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Design of Low Threshold Voltage AlGaN/GaN High Electron Mobility Transistors for High Power Switching and Digital Logic Applications

Bhubesh Chander Joshi, Dinesh Kumar, Raj Kumar Tyagi, Chenna Dhanavantri

AlGaN/GaN HEMTs has very high threshold voltage, which makes it un-suitable for power devices and digital logic applications. In this study a polarization model for graded channel AlGaN in AlGaN/GaN high electron mobility transistors (HEMTs) has been developed by dividing the graded region into small numbers of elements, of constant Aluminum compositions. The proposed model is further extended to find an expression of total charge density due to non-vanishing polarization charge inside the graded region. A 3 dimensional electron gas (3DEG) is obtained in graded AlGaN/GaN HEMT structures. Predicted threshold voltage for graded HEMTs is lower than in conventional HEMTs. Threshold voltage of the graded device can further be tailored by using different Al composition in graded region. Maximum channel current in graded HEMT device is lower than conventional HEMT. However, with grading in AlGaN, one can grow with higher Al composition in AlGaN layer and can enhance the performance of graded AlGaN/GaN HEMT.