MTL Annual Report

Our group is focusing on the development of GaN power transistors grown on Si substrates. Si substrates are preferred to SiC due to their much lower cost; however, GaN devices on Si substrates suffer from lower breakdown. To increase the breakdown voltage of AlGaN/GaN HEMTs grown on Si substrates, we have developed a new technology based on the removal of the original Si substrate and subsequent transfer of the AlGaN/GaN HEMT structure to an insulating carrier wafer (e.g., glass or polycrystalline AlN) ^[1]. By applying this new technology to standard AlGaN/GaN HEMTs with a total epitaxial thickness of only 2 mm grown on a Si substrate, AlGaN/GaN HEMTs transferred to a glass substrate with breakdown voltage above 1500 V and specific on-resistance of 5.3 mΩ·cm² has been achieved, as shown in Figure 1.

The standard AlGaN/GaN HEMTs are depletion-mode (D-mode) devices. However, enhancement-mode (E-mode) devices are highly desirable for power electronics as they can greatly simplify circuit designs and improve system reliability. We have recently demonstrated a new AlGaN/GaN E-mode HEMT based on a dual-gate structure ^[2]. The device utilizes an integrated gate structure with a narrow gate controlling the threshold voltage and a long gate supporting the high voltage drop from the drain. Using this new dual-gate technology, AlGaN/GaN E-mode HEMTs grown on a Si substrate have demonstrated  a high threshold voltage of 2.9 V with a maximum drain current of 434 mA/mm and a breakdown voltage of 643 V (Figure 2).

1. B. Lu and T. Palacios, “High Breakdown (>1500 V) AlGaN/GaN HEMTs by Substrate Transfer Technology,” submitted to IEEE Elec. Dev. Lett., Mar. 2010. [↩]
2. B. Lu and T. Palacios, “High Performance Dual-Gate AlGaN/GaN Enhancement-Mode Transistor,” submitted to IEEE Elec. Dev. Lett., Mar. 2010. [↩]