Ch 1b 2006

Ch 1b 2006 - The important thing to note for semiconductor...

Info iconThis preview shows pages 1–7. Sign up to view the full content.

View Full Document Right Arrow Icon
The important thing to note for semiconductor operations is that the only e- of interest are the ones in the CB. These e- in the CB are the only charge carriers that we care about in device physics. All of the previous analysis holds for holes where the only holes of interest (the charge carriers) are located in the VB. A hole is the empty state in the VB that we discussed previously. A hole can also be visualized as the motion of an empty state on a bond (missing bond) of an atom that propagates when it is filled by an electron from a neighboring bond. The motion of this missing bond (hole) is exactly opposite to the electron that was just captured by the atom with the missing bond. We can also can look at this in terms of the energy band diagram where the removal of an e- from the VB creates and empty state in a vast sea of filled states. This empty state moves about freely in the lattice (like a bubble in a liquid) because of the cooperative motion of the valence e-. EE 329 Introduction to Electronics Spring 2006 14
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
So what exactly is a hole? We know from quantum mechanics (QM) that electrons can move only between allowed quantum states. If we envision a series of allowed states with each of them occupied by an electron except for one at the end (empty state), and we apply a + charge at that end, we see the electrons moving towards the + charge hopping from one allowed state to the next. We now look at the process of e- and h+ creation in detail. At 0 K all the bonds are intact as shown below and all the e- are in the VB and the CB is empty. EE 329 Introduction to Electronics Spring 2006 15
Background image of page 2
Next we raise the temperature of the crystal and some of the covalent bonds begin breaking as shown below. Note that by breaking a Si – Si bond we always create an e- h+ pair (ehp). EE 329 Introduction to Electronics Spring 2006 16
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
If we apply an external electric field we get movement of the e- and h+ (in opposite directions). Look at the apparent motion of the empty state (hole) in the figure below as it moves to the right (equivalent to an e- moving to the left). What we have here could be described as the motion of a positively charged particle and this is what the hole represents. The interesting thing in a semiconductor is that this empty state actually “appears” to have mass and momentum just like a “real” particle. Another interesting note is that the hole generally has a different mass than the electron. From here on we will treat the electron and hole as equivalent charge carrying particles with opposite charge and slightly different masses. EE 329 Introduction to Electronics Spring 2006 17
Background image of page 4
EE 329 Introduction to Electronics Spring 2006 18
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Another way to look at this would be to take one e- from a perfect Si lattice. The lattice becomes + charged and the Si atom that lost that e- will soon pull an e- from a nearby Si atom and this process will continue. We know that the overall lattice is + charged, and we can say that the hole is the localization of that + charge
Background image of page 6
Image of page 7
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 09/10/2011 for the course EE 3114 taught by Professor Moon during the Spring '10 term at NYU Poly.

Page1 / 16

Ch 1b 2006 - The important thing to note for semiconductor...

This preview shows document pages 1 - 7. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online