Characteristics   4 Electrical properties of HEMT

   4.2 RF performance


HEMT RF structure

To study dynamic characteristics it is needed to demonstrate a simulation of an appropriated and recessed n-GaN/AlxGa1-xN/GaN HEMT which schematic cross section is shown on figure left. Aluminum content equal to 10% in AlxGa1-xdonor layer, the gate-source spacing equal to 0.35µm, and the gate length equal to 50nm was set. The cap-layer is n-doped with a concentration equal to 5×1021cm-3, and the donor layer is n-doped with a concentration equal to 2×1020cm-3. All other layers are nonintentionally doped.

At high frequencies, the HEMTs are characterized by two important parameters: the cut-off frequency fT for which the modulus of the current gain is equal to 1 (0dB), and the maximum oscillation frequency fmax for which the unilateral power gain is equal to 1 (0dB). We calculate these two frequencies at room temperature; results are given respectively in Figs. 4.4 a) and b). At room temperature, the simulated cut-off frequency fT of about 331 GHz, and a maximum oscillation frequency fmax of about 1.1 THz which is a very promissing result for high frequency applications.(1)

  HEMT RF AD gain    HEMT RF power gain

Fig. 4.4 Evolution of the a) current gain as a function of frequency b) power gain as a function of frequency(1)


(1) A. Hamdoune, M. Abdelmoumene, A. Hamroun, Static and Dynamic Characteristics of an Appropriated and Recessed n-GaN/AlGaN/GaN HEMT, World Academy of Science, Engineering and Technology International Journal of Electrical, Computer, Energetic, Electronic and Communication Engineering Vol:7, No:1, 2013, [online]