Yu-Shyan Lin

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.

High breakdown characteristic /spl delta/-doped InGaP/InGaAs/AlGaAs tunneling real-space transfer HEMT

A novel /spl delta/-doped InGaP/InGaAs/AlGaAs tunneling real-space transfer high-electron mobility transistor (TRST-HEMT) has been successfully fabricated by low-pressure metal organic chemical vapor deposition (LP-MOCVD). Three-terminal N-shaped negative differential resistance (NDR) phenomenon due to the hot electrons real-space transfer (RST) at high electric field is observed. Two-terminal gate-to-drain breakdown voltage is more than 40 V with a leakage current as low as 0.27 mA/mm. High three-terminal on-state breakdown voltage as high as 19.2 V and broad plateau of current valley as high as 15 V are achieved. These characteristics are attributed to the use of high Schottky barrier height, high bandgap of InGaP Schottky layer, /spl delta/-doping, and GaAs subspacer layers. The measured maximum peak-to-valley ratio (PVR) value is 2.7.

Mobility Enhancement and Breakdown Behavior in InP-Based Heterostructure Field-effect Transistor

This study proposes an InAlAsSb/InP heterostructure field-effect transistor (HFET) grown by a low-pressure metallorganic chemical vapor deposition system. Its InAlAsSb Schottky layer and coupled 8-doped InP channels causethis HFET to exhibit high two- and three-terminal breakdown voltages. Mobility and two-dimensional electron gas concentration are increased. Additionally, this HFET does not exhibit the frequently observed parallel conduction and bell-shaped characteristics of conventional HFETs. The activation energy is also determined.

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.

Effect of Temperature on Novel InAlGaP ∕ GaAs ∕ InGaAs Camel-Gate Pseudomorphic High-Electron-Mobility Transistors

As an alternative to AlGaAs/GaAs and InGaP/GaAs camel-gate heterostructure field-effect transistors (CAMFETs) for microwave applications, InAlGaP/GaAs/InGaAs pseudomorphic high-electron-mobility transistors (CAM-pHEMTs) are shown to have high breakdown voltage, high broad-plateau extrinsic transconductance (g m ), and small leakage current. Two-terminal gate-source breakdown voltage exceeding 20 V is achieved for CAM-pHEMT with Ni/Au gate metal. The transconductance curve is quite broad for a gate voltage range of approximately 3.6 V. Additionally, CAM-pHEMT exhibits relatively negligible temperature- dependent characteristics over the operating temperature range. Therefore, the studied device displays promise for high-temperature applications.

Enhancing the current gain in InP/InGaAs double heterojunction bipolar transistors using emitter edge thinning

This paper reports InP/InGaAs double heterojunction bipolar transistors (DHBTs) made with composite-collector designs. The current gains of the DHBTs without and with emitter edge-thinning designs are 125 and 180, respectively. The composition of the collector and the base currents is analysed from the Gummel plots. Experimental data demonstrate that emitter edge thinning can further reduce the surface recombination current of the InP/InGaAs DHBTs and thus dramatically improve current gain, even though the surface recombination in InP/InGaAs DHBTs is much less than in GaAs-based DHBTs.

Comprehensive Characterization of In0.45Al0.55As ∕ In0.5Ga0.5As ∕ In x Al1 − x As Metamorphic High-Electron-Mobility Transistors on GaAs Substrates

An In 0.45 Al 0.55 As/In 0.5 Ga 0.5 As metamorphic high-electron-mobility transistor (MHEMT) with an inverse-step InAlAs metamorphic buffer, grown by molecular beam epitaxy on GaAs substrate, is presented. A typical 1 μm gate-length MHEMT has a drain current density of 471 mA/mm and a peak extrinsic transconductance of 258 mS/mm. High-frequency scattering parameter measurements yield a unity current gain cutoff frequency of f T = 35.2 GHz as well as a maximum frequency oscillation f max = 48 GHz. High two-terminal and three-terminal breakdown voltages are achieved mainly because of the high bandgap of the In 0.45 Al 0.55 As Schottky layer and the large conduction-band discontinuity (ΔE C ) at the InAlAs/InGaAs heterojunction. The large-signal power performance and noise characteristics are measured. Experimental results on the temperature-dependence study of the saturation drain current density, the extrinsic transconductance, the leakage current, the off-state breakdown voltage, and the threshold voltage (V th ) are presented. The V th shift of the device at elevated temperatures is as small as -0.294 mV/K. All of the experimental results confirm the exceptional potential of the InAlAs/InGaAs/GaAs MHEMT in microwave circuit and high-temperature applications.

Novel Delta-Doped InAlGaP/GaAs Heterojunction Bipolar Transistor

The first successful demonstration of a delta-doped InAlGaP/GaAs heterojunction bipolar transistor (HBT) is reported. A comparison to a baseline InAlGaP/GaAs HBT without a delta-doping layer is made. Both of these devices exhibit near-ideal current gain (beta) versus the collector current (<i>I</i> _C) characteristics (i.e., beta independent of <i>I</i> _C) at high currents. The delta-InAlGaP/GaAs HBT exhibits a 40% reduction in offset voltage (<i>V</i> _CE, _offset) and a 250-mV reduction in knee voltage (<i>V</i> _k) without sacrificing beta compared with the baseline InAlGaP/GaAs HBT. At a higher <i>I</i> _C, the decrease in beta of the InAlGaP/GaAs HBTs with increasing temperature is significantly smaller than the corresponding effect measured in the formerly reported GaAs-based HBTs. The rather temperature-insensitive characteristics of these two InAlGaP/GaAs HBTs originate from their large valence-band discontinuity (Delta<i>E</i> _V) at the emitter-base (E-B) junction. Furthermore, at intermediate base current <i>I</i> _B levels (0.4-1.6 mA), <i>V</i> _CE, _offset falls as <i>I</i> _B increases, which is a trend contrary to that of most HBTs in the literature. Finally, the experimental dependence of <i>V</i> _CE, _offset on temperature, <i>I</i> _B, and the effective barrier height at the E-B junction is explained with reference to an extended large-signal model.

Comprehensive Characterization of AlGaAs ∕ InGaAs ∕ GaAs Composite-Channel High-Electron Mobility Transistor

This investigation addressed an AlGaAs/InGaAs/GaAs pseudomorphic high-electron mobility transistor (pHEMT), incorporating double δ-doping carrier supply layers and a composite channel, grown by metallorganic chemical vapor deposition (MOCVD). The AlGaAs/InGaAs/GaAs pHEMT was fully characterized. When dc was applied, the device had a maximum drain current (I D,max ) of 302 mA/mm, a peak extrinsic transconductance (g m,peak ) of 186 mS/mm, and a gate-to-drain breakdown voltage of 27.7 V. At RF, the f T of the device was 16.92 GHz with an extrapolated f max of 37.37 GHz. Furthermore, this transistor underwent high-temperature tests. At high temperature, the device fabricated from the composite-channel structures still performed excellently.

Electrical characteristics of heterostructure-emitter bipolar transistors using spacer layers

We propose an improved In0.5Ga0.5P/GaAs heterostructure-emitter bipolar transistor (HEBT) grown by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The recombination at p-n interface can be significantly reduced at low collector current using 100 A undoped GaAs spacers. Meanwhile, the emitter edge thinning technique is used to reduce the surface recombination current. The passivated device reveals a current gain as high as 360, along with an offset voltage as low as 80 mV. Moreover, the measured results indicate that the current gains vary slowly with temperature. In order to demonstrate that the emitter edge-thinning technique can effectively reduce the surface recombination current, the emitter size effect on current gain is also investigated.