Surface passivation of GaN and GaN/AlGaN heterostructures by dielectric films and its application to insulated-gate heterostructure transistors

Abstract

We have systematically investigated effects of plasma processing, formation of Si-based dielectrics, and formation of a thin Al 2 O 3 film on the chemical and electronic properties of GaN and GaN/ AlGaN heterostructure surfaces. The surface treatment in H 2 -plasma excited by electron-cyclotron-resonance ͑ECR͒ source, produced nitrogen-vacancy-related defect levels at GaN and AlGaN surfaces, while the ECR-N 2 -plasma treatment improved electronic properties of the surfaces. The deposition of a SiO 2 film on GaN and AlGaN surfaces was found to induce high-density interface states, due to unexpected and uncontrollable oxidation reactions on the surfaces during the deposition process. In comparison, the SiN x /GaN passivation structure prepared by ECR-plasma assisted chemical vapor deposition showed good interface properties with the minimum D it value of 1ϫ10 11 cm Ϫ2 eV Ϫ1 . However, excess leakage currents governed by FowlerNordheim tunneling were observed in the SiN x /Al 0.3 Ga 0.7 N structure, due to a relatively small conduction band offset of 0.7 eV between SiN x and Al 0.3 Ga 0.7 N. A novel Al 2 O 3 -based passivation structure was proposed and fabricated by molecular beam deposition of Al and subsequent ECR O 2 -plasma oxidation. In situ x-ray photoelectron spectroscopy showed successful formation of the Al 2 O 3 layer with a thickness of 3.5 nm and a large conduction band offset of 2.1 eV between Al 2 O 3 and A 0.3 Ga 0.7 N. The GaN/AlGaN insulated-gate heterostructure field-effect transistors ͑IG HFETs͒ having the Al 2 O 3 -based passivation structure showed a good gate control of drain currents up to V GS ϭϩ3 V and achieved drain saturation current of 0.8 A/mm. The observed maximum g m value is 120 mS/mm. No current collapse was observed in the Al 2 O 3 IG HFETs, indicating a remarkable advantage of the present Al 2 O 3 -based passivation structure.

Investigation of the interface between silicon nitride passivations and AlGaN/AlN/GaN heterostructures by C(V) characterization of metal-insulator-semiconductor-heterostructure capacitors

“…Similar curves can also be found in other reports. 18,19 The characteristic can be split into three intervals. The small MISH structure in each interval of the characteristic schematically presents the depletion region ͑dashed region͒ and electron distribution ͑minus signs͒ in the structure.…”

Characterization of interface states in Al2O3/AlGaN/GaN structures for improved performance of high-electron-mobility transistors

“…GaN-based MOS-HEMTs using an Al 2 O 3 as the insulator have been demonstrated by many groups. 3,4,[6][7][8][9] The typical values of bandgap and permittivity reported for the Al 2 O 3 film are 7-9 eV and 8-10, respectively. [6][7][8][9][10] The Al 2 O 3 film prepared by atomic layer deposition (ALD), in particular, showed relatively low electronic state densities in the Al 2 O 3 /n-GaN system.…”

“…3,4,[6][7][8][9] The typical values of bandgap and permittivity reported for the Al 2 O 3 film are 7-9 eV and 8-10, respectively. [6][7][8][9][10] The Al 2 O 3 film prepared by atomic layer deposition (ALD), in particular, showed relatively low electronic state densities in the Al 2 O 3 /n-GaN system. 9,[11][12][13] However, in the MOS-HEMT structures, the insulator/semiconductor interface is usually formed on the AlGaN/GaN heterostructures, resulting in the existence of two interfaces under the gate electrode.…”

Non-localized trapping effects in AlGaN/GaN heterojunction field-effect transistors subjected to on-state bias stress

“…Furthermore, very recently, Tajima and Hashizume 5 proposed a third model, in which current collapse can also be induced by surface trapping at the source side of the gate edge, where an electric field of as high as 5 MV/cm exists during the application of off-stress. Owing to the success of using surface passivation to suppress the current collapse, [6][7][8][9] the virtual gate mechanism has become widely accepted as the main mechanism for current collapse. 10 Following this understanding, regarding the reliability of AlGaN/ GaN HFETs, degradation at the gate edge has been recognized as the only degradation mechanism regardless of whether onstress or off-stress is applied.…”