3.1 GaN usage trend

There is a direct relationship between the band gap and the critical strength of the breakdown field of the (electrical) conductor. Gallium nitride boasts a breakdown field strength of 3000 kV/cm, while the breakdown field strength of silicon is 300 kV/cm, which demonstrates approximately ten times the ability of gallium nitride to maintain high voltages. Such breakdown field strengths make the connections significantly more adapted to work with higher voltages and generate lower leakage currents [30].

he high mobility of electrons and the rate of their saturation in WBG semiconductors make it possible to work at higher frequencies. Gallium nitride demonstrates electron mobility of the order of 1500 cm²/V s. That is, gallium nitride (GaN) is suitable for high-speed switching.

The wide band gap makes it possible for the GaN transistor to operate at high levels of temperature and radiation. Theoretically, GaN-based transistors with a band gap of 3,4 eV should remain operational at temperatures up to 400°С. In practice, at present, the maximum temperature of stable operation of transistors made on silicon carbide substrates is more than 200°С.

The record specific power density is one of the most outstanding achievements in the field of creating high-frequency GaN components of a new generation. The maximum critical electric field strength (10 times greater than that of silicon) makes it possible to realize breakdown voltages of 100 - 300 V and raise the operating drain voltage to 50 - 100 V, which, combined with a high current density, provides a specific output power of industrial GaN transistors of 3 - 10 W per 1 millimeter of gate width (up to 30 W/mm in laboratory samples), which is an order of magnitude higher than the specific output power of GaAs transistors. A high drain supply voltage leads to an order of magnitude increase in the impedance of the drain load and a significant facilitation of matching the transistor with the load [31].

 Due to the significantly higher thermal conductivity of both epitaxial films and the carrier substrate, as well as due to the three times greater band gap in transistors based on gallium nitride (GaN), large power values from one component are achieved, while reducing the size of the final products and eliminating the need for cooling systems.

The use of GaN transistors will reduce energy consumption in electric motor start-up systems, protect power grids from overloads and unexpected outages. In addition, a very high concentration of electrons in the region of a two-dimensional electron gas, combined with acceptable electron mobility, makes it possible to realize a large transistor current density and a high gain. 

Table 2. Microsemi GaN transistors [31]

Transistor	Operating frequencies, GHz	Power, W	Gain, dB	Drain-source breakdown voltage, V
2729GN-150	2,7-2,9	160	14	250
2729GN-270	2,7-2,9	280	14	250
2731GN-110	2,7-3,1	120	12	250
2731GN-200	2,7-3,1	220	12	250
3135GN-100	3,1-3,5	115	12	250
3135GN-170	3,1-3,5	180	12	250
2735GN-35	2,7-3,5	30	11	250
2735GN-100	2,7-3,5	100	11	250

Thus, the advantages of GaN are:

1. A high value of the critical field strength and the associated high breakdown voltage;

2. High electron mobility;

3. Stability of operation at high temperatures;

4. Simplicity and cheapness of circuit implementation;

5. Ease of obtaining wide gain bands, overlapping of several frequency ranges with one powerful transistor.