Cheng-Zu Wu

A novel InGaP/GaAs S-shaped negative-differential-resistance (NDR) switch for multiple-valued logic applications

In this paper, a novel InGaP/GaAs multiple S-shaped negative-differential-resistance (NDR) switch based on a heterostructure-emitter bipolar transistor (HEBT) structure is fabricated and demonstrated. An interesting multiple NDR phenomenon resulting from an avalanche multiplication and successive two-stage barrier lowering process is observed under the inverted operation mode. The three-terminal-controlled and temperature-dependent NDR characteristics are also investigated. In addition, a typical transistor performance is found under the normal operation mode. Consequently, owing to the presented different stable operation points and transistor action, the studied device shows a good potential for multiple-valued logic and analog amplification circuit applications.

A novel Pd/oxide/GaAs metal-insulator-semiconductor field-effect transistor (MISFET) hydrogen sensor

A novel and high-performance Pd/oxide/GaAs hydrogen sensor based on a metal-insulator-semiconductor field-effect transistor (MISFET) is fabricated and studied. In the presence of the interfacial oxide, high sensitivity and significant increase in output drain current are observed. In the presence of hydrogen, a 2×200 µm2 gate dimension device shows good dc characteristics including high turn-on voltage, an obvious variation of drain current and a short response time. In addition, under the applied voltage of -4 V and 537 ppm hydrogen in air, a very high sensitivity of 9473 is obtained. This performance shows that the device studied has a good potential for high-speed and high-sensitivity hydrogen sensor and MISFET integrated circuit applications.

On the InGaP/GaAs/InGaAs camel-like FET for high-breakdown, low-leakage, and high-temperature operations

A new field-effect transistor using a high-barrier n/sup +/ -GaAs/p/sup +/-InGaP/n-GaAs camel-like gate and GaAs/InGaAs heterostructure-channel has been fabricated successfully and demonstrated. Experimentally, an ultra high gate-drain breakdown voltage of 52 V, a high drain-source operation voltage over 20 V with low leakage currents, and a high drain-source off-state breakdown voltage of 39.7 V are obtained for a 1/spl times/100 /spl mu/m/sup 2/ device. The high breakdown behavior is attributed to the use of high barrier camel-like gate and heterostructure channels to reduce the undesired leakage current. Furthermore, the studied device also shows high breakdown behavior in a high temperature environment and good microwave characteristics. Therefore, based on these characteristics, the studied device is suitable for high-breakdown, low-leakage, and high-temperature applications.

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.

Investigation of temperature-dependent performances of InP/In0.53Ga0.34Al0.13As heterojunction bipolar transistors

Temperature-dependent dc performances of lattice-matched InP/InGaAlAs heterojunction bipolar transistors (HBTs) using the InGaAlAs quaternary alloy as the base and collector layers are studied and reported. When compared with conventional InP/InGaAs HBTs, the device studied exhibits a higher common-emitter breakdown voltage and a lower output conductance even at high temperature. The variations of offset voltage and ideality factor at different temperatures have been analysed. In addition, with decreasing temperature from 25 °C toward -196 °C, an irregular temperature behaviour of current gain is observed. At high current levels, the temperature-dependent current gain is mainly determined by the reduced reverse hole injection current. As the current level is lowered, the dominance of reverse hole injection current is correspondingly replaced by the recombination current.

Characteristics of metal-insulated-semiconductor (MIS) like In0.2Ga0.8AsGaAs doped-channel structure

Abstract A metal-insulated-semiconductor (MIS) like In 0.2 Ga 0.8 As GaAs doped-channel structure has been proposed. Furthermore, a field-effect transistor (FET) based on the proposed structure is also fabricated. Both theoretical simulations and experiments are made and compared in this paper. First, the theoretical analysis by using the self-consistent method with a quadratic expression of the charge control process is employed to simulate the basic electronic properties of the doped-channel FET. From the simulation results, we can find that the d.c. performances show good transistor characteristics. For the experimental results, a high breakdown voltage of 17.4 V, a maximum drain saturation current of 930 mA/mm, a maximum transconductance of 235 mS/mm, and a very broad gate voltage range larger than 3 V with the transconductance higher than 200 mS/mm are obtained for a 2 × 100 μm2 gate-dimension FET. From the comparison, we find that experiment results are in a good agreement with the theoretical simulations. The performances provide a promise of the proposed device to be a good candidate for practical circuit applications.

Multiple negative-differential-resistance (NDR) of InGaP/GaAs heterostructure-emitter bipolar transistor (HEBT)

An interesting multiple S-shaped negative-differential-resistance (NDR) phenomenon is observed for an InGaP/GaAs heterostructure-emitter bipolar transistor (HEBT) under the inverted operation mode. This behavior results from a sequential avalanche multiplication and two-stage barrier lowering effect. The two-stage barrier lowering effect is assumed to be caused by the high valence-band-discontinuity (/spl Delta/E/sub v/) to conduction-band-discontinuity (/spl Delta/E/sub c/) ratio at InGaP/GaAs heterointerface which gives holes and electrons accumulation effect successively. Under normal operation mode, a typical common-emitter current gain of 60 is obtained at collector current density of 400 A/cm/sup 2/ for the studied HEBT without emitter-edge thinning structure. Consequently, the controlled switching and transistor performances provide a promise of the studied device for circuit applications.

Improved n+-GaAs/p+-In0.49Ga0.51P/n-GaAs camel-like gate structure for high-breakdown, low-leakage, and high-temperature applications

A n+-GaAs/p+-In0.49Ga0.51P/n-GaAs camel-like gate structure has been applied to fabricate high-performance transistors. The studied heterostructure field-effect transistor exhibits a large barrier height, high breakdown voltage, low leakage current, and good temperature-dependent characteristics. Experimentally, for a 1×100 μm2 device, the gate-drain breakdown voltage and gate leakage current are 52 (31.5) V, and 37 μ A/mm (3.5 mA/mm) at the gate-drain voltage of 40 V, respectively, at the temperature of 300 (480) K. In addition, the high drain-source operation voltage over 20 V with low leakage current is obtained.

Investigation of an InGaP/GaAs resonant-tunneling heterojunction bipolar transistor

Abstract An interesting InGaP/GaAs resonant-tunneling heterojunction bipolar transistor incorporating a superlattice (SL) structure in the emitter has been fabricated and studied. With the n-type doped well, the strongly coupling effect dominating the biased SL behaves like a double barrier operation. On the basis of the transfer matrix method, the transport mechanism of sequential miniband conduction can be developed by the theoretical calculation associated with the RT in the studied SL structure. Experimentally, the double negative differential resistance phenomena are presented both in the two-and three-terminal current–voltage characteristics at 300 K. In addition, excellent transistor behaviors including the high dc current gain as high as 70, low saturation voltage smaller than 1.2 V, low offset voltage of 110 mV and high breakdown voltage larger than 20 V are obtained.

Observation of the anomalous current–voltage characteristics of GaAs/n+‐InGaAs/GaAs doped‐channel structure

A GaAs/n+‐In0.2Ga0.8As/GaAs doped‐channel field‐effect transistor structure has been fabricated and studied. A typical transistor performance with a threshold voltage of about −3.0 V and transconductance of up to 160 mS/mm is obtained in the lower gate‐source voltage (VGS <−1.0 V) regime. However, for some devices, the three‐terminal‐controlled N‐shaped negative‐differential‐resistance (NDR) behavior is observed at the saturation regime of current–voltage characteristics under higher gate‐source bias (VGS≥−1.0 V) condition. The interesting NDR phenomenon is believed to be attributed to the real‐space transfer and deep‐level electron trapping effect.