**4. Drain characteristics**

device vary with the doping concentration. Confinement of the electron makes it at higher ener‐ gies resulting in formation of discrete sub‐bands. The confined structures make a two‐dimen‐ sional electron gas (2DEG) resulting in less scattering and improved mobility. Considering the electron confinement and the 2DEG structure, the electron transport and band alignment is

The number of electrons confined in 2DEG depends on the thickness of the layers and the

Electron mobility in the band of the different layers with low electric field depends on the doping density in regards to the ionized impurity scattering effects at rated temperature. Reduced ionized impurity scattering with modulated doping makes a smaller number of car‐ riers with high mobility. Higher doping concentration of the doping in the HEMT devices makes the career screening resulting in higher mobility of the carriers. So the carrier concen‐ tration, mobility of the electrons, ionized scattering effect and the temperature have the cor‐

The 2DEG electrons attain greater energy and become hot with the moderate or higher elec‐ tric field. There will be an energy separation between the sub‐bands, and the high mobility electrons in the lower sub‐band get the needed energy from the applied electric field to move into the lower energy adjacent sub‐band. Higher initial mobility in the lower sub‐band results in the faster decay in mobility with the applied voltage [25]. Hence with the applied electric field, the electrons at different sub‐bands get the needed energy to move from their initial

relation between each other factor resulting in the HEMT device conductivity.

shown in **Figure 5**.

doping concentration [25].

**Figure 5.** Band alignment and 2DEG.

94 Different Types of Field-Effect Transistors - Theory and Applications

**3. HEMT electron mobility**

**3.1. Mobility with low electric field**

**3.2. Mobility with high electric field**

Drain current and the drain source voltage characteristics of the proposed HEMT device is shown in **Figure 6**. The curve reached a stable drain current at 2.5 mA and continues to be stable. Further increase in the drain current will be achieved with the increasing gate source voltage of the device. The stable saturation region in the drain characteristics will make the device operate at stable Q point resulting in proper amplification of the device when used in amplifier applica‐ tions. Increasing drain current with the lower gate voltage makes the device more suitable for faster switching operation. Faster switching speed makes the devices more suitable for the high frequency applications. This improved drain characteristics of the device proves the ability of the device to be used for the microwave application. Similar to the drain characteristics, proposed device transfer characteristics is also very high when compared to the other HEMT devices.

**Figure 6.** Drain characteristics of proposed HEMT.
