电子器件-金半接触ppt课件

1、acceptor 受主受主 donor 施主施主recombination 复合复合majority 多子多子 minority 少子少子transition region 过渡区过渡区depletion region 耗尽区耗尽区 contact barrier 接触势垒接触势垒p-n junction pn结结 heterojunction/异质结异质结EHP 电子空穴对电子空穴对 homojunction/同质结同质结 Schottky barrier /肖特基势垒肖特基势垒 barrier height/势垒高度势垒高度 ideal/理想的理想的work function/功函数功函数

2、 practical/实际的实际的electron affinity/电子亲和能电子亲和能 Fermi level/费米能级费米能级 rectifier /整流器整流器electrostatic potential/静电势静电势 breakdown /击穿击穿rectifying contacts/整流接触整流接触 Ohmic contacts/欧姆接触欧姆接触 surface state/表面态表面态lattice-matched/晶格匹配的晶格匹配的tunneling effect/隧道效应隧道效应半导体器件工作的基本方程泊松方程泊松方程电流密度方程电流密度方程电流连续性方程电流连续性方程

3、pppnnnpnpppnnnADsJqRGtpJqRGtnJJJpqDqpJnqDqnJnpNNqrr11)()()(02Many of the useful properties of a p-n junction can be achieved by simply forming an appropriate metal-semiconductor(MS) contact.5.7 Metal-Semiconductor junctions or contacts(金属金属-半导体结、金半导体结、金-半接触）半接触）5.7.1 Schottky Barriersen.wikipedia.or

4、g/wiki/Walter_H._SchottkyPossibly, in retrospect, Schottkys most important scientific achievement was to develop (in 1914) the well-known classical formula, now written -q2/40 x, for the interaction energy between a point charge q and a flat metal surface, when the charge is at a distance x from the

5、 surface. Owing to the method of its derivation, this interaction is called the image potential energy (image PE). Schottky based his work on earlier work by (Lord) Kelvin relating to the image PE for a sphere. Schottkys image PE has become a standard component in simple models of the barrier to mot

6、ion, M(x), experienced by an electron on approaching a metal surface or a metal-semiconductor interface from the inside.1. Schottky effect(The image PE is usually combined with terms relating to an applied electric field F and to the height h (in the absence of any field) of the barrier. This leads

7、to the following expression for the dependence of the barrier energy on distance x, measured from the electrical surface of the metal, into the vacuum or into the semiconductor: Here, e is the elementary positive charge, 0 is the electric constant and r is the relative permittivity of the second med

8、ium (=1 for vacuum). In the case of a metal-semiconductor junction, this is called a Schottky barrier; in the case of the metal-vacuum interface, this is sometimes called a Schottky-Nordheim barrier. In many contexts, h has to be taken equal to the local work function .This Schottky-Nordheim barrier

9、 (SN barrier) has played in important role in the theories of thermionic emission and of field electron emission. Applying the field causes lowering of the barrier, and thus enhances the emission current in thermionic emission. This is called the Schottky effect, and the resulting emission regime is

10、 called Schottky emission. xeeFxhxMr024/)(The work function(功函数功函数): The energy with the work function is required to remove an electron at the Fermi level to the vacuum outside the metal.(Al=4.3eV)the electron affinity(电子亲和能电子亲和能): The energy with the electron affinity is required to remove an elec

11、tron at the bottom of the conduction band to the vacuum outside the semiconductors.(Si=4.1eV)(00FsCsCFmmEEqqEEqEEq Four sets of combination: (1)metal-n type semiconductor, qm qs (2)metal-n type semiconductor, qm qs (4)metal-p type semiconductor, qmqs Metal/n-type semiconductor 2. Schottky barriers肖特

12、基势垒）肖特基势垒）charge transfer occurs until the Fermi levels align at equilibrium)()(sFscsmFmFsqEEqEEp the electrostatic potential of the semiconductor must be raised V0p the electron energy must be lowered. qV0p the depletion region is formed near the junction.p Contact potential barrier: qV0=qm-qsp pot

13、ential barrier height qB= qm-qB is called Schottky barrier)()(sFscsmFmFsqEEqEE（2Metal/p type semiconductor, qmq spElectrons flow from metal to semiconductor till the Fermi levels align at equilibriump the electrostatic potential of the semiconductor must be lowered V0p the electron energy must be ra

14、ised qV0p the depletion region is formed near the junction.p Contact potential barrier: qV0=qs-qmV0 retards hole diffusion from the semiconductor to the metal5.7.2 Rectifying contacts(diode)You can treat the Schottky barrier for M/n-type S (or M/p-type S) as the P+N (or N+P)junction except that no h

15、ole injection occurs from the metal into the semiconductor. (a)Forward bias Electrons flow from semiconductor to Metal under forward bias.Case 1: Metal-n type contact1/0KTqVeII(b)Reverse bias One important feature is that the saturation current I0 depends upon B and is unaffected by the bias voltage

16、. I0Exp(-q B /kT)How about p-n junction? For pn junction : For M-S junction )/exp(*2kTqTAJBsT)(pnnnppsnLDpLDqJ10-11A/cm2Case 2: metal-p type Schottky contact? (a)Forward bias (b)Reverse bias Holes flow from semiconductor to metal under forward bias. A reverse voltage increases the barrier for hole f

17、low and the current becomes negligible.5.7.3 Ohmic contacts(ideal, resistor)In many cases we wish to have an ohmic metal-semiconductor contact, having a linear I-V characteristic in both biasing directions. For example, the interconnected lines (互连线互连线)are required in IC. So, it is important that su

18、ch contacts be ohmic, with minimal resistance and no tendency to rectify signals.RThe barrier to electron flow between the metal and semiconductor is small and easily overcome by a small voltage.Case 1 M/n type, qm qsUnlike the rectifying contacts, no depletion region occurs in the semiconductor in

19、these two cases since the electrostatic potential difference required to align the Fermi level at equilibrium calls for accumulation of majority carriers in the semiconductor.5.7.3 Ohmic contacts(practical)In practice, it is always impossible for us to form the ohmic contacts of metal-semiconductor

20、by choosing the appropriate work function of the metal. The reason is that the semiconductor surface contains surface states due to incomplete covalent bonds. The metal/semiconductor contacts form always a barrier whatever metals are used. So, to obtain the ohmic contacts for metal/semiconductor, a

21、practical method is by doping the semiconductor heavily in the contact regions. Therefore, if a barrier exists at the interface, the depletion width is small enough to allow carriers to tunnel through the barrier.Tunneling probability can be referred to(P236-238). 5.7.4 Typical Schottky BarriersPinning effect (钉扎效应）钉扎效应）: because of surface states and interfacial layer P168 It is easier to obtain the width of the depletion region at M-S Schot