微电子专业英语翻译资料下载.pdf

1、视复合过程的本征而定，复合过程所释放出的能量，一般以光子形式辐射出或是对晶格产生热而消耗掉。一个光子被辐射出，此过程称为辐射复合，反之则称为非辐射复合。2.5 Generation and Recombination Processes载流子产生与复合过程Recombinationphenomenacan be classified asdirect and indirectprocesses.Direct recombination,also called band-to-band recombination,usually dominates in direct-bandgap semic

2、onductors,such as galliumarsenide;while indirect recombination via bandgap recombination centersdominates in indirect bandgap semiconductors,such as silicon.复合现象可分为直接和间接过程。直接复合，又称为带至带复合，通常在直接禁带的半导体中较为显著，如砷化镓；而通过禁带复合中心的间接复合则在间接禁带的半导体中较为显著，如硅晶。Consider a direct-bandgap semicond uctor in thermal equili

3、brium.The continuousthermal vibration of lattice atoms causes some bonds between neighboring atomsto be broken.When a bond is broken,an electron-hole pair is generated.In termsof the band diagram,the thermal energy enables a valence electron to make anupward transition to the conduction band leaving

4、 a hole in the valence band.Thisprocess is called carrier generation and is represented by the generation rateGth（number of electron-hole pairs generated per cm3per second）in Fig.2.11（a）.考虑一个在热平衡状态下的直接禁带半导体。晶格原子连续的热扰动造成邻近原子间的键断裂。当一个键断裂，一对电子空穴对就产生了。以能带图的观点而言，热能使得一个价电子向上移到导带，而留下一个空穴在价带。这个过程称为载流子产生，并以产

5、生速率Gth（每立方厘米每秒产生的电子-空穴对数目）表示，如图2.11（a）所示。When an electron makes a transition downward from the conduction band to thevalence band,an electron-hole pair is annihilated.This reverse process is calledrecombination;it is represented by the recombination rate Rthin Fig.2.11（a）.Under thermal equilibrium c

6、onditions,the generation rate Gthmust equal therecombination rate Rth,so that the carrier concentrations remain constant andthe condition pn=ni2is maintained.当电子从导带向下移到价带，一个电子-空穴对消失。这种反向过程称为复合，并以复合率Rth表示，如图2.11（a）所示。在热平衡状态下，产生速率Gth必定等于复合率 Rth，所以载流子浓度维持常数，且维持pn=ni2的状况。当超量载流子被导入一个直接禁带半导体时，电子与空穴直接复合的几率

7、较高，这是因为导带的底部与价带的顶端位于同一线上，因此在禁带间跃迁时，无需额外的动量。直接复合率R应正比于导带中含有的电子数目及价带中含有的空穴数目。也就是R=np。其中为比例常数。When excess carries are introduced to a direct-bandgap semiconductor,theprobabilityishighthatelectronsandholeswillrecombinedirectly,because the bottom of the conduction band and the top of thevalence band are

8、lined up and no additional crystal momentum isrequired for the transition across the bandgap.The rate of the directrecombination R is expected to be proportional to the number of holesavailableinthevalenceband;thatisR=npwhereistheproportionality constant.As discussed previously,in thermal equilibriu

9、m the recombination ratemust be balanced by the generation rate.Therefore,for an n-typesemiconductor,we have Gth=Rth=nnopnowhere nnoand pnorepresentelectron and hole densities in an n-type semiconductor at thermalequilibrium.When we shine a light on the semiconductor to produceelectron-hole pairs at

10、 a rate GL（Fig.2.11（b）,the carrier concentrationsare above their equilibrium values.如前面所讨论的，在热平衡下复合率必定与产生速率保持平衡，因此，对以n型半导体而言，我们可以得到Gth=Rth=nnopno。nno及pno分别表示在热平衡下，n型半导体中的电子及空穴浓度。我们在半导体上照光，使它以GL的速率产生电子-空穴对（如图2.11（b），载流子浓度将大于平衡时的值。Therefore,the net recombination rate is proportional to the excess mino

11、ritycarrier concentration.The proportionality constant 1/nnois called the lifetimeTpof the excess minority carriers.The physical meaning of lifetime can bestbe illustrated by the transient response of a device after the sudden removalof the light source.Consider an n-type sample,as shown in Fid.2.12

12、（a）,thatis illuminated with light and in which the electron-hole pairs are generateduniformly throughout the sample with a generation rate GL.Fig.1.12（b）showsthe variation of pnwith time.The minority carriers recombine with majoritycarriers and decay exponentially with a time constant Tpwhich corres

13、ponds tothe lifetime.因此，净复合率正比于超量少数载流子浓度。比例常数1/nno称为超量少数载流子的寿命Tp。寿命的物理意义可通过器件在瞬间移去光源后的暂态响应作最好的说明。考虑一个n型样品，如图2.12（a），光照射其上且整个样品中以一个产生速率GL均匀地产生电子-空穴对。图2.12（b）显示pn随时间的变化。少数载流子与多数载流子复合，且寿命Tp成指数衰减。The above case illustrates the main idea of measuring the carrier lifetime usingphotoconductivity method.Fig.2.12（c）shows a schematic setup.The excesscarriers,generated uniformly throughout the sample by the light pulse,cause amomentary increase in the conductivity.The increase in conductivity manifestsitself by a drop in voltage across the sample when a const