When studying the mechanism of rectification of a variablecurrent in the contact area of two different media - a semiconductor and a metal, a hypothesis was advanced that it is based on the so-called tunneling effect of charge carriers. However, at that time (1932) the level of development of semiconductor technologies did not allow us to confirm the guess by experience. Only in 1958 the Japanese scientist Esaki managed to confirm it brilliantly, creating the first-ever tunnel diode. Due to its amazing qualities (in particular, speed), this device attracted the attention of specialists of various technical fields. Here it is worth explaining that a diode is an electronic device, which is a combination of two different materials in a single case with different types of conductivity. Therefore, the electric current can pass through it in only one direction. The polarity reversal leads to a "closing" of the diode and an increase in its resistance. Increasing the voltage leads to "breakdown".
Consider how the tunnel diode works.The classical rectifier semiconductor device uses crystals with an amount of impurities not exceeding 10 to the power of 17 (-3 centimeter). And since this parameter is directly related to the number of free charge carriers, it turns out that the latter can never be greater than the specified limit.
There is a formula that allows us to determine the thickness of the intermediate zone (the p-n transition):
L = ((E * (Uk-U)) / (2 * Pi * q)) * ((Na + Nd) / (Na * Nd)) *
where Na and Nd are the number of ionized acceptorsand donors, respectively; Pi-3.1416; q is the value of the electron charge; U is the input voltage; Uk is the potential difference at the transition section; E is the value of the dielectric constant.
The consequence of the formula is the fact that forp-n junction of the classical diode is characterized by low field strength and a relatively large thickness. In order for electrons to get into the free zone, they need additional energy (communicated from outside).
The tunnel diode uses in its constructionsuch types of semiconductors, which change the content of impurities to 10 to the power of 20 (-3 centimeter), which is an order of magnitude different from the classical ones. This leads to a drastic reduction in the thickness of the transition, a sharp increase in the field strength in the region of the p-n region and, as a consequence, the appearance of a tunnel junction, when the electron does not need additional energy to enter the valence band. This is because the energy level of the particle does not change as the barrier passes. The tunnel diode can be easily distinguished from conventional ones by its current-voltage characteristic. This effect creates a kind of splash on it - a negative value of the differential resistance. Due to this, tunnel diodes are widely used in high-frequency devices (a decrease in the thickness of the p-n gap makes such a device high-speed), accurate measuring equipment, generators and, of course, computer technology.
Although the current in the tunnel effect is capable offlow in both directions, with a direct connection of the diode, the intensity in the transition zone increases, decreasing the number of electrons capable of tunneling. An increase in voltage leads to the complete disappearance of the tunneling current and the effect is only on the ordinary diffuse (as in classical diodes).
There is also another representative of similardevices - the reversed diode. It is the same tunnel diode, but with changed properties. The difference is that the value of conduction at the reverse connection, in which the ordinary rectifying device "closes", it has higher than with the direct one. The remaining properties correspond to the tunnel diode: speed, small intrinsic noise, the ability to straighten the variable components.
