**3. HEMT electron mobility**

#### **3.1. Mobility with low electric field**

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

#### **3.2. Mobility with high electric field**

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 state and to move into the next state. This process makes the generation and recombination rate much faster resulting in better conduction of the device.
