二(er)極管(guan)(guan)又(you)稱晶體(ti)(ti)二(er)極管(guan)(guan),簡稱二(er)極管(guan)(guan)(diode)，另外，還有早期(qi)的(de)(de)(de)(de)(de)(de)(de)真空電(dian)(dian)(dian)子(zi)(zi)二(er)極管(guan)(guan)；它是(shi)一種(zhong)具(ju)有單向(xiang)(xiang)傳導電(dian)(dian)(dian)流(liu)的(de)(de)(de)(de)(de)(de)(de)電(dian)(dian)(dian)子(zi)(zi)器(qi)件。在半(ban)導體(ti)(ti)二(er)極管(guan)(guan)內部(bu)有一個(ge)PN結(jie)兩(liang)個(ge)引(yin)線端子(zi)(zi)，這(zhe)種(zhong)電(dian)(dian)(dian)子(zi)(zi)器(qi)件按照外加(jia)電(dian)(dian)(dian)壓(ya)的(de)(de)(de)(de)(de)(de)(de)方向(xiang)(xiang)，具(ju)備單向(xiang)(xiang)電(dian)(dian)(dian)流(liu)的(de)(de)(de)(de)(de)(de)(de)轉導性。一般來講(jiang)，晶體(ti)(ti)二(er)極管(guan)(guan)是(shi)一個(ge)由p型半(ban)導體(ti)(ti)和n型半(ban)導體(ti)(ti)燒結(jie)形成的(de)(de)(de)(de)(de)(de)(de)p-n結(jie)界(jie)面(mian)。在其界(jie)面(mian)的(de)(de)(de)(de)(de)(de)(de)兩(liang)側(ce)形成空間(jian)電(dian)(dian)(dian)荷層，構成自建(jian)電(dian)(dian)(dian)場(chang)。當外加(jia)電(dian)(dian)(dian)壓(ya)等于(yu)(yu)零(ling)時，由于(yu)(yu)p-n 結(jie)兩(liang)邊載流(liu)子(zi)(zi)的(de)(de)(de)(de)(de)(de)(de)濃度差引(yin)起(qi)擴散電(dian)(dian)(dian)流(liu)和由自建(jian)電(dian)(dian)(dian)場(chang)引(yin)起(qi)的(de)(de)(de)(de)(de)(de)(de)漂(piao)移(yi)相等而處(chu)于(yu)(yu)電(dian)(dian)(dian)平衡狀態，這(zhe)也(ye)是(shi)常態下的(de)(de)(de)(de)(de)(de)(de)二(er)極管(guan)(guan)特(te)性。

二極管（：Diode），電子元件當中，一種(zhong)具有(you)兩個的(de)(de)裝置，只(zhi)允許電流(liu)由單一方向流(liu)過(guo)。許多的(de)(de)使用(yong)是應用(yong)其整流(liu)的(de)(de)功能。而(er)變容二極管（Varicap Diode）則用(yong)來當作(zuo)電子式的(de)(de)可調。

大部分二極(ji)(ji)(ji)管(guan)(guan)所(suo)具備的(de)(de)(de)電(dian)流(liu)方(fang)向(xiang)性(xing)我(wo)們通常稱(cheng)之為“整流(liu)（Rectifying）”功(gong)能。二極(ji)(ji)(ji)管(guan)(guan)最普(pu)遍的(de)(de)(de)功(gong)能就是(shi)只允許電(dian)流(liu)由(you)單一方(fang)向(xiang)通過(guo)（稱(cheng)為順(shun)向(xiang)偏壓），反(fan)向(xiang)時阻(zu)斷 （稱(cheng)為逆(ni)向(xiang)偏壓）。因此(ci)，二極(ji)(ji)(ji)管(guan)(guan)可(ke)以想(xiang)成電(dian)子(zi)版的(de)(de)(de)逆(ni)止(zhi)閥。然而實際上二極(ji)(ji)(ji)管(guan)(guan)并不會(hui)表現(xian)出如此(ci)完美的(de)(de)(de)開(kai)與(yu)關的(de)(de)(de)方(fang)向(xiang)性(xing)，而是(shi)較為復雜的(de)(de)(de)非線(xian)性(xing)電(dian)子(zi)特(te)(te)征——這是(shi)由(you)特(te)(te)定(ding)類(lei)型的(de)(de)(de)二極(ji)(ji)(ji)管(guan)(guan)技術決定(ding)的(de)(de)(de)。二極(ji)(ji)(ji)管(guan)(guan)使用(yong)上除(chu)了用(yong)做開(kai)關的(de)(de)(de)方(fang)式(shi)之外還有(you)很(hen)多(duo)其(qi)他的(de)(de)(de)功(gong)能。

早期的二極管包(bao)含“貓須晶體(ti)（"Cat's Whisker" Crystals）”以及真空(kong)管(英國稱為“熱游離閥(fa)（Thermionic Valves）”)。現今最普遍(bian)的二極管大多是使(shi)用(yong)材(cai)料如(ru)硅或。

外加(jia)正向電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)時(shi)(shi)，在(zai)(zai)正向特(te)性(xing)的起(qi)始部分，正向電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)很小，不(bu)足以(yi)克服PN結(jie)內(nei)電(dian)(dian)(dian)(dian)(dian)場的阻擋作用，正向電(dian)(dian)(dian)(dian)(dian)流幾(ji)乎(hu)為(wei)零(ling)，這一段稱為(wei)死(si)區(qu)。這個不(bu)能使(shi)二(er)極管導(dao)通的正向電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)稱為(wei)死(si)區(qu)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)。當正向電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)大于死(si)區(qu)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)以(yi)后，PN結(jie)內(nei)電(dian)(dian)(dian)(dian)(dian)場被克服，二(er)極管導(dao)通，電(dian)(dian)(dian)(dian)(dian)流隨電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)增大而迅速上升(sheng)。在(zai)(zai)正常使(shi)用的電(dian)(dian)(dian)(dian)(dian)流范(fan)圍內(nei)，導(dao)通時(shi)(shi)二(er)極管的端電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)幾(ji)乎(hu)維持(chi)不(bu)變，這個電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)稱為(wei)二(er)極管的正向電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)。

外(wai)加反(fan)向(xiang)電(dian)壓不超過一定(ding)范圍時，通(tong)過二(er)極管的電(dian)流(liu)(liu)是(shi)少數載流(liu)(liu)子漂移(yi)運(yun)動所形成反(fan)向(xiang)電(dian)流(liu)(liu)，由(you)于反(fan)向(xiang)電(dian)流(liu)(liu)很小，二(er)極管處(chu)于截止狀態。這個反(fan)向(xiang)電(dian)流(liu)(liu)又稱為反(fan)向(xiang)飽(bao)和(he)電(dian)流(liu)(liu)或漏電(dian)流(liu)(liu)，二(er)極管的反(fan)向(xiang)飽(bao)和(he)電(dian)流(liu)(liu)受(shou)溫度影響很大。

外加(jia)反(fan)(fan)向電(dian)(dian)(dian)(dian)(dian)壓(ya)超(chao)過(guo)某一數(shu)值時，反(fan)(fan)向電(dian)(dian)(dian)(dian)(dian)流會(hui)突然增大，這種現(xian)象(xiang)稱為電(dian)(dian)(dian)(dian)(dian)擊(ji)穿。引(yin)起(qi)(qi)電(dian)(dian)(dian)(dian)(dian)擊(ji)穿的臨界電(dian)(dian)(dian)(dian)(dian)壓(ya)稱為二(er)極(ji)(ji)(ji)管(guan)反(fan)(fan)向擊(ji)穿電(dian)(dian)(dian)(dian)(dian)壓(ya)。電(dian)(dian)(dian)(dian)(dian)擊(ji)穿時二(er)極(ji)(ji)(ji)管(guan)失去單(dan)向導電(dian)(dian)(dian)(dian)(dian)性(xing)(xing)。如果二(er)極(ji)(ji)(ji)管(guan)沒有因(yin)電(dian)(dian)(dian)(dian)(dian)擊(ji)穿而(er)(er)引(yin)起(qi)(qi)過(guo)熱，則(ze)(ze)單(dan)向導電(dian)(dian)(dian)(dian)(dian)性(xing)(xing)不一定會(hui)被永久破壞，在撤除外加(jia)電(dian)(dian)(dian)(dian)(dian)壓(ya)后，其性(xing)(xing)能仍可(ke)恢復，否則(ze)(ze)二(er)極(ji)(ji)(ji)管(guan)就損壞了(le)。因(yin)而(er)(er)使用時應避免(mian)二(er)極(ji)(ji)(ji)管(guan)外加(jia)的反(fan)(fan)向電(dian)(dian)(dian)(dian)(dian)壓(ya)過(guo)高。

二(er)極(ji)管是(shi)一(yi)種具有單向導(dao)電(dian)(dian)的(de)二(er)端器(qi)件，有電(dian)(dian)子(zi)二(er)極(ji)管和(he)晶體(ti)(ti)二(er)極(ji)管之(zhi)分(fen)，電(dian)(dian)子(zi)二(er)極(ji)管現(xian)已很少見(jian)到，比較常(chang)見(jian)和(he)常(chang)用的(de)多是(shi)晶體(ti)(ti)二(er)極(ji)管。二(er)極(ji)管的(de)單向導(dao)電(dian)(dian)特性，幾乎在所有的(de)電(dian)(dian)子(zi)電(dian)(dian)路(lu)中，都要(yao)用到半導(dao)體(ti)(ti)二(er)極(ji)管，它在許多的(de)電(dian)(dian)路(lu)中起著(zhu)重(zhong)要(yao)的(de)作用，它是(shi)誕(dan)生最早的(de)半導(dao)體(ti)(ti)器(qi)件之(zhi)一(yi)，其應用也非常(chang)廣泛。

二極(ji)(ji)管(guan)(guan)(guan)的(de)管(guan)(guan)(guan)壓(ya)(ya)(ya)降(jiang)(jiang)：硅二極(ji)(ji)管(guan)(guan)(guan)（不發(fa)(fa)光(guang)(guang)類型(xing)）正(zheng)向管(guan)(guan)(guan)壓(ya)(ya)(ya)降(jiang)(jiang)0.7V，鍺管(guan)(guan)(guan)正(zheng)向管(guan)(guan)(guan)壓(ya)(ya)(ya)降(jiang)(jiang)為(wei)0.3V，發(fa)(fa)光(guang)(guang)二極(ji)(ji)管(guan)(guan)(guan)正(zheng)向管(guan)(guan)(guan)壓(ya)(ya)(ya)降(jiang)(jiang)會隨(sui)不同(tong)發(fa)(fa)光(guang)(guang)顏(yan)(yan)色(se)(se)而(er)不同(tong)。主要有三種顏(yan)(yan)色(se)(se)，具體壓(ya)(ya)(ya)降(jiang)(jiang)參(can)考值如(ru)下：紅色(se)(se)發(fa)(fa)光(guang)(guang)二極(ji)(ji)管(guan)(guan)(guan)的(de)壓(ya)(ya)(ya)降(jiang)(jiang)為(wei)2.0--2.2V，黃色(se)(se)發(fa)(fa)光(guang)(guang)二極(ji)(ji)管(guan)(guan)(guan)的(de)壓(ya)(ya)(ya)降(jiang)(jiang)為(wei)1.8—2.0V，綠(lv)色(se)(se)發(fa)(fa)光(guang)(guang)二極(ji)(ji)管(guan)(guan)(guan)的(de)壓(ya)(ya)(ya)降(jiang)(jiang)為(wei)3.0—3.2V，正(zheng)常發(fa)(fa)光(guang)(guang)時的(de)額定電(dian)流約為(wei)20mA。

二(er)(er)極(ji)管的(de)與電流不是線性關系，所(suo)以在將不同的(de)二(er)(er)極(ji)管并聯(lian)的(de)時(shi)候要接相(xiang)適應(ying)的(de)電阻(zu)。

與PN結一樣，二(er)極(ji)管(guan)具有單向(xiang)導電(dian)性(xing)。硅二(er)極(ji)管(guan)典型(xing)（圖）。在二(er)極(ji)管(guan)加有正向(xiang)電(dian)壓，當電(dian)壓值較小時，電(dian)流極(ji)小；當電(dian)壓超過0.6V時，電(dian)流開始按指數規律增(zeng)大，通(tong)(tong)常稱此為二(er)極(ji)管(guan)的開啟電(dian)壓；當電(dian)壓達到(dao)約0.7V時，二(er)極(ji)管(guan)處于完(wan)全導通(tong)(tong)狀態(tai)，通(tong)(tong)常稱此電(dian)壓為二(er)極(ji)管(guan)的導通(tong)(tong)電(dian)壓，用符(fu)號UD表示。

對于鍺二極(ji)管，開啟電(dian)(dian)(dian)壓為(wei)0.2V，導通電(dian)(dian)(dian)壓UD約為(wei)0.3V。在二極(ji)管加有反向電(dian)(dian)(dian)壓，當電(dian)(dian)(dian)壓值(zhi)(zhi)較小時，電(dian)(dian)(dian)流極(ji)小，其(qi)電(dian)(dian)(dian)流值(zhi)(zhi)為(wei)反向飽(bao)和電(dian)(dian)(dian)流IS。當反向電(dian)(dian)(dian)壓超過(guo)某個值(zhi)(zhi)時，電(dian)(dian)(dian)流開始急劇增大，稱之為(wei)反向擊(ji)穿，稱此電(dian)(dian)(dian)壓為(wei)二極(ji)管的(de)反向擊(ji)穿電(dian)(dian)(dian)壓，用(yong)符號(hao)UBR表示(shi)。不(bu)同型號(hao)的(de)二極(ji)管的(de)擊(ji)穿電(dian)(dian)(dian)壓UBR值(zhi)(zhi)差別很大，從幾十伏到幾千伏。

齊(qi)納(na)擊穿

反向(xiang)擊(ji)穿(chuan)按機理分為齊納擊(ji)穿(chuan)和雪崩擊(ji)穿(chuan)兩種情況。在高摻雜(za)(za)濃(nong)度(du)的情況下，因勢(shi)壘區寬度(du)很小，反向(xiang)電(dian)(dian)壓較(jiao)大(da)時，破壞了勢(shi)壘區內(nei)共價(jia)鍵結構，使價(jia)電(dian)(dian)子脫離共價(jia)鍵束縛，產生(sheng)電(dian)(dian)子-空穴對(dui)，致使電(dian)(dian)流(liu)急劇(ju)增大(da)，這種擊(ji)穿(chuan)稱為齊納擊(ji)穿(chuan)。如果摻雜(za)(za)濃(nong)度(du)較(jiao)低(di)，勢(shi)壘區寬度(du)較(jiao)寬，不容(rong)易產生(sheng)齊納擊(ji)穿(chuan)。

雪崩擊穿　　

另一種擊穿為(wei)雪(xue)崩(beng)擊穿。當反向電(dian)壓增(zeng)加(jia)到(dao)較(jiao)大數值時(shi)，外加(jia)電(dian)場(chang)使電(dian)子(zi)(zi)(zi)漂移速(su)度加(jia)快，從而(er)與共價(jia)鍵(jian)中的價(jia)電(dian)子(zi)(zi)(zi)相碰撞(zhuang)(zhuang)，把價(jia)電(dian)子(zi)(zi)(zi)撞(zhuang)(zhuang)出共價(jia)鍵(jian)，產生(sheng)新的電(dian)子(zi)(zi)(zi)-空穴對(dui)。新產生(sheng)的電(dian)子(zi)(zi)(zi)-空穴被電(dian)場(chang)加(jia)速(su)后又撞(zhuang)(zhuang)出其它價(jia)電(dian)子(zi)(zi)(zi)，載流(liu)子(zi)(zi)(zi)雪(xue)崩(beng)式地增(zeng)加(jia)，致(zhi)使電(dian)流(liu)急劇增(zeng)加(jia)，這種擊穿稱(cheng)為(wei)雪(xue)崩(beng)擊穿。無(wu)論哪種擊穿，若(ruo)對(dui)其電(dian)流(liu)不加(jia)限(xian)制，都(dou)可能造成PN結(jie)永久(jiu)性損壞。

二極(ji)(ji)管最重要的特性(xing)就(jiu)是單方向(xiang)(xiang)。在電(dian)路中(zhong)，電(dian)流只能從二極(ji)(ji)管的正極(ji)(ji)流入(ru)，負極(ji)(ji)流出。下面通過簡單的實驗說(shuo)明二極(ji)(ji)管的正向(xiang)(xiang)特性(xing)和(he)反(fan)向(xiang)(xiang)特性(xing)。

在(zai)電(dian)(dian)(dian)(dian)子電(dian)(dian)(dian)(dian)路中(zhong)，將二(er)極(ji)管(guan)(guan)的(de)(de)正(zheng)(zheng)極(ji)接(jie)在(zai)高電(dian)(dian)(dian)(dian)位端(duan)(duan)，負極(ji)接(jie)在(zai)低電(dian)(dian)(dian)(dian)位端(duan)(duan)，二(er)極(ji)管(guan)(guan)就會導(dao)通，這(zhe)種連接(jie)方式，稱為(wei)正(zheng)(zheng)向偏置(zhi)。必(bi)須說明，當加(jia)在(zai)二(er)極(ji)管(guan)(guan)兩端(duan)(duan)的(de)(de)正(zheng)(zheng)向電(dian)(dian)(dian)(dian)壓(ya)很小時，二(er)極(ji)管(guan)(guan)仍然不(bu)能(neng)導(dao)通，流(liu)過(guo)二(er)極(ji)管(guan)(guan)的(de)(de)正(zheng)(zheng)向電(dian)(dian)(dian)(dian)流(liu)十分(fen)微弱。只有當正(zheng)(zheng)向電(dian)(dian)(dian)(dian)壓(ya)達到某一數(shu)值(zhi)（這(zhe)一數(shu)值(zhi)稱為(wei)“門坎電(dian)(dian)(dian)(dian)壓(ya)”，又(you)稱“死區電(dian)(dian)(dian)(dian)壓(ya)”，鍺管(guan)(guan)約為(wei)0.1V，硅(gui)管(guan)(guan)約為(wei)0.5V）以后，二(er)極(ji)管(guan)(guan)才能(neng)直正(zheng)(zheng)導(dao)通。導(dao)通后二(er)極(ji)管(guan)(guan)兩端(duan)(duan)的(de)(de)電(dian)(dian)(dian)(dian)壓(ya)基本上保持不(bu)變（鍺管(guan)(guan)約為(wei)0.3V，硅(gui)管(guan)(guan)約為(wei)0.7V），稱為(wei)二(er)極(ji)管(guan)(guan)的(de)(de)“正(zheng)(zheng)向壓(ya)降”。

在(zai)(zai)電(dian)子(zi)電(dian)路中，二(er)(er)極管(guan)的正極接在(zai)(zai)低電(dian)位(wei)端(duan)，負(fu)極接在(zai)(zai)高電(dian)位(wei)端(duan)，此時(shi)二(er)(er)極管(guan)中幾乎沒有電(dian)流(liu)流(liu)過，此時(shi)二(er)(er)極管(guan)處于(yu)截(jie)止狀態(tai)，這(zhe)種(zhong)連接方(fang)式(shi)，稱(cheng)為反(fan)向(xiang)(xiang)偏(pian)置。二(er)(er)極管(guan)處于(yu)反(fan)向(xiang)(xiang)偏(pian)置時(shi)，仍然會有微弱的反(fan)向(xiang)(xiang)電(dian)流(liu)流(liu)過二(er)(er)極管(guan)，稱(cheng)為。當二(er)(er)極管(guan)兩(liang)端(duan)的反(fan)向(xiang)(xiang)電(dian)壓增(zeng)大到某(mou)一數值(zhi)，反(fan)向(xiang)(xiang)電(dian)流(liu)會急劇增(zeng)大，二(er)(er)極管(guan)將失去單(dan)方(fang)向(xiang)(xiang)導電(dian)特性，這(zhe)種(zhong)狀態(tai)稱(cheng)為二(er)(er)極管(guan)的擊穿。

點(dian)接觸(chu)型(xing)(xing)二(er)極(ji)管(guan)是在鍺或(huo)硅材料(liao)的單(dan)晶片上(shang)壓觸(chu)一根金(jin)屬針后，再通過電(dian)(dian)流法而形成的。因此(ci)，其PN結的容量小，適(shi)用(yong)于高頻電(dian)(dian)路(lu)。但是，與面結型(xing)(xing)相比較，點(dian)接觸(chu)型(xing)(xing)二(er)極(ji)管(guan)正向特性(xing)和反向特性(xing)都差，因此(ci)，不能使用(yong)于大電(dian)(dian)流和整流。因為構(gou)造簡單(dan)，所以價格便宜。