A p–n junction is formed at the boundary between a P-type and N-type semiconductor created in a single crystal of semiconductor by doping, for example by ion implantation, diffusion of dopants, or by epitaxy (growing a layer of crystal doped with one type of dopant on top of a layer of crystal doped with another type of dopant).
If a diode is reverse biased, the voltage at the cathode is higher than that at the anode. Therefore, no current will flow until the diode breaks down. Connecting the P-type region / layer to the negative terminal of the battery and the N-type region / layer to the positive terminal, corresponds to reverse bias. Because the p-type material is now connected to the negative terminal of the power supply, the ‘holes’ in the P-type material are pulled away from the junction, causing the width of the depletion zone to increase. Similarly, because the N-type region is connected to the positive terminal, the electrons will also be pulled away from the junction. Therefore the depletion region widens, and does so increasingly with increasing reverse-bias voltage. This increases the voltage barrier causing a high resistance to the flow of charge carriers thus allowing minimal electric current to cross the p–n junction. The increase in resistance of the p–n junction results in the junction behaving as an insulator.
Electric field is an electric property associated with each point in space when charge is present in any form. The magnitude and direction of the electric field are expressed by the value of E (in unit of Volt/cm), called electric field strength or electric field intensity or simply the electric field. The picture below shows a simulation of electric field simulation in a reverse-biased p-n junction diode.