Q14Basic Electrical Engineering

1. Forward Bias Operation: When the positive terminal of a battery is connected to the P-type (anode) and the negative to the N-type (cathode), the diode is in forward bias. This external voltage opposes the internal built-in potential barrier. As voltage increases, the depletion region narrows significantly. Once the external voltage exceeds the cut-in voltage (approx 0.7V for Silicon), electrons from the N-side are pushed across the junction into the P-side, and holes cross from P to N, resulting in a large, exponential forward current (majority carrier flow).

2. Reverse Bias Operation: When the connections are reversed, the external voltage aids the internal potential barrier. The depletion region widens, acting as an impenetrable insulator. Almost zero current flows, except for a tiny, constant 'Reverse Saturation Current' ($I_0$) caused by thermally generated minority carriers. If reverse voltage is increased too much, avalanche breakdown occurs, causing massive current flow that can destroy the device.

3. Effect of Temperature: Temperature has a profound effect on diode behavior: - In Forward Bias: The cut-in (threshold) voltage decreases linearly with an increase in temperature (by approx $-2.5\text{ mV}{/}^{\circ }\text{C}$). The V-I curve shifts to the left. - In Reverse Bias: The reverse saturation current ($I_0$) depends heavily on temperature. It roughly doubles for every $10^{\circ }\text{C}$ rise in temperature, meaning hot diodes leak significantly more current.