半导体英文课件-Electrons and Holes in Semiconductors.ppt

Modern Semiconductor Devices for Integrated Circuits (C. Hu) Slide 1-* GaAs, III-V Compound Semiconductors, and Their Dopants As As Ga Ga · GaAs has the same crystal structure as Si. · GaAs, GaP, GaN are III-V compound semiconductors, important for optoelectronics. · Wich group of elements are candidates for donors? acceptors? Ga As As Ga Ga Modern Semiconductor Devices for Integrated Circuits (C. Hu) Slide 1-* 1.3 Energy Band Model · Energy states of Si atom (a) expand into energy bands of Si crystal (b). · The lower bands are filled and higher bands are empty in a semiconductor. · The highest filled band is the valence band. · The lowest empty band is the conduction band . Modern Semiconductor Devices for Integrated Circuits (C. Hu) Slide 1-* 1.3.1 Energy Band Diagram Conduction band E c E v E g Band gap Valence band · Energy band diagram shows the bottom edge of conduction band, Ec , and top edge of valence band, Ev . · Ec and Ev are separated by the band gap energy, Eg . Modern Semiconductor Devices for Integrated Circuits (C. Hu) Slide 1-* Measuring the Band Gap Energy by Light Absorption photons photon energy: h v E g E c E v E g electron hole Bandgap energies of selected semiconductors Eg can be determined from the minimum energy (hn) of photons that are absorbed by the semiconductor. Semi-conductor InSb Ge Si GaAs GaP ZnSe Diamond Eg (eV) 0.18 0.67 1.12 1.42 2.25 2.7 6 Modern Semiconductor Devices for Integrated Circuits (C. Hu) Slide 1-* 1.3.2 Donor and Acceptor in the Band Model Conduction Band E c E v Valence Band Donor Level Acceptor Level E d E a Donor ionization energy Acceptor ionization energy Ionization energy of selected donors and acceptors in silicon Modern Semiconductor Devices for Integrated Circuits (C. Hu) Slide 1-* 1.4 Semiconductors, Insulators, and Conductors · Totally filled bands and totally empty bands do not allow · Metal conduction band is half-filled. E c E v E g = 1.1 e