Fluorine Plasma Ion Implantation Research Articles

High-densities of free holes in homoepitaxial n-GaN induced by fluorine-plasma ion implantation

In this work, fluorine plasma ion implantation is used to induce high densities of free holes in homoepitaxial n-GaN for the first time, as evidenced by electroluminescence and p-n junction rectification. F+ ions implanted into the near-surface layer capture electrons from shallow bulk donors, bending the band upward until a high density of free holes is induced at the valence band maximum, and surface donors, depinning the Fermi level to form p-type ohmic contact. Free holes tunnel from the metal into states at the valence band maximum, where they form a conductive p-type channel, benefitting the development of GaN-based junction devices.

Device physics towards high performance GaN-based power electronics

Gallium-nitride-based power electronic devices, with the inherent high breakdown voltage, high working frequency, high output current density and high temperature operating capability, are promising candidates for next-generation high-efficiency and compact power management systems. In this work, the scientific and technical challenges towards high-performance GaN power devices, including threshold voltage instability, dynamic ON-resistance degradation, enhancement-mode gate techniques and long-term reliability of gate dielectrics, are investigated based on in-depth analysis of the physical origin of interface states and high-voltage current collapse. Oxidation of (Al) GaN surface are suggested to be the primary cause for the surface/interface states in GaN-based power devices. State-of-the-art device technologies, including nitridation-interficial-layer to suppress dielectric/(Al) GaN interface oxidation, polarized PEALD-AlN passivation for compensation of deep interface states, E-mode techniques of fluorine plasma ion implantation and high-temperature low-damage gate-recess, high-breakdown-strength LPCVD-SiN x and O3-sourced ALD-Al2O3 gate dielectrics are introduced for fabrication of high performance and reliability GaN-based power electronic devices.

Degradation mechanism of enhancement-mode AlGaN/GaN HEMTs using fluorine ion implantation under the on-state gate overdrive stress**Project supported by the National Natural Science Foundation of China (Grant Nos. 61334002, 61106106, and 61474091), the Opening Project of Science and Techology on Reliability Physics and Application Technology of Electronic Component Laboratory (Grant No. ZHD201206), the New Experiment Development Funds for Xidian University, China

The degradation mechanism of enhancement-mode AlGaN/GaN high electron mobility transistors (HEMTs) fabricated by fluorine plasma ion implantation technology is one major concern of HEMT’s reliability. It is observed that the threshold voltage shows a significant negative shift during the typical long-term on-state gate overdrive stress. The degradation does not originate from the presence of as-grown traps in the AlGaN barrier layer or the generated traps during fluorine ion implantation process. By comparing the relationships between the shift of threshold voltage and the cumulative injected electrons under different stress conditions, a good agreement is observed. It provides direct experimental evidence to support the impact ionization physical model, in which the degradation of E-mode HEMTs under gate overdrive stress can be explained by the ionization of fluorine ions in the AlGaN barrier layer by electrons injected from 2DEG channel. Furthermore, our results show that there are few new traps generated in the AlGaN barrier layer during the gate overdrive stress, and the ionized fluorine ions cannot recapture the electrons.

600-V Normally Off ${\rm SiN}_{x}$/AlGaN/GaN MIS-HEMT With Large Gate Swing and Low Current Collapse

In this letter, 600-V normally-OFF SiNx/AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistor (MIS-HEMT) is reported. Normally-OFF operation and low OFF-state gate leakage are obtained by using fluorine plasma ion implantation in conjunction with the adoption of a 17-nm SiNx thin film grown by plasma-enhanced chemical vapor deposition as the gate insulator. The normally-OFF MIS-HEMT exhibits a threshold voltage of +3.6 V, a drive current of 430 mA/mm at a gate bias of 14 V, a specific ON-resistance of 2.1 mΩ·cm2 and an OFF-state breakdown voltage of 604 V at a drain leakage current of 1 μA/mm with VGS=0 V, and the substrate grounded. Effective current collapse suppression is obtained by AlN/SiNx passivation as proved by high-speed pulsed I-V and low-speed high-voltage switching measurement results.

18-GHz 3.65-W/mm Enhancement-Mode AlGaN/GaN HFET Using Fluorine Plasma Ion Implantation

Enhancement-mode (E-mode) AlGaN/GaN heterojunction field effect transistors (HFETs) with a nominal gate length of 0.35 μm are fabricated on a SiC substrate by fluorine plasma ion implantation without the use of gate recess. The threshold voltage is measured to be +0.2 V by linear extrapolation from the transfer characteristics. The E-mode device exhibits a saturation drain current density of 735 mA/mm at a gate bias of 4 V, a peak transconductance of 269 mS/mm, a current-gain cutoff frequency ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">fT</i> ) of 39 GHz, and a maximum oscillation frequency ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> ) of 91 GHz. At 18 GHz, the fabricated E-mode device exhibits a maximum output power density of 3.65 W/mm, a linear gain of 11.6 dB, and a peak power-added efficiency of 42%. This is the first report of the large-signal performance of AlGaN/GaN E-mode HFETs in the Ku-band.

Fluorine plasma ion implantation in AlGaN∕GaN heterostructures: A molecular dynamics simulation study

Fluoride-based plasma treatment is a robust technique that enables shallow implantation of fluorine ions into group III-nitride epitaxial structures. This technique has been used to achieve robust threshold voltage control of the AlGaN∕GaN high electron mobility transistors and led to the realization of self-aligned enhancement-mode devices. To reveal the atomic scale interactions and provide a modeling tool for process design and optimization, a molecular dynamics (MD) simulation is conducted for fluorine plasma ion implantation. Specific potential functions are applied to calculate the interactions among atoms and simulate the dynamic process of fluorine ions’ penetration and stopping in III-nitride materials. The MD simulation provides accurate information on dopant profiles that are verified by secondary-ion-mass-spectrum measurements. Defect formation and distributions, that are critical in process development, are also investigated.