Tzong-Bin Wang

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.

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.

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.

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

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.

Comparison of Al0.32Ga0.68N ∕ GaN Heterostructure Field-Effect Transistors with Different Channel Thicknesses

Al 0. 32 Ga 0. 68 N/GaN heterostructure field-effect transistors (HFETs) grown by low-pressure metallorganic chemical vapor deposition are successfully fabricated. A Mg-doped insulating GaN layer is inserted to suppress the leakage current, improve the breakdown voltages, and yield excellent pinch-off characteristics. Moreover, HFETs with different channel thicknesses of 1200, 1500, and 1800 A are investigated. Experimental results show that an HFET with a 1800 A thick channel layer has the highest electron mobility, electron concentration, drain current, and extrinsic transconductance.

Improved InAlGaP-based heterostructure field-effect transistors

This investigation proposes the improved double δ-doped InGaP/InGaAs heterostructure field-effect transistor (HFET) grown by metalorganic chemical vapour deposition. The extrinsic transconductance (gm) and saturation current density (Imax) of the double δ-doped InGaP/InGaAs HFET are superior to those of the previously reported single δ-doped InGaP/InGaAs HFETs. The first n-InAlGaP/GaAs HFET is also investigated because it has a high Schottky barrier, a large high band gap and a large conduction-band discontinuity (ΔEC). Even without indium in the channel of the InAlGaP/GaAs HFET, gm and Imax are as high as 170 mS mm−1 and 410 mA mm−1, respectively. The gm values of these two HFETs remain large even when the gate voltages are positive. Moreover, the breakdown voltages of the two examined HFETs both exceed 40 V.

Single-mode InGaAs photonic crystal vertical-cavity surface-emitting lasers emitting at 1170 nm

We have made MOCVD-grown InGaAs photonic crystal vertical-cavity surface-emitting lasers (PhC-VCSELs) for fiber-optic applications. Multi-mode InGaAs VCSELs have achieved a maximum power of over 1 mW. Single-mode characteristics of 0.18 mW of the PhC-VCSELs have been made by using the combined AlOx oxide layer with proton-implantion for better current confinement.

n + -GaAs ∕ p + -InAlGaP ∕ n + -InAlGaP Camel-Gate High-Electron Mobility Transistors

This investigation proposes InAlGaP/InGaAs camel-gate high-electron mobility transistors with inverted δ-doping layers (CAM-HEMTs). CAM-HEMTs with various gate metals, including Au, Pt/Au, Ti/Au, and Ni/Au, are investigated. The CAM-HEMT with the Ni/Au gate metal exhibits the benefits of a large gate voltage swing (3.6 V), a high two-terminal gate-source breakdown voltage (>20 V), no bell-shaped gate current and temperature-insensitive threshold voltages. These characteristics are attributable to the inverted δ-doping layer, the large conduction-band discontinuity of the InAlGaP/InGaAs heterojunction, the large bandgap of InAlGaP and the high camel-gate barrier with the Ni/Au gate metal.

Improved In0.45Al0.55As/In0.45Ga0.55As/In0.65Ga0.35As Inverse Composite Channel Metamorphic High Electron Mobility Transistor

A δ-doped In0.45Al0.55As/InGaAs metamorphic high-electron-mobility transistor (MHEMT) using an In0.45Ga0.55As/In0.65Ga0.35As inverse composite channel has been fabricated successfully and demonstrated. The inverse composite channel significantly reduces Coulomb scattering and consequently improves electron mobility as well as carrier confinement. Experimentally, a high extrinsic transconductance of 321 mS/mm and a drain–source saturation current density of 342 mA/mm are obtained for a 0.65 ×200 µm2 gate at 300 K. Meanwhile, degradation of the studied device, in terms of parameters such as Gm,max, IDSS, and Vth, with increasing temperature is not evident. A positive temperature coefficient of Vth is observed. The measured fT and fmax for a 0.65-µm-gate device are 41.6 and 53 GHz, respectively. In addition, the studied device also shows good microwave performances in a flat and wide operation region. From VGS = -2.5 to 0.5 V, the values of fT and fmax are still over 33 GHz.