1. A silicon pn junction diode at T=300kelvin has a reverse-saturation current of Is=10^-3A. The diode is?

Question

forward-biased with a resulting current of 1mA. Determine Vd.

2. Use a computer simulation to generate the current-voltage characteristics of a diode with Is=10^-12 at temperature of a. T=0degrees b. T=75degrees celsius.

Answer 1

1) I rev = 1mA at room temperature? not a very good diode.

VF is about 0.6 volts if it is a silicon diode, but from the reverse leakage, it could be a geranium diode, with VF about 0.3 volts.

2) not enough info

Answer 2

Shockley diode equation:

If = Is * (e^[qV/kT] - 1)

If is the forward current

Is is the saturation current

V is the forward voltage across the diode.

q is the charge on an electron : 1.602E-19 Coulomb

k is Boltzmanns constant: 1.38065 Joules/Kelvin

T is 300 Kelvin

q/kT = 38.7

0.001 = 0.001*(e^[V*38.7]  - 1)

V = 18 mV

For question 2, simply use Microsoft Excel and set up an array of voltages starting with negative voltages, increasing into positive values in Column A, then in column B use the Shockley equation and calculate the corresponding current fir each voltage in col. A.  

Then plot columns A and B in an X-Y scatter plot.  

Repeat for the 2 different temperatures.

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