1 / 26

Introduction

Introduction. Semiconductor Physics. Introduction: Semiconductor Physics. Silicon bond model: electrons and holes Generation and recombination Thermal equilibrium Intrinsic semiconductor Extrinsic semiconductor. Silicon Bond Model: Electrons and Holes .

lixue
Download Presentation

Introduction

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Introduction Semiconductor Physics

  2. Introduction: Semiconductor Physics • Silicon bond model: electrons and holes • Generation and recombination • Thermal equilibrium • Intrinsic semiconductor • Extrinsic semiconductor

  3. Silicon Bond Model: Electrons and Holes Si is in column IV of periodic table

  4. Silicon Bond Model: Electrons and Holes • Electronic structure of Si atom: • 10 core electrons (tightly bound) • 4 valence electrons (loosely bound, responsible for most chemical properties) • Other semiconductors: • Ge, C (diamond form), SiGe • GaAs, InP, InGaAs, ZnSe, CdTe (on average, 4 valenceelectrons per atom)

  5. Silicon Bond Model: Electrons and Holes • Silicon crystal structure • Silicon is a crystalline material • Long range atomic arrangement • Diamond lattice: • Atoms tetrahedrally bonded by sharing valence electrons (covalent bonding) • Each atom shares 8 electrons • In low energy and stable situation • Si atomic density: 5 x 1022 cm-3

  6. Simple “flattened model of Si crystal:

  7. Silicon Bond Model: Electrons and Holes • At 0K • All bonds satisfied  all valence electrons engaged in bonding • No free electrons • At finite temperature • Finite thermal energy • Some bonds are broken • “free” electrons (mobile negative charge, -1.6x 10-19 C) • “free” holes (mobile positive charge , 1.6x 10-19 C)

  8. Silicon Bond Model: Electrons and Holes

  9. Silicon Bond Model: Electrons and Holes “Free” electrons & holes are called carriers • Mobile charged particles • “electron” means free electron • not concerned with bonding electrons or core electrons n = (free) electron concentration [cm -3] p = hole concentration [cm -3]

  10. Generation and Recombination • Generation = break up of covalent bond to form electron and hole • Requires energy from thermal or optical sources (or other external sources) • Recombination = formation of bond by bringing together electron and hole • Releases energy in thermal or optical form • A recombination event requires 1 electron + 1 hole Generation & recombination most likely at surfaces where periodic crystalline is broken.

  11. Thermal Equilibrium • Thermal Equilibrium= steady state + absence of external energy sources • Important consequence: • In thermal equilibrium and for a given semiconductor,np product is a constant that depends only on temperature!

  12. Intrinsic Semiconductor • When a bond breaks, an electron and a hole are produced: n0= p0 Also: n0p0 = ni2 Then: n0= p0 = ni ni = intrinsic carrier concentration [cm -3 ] In Si at 300K (room temperature): ni = 1x 1010 cm -3

  13. Extrinsic Semiconductor • Doping • introduction of foreign atoms to engineer semiconductor electrical properties • Donors • Introduce electron to the semiconductor • For Si, group-V atoms with 5 valence electrons (As, P, Sb) • 4 electrons of donor atom participate in bonding • 5th electron is easy to release • Donor site become positively charged

  14. Periodic Table Source: http://www.chemicool.com/

  15. Valence Electrons • The valence electrons are the electrons in the last shell or energy level of an atom. • The valence electrons increase in number as you go across a period • The number of valence electrons stays the same as you go up or down a group, but they increase as you go from left to right across the periodic table

  16. Extrinsic Semiconductor: Donor • Nd = donor concentration [cm -3 ] • IfNd<< ni , doping irrelevant • Intrinsic semiconductor  n0= p0 = ni • IfNd>> ni , doping controls carrier concentrations • Extrinsic semiconductor  n0= Nd , p0 = ni2 /Nd Note: n0 >> p0 n-type semiconductor

  17. Extrinsic Semiconductor: Donor group-V atoms with 5 valence electrons

  18. Extrinsic Semiconductor: Acceptor • Acceptors • Introduce holes to the semiconductor • For Si, group-III atoms with 3 valence electrons (B) • 3 electrons used in bonding to neighboring Si atoms • 1 bonding site “unsatisfied” • Easy to accept neighboring bonding electron to complete all bonds • At room temperature, each acceptor releases 1 hole that is available to conduction • Acceptor site become negatively charged

  19. Extrinsic Semiconductor: Acceptor • Na = acceptor concentration [cm -3 ] • If Na << ni , doping irrelevant • Intrinsic semiconductor  n0= p0 = ni • If Na >> ni , doping controls carrier concentrations • Extrinsic semiconductor  p0= Na , n0 = ni2 /Na Note: p0 >> n0 p-type semiconductor

  20. Extrinsic Semiconductor: Acceptor • group-III atoms with 3 valence electrons

  21. Extrinsic Semiconductor Trivalent impurities - impurity atoms with 3 valence electrons - produce p-type semiconductors by producing a "hole" or electron deficiency • Pentavalent impurities • impurity atoms with 5 valence electrons • produce n-type semiconductors by contributing extra electrons

  22. Extrinsic SemiconductorP-type & N-type Semiconductor

  23. Summary • In a semiconductor, there are two types of “carriers”: electrons and holes • In thermal equilibrium and for a given semiconductor n0p0 is a constant that only depends on temperature: n0p0 = ni2 • For Si at room temperature: ni = 1x 1010 cm -3 • Intrinsic semiconductor: pure semiconductor n0= p0 = ni

  24. Summary • Carrier concentration can be engineered by addition of “dopants” (selected foreign atoms): • Pentavalent impurities (P, As, Sb)  n-type semiconductor: n0= Nd , p0 = ni2 /Nd • Trivalent impurities (B, Al, Ga)  p-type semiconductor: p0= Na , n0 = ni2 /Na

  25. Video Links from Youtube AMD MICROPROCESSOR http://www.youtube.com/watch?v=-GQmtITMdas&feature=related From Sand to Silicon http://www.youtube.com/watch?v=Q5paWn7bFg4 CH IP MANUFACTURING PROCESS http://www.youtube.com/watch?v=9rCyu8B0tYs&feature=related Semiconductor Electronics Theory Lesson 1 Segment 1 - Semiconductor Atoms http://www.youtube.com/watch?v=qkjCe0r5-cw Introduction to Semiconductor Materials (2) http://www.youtube.com/watch?v=AgkQrCeJF1Y&NR=1 Semiconductors Theory 1 Segment 2A - Doped Silicon Crystal http://www.youtube.com/watch?v=U8daujO20nM&feature=related

More Related