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We study and demonstrate the dc performance of two InP/InGaAs double-heterojunction bipolar transistor (DHBTs) with the undoped tunnelling barrier and composite collector structures. Due to the mass filtering effect for holes, a thin InP tunnelling barrier can be used to replace the wide-gap emitter. By varying the thickness of the barrier, distinct collector current ideality factors can be obtained which reveal different injection mechanisms at the emitter. The 4000 A InP collectors with InP/InGaAs abrupt junctions and InP/InGaAsP/InGaAs step-graded junctions achieve high breakdown voltages of 9.2 and 14.6 V, respectively. Furthermore, the abrupt junction and δ-doping structure eliminate carrier blocking across the base-collector heterojunction more effectively than the step-graded junction. We find that the reduction of the multiplication avalanche of the step-graded junction DHBT leads to the severe self-heating effect. For the abrupt junction DHBT, the dc current gain is almost independent of the perimeter-to-area ratio of the emitter due to the low surface recombination.

We propose two InGaP/GaAs resonant tunneling bipolar transistors (RTBT's) with different superlattice (SL) structures in the emitters. Based on the calculations of transmission probability, the ground-state and first excited-state minibands are estimated. The electron transmission through SL structures is significantly determined by the electric field behaviors across the barriers. The specific designs of barrier width in the SL structures are responsible for two electron transport mechanisms of sequential RT conduction associated with the minibands. Experimentally, at higher current levels, the double- and quaternary-negative difference resistance (NDR) phenomena are respectively observed for both devices at 300K. Furthermore, the experimental results are in good agreement with the theoretical prediction.

Two InGaP/GaAs resonant tunneling bipolar transistors (RTBTs) with different superlattice (SL) structures in the emitters are fabricated and studied. The uniform and modulated widths of barriers are respectively utilized in the specific SL structures. Based on the calculations, the ground state and first excited state minibands are estimated from the transmission probability. The electron transport of RT through SL structures is significantly determined by the electric field behaviors across the barriers. Experimentally, the excellent transistor characteristics including the small saturation voltage, small offset voltage and high breakdown voltages are obtained due to the insertion of /spl delta/-doping sheet at the base-collector (B-C) heterointerface. Furthermore, at higher current regimes, the double- and quaternary-negative difference resistance (NDR) phenomena are observed in agreement with the theoretical prediction at 300 K.

A novel photonic-sensitive InAlGaAs/InP negative-differential-resistance heterojunction bipolar transistor (NDR-HBT) is fabricated and demonstrated. Due to the appropriately designed narrow base width and the employment of a δ -doped sheet at the emitter–base (E–B ) heterojunction, the base resistance effect results in the significant NDR phenomenon. In addition, the experimental results show that the device studied is very sensitive to the applied light source. The N-shaped NDR phenomena are clearly observed under illumination. This phenomenon is attributed to the base resistance and barrier lowering effect resulting from holes induced by the applied light source.

A novel narrow-base heterojunction bipolar transistor and a multiple-state switching device based on the InP/InGaAlAs material system have been fabricated and demonstrated. Common-emitter current gains up to 28 and 25 are obtained. Due to the use of an InGaAlAs narrow base, interesting topee-shaped current-voltage characteristics presented in the transistor active regime and negative-differential-resistance (NDR) loci are observed under the applied base current of IB = 2 µA/step. In addition, multiple-route and multiple-state S-shaped NDR characteristics are observed at 77 K due to the insertion of the InGaAs quantum well in the base-collector junction. The topee-shaped NDR phenomena are attributed to the modulation of the potential spike at the base-emitter heterojunction. However, the switching behaviours are due to the avalanche multiplication, confinement effect and two-stage barrier lowering effect.

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.

An InP/InGaAs superlattice-emitter resonant tunneling bipolar transistor (SE-RTBT) has been fabricated and demonstrated. The influence of the superlattice and emitter thickness on the device characteristics is studied. The insertion of the superlattice and a well-designed emitter improve the characteristics of the SE-RTBT. Common-emitter current gains up to 170 and 54 are obtained for the studied devices with emitter thicknesses of 800 A and 150 A, respectively. Based on the specified structure, the lower offset voltage and saturation voltage ( ≤ 1.5 V) are obtained. Experimentally, the device with a 5-period superlattice and an emitter thickness of 800 A provides higher dc performance and stable temperature-dependent characteristics.

In this paper, we demonstrate multiple-negative-differential-resistance (MNDR) switching behaviors based on the InGaP/GaAs heterostructure-emitter bipolar transistor (HEBT) and InGaAlAs/InP heterojunction bipolar transistor (HBT) structures. The devices act like conventional HBTs under forward operation mode. The proposed HEBTs show lower offset voltage due to the correct design of the emitter thickness. On the other hand, MNDR phenomena resulting from avalanche multiplication, confinement effects and the potential redistribution process are observed under inverted operation mode for both devices. In addition, three-terminal NDR characteristics are investigated under the applied base current I B . Moreover, for the InGaAlAs/InP HBT, anomalous multiple-route and multiple-step current–voltage ( I – V ) characteristics at 77 K are observed due to the insertion of a InGaAs quantum well (QW) between the base and collector layers.

Steady-state and transient hydrogen-sensing characteristics of a novel Pd/InP metal-oxide-semiconductor (MOS) Schottky diode under atmospheric conditions are presented and studied. In presence of oxide layer, the significant increase of barrier height improves the hydrogen sensitivity even at lower operating temperatures. Even at a very low hydrogen concentration environment, e.g., 15 ppm H/sub 2/ in air, a significant response is obtained. Two effects, i.e., the removal of Fermi-level pinning caused by the donor level in the oxide and the reduction of Pd metal work function dominate the hydrogen sensing mechanism. Furthermore, the reaction kinetics incorporating the water formation upon hydrogen adsorption is investigated. The initial heat of adsorption for the Pd/oxide interface is estimated to be 0.42 eV/hydrogen atom. The coverage dependent heat of adsorption plays an important role in hydrogen response under steady-state conditions. In accordance with the Temkin isotherm behavior, the theoretical prediction of interface coverage agrees well with the experimental results over more than three decades of hydrogen partial pressure.

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.

In this work, we report the temperature-dependent characteristics of a new InP/InGaAlAs heterojunction bipolar transistor (HBT). In order to improve the dc performance of conventional InGaAs-based single HBTs, the quaternary In/sub 0.53/Ga/sub 0.34/Al/sub 0.13/As with a wider bandgap is employed as the material for both the base and collector layers. Experimentally, the studied device exhibits a relatively high common-emitter breakdown voltage and low output conductance even at high temperature. Based on the breakdown mechanism of avalanche multiplication, the negative temperature dependence of breakdown voltage is attributed to the positive temperature-dependent impact ionization coefficient. Furthermore, the temperature dependence of current gain is investigated and reported. It is believed that the suppression of hole injection current with decreasing temperature is responsible for the opposite variation of current gains at high current levels.

The temperature-dependent characteristics of an InP/InGaAs superlattice-emitter resonant-tunnelling bipolar transistor have been studied and demonstrated. Due to the use of a five-period InP/InGaAs superlattice, the RT effect is observed at cryogenic temperature. In addition, the temperature-dependent dc characteristics of the studied device from room temperature to 398 K are reported. Dc current gain remains at an approximately constant value over the measured temperature range. The temperature coefficients of base-emitter and base-collector turn-on voltages are -2 and -3 mV K-1, respectively. The ideality factors of base current (nB) and collector current (nC) exhibit negative temperature coefficients. nB≈1 indicates that the bulk base recombination current component dominates the whole base current as the temperature is increased.

Structure of a wide voltage operation regime double heterojunction bipolar transistor, specifically a modified InGaP/GaAs double heterojunction bipolar transistor featuring a very broad collector-emitter voltage operation range, an invention of high speed, low power consumption and high breakdown voltage rated microwave power transistor. Unique in the incorporation of In 0 .49 Ga 0 .51 P collector layer, GaAs delta-doping sheet and undoped GaAs spacer in the collector zone. The introduction of a spacer with a delta doping sheet into the effective base-collector heterojunction serves to eliminate potential spike from appearing at base-collector interfacing any more, thus effectively precludes electron blocking effect. In the emitter zone the inventive design comprises a five-period In 0 .49 Ga 0 .51 P/GaAs superlatticed confinement layer to GaAs emitter homojunction, with superlatticed confinement layer functioning as a containment layer for minority (hole), while the base-emitter homojunction homojunction serves to control the majority (electron) being emitted from the emitter into the base. That achieves an enhanced emitter injection efficiency and lowered offset voltage at the same time, as such, the invention transistor is very fit for application in digital as well as analogue circuits preconditioned by high speed, low power consumption, and high breakdown voltage performances.

A novel multiple-state switching device based on an InP/AlInGaAs heterojunction bipolar transistor (HBT) structure has been successfully fabricated and demonstrated. The common-emitter current gain up to 25 is obtained under the forward operation mode. However, the anomalous multiple-negative-differential-resistance (MNDR) phenomena controlled either by electrical or optical input signals are observed under the inverted operation mode. The studied device exhibits a single-route S-shaped NDR behavior in the dark and a distinct significant S-shaped MNDR phenomena by introducing an incident light source at room temperature. Moreover, the anomalous multiple-route and multiple-step current-voltage (I-V) characteristics are also observed at 77 K. The switching behaviors are attributed to the avalanche multiplication, barrier lowering effect and potential redistribution process. Experimental results show that the studied device provides a good potentiality for multiple-valued logic and optoelectronic switching system applications.

Novel double delta-doped sheet (D3 S) Ga0.51 In0.49 P/In0.15 Ga0.85 As/Ga0.51 In0.49 P pseudomorphic high-electron-mobility transistors (PHEMTs) have been fabricated successfully and studied. A wide-gap Ga0.51 In0.49 P Schottky layer and a D3 S structure are used to improve device performance. Furthermore, an airbridge-gate structure is employed to achieve good dc and RF performances. For a 1 µm gate length device, a high gate-to-drain breakdown voltage over 35 V, an available output current density up to 615 mA mm-1 , a maximum transconductance of 110 mS mm-1 and a high dc gain ratio of 487 are obtained. On the other hand, the maximum values of unity current gain cut-off frequency fT and maximum oscillation frequency fmax are 19.5 and 40.5 GHz, respectively. The output power of 15.6 dB m (363 mW mm-1 ), power gain of 5.6 dB, power added efficiency (PAE) of 37% and drain efficiency (DE) of 51% are obtained at an input power of 10 dB m and the measured frequency of 2.4 GHz.

An i-InGaP/n-In x Ga 1 − x As/i- GaAs step-graded doped-channel field-effect transistor (SGDCFET) has been fabricated and studied. Due to the existence of a V-shaped energy band formed by the step-graded structure, a large output current density, a large gate voltage swing with high average transconductance, and a high breakdown voltage can be expected. In this study, first, a theoretical model and a transfer matrix technique are employed to analyze the energy states and wavefunctions in the step-graded quantum wells. Experimentally, for a 1 × 80 μ m 2 gate dimension device, a maximum drain saturation current density of 830 mAmm − 1 , a maximum transconductance of 188 mSmm − 1 , a high gate breakdown voltage of 34 V, and a large gate voltage swing 3.3 V with transconductance larger than 150 mSmm − 1 are achieved. These performances show that the device studied has a good potentiality for high-speed, high-power, and large input signal circuit applications.

A new and interesting negative-differential-resistance heterojunction bipolar transistor (NDR-HBT) based on the InP/InAlGaAs material system is fabricated successfully and demonstrated. Due to the employment of narrow base and /spl delta/-doped sheet at the emitter-base (E-B) heterojunction, the significant and interesting topee-shaped current-voltage (I-V) characteristics are observed in the low current regime. A peak-to-valley current ratio (PVCR) up to 11 in the NDR loci is found. In the higher current regimes, on the other hand, NDR phenomena disappear and the device acts as a normal bipolar transistor. These interesting properties are believed to be attributed mainly to the modulation of potential spike resulting from the specified device structure.

An InGaP/GaAs heterojunction bipolar transistor (HBT) with an 50A undoped spacer and δ-doped sheet at B-E heterointerface is fabricated and studied. A common-emitter current gain of 280 and an offset voltage as small as 55mV are obtained, respectively. This results show that high current gain and low offset voltage can be attained simultaneously without the passivation of E-B junction. From the experimental results, it shows that the potential spike is indeed reduced by the employment of an δ-doped layer simultaneously.

This paper reports on the characteristics of n + -GaAs/δ(p + )-GaInP/n-GaAs camel-gate heterojunction field-effect transistor (CAMFET) with the triple-step doped-channel. Due to the newly designed structure, the measured gate-drain tum-on and breakdown voltages are as high as 1.6 and 40 V for a fabricated 1×100 μm 2 device, respectively. Furthermore, the measured maximum transconductance is 145 mS/mm with the current gain cut-off frequency f T of 17 GHz and the maximum oscillation frequency f max of 33 GHz, respectively. Based on excellent device characteristics, the studied device shows a promise for circuit applications.

A new In 0.5 Ga 0.5 P/GaAs double heterojunction bipolar transistor (DHBT) with a δ-doped wide-gap collector structure has been grown by a LPMOCVD system. Experimental results show that this device exhibits the advantages of a small offset voltage of 50 mV, a small saturation voltage of I V, and a large breakdown voltage of 20 V with a current gain of 20. These good characteristics are mainly due to the complete elimination of potential spike at emitter-base (E-B) and base-collector (B-C) heterojunction. Consequently, the studied device shows a good promise for high-speed, high-power, lower-power consumption and large input signal circuit applications.

A lattice-matched In0.49Ga0.51P/GaAs/In0.49Ga0.51P doubleδ -doped heterojunction bipolar transistor, prepared by low-pressure metal organic chemical vapor deposition (LP-MOCVD), is fabricated successfully and reported. Due to the insertion of δ -doped sheets and setback layers both at base–emitter (B–E) and base–collector (B–C) heterojunctions, the potential spikes are suppressed significantly. In addition, the electron blocking effect is removed and a dramatic improvement of current gain is obtained. A modified Ebers–Moll model is employed to study and analyse the device performances. The experimental results show that the common-emitter current gain over 210 at the collector current of 35 mA and an offset voltageΔVCE smaller than 50 mV are obtained. Also, a lower knee-shaped voltage of 1.4 V at the collector current of 40 mA is observed. These results indicate that the device studied is a good candidate for high-speed and high-power circuit applications.

A new InGaP/GaAs resonant-tunneling transistor (RTT) has been fabricated successfully and demonstrated. A 5-period InGaP/GaAs superlattice is used as a confinement barrier for holes and an RT route for electrons. A transistor action with a common-emitter current gain up to 220 and an offset voltage of 85 mV are obtained. Due to the RT effect within the 5-period superlattice near the emitter–base p–n junction region, the N-shaped negative-differential-resistance (NDR) phenomena are observed at room temperature. Furthermore, the N-shaped NDR is found both in the saturation and forward-active region. The widely operating regime of NDR may provide the potential for practical applications.

In this paper, the different designs of emitter-base junction including the employment of the δ -doping sheet and setback layer are presented and studied. A theoretical model is used to analyze the performances of the proposed different InGaP/GaAs heterojunction bipolar transistors (HBTs). Experimentally, a new InGaP/GaAs HBT with a δ -doping sheet and a setback layer inserting between emitter-base heterointerface is fabricated successfully. From the theoretical analysis and experimental results, it is found that the insertion of the δ -doping sheet and the setback layer can effectively eliminate the undesired potential spike at N-InGaP/p + -GaAs heterointerface. The experimental common-emitter current gain of 280 at collector current of 85 mA and a low offset voltage of 55 mV are achieved. In addition, a current gain of 11 at very small collector current of 0.5 μ A without passivation is obtained.

A new low-medium-high step-modulation-doped-channel (LMH-SMDC) GaInP/GaAs high barrier gate heterosturcture field-effect transistor (HFET) has been successfully fabricated and demonstrated. A very thin and heavily doped δ(p+)-GaInP layer is introduced to increase high gate turn-on and breakdown voltage and reduce the gate leakage current. A LMH-SMDC structure is used to improve the output current drivability and average transconductance. In addition, a LMH-SMDC metal-semiconductor field-effect transistor (MESFET) has also been fabricated for comparison. The studied devices show good performances of high breakdown voltage, high output drain saturation current and flat and wide transconductance operation regimes. The measured cut-off frequency (fT) is higher than 15 GHz. From experimental results, the studied devices show good potential in high-power and large input signal circuit applications.

A newly designed n-GaAs camel-type field-effect transistor (CAMFET) with a triple-step doped channel has been successfully fabricated and demonstrated. Experimentally, the high gate turn-on voltage of 1.6 V and breakdown voltage of 40 V and the very low gate leakage current of are obtained for the studied CAMFET. In addition, good transistor properties are obtained. The measured current gain cut-off frequency and the maximum oscillation frequency for a m gate device are 17 and 31 GHz, respectively. Based on experimental results, the studied device shows promise for circuit applications.

In this paper, we will investigate three GaAs-based heterostructure-emitter bipolar transistors (HEBTs). These HEBTs have different heterostructure-confinement material systems, e.g., Al0.5Ga0.5As/GaAs, In0.49Ga0.51P/GaAs, and Al0.45Ga0.55As/In0.2Ga0.8As/GaAs. For the studied devices, an n-GaAs emitter layer inserted between the confinement and base layer is expected to eliminate the potential spike at emitter–base (E–B) junction. Therefore, the low collector–emitter offset voltage (ΔVCE) is obtained. For the AlGaAs/GaAs HEBT, experimental results show that a current gain of 180 and a low offset voltage of 80 mV are acquired. In addition, for the InGaP/GaAs HEBT, the current gain is only 60 attributed to the use of larger emitter layer thickness (700 A) which causes a large recombination current in neutral-emitter regime even when a large valence band discontinuity to conduction band discontinuity ratio (ΔEv/ΔEc) is presented. On the other hand, for the AlGaAs/InGaAs/GaAs HEBT, the ΔEv value can be enhanced due to the insertion of InGaAs quantum well (QW) between the n-GaAs emitter and the p+-GaAs base layer. Thus, the confinement effect of minority carriers is enhanced and a current gain of 280 is obtained, simultaneously. Consequently, our studied devices will provide a good promise for the transistor design and circuit applications.

The double-delta-doped heterojunction bipolar transistor is successfully fabricated with improved current-voltage characteristics by employing the insertion of delta-doped sheets at emitter-base (E-B) and base-collector (B-C) heterojunction. Because of the use of delta-doped sheets, the potential spikes at E-B and B-C heterojunction are suppressed substantially. Thus a higher emitter injection efficiency (current gain) and a lower knee voltage are obtained. From experimental results, it is shown that the studied device is a good candidate for high-speed and high-power circuit applications.

We demonstrate a new and improved borderless contact (BLC) Ti-salicide process for the fabrication of sub-quarter micron CMOS devices. A low-temperature chemical vapor deposition (CVD) SiO/sub x/N/sub y/ film to act as the selective etching stop layer and the additional n/sup +/ and p/sup +/ source-drain double implant structure (DIS) are employed in the studied device. The additional n/sup +/ and p/sup +/ DIS can reduce the junction leakage current, which is usually enhanced by BLC etching near the edge of shallow trench isolation (STI). The process window is enlarged. Furthermore, the employed low-thermal oxynitride and high deposition rate can improve the salicide thermal stability and avoid the salicide agglomeration.

This letter reports a new and high-performance InGaP/In/sub x/Ga/sub 1-x/As high electron mobility transistor (HEMT) with an inverted delta-doped V-shaped channel. Due to the presence of V-shaped inverted delta-doped InGaP/In/sub x/Ga/sub 1-x/As structure, good carrier confinement and a flat and wide transconductance operation regime are expected. Experimentally, the fabricated device (1/spl times/100 /spl mu/m/sup 2/) shows a high gate-to-drain breakdown voltage of 30 V and a high output drain saturation current density of 826 mA/mm at V/sub GS/=2.5 V. The high transconductance expands over a very broad operation range with the maximum value of 201 mS/mm at 300 K. Meanwhile, the studied device exhibits a good microwave frequency linearity.

Based on the compositional dependence on the conduction band discontinuity, a significant heterojunction bipolar transistor (HBT) with a continuous conduction band heterointerface between the InP emitter and the In0.53Ga0.25Al0.22As base is fabricated. Experimentally, due to the elimination of the potential spike, a very low offset voltage of 50 mV is observed. Also, the studied device exhibits better breakdown characteristics and lower output conductance as compared with other InP/InGaAs or AlInAs/InGaAs HBTs. Furthermore, attributed to the enhancement of the hole confinement by an inserted δ-doped sheet at the emitter–base interface, a dramatic current gain about 4 is found even under an ultralow current operation regime (IC⩽5 nA).

An AlInAs/GaInAs superlatticed resonant-tunneling transistor (SRTT) is fabricated and demonstrated. A five-period AlInAs/GaInAs superlattice is used to provide resonant tunneling (RT) and confinement of minority carriers. Experimentally, an interesting impulse-like multiple negative-differential-resistance (MNDR) phenomenon and transistor action are obtained for the studied SRTT device at room temperature. It is believed that the N-shaped MNDR results mainly from RT within the five-period AlInAs/GaInAs superlattice.

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/sub T/ and maximum oscillation frequency f/sub max/ for a 1-/spl mu/m gate device are 12 and 28.4 GHz, respectively.

High-linearity Ga0.51In0.49P/In0.15Ga0.85As pseudomorphic high electron-mobility transistors have been successfully fabricated and demonstrated in both direct-current and alternating-current performance. Together with a wide-gap Ga0.51In0.49P gate insulator, a gate-to-drain breakdown voltage of 33 V is further improved to over 40 V by selectively removing mesa sidewalls. The transconductance and current density of a 1×100 μm2 device at room temperature (77 K) are 90 (120) mS/mm and 646 (780) mA/mm, respectively. The measured fT and fmax are 12 and 28.4 GHz, respectively. These are consistent with 1 μm gate devices when the parasitic capacitance is reduced by selectively removing mesa sidewalls.

A new high-performance Ga0.51In0.49P/In0.15Ga0.85As/GaAs pseudomorphic heterostructure field-effect transistor, based on a novel airbridge-gate structure with multiple piers, has been fabricated successfully. Due to the employment of high Schottky barrier GaInP layer and the newly designed double delta-doped sheets (D3S) InGaAs channel, the high gate-to-drain breakdown voltage and broad and linear transconductance are obtained simultaneously. Moreover, the use of airbridge-gate technique not only suppresses the parasitic capacitance, but also exhibits a wide and flat operation regime of the current gain cutoff frequency fT and maximum oscillation frequency fmax.

An In0.5Ga0.5P/GaAs double heterojunction bipolar transistor with a δ-doped wide-gap collector structure has been fabricated and studied. Experimental results show that this device exhibits the advantages of a small offset voltage of 50 mV, a small saturation voltage of 1 V, and a large breakdown voltage of 20 V with a current gain of 20. These good characteristics are mainly due to the complete elimination of potential spike at emitter–base and base–collector heterojunctions. Consequently, the studied device shows a good promise for high-speed, high-power, lower-power consumption and large input signal circuit applications.

Temperature-dependent DC performances of 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. In addition, with decreasing temperature from 25 toward -196/spl deg/C, an irregular temperature behavior of current gain has been investigated.

We specifically studied the influence of a setback-layer thickness on the device performances so as to optimize the required value. Theoretical analysis shows that an optimized setback-layer thickness is available to effectively reduce the barrier height while maintain good device performances. In this work, the effects of a setback-layer thickness on the DC and RF performances of an InGaP/GaAs heterojunction bipolar transistor (HBT) are investigated. Based on the theoretical analysis, the optimized setback-layer thickness W SB is about of 10~30A for analog amplification. On the other hand, for digital saturated logic application, i.e., a small offset voltage with an acceptable current gain, the optimized W SB could be up to 50 A. Therefore, this analysis and predication may cause the considerable promise for practical circuit applications. Keywords: Polysilicon Resistor, Diffused Resistor, TCR. 1. INTRODUCTION Recently, many researchers have focused on the aluminum-free In

A new AlInAs/GaInAs superlatticed negative-differential-resistance switch (SNDRS) is fabricated successfully and demonstrated. A 5-period AlInAs/GaInAs superlattice is used to serve the resonant tunneling route and the confinement barrier for minority carriers. Experimentally, an interesting three-terminal-controlled N-shaped multiple negative-differential-resistance (MNDR) phenomenon and transistor action are,obtained for the studied SNDRS device in the saturation and forward active mode at room temperature, respectively. It is believed that the N-shaped MNDR results mainly from resonant tunneling within the 5-period AlInAs/GaInAs superlattice.

A new AlInAs/GaInAs superlattice negative-differential-resistance switch (SNDRT) is fabricated successfully and demonstrated. A 5-period AlInAs/GaInAs superlattice is used to serve the resonant tunneling route and the confinement barrier for minority carriers. Experimentally, an interesting three-terminal-controlled N-shaped multiple negative-differential-resistance (MNDR) phenomenon and transistor action are obtained for the studied SNDRT device in the saturation and forward active mode at room temperature, respectively. It is believed that the N-shaped MNDR results mainly from resonant tunneling within the 5-period AlInAs/GaInAs superlattice.

The double delta-doped heterojunction bipolar transistor (D/sup 3/HBT) is successfully fabricated with improved current-voltage characteristics by employing the insertion of delta-doped layers at the emitter-base (E-B) and base-collector (B-C) heterojunction. Due to the use of delta-doped layers, the potential spikes at the E-B and BC heterojunctions are suppressed substantially. Thus a higher emitter injection efficiency (current gain) and a lower knee voltage are obtained. From the experimental results, it is shown that the studied D/sup 3/HBT device is a good candidate for high-speed and high-power circuit applications.

A new GaInP/GaAs high-barrier gate and tri-step doped channel heterostructure field-effect transistor (HFET) has been successfully fabricated and demonstrated. A very thin and heavily doped /spl delta/(p/sup +/)-GaInP layer is introduced to increase the high gate turn-on and breakdown voltage and reduce the gate leakage current. A low-medium-high tri-step doped channel structure is used to improve the output current drivability and average transconductance. In addition, a metal-semiconductor field-effect transistor (MESFET) with the same tri-step doped channel structure has also been fabricated for comparison. The studied devices show the good performances of high breakdown voltage, high output drain saturation current and flat and wide transconductance operation regimes. The measured cut-off frequency (f/sub T/) is higher than 15 GHz. From experimental results, the studied devices show good potential in high-power and large input signal circuit applications.

An InGaP/GaAs resonant tunnelling bipolar transistor (RTBT) with superlattice (SL) in the emitters is fabricated and studied. The modulated widths of SL barriers are utilized in the specific SL structure. Based on the calculations, the ground state and first excited state minibands are estimated from the transmission probability. The electron transport of RT through SL structure is significantly determined by the electric field behaviors across SL barriers. Experimentally, the excellent transistor characteristics including the small saturation voltage, small offset voltage, high breakdown voltages are obtained due to the insertion of δ-doping sheet at the base-collector heterointerface. Furthermore, at higher current regimes, the quaternary negative difference resistance (NDR) phenomena are observed in agreement with the theoretical prediction at 300K.

A highly hydrogen-sensitive Pd/InP metal-oxide-semiconductor (MOS) Schottky diode hydrogen sensor is presented. The role of donor level in the interfacial oxide layer replacing the amphoteric native defects leads to enhanced barrier height and high sensitivity. According to reaction kinetics studies, the maximum change in barrier height achieves 0.31 eV. Short response and recovery times in the transient characteristics demonstrate the high hydrogen adsorption and desorption rates at high temperatures.

In this work, the hydrogen response characteristics and sensing properties of catalytic Pd metal-oxide-semiconductor (MOS) Schottky diodes based on both GaAs and InP substrates are comparatively investigated. The behaviors of interface Fermi-level pinning causing the apparent difference in the barrier height modulation and the sensitivity are discussed. Furthermore, the effects of temperature and hydrogen concentration in the initial rate of change in current and the response time are examined. In order to study the steady-state reaction kinetics, we also performed the Langmuir analysis to estimate the values of initial heat of adsorption for both devices. Based on the adsorption isotherm of Temkin type, the interface coverage dependent heat of adsorption is responsible for the wide hydrogen sensing range. From the theoretical prediction, both devices have a very low sensitivity limit under atmospheric conditions.

An InGaP/GaAs heterojunction bipolar transistor with a δ-doped sheet structure has been fabricated successfully. High current gain, especially in the very low collector current regime, low collector-emitter offset voltage (ΔVCE) characteristics are obtained. There is an extremely small offset voltage of about 55 meV due to the elimination of the potential spike at the emitter-base heterojunction by a δ-doped sheet and a 50 A very thin setback layer. On the other hand, the high current gain of 280 also reveals that the degradation of current gain due to the potential spike can be avoided. In addition, the influence of the δ-doped sheet and the undoped setback on device properties is studied.

The temperature-dependent characteristics of InGaP/In x Ga1-x As/GaAs pseudomorphic transistors with an inverted delta-doped V-shaped channel have been studied. Due to the presented wide-gap InGaP Schottky layer and the V-shaped channel structure, the degradation of device performance with increasing the temperature is not so significant. Experimentally, for a 1×100 µm2 device, the gate-drain voltages at a gate leakage current of 260 µA/mm and the maximum transconductances g m,max are 30 (22.2) V and 201 (169) mS/mm at the temperature of 300 K (450 K), respectively. Meanwhile, the broad and flat drain current operation regimes for high g m, f T, and f max are obtained.

A new In/sub 0.53/Al/sub 0.22/Ga/sub 0.25/As/InP heterojunction bipolar transistor with a /spl delta/-doped continuous-conduction-band (CCB) structure has been fabricated successfully and studied. The use of the /spl delta/-doped CCB structure can effectively eliminate the potential spike in the E-B heterojunction. An offset voltage as low as 50 mV and a relatively high current gain of 80 have been obtained experimentally. The studied device is therefore promising for practical circuit applications.