Ke-Hua Su

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-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.

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.

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}

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.

HEMT

This work provides comparative studies of a double δ-doped Al 0.3 Ga 0.7 As/In ℵ Ga 1-ℵ As/GaAs symmetrically graded (x = 0.15 → 0.2 → 0.15) doped-channel field-effect transistor (DD-DCFET) with respect to a conventional double 8-doped pseudomorphic high electron mobility transistor (pHEMT) and a conventional DCFET structure. All threes samples, grown by the low-pressure metallorganic chemical vapor deposition (LP-MOCVD) system, have identical layer structures except for their different doping schemes. Comprehensive investigations on the static, microwave, and temperature-dependent characteristics have been made. Possessing the advantages of DCFETs and pHEMTs, the proposed DD-DCFET has demonstrated comprehensively superior linearity, current drive, voltage gain, high-frequency characteristics, and thermal stability characteristics. It is promisingly suitable for millimeter-wave integrated circuit applications.

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

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.

Comparative Studies on Double δ -Doped Al0.3Ga0.7As ∕ In x Ga1 − x As ∕ GaAs Symmetrically Graded Doped-Channel Field-Effect Transistors

The performance characteristics of InGaAsN quantum well (QW) lasers with and without trimethylantimony (TMSb) preflow have been studied. The TMSb preflow before the growth of InGaAsN QWs can suppress the Al-contamination effect and decrease the threshold current density compared with conventional InGaAsN QW lasers without preflow. The photoluminescence (PL) intensity increased and linewidth decreased when TMSb flow rate increased. According to the atomic force microscopy (AFM) measurement, the surface roughness was also reduced significantly after TMSb treatment which manifested that the preflow prevented the Al and N precursors from reacting with each other and resulted in a higher optical quality in InGaAsN QWs.

Improved InAlGaP-based heterostructure field-effect transistors

This work reports for the first time a novel In0.2Ga0.8AsSb/GaAs heterostructure doped-channel field-effect transistor (DCFET) grown by the molecular beam epitaxy system. The interfacial quality within the InGaAsSb/GaAs quantum well of the DCFET device has been effectively improved by introducing surfactant-like Sb atoms during the growth of the Si-doped InGaAs channel layer. The improved device characteristics include the peak extrinsic transconductance (gm, max) of 161.5 mS mm−1, the peak drain–source saturation current density (IDSS, max) of 230 mA mm−1, the gate–voltage swing (GVS) of 1.65 V, the cutoff frequency (fT) of 12.5 GHz and the maximum oscillation frequency (fmax) of 25 GHz at 300 K with the gate dimensions of 1.2 × 200 µm2. The proposed design has also shown a stable thermal threshold coefficient (∂Vth/∂T) of −0.7 mV K−1.

Performance Improvement of InGaAsN/GaAs Quantum Well Lasers by Using Trimethylantimony Preflow

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.