1. Chapter 3, Current in Homogeneous Semiconductors
Carrier Motion
Current Flow
Drift
Diffusion
Recombination/Generation
Continuity Equations
Use of Continuity Equations

2. Drift: Motion due to the electric field.
Diffusion: Net motion from high to low concentration.
Both very important in devices.
Apply electric field, what happens to an electron.
F=qE, so the (quasi) free electron accelerates.
The velocity increases
Velocity is limited by collisions with imperfections like:
phonons
impurities
Eventually the effective mass approximation may not be valid.

4. Optical Phonons
Ionization
Intra-valley scattering
Inter-valley scattering

16. Optical Phonons
Ionization
Intra-valley scattering
Inter-valley scattering

19. Notation Reminder
no, po: equilibrium
n, p: general carrier concentrations

24. Reference: Pierret, Section 5.2

27. Electrons added to condution band. Electrons removed.
Holes removed.
Holes added to valence band. 3

28. (Definitions)

30. From nT/NT no

36. Note: R corresponds to generation here!!

37. Reference: Pierret, Section 5.3.

38. Next: Continuity Equations

39. (Fn – flux of electrons)

40. Depend on details of situation.
Equilibrium
Excess carriers
Gop is from light shining on the semiconductor
Normal recombination.
Depend on details of situation.

41. + - -
(Error in eq. 3.66, Text, p. 141)

44. For normal, low-level injection, p<<ND

46. Minority carrier diffusion length for holes.

48. For direct bandgap semiconductors, R=βnp for direct band to band recombination.