In GaN-based high-electron mobility transistors, although excellent electron confinement has been demonstrated using a graded AlGaN buffer with linearly decreasing Al-content along [0001] direction, guidelines for graded buffer design are still lacking. To obtain overall pictures of the carrier distribution and energy-band profile in AlGaN/GaN/graded AlGaN buffer heterostructures, the influences of the related physical parameters of the buffer are studied by one-dimensional self-consistent simulation. The results show that the negative polarization charge over the buffer can induce free holes in the depths of the buffer, resulting in the coexistence of electrons and holes. By adjusting the related physical parameters of the buffer, it is even possible to form two-dimensional holes gas (2DHG) at the channel/graded buffer interface. The cause of the coexistence of electrons and holes and the formation condition of 2DHG are analyzed. In addition, in the course of the variation of the related physical parameters, the characteristics of the two-dimensional electron gas density are also exhibited. This study can provide a reference for graded AlGaN buffer design in GaN-based field-effect transistors.
Using the semi-insulating property and small lattice constant a of wurtzite BGaN alloy, we propose a BGaN buffer with a B-content of 1% to enhance two-dimensional electron gas (2DEG) confinement in a short-gate AlGaN/GaN highelectron mobility transistor (HEMT). Based on the two-dimensional TCAD simulation, the direct current (DC) and radio frequency (RF) characteristics of the AlGaN/GaN/B 0.01 Ga 0.99 N structure HEMTs are theoretically studied. Our results show that the BGaN buffer device achieves good pinch-off quality and improves RF performance compared with GaN buffer device. The BGaN buffer device can allow a good immunity to shift of threshold voltage for the aspect ratio (L G /d) down to 6, which is much lower than that the GaN buffer device with L G /d=11 can reach. Furthermore, due to a similar manner of enhancing 2DEG confinement, the B 0.01 Ga 0.99 N buffer device has similar DC and RF characteristics to those the AlGaN buffer device possesses, and its ability to control short-channel effects (SCEs) is comparable to that of an Al 0.03 Ga 0.97 N buffer. Therefore, this BGaN buffer with very small B-content promises to be a new method to suppress SCEs in GaN HEMTs.
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