Do-Kywn Kim

A New Unified Mobility Extraction Technique of In 0.7 Ga 0.3 As QW MOSFETs

Conventional methods to extract an effective mobility (μeff) in a metal-oxide-semiconductor field-effect-transistor (MOSFET) tend to ignore the portions of parasitic components of the device. This can cause a substantial error in the extracted value of the effective mobility. In this letter, we have proposed a unified procedure that enables to accurately capture each portion of parasitic series resistance (RSD) and parasitic gate capacitance (Cg_par) components. Then, we have investigated the impact of the parasitic components on the extracted value of the effective mobility in a gate-last surface-channel In0.7Ga0.3As quantum-well MOSFET. We have found that the extracted effective mobility using our method turns out to be independent upon gate length (Lg) from 10 to 4 μm, which verifies the accuracy of the approach proposed in this letter.

Growth of AlN/GaN HEMT structure Using Indium-surfactant

We have grown AlN/GaN heterostructure which is a promising candidate for mm-wave applications. For the growth of the high quality very thin AlN barrier, indium was introduced as a surfactant at the growth temperature varied from 750 to 1070 ℃, which results in improving electrical properties of two-dimensional electron gas (2DEG). The heterostructure with barrier thickness of 7 ㎚ grown at of 800 ℃ exhibited best Hall measurement results; such as sheet resistance of 215 Ω/□, electron mobility of 1430 ㎠/V·s, and two-dimensional electron gas (2DEG) density of 2.04 ｘ 10 13 /㎠. The high electron mobility transistor (HEMT) was fabricated on the grown heterostructure. The device with gate length of 0.2 ㎛ exhibited excellent DC and RF performances; such as maximum drain current of 937 ㎃/㎜, maximum transconductance of 269 mS/㎜, current gain cut-off frequency of 40 ㎓, and maximum oscillation frequency of 80 ㎓.

Device Performances Related to Gate Leakage Current in Al 2 O 3 /AlGaN/GaN MISHFETs

In this paper, we have characterized the electrical properties related to gate leakage current in AlGaN/GaN MISHFETs with varying the thickness (0 to 10 nm) of Al₂O₃ gate insulator which also serves as a surface protection layer during high-temperature RTP. The sheet resistance of the unprotected TLM pattern after RTP was rapidly increased to 1323 Ω/□ from the value of 400 Ω/□ of the as-grown sample due to thermal damage during high temperature RTP. On the other hand, the sheet resistances of the TLM pattern protected with thin Al₂O₃ layer (when its thickness is larger than 5 nm) were slightly decreased after high-temperature RTP since the deposited Al₂O₃ layer effectively neutralizes the acceptor-like states on the surface of AlGaN layer which in turn increases the 2DEG density. AlGaN/GaN MISHFET with 8 nmthick Al₂O₃ gate insulator exhibited extremely low gate leakage current of 10 -9 A/mm, which led to superior device performances such as a very low subthreshold swing (SS) of 80 mV/dec and high Ion/Ioff ratio of ~ 1010. The PF emission and FN tunneling models were used to characterize the gate leakage currents of the devices. The device with 5 nm-thick Al₂O₃ layer exhibited both PF emission and FN tunneling at relatively lower gate voltages compared to that with 8 nm-thick Al₂O₃ layer due to thinner Al₂O₃ layer, as expected. The device with 10 nm-thick Al₂O₃ layer, however, showed very high gate leakage current of 5.5 ×10 -4 A/mm due to poly-crystallization of the Al₂O₃ layer during the high-temperature RTP, which led to very poor performances.

Performance of GaN Metal–Oxide–Semiconductor Field-Effect Transistor with Regrown n+-Source/Drain on a Selectively Etched GaN

We proposed and fabricated normally off GaN MOSFETs with an epitaxially regrown n+ GaN source/drain after a short period of dry etching on a sapphire substrate. The regrown S/D MOSFET after dry etching (MOSFET A) exhibited enhanced performance in terms of current drivability and access resistance compared with the same MOSFET without the surface etching before the regrowth (MOSFET B). While MOSFET A has a saturation drain current of 10 mA/mm at VG = 8 V, a field-effect mobility of 22 cm2 V-1 s-1, and a series resistance RSD of 0.57 kΩ, MOSFET B has 3 mA/mm, 12 cm2 V-1 s-1, and 0.93 kΩ, respectively. The electrical characteristic of MOSFET A was also much more improved than that of MOSFET B at low temperatures. Mobility degradation at low temperatures was related to the effect of impurity scattering caused by crystal defects generated during the metal organic chemical vapor deposition (MOCVD) growth.

Low-temperature characteristics of In 0.7 Ga 0.3 As PHEMTs

In this paper, we report on temperature dependent DC characteristics of In_0.7Ga_0.3As Pseudomorphic-HEMTs (PHEMTs) on InP substrate. First, we have fabricated the In_0.7Ga_0.3As PHEMTs with various values of L_g, ranging from 10 μm to 2.5 μm. The fabricated device with L_g = 2.5 μm exhibits excellent subthreshold-swing (SS) of 64 mV/decade at room temperature. Note that this is close to 60 mV/decade, which is a theoretical limit at room temperature in a FET configuration. Next, we have measured current-voltage characteristics at various values of temperatures, from 300 K to 80 K. Finally, we have investigated the temperature-dependent DC characteristics of the In_0.7Ga_0.3As PHEMTs, in terms of output, subthreshold, and transconductance characteristics.

Electrical characterization of GaN-channel MOSFETs

The channel mobility and reliability of NMOSFETs with GaN channel are investigated by means of split CV and constant-voltage-stress techniques. The influence of stress polarity and duration on current in the off-state, threshold voltage and subthreshold slope is studied.

Dual-band responsivity of AlGaN/GaN MSM UV photodiode

We proposed a AlGaN/GaN Schottky MSM diode for double-window UV sensing and realized it using three metals. They showed a significantly different value of currents between 300 nm and other wavelengths in both Fowler-Nordheim and Poole-Frenkel plots at the low voltage region, which is attributed to the direct electron conduction to the anode, and/or hole conduction to the cathode from the AlGaN region. Since the ln(I/V) levels is high for the shorter wavelength and low for the longer UV, we may apply to detect the dual windows of UV.

Vertical GaN schottky barrier diode on an N-face GaN layer formed by ELOG and laser-lift-off technique for high-power application

We studied a vertical type GaN schottky barrier diode (SBD) on the laser-lift-off (LLO) GaN layer with top schottky contact metals such as nickel and aluminium. The I-V characteristic was not strongly dependent on the schottky metals and the forward voltage drop was higher than the theoretical value. The C-V characteristic of metal-oxide-semiconductor (MOS) capacitor exhibits from the accumulation to inversion around •10 V. These results suggest that the wide band gap thin film layer remains at the surface of the N-face GaN layer.