When we talk about electrical and electronic circuits, we use the old convention, called the conventional current flow (from positive to negative). To get rid of any idea of thinking about “electrons,” we say “electricity flows from positive to negative.” We say this in order to track all electrical and electronic circuits using the arrows indicating the direction of the conventional current.
When we talk about ELECTRON-FLOW, we use NEGATIVE to positive. We keep the ELECTRON FLOW arrows in the component we are talking about (such as a radio valve or a transistor model) and do not put electronic flow arrows on the rest of the circuit.
The most common function of a diode is to allow an electric current to pass in one direction (called the forward direction of the diode) by blocking it in the opposite direction (reverse direction). As such, the diode can be seen as an electronic version of a retention valve. This unidirectional behavior is called rectifying and is used to convert alternating current (AC) to direct current (DC). Forms of rectifiers, diodes can be used for such tasks as to extract the modulation from radio signals into radio receivers.
However, diodes may have more complicated behavior than this simple on / off action due to non-linear current voltages. Semiconductor diodes start driving electricity only if there is a certain threshold voltage or cutting voltage in the forward direction (a state in which the diode is considered to be tilted forward). The voltage drop on a biased front diode varies very little with the current and is a function of the temperature; this effect can be used as a temperature sensor or as a voltage reference.
The voltage characteristic of a semiconductor diode can be adapted by selecting semiconductor materials and doping impurities introduced into the materials during manufacture.
These techniques are used to create special purpose diodes that perform several different functions. For example, diodes are used to adjust the voltage (Zener diodes) to protect overvoltage circuits (avalanche diodes) in order to electronically adjust radio and TV receivers (varactor diodes) to generate radio frequency oscillations (tunnel diodes , diodes Gunn, IMPATT diodes), and to produce light (light emitting diodes). The tunnels, Gunn and IMPATT diodes have negative resistance, which is useful in microwave and switching circuits.