Yu-Huei Wu

On the improvement of gate voltage swings in delta -doped GaAs/In/sub x/Ga/sub 1-x/As/GaAs pseudomorphic heterostructures

Significant improvements in gate voltage swings in heterostructures prepared by low-pressure metalorganic chemical vapor deposition are discussed. Structures utilizing a compositionally graded In/sub x/Ga/sub 1-x/As channel exhibited a very flat transconductance region of 2 V. The gate voltage swings of single and double delta -doped GaAs/In/sub 0.25/Ga/sub 0.75/As/GaAs structures were 2.5 and 2.8 V, respectively. All structures also exhibited high extrinsic transconductance as well as high saturation current densities. >

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.

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.

Continuous-time photoelectron spectroscopy for monitoring monochromatic soft x-ray photodissociation of CF3Cl adsorbed on Si(111)−7×7

The continuous-time photoelectron spectroscopy was proposed to study the monochromatic soft x-ray photodissociation of CF3Cl molecules adsorbed on Si(111)−7×7. Evolution of adsorbed CF3Cl was monitored at two photon energies of 240 and 730eV to deduce the photolysis cross section as a function of energy. Dissociation of adsorbed CF3Cl by 240∕730eV photons is attributed to the C–Cl∕C–F bond scission following the excitation of Cl(2p)∕F(1s) core electron. Observation of time-dependent photodissociation also demonstrates the capability for “real-time” monitoring of the variations of electronic structure and chemical bonding of adsorbate in bond-selective photochemistry.

A novel InAlAs/InGaAs two-terminal real-space transfer diode

We report a two-terminal real-space transfer diode (RSTD) using a InAlAs/InGaAs heterojunction grown by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). By virtue of nonalloyed ohmic contacts as well as a sewer layer which is electrically separated from ohmic electrodes, a carrier density modulation and a strong negative differential resistance can be obtained. A peak-to-valley current ratio up to 140000 (1/spl times/10/sup 6/) at 300 (77) K are, to our knowledge, among the best for InAlAs/InGaAs structures. The proposed device also reveals sharp charge injection and broad valley range.

Characteristics of graded‐like multiple‐delta‐doped GaAs field effect transistors

Multiple‐δ‐doped GaAs field effect transistors using graded‐like δ‐doping profile are demonstrated and investigated. An extremely high carrier density of 1.2×1013 (7.9×1012) cm−2 along with an enhanced Hall mobility of 1700 (3300) cm2/v s at 300 (77) K for a triple‐δ‐doped GaAs structure are achieved. The dc characteristic reveals an extrinsic transconductance as high as 110 mS/mm at room temperature with a gate length of 2 μm. Three separated peaks in the transconductance versus gate bias curve are observed. Meanwhile, a broad and flat transconductance region is obtained.

Characteristics of In0.53Ga0.47As/InP double and single heterostructure-emitter bipolar transistors grown by LP-MOCVD

Abstract We have successfully fabricated InGaAs/InP double and single heterostructure-emitter bipolar transistors. The double and single HEBTs exhibit common-emitter current gain of 120 and 41 along with offset voltage of 45 and 50 mV, respectively. These preliminary results demonstrate that HEBT structure can effectively provide a high electron injection and better hole confinement. Moreover, a symmetric structure for reducing the offset voltage is also proposed.

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.

Electrical characteristics of a lattice-matched In0.53Al0.22Ga0.25AsInP heterojunction bipolar transistor with zero potential spike at emitter-base heterojunction

Abstract We report qualitatively a lattice-matched In 0.53 Al 0.22 Ga 0.25 As InP heterojunction bipolar transistor grown by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The In 0.53 Al 0.22 Ga 0.25 As InP heterostructure has a large valence band discontinuity and a zero conduction band discontinuity which are suitable for the HBTs. A common-emitter current gain of 85 along with a low offset voltage 50 mV are obtained. The junction ideality factors of collector and base current are 1.18 and 1.35, respectively. The current gain ( h FE ) slightly increases with the increase of collector current.

Emitter Edge-Thinning Effect on InGaAs/InP Double-Heterostructure-Emitter Bipolar Transistor

An emitter edge-thinning design is used for a lattice-matched InGaAs/InP double-heterostructure-emitter bipolar transistor (DHEBT) grown by low-pressure metalorganic chemical vapor deposition (MOCVD). Using the emitter edge-thinning technique, the surface recombination current is reduced and the current gain is improved. This structure reveals a typical current gain as high as 120 at a collector current density of 241 A/cm2, along with an offset voltage as low as 45 mV. Furthermore, the problem of surface recombination current is also discussed in terms of the emitter size effect on current gain. The Gummel plots are shown to explain the influence of the emitter edge-thinning process on the base current ideality factor.