No abstract

Demonstration of submicron-gate AlGaN/GaN high-electron-mobility transistors on silicon with complementary metal-oxide-semiconductor-compatible non-gold metal stack.

The gate leakage current mechanism of AlGaN/GaN Schottky barrier diodes (SBDs) and highelectron-mobility transistors (HEMTs) with sputtered TiN is systematically investigated. The reverse leakage current (J R ) of TiN SBDs increases exponentially with the increase of reverse voltage (V R ) from 0 to À3.2 V (Reg. I). This conduction behavior is dominated by Poole-Frenkel emission from TiN through an interface state of 0.53 eV to the conductive dislocation-related continuum states. The obtained interface state of 0.53 eV may be due to the plasma damage to the surface of the AlGaN/GaN HEMT structure during the TiN sputtering. When the TiN SBDs are biased with À20 < V R < À3.2 V, J R saturated due to the depletion of the 2-dimensional electron gas (2DEG) channel (Reg. II). This conduction behavior is dominated by the trap-assisted tunneling through the interface state at $0.115 eV above the Fermi level. The three terminal OFF-state gate leakage current of AlGaN/GaN HEMTs exhibited an activation energy of 0.159 eV, which is in close agreement with the obtained interface state of $0.115 eV from saturated J R (Reg. II) of the SBDs. The observation of the negative temperature coefficient (À1.75 V/K) from the OFF-state breakdown voltage (at 1 lA/mm) of AlGaN/GaN HEMTs is due to the trap-assisted tunneling mechanism, which is also well correlated with the conduction mechanism realized from the reverse leakage current of the SBDs.

AlGaN/GaN high-electron-mobility transistors (HEMTs) with a 0.15-µm gate were fabricated on a Si substrate with an 8-nm-thick AlGaN barrier. The device exhibited a unity current gain cutoff frequency fT of 63 GHz and maximum oscillation frequency fmax of 124 GHz. Its three-terminal OFF-state breakdown voltage BVgd is as high as 132 V. The estimated Johnson’s figure of merit (=BVgd × fT) is 8.32 × 1012 V/s (8.32 THz·V), which is the highest value ever reported for a conventional SiN-passivated T-gate AlGaN/GaN HEMTs on a Si substrate without an additional field plate or gamma gate.

Multiple energies of heavy ion implantation with inert-gas ion (84Kr+) were carried out on AlGaN/GaN high-electron-mobility transistors (HEMTs) for planar device isolation. Thermal stability of the implantated samples were also investigated by isochronal annealing at 500, 600, 700, and 800 °C (each temperature for 1 h.). Due to the damages created by heavy ions (84Kr+) in the GaN lattice, the implant-isolated Al0.27Ga0.73N/GaN HEMT samples exhibited better thermal stability than 40Ar+-implant-isolation. This was also confirmed by Rutherford backscattering spectrometry in channeling condition and ultraviolet micro-Raman spectroscopy measurements. With reference to mesa-isolated AlGaN/GaN HEMTs, the buffer breakdown voltage is also stable in the implant-isolated AlGaN/GaN HEMTs. An enhanced OFF-state breakdown voltage was also realized in the implant-isolated AlGaN/GaN HEMTs. The inert gas heavy ion implantation (84Kr+) is a viable solution for the fabrication of thermally stable planar AlGaN/GaN HEMTs even up to 800 °C under long-term isochronal annealing.