Semiconductor Device Physics Lecture 1 Dr Ing Erwin

Semiconductor Device Physics Lecture 1 Dr. -Ing. Erwin Sitompul President University http: //zitompul. wordpress. com 2 President University 0 1 3 Erwin Sitompul SDP 1/1

Semiconductor Device Physics Textbook and Syllabus Textbook: “Semiconductor Device Fundamentals”, Robert F. Pierret, International Edition, Addison Wesley, 1996. Syllabus: Chapter 1: Semiconductors: A General Introduction Chapter 2: Carrier Modeling Chapter 3: Carrier Action Chapter 5: pn Junction Electrostatics Chapter 6: pn Junction Diode: I–V Characteristics Chapter 7: pn Junction Diode: Small-Signal Admittance Chapter 8: pn Junction Diode: Transient Response Chapter 14: MS Contacts and Schottky Diodes Chapter 9: Optoelectronic Diodes Chapter 10: BJT Fundamentals Chapter 11: BJT Static Characteristics Chapter 12: BJT Dynamic Response Modeling President University Erwin Sitompul SDP 1/2

Semiconductor Device Physics Grade Policy Final Grade = 10% Homework + 20% Quizzes + 30% Midterm Exam + 40% Final Exam + Extra Points § Homeworks will be given in fairly regular basis. The average of homework grades contributes 10% of final grade. § Homeworks are to be written on A 4 papers, otherwise they will not be graded. § Homeworks must be submitted on time, one day before the schedule of the lecture. Late submission will be penalized by point deduction of – 10·n, where n is the total number of lateness made. § There will be 3 quizzes. Only the best 2 will be counted. The average of quiz grades contributes 20% of final grade. § The maximum lateness in coming to class is 25 minutes, otherwise attendance will not be counted. President University Erwin Sitompul SDP 1/3

Semiconductor Device Physics Grade Policy Semiconductor Device Physics Homework 2 Ito Chen 009201700008 21 March 2021 D 6. 2. Answer: . . . . • Heading of Homework Papers (Required) § Midterm and final exams follow the schedule released by AAB (Academic Administration Bureau). § Make up of quizzes must be held within one week after the schedule of the respective quiz. § Make up for mid exam and final exam must be requested directly to AAB. President University Erwin Sitompul SDP 1/4

Semiconductor Device Physics Grade Policy § In order to maintain the integrity, the score of a make up quiz or exam can be multiplied by 0. 9 (i. e. , the maximum score for a make up will be 90). § Extra points will be given every time you solve a problem in front of the class or answer a question. You will earn 1 or 2 points. § Lecture slides can be copied during class session. The updated version will be available on the lecture homepage around 1 day after class schedule. Please check regularly. http: //zitompul. wordpress. com § The use of internet for any purpose during class sessions is strictly forbidden. § You are expected to write a note along the lectures to record your own conclusions or materials which are not covered by the lecture slides. President University Erwin Sitompul SDP 1/5

Semiconductor Device Physics Greek Alphabet —new —zz-eye —pie —taw —fie —k-eye —sigh —mew President University Erwin Sitompul SDP 1/6

Semiconductor Device Physics Chapter 1 Semiconductors: A General Introduction President University Erwin Sitompul SDP 1/7

Chapter 1 Semiconductors: A General Introduction What is a Semiconductor? n Low resistivity “conductor” n High resistivity “insulator” n Intermediate resistivity “semiconductor” n The conductivity (and at the same time the resistivity) of semiconductors lie between that of conductors and insulators. President University Erwin Sitompul SDP 1/8

Chapter 1 Semiconductors: A General Introduction What is a Semiconductor? n Semiconductors are some of the purest solid materials in existence, because any trace of impurity atoms called “dopants” can change the electrical properties of semiconductors drastically. n Unintentional impurity level: 1 impurity atom per 109 semiconductor atom. n Intentional impurity ranging from 1 per 108 to 1 per 103. No recognizable long-range order Entire solid is made up of atoms in an orderly three- dimensional array Completely ordered in segments polycrystalline amorphous crystalline n Most devices fabricated today employ crystalline semiconductors. President University Erwin Sitompul SDP 1/9

Chapter 1 Semiconductors: A General Introduction Semiconductor Materials Elemental: Si, Ge, C Compound: IV-IV III-VI Alloy: Si 1 -x. Gex Alx. Ga 1 -x. As As Cd Se Ga Si. C Ga. As, Ga. N Cd. Se : Arsenic : Cadmium : Selenium : Gallium President University Erwin Sitompul SDP 1/10

Chapter 1 Semiconductors: A General Introduction From Hydrogen to Silicon President University Erwin Sitompul SDP 1/11

Chapter 1 Semiconductors: A General Introduction The Silicon Atom n 14 electrons occupying the first 3 energy levels: n 1 s, 2 p orbitals are filled by 10 electrons. n 3 s, 3 p orbitals filled by 4 electrons. n To minimize the overall energy, the 3 s and 3 p orbitals hybridize to form four tetrahedral 3 sp orbital. n Each has one electron and is capable of forming a bond with a neighboring atom. President University Erwin Sitompul SDP 1/12

Chapter 1 Semiconductors: A General Introduction The Si Crystal • Each Si atom has 4 nearest • neighbors. Atom lattice constant (length of the unit cell side) ° 1 A=10 ° – 10 m a = 5. 431 A, • Each cell contains: 8 corner atoms 6 face atoms 4 interior atoms a “Diamond Lattice” President University Erwin Sitompul SDP 1/13

Chapter 1 Semiconductors: A General Introduction How Many Silicon Atoms per cm– 3? n Number of atoms in a unit cell: n 4 atoms completely inside cell n Each of the 8 atoms on corners are shared among 8 cells count as 1 atom inside cell n Each of the 6 atoms on the faces are shared among 2 cells count as 3 atoms inside cell Total number inside the cell = 4 + 1 + 3 = 8 n Cell volume = (. 543 nm)3 = 1. 6 x 10– 22 cm 3 n Density of silicon atom = (8 atoms) / (cell volume) = 5 × 1022 atoms/cm 3 • What is density of silicon in g/cm 3? President University Erwin Sitompul SDP 1/14

Chapter 1 Semiconductors: A General Introduction Compound Semiconductors n “Zincblende” structure n III-V compound semiconductors: Ga. As, Ga. P, Ga. N, etc. President University Erwin Sitompul SDP 1/15

Chapter 1 Semiconductors: A General Introduction Crystallographic Notation Miller Indices Notation Interpretation (hkl) crystal plane {hkl} equivalent planes [hkl] crystal direction <hkl> equivalent directions h: inverse x-intercept of plane k: inverse y-intercept of plane l: inverse z-intercept of plane (h, k and l are reduced to 3 integers having the same ratio. ) President University Erwin Sitompul SDP 1/16

Chapter 1 Semiconductors: A General Introduction Crystallographic Planes (632) plane President University (001) plane Erwin Sitompul _ (221) plane SDP 1/17

Chapter 1 Semiconductors: A General Introduction Crystallographic Planes President University Erwin Sitompul SDP 1/18

Chapter 1 Semiconductors: A General Introduction Crystallographic Planes of Si Wafers n Silicon wafers are usually cut along a {100} plane with a flat or notch to orient the wafer during integrated-circuit fabrication. n The facing surface is polished and etched yielding mirror-like finish. President University Erwin Sitompul SDP 1/19

Chapter 1 Semiconductors: A General Introduction Crystal Growth Until Device Fabrication President University Erwin Sitompul SDP 1/20

Chapter 1 Semiconductors: A General Introduction Crystallographic Planes of Si Unit cell: View in <111> direction View in <100> direction President University View in <110> direction Erwin Sitompul SDP 1/21

Chapter 2 Carrier Modeling President University Erwin Sitompul SDP 1/22

Chapter 2 Carrier Modeling Electronic Properties of Si n Silicon is a semiconductor material. n Pure Si has a relatively high electrical resistivity at room temperature. n There are 2 types of mobile charge-carriers in Si: n Conduction electrons are negatively charged, e = – 1. 602 10– 19 C n Holes are positively charged, p = +1. 602 10– 19 C n The concentration (number of atom/cm 3) of conduction electrons & holes in a semiconductor can be influenced in several ways: n Adding special impurity atoms (dopants) n Applying an electric field n Changing the temperature n Irradiation President University Erwin Sitompul SDP 1/23

Chapter 2 Carrier Modeling Bond Model of Electrons and Holes n 2 -D Representation Hole n When an electron breaks loose and becomes a conduction electron, then a hole is created. Si Si President University Erwin Sitompul Si Si Conduction electron SDP 1/24

Chapter 2 Carrier Modeling What is a Hole? n A hole is a positive charge associated with a half-filled covalent bond. n A hole is treated as a positively charged mobile particle in the semiconductor. President University Erwin Sitompul SDP 1/25

Chapter 2 Carrier Modeling Conduction Electron and Hole of Pure Si • Covalent (shared e–) bonds exists • between Si atoms in a crystal. Since the e– are loosely bound, some will be free at any T, creating hole-electron pairs. ni = intrinsic carrier concentration President University ni ≈ 1010 cm– 3 at room temperature Erwin Sitompul SDP 1/26

Chapter 2 Carrier Modeling Si: From Atom to Crystal Energy states (in Si atom) Energy bands (in Si crystal) • The highest mostly-filled • President University band is the valence band. The lowest mostly-empty band is the conduction band. Erwin Sitompul SDP 1/27

Chapter 2 Carrier Modeling Energy Band Diagram Electron energy Ec EG, band gap energy Ev • For Silicon at 300 K, EG = 1. 12 e. V • 1 e. V = 1. 6 x 10– 19 J n Simplified version of energy band model, indicating: n Lowest possible conduction band energy (Ec) n Highest possible valence band energy (Ev) n Ec and Ev are separated by the band gap energy EG. President University Erwin Sitompul SDP 1/28

Chapter 2 Carrier Modeling Measuring Band Gap Energy n EG can be determined from the minimum energy (hn) of photons that can be absorbed by the semiconductor. n This amount of energy equals the energy required to move a single electron from valence band to conduction band. Electron Ec Photon photon energy: hn = EG Ev Hole Band gap energies President University Erwin Sitompul SDP 1/29

Chapter 2 Carrier Modeling Carriers n Completely filled or empty bands do not allow current flow, because no carriers available. n Broken covalent bonds produce carriers (electrons and holes) and make current flow possible. n The excited electron moves from valence band to conduction band. n Conduction band is not completely empty anymore. n Valence band is not completely filled anymore. President University Erwin Sitompul SDP 1/30

Chapter 2 Carrier Modeling Band Gap and Material Classification Ec Ev Ec EG= ~8 e. V Ev Si. O 2 EG = 1. 12 e. V Si Ec Ec Ev Ev Metal n Insulators have large band gap EG. n Semiconductors have relatively small band gap EG. n Metals have very narrow band gap EG. n Even, in some cases conduction band is partially filled, Ev > Ec. President University Erwin Sitompul SDP 1/31

Chapter 2 Carrier Modeling Carrier Numbers in Intrinsic Material n More new notations are presented now: n n : number of electrons/cm 3 n p : number of holes/cm 3 n ni : intrinsic carrier concentration n In a pure semiconductor, n = p = ni. n At room temperature, ni = 2 106 /cm 3 in Ga. As ni = 1 1010 /cm 3 in Si ni = 2 1013 /cm 3 in Ge President University Erwin Sitompul SDP 1/32

Semiconductor Device Physics Semester Schedule FCS 1 SDP 1 FCS 2 SDP 2 Rec 1 President University Erwin Sitompul SDP 1/33

Semiconductor Device Physics Semester Schedule SDP 3 FCS 5 SDP 5 FCS 6 SDP 4 FCS 4 Rec 2 Rec 3 Rec 4 SDP 6 Rec 5 Mid President University Mid Erwin Sitompul Mid SDP 1/34

Semiconductor Device Physics Semester Schedule Mid FCS 7 FCS 8 SDP 7 FCS 9 ? SDP 9 FCS 10 Rec 5 SDP 8 Rec 6 Rec 7 Rec 8 President University Erwin Sitompul SDP 1/35

Semiconductor Device Physics Semester Schedule SDP 10 FCS 11 FCS 12 SDP 11 Rec 9 Rec 10 Final President University Final Erwin Sitompul Final SDP 1/36