A pn-junction diode is fabricated of p-type and n-type semiconductor material. It is a two-terminal device. The terminal connected to the p-type material is called the anode; the terminal connected to the n-type material is called the cathode.
A diode is an inherently non-linear device that conducts current when the voltage across it is of one polarity and does not conduct current when the voltage across it is of the other polarity. Using the notation shown in figure 1 we can write
An analytical expression relatively 
is given as follows and is graphed in
Figure 2.
Where 
thermal
voltage = 
26m V at
room temperature
n = phenomenological factor = 1 to 2
IS = scaling current
The expression given above is valid only for steady-state conditions. When the diode voltage is switched suddenly from one value to another the current can be considerably different from that indicated above. Switching from no bias or reverse bias to forward bias is a relatively fast process in a pn-junction diode, and the current given by the ideal diode equation above is quickly established. The same can not be said about the opposite switching procedure, however. When a diode is forward biased in has a large amount of excess charge in the region near the pn-junction. When the diode is reverse biased or unbiased it does not. Thus when the diode is switched from forward to reverse bias a large reverse current flows until this charge is removed. The time it takes for this to occur is called the storage time, or ts. After the storage time the current gradually reverts to its steady-state value. The total time after it takes for the diode current and voltage to go to their steady-state values is refereed to as the reverse recovery time, or trr. See Figure 6 for the practical laboratory definitions of ts and trr.
Note: bias means applied voltage.
: -2 V to -20 V in increments of -2 V, and 0.1 to 2 V
in units of 0.1 V. For these values measure 
and 
using the DVM. The
easiest way to find 
is to measure 
and calculate 
using ohm's law. Note it may be necessary to use
different values of Rx to get the desired range of currents. Make sure to
choose values of Rx which
will allow you to plot the knee in the I-V characteristics at 
You will not be able to
measure the reverse breakdown characteristics of this diode since
it occurs at such large negative voltages.
-
data. Plot 
vs. 
. In your report
compare your data with the theory. 
along the x-axis
(channel 1) and 
(or
equivalently 
)
along the y-axis (channel 2). 
to zero.
Set volts/div (sensitivity) of channel 1 to 200mV/div. Set
volts/div of channel 2 such that each division on the vertical
axis represents 1.0mA. Adjust the position knobs so the
"dot" on the scope screen is centered. Push the
AUTO-STORE button; "STORE" should be visible in the
upper left of the scope screen. Increase 
and note the forward bias characteristic
of the diode. Turn off the storage feature by pushing the
AUTO-STORE button. Return the "dot" to the scope screen
center by turning 
to
zero. 
and repeat the procedure of the above paragraph to
obtain the reverse bias characteristic. 
. 
, and estimate the Zener resistance, 
. 
, and reverse recovery time, 
, of the diode. 
