2 Chapter 7 PN Junction PN junction can be fabricated by implanting or diffusing donors into a P-type substrate such that a layer of semiconductor is converted into N type. Converting a layer of an N-type semiconductor into P type with acceptors would also create a PN junction
3 Chapter 7 PN Junction A PN junction has rectifying current voltage (I V or IV) characteristics as shown in Fig As a device, it is called a rectifier or a diode. The PN junction is the basic structure of solar cell, light-emitting diode, and diode laser, and is present in all types of transistors
4 7.1 Basic structure of the PN junction The interface separating the n and p region is referred to as the metallurgical junction
5 7.1 Basic structure of the PN junction For simplicity, it is usually assumed that the P and N layers are uniformly doped at acceptor density N a, and donor density N d, respectively. This idealized PN junction is known as a step junction or an abrupt junction in which the doping concentration in uniform in the p and n region and there is an abrupt change in doping at the junction.
6 8.1.2 Qualitative 7.1 Basic Description structure of of Charge the PN Flow junction in a pn Junction
7 7.1 Basic structure of the PN junction As electron diffuse from n to p region, positively charged donor are left in the n region As holes diffuse from p to n region, negatively charged acceptor are left in the p region The two region are referred to as the space charge region The charges will induce electric field
8 7.1 Basic structure of the PN junction Let us construct a rough energy band diagram for a PN junction at equilibrium or zero bias voltage First draw a horizontal line for because there is only one Fermi level at equilibrium
9 7.1 Basic structure of the PN junction Far from the junction, we simply have an N-type semiconductor on one side (with E c close to E F ), and a P-type semiconductor on the other side (with E v close to E F ).
10 7.1 Basic structure of the PN junction Finally, in we draw an arbitrary (for now) smooth curve to link the E c from the N layer to the P layer. E v of course follows Ec, being below Ec by a constant E g.
11 7.2.1Built-in Potential Barrier Ec and Ev are not flat. This indicates the presence of a voltage differential. The conduction and valence band must bend through the space charge region. V bi Fn Fp
12 7.2.1Built-in Potential Barrier Electron in the conduction band of the n region see a potential barrier when moving into the conduction band in the p region. This built-in potential barrier is denoted as ev bi V bi Fn Fp
13 7.2.1Built-in Potential Barrier This built-in potential barrier maintain equilibrium between i.majority carrier electron in the n region and minority electron carrier in the p region ii.majority carrier holes in the p region and minority holes carrier in the n region V bi Fn Fp
14 7.2.1Built-in Potential Barrier The built-in potential barrier is the difference between the intrinsic Fermi levels in the p and n regions V bi Fn Fp In the n region the electron concentration is given by ( EC EF) no NC exp kt which can also be written in the form ( EC EF ) EF EFi no NC exp ni exp kt kt
15 7.2.1Built-in Potential Barrier The built-in potential barrier is the difference between the intrinsic Fermi levels in the p and n regions V bi Fn Fp We can define potential F n in the n region as e Fn EFi EF Thus, n 0 may be written as EF EFi e Fn no ni exp ni exp kt kt
16 7.2.1Built-in Potential Barrier Taking the natural log of both sides of where n 0 = N d It becomes n o e Fn niexp kt Fn kt N d ln e ni
17 7.2.1Built-in Potential Barrier Similarly in the p region, the hole concentration is given as ( EF Ev ) ( EF EFi ) po Na Nv exp ni exp kt kt We can define potential F p e Fp EFi EF Thus, p 0 may be written as in the n region as p 0 n i ( EF exp[ kt E Fi ] n i e exp[ kt Fp ]
18 7.2.1Built-in Potential Barrier Taking the natural log of both sides of where n 0 = N d p 0 n i e exp[ kt Fp ] It becomes Fp kt N a ln e ni
19 7.2.1Built-in Potential Barrier Therefore, the built-in potential barrier becomes V bi Fn Fp kt N d kt N a ln ln e ni e ni kt NaN d NaN d ln V ln 2 t 2 e ni ni
20 7.3 Reverse applied bias W dep 2 s ( bi Vr ) 2 s qn potential barrier qn 1 N 1 N d 1 N a lighter 1 dopant density Does the depletion layer widen or shrink with increasing reverse bias?
21 7.3.1 Space charge width and electric field The maximum electric field at the metallurgical junction is that yield Maximum Electric Field E max en x en x d n a n s 2 e Vbi VR NN a d Emax s Na Nd The maximum electric field in the pn junction can also be written as s 12 E max 2 V bi V R W
23 7.4 Junction breakdown Zener Breakdown As the reverse voltage increases the diode can avalanche breakdown and zener breakdown. Zener breakdown occurs when the electric field near the junction becomes large enough for valence electrons directly tunneling into the conduction band and generate carriers
24 7.4 Junction breakdown Avalanche Breakdown The avalanche process occurs when the carriers in the transition region are accelerated by the electric field to energies sufficient to free electron-hole pairs via collisions with bound electrons.
25 7.4 Junction breakdown The breakdown voltage can be given as V B E s 2eN 2 crit B Where N B is the semiconductor doping in the low-doped region of the one sided junction while E crit is actually E max at breakdown
26 Consider a silicon n+p junction diode. The critical electric field for breakdown in silicon is approximately E crit = V/cm. Determine the maximum p-type doping concentration such that the breakdown voltage is a)40v Example 1
27 Consider a silicon n+p junction diode. The critical electric field for breakdown in silicon is approximately E crit = V/cm. Determine the maximum p-type doping concentration such that the breakdown voltage is a)40v b)20 V V B N N B B s 2eN 2 crit B B or N cm a Example s crit 2eV
28 8.1.1 Qualitative Description of Charge Flow in a pn Junction In Figure 8.1c, the total potential barrier is reduced. There will be a diffusion of holes from the p region across the space charge region where they will flow into the n region. Similarly, there will be a diffusion of electrons from the n region across the space charge region where they will flow into the p region.
29 8.1.3 Boundary Conditions The electric field E app induced by the applied voltage is in the opposite direction to the thermal-equilibrium space charge electric field, so the net electric field in the space charge region is reduced below the equilibrium value. The electric field force that prevented majority carriers from crossing the space charge region is reduced ; majority carrier electrons from the n side are now injected across the depletion region int o the p material, and majority carrier holes from the p side are injected across the depletion region into the n material. V V N n n bi N a 2 ni d t NaN ln( 2 n n0 Nd, np0 p0 n i d ev exp( kt n0 bi ) n N ev exp( kt ) 2 i a bi ) 5
30 8.1.3 Boundary Conditions
31 8.1.4 Minority Carrier Distribution If a reverse biased voltage greater than a few tenths of a volt is applied to the pn junction, then we see from Equations (8.6) and (8.7) that the minority carrier concentrations at the space charge edge are essentially zero.
32 8.1.4 Minority Carrier Distribution
33 8.1.4 Minority Carrier Distribution
34 8.1.5 Ideal pn Junction Current
35 8.1.6 Summary of Physics Comment of Ex 8.4, We assumed, in the derivation of the current voltage equation, that the electric field in the neutral p and n regions was zero. Although the electric field is not zero, this example shows that the magnitude is very small thus the approximation of zero electric field is very good.
36 8.2.1 Generation Recombination Currents
37 8.2.1 Generation Recombination Currents The negative sign implies a negative recombination rate; hence, we are really generating electron hole pairs within the reverse biased space charge region.
38 8.2.1 Generation Recombination Currents
39 Forward Bias Recombination Current Generation Recombination Currents
40 8.2.1 Generation Recombination Currents At the center of the space charge region,
41 8.2.1 Generation Recombination Currents Total Forward Bias Current The total forward bias current density in the pn junction is the sum of the recombination and the ideal diffusion current densities. If some of the injected holes in the space charge region are lost due to recombination, then additional holes must be injected from the p region to make up for this loss. The flow of these additional injected carriers, per unit time, results in the recombination current.
42 8.2.2 High-Level injection
43 8.2.2 High-Level injection
44 8.2.2 High-Level injection In the high level injection region, it takes a larger increase in diode voltage to produce a given increase in diode current.
45 *8.4.1 The turn-off transient
46 the reverse biased density gradient is constant; thus, the minority carrier concentrations at the space charge edge decrease with time This reverse current IR will be approximately constant for 0< t< ts, where ts is called the storage time. *8.4.1 The turn-off transient
47 *8.5 The tunnel diode The tunnel diode is a pn junction in which both the n and p regions are degenerately doped. The depletion region width decreases as the doping increases and may be on the order of approximately 100 Å
48 *8.5 The tunnel diode (b) There is a finite probability that some of these electrons will tunnel directly into the empty states, producing a forward bias tunneling current (e) the tunneling current will be zero and the normal ideal diffusion current will exist
49 *8.5 The tunnel diode Electrons in the valence band on the p side are directly opposite empty states in the conduction band on the n side, so electrons can now tunnel directly from the p region into the n region, resulting in a large reversebiased tunneling current.
CHAPTER 7 The PN Junction Consider a uniformly doped PN junction, in which one region of the semiconductor is uniformly doped with acceptor atoms and the adjacent region is uniformly doped with donor atoms.
Peak Electric Field Junction breakdown occurs when the peak electric field in the P junction reaches a critical value. For the + P junction, qa E ( x) ( xp x), s W dep 2 s ( bi Vr ) 2 s potential barrier
EECS130 Integrated Circuit Devices Professor Ali Javey 9/18/2007 P Junctions Lecture 1 Reading: Chapter 5 Announcements For THIS WEEK OLY, Prof. Javey's office hours will be held on Tuesday, Sept 18 3:30-4:30
Session 6: Solid State Physics Diode 1 Outline A B C D E F G H I J 2 Definitions / Assumptions Homojunction: the junction is between two regions of the same material Heterojunction: the junction is between
Summary of electron and hole concentration in semiconductors Intrinsic semiconductor: E G n kt i = pi = N e 2 0 Donor-doped semiconductor: n N D where N D is the concentration of donor impurity Acceptor-doped
8 Semiconductor Junctions Almost all solar cells contain junctions between different materials of different doping. Since these junctions are crucial to the operation of the solar cell, we will discuss
Fall 2007 Fundamentals of Semiconductor Physics 万 歆 Zhejiang Institute of Modern Physics email@example.com http://zimp.zju.edu.cn/~xinwan/ Transistor technology evokes new physics The objective of
Semiconductor Physics fall 2012 problems 1. An n-type sample of silicon has a uniform density N D = 10 16 atoms cm -3 of arsenic, and a p-type silicon sample has N A = 10 15 atoms cm -3 of boron. For each
1 Name: DEPARTMENT OF PHYSICS AND PHYSICAL OCEANOGRAPHY MEMORIAL UNIVERSITY OF NEWFOUNDLAND Final Exam Physics 3000 December 11, 2012 Fall 2012 9:00-11:00 INSTRUCTIONS: 1. Answer all seven (7) questions.
Technische Universität Graz Institute of Solid State Physics Schottky diodes JFETs - MESFETs - MODFETs Quasi Fermi level When the charge carriers are not in equilibrium the Fermi energy can be different
PHYSICAL ELECTRONICS(ECE3540) CHAPTER 9 METAL SEMICONDUCTOR AND SEMICONDUCTOR HETERO-JUNCTIONS Tennessee Technological University Monday, November 11, 013 1 Introduction Chapter 4: we considered the semiconductor
Chapter 6 P-N DODES Junctions between n-and p-type semiconductors are extremely important foravariety of devices. Diodes based on p-n junctions produce nonlinear current voltage characteristics which can
ECE442 Power Semiconductor Devices and Integrated Circuits Schottky Rectifiers Zheng Yang (ERF 3017, email: firstname.lastname@example.org) Power Schottky Rectifier Structure 2 Metal-Semiconductor Contact The work function
Semiconductor Physics fall 2012 problems 1. An n-type sample of silicon has a uniform density N D = 10 16 atoms cm -3 of arsenic, and a p-type silicon sample has N A = 10 15 atoms cm -3 of boron. For each
Effective masses in semiconductors The effective mass is defined as: In a solid, the electron (hole) effective mass represents how electrons move in an applied field. The effective mass reflects the inverse
ECE 340 Lecture 27 : Junction Capacitance Class Outline: Breakdown Review Junction Capacitance Things you should know when you leave M.J. Gilbert ECE 340 Lecture 27 10/24/11 Key Questions What types of
Benha University Faculty of Engineering Shoubra Electrical Engineering Department First Year communications. Answer all the following questions Illustrate your answers with sketches when necessary. The
Technische Universität Graz Institute of Solid State Physics 8. Schottky contacts / JFETs Nov. 21, 2018 Technische Universität Graz Institute of Solid State Physics metal - semiconductor contacts Photoelectric
Semiconductor Physics Problems 2015 Page and figure numbers refer to Semiconductor Devices Physics and Technology, 3rd edition, by SM Sze and M-K Lee 1. The purest semiconductor crystals it is possible
Diodes mplest nonlinear circuit element Basic operation sets the foundation for Bipolar Junction Transistors (BJTs) Also present in Field Effect Transistors (FETs) Ideal diode characteristic anode cathode
The pn junction [Fonstad, Ghione] Band diagram On the vertical axis: potential energy of the electrons On the horizontal axis: now there is nothing: later we ll put the position qf s : work function (F
Avalanche breakdown Impact ionization causes an avalanche of current Occurs at low doping Zener tunneling Electrons tunnel from valence band to conduction band Occurs at high doping Tunneling wave decays
ECE 342 2. PN Junctions and iodes Jose E. Schutt-Aine Electrical & Computer Engineering University of Illinois email@example.com ECE 342 Jose Schutt Aine 1 B: material dependent parameter = 5.4 10
ECE 541/ME 541 Microelectronic Fabrication Techniques Review of Semiconductor Fundamentals Zheng Yang (ERF 3017, email: firstname.lastname@example.org) Page 1 Semiconductor A semiconductor is an almost insulating material,
Spring Semester 2012 Final Exam Note: Show your work, underline results, and always show units. Official exam time: 2.0 hours; an extension of at least 1.0 hour will be granted to anyone. Materials parameters
CHAPTER 4: P-N P N JUNCTION Part 2 Part 2 Charge Storage & Transient Behavior Junction Breakdown Heterojunction CHARGE STORAGE & TRANSIENT BEHAVIOR Once injected across the junction, the minority carriers
Final Examination EE 130 December 16, 1997 Time allotted: 180 minutes Problem 1: Semiconductor Fundamentals [30 points] A uniformly doped silicon sample of length 100µm and cross-sectional area 100µm 2
UNIVERSITY OF CALIFORNIA College of Engineering Department of Electrical Engineering and Computer Sciences EECS 130 Spring 2008 Professor Chenming Hu Midterm I - Solutions Name: SID: Grad/Undergrad: Closed
Lecture (02) PN Junctions and Diodes By: Dr. Ahmed ElShafee ١ I Agenda N type, P type semiconductors N Type Semiconductor P Type Semiconductor PN junction Energy Diagrams of the PN Junction and Depletion
Semiconductor Physics Lecture 6 Recap pn junction and the depletion region Driven by the need to have no gradient in the fermi level free carriers migrate across the pn junction leaving a region with few
ECE 440 Lecture 20 : PN Junction Electrostatics II Class Outline: Depletion Approximation Step Junction Things you should know when you leave Key Questions What is the space charge region? What are the
B12: Semiconductor Devices Example Sheet 2: Solutions Question 1 To get from eq. (5.70) of the notes to the expression given in the examples sheet, we simply invoke the relations n 0 p 0, n 0 n 0. In this
Metal Semiconductor Contacts The investigation of rectification in metal-semiconductor contacts was first described by Braun [33-35], who discovered in 1874 the asymmetric nature of electrical conduction
Band-bending In the p-n junction and BJT, we saw that the semiconductor band edges were bent in the depletion layers. We used the depletion approximation and Poisson s equation to relate the band-bending
Consider the the band diagram for a homojunction, formed when two bits of the same type of semicondutor (e.g. Si) are doped p and ntype and then brought into contact. Electrons in the two bits have different
Current mechanisms Exam January 27, 2012 There are four mechanisms that typically cause currents to flow: thermionic emission, diffusion, drift, and tunneling. Explain briefly which kind of current mechanisms
The pn Junction: The Shockley Model ( S. O. Kasap, 1990-001) 1 pn JUNCTION THE SHOCKLEY MODEL Safa Kasap Department of Electrical Engineering University of Saskatchewan Canada Although the hole and its
Basic Physics of Semiconductors Semiconductor materials and their properties PN-junction diodes Reverse Breakdown EEM 205 Electronics I Dicle University, EEE Dr. Mehmet Siraç ÖZERDEM Semiconductor Physics
8/30/2012 Page 1 of 5 Reference:C:\Users\Bernhard Boser\Documents\Files\Lib\MathCAD\Default\defaults.mcd L03: pn Junctions, Diodes Intrinsic Si Q: What are n, p? Q: Is the Si charged? Q: How could we make
Lecture (02) Introduction to Electronics II, PN Junction and Diodes I By: Dr. Ahmed ElShafee ١ Agenda Current in semiconductors/conductors N type, P type semiconductors N Type Semiconductor P Type Semiconductor
Name: Student Number: ELEC 3908 Physical Electronics Quiz #1 Practice Problem Set? Minutes January 22, 2016 - No aids except a non-programmable calculator - All questions must be answered - All questions
16EC401 BASIC ELECTRONIC DEVICES UNIT I PN JUNCTION DIODE Energy bands in Intrinsic and Extrinsic silicon: Energy Band Diagram of Conductor, Insulator and Semiconductor: 1 2 Carrier transport: Any motion
EE321 Fall 2015 Semiconductor Phyic and Device November 30, 2015 Weiwen Zou ( 邹卫文 ) Ph.D., Aociate Prof. State Key Lab of advanced optical communication ytem and network, Dept. of Electronic Engineering,
Semiconductor A semiconductor is an almost insulating material, in which by contamination (doping) positive or negative charge carriers can be introduced. Page 2 Semiconductor materials Page 3 Energy levels
ECE 340 Lecture 21 : P-N Junction II Class Outline: Contact Potential Equilibrium Fermi Levels Things you should know when you leave Key Questions What is the contact potential? Where does the transition
1 emiconductor Device Physics Lecture 8 http://zitompul.wordpress.com 2 0 1 3 emiconductor Device Physics 2 M Contacts and chottky Diodes 3 M Contact The metal-semiconductor (M) contact plays a very important
Electrical Characteristics of MOS Devices The MOS Capacitor Voltage components Accumulation, Depletion, Inversion Modes Effect of channel bias and substrate bias Effect of gate oide charges Threshold-voltage
Section 12: Intro to Devices Extensive reading materials on reserve, including Robert F. Pierret, Semiconductor Device Fundamentals EE143 Ali Javey Bond Model of Electrons and Holes Si Si Si Si Si Si Si
Junction Diodes Most elementary solid state junction electronic devices. They conduct in one direction (almost correct). Useful when one converts from AC to DC (rectifier). But today diodes have a wide
SEMICONDUCTOR DIODE Semiconductor diode is an electronic element made of different types of extrinsic semiconductor: N-type semiconductor doped by donor impurities and P-type semiconductor doped by acceptor
FYS3410 Condensed matter physics Lecture 23 and 24: pn-junctions and electrooptics Randi Haakenaasen UniK/UiO Forsvarets forskningsinstitutt 11.05.2016 and 18.05.2016 Outline Why pn-junctions are important
1 Lecture-4 Junction Diode Characteristics Part-II Q: Aluminum is alloyed into n-type Si sample (N D = 10 16 cm 3 ) forming an abrupt junction of circular cross-section, with an diameter of 0.02 in. Assume
1 PHYS208 P-N Junction Olav Torheim May 30, 2007 1 Intrinsic semiconductors The lower end of the conduction band is a parabola, just like in the quadratic free electron case (E = h2 k 2 2m ). The density
UNIVERSITY OF CALIFORNIA College of Engineering Department of Electrical Engineering and Computer Sciences EECS 130 Professor Ali Javey Fall 2006 Midterm I Name: Closed book. One sheet of notes is allowed.
CLASS 6&7 p-n junction biasing, p-n I-V characteristics, p-n currents 1 p-n junction biasing Unbiased p-n junction: the potential barrier is 0.7 V for Si and 0.3 V for Ge. Nett current across the p-n junction
UNIVERSITY OF CALIFORNIA College of Engineering Department of Electrical Engineering and Computer Sciences EECS 130 Professor Ali Javey Fall 2006 Midterm 2 Name: SID: Closed book. Two sheets of notes are
1.9. Temperature Dependence of Semiconductor Conductivity Such dependence is one most important in semiconductor. In metals, Conductivity decreases by increasing temperature due to greater frequency of
Sheng S. Li Semiconductor Physical Electronics Second Edition With 230 Figures 4) Springer Contents Preface 1. Classification of Solids and Crystal Structure 1 1.1 Introduction 1 1.2 The Bravais Lattice
EECS130 Integrated Circuit Devices Professor Ali Javey 10/02/2007 MS Junctions, Lecture 2 MOS Cap, Lecture 1 Reading: finish chapter14, start chapter16 Announcements Professor Javey will hold his OH at
ECE442 Power Semiconductor Devices and Integrated Circuits Introduction to Power Semiconductor Devices Zheng Yang (ERF 3017, email: email@example.com) Power Semiconductor Devices Applications System Ratings
ECE321 Electronics I Lecture 4: Physics of Semiconductor iodes Payman Zarkesh-Ha Office: ECE Bldg. 230B Office hours: Tuesday 2:00-3:00PM or by appointment E-mail: pzarkesh.unm.edu Slide: 1 Review of Last
Charge Carriers in Semiconductor To understand PN junction s IV characteristics, it is important to understand charge carriers behavior in solids, how to modify carrier densities, and different mechanisms
EE 13 Intro to S Junctions eek 6 Notes Problem 1 hat is the work function? Energy to ecite electron from Fermi level to the vacuum level Electron affinity of 4.5eV Electron affinity of Ge 4.eV orkfunction
ECE 440 Lecture 28 : P-N Junction II Class Outline: Contact Potential Equilibrium Fermi Levels Things you should know when you leave Key Questions What is the contact potential? Where does the transition
ECE 66: SOLUTIONS: ECE 66 Homework Week 8 Mark Lundstrom March 7, 13 1) The doping profile for an n- type silicon wafer ( N D = 1 15 cm - 3 ) with a heavily doped thin layer at the surface (surface concentration,
KATIHAL FİZİĞİ MNT-510 YARIİLETKENLER Kaynaklar: Katıhal Fiziği, Prof. Dr. Mustafa Dikici, Seçkin Yayıncılık Katıhal Fiziği, Şakir Aydoğan, Nobel Yayıncılık, Physics for Computer Science Students: With
Solid State Physics SEMICONDUCTORS - IV Lecture 25 A.H. Harker Physics and Astronomy UCL 9.9 Carrier diffusion and recombination Suppose we have a p-type semiconductor, i.e. n h >> n e. (1) Create a local
3. Two-dimensional systems Image from IBM-Almaden 1 Introduction Type I: natural layered structures, e.g., graphite (with C nanostructures) Type II: artificial structures, heterojunctions Great technological
Classification of Solids Classification by conductivity, which is related to the band structure: (Filled bands are shown dark; D(E) = Density of states) Class Electron Density Density of States D(E) Examples
Semiconductor Physics Lecture 3 Intrinsic carrier density Intrinsic carrier density Law of mass action Valid also if we add an impurity which either donates extra electrons or holes the number of carriers
Qualitative Picture of the Ideal Diode G.R. Tynan UC San Diego MAE 119 Lecture Notes Band Theory of Solids: From Single Attoms to Solid Crystals Isolated Li atom (conducting metal) Has well-defined, isolated
3.. Intrinsic semiconductors: Unbroken covalent bonds make a low conductivity crystal, and at 0 o k the crystal behaves as an insulator, since no free electrons and holes are available. At room temperature,
Lecture 2 Introduction to semiconductors Structures and characteristics in semiconductors Semiconductor p-n junction Metal Oxide Silicon structure Semiconductor contact Literature Glen F. Knoll, Radiation
4- P-N Junction We begin our study of semiconductor devices with the junction for three reasons. (1) The device finds application in many electronic systems, e.g., in adapters that charge the batteries
Microelectronic Devices and Circuits October 9, 013 - Homework #3 Due Nov 9, 013 1 Te pn junction Consider an abrupt Si pn + junction tat as 10 15 acceptors cm -3 on te p-side and 10 19 donors on te n-side.