Diodes are the basic element of digital electronics . There are number of application of diodes from making simple digital switch to making Light Emitting Diodes . Diode is Two terminal electronic component one terminal is called anode which is positive terminal another is negative terminal called cathode .
If we connect diode in a circuit in such a way that positive terminal of diode is connected to positive part of circuit and negative terminal to negative part of circuit then in this case the diode act as a closed switch and if negative terminal of diode is connected to positive part of the circuit and positve terminal of diode is connected to negative part of circuit then it acts as a open switch hence no current flow in this case . This open close property of the diode is useful to make digital switch . we should not connect any mechanical swich to operate the device .
If we observe the current in the circuit with different voltage we can find exponential curve of the diode . This is called characteristic curve of diode . Since there is P-type material in anode terminal and N-type material at negative side of the diode , after biasing(connected to battery ) there form a region called depletion region .