lecture 2 l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Lecture #2 PowerPoint Presentation
Download Presentation
Lecture #2

Loading in 2 Seconds...

play fullscreen
1 / 11

Lecture #2 - PowerPoint PPT Presentation


  • 140 Views
  • Uploaded on

Lecture #2. OUTLINE Electrons and holes Energy-band model Read: Chapter 2 (Section 2.2). Electronic Properties of Si.  Silicon is a semiconductor material. Pure Si has a relatively high electrical resistivity at room temperature.  There are 2 types of mobile charge-carriers in Si:

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Lecture #2' - mandana


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.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
lecture 2

Lecture #2

OUTLINE

Electrons and holes

Energy-band model

Read: Chapter 2 (Section 2.2)

electronic properties of si
Electronic Properties of Si

Silicon is a semiconductor material.

  • Pure Si has a relatively high electrical resistivity at room temperature.

 There are 2 types of mobile charge-carriers in Si:

  • Conduction electronsare negatively charged;
  • Holesare positively charged.

 The concentration (#/cm3) of conduction electrons & holes in a semiconductor can be modulated in several ways:

    • by adding special impurity atoms ( dopants )
    • by applying an electric field
    • by changing the temperature
    • by irradiation

EE130 Lecture 2, Slide 2

bond model of electrons and holes

Si

Si

Si

Si

Si

Si

Si

Si

Si

Bond Model of Electrons and Holes

2-D representation:

When an electron breaks loose and becomes a

conduction electron, a hole is also created.

EE130 Lecture 2, Slide 3

what is a hole
Mobile positive charge associated with a half-filled covalent bond

Treat as positively charged mobile particle in the semiconductor

Fluid analogy:

What is a Hole?

EE130 Lecture 2, Slide 4

the hole as a positive mobile charge
The Hole as a Positive Mobile Charge

EE130 Lecture 2, Slide 5

pure si
Pure Si

conduction

ni 1010 cm-3 at room temperature

EE130 Lecture 2, Slide 6

definition of terms
Definition of Terms

n = number of electrons/cm3

p = number of holes/cm3

ni= intrinsic carrier concentration

In a pure semiconductor,

n = p = ni

EE130 Lecture 2, Slide 7

si from atom to crystal
Si: From Atom to Crystal

Energy states in Si atom  energy bands in Si crystal

  • The highest nearly-filled band is the valence band
  • The lowest nearly-empty band is the conduction band

EE130 Lecture 2, Slide 8

energy band diagram
Energy Band Diagram

Ec

electron energy

Ev

distance

Simplified version of energy band model, indicating

  • bottom edge of the conduction band (Ec)
  • top edge of the valence band (Ev)
  • Ec and Ev are separated by the band gap energy EG

EE130 Lecture 2, Slide 9

summary
Summary
  • In a pure Si crystal, conduction electrons and holes are formed in pairs.
    • Holes can be considered as positively charged mobile particles which exist inside a semiconductor.
    • Both holes and electrons can conduct current.
  • Splitting of allowed atomic energy levels occurs in a crystal
    • Separation between energy levels is small, so we can consider them as bands of continuous energy levels
      • Highest nearly-filled band is the valence band
      • Lowest nearly-empty band is the conduction band

EE130 Lecture 2, Slide 10

slide11
Energy-band diagram:
    • Shows only bottom edge of conduction band Ecand top edge of valence band Ev
    • Ec and Ev are separated by the band-gap energy EG

EE130 Lecture 2, Slide 11