Diode gunn

The Gunn diode is traditionally a gallium arsenide layer with ohmic contacts on both sides. The active part of the Gunn diode usually has a length of l to 100 μm with concentrations of doping donor impurities of 10 ¹⁴ −10 ¹⁶ cm ⁻³ . In this material, in the conduction band, there are two energy minimums, which correspond to two states of electrons - “heavy” and “light”. In this regard, with an increase in the electric field strength, the average drift velocity of electrons increases until the field reaches a certain critical value, and then decreases, tending to the rate of saturation.

Thus, if a voltage is applied to the diode that exceeds the product of the critical field strength by the thickness of the gallium arsenide layer in the diode, the uniform distribution of the voltage across the layer thickness becomes unstable. Then, even if a slight increase in the field strength occurs, the electrons located closer to the anode will “depart” from this region to it, and the electrons located at the cathode will try to “catch up” the resulting double layer of charges moving towards the anode. During movement, the field strength in this layer will continuously increase, and outside it will decrease until it reaches an equilibrium value. Such a moving double layer of charges with a high electric field strength inside is called the domain of a strong field , and the voltage at which it arises is called the threshold.

At the moment of domain nucleation, the current in the diode is maximum. As the domain is formed, the current decreases and reaches its minimum at the end of the formation. Reaching the anode, the domain is destroyed, and the current increases again. But as soon as it reaches a maximum, a new domain is formed at the cathode. The frequency with which this process is repeated is inversely proportional to the thickness of the semiconductor layer and is called the span frequency.

On the I – V characteristic of a semiconductor device, the presence of a falling section is not a sufficient condition for the appearance of microwave oscillations in it, but is necessary. The occurrence of oscillations means that instability develops in a semiconductor crystal. The nature of this instability depends on the parameters of the semiconductor (doping profile of the crystal, its size, carrier concentration, etc.).

When the Gunn diode is placed in the resonator, other oscillation modes are possible in which the oscillation frequency can be made either lower or higher than the span frequency. The efficiency of such a generator is relatively high, but the maximum power does not exceed 200-300 mW.

The effect of ohmic (non-rectifying) contacts to the crystal is significant. There are two approaches to making low-ohmic ohmic contacts necessary for supplying current for the operation of Gunn diodes:

• the first of them consists in choosing an acceptable technology for applying such contacts directly to a high-impedance gallium arsenide crystal;
• in the second approach, the crystal of the device is multilayer. In diodes with this structure, epitaxial layers of low-resistance high-alloyed gallium arsenide with n-type conductivity are grown on both sides of the layer of high-resistance low-alloyed gallium arsenide. These highly alloyed layers serve as transition substrates from the working part of the crystal to metal electrodes.

The Gunn diode can be used to create a generator in the 10 GHz and higher (up to THz) frequency range. The resonator, which can be made in the form of a waveguide is used to control the frequency.

The frequency of the generators on the Gunn diode is determined mainly by the resonant frequency of the oscillatory system taking into account the capacitive conductivity of the diode and can be tuned over a relatively wide range by mechanical (by changing the geometric dimensions of the resonator) and electric methods.

However, the service life of Gunn generators is relatively small, which is associated with the simultaneous exposure of a semiconductor crystal to factors such as a strong electric field and overheating of the semiconductor crystal of the device with the power released in it.

Gann diodes operating in various modes are used in the frequency range 1-100 GHz. In the continuous generation mode, Gann diode generators have an efficiency of about 2-4% and provide output power from units of mW to units of W. But, when using the device in pulsed mode, the efficiency increases by 2-3 times. Special broadband resonant systems allow you to add higher harmonics to the power of a useful output signal and serve to increase efficiency. This mode of operation of the generator is called relaxation.

There are several different modes of using generators on the Gunn diode depending on the supply voltage, temperature, and the nature of the load: domain mode, hybrid mode, mode of limited accumulation of space charge, and negative conductivity mode.

The most commonly used mode is the domain mode in which, for most of the oscillation period, the domain existence mode is characteristic. The domain mode can be implemented in three different types: span, with a delay in the formation of domains and with domain blanking. The transition between these types occurs when the load resistance changes.

For Gunn diodes, the mode of limiting and accumulating a space charge was also proposed and implemented. This mode takes place at large voltage amplitudes at the diode and at frequencies several times higher than the span frequency, and at average constant diode voltages that are several times higher than the threshold value. However, there are certain requirements for the implementation of this mode: the semiconductor material of the diode must be with a very uniform doping profile. In this case, a uniform distribution of the electric field and electron concentration along the length of the sample is provided due to the high rate of change of voltage on the diode.

In addition to gallium arsenide (GaAs) and indium phosphide (InP, used at frequencies up to 170 GHz), epitaxial growth is used in the manufacture of diodes, and gallium nitride (GaN) is also used to manufacture Gunn diodes. In diodes made from this material, the highest oscillation frequency of 3 THz was achieved.

The Gunn diode has a low level of amplitude noise and a low operating voltage (from units to tens of V).

When used, diodes are mounted in resonant chambers made on the surface of microcircuits with dielectric substrates in combination with capacitive and inductive components, or are used as a combination of external resonators and microcircuits.

• Semiconductors
• Gunn effect

• Avaev N.A., Shishkin G.G. Electronic devices. MAI Publishing House, 1996.
• Zi S. M. Physics of semiconductor devices (in 2 books). M., Mir, 1984, v. 2, pp. 226-269.
• Lebedev A.I. Physics of semiconductor devices. M., Fizmatlit, 2008.
• Kuleshov V.N., Udalov N.N., Bogachev V.M. and others. Generation of oscillations and the formation of radio signals. - M .: MPEI, 2008 .-- 416 p. - ISBN 978-5-383-00224-7 .

• Gann diode model program with source code (C ++, works on Windows)
• Generator diodes
• Gann effect in the Great Soviet Encyclopedia.
• Gunn effect