Close-up view of a silicon diode. The anode is at the right side; the cathode is at the left side (where it is marked with a black band). The square silicon crystal can be seen between the two leads.
Various semiconductor diodes. Bottom: A bridge rectifier. In most diodes, a white or black painted band identifies the cathode into which electrons will flow when the diode is conducting. Electron flow is the reverse of conventional current flow.[1][2][3][4]
Structure of a vacuum tube diode. The filament itself may be the cathode, or more commonly (as shown here) used to heat a separate metal tube which serves as the cathode.

A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other. A diode vacuum tube or thermionic diode is a vacuum tube with two electrodes, a heated cathode and a plate, in which electrons can flow in only one direction, from cathode to plate. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material with a p–n junction connected to two electrical terminals.[5] Semiconductor diodes were the first semiconductor electronic devices. The discovery of asymmetric electrical conduction across the contact between a crystalline mineral and a metal was made by German physicist Ferdinand Braun in 1874. Today, most diodes are made of silicon, but other materials such as gallium arsenide and germanium are used.[6]

Main functions

The most common function of a diode is to allow an electric current to pass in one direction (called the diode's forward direction), while blocking it in the opposite direction (the reverse direction). As such, the diode can be viewed as an electronic version of a check valve. This unidirectional behavior is called rectification, and is used to convert alternating current (ac) to direct current (dc). Forms of rectifiers, diodes can be used for such tasks as extracting modulation from radio signals in radio receivers.

However, diodes can have more complicated behavior than this simple on–off action, because of their nonlinear current-voltage characteristics.[7] Semiconductor diodes begin conducting electricity only if a certain threshold voltage or cut-in voltage is present in the forward direction (a state in which the diode is said to be forward-biased). The voltage drop across a forward-biased diode varies only a little with the current, and is a function of temperature; this effect can be used as a temperature sensor or as a voltage reference. Also, diodes' high resistance to current flowing in the reverse direction suddenly drops to a low resistance when the reverse voltage across the diode reaches a value called the breakdown voltage.

A semiconductor diode's current–voltage characteristic can be tailored by selecting the semiconductor materials and the doping impurities introduced into the materials during manufacture.[7] These techniques are used to create special-purpose diodes that perform many different functions.[7] For example, diodes are used to regulate voltage (Zener diodes), to protect circuits from high voltage surges (avalanche diodes), to electronically tune radio and TV receivers (varactor diodes), to generate radio-frequency oscillations (tunnel diodes, Gunn diodes, IMPATT diodes), and to produce light (light-emitting diodes). Tunnel, Gunn and IMPATT diodes exhibit negative resistance, which is useful in microwave and switching circuits.

Diodes, both vacuum and semiconductor, can be used as shot-noise generators.

Other Languages
Afrikaans: Diode
Alemannisch: Diode
አማርኛ: ዳዮድ
العربية: صمام ثنائي
aragonés: Diodo
অসমীয়া: ডায়ড
asturianu: Diodu
azərbaycanca: Diod
تۆرکجه: دیود
বাংলা: ডায়োড
Bân-lâm-gú: Jī-ke̍k-thé
башҡортса: Диод
беларуская: Дыёд
беларуская (тарашкевіца)‎: Дыёд
български: Диод
bosanski: Dioda
català: Díode
čeština: Dioda
chiShona: Diode
dansk: Diode
Deutsch: Diode
eesti: Diood
Ελληνικά: Δίοδος
español: Diodo
Esperanto: Diodo
euskara: Diodo
فارسی: دیود
français: Diode
Gaeilge: Dé-óid
galego: Díodo
贛語: 二極管
한국어: 다이오드
հայերեն: Դիոդ
हिन्दी: डायोड
hrvatski: Dioda
Ido: Diodo
Bahasa Indonesia: Diode
interlingua: Diodo
íslenska: Tvistur
italiano: Diodo
עברית: דיודה
Basa Jawa: Dhiodha
ಕನ್ನಡ: ಡಯೋಡ್
ქართული: დიოდი
қазақша: Диод
Kiswahili: Diodi
Kreyòl ayisyen: Dyòd
Кыргызча: Диод
ລາວ: ດີອົດ
Latina: Diodus
latviešu: Diode
lumbaart: Diod
magyar: Dióda
македонски: Диода
Malagasy: Roalahiny
മലയാളം: ഡയോഡ്
मराठी: डायोड
مصرى: دايود
مازِرونی: دیود
Bahasa Melayu: Diod
монгол: Диод
မြန်မာဘာသာ: ဒိုင်အုတ်
Nederlands: Diode
नेपाली: डायोड
नेपाल भाषा: दायोद
日本語: ダイオード
нохчийн: Диод
Nordfriisk: Diode
norsk: Diode
norsk nynorsk: Diode
occitan: Diòde
Oromoo: Daayoodii
oʻzbekcha/ўзбекча: Diod
ਪੰਜਾਬੀ: ਡਾਇਓਡ
پنجابی: ڈائیوڈ
Patois: Dayuod
Plattdüütsch: Diood
polski: Dioda
português: Diodo semicondutor
română: Diodă
русиньскый: Діода
русский: Диод
Scots: Diode
Seeltersk: Dioden
shqip: Dioda
සිංහල: දියෝඩ
Simple English: Diode
slovenčina: Dióda
slovenščina: Dioda
کوردی: دایۆد
српски / srpski: Диода
srpskohrvatski / српскохрватски: Dioda
Basa Sunda: Dioda
suomi: Diodi
svenska: Diod
Tagalog: Duhandas
татарча/tatarça: Диод
తెలుగు: డయోడ్
ไทย: ไดโอด
Türkçe: Diyot
Türkmençe: Diod
українська: Діод
اردو: ڈائیوڈ
ئۇيغۇرچە / Uyghurche: ئىككى پۇتلۇق لامپا
Tiếng Việt: Điốt bán dẫn
文言: 二極管
Winaray: Diodo
吴语: 二极管
ייִדיש: דיאדע
粵語: 二極管
中文: 二極管