Tunneldiode
The tunnel diode, discovered in 1957 by the Japanese Leo Esaki ( therefore also referred to as Esaki diode ), a high-frequency semiconductor device.
Construction
It consists of a pn-junction, in which both sides are heavily doped. A plurality of commercial tunnel diodes are made of an n-doped germanium, or gallium arsenide layer in a smaller layer of indium is alloyed (also called Indiumpille ). And silicon, and gallium have been used for the production, but it is difficult with the use of these materials to achieve an acceptable figure of merit ( a high ratio ).
The doping of the p- and n-side is so high that they are above the effective density of states Nc and Nv. The densities are in ranges 1019-1021 cm -3. Thus, the semiconductor regions are degenerate. The Fermi level is in the conduction band of the n-type semiconductor and in the valence band of the p-type semiconductor. This means that electrons occupied and unoccupied areas on ( almost) the same potential ( energy level ) are, thus, the tunnel effect occurs. Because of the high doping on either side of the width W of the barrier layer is less than 10 nm at zero bias Therefore, values greater than 106 V / cm achieve the electrical field in this region. Is the general formula for the barrier layer width
In this formula, εH are the permittivity of the semiconductor, UD is the diffusion and the applied voltage U, q is the elementary charge, and NA and ND acceptor and donor concentrations.
In the picture can be seen that the diode in the range is a negative differential resistance; That is, in this range results in an increasing voltage to a descending current, instead - as in all the conventional materials - in a rising current. For example, a connected resonant circuit are undamped ( oscillator ). Therefore belongs to the active dynamic components.
A similar function, but with a greater range of operation, have lambda diodes, which can be modeled by a simple electronic circuit, consisting of JFETs.
Life
Germanium tunnel diodes are very sensitive to temperature and may already be happening degrade that they are inoperable when careless soldering. Both germanium and GaAs tunnel diodes are sensitive to overload. In particular, GaAs TD age within months and no longer work, if operated up to the range of the normal -state voltage with Ip, even if the allowable power dissipation is not exceeded.
Rule of thumb for the limit for safe operation:
- I avg: Average operating current
- Cj: junction capacitance
Applications
Tunnel diodes ( up to a few 10 GHz), switches and oscillators ( up to 100 GHz ) may be used at very high frequencies as an amplifier. This is due to the inertia-free quantum mechanical tunneling process, which can be seen in the current -voltage characteristic.
Superconducting tunnel diodes can be used as Phononenemitter or Phononendetektor.