去年材料物理答案整理.docx

1、去年材料物理答案整理1.what is the wave particle duality theory? Does any matter have both wave and particle characteristics?(33号)1）Particle-like Character: light propagating through free space consisting of a stream of photons suggested by photoelectric effect. Its kinetic energy is given: Wave-like Character

2、: its correctness is indicated by electron microscope as well as by diffraction and interference. The De Broglie wavelength of a particle moving with momentum mv is given by:2）any matter have both wave and particle characteristics2.What is the uncertainty principle?( For an example) (33号)Uncertainty

3、 principle states that certain pairs of physical properties, like position and momentum, cannot both be known to arbitrary precision. That is, the more precisely one property is known, the less precisely the other can be known.3.Wavefunction and its meaning. (33号)A wave function or wave function is

4、a mathematical tool used in quantum mechanics to describe the momentary states of subatomic particles.Statistical explanation of wavefunction The values of the wave function are probability amplitudes complex numbers the squares of the absolute values of which give the probability distribution that

5、the system will be in any of the possible states.4.The solution of Schrodinger equation of the particles bound in one-dimensional potential wells. (1/2号)Single particle in one dimensions：Free particle Time dependent 5,What is the best obvious characteristics of crystal lattice ? (3/4号)The best obvio

6、us characteristics of crystal lattice is that atoms are arranged periodically in crystal lattice.A crystal or crystalline solid is a solid material, whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions.6.what is the forbid

7、den band, empty band, valence band ,conduction band? (5/6号) allowed band: the energy band which allow to be occupied by electron forbidden band: the region between allow band, in which electron is not allowed to occupy empty band: the energy band in which electron cannot be found in each level valen

8、ce band: the energy band corresponding to valence electron conduction band: above Valence band the allow band which have the lowest energy7.Use the theory of energy band to explain what is the insulator, semiconductor and conductor.(7/8号)Solution：As is shown in the above picture , in metal the highe

9、st energy band filled by electrons is not full，furthermore，the density of electron in the energy band is very high, it has the same magnitude as the density of the atom, so the conductivity of metal is very high.In the case of insulator, there is an energy gap, a finite excitation energy is required

10、 to carry the electrons up over the gap into the next band. This cant be supplied by small constant electric field, then the conductivity is very low，almost zero.As for semiconductor, the energy gap is small. At the temperature T there will be a small, but not zero, density of electrons excited by t

11、hermal fluctuations into the upper band. These electrons can easily carry a current, which would increase rapidly at higher temperature.8,What is the mobility of semiconductor? What are the factors which have effect on the mobility? (第4个ppt, 33-36页)（9/10号）Answer: It is the average drift velocity of

12、carrier in unit electric field. assume the semiconductor is n-type semiconductor, electron concentration is n0, the average drift velocity of electrons is vd. we know the current density ( J ) is :According to the ohms law, We can get, , it is the electron mobilitySimilarily , is the hole mobilitySo

13、 in the actual semiconductor,But in n-type semiconductor, n0 p0 In p-type semiconductor, p0 n0 In intrinsic semiconductor, n0=p0载流子迁移率的影响因素很多，关于这方面比较系统的信息没有找到，但老师强调了一点，随着半导体中掺杂浓度的升高，其载流子的迁移率降低。9,P-semiconductor and N-semiconductor. The energy band sketch of a p-n junction.（11/12号） N-semiconductor: T

14、he addition of pentavalent impurities, such as antimony, arsenic or phosphorous contributes free electrons, greatly increasing the conductivity of the intrinsic semiconductor. In n-type material there are electron energy levels near the top of the band gap so that they can be easily excited into the

15、 conduction band. P-semiconductor: The addition of trivalent impurities, such as boron, aluminum or gallium to an intrinsic semiconductor creates deficiencies of valence electrons, called “holes”. In p-type material, extra holes in the band gap allow excitation of valence band electrons, leaving mob

16、ile holes in the valence band.The energy band of a p-n junction:The open circles on the left side of the junction above represent holes or deficiencies of electrons in the lattice which can act like positive charge carriers. The solid circles on the right of the junction represent the available elec

17、trons from the n-type dopant. Near the junction, electrons diffuse across to combine with holes, creating a depletion region. The energy level sketch above right is a way to visualize the equilibrium condition of the P-N junction. 10,What is the direct band gap semiconductor? What is the indirect ba

18、nd gap semi-conductor? （13/14号）In semiconductor physics, the band gap of a semiconductor is always one of two types, a direct band gap or an indirect band gap. The minimal-energy state in the conduction band, and the maximal-energy state in the valence band, are each characterized by a certain k-vec

19、tor in the Brillouin zone. If the k-vectors are the same, it is called a direct gap. If they are different, it is called an indirect gap.11.What are functions of the diodes and dynatrons（15/16号）The most obvious nature of the diodes is its one-way electrical conductivity.They can be used for rectific

20、ation, clamp, detection and regulation。They have two types of spot contact and face contact。 Rectifier Diode: The diode is one-way electrical conductivity, can change the direction of AC transform into a single DC pulse. Switching elements: diodes under forward voltage resistance in small in-state,

21、is equivalent to a connected switch; in the role of reverse voltage, the resistance of large, is off,Dynatrons have a role on Amplification and switching. They can be used for signal amplification, oscillation, on-off control. They have two types of PNP and NPN transistor。12.Show the types of field

22、effect transistors (FET) and their functions;Please give the basic structure and function of thin film transistor (TFT).(17/18号)答： （1）Two kinds of FET: Junction FET (JFET) Melt-oxide semiconductor FET (MOSFET)The functions of FET: Amplify Electronic switch Variable resistor(2) TFT 2) Functions of TF

23、T: It can be used as Semiconductor switches in LCD. Each liquid crystal pixel is drived by integrated thin-film transistors, which can be high speed, high brightness, high contrast display screen information13What are the basic conditions of a material which can produce visible light emission?（19/20

24、号）Solution: 1、The energy width of the band gap is located at visible zone.2、The excitons (electron and hole pairs) have bond energy.3、The excitons have enough lifetime.14what is the Photoluminescence (PL) and what is the Electroluminescence (EL).（21/22号）(电致发光( electroluminescent)是通过加在两电极的电压产生电场，被电场激

25、发的电子碰击发光中心，而引致电子解级的跃进、变化、复合导致发光的一种物理现象。光致发光 物体依赖外界光源，从而获得能量，产生激发导至发光的现象。）Photoluminescence (PL)：the object irradiated depends on external light source，to gain energy，produce excitation，lead to the phenomenon of light。Electroluminescence (EL)：By adding two voltage electrodes creates an electric field

26、, the electronic excited by electric field crashing luminescence center, resulting in e-solution-level leap, change,composite leading light of a physical phenomenon。 Electroluminescence(EL)Photoluminescence(PL)15. Measurement of light-emitting diode (LED).(23/24号)Solution: the luminous efficiency is

27、 the ratio of the luminous flux emitted by the device and the consumed electric power.16：How many types of photovoltaic solar cells do you know?(25/26号)Answer:1. Crystalline silicon(Si) solar cell, which includes single crystal Si solar cell and polycrystalline Si solar cell;2. Thin film solar cell,

28、 which includes Si substrate thin film solar cell, Cu/In/Ga/Se(CIGS) thin film solar cell, organic thin film solar cell;3. Multiple compounds solar cell, which includes CdTe/CdS solar cell, - group compound solar cell;4. Dye-sensitized cell;5. Organic solar cell;6. Nano-crystal solar cell; e.g. nano

29、 TiO2 crystal chemical energy solar cell.(From Baidu website)17.Current-Voltage curve of photodiodes. What are the differences of the photovoltaic cells and photo-detectors?(27/28号)It is the current-voltage characteristic of a photodiode. When the photodiode is forward biased, there is an exponentia

30、l increase in the current. When a reverse bias is applied, a small reverse saturation current appears. Photovoltaic cells are arrays of cells containing a solar photovoltaic material that converts solar radiation into direct current electricity. Operating diode in fourth quadrant generates power.Pho

31、to-detector Diode can transform optical information into electrical information. It is operated in the third quadrant. In principle, all photovoltaic devices are also photo-detector devices. The most important Factors different from photovoltaic devices:1、the ratio of the current under photo illumin

32、ated to dark state Iphoto/I dark;2、the response velocity of the device.3、the response is partially located infrared zone 18 the energy efficiency, Voc, I sc and F.F of photovoltaic cells.(29/30号)Energy efficiency: Voc:开路电压，open circuit voltageIsc :短路电流。Short circuit currentFF填充因子19, Measurement of solar cells.(31/32号)I-V Curve of solar Cell Measure DiagramFigure 1 Figure 2