The following is part of a student’s report of an experiment to investigate the variation of current I with potential difference V for a semiconductor diode - Leaving Cert Physics - Question 4 - 2007

The student varied and measured the potential difference using the following methods:

1. Adjust Voltage: The student adjusted the potential difference by using a variable power supply.
2. Measurement: The current was measured by connecting a voltmeter across the diode to note the voltage at various current readings. This was done at each step of increasing potential until the circuit reached a point where current began to flow.

To draw the graph:

1. Axes: Label the x-axis as 'Voltage (V)' and the y-axis as 'Current (mA)'.
2. Plotting Points: Plot the recorded data points on the graph:
   • (0.60, 2)
   • (0.64, 4)
   • (0.68, 10)
   • (0.72, 18)
   • (0.76, 35)
   • (0.80, 120)
3. Curve Shape: Connect the points to show how the current increases exponentially with increasing voltage, which typically indicates diode behavior. Ensure correct curvature and labeling.

The junction voltage can be estimated by examining the graph and identifying the voltage at which the current begins to increase significantly. Based on the data provided and the curve shape, the junction voltage of the diode is approximately:

$V_{junction} ext{ } approximately ext{ } 0.60 ext{ } to ext{ } 0.68 ext{ } V$

When placing the diode in reverse bias, the student made the following changes:

1. Reversed Polarity: The diode was connected in reverse orientation, meaning the anode was connected to the negative terminal of the battery.
2. Measurement Changes: The ammeter remained in series, but the measurements were now expected to show little to no current flow until the diode's breakdown voltage was reached.

To sketch the graph for the diode in reverse bias:

1. Axes: Label the x-axis as 'Voltage (V)' and the y-axis as 'Current (mA)'.

2. Curve Shape: Initially, the current should remain at zero until a certain reverse voltage (the breakdown voltage) is reached. After this point, the current might increase significantly. The sketch should resemble:

   • A horizontal line close to zero for small reverse voltage.
   • A steep curve indicating a sudden increase if breakdown occurs.

3. Labeling: Clearly label any significant points, such as breakdown voltage and negative current values.