1 / 20

KKK3201

KKK3201. Lecture 2. EXTRINSIC MATERIAL. The characteristic of semiconductor can be altered by adding impurity through doping process (extrinsic material) Two type: N-type P-type. N-TYPE.

vilmos
Download Presentation

KKK3201

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. KKK3201 Lecture 2

  2. EXTRINSIC MATERIAL • The characteristic of semiconductor can be altered by adding impurity through doping process (extrinsic material) • Two type: • N-type • P-type

  3. N-TYPE • N-type is created by introducing impurity elements that have five valence electrons (pentavalent) – antimony, arsenic, phosphorus • Note that four covalent bonds are still present, however there is additional fifth electron due to impurity atom • The remaining electron is free to move within the newly formed n-type material • Diffused impurities with five valence electrons are called donor atoms Figure 1.9 Antimony impurity in n-type material

  4. P-TYPE • P-type is created by doping with impurity atoms having three valence electrons – boron gallium, indium • Note that there are insufficient number of electrons to complete covalent bonds resulting a hole • This hole is ready to accept a free electron • The diffused impurities with three valence electrons are called acceptor atoms. Figure 1.11 Boron impurity in p-type material

  5. Electron versus Hole Flow

  6. Majority and Minority Carriers • In an n-type material - electron is called majority carrier and hole the minority carrier • In a p-type material – hole is majority carrier and electron is the minority carrier

  7. Semiconductor Diode • Diode is formed by bringing these two material together p- and n-type • Electrons and holes at joined region will combine, resulting in a lack of carriers in the region near the junction (depletion region)

  8. Since the diode is two-terminal device, the application of a voltage across its terminals leaves three possibilities: • No bias (VD = 0V) • Foreard bias (VD > 0V) • Reversed bias (VD < 0V) • Each condition will result in a response

  9. No Applied Bias (VD = 0V) • Under no-bias conditions, any minority carries (holes) in the n-type material find themselves within the depletion region will pass directly into p-type material • Majority carriers (electrons) of n-type material must overcome the attractive forces of the layer of positive ions in n-type material and the shield of negative ions in p-type material to migrate into the area beyond the depletion region of p-type material. • In the absence of an applied bias voltage, the net flow of charge in any one direction for semiconductor diode is zero

  10. Figure 1.14 p-n junction with no external bias

  11. Reverse-Bias Condition (VD < 0V) • The number of uncovered positive ions in the depletion region of n-type will increase due to large number of free electrons drawn to the positive potential • The number of uncovered negative ions will increase in p-type resulting widening of depletion region • This region established great barrier for the majority carriers to overcome – resulting Imajority = 0 • The number pf minority carriers find themselves entering the depletion region will not change resulting in minority-carrier flow vectors of the same magnitude • The current exists under reverse-bias conditions is called the reverse saturation current and represented by Is • Therefore, ID= -Is

  12. Figure 1-16 Reverse-biased p-n junction

  13. Forward-Bias Condition (VD = 0V) • A semiconductor diode is forward-biased when the association p-type and positive and n-type and negative has been established • The application of forward-bias potential will pressure the electrons in n-type and hole in p-type to recombine with ions near the boundary and reduce the width of depletion region • The resulting minority-carrier flow of electrons from p-type to n-type has not changed in magnitude, but the reduction in width of depletion region has resulted in a heavy majority flow across the junction

  14. Figure 1.18 Forward-biased p-n junction

  15. (1.4) For Forward-bias and Reverse-bias

  16. Figure 1.19 Silicon semiconductor diode characteristics

More Related