Physical and electrical characterizations of AlGaN/GaN MOS gate stacks with AlGaN surface oxidation treatment

Abstract

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.

Controlled oxide interlayer for improving reliability of SiO2/GaN MOS devices

“…As for the gate insulators in GaN power devices, deposited dielectric films with sufficiently large band offset against the GaN-based semiconductors, such as Al 2 O 3 , SiO 2 , and their oxynitrides, can be possible candidates for limiting the gate leakage current. [13][14][15][16][17][18][19][20][21][22][23][24] Actually, these wide bandgap insulators have been used in recent development of AlGaN/ GaN MOS-HFETs; advanced deposition techniques, postdeposition annealing, and their combinations have been investigated by many researchers. While the two-dimensional electron gas in AlGaN/GaN MOS-HFETs is separated from the insulator/semiconductor interface with the AlGaN barrier layer, inversion carriers in the GaN MOSFETs are directly accumulated at the interface.…”

Low Threshold Voltage Shift in AlGaN/GaN MIS-HEMTs on Si Substrate Using SiNx/SiON as Composite Gate Dielectric

“…Therefore, the SiN x /SiON composite gate dielectric can effectively improve the stability of the threshold voltage and reduce the threshold voltage hysteresis compared with SiN x only gate dielectric. The positive shift of the V th at V max > 2 V indicates a trapping process of electrons by the interface states between the dielectric layer and the barrier layer, or the acceptor-like traps in the barrier layer [10,29] thereby requiring a higher V th for ON-state. Figure 2d shows the comparison of the gate leakage for the two kinds of devices.…”

SiO2/AlON stacked gate dielectrics for AlGaN/GaN MOS heterojunction field-effect transistors

“…32,33) Moreover, we have recently found that the initial thermal oxidation of the AlGaN surface proceeds at lower temperatures (around 400 °C) and that, in contrast with thermal oxides on GaN surfaces, those on AlGaN surfaces do not always improve the electrical properties of the interface, especially thick thermal oxides composed of a mixture of Al and Ga oxides. 34,35) This suggests difficulties in controlling the interface with oxide interlayers and a narrow process window for fabricating highquality SiO 2 =AlGaN stacks. Figure 2 shows our preliminary study on the direct deposition of SiO 2 films on AlGaN=GaN substrates, in which bidirectional C-V curves obtained over a range of frequencies from the MOS capacitors with PECVD-SiO 2 dielectrics formed at different RF input powers are plotted.…”

“…These results mean that, while low-damage CVD conditions are preferable for fabricating AlGaN=GaN MOS devices, the SiO 2 =AlGaN interface is very sensitive to deposition conditions probably because of ion-induced damage together with the unintentional oxidation of AlGaN surfaces in the initial stage of SiO 2 growth. 35) To take advantage of the high-quality AlON=AlGaN interface and wide-bandgap SiO 2 insulator, we considered SiO 2 =AlON stacked gate dielectrics and examined the optimum stacked structure. 22) The multifrequency C-V characteristics of AlGaN=GaN MOS capacitors with SiO 2 single and SiO 2 =AlON stacked gate dielectrics with different interlayer thicknesses are summarized in Fig.…”