In this paper, we present a novel GaN-based normally-off transistor with an integrated Si Schottky barrier diode (SBD) for low voltage DC-DC converters. The integrated SBD is formed by the Si substrate for the epitaxial growth of AlGaN/GaN hetero-structure, which is connected to the normally-off GaN Gate Injection Transistor (GIT) over it with via-holes. The diode can flow the reverse current in the conversion operation with lower forward voltage than that of the lateral GaN transistor enabling lower operating loss. A DC-DC converter from 12V down to 1.3V using the integrated devices with the reduced gate length down to 0.5μm exhibits a high peak efficiency of 89% at 2MHz demonstrating the promising potential of GaN devices for the application.
A normally-off AlGaN/GaN MOS heterojunction field-effect transistor (MOS-HFET) with a recessed gate structure formed by selective area regrowth is demonstrated. The fabricated MOS-HFET exhibits a threshold voltage of 1.7 V with an improved hysteresis of 0.5 V as compared with a device fabricated by a conventional dry etching process. An analysis of capacitance–voltage (C–V) characteristics reveals that the dry etching process increases interface state density and introduces an additional discrete trap. The use of the selective area regrowth technique effectively suppresses such degradation, avoiding the MOS interface from being exposed to dry etching. The results presented in this paper indicate that the selective area regrowth technique is promising for the fabrication of normally-off AlGaN/GaN MOS-HFETs.
High output power AlGaN/GaN metal-insulator-semicon-ductor (MIS) hetero-junction field effect transistor (HFET) on Si substrate for millimeter-wave application has developed. High temperature chemical vapor deposition (HT-CVD) grown SiN as a gate insulator improves the breakdown characteristics which enables the operation at high drain voltage of 55V. The device exhibits high drain current of 1.1A/mm free from the current collapse and high RF gain of 10.4dB. The amplifier module developed AlGaN/GaN MIS-HFET with the gate width of 5.4mm exhibits an output power of 10.7W and a linear gain of 4dB at 26.5GHz. The resultant high output power is very promising for long-distance communication at millimeter-wave in the future which would enable high speed and high density data transmission.
In this paper, high current and high voltage AlGaN/GaN metal-insulator-semiconductor (MIS) heterojunction field-effect transistors (HFETs) on Si are demonstrated. The devices exhibit a drain current of 20 A as well as a breakdown voltage of 730 V, serving normally-off operations. Stable interfacial characteristics free from the hysteresis in the transfer characteristics are enabled by the introduction of AlON gate insulator. A recessed gate structure formed by epitaxial regrowth of AlGaN over the grooved AlGaN/GaN heterojunction successfully reduces the on-state resistance and eliminates the processing damage on the surface of the grooved structure. Note that an oxygen annealing followed by the deposition of AlON shifts the threshold voltage V th to positive side. The resultant switching performance by the 20 A / 730 V AlGaN/GaN MIS-HFET is very fast with dV/dt of 78 V/ns and 169 V/ns for turn-on and turn-off transitions, respectively, indicating that the proposed MIS-HFETs are very promising for practical power switching applications.
The impacts of inserting ultrathin oxides into insulator/AlGaN interfaces on their electrical properties were investigated to develop advanced AlGaN/GaN metal–oxide–semiconductor (MOS) gate stacks. For this purpose, the initial thermal oxidation of AlGaN surfaces in oxygen ambient was systematically studied by synchrotron radiation X-ray photoelectron spectroscopy (SR-XPS) and atomic force microscopy (AFM). Our physical characterizations revealed that, when compared with GaN surfaces, aluminum addition promotes the initial oxidation of AlGaN surfaces at temperatures of around 400 °C, followed by smaller grain growth above 850 °C. Electrical measurements of AlGaN/GaN MOS capacitors also showed that, although excessive oxidation treatment of AlGaN surfaces over around 700 °C has an adverse effect, interface passivation with the initial oxidation of the AlGaN surfaces at temperatures ranging from 400 to 500 °C was proven to be beneficial for fabricating high-quality AlGaN/GaN MOS gate stacks.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)