Enhanced sheet carrier densities in polarization controlled AlInN/AlN/GaN/InGaN field-effect transistor on Si (111)

We report on GaN based field-effect transistor (FET) structures exhibiting sheet carrier densities of n = 2.9 10¹³ cm⁻² for high-power transistor applications. By grading the indium-content of InGaN layers grown prior to a conventional GaN/AlN/AlInN FET structure control of the channel width at the GaN/AlN interface is obtained. The composition of the InGaN layer was graded from nominally x_In = 30 % to pure GaN just below the AlN/AlInN interface. Simulations reveal the impact of the additional InGaN layer on the potential well width which controls the sheet carrier density within the channel region of the devices. Benchmarking the In_xGa_1−xN/GaN/AlN/Al_0.87In_0.13N based FETs against GaN/AlN/AlInN FET reference structures we found increased maximum current densities of I_SD = 1300 mA/mm (560 mA/mm). In addition, the InGaN layer helps to achieve broader transconductance profiles as well as reduced leakage currents