2.3 Calculation of the thickness of the high-alloyed hemt region
The thickness of the high - alloyed HEMT region is expressed from the following formula [27]:
=
(30)
where
A – thickness of the high-alloy area;
=
,
at the same time
= 12,5 – for GaAs;
= 8,85
10-12
F/m.
Then, from formula (30) we express A:
A =
(31)
Hence, by the formula (31) we calculate A:
A =
=
=
32,69
10-9
m
=
32,69 nm
2.4 Estimation of the distance by which an electron can move from the equilibrium position in this layer at T = 300 K
The distance by which an electron can shift is determined from the expression for the Debye length [28]:
LD
=
(32)
From here, we calculate the distance by which an electron can move from the equilibrium position at T = 300 K:
LD
=
=
=
8,12
10-9
m
=
8,12 nm
3. Substantiation of the trend of using materials such as GaN, InP, SiC, diamond C in modern transistors, using the concepts: band gap width, low-field mobility, maximum drift velocity, crystal lattice constant
Table 1. Comparative characteristics of materials [29]
Material characteristics |
Si |
GaAs |
GaN |
6H-SiC |
|
C, (Diamond) |
InP |
1. Width of the bandgap, eV |
1,12 |
1,42 |
3,4 |
3,03 |
3,26 |
5,45 |
1,34 |
2. Critical field strength, kV/cm |
300 |
400 |
3000 |
2500 |
2200 |
10000 |
350 |
3. Mobility, cm2/(V s) |
1300 |
8500 |
1500 |
260 |
500 |
2200 |
5000 |
4. Saturation velocity, 105 m/s |
1,0 |
2,0 |
2,7 |
2,0 |
2,0 |
2,7 |
2,2 |
5. Heat conductivity, W/(m K) |
150 |
50 |
150 |
490 |
4901 |
2200 |
68 |
6. Relative dielectric permeability |
11,9 |
12,5 |
9,5 |
9,66 |
10,1 |
5,5 |
12,4 |
7. Maximal work temperature, K |
100 |
150 |
400 |
300 |
300 |
500 |
100 |
4H-SiCThe properties of materials with a wide band gap allow the devices to operate at extreme temperatures, excessive specific powers, increased voltages and higher frequencies, which makes them ideal for use in future electronic systems. For example, silicon carbide (SiC) and gallium nitride (GaN) are specialized WBG semiconductor materials (with a wide band gap) based on the fact that a large amount of energy is required to move electrons in these materials from the valence band to the conduction band. In the case of silicon carbide (SiC), the value is approximately 3,2 eV; in the case of gallium nitride (GaN), it is 3,4 eV, while for silicon (Si) it is 1,1 eV. The physical property of a three times wider band gap leads to a higher voltage required for breakdown, in some applications reaching up to 1700 V [30].