The Science & Engineering of Materials Semiconductors. 주요반도체재료에서전자와홀의 mobility 대표적인값은? 어떤 carrier 가빠른지?

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1 18.6 Semiconductors 주요반도체재료에서전자와홀의 mobility 대표적인값은? 어떤 carrier 가빠른지?

2 18.6 Semiconductors [Fig ] - + When a voltage is applied to a semiconductor, the electrons move through the conduction band, while the electron holes move through the valance band in the opposite direction. 반도체재료에서전자와홀이이동해서전기전도에기여하는각각의 band 의이름은?

3 Intrinsic semiconductor: ) 2 )exp( ( ) ( ) 2 2( ) 2 exp( ) ( p : n Intrinsic semiconductor * * i i T k E q n m m h T k n T k E n p n n n q q p q n B g p e p n B B g i i p e i p n + = = = = = + = = + = µ µ σ π µ µ σ µ µ σ 18.6 Semiconductors 주요공식들 : Conductivities in Semiconductors : 온도의존성

4 18.6 Semiconductors [Fig ] CB VB The distribution of electrons and holes in the valance and conduction bands (a) at absolute zero and (b) at an elevated temperature. 반도체에서전기가흐른다는의미? 전자는 CB 에서정공은 VB 에서유동을해야함!!

5 18.6 Semiconductors [Fig ] 온도증가에따른전기전도도변화 : 금속과반도체의경향차이발생이유? 전기전도도의절대값차이 Example 18-7 참조 The electrical conductivity versus temperature for intrinsic semiconductors composed with metals. Note the break in y-axis scale.

6 18.6 Semiconductors Extrinsic Semiconductor The conductivity depends primarily on the number of impurity, or dopants, atom, and, in a contain temperature range, is independent of temperature. [Fig : Extrinsic range] Electrical neutrality: p 0 + N d = n 0 + N a n-type (N d >>n i ) : n 0 ~ N d P-type (N a >>p i ) : p 0 ~ N a The amount of dopants controls the conductivity of a semiconductor. Extrinsic semiconductor 를 device 에사용하는이유 tunable conductivity!!

7 18.6 Semiconductors [Fig ] E d << E g When a dopant atom with a valence greater than four is added to silicon, an extra electron is introduced and a donor energy state is created. Now electrons are more easily excited into the conduction band. n-type semiconductor 의특징 : donor level Ed 위치 in energy band structure

8 18.6 Semiconductors [Fig ] When a dopant atom with a valence of less than four is substituted into the silicon structure, a hole is created in the structure and acceptor energy level is created just above the valence band. Little energy is required to excite the holes into motion. p-type semiconductor 의특징 : acceptor level Ea 위치 in energy band structure

9 18.6 Semiconductors Ed 와 Ea 의크기는 Eg 에비해서아주작지만 P 와 B 의경우대략 0.05 ev 정도임.

10 18.6 Semiconductors [Fig ] 357K[84 C] 100 K The effect of temperature on the carrier concentration of n-type semiconductor. Extrinsic semiconductor 에 doping 량의조절 conductivity 조절가능!! Example 18-8 참조

11 18.6 Semiconductors Temperature dependent of extrinsic semiconductor [Fig 해설 / 3 개의범위설명 ] Impurity range - electron are excited from donor level to the conduction band or from valance band to the acceptor level. Exhausting range - donor level becomes exhausted or the acceptor level becomes saturated. Intrinsic range - thermal energy excited a large number of electron from the valance to the conduction bands. Direct and Indirect Bandgap Semiconductor 를정의하시오 Radiative recombination 과 nonradiative recombination 를비교해서정의하시오 [ Eq. (18-16a) 와 (18-16b) 의차이 ] Example 18-9 참조

12 18.7 Applications of Semiconductors Behavior of a p-n junction device (a)when no bias is applied electron and hole currents (b) Under a forward bias (c) Under reverse bias [Fig ] 참고 : Example 5-2 / diffusion 과 drift? Current flow 의방향?? The internal electric field that develops is shown as ε. Drift velocity 의의미 : in Glossary Depletion layer(w) 의두께?? p-n Junction 에서 forward 와 reverse bias 의의미와 band 구조의변화?

13 18.7 Applications of Semiconductors [Fig ] (a) The current-voltage characteristic for a p-n junction. (b) If an alternating signal is applied, rectification occurs and only half of the input signal passes the rectifier. [diode 의응용 : AC to DC converter]

14 18.7 Applications of Semiconductors [Fig ] Base layer should be very thin!!! (a)a circuit for an n-p-n bipolar junction transistor(bjt). The input creates a forward and reverse bias that causes electrons to move from the emitter, through the base, and into the collector, creating an amplified output. (b) Sketch of the cross-section of the transistor. [Emitter, Base, Collector] BJT 의동작원리와 Application??

15 18.7 Applications of Semiconductors [Fig ] Channel 통해전자흐름 : on + 가많음 [N channel 형성 NMOS] - 가몰려감 Channel 사라짐 : off FET(field effect transistor, MOSFET) 의동작원리와주요 application Switching! 3 극 : (Source, Gate, Drain) in FET / Unipolar junction transistor(ujt)

16 18.7 Applications of Semiconductors [Fig ] Si = 1414 Czochralski growth technique 으로단결정 Si 잉곳의제조원리이해 잉곳 Wafer IC 제조공정 Chip(die) Packing 공정이해

17 18.7 Applications of Semiconductors [Fig ] 반도체 IC 제조공정 : 코팅은전체면적에, 에칭은선택적방법 [photolithography] 으로!!

18 18.8 Insulators & Dielectric Properties Electrical insulators obviously must have a very low conductivity, or high resistivity, to prevent the flow of current. Insulators are produced from ceramic and polymeric materials in which there is a large energy gap between the valence and conduction bands. The resistivity of most of these is >10 14 Ω- cm and the breakdown electric fields are ~5 to 15 kv/mm. In order to select an insulating materials properly, we must understand how the material stores, as well as conducts, electrical charge. * Store the electrical current in the capacitor Insulator 의적당한용도는다음의몇가지측면에서고려되어야함 resistivity breakdown electric field how the material stores electrical charge dielectric properties

19 18.9 Polarization in Dielectrics Polarization mechanism in materials: (a) electronic [Example 18-10] (b) atomic or ionic (c) high-frequency dipolar or orientation (d) low-frequency dipolar [Fig ] (e) interfacial-space charge at electrodes (f) interfacial-space charge at heterogeneities Polarization( 분극 ) 은전계에반응하는원자 / 분자 / 이온등 ** What is dipole?

20 18.9 Polarization in Dielectrics Schematic representation of different mechanisms of polarization. Electric field 에반응하는 Polarization 기구의종류 charged 입자의거동!! A dipole : a pair of opposite charges separated by a certain distance!!

21 18.9 Polarization in Dielectrics [Fig ] An electric dipole is a separation of positive and negative charges. [Dipolar or Orientation Polarization 의예 ] (a) The Oxygen ions are at face centers, Ba 2+ ions are at cube corners and Ti 4+ is at cube center in cubic BaTiO 3. (b) In tetragonal BaTiO 3, the Ti 4+ is off-center and the unit cell has a net polarization.

22 18.9 Polarization in Dielectrics [Fig ] A charge can be stored a the conductor plates in a vacuum (a). However, when a dielectric is placed between the plane (b), dielectric polarizes and additional charge is stored. Dielectric 특성의응용 : charge 의 store Capacitor 에응용됨

23 18.9 Polarization in Dielectrics Ceramic Insulator Ceramic Insulator Shift in the distribution of charge in a ceramic insulator when it is placed in an electric field between two electrically conductive electrodes.

24 18.9 Polarization in Dielectrics [Fig ] Dielectric constant K가클수록 store 용량이증가함. Dielectric constant K가클수록 store 용량이증가함. Dielectric loss 는 K 가변화하는부분에서발생 Dielectric loss 가작을수록좋음!! Dielectric constant K 의의존성 : 조성, 온도, 미세구조, electrical frequency,

25 18.9 Polarization in Dielectrics Dielectric constant 가커지면??

26 18.10 Electrostriction, Piezoelectricity, Pyroelectricity & Ferroelectricity 각각의정의? electrostriction, piezoelectricity, pyroelectricity, and ferroelectricity Electrostriction: polarization ions and electronic clouds are displaced Materials 에서 mechanical strain 발생 Piezoelectricity: 물질이 stress 를받으면, voltage 를 develop [direct piezo- ]. Pyroelectricity: 물질에온도변화 dielectric polarization charge 발생 Ferroelectricity: spontaneous and reversible dielectrical polaization 발생 [ reversible using an electrical field ]

27 18.10 Electrostriction, Piezoelectricity, Pyroelectricity & Ferroelectricity Strain(stress) voltage 발생!! [Fig ] The (a) direct and (b) converse piezoelectric effect. In the direct piezoelectric effect, applied stress cause a voltage to appear. In the converse (b), an applied voltage leads to development of strain. 각각의용도? electrostriction, piezoelectricity, pyroelectricity, and ferroelectricity

28 18.10 Electrostriction, Piezoelectricity, Pyroelectricity & Ferroelectricity [Fig ] Example of ceramic capacitor. (a)single-layer ceramic capacitor (disk capacitor) (b) Multilayer ceramic capacitor (stack ceramic layers)

29 18.10 Electrostriction, Piezoelectricity, Pyroelectricity & Ferroelectricity [Fig ] (a) Different polymorphs of BaTiO 3 and accompanying changes on lattice constant and dielectric constant.

30 18.10 Electrostriction, Piezoelectricity, Pyroelectricity & Ferroelectricity [Fig ] (b) Single crystal. (c) Polycrystalline BaTiO 3 showing the influence of the electric filed on polarization.

31 18.10 Electrostriction, Piezoelectricity, Pyroelectricity & Ferroelectricity [Fig ] (a)the effect of temperature and grain size on the dielectric constant of barium titanate. (b) Ferroelectric domain can be seen on the microstructure of polycrystalline BaTiO 3.

32 Chapter 18. Electronic materials [18 장에서공부의 Key Point]: 공부잘하는방법!! 이웃원자간 bonding 의 type 물질의특성을지배합니다!! 마지막부분의 Summary 를여러번읽어서완전히이해해야합니다. 내용정리 마지막부분의 Glossary 를여러번읽어서이해해야합니다. 용어정리 첫페이지의 Have You Ever Wondered? 부분이이해되어야합니다. 의문점 ( 목적 ) 을가지고공부

33 Chapter 18. Electronic materials 숙제 1. Example 18-1 부터 18-1부터 10까지풀이를이해후, 작성해서제출하세요. 2. 온도증가에따른전기전도도변화는? 금속, 반도체각각의대해논하시오 3. 반도체에서 intrinsic과 extrinsic의차이는? 4. n-type과 p-type 반도체의제조방법과에너지밴드구조를도시하시오. 5. BJT와 UJT의동작특성과용도를비교설명하세요. 6. Polarization 특성을응용한사례를몇가지논하시오. σ = n e µ (18-15a)

34 18 장에서무엇을새롭게알았습니까?