (PDF)". Datasheetcatalog.com. Retrieved 2013-01-14.
  8. Johns, David A. and Martin, Ken. Analog Integrated Circuit Design (1997), Wiley. Page 351. ISBN 0-471-14448-7
  9. Couto, O. D. D.; Puebla, J.; Chekhovich, E. A.; Luxmoore, I. J.; Elliott, C. J.; Babazadeh, N.; Skolnick, M. S.; Tartakovskii, A. I.; Krysa, A. B. (2011-09-01). "Charge control in InP/(Ga,In)P single quantum dots embedded in Schottky diodes". Physical Review B. 84 (12). American Physical Society (APS): 125301. arXiv:1107.2522. Bibcode:2011PhRvB..84l5301C. doi:10.1103/physrevb.84.125301. ISSN 1098-0121. S2CID 119215237.
  10. ^ "SS14 Datasheets (PDF)". Datasheetcatalog.com. Retrieved 2013-11-23.
  11. "1N5820 Datasheets (PDF)". Datasheetcatalog.com. Retrieved 2013-11-23.
  12. "SS34 Datasheets (PDF)". Datasheetcatalog.com. Retrieved 2013-11-23.
  13. Bourns Schottky Rectifiers.
  14. Vishay Schottky Rectifiers.
  15. "1N6263 Datasheets (PDF)". Datasheetcatalog.com. Retrieved 2013-01-14.
  16. "1SS106 Datasheets (PDF)". Datasheetcatalog.com. Retrieved 2013-01-14.
  17. "1SS108 Datasheets (PDF)". Datasheetcatalog.com. Retrieved 2013-01-14.
  18. "BAT4 Datasheets (PDF)". Datasheetcatalog.com. Retrieved 2013-01-14.
  19. Vishay Small-Signal Schottky Diodes.
  20. Arscott, Steve; Gaudet, Matthieu (2013-08-12). "Electrowetting at a liquid metal-semiconductor junction" (PDF). Applied Physics Letters. 103 (7). AIP Publishing: 074104. Bibcode:2013ApPhL.103g4104A. doi:10.1063/1.4818715. ISSN 0003-6951.
  21. Arscott, Steve (2014-07-04). "Electrowetting and semiconductors". RSC Advances. 4 (55). Royal Society of Chemistry (RSC): 29223. Bibcode:2014RSCAd...429223A. doi:10.1039/c4ra04187a. ISSN 2046-2069.

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