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2013-08-15 22页 ppt 1023KB 100阅读

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微电子专业英语_文库null微电子技术专业英语微电子技术专业英语 微电子 Princess 学号:XXXXXXXXXX3.2.1 Energy Band Diagrams of Prototype Junctions (理想型结的能带图) 3.2.1 Energy Band Diagrams of Prototype Junctions (理想型结的能带图) P.47~54null In separate n or p type semiconductor, electrically neutral is exis...
微电子专业英语_文库
null微电子技术专业微电子技术专业英语 微电子 Princess 学号:XXXXXXXXXX3.2.1 Energy Band Diagrams of Prototype Junctions (理想型结的能带图) 3.2.1 Energy Band Diagrams of Prototype Junctions (理想型结的能带图) P.47~54null In separate n or p type semiconductor, electrically neutral is exist in every macroscopic region. By electrically neutral(电中性),there is no region having more positive charges than negative, but this situation will change when the materials are in contact.Fig.3.2 shows the energy band diagram of each of the two isolated semiconductors. 在单独的n型或p型半导体中,每一个宏观区域都呈电中性。在电中性的情况下,空间负电荷不少于正电荷,但是当材料处于接触点的时候,这一状况会改变。如图3.2所示,两个孤立半导体的能带图。null 不同材料的边缘是以真空能级作为参考的。在硅材料的两边,χn=χp,Egn=Egp,以及γn=γp。这就意味着在导带底,两种材料能量相同。同样的, Egn=Egp,EVn=EVp. 电子的吸引力和电离势不变,材料边缘的Ec和Ev是次要参考条件。然而,因为两种材料的掺杂不同,费米能级的位置是不同的,因而Φn≠Φp。 The vacuum level is chosen as reference for each material on the edge facing the other material. Since the material is silicon on both sides, χn=χp, Egn=Egp, and γn=γp. This implies that the bottom of the conduction band is (for neutrality) at the same energy for both materials, and ECn=ECp. Similarly Egn=Egp and EVn=EVp. Since electron affinities and ionization potentials are constant, EC and EV at the material edges are secondary references. However, because the doping is different in the two materials, the positions of the Fermi levels are not the same, and thus Φn≠Φp.null 电子亲和力χ,电离势γ,能量差Eg示各种材料的特性。下标n表示n型半导体,下标p表示p型半导体。另外还显示了一个参数,也就是功函数Φ。功函数等于真空能级和费米能级的能量差。 Φ=Evac-Ef. The electron affinity(亲和力) χ,the ionzation potential(潜能,潜力) γ, and the energy gap Eg are indicated for each material. The subscript n indicates n type semiconductor while the subscript p indicates p-type semiconductor. Also shown is an additional parameter, the work function Φ. The work function is equal to the energy difference between the vacuum level and the Fermi level, Φ=Evac-Ef.null在两种材料的接触点,由于n区的近似自由电子多于p区,所以,电子由n型半导体向p型半导体扩散。当电子扩散到p区,它们将离子化施主(带正电)留在晶格中。同时,空穴从p型半导体向n型半导体扩散,留下带负电的受主。这种独立的电荷建立起电场,如图3.3所示。 Upon contact between the two materials, because there are more quasi-free electrons on the n side than on the p side, electrons flow (diffuse) from the n-type semiconductor to the p-type semiconductor. As the electrons move toward file p-type region, they leave behind ionized donors (charged positively) that are locked into the crystal lattice. At the same time, holes flow from the p semiconductor to the n semiconductor, leaving behind negatively charged acceptors. This separation of charges sets up an electric field, as shown in Fig.3.3. null在平衡状态下,费米能级是连续的(pn结中有统一的费米能级)。热平衡条件下,Ef处处相同,甚至是在层不同的复合结构材料中。在n型和p型的空间电荷区,电子电流和空穴电流方程如下: At equilibrium, the Fermi level is continuous across the entire sample. Ef must be the same everywhere in a solid under thermal equilibrium even for a composite structure with layers of different materials. In the transition region between n and p, the electron and hole currents are, from following Equations null热平衡状态下的能带图 由于没有净电流通过pn结,所以Jn=Jp=0,而且费米能级相等。内建电场ξ被称作过渡区(?空间电荷区?)。在空间电荷区,电场产生电子的漂移电流,该漂移电流用于补偿由于浓度梯度引起的扩散电流。同理,对于空穴的漂移电流和扩散电流,情况完全类似。结中的内建电场改变了能带。因为我们参考的是真空能级,所以这一观点维持不变。 There is no net current, so Jn=Jp=0 and the Fermi levels are equalized. A built-in field ξ is generated in what is referred to as the transition region. In the transition region, the field produces a drift current for electrons that at every position exactly compensates the diffusion current caused by the electron concentration gradient. A similar balance of hole drift and diffusion currents exists. The built-in field at the junction, however, alter the bands. Since we are using the vacuum levels at the interface as a reference, this point will remain unchanged. null所以,在pn结中,有以下情况:(1)在n型和p型的交界处,n型半导体上的电子填补p区一侧的空穴导致p区一侧出现负电荷区域(未中和的受主)。同理,电子消灭扩散到n区的空穴,在n区形成带正电荷的区域(未中和的施主)。这样,在n型区和p型区的交界面处的两侧形成了带正、负电荷的区域。通过电离,没有相应的自由电子或自由空穴在同一个区域中和离子带的电荷。 So there are some following statuses in pn junction:(1) Near the interface between n type and p type, the electrons from the n-type semiconductor fill the holes on the p side resulting in a region of negative charge (non-neutralized accepters) on the p side. Similarly, electrons annihilate(消灭) holes that diffused into the n-type region, giving a region of positive charge (non-neutralized donors) on the n side. This creates an electric field at the interface between non-neutralized (positive) donor ions in the n region and non-neutralized (negative) acceptor ions in the p region. By non-neutralized, there are no corresponding free electrons or free holes in the same region to neutralize the charge of the ions. null(2)Evac,Ec和Ev在任何时刻都是平行的,因为Χ, γ和Eg都是常量。(3)在整个装置中,电子吸引力是不变的。然而,电子脱离n区导带底部到达真空能级右边,必须克服除了材料上电子亲和力的内建电场的静电势能。 (2) The energies Evac, Ec, and Ev are everywhere parallel because the quantitiesΧ, γ, and Eg are constant. (3) The electron affinity is unchanged across the device. However, an electron escaping from the bottom of the conduction band in the n region to the vacuum level on the right side must overcome the electrostatic potential of the built-in field in addition to the electron affinity of the material.null(4)在pn结的两侧,有一个未补偿电荷的区域。这个空间电荷区扩展了界面的两边,并且包含了电离杂质离子。它的宽度取决于两边的杂质浓度和电荷转移,并要求与费米能级一致,且空间电荷区的自由载流子浓度可以忽略不计。这样的空间电荷区就像是耗尽了载流子,所以空间电荷区也被称为耗尽区。(4) On each side of the junction, there is a region of uncompensated charge. This space charge region extends on both sides of the interface, and contains non-neutralized impurity ions. Its width depends on the concentration of impurities on each side and the charge transfer required to align(与……一致) the Fermi levels and the concentration of free carriers in the space charge region is negligible. The space charge region is said to be(据说是) depleted of carriers, and thus is often also referred to as the depletion region.null在结的两边总的空间电荷是相同的,但是它们符号相反,而且内建电势能势垒qVbi(以下简称内建电压)存在于整个结。在电中性情况下,Vbi在费米能级上成正比,如图3.2所示。 Vbi是一个正数。(6)电势能势垒的导带与价带相同,电子和空穴也相同。(5) The total space charge on either side of the junction is the same, but they have opposite sign, and a built-in potential energy barrier qVbi (referred to as the built-in voltage) exists across the junction. The magnitude(级) of Vbi is proportional to the energy difference in the Fermi levels in Fig.3.2 for the case of neutrality Vbi is taken as a positive quantity. (6) The potential energy barrier is the same for the conduction band as for the valence band and the potential energy barrier is the same for electrons as for holes. null均匀掺杂时,在结点两侧,空间电荷区域宽度是相等的。非均匀掺杂时,多数空间电荷区都在轻掺杂的一侧。如果结的一侧简并,另一侧非简并,本质上所有的耗尽区都在轻掺杂的一侧,如图3.4所示。这被看作是一个单边的结。也就是n+p结和p+n结。(7) For equal doping levels, the width of the space charge region is the same on each side of the junction. For unequal doping level most of the space charge region is on the side with the lighter doping. For a junction with one side degenerate and the other side nondegenerate, essentially all of the depletion region will be on the lightly doped side, as indicated in Fig.3.4. This is referred to as a one-sided step junction. In this class are n+p and p+n junctions. null符号n+表示非简并或重掺杂n型,p+表示重掺杂p型材料。在图3.4中,单边n+ p结有一个重掺杂区。令n+表示非简并掺杂n型。在非简并掺杂的一侧,我们近似认为费米能级在导带边缘。 This notation n+ indicates degenerately or heavily doped n type, and p+ indicates heavily doped p-type material. In Fig.3.4 the one-sided n+p junction has one heavily doped side. The designtion n+ indicates degenerately doped n type. On the degenerately doped side, we approximate that the Fermi level is at the conduction band edge. null偏置条件下的能带图 当运用外加电压时,能带图会发生什么变化呢?如图3.5所示,给p区加上负电压,n区加上正电压(成反向偏置),如果Va和内建电场同向,此时为反向偏置,如果和内建电场反向,是为同向偏置。我们以反向偏置为例,即Va为负数。What happens to the energy band diagram when a voltage is applied? Consider the case of Fig.3.5, the p region is made negative with respect to the n region by the applied voltage Va with the n side as reference, and Va is considered to be negative (reverse bias) if it has the same polarity as the built-in voltage and to be positive (forward bias) if it is of opposite polarity. We will consider the case of reverse bias first, so Va is negative.null该装置有两个区域:近似中性区(n区的左端到结的耗尽区边缘或者p区的耗尽区边缘到右端)和耗尽区(包括电离杂质离子)。我看把pn结看成两个相互抵抗的区域串联。在过渡区,内建电场清除所有的自由载流子,而且过渡区的抵抗力比其他两个区域大,所以,在耗尽区外加电压很小。 By convention, the device is consisted of two regions: quasi-neutral region (the region from the left terminal to the edge of the junction depletion region on the n side or from the edge of the depletion region on the p side to the right terminal), depletion region (contains non-neutralized impurity ions). We proceed by considering the pn junction as a series connection of the resistances of these regions. In the transition region, all the free carriers are swept out by the built-in electric field and the resistance of the transition region is much greater than that of the other two, so all of the applied voltage is dropped across this depletion region.null调节热平衡的能带图反映运用偏置,能带图如图3.6所示。实线表示平衡状态下的能带图;虚线表示反向偏置下的能带图。区域增加,需要更多的电离受主和施主,所以,反向偏置下耗尽区变宽。用负偏压的作用增加电子和空穴的势垒。 To adjust the equilibrium energy band diagram to reflect the applied bias, the energy band diagrams are shown in Fig.3.6. Solid line is equilium energy band diagram; dashed line is energy band diagram under reverse bias. The field increases; this requires more ionized acceptors and donors, so the depletion region gets wider under reverse bias. The applied negative bias effectively increases the potential barriers for both electrons and holes. null我们看图3.6,结电压Vj增加 (3.2) (因为反偏,Va为负)导致在冶金结产生了大的电场。带正电荷的受主和结附近的施主离子产生了内部电场,所以增大的电场需要在结的任意一侧增加电荷量。由于电荷是被固定在晶格里的杂质离子产生的,过渡区产生在每一侧。 We can see from Fig.3.6 that the junction voltage Vj is increased (3.2) (with Va negative because of reverse bias), resulting in a greater electric field at the metallurgical junction. The internal electric field is generated by the positively charged accepter and donor ions near the junction, so this increased field requires an increased quantity of charge on either side of the junction. Since the charge is a result of ionized impurities that are fixed in the crystal lattice, the transition region must expend on each side. null因此,过渡区宽度增加,如图3.6所示。同理,由于加上一个正的或是正向偏置的Va,结上的电压Vj和过渡区宽度都减小,如图3.7所示。Therefore the width of the transition region increases, as shown in Fig.3.6. Similarly, for a positive or forward bias Va, the voltage across the junction Vj and the transition width both decrease as shown in Fig.3.7. nullnullnull
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