Find the diffusion capacitance for a silicon diode with a 15 mA forward current, if the charge carrier transit time is 70ns
Answers
Answer:
1. The diffusion capacitance of a P – N junction
(a) Decreases with increasing current and increasing temperature
(b)Decreases with decreasing current and increasing temperature
(c) Increases with increasing current and increasing temperature
(d)Does not depend on current and temperature
[GATE 19987: 2 Marks]
Soln. Diffusion capacitance exists when the junction is forward biased. The
value of Diffusion capacitance () is usually much greater than
transition Capacitance ( ). Diffusion capacitance is important for
minority change carriers.
It is given by the following relation
=
Where,
−
−
−
= 1 for Ge
= 2 for Si
VT – volt equivalent of temperature
( =
, )
If the current decreases the value of CD also decreases. Also with
temperature the value of CD decreases.