Question

Plot a graph showing the variation of current with voltage for the material GaAs. On the graph, mark the region where: (a) resistance is negative, and (b) Ohm's law is obeyed.

Hint:

GaAs and similar semiconductors show negative differential resistance, which is used in devices like Gunn diodes for microwave generation.

Answer 1

Study of Gallium Arsenide (GaAs) Characteristics

Step 1: Behaviour of GaAs

Gallium Arsenide (GaAs) is a semiconductor that exhibits negative differential resistance at higher electric fields. This unique property implies that within a specific region of its operation, an increase in voltage leads to a decrease in current.

Step 2: Ohmic Region

At low voltage levels, the current increases linearly with the applied voltage. In this phase, the material obeys Ohm's law ($V = IR$) and functions like a standard conductor. This is defined as the Ohmic region.

Step 3: Negative Resistance Region

Once the voltage exceeds a specific threshold, the current begins to drop despite a further increase in voltage. This non-linear behavior is referred to as the negative resistance region.

Step 4: Graph Representation

The relationship between Voltage ($V$) and Current ($I$) for GaAs can be visualized as follows:

Step 5: Interpretation of the Graph

The interpretation of the $V-I$ curve is divided into two main segments:

• Linear Segment: The straight line starting from the origin represents the area where Ohm’s law is strictly obeyed.
• Descending Segment: The downward-sloping portion of the curve illustrates the negative resistance region where $\frac{dV}{dI} < 0$.