the study of the mechanism of rectification of alternating current in the area of contact between two different environments - the semiconductor and the metal, it has been hypothesized that it is based on the so-called tunnel effect of carriers.However, at that time (1932) the level of development of semiconductor technology is not allowed to confirm the conjecture empirically.Only in 1958, a Japanese scientist Esaki was able to confirm it brilliantly, creating the first in the history of the tunnel diode.Thanks to its amazing quality (particularly speed), this product has attracted the attention of specialists in various technical areas.It is clear that the diode - an electronic device that is a union in a single case of two different materials with different types of conductivity.Therefore, electric current can flow through it in one direction only.Change of polarity leads to the "closed" diode and increase its resistance.The increase in voltage leads to a "breakdown".
Consider how the tunnel diode.Classic rectifier semiconductor device uses a crystal having a number of impurities not more than 10 at 17 degree (degree -3 centimeters).And since this parameter is directly related to the number of free charge carriers, it turns out that the past can never be more than the specified boundary.
There is a formula that allows to determine the thickness of the intermediate zone (transition pn):
L = ((E * (Uk-U)) / (2 * Pi * q)) * ((Na + Nd) / (Na* Nd)) * 1050000,
where Na and Nd - number of ionized donors and acceptors, respectively;Pi - 3.1416;q - the value of the electron charge;U - applied voltage;Uk - potential difference at the transition area;E - dielectric constant.
consequence of the formula is the fact that the pn junction diode classic characterized by low field strength and a relatively large thickness.To the electrons could get a free zone, they need additional energy (imparted from the outside).
tunnel diode in its design uses these types of semiconductors, which alter the impurity content to 10 to 20 degree (degree -3 cm) which is much different from the classical ones.This leads to a drastic reduction in the thickness of the transition, a sharp increase of the field strength in the pn region and, as a consequence, the emergence of the tunnel junction, when the electron to get into the valence band does not need additional energy.This occurs because the energy level of the particles is not changed during the passage barrier.The tunnel diode can be easily distinguished from the ordinary by its current-voltage characteristic.This effect makes her a kind of surge - negative differential resistance.Through this tunnel diodes are widely used in high-frequency devices (thickness reduction pn period makes such a fast device), precision measuring equipment, generators and, of course, computers.
Although current at the tunnel effect is able to flow in both directions, with a direct connection diode tension in the transition zone is increased by reducing the number of electrons capable of tunnel passage.The increase in voltage leads to the complete disappearance of the tunnel current and the impact is only on the usual diffuse (as in classical diodes).
There is also one more representative of such devices - facing diode.It is the same tunnel diode, but with altered characteristics.The difference is that the value of the conductivity of the reverse connection, in which a conventional rectifying device "locked", it is higher than the direct.The other properties correspond to the tunnel diode: performance, low self-noise, the ability to straighten the variable components.
