Final answer:
Negative voltage to P-type and positive to N-type results in a reverse-biased diode, while positive to P-type and negative to N-type results in a forward-biased diode.
Step-by-step explanation:
When a negative voltage is applied to the P-type material of a diode and positive voltage is applied to the N-type material, the diode is reverse-biased. When a positive voltage is applied to the P-type material of a diode and negative voltage is applied to the N-type material, the diode is forward-biased.
In forward bias, the depletion layer is narrowed, allowing electrons and holes to recombine and current to flow easily through the diode. In reverse bias, the depletion layer is widened and the potential energy difference across the p-n junction is increased, significantly reducing the current flow. The semiconductor diode acts like a one-way valve for current flow, only allowing current to pass in one direction under a forward bias condition.