Yaming Fan

Studies on High-Voltage GaN-on-Si MIS-HEMTs Using LPCVD Si 3 N 4 as Gate Dielectric and Passivation Layer

This paper investigates the performance of AlGaN/gallium nitride (GaN) MIS high electron mobility transistors (MIS-HEMTs). The gate dielectric layer and the surface passivation layer are formed by the low-pressure chemical vapor deposition (LPCVD) Si₃N₄. The LPCVD-Si₃N₄ MIS-HEMTs exhibit a high breakdown voltage (BV) of 1162 V at I_DS = 1 μA/mm, a low OFF-state leakage of 7.7 × 10^-12 A/mm, and an excellent ON/OFF-current ratio of ~10¹¹. Compared with the static ON-resistance of 2.88 mΩ · cm², the dynamic ON-resistance after high OFF-state drain bias stress at 600 V only increases to 4.89 mΩ · cm². The power device figure of merit = BV²/R_ON.sp is calculated to be 469 MW · cm^-2. The LPCVD-Si₃N₄/GaN interface state density is in the range of (1.4-5.3) × 10¹³ eV^-1 cm^-2 extracted by the conventional conductance method. Finally, the gate insulator degradation of GaN-based MIS-HEMTs is analyzed by time-dependent dielectric breakdown test. The lifetime is extrapolated to 0.01% of failures after ten years at 300 K by fitting the data with a power law to a gate voltage of 10.1 V.

Normally Off AlGaN/GaN MIS-High-Electron Mobility Transistors Fabricated by Using Low Pressure Chemical Vapor Deposition Si 3 N 4 Gate Dielectric and Standard Fluorine Ion Implantation

This letter presents a fabrication technology of enhancement-mode (E-mode) AlGaN/GaN metal-insulator- semiconductor high-electron mobility transistors (MIS-HEMTs) using 10 keV fluorine ion implantation. An 8 nm low-pressure chemical vapor deposition silicon nitride layer was deposited on the AlGaN as gate dielectric and energy-absorbing layer that slows down the high energy (10 keV) fluorine ions to reduce the implantation damage. The E-mode MIS-HEMTs exhibit a threshold voltage as high as +3.3 V with a maximum drain current over 200 mA/mm (250 mA/mm for depletion-mode MIS-HEMTs) and a high on/off current ratio of 109. Meanwhile, the E-mode MIS-HEMT dynamic RON is only 1.53 times larger than the static RON after off-state VDS stress of 500 V.

Fabrication of normally-off AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors by photo-electrochemical gate recess etching in ionic liquid

We characterized an ionic liquid (1-butyl-3-methylimidazolium nitrate, C8H15N3O3) as a photo-electrochemical etchant for fabricating normally-off AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs). Using the ionic liquid, we achieved an etching rate of ~2.9 nm/min, which is sufficiently low to facilitate good etching control. The normally-off AlGaN/GaN MIS-HEMT was fabricated with an etching time of 6 min, with the 20 nm low-pressure chemical vapor deposition (LPCVD) silicon nitride (Si3N4) gate dielectric exhibiting a threshold voltage shift from −10 to 1.2 V, a maximum drain current of more than 426 mA/mm, and a breakdown voltage of 582 V.

Degradation of AlGaN/GaN metal–insulator–semiconductor high electron mobility transistors under off-state electrical stress

In this paper, the authors have fabricated AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors employing the low-pressure chemical vapor deposition (LPCVD) SiNx as the gate insulator with field plate structure and the long-term degradation was investigated under off-state stress with degradation process monitoring. The gate leakage and drain leakage under off-state electrical stress showed different change rules while the former was expected to be effectively suppressed by LPCVD-SiNx dielectric. The output and transfer characteristics between the stress were obtained periodically to investigate the degradation process. Through the analysis of the degradation of the parameters and the shifts of the Raman spectra, the inverse piezoelectric effect is believed to be the dominant degradation mechanism.

Influence factors and temperature reliability of ohmic contact on AlGaN/GaN HEMTs

In this paper, we have studied the performance of Ti/Al/Ni/Au ohmic contact with different Al and Au thicknesses and pretreatments. The temperature dependence of contact resistances (Rc) was investigated and it shows that there are different optimal annealing temperatures with different metal thicknesses and pretreatments. The optimal annealing temperature is affected by Al and Au thickness and AlGaN thickness. The etched AlGaN barrier is useful to achieve good ohmic contact (0.24 Ω·mm) with a low annealing temperature. Only the contact resistances of the samples with 130 nm Al layer kept stable and the contact resistances of the samples with 100nm and 160 nm Al layers increased with the measurement temperatures. The contact resistances showed a similar increase and then keep stable trend for all the samples in the long-term 400 °C aging process. The ohmic metal of 20/130/50/50 nm Ti/Al/Ni/Au with ICP etching is the superior candidate considering the contact resistance and reliability.In this paper, we have studied the performance of Ti/Al/Ni/Au ohmic contact with different Al and Au thicknesses and pretreatments. The temperature dependence of contact resistances (Rc) was investigated and it shows that there are different optimal annealing temperatures with different metal thicknesses and pretreatments. The optimal annealing temperature is affected by Al and Au thickness and AlGaN thickness. The etched AlGaN barrier is useful to achieve good ohmic contact (0.24 Ω·mm) with a low annealing temperature. Only the contact resistances of the samples with 130 nm Al layer kept stable and the contact resistances of the samples with 100nm and 160 nm Al layers increased with the measurement temperatures. The contact resistances showed a similar increase and then keep stable trend for all the samples in the long-term 400 °C aging process. The ohmic metal of 20/130/50/50 nm Ti/Al/Ni/Au with ICP etching is the superior candidate considering the contact resistance and reliability.

Design and simulation of a novel E-mode GaN MIS-HEMT based on a cascode connection for suppression of electric field under gate and improvement of reliability*

We proposed a novel AlGaN/GaN enhancement-mode (E-mode) high electron mobility transistor (HEMT) with a dual-gate structure and carried out the detailed numerical simulation of device operation using Silvaco Atlas. The dual-gate device is based on a cascode connection of an E-mode and a D-mode gate. The simulation results show that electric field under the gate is decreased by more than 70% compared to that of the conventional E-mode MIS-HEMTs (from 2.83 MV/cm decreased to 0.83 MV/cm). Thus, with the discussion of ionized trap density, the proposed dual-gate structure can highly improve electric field-related reliability, such as, threshold voltage stability. In addition, compared with HEMT with field plate structure, the proposed structure exhibits a simplified fabrication process and a more effective suppression of high electric field.

Interface Si donor control to improve dynamic performance of AlGaN/GaN MIS-HEMTs

In this letter, we have studied the performance of AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs) with different interface Si donor incorporation which is tuned during the deposition process of LPCVD-SiNx which is adopted as gate dielectric and passivation layer. Current collapse of the MIS-HEMTs without field plate is suppressed more effectively by increasing the SiH2Cl2/NH3 flow ratio and the normalized dynamic on-resistance (RON) is reduced two orders magnitude after off-state VDS stress of 600 V for 10 ms. Through interface characterization, we have found that the interface deep-level traps distribution with high Si donor incorporation by increasing the SiH2Cl2/NH3 flow ratio is lowered. It’s indicated that the Si donors are most likely to fill and screen the deep-level traps at the interface resulting in the suppression of slow trapping process and the virtual gate effect. Although the Si donor incorporation brings about the increase of gate leakage current (IG...

High-resistivity unintentionally carbon-doped GaN layers with nitrogen as nucleation layer carrier gas grown by metal-organic chemical vapor deposition

In this letter, high-resistivity unintentionally carbon-doped GaN layers with sheet resistivity greater than 106 Ω/□ have been grown on c-plane sapphire substrates by metal-organic chemical vapor deposition (MOCVD). We have observed that the growth of GaN nucleation layers (NLs) under N2 ambient leads to a large full width at half maximum (FWHM) of (102) X-ray diffraction (XRD) line in the rocking curve about 1576 arc sec. Unintentional carbon incorporation can be observed in the secondary ion mass spectroscopy (SIMS) measurements. The results demonstrate the self-compensation mechanism is attributed to the increased density of edge-type threading dislocations and carbon impurities. The AlGaN/GaN HEMT grown on the high-resistivity GaN template has also been fabricated, exhibiting a maximum drain current of 478 mA/mm, a peak transconductance of 60.0 mS/mm, an ON/OFF ratio of 0.96×108 and a breakdown voltage of 621 V.