0195136047.pdf

342 SEMICONDUCTOR DEVICES

pnElectrons

diffuse

Holes

diffuse

(a)

(b)

(c)

p

p

n

n

x

x

x

Immobile ions

Depletion region

Donor

Space-charge density

Electric field

Electric field

Holes drift

Electrons drift

Potential

Acceptor

−

−

−

+

+

+

Figure 7.2.2pn-junction diode with no external

voltage source.(a)Hole and electron diffusion.

(b)Depletion region.(c)Drift of electrons and holes.

junction. Increasing the reverse bias, however, does not affect the reverse current significantly

until breakdown occurs.

The static characteristic of a junction diode is shown in Figure 7.2.4(a), which describes

the dc behavior of the junction and relates the diode currentIand the bias voltageV. Such a

characteristic is analytically expressed by theBoltzmann diode equation

I=IS(eV/ηVT− 1 ) (7.2.1)

(a)

p

I

V

+−

n

(b)

I

V

+−

Figure 7.2.3pn-junction under

bias. (a) Physical structure.

(b)Semiconductor diode symbol.