TABLE OF CONTENTS Recombination of carriers plays an important role in transistor physics. Imperfections within the semiconductor crystal can introduce energy levels in the forbidden gap, usually called traps or recombination centers.
The four possible transitions of an electron between an energy level in the forbidden band and the conduction or the valence bands are indicated in Fig. F.1.
The rate of electron capture r a is proportional to the concentration of free electrons n and to the concentration of traps not occupied by electrons. Thus,
where r a is the electron capture rate, v th is the thermal velocity, ? n is the capture cross-section for electrons, n is the electron concentration, N t is the trap volumetric density and f HSR is the probability of occupation of a center by an electron.
The rate of electron emission r b is proportional to the concentration of traps which are occupied by electrons. Thus,
where r b is the electron emission rate and e n is the emission probability of an electron.
The rate of capture of holes, by analogy to process (a), is given by
where r c is the hole capture rate, ? p is the capture cross-section for holes, and p is the hole concentration.
Finally, the rate...
