Ching-Sung Lee

Characteristics of In/sub 0.425/Al/sub 0.575/As-InxGa/sub 1-x/As metamorphic HEMTs with pseudomorphic and symmetrically graded channels

In/sub 0.425/Al/sub 0.575/As-In/sub x/Ga/sub 1-x/As metamorphic high electron mobility transistors (MHEMTs) with two different channel designs, grown by molecular beam epitaxy (MBE) system, have been successfully investigated. Comprehensive dc and high-frequency characteristics, including the extrinsic transconductance, current driving capability, device linearity, pinch-off property, gate-voltage swing, breakdown performance, unity-gain cutoff frequency, max. oscillation frequency, output power, and power gain, etc., have been characterized and compared. In addition, complete parametric information of the small-signal device model has also been extracted and discussed for the pseudomorphic channel MHEMT (PC-MHEMT) and the V-shaped symmetrically graded channel MHEMT (SGC-MHEMT), respectively.

Novel Oxide-Passivated AlGaN/GaN HEMT by Using Hydrogen Peroxide Treatment

This brief reports, for the first time, an oxide passivated AlGaN/GaN high electron mobility transistor by using the hydrogen peroxide (H2O2) treatment. Characterizations by using electron spectroscopy for chemical analysis and transmission electron microscopy have been performed to verify the formation of surface oxide on the AlGaN barrier layer. The present design has demonstrated superior improvements of 41% in the maximum drain/source current density IDS,max; 39% in the drain/source saturation current density at zero gate bias IDSSO, 47% in the maximum extrinsic transconductance gm,max, 53.2% in the two-terminal gate/drain breakdown voltage BVGD 36% in the cutoff frequency fT, and 20% in the maximum oscillation frequency fmax, as compared with an unpassivated conventional device.

A Simple Gate-Dielectric Fabrication Process for AlGaN/GaN Metal–Oxide–Semiconductor High-Electron-Mobility Transistors

This letter reports a simple processing method for fabricating metal-oxide-semiconductor high-electron-mobility transistors (MOS-HEMTs) by using hydrogen peroxide (H₂O₂) oxidation technique. Aluminum oxide (AlO_x) was formed on the surface of the AlGaN barrier as the gate dielectric of the MOS-gate structure. By using the capacitance-voltage measurement, the dielectric constant (κ) of AlO_x was determined to be 9.2. The present MOS-HEMT has demonstrated enhanced saturation drain current density at V_GS = 0 V (I_DSS0) of 552.3 mA/mm, maximum extrinsic transconductance (g_{m, max}) of 136 mS/mm, wide gate voltage swing of 2.9 V, and two-terminal gate-drain breakdown/turn-on voltages (BV_GD/V_on) of -132.2/1.82 V.

High-temperature thermal stability performance in /spl delta/-doped In/sub 0.425/Al/sub 0.575/As--In/sub 0.65/Ga/sub 0.35/As metamorphic HEMT

We report, to our knowledge, the best high-temperature characteristics and thermal stability of a novel /spl delta/-doped In/sub 0.425/Al/sub 0.575/As--In/sub 0.65/Ga/sub 0.35/As--GaAs metamorphic high-electron mobility transistor. High-temperature device characteristics, including extrinsic transconductance (g/sub m/), drain saturation current density (I/sub DSS/), on/off-state breakdown voltages (BV/sub on//BV/sub GD/), turn-on voltage (V/sub on/), and the gate-voltage swing have been extensively investigated for the gate dimensions of 0.65/spl times/200 /spl mu/m/sup 2/. The cutoff frequency (f/sub T/) and maximum oscillation frequency (f/sub max/), at 300 K, are 55.4 and 77.5 GHz at V/sub DS/=2 V, respectively. Moreover, the distinguished positive thermal threshold coefficient (/spl part/V/sub th///spl part/T) is superiorly as low as to 0.45 mV/K.

High-temperature threshold characteristics of a symmetrically graded InAlAs∕InxGa1−xAs∕GaAs metamorphic high electron mobility transistor

High-temperature threshold characteristics of a symmetrically graded δ-doped InAlAs∕InxGa1−xAs∕GaAs (x=0.5→0.65→0.5) metamorphic high electron mobility transistor (MHEMT) have been investigated. The thermal threshold coefficients, defined as ∂Vth∕∂T, are superiorly low at 0.9mV∕K from 300to420K and at −0.75mV∕K from 420to500K. An interesting polarity change of the thermal threshold coefficient was observed around 420K due to the variation of thermal modulation effects. The present MHEMT device, with stabilized thermal threshold variations and superior high-temperature linearity characteristics, is promising for high-temperature circuit applications.

Investigations of AlGaN/AlN/GaN MOS-HEMTs on Si Substrate by Ozone Water Oxidation Method

Al_0.3Ga_0.7N/AlN/GaN metal-oxide-semiconductor high electron mobility transistors (HEMTs) grown on Si substrates by using ozone water oxidation method are investigated. Superior improvements of 52.2% in two-terminal gate-drain breakdown voltage (BV_GD), 30.3% in drain-source current density (I_DS) at V_GS = 0 V (I_DSS0), 43.6% in maximum I_DS (I_DS,max), 34.7% in maximum extrinsic transconductance (<i>gm</i>,max), and 52.7%/34.3% in unity-gain cutoff/maximum oscillation frequency (<i>fT</i>/<i>f</i>_max) are achieved as compared with a reference Schottky-gated HEMT. Thermal stability is studied by conducting temperature-dependent characterizations of devices at ambient temperatures of 300-550 K. Time-dependent electrical reliability analyses for the devices stressed in off-state (V_GS = -20 V and V_DS = 0 V) for 0-60 h and on-state (V_GS = 2 V and V_DS = 20 V) for 0-20 h are also made to physically investigate the dominant degradation mechanisms. Excellent reliability and thermal stability at 300-550 K are achieved by the present design.

A Novel Dilute Antimony Channel

This letter reports, for the first time, a high-electron mobility transistor (HEMT) using a dilute antimony In0.2Ga0.8 AsSb channel, which is grown by a molecular-beam epitaxy system. The interfacial quality within the InGaAsSb/GaAs quantum well of the HEMT device was effectively improved by introducing the surfactantlike Sb atoms during the growth of the InGaAs layer. The improved heterostructural quality and electron transport properties have also been verified by various surface characterization techniques. In comparison, the proposed HEMT with (without) the incorporation of Sb atoms has demonstrated the maximum extrinsic transconductance gm,max of 227 (180) mS/mm, a drain saturation current density IDSS of 218 (170) mA/mm, a gate-voltage swing of 1.215 (1.15) V, a cutoff frequency fT of 25 (20.6) GHz, and the maximum oscillation frequency fmax of 28.3 (25.6) GHz at 300 K with gate dimensions of 1.2times200 mum2

\hbox{In}_{0.2}\hbox{Ga}_{0.8}\hbox{AsSb}/\hbox{GaAs}

Gate-metal-related kink effects in InAlAs∕InGaAs∕GaAs metamorphic high-electron-mobility transistors have been investigated. Improvements on the kink effect have been observed by using the higher Schottky barrier height gate alloys, including Ti∕Au, Ni∕Au, and Pt∕Au, as compared to the use of the conventional Au gate metal. In comparison with gate alloy combinations, the devices with Ti∕Au alloy exhibit superior noise characteristics, whereas those with Ni∕Au alloy demonstrate the highest power characteristics. With the gate dimensions of 1.2×200μm2, the device minimum noise figure, NFmin, is 1.17dB at 2.4GHz by using Ti∕Au and the output power is 13.14dBm at 2.4GHz by using Ni∕Au. Significant rf characteristics have also been improved upon that with Au gate.

HEMT

Various static and microwave performances on InAlAs/InGaAs/InP HEMTs with a linearly-graded InxGa1−xAs channel (LGC-HEMT) have been comprehensively investigated and compared to those having a conventional lattice-matched In0.53Ga0.47As channel (LM-HEMT). Improved carrier transport characteristics and confinement capability by employing the linearly-graded channel have contributed to superior extrinsic transconductance (gm) of 346 mS mm−1, gate-voltage swing (GVS) of 0.5 V (182 mA), unity-gain cut-off frequency (ft) of 41 GHz and maximum oscillation frequency (fmax) of 63 GHz, with an improved frequency operation plateau at 300 K for a gate dimension of 0.65 × 200 µm2. Furthermore, improved kink effects leading to a lower gate leakage current of 0.7 µA mm−1, lower output conductance (gd) of 3.6 mS mm−1, higher voltage gain (AV) of 93.1, higher off-state breakdown voltage of 16.3 V and superior output power characteristics have also been discussed.

Gate-alloy-related kink effect for metamorphic high-electron-mobility transistors

Al0.22Ga0.78As/In0.24Ga0.76As pseudomorphic high-electron-mobility transistors (pHEMTs) with metal-oxide-semiconductor (MOS)-gate structure or oxide passivation by using ozone water oxidation treatment have been comprehensively investigated. Annihilated surface states, enhanced gate insulating property and improved device gain have been achieved by the devised MOS-gate structure and oxide passivation. The present MOS-gated or oxide-passivated pHEMTs have demonstrated superior device performances, including superior breakdown, device gain, noise figure, high-frequency characteristics and power performance. Temperature-dependent device characteristics of the present designs at 300–450 K are also studied.