EE105 Fall 2011Lecture 3, Slide 1Prof. Salahuddin, UC Berkeley Lecture 3 OUTLINE Semiconductor Basics (cont’d) – Carrier drift and diffusion PN Junction.

Slides:



Advertisements
Similar presentations
Agenda Semiconductor materials and their properties PN-junction diodes
Advertisements

Chapter 6-1. PN-junction diode: I-V characteristics
Semiconductor Device Physics Lecture 3 Dr. Gaurav Trivedi, EEE Department, IIT Guwahati.
Lecture 5 OUTLINE PN Junction Diodes I/V Capacitance Reverse Breakdown
© Electronics ECE 1312 Recall-Lecture 2 Introduction to Electronics Atomic structure of Group IV materials particularly on Silicon Intrinsic carrier concentration,
1 Fundamentals of Microelectronics  CH1 Why Microelectronics?  CH2 Basic Physics of Semiconductors  CH3 Diode Circuits  CH4 Physics of Bipolar Transistors.
ECE 4339: Physical Principles of Solid State Devices
PN Junction Diodes.
Integrated Circuit Devices
Carrier Transport Phenomena
Lecture #6 OUTLINE Carrier scattering mechanisms Drift current
EE105 Fall 2007Lecture 3, Slide 1Prof. Liu, UC Berkeley Lecture 3 ANNOUNCEMENTS HW2 is posted, due Tu 9/11 TAs will hold their office hours in 197 Cory.
Lecture 2 OUTLINE Semiconductor Basics Reading: Chapter 2.
Lecture 15, Slide 1EECS40, Fall 2004Prof. White Lecture #15 OUTLINE The pn Junction Diode -- Uses: Rectification, parts of transistors, light-emitting.
Lecture 15 OUTLINE MOSFET structure & operation (qualitative)
Department of EECS University of California, Berkeley EECS 105 Fall 2003, Lecture 9 Lecture 9: PN Junctions Prof. Niknejad.
OUTLINE pn junction I-V characteristics Reading: Chapter 6.1
Announcements HW1 is posted, due Tuesday 9/4
Lecture 27: PN Junctions Prof. Niknejad.
EE105 Fall 2011Lecture 6, Slide 1Prof. Salahuddin, UC Berkeley Lecture 6 OUTLINE PN Junction Diodes – Reverse Breakdown – Large and Small signal models.
Department of EECS University of California, Berkeley EECS 105 Fall 2003, Lecture 8 Lecture 8: Capacitors and PN Junctions Prof. Niknejad.
Lecture #12 OUTLINE Metal-semiconductor contacts (cont.)
Lecture #18 OUTLINE pn junctions (cont’d)
Week 8a OUTLINE The pn Junction Diode Reference Reading
Lecture #7 OUTLINE Carrier diffusion Diffusion current Einstein relationship Generation and recombination Read: Sections 3.2, 3.3.
Chapter V July 15, 2015 Junctions of Photovoltaics.
Spring 2007EE130 Lecture 17, Slide 1 Lecture #17 OUTLINE pn junctions (cont’d) – Reverse bias current – Reverse-bias breakdown Reading: Chapter 6.2.
Lecture 3. Intrinsic Semiconductor When a bond breaks, an electron and a hole are produced: n 0 = p 0 (electron & hole concentration) Also:n 0 p 0 = n.
Dr. Nasim Zafar Electronics 1 EEE 231 – BS Electrical Engineering Fall Semester – 2012 COMSATS Institute of Information Technology Virtual campus Islamabad.
EE415 VLSI Design The Devices: Diode [Adapted from Rabaey’s Digital Integrated Circuits, ©2002, J. Rabaey et al.]
The Devices: Diode.
Depletion Region ECE Depletion Region As electrons diffuse from the n region into the p region and holes diffuse from the p region into the n region,
Drift and Diffusion Current
Lecture 4 OUTLINE Semiconductor Fundamentals (cont’d)
Farzana R ZakiEEE 231: Electronics I1 Semiconductor Diode Instructor: Farzana Rahmat Zaki Senior Lecturer, EEE Eastern University.
Lecture 9 OUTLINE pn Junction Diodes – Electrostatics (step junction) Reading: Pierret 5; Hu
Electronics 1 Lecture 3 Moving Charge Carriers
Lecture 2 Instructor: Rashedul Islam Course: Electronics I.
President UniversityErwin SitompulSDP 8/1 Dr.-Ing. Erwin Sitompul President University Lecture 8 Semiconductor Device Physics
EE130/230A Discussion 6 Peng Zheng.
Dr. Nasim Zafar Electronics 1 EEE 231 – BS Electrical Engineering Fall Semester – 2012 COMSATS Institute of Information Technology Virtual campus Islamabad.
CHAPTER 4: P-N JUNCTION Part I.
Semiconductor Device Physics
Slide 1EE40 Fall 2007Prof. Chang-Hasnain EE40 Lecture 32 Prof. Chang-Hasnain 11/21/07 Reading: Supplementary Reader.
President UniversityErwin SitompulSDP 3/1 Dr.-Ing. Erwin Sitompul President University Lecture 3 Semiconductor Device Physics
CSE251 CSE251 Lecture 2 and 5. Carrier Transport 2 The net flow of electrons and holes generate currents. The flow of ”holes” within a solid–state material.
CSE251 CSE251 Lecture 2. Carrier Transport 2 The net flow of electrons and holes generate currents. The flow of ”holes” within a solid–state material.
Lecture 5 OUTLINE Semiconductor Fundamentals (cont’d) – Carrier diffusion Diffusion current Einstein relationship – Generation and recombination Excess.
Recall-Lecture 3 Atomic structure of Group IV materials particularly on Silicon Intrinsic carrier concentration, ni.
Recall-Lecture 3 Atomic structure of Group IV materials particularly on Silicon Intrinsic carrier concentration, ni.
Lecture #14 OUTLINE Midterm #1 stats The pn Junction Diode
Lecture 10 OUTLINE pn Junction Diodes (cont’d)
Lecture 10 OUTLINE pn Junction Diodes (cont’d)
Lecture 13 OUTLINE pn Junction Diodes (cont’d) Charge control model
Announcements HW1 is posted, due Tuesday 9/4
Recall-Lecture 3 Atomic structure of Group IV materials particularly on Silicon Intrinsic carrier concentration, ni.
Lecture #12 OUTLINE Metal-semiconductor contacts (cont.)
Lecture #17 OUTLINE pn junctions (cont’d) Reverse bias current
Lecture #18 OUTLINE pn junctions (cont’d)
Deviations from the Ideal I-V Behavior
Chapter 1 – Semiconductor Devices – Part 2
Lecture 10 OUTLINE pn Junction Diodes (cont’d)
Lecture 3 OUTLINE Semiconductor Basics (cont’d) PN Junction Diodes
Lecture 10 OUTLINE pn Junction Diodes (cont’d)
Lecture 12 OUTLINE pn Junction Diodes (cont’d)
Lecture 13 OUTLINE pn Junction Diodes (cont’d) Charge control model
Lecture 10 OUTLINE pn Junction Diodes (cont’d)
Lecture 12 OUTLINE pn Junction Diodes (cont’d)
Semiconductor Physics
PN-JUNCTION.
Presentation transcript:

EE105 Fall 2011Lecture 3, Slide 1Prof. Salahuddin, UC Berkeley Lecture 3 OUTLINE Semiconductor Basics (cont’d) – Carrier drift and diffusion PN Junction Diodes – Electrostatics – Capacitance Reading: Chapter

EE105 Fall 2011Lecture 3, Slide 2Prof. Salahuddin, UC Berkeley Recap: Drift Current Drift current is proportional to the carrier velocity and carrier concentration:  Hole current per unit area (i.e. current density) J p,drift = q p v h Total current J p,drift = Q/t Q= total charge contained in the volume shown to the right t= time taken by Q to cross the volume Q=qp(in cm 3 )X Volume=qpAL=qpAv h t

EE105 Fall 2011Lecture 3, Slide 3Prof. Salahuddin, UC Berkeley Recap: Conductivity and Resistivity In a semiconductor, both electrons and holes conduct current: The conductivity of a semiconductor is – Unit: mho/cm The resistivity of a semiconductor is – Unit: ohm-cm

EE105 Fall 2011Lecture 3, Slide 4Prof. Salahuddin, UC Berkeley Electrical Resistance where  is the resistivity Resistance (Unit: ohms) V + _ L t W I homogeneously doped sample

EE105 Fall 2011Lecture 3, Slide 5Prof. Salahuddin, UC Berkeley Resistivity Example

EE105 Fall 2011Lecture 3, Slide 6Prof. Salahuddin, UC Berkeley A Second Mechanism of Current Flow is Diffusion

EE105 Fall 2011Lecture 3, Slide 7Prof. Salahuddin, UC Berkeley Carrier Diffusion Due to thermally induced random motion, mobile particles tend to move from a region of high concentration to a region of low concentration. – Analogy: ink droplet in water

EE105 Fall 2011Lecture 3, Slide 8Prof. Salahuddin, UC Berkeley Carrier Diffusion Current flow due to mobile charge diffusion is proportional to the carrier concentration gradient. – The proportionality constant is the diffusion constant. Notation: D p  hole diffusion constant (cm 2 /s) D n  electron diffusion constant (cm 2 /s)

EE105 Fall 2011Lecture 3, Slide 9Prof. Salahuddin, UC Berkeley Diffusion Examples Non-linear concentration profile  varying diffusion current Linear concentration profile  constant diffusion current

EE105 Fall 2011Lecture 3, Slide 10Prof. Salahuddin, UC Berkeley Diffusion Current Diffusion current within a semiconductor consists of hole and electron components: The total current flowing in a semiconductor is the sum of drift current and diffusion current:

EE105 Fall 2011Lecture 3, Slide 11Prof. Salahuddin, UC Berkeley The Einstein Relation The characteristic constants for drift and diffusion are related: Note that at room temperature (300K) – This is often referred to as the “thermal voltage”.

EE105 Fall 2011Lecture 3, Slide 12Prof. Salahuddin, UC Berkeley The PN Junction Diode When a P-type semiconductor region and an N-type semiconductor region are in contact, a PN junction diode is formed. VDVD IDID +–

EE105 Fall 2011Lecture 3, Slide 13Prof. Salahuddin, UC Berkeley Diode Operating Regions In order to understand the operation of a diode, it is necessary to study its behavior in three operation regions: equilibrium, reverse bias, and forward bias. V D = 0V D > 0V D < 0

EE105 Fall 2011Lecture 3, Slide 14Prof. Salahuddin, UC Berkeley Carrier Diffusion across the Junction Because of the differences in hole and electron concentrations on each side of the junction, carriers diffuse across the junction: Notation: n n  electron concentration on N-type side (cm -3 ) p n  hole concentration on N-type side (cm -3 ) p p  hole concentration on P-type side (cm -3 ) n p  electron concentration on P-type side (cm -3 )

EE105 Fall 2011Lecture 3, Slide 15Prof. Salahuddin, UC Berkeley Depletion Region As conduction electrons and holes diffuse across the junction, they leave behind ionized dopants. Thus, a region that is depleted of mobile carriers is formed. – The charge density in the depletion region is not zero. – The carriers which diffuse across the junction recombine with majority carriers, i.e. they are annihilated. width=W dep quasi- neutral region

EE105 Fall 2011Lecture 3, Slide 16Prof. Salahuddin, UC Berkeley Some Important Relations Energy=-qV

EE105 Fall 2011Lecture 3, Slide 17Prof. Salahuddin, UC Berkeley The Depletion Approximation In the depletion region on the N side: (x)(x) x -qN A qN D In the depletion region on the P side: a -b Because charge density ≠ 0 in the depletion region, a large E-field exists in this region:

EE105 Fall 2011Lecture 3, Slide 18Prof. Salahuddin, UC Berkeley Carrier Drift across the Junction

EE105 Fall 2011Lecture 3, Slide 19Prof. Salahuddin, UC Berkeley PN Junction in Equilibrium In equilibrium, the drift and diffusion components of current are balanced; therefore the net current flowing across the junction is zero.

EE105 Fall 2011Lecture 3, Slide 20Prof. Salahuddin, UC Berkeley Built-in Potential, V 0 Because there is a large electric field in the depletion region, there is a significant potential drop across this region: (Unit: Volts)

EE105 Fall 2011Lecture 3, Slide 21Prof. Salahuddin, UC Berkeley Built-In Potential Example Estimate the built-in potential for PN junction below. – Note that NP N D = cm -3 N A = cm -3

EE105 Fall 2011Lecture 3, Slide 22Prof. Salahuddin, UC Berkeley A forward bias decreases the potential drop across the junction. As a result, the magnitude of the electric field decreases and the width of the depletion region narrows. PN Junction under Forward Bias (x)(x) x -qN A qN D a -b V(x)V(x) x a V0V0 IDID 0