Jong-Bong Ha

Effects of TMAH Treatment on Device Performance of Normally Off

Normally off Al2O3/GaN MOSFETs are fabricated by utilizing a simple tetramethylammonium hydroxide (TMAH) treatment as a postgate-recess process. The TMAH-treated device with a gate length of 2.5 μm exhibited excellent device performances, such as a threshold voltage of 3.5 V, a maximum drain current of 336 mA/mm, and a breakdown voltage of 725 V, along with extremely small gate leakage current of about 10-9 A/mm at Vgs = 15 V, which is approximately six orders lower in magnitude compared to that of the device without TMAH treatment.

\hbox{Al}_{2}\hbox{O}_{3}/\hbox{GaN}

The impact of gate metals on the threshold voltage (VTH) and the gate current of p-GaN gate high-electron-mobility transistors (HEMTs) is investigated by fabricating p-GaN gate HEMTs with different work function gate metals-Ni and W. p-GaN gate HEMTs incorporate a p-GaN layer under the gate electrode as the gate stack on top of the AlGaN/GaN layer. In comparison to the Ni-gate p-GaN HEMTs, the W-gate p-GaN HEMTs showed a higher VTH of 3.0 V and a lower gate current of 0.02 mA/mm at a gate bias of 10 V. Based on TCAD device simulations, we revealed that these high VTH and low gate current are attributed to the low gate metal work function and the high Schottky barrier between the p-GaN and the W gate metal.

MOSFET

The electrical characteristics of the Al2O3/GaN metal‐insulator‐semiconductor capacitors are investigated focusing on the effect of post-deposition annealing (PDA) in O2 ambient. X-ray photoelectron spectroscopy analyses reveal that gallium oxynitride (GaOxNy) interfacial layer is formed at Al2O3/GaN interface even in non-annealed sample due to incorporation of the released oxygen from Al2O3. After PDA in O2 ambient, the GaOxNy interfacial layer becomes oxygen-rich which plays a role in increasing negative effective oxide charge at the Al2O3/GaN interface and hence positively shifting the flat band voltage (VFB) for the capacitors. (Some figures may appear in colour only in the online journal)

p-GaN Gate HEMTs With Tungsten Gate Metal for High Threshold Voltage and Low Gate Current

Traps and trap-related effects in recessed-gate normally-off AlGaN/GaN-based MOSHEMT with SiO2 gate dielectric were characterized. Hysteresis in ID-VG was observed at elevated temperature (~120°C) due to the traps. To understand the traps, current transient in drain was investigated at given gate and drain pulses with different temperatures. Two groups of time constants were extracted: one is nearly constant and the other is decreased with temperature. Extracted activation energies from the drain current transients with temperature are 0.66 eV and 0.73 eV, respectively, for given gate and drain pulses. Using extracted exponential trap density profile from frequency dependent conductance method [4], we could understand C-V behavior with frequency. It was shown that traps inside AlGaN layer are a main cause for the decrease of capacitance at high frequency in inversion region. The pulsed I-V characteristics also show frequency dependence.

Effect of oxygen species on the positive flat-band voltage shift in Al2O3/GaN metal–insulator–semiconductor capacitors with post-deposition annealing

A p-GaN/AlGaN/GaN based normally-off HEMT device has been demonstrated on a Si substrate. Our p-GaN based device shows not only a high threshold voltage of 3 V but also low gate leakage current. Buffer and device breakdown voltages exceed 1600 V with 5.2 um GaN buffer thickness and specific on-state resistance is 2.9mΩ cm2. The calculated figure of merit is 921 MV2/Ωcm2, which is the highest value reported for the GaN E-mode devices.

Characterization of traps and trap-related effects in recessed-gate normally-off AlGaN/GaN-based MOSHEMT

A BF/sub 3/ Plasma doping (PLAD) process has been utilized in source/drain/gate and shallow S/D extension for high performance 0.18 /spl mu/m pMOSFET. Gate oxide reliability, drain current, and transconductance of the pMOSFET with BF/sub 3/ PLAD are remarkably improved compared to those of BF/sub 2/ ion implanted devices. Cobalt salicide formation is also compatible with the plasma doped S/D junction.

1.6kV, 2.9 mΩ cm 2 normally-off p-GaN HEMT device

In this paper, we present high threshold voltage, low on-resistance, and high speed GaN-HEMT devices using a p-GaN layer in the gate stack. There are three novel features - first, for the first time, p-GaN gate HEMTs were fabricated on a 200-mm GaN on Si substrate using a Au-free fully CMOS-compatible process. Second, good electrical characteristics, including a threshold voltage of higher than 2.8 V, a low gate leakage current, no hysteresis, and fast switching, were obtained by employing a p-GaN and W gate stack. Finally, TO-220 packaged p-GaN gate HEMT devices, which can sustain a gate bias of up to 20 V, were demonstrated. Such properties indicate that our p-GaN HEMT devices are compatible with the conventional gate drivers for Si power devices.

High performance pMOSFET with BF/sub 3/ plasma doped gate/source/drain and S/D extension

Trap-related transient characteristics and RTN in p-GaN gate HEMT were characterized, for the first time to our knowledge. Current conduction mechanism in DC IG is explained based on proposed model. Hopping conduction mechanism is responsible for IG at VG <; 0. IG at VG > 0 seems to be controlled by thermionic emission and affected by the action of floating-base n(W)-p(p-GaN)-n(AlGaN/GaN) bipolar transistor. Transient current behavior is related to the DC conduction mechanism and could be explained by thermal emission and charge trapping in p-GaN and AlGaN layers. Measured transient behavior of gate capacitance corresponds to that of the transient currents. Hole trapping into the AlGaN layer and existence of percolation path in gate and drain currents are verified by analyzing RTNs in IG and ID. Trap position and activation energy regarding RTN are firstly extracted. RTN time constants are similar to those in IG and ID transient behavior.

High threshold voltage p-GaN gate power devices on 200 mm Si

The electron beam (EB) irradiation process has been investigated to control the channel dopant profile of 0.2 /spl mu/m surface channel pMOSFETs for the first time. The results show that the channel dopants are redistributed along the EB-induced point defects by subsequent annealing when the EB is used to directly irradiate the pMOSFETs. As compared to the control process, EB treatment not only increases drive current by 14% but also reduces junction capacitance by 20% in pMOSFETs, despite the fact that EB treatment causes a reverse short channel effect. No degradation of the gate oxide reliability was identified for the EB treated sample.