SEMICONDUCTOR DEVICE PHYSICS AND DESIGN

316 CHAPTER 7. TEMPORAL RESPONSE OF DIODES AND BIPOLAR TRANSISTORS

+

R

i(t)

v(t)

VR

VF

0

t 2

Time t

+

(a)

(b)

i(t)

t (^2) T/2
t
t 3
τsd τt
–IR
IF
0
i
I 0
I
–IR
IF
Va
0
Static
current
Switching
current
(d)
t 2
Time
t
τsd τt
VR
v(t)
V
0
Diode voltage
(c)
EXCESS Increasing time
MINORITY CHARGE
n-region x
pn
0
Current
t< t 2
t =
pno
TURN OFF
Dynamic current
in the diode
Figure 7.5: Turn-OFF characteristics of ap−ndiode: (a) The external voltage switches from
VFtoVRatt=t 2. (b) A schematic of the current in the circuit and the current path (right)
superimposed on the steady state I-V of a diode. (c) Minority charge distribution change. (d)
Voltage across the diode.