Characterization of AlGaN/GaN and AlGaN/AlN/GaN HEMTs in terms of mobility and subthreshold slope

This paper presents two structures of wide band gap high electron mobility transistor (HEMT). One structure is made-up of a stack of AlGaN layer over GaN layer. This structure is characterized by two-dimensional (2-D) electron gas layer formed at the interface of the AlGaN and GaN layers. The 2-D electron gas plays an important role in determining the carrier-mobility and hence drain-to-source current of HEMT. The other structure introduces an AlN spacer layer between the AlGaN and GaN layers to improve these characteristics. This paper compares the output characteristics curves and transconductance characteristics curves obtained from simulations performed using Silvaco . The modified structure with spacer layer shows improvements in carrier-mobility and hence drain-to-source current. This paper estimates and compares the subthreshold slope (SS) of the two devices. AlGaN/AlN/GaN HEMT offers an SS of 80 mV/decade whereas AlGaN/GaN HEMT offers an SS of 95 mV/decade. Thus, an improvement in SS of about 18.75 % is achieved in AlGaN/AlN/GaN HEMT compared to AlGaN/GaN HEMT. HEMT with spacer layer also offers 10 improvement in as compared to HEMT without spacer layer. The proposed HEMTs achieve 3.19 improvement in breakdown voltage, 1.3 improvement in SS compared to HEMTs previously proposed in the literature.