InGaP/InGaAs Pseudomorphic Heterodoped-Channel FETs With a Field Plate and a Reduced Gate Length by Splitting Gate Metal

Depositing gate metal across a step undercut between the Schottky barrier layer and the insulator-like layer is employed to obtain a reduced gate length of 0.4 mum with an additional 0.6-mum field plate from a 1-mum gate window. Most dc and ac characteristics including current density (I_DSS=451mA/mm), transconductance (g_m,max=225mS/mm), breakdown voltages (V_BD(DS)/V _BD(GD)=22/-25.5V), gate-voltage swing (GVS=2.24V), cutoff, and maximum oscillation frequencies (f_t/f_max=17.2/32GHz) are improved as compared to those of a 1-mum gate device without field plate. At a V_DS of 4.0 V, a maximum power added efficiency of 36% with an output power of 13.9 dBm and a power gain of 8.7 dB are obtained at a frequency of 1.8 GHz. The saturated output power and the linear power gain are 316 mW/mm and 13 dB, respectively     

InP/GaAsSb type-II DHBTs with GaAsSb/lnGaAs superlattice-base and GaAsSb bulk-base structures

High-performance InP/GaAsSb double heteroj unction bipolar transistor (DHBT) employing GaAsSb/lnGaAs superlattice-base structure is demonstrated and compared with GaAsSb bulk-base structure by two-dimensional simulation analysis. The proposed device exhibits a higher current gain of 257 than the conventional InP/GaAsSb type-II DHBT with a lower current gain of 180, attributed to the tynneling behavior of minority carriers in the GaAsSb/lnGaAs superlattice-base region under large forward base—emitter bias. In addition, a larger unity gain cutoff frequency of 19.1 GHz is botained for the superlattice-base device than that of 17.2 GHz for the bulk-base device.     

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     

Multiple-route current-voltage (I-V) characteristics of GaAs-InGaAsmetal-insulator-semiconductor-like (MIS) structure for multiple-valuedlogic applications

A new GaAs-In_xGa_1-xAs metal-insulator-semiconductor-like (MIS) device with the interesting dual-route and multiple-negative-differential-resistance (MNDR) current-voltage (I-V) characteristics has been fabricated and demonstrated. These performances are caused by the successive barrier lowering and potential redistribution effect. A novel multiple-route I-V characteristic is obtained in the studied device at low temperature (-130°C). This performance is different from the previously reported NDR switching device and has not yet been found in other devices. The interesting property of the studied structure provides a promising candidate for switching device applications     

Temperature-dependent investigation of a high-breakdown voltage andlow-leakage currentGa0.51In0.49P/In0.15Ga0.85Aspseudomorphic HEMT

We reported a newly designed double delta-doped GaInP/InGaAs pseudomorphic HEMT with high temperature-dependent performances. In addition to the novel aspects of the proposed HEMT structure, temperature-dependent behaviors including a high-voltage (40 V) and a low-leakage current (17 nA/mm) are further improved by eliminating mesa-sidewall effect. We obtained nearly current-independent transconductance in the temperature of 300-450 K. The measured current gain cutoff frequency f_T and maximum oscillation frequency f _max for a 1-μm gate device are 12 and 28.4 GHz, respectively     

New self-aligned T-gate InGaP/GaAs field-effect transistors grownby LP-MOCVD

This paper reports on self-aligned T-gate InGaP/GaAs FETs using n ⁺/N⁺/δ(P⁺)/n structures. N⁺ -InGaP/δ(P⁺)-InGaP/n-GaAs forms a planar-doped barrier. The inherent ohmic gate of camel-gate FETs together with a highly selective etch between an InGaP and a GaAs layers offers a self-aligned T-shape gate with a reduced effective length. A fabricated device with a reduced gate dimension of 1.5×100 (0.6×100) μm² obtained from 2×100 (1×100) μm² gate metal exhibits an extrinsic transconductance, unity-current gain frequency, and unity-power gain frequency of 78 (80) mS/mm, 9 (19.5), and 28 (30) GHz, respectively     

Temperature-dependence investigation of a high-performance inverteddelta-doped V-shaped GaInP/InxGa1-xAs/GaAspseudomorphic high electron mobility transistor

A newly designed inverted delta-doped V-shaped GaInP/In_xGa_1-xAs/GaAs pseudomorphic high electron mobility transistor (PHEMT) has been successfully fabricated and studied. For a 1×100 μm² device, a high gate-to-drain breakdown voltage over 30 V at 300 K is found. In addition, a maximum transconductance of 201 mS/mm with a broad operation regime for 3 V of gate bias (565 mA/mm of drain current density), a very high output drain saturation current density of 826 mA/mm, and a high DC gain ratio of 575 are obtained. Furthermore, good temperature-dependent performances at the operating temperature ranging from 300 to 450 K are found. The unity current gain cutoff frequency f_T and maximum oscillation frequency f_max up to 16 and 34 GHz are obtained, respectively. Meanwhile, the studied device shows the significantly wide and flat gate bias operation regime (3 V) for microwave performances     

High-performance InGaP/GaAs pnp δ-doped heterojunction bipolar transistor

In this article, a novel InGaP/GaAs pnp δ-doped heterojunction bipolar transistor is first demonstrated. Though the valence band discontinuity at InGaP/GaAs heterojunction is relatively large, the addition of a δ-doped sheet between two spacer layers at the emitter-base (E-B) junction effectively eliminates the potential spike and increases the confined barrier for electrons, simultaneously. Experimentally, a high current gain of 25 and a relatively low E-B offset voltage of 60 mV are achieved. The offset voltage is much smaller than the conventional InGaP/GaAs pnp HBT. The proposed device could be used for linear amplifiers and low-power complementary integrated circuit applications. The article is published in the original.     

Comprehensive investigation on planar type of Pd–GaN hydrogen sensors

This paper reviews both static and dynamic characteristics of a planar-type Pd–GaN metal–semiconductor–metal (MSM) hydrogen sensor. The sensing mechanism of a metal–semiconductor (MS) hydrogen sensor was firstly reviewed to realize the sensing mechanism of the proposed sensor. Symmetrically bi-directional current–voltage characteristics associated with our sensor were indicative of easily integrating with other electrical/optical devices. In addition to the sensing current, the sensing voltage was also used as detecting signals in this work. With regard to sensing currents (sensing voltages), the proposed sensor was biased at a constant voltage (current) in a wide range of hydrogen concentration from 2.13 to 10,100 ppm H₂/N₂. Experimental results reveal that the proposed sensor exhibits effective barrier height variations (sensing responses) of 134 (173) and 20 mV (1) at 10,100 and 2.13 ppm H₂/N₂, respectively. A sensing voltage variation as large as 18 V was obtained at 10,100 ppm H₂/N₂, which is the highest value ever reported. If an accepted sensing voltage variation is larger than 3 (5) V, the detecting limit is 49.1 (98.9) ppm. Moreover, voltage transient response and current transient response to various hydrogen-containing gases were experimentally studied. The new finding is that the former response time is shorter than the latter one. Other dynamic measurements by switching voltage polarity and/or continuously changing hydrogen concentration were addressed, showing the proposed sensor is a good candidate for commonly used MS sensors.     

Hydrogen-sensitive sensor with stabilized Pd-mixture forming sensing nanoparticles on an interlayer

Pd-based mixtures comprising silicon dioxide (SiO₂) were used as sensing materials in fabrication of GaN-based hydrogen sensors. The mixture as-deposited has a rough surface with many pores. After wet selectively etching to remove SiO₂, the mixture turns into Pd nanoparticles with a size of ∼ 30 nm on an interlayer with oxygen, as indicated by SEM, EDX, and SIMS methods. A careful study of the Pd-mixture on a metal-semiconductor-metal type of hydrogen sensor provides significant information on the roles of oxygen and the interlayer. Experimental results reveal that hydrogen atoms trapped inside the mixture as-deposited cannot contribute to changes in barrier height as an applied voltage is not large enough. Improved sensing properties such as hydrogen dissociation rate, diffusion rate, and storage capability were obtained when Pd nanoparticles were formed by selectively etching the mixture. The situation that hydrogen atoms were blocked and disturbed by oxygen will exist no more. Uniform sensing responses of higher than 10⁵ (defined as (J_H2-J_N2)/J_N2, J_H2 and J_N2 are current densities measured in H₂/N₂ and N₂ ambiences, respectively), voltage shifts of larger than 20 V were obtained at 2.13 ppm H₂/N₂. In addition, hydrogen transport through grain boundaries of Pd nanoparticles is much faster than diffusion through a Pd-mixture layer. A much shorter response time was obtained from the sensors with the Pd-mixture wet etched. Furthermore, stable and reliable sensing characteristics were also expected.