week3 - Devices Semiconductor Physics review Diode MOS...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Devices Semiconductor Physics review Diode MOS transistor Semiconductor Physics Charge carriers in semiconductors : electrons, holes Why do we consider holes? Æ In metals, there are so many electrons that we don’t really care about holes . Æ Metals are often conductor. Æ In semiconductor, number of free electrons may not be a lot but you will still see some condition which is due to holes. Æ This is the concept of hole and why it is slower. Empty parking lot Full parking lot 1 2 3 4 Æ Much slower process Æ If you look at the empty space it looks like empty space is moving in the other direction. Æ Fast process
Background image of page 1

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

View Full DocumentRight Arrow Icon
NMOS transistor Æ conduction using electrons, much faster devices PMOS transistor Æ conduction using holes, slow devices Semiconductors Intrinsic Æ # of holes # of electrons, pure semiconductors are intrinsic N-type Æ # of electrons >> # of holes P-type Æ # of electrons << # of holes How to make n-type Add impurities that have an extra electron to give How to make p-type Si Si Si Si Si Si Si P Extra electron becomes a free electron with a very small energy received from thermal energy. 10 23 /cm 3 Si atom If you have 10 19 /cm 3 P you get a very good conductor. Material is neutral for every free electron Material is neutral for every free holes Si Si Si Si Si Si Si In Empty space , a hole is generated. There is a negative charged ion (In). There is a positive charged ion (P).
Background image of page 2
Diode Diode is made when you connect an N-type and P-type semiconductors together. P N What happens next? There will be a current flowing since positive and negative free charges attract each others and recombine. Æ Electron fills up the hole. Now electron and holes cannot go to the opposite side unless give them enough potential to go through the depletion region. No free electron or hole but ions are there so material is charged N D : number of free electrons in N-type (Donor) = number of charged ions ~ number of n- impurity N A : number of free holes in P-type (Acceptor) = number of charged ions ~ number of p- impurity Depletion region Neutral Neutral Free electrons Free holes There is an electric field in the depletion region.
Background image of page 3

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

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 15

week3 - Devices Semiconductor Physics review Diode MOS...

This preview shows document pages 1 - 4. Sign up to view the full document.

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