Review of P-N diode characteristics
Fig: Space change density the electric field and the electric potential inside a p-n junction under (a) thermal equilibrium condition, (b) reverse biased condition, (c) forward biased condition.
- A p-n junction diode is formed by placing p and n type semiconductor materials in intimate contact on an atomic scale. This may be achieved by diffusing acceptor impurities in to an n type silicon crystal or by the opposite sequence.
- In an open circuit p-n junction diode, majority carriers from either side will defuse across the junction to the opposite side where they are in minority.
- These diffusing carriers will leave behind a region of ionized atoms at the immediate vicinity of the metallurgical junction. This region of immobile ionized atoms is called the space charge region.
- This process continues till the resultant electric field (created by the space charge density) and the potential barrier at the junction builds up to sufficient level to prevent any further migration of carriers.
- At this point the p-n junction is said to be in thermal equilibrium condition. Variation of the space charge density, the electric field and the potential along the device is shown in Fig above.