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The comparison of DC performance on InGaP/InGaAs pseudomorphic field-effect transistors with triple doped-channel profiles is demonstrated. As compared to the uniform and high-medium-low doped-channel devices, the low-medium-high doped-channel device exhibits the broadest gate voltage swing and the best device linearity. Experimentally, the transconductance within 50% of its maximum value for gate voltage swing is 4.62 V in the low-medium-high doped-channel device, which is greater than 3.58 (3.30) V in the uniform (high-medium-low) doped-channel device.

It is proposed that the metal-oxide-semiconductor (MOS) solar cells with sol-gel oxides deposited by spin coating are produced in this study. This sol-gel-derived SiO 2 layer is not very thin and the deviation in the thickness of the sol-gel layer is not slight. In general, the characteristics of MOS solar cells are significantly affected by the thickness of the SiO 2 layer. Particularly, the thermal grown oxide thickness required is less than 2nm for MOS solar cell applications. It is useful for large-scale and large-amount manufacturing that the influence of nonuniformity of oxide thickness on the characteristics of MOS solar cells with sol-gel oxides is reduced. It is observed that the short-circuit current density (J sc ) of 15.56 mA/cm2, the open-circuit voltage (V oc ) of 0.49V, the fill factor (FF) of 0.723 and the conversion efficiency (η%) of 5.44% are obtained by means of the current-voltage (I-V) measurements under AM 1.5 illumination at 25°C in the MOS solar cell with sol-gel oxides.

In this article, the performance of a novel InGaP/GaAs superlattice-emitter bipolar transistor with InGaAs/GaAs superlattice-base structure is demonstrated by experimental results. The injecting electrons from superlattice emitter are easy to transport into the superlattice-base region for promoting the collector current by tunneling behavior. Furthermore, the average energy gap of base regime is substantially reduced by the use of InGaAs/GaAs superlattice structure for the requirement of low turn-on voltage. Experimentally, the transistor exhibits a maximum common-emitter current gain of 295 and a relatively low collector-emitter voltage of only 16 mV. In particular, the ideality factor of collector current near to unity is obtained. Based on the excellent transistor performance, the studied can provide a promise for signal amplifier and low-power circuit applications.

In this article, we first fabricate and demonstrate the InGaP/GaAs camel-like gate field-effect transistor with InGaAs pseudomorphic heavy-doped channel. Due to the large gate potential barrier for the use of the n+-GaAs/p+-InGaP/n-GaAs camel-like gate and the thin as well as heavy doping n+-InGaAs channel layer, the effective conduction band discontinuity (ΔEc) is substantially extended and a high gate turn-on voltage up to 2.0 V is obtained. The device exhibits a relatively broad gate voltage swing resulting from the high gate turn-on voltage. In addition, a maximum drain current of 393 mA/mm and a maximum transconductance of 96 mS/mm are measured. These results indicate that the studied device is suitable for signal amplifier and linear circuit applications.

A GaAs-InGaAs optoelectronic switch, grown by molecular beam epitaxy (MBE), has been fabricated. Owing to the avalanche multiplication and hole accumulation in the transport mechanism, bistable states, i.e., a high-impedance OFF state and a low-impedance ON state, are observed in the current-voltage (I–V) characteristics. The device shows a flexible optical function related to the potential barrier height controllable by incident light. The dependence of the I–V characteristics on illumination is attributed to the photogenerated hole accumulation in the device operation.

The dynamic performance of a dual-emitter phototransistor (DEPT) was studied. In the static case of a DEPT under a 12.5 muW optical power, the emitter-induced gain effect from photocurrent modulation improves collector photocurrent (88 to 129 muA). For the DEPT as an electro-optical switch with a 2 V supply voltage, the stable electrical logic swing is 0.41 V for a 1 V clock signal. When a short-period clock signal is applied, a clear electrical logic swing larger than 1.2 V is achieved. The emitter-induced gain effect from both photocurrent modulation and junction-voltage modulation is also introduced to clearly describe DEPT dynamic performance.

In this work, we report a metal-splitting field plate gate on heterojunction doped-channel field effect transistors (HDCFETs) with an application of GaAs-bulk. Experimentally, a HDCFET with a gate-metal length of 0.4 mum, a field-plate length of 0.6 mum, and a bulk thickness of 120 nm was successfully fabricated for comparing to that with a 1-mum traditional planar-gate. The current density (451 mA/mm), transconductance (225 mS/mm), breakdown voltages (VBD(DS)/VBD(GD)=22/-25.5 V), gate-voltage swing (2.24 V), unity current-gain and power-gain frequencies (ft/fmax=17.2/32 GHz) are improved as compared to those of 1-mum gate device without field plates. At 1.8 GHz with a VDS of 4.0 V operation, a maximum power-added efficiency (PAE) of 36% with an output power of 13.9 dBm and a power gain of 8.7 dB was obtained. Saturated output power and linear power gain are 316 mW/mm and 13 dB, respectively.

An interesting InP/InGaAs double heterojunction bipolar transistor (DHBT) with a step-graded InAlGaAs/InP collector structure are demonstrated and studied. By use of the step-graded InAlGaAs/InP collector structure at the base-collector heterojunction, the current blocking effect is effectively eliminated. Experimentally, the studied device shows a relatively better common-emitter breakdown voltage and low output conductance though at high temperature. Also, the studied device shows a wider collector current density operation region which over 11 decades in magnitude of collector current density (10~6 to 105 A/cm2). Moreover, the studied device also shows the relatively weaker temperature dependence on the electron impact ionization alpha. Consequently, the studied DHBT device provides the promise for low-voltage and low-power circuit applications.

A comprehensive study of the InGaP ledge width effect on the performance of InGaP/GaAs heterojunction bipolar transistors (HBTs) is demonstrated. It is shown that the electron density and recombination rate at the surface channel are decreased with increasing the InGaP ledge width. However, the longer InGaP ledge width increases the base-collector junction area which in turn deteriorates the high frequency performance. According to the theoretical analysis and experimental results, the device with an InGaP ledge width of 0.8 mum shows the best and acceptable DC and RF performance.

Temperature-dependent characteristics of high electron mobility transistors (HEMTs) with sulfur and SiNx passivations are comprehensively studied and demonstrated. Experimentally, for the studied device with formal passivations, better DC and microwave characteristics are obtained over wide operating temperature range. In particular, as compared with the device only with sulfur passivation, the slightly degradations of device performance are caused by the temperature stress during the deposition of SiNx layer and presence of surface traps at the SiNx/AlGaAs interface. Based on these good results, the formal-passivated HEMT is expected to exhibit relatively better long-term operation stability and reliable device characteristics.

An optoelectronic switch with both n- and p-type delta-doped (delta-doped) quantum wells was investigated. The delta-doped structures formed potential wells for the carrier accumulation and potential barriers for the carrier injection. Being possessed of delta-doped sheets with different doping levels, the potential barriers were sequentially collapsed to produce a double negative-differential-resistance (NDR) phenomenon in the current-voltage (I-V) characteristics of the device due to the carrier accumulation in the potential wells. The device also showed an optical function related to the barrier heights controllable by incident light.

A Schottky-contact triangular-barrier optoelectronic switch (STOS), grown by molecular beam epitaxy (MBE), has been fabricated. The triangular barrier, formed by inserting an InGaAs delta-doped (delta-doped) quantum well into an n -GaAs layer, provides a potential well for hole accumulation. Due to the hole accumulation in the delta-doped well and the sequential avalanche multiplications in the reverse-biased pn and metal-semiconductor (M-S) junctions, a double S-shaped negative-differential-resistance (NDR) phenomenon is observed in the current-voltage (I-V) characteristics. The STOS shows a flexible optical function related to the triangular barrier height controllable by incident light. The multistate is switchable by both optical and electrical inputs.

A new Pt-InAlP metal-oxide-semiconductor (MOS) Schottky diode hydrogen sensor with high-sensitive hydrogen detection among wide operating temperature regime is demonstrated and studied. Experimentally, the studied hydrogen sensor can be operated systematically either under forward or reverse bias conditions. At 30degC, the relatively hydrogen detection ratio Sr value is increased from 108.8% (107.4%) to 943.1% (1337.3%), under the forward (reverse) bias of 0.3 V, when the hydrogen concentration is increased from 4.3 to 9970 ppm H2/air. In addition, it is worth to note that even an extremely low hydrogen concentration of 4.3 ppm H2/air can be effectively detected at the temperature of 30~250degC.

A high-performance InGaP/GaAs/InGaAs step-emitter bipolar transistor is demonstrated. The energy bands and carrier distributions are described by theoretical analysis. Because the confinement effect for holes is substantially enhanced by the addition of an InGaAs quantum well between base-emitter junction as compared to the conventional InGaP/GaAs heterojunction bipolar transistor, the experimental device exhibits a high current gain up to 220. In particular, a relatively low collector-emitter offset voltage of 70 mV is observed, attributed to the neglect of potential spike at base-emitter junction by the employments of an n-type GaAs emitter and an n-InGaAs quantum well. Consequently, the excellent performances of the studied device provide a promise for linear amplifiers and circuit applications.

The characteristics and device mechanism of InP/InGaAs pnp δ-doped heterojunction bipolar transistor are demonstrated. The additions of a δ-doped sheet and two spacer layers efficiently eliminate the potential spike at emitter-base junction, lower the emitter-collector offset voltage, and increase the confinement effect for electrons, simultaneously. The components of base current and the influence of delta-doped sheet on the potential spike are depicted. Experimentally, excellent device performances including a maximum current gain of 50 and a low offset voltage of 70 mV are achieved for the device with a δ-doped density of 2 x 1012 cm-2 . The experimental results are consistent with the theoretical analysis.

Two-terminal switching performance is observed in a new AlGaAs/GaAs/InAlGaP optoelectronic device. The device shows that the switching action takes place from a low current state to a high current state through a region of negative differential resistance (NDR). The transition from either state to the other may be induced by an appropriate optical or electrical input. It is seen that the effect of illumination increases the switching voltage V s and decreases the switching current I s , which is quite different from other results reported. In addition, it possesses obvious NDR even up to 160°C. This high-temperature performance provides the studied device with potential high-temperature applications.

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.

In this article, a novel InGaP/GaAs pnp delta-doped heterojunction bipolar transistor is first demonstrated. Though the valence band discontinuity at InGaP/GaAs heterojunction is relatively large, the addition of a delta-doped sheet between two spacer layers at the emitter-base junction effectively eliminates the potential spike and increases the barrier for electrons, simultaneously. Experimentally, a high current gain of 22 and an offset voltage of 100 mV are achieved. The offset voltage is much smaller than the reported InGaP/GaAs npn HBTs. The proposed device can be used for linear amplifiers and low power complementary integrated circuit applications

Extremely high potential barrier height and gate turn-on voltage of a novel GaAs field-effect transistor with n+/p+/n+/p+/n double camel-like gate structure are demonstrated. The maximum electric field and potential barrier height of the double camel-like gate are substantially enhanced by the addition of another n+/p+ layers in gate region, as compared with the conventional n+ /p+/n single camel-like gate. For a 1 times 100 mum 2 device, a potential barrier height up to 2.741 V is obtained. Experimentally, a high gate turn-on voltage up to + 4.9 V is achieved because two reverse-biased junctions of the double camel-like gate absorb part of positive gate voltage. In addition, the transistor action shows a maximum saturation current of 730 mA/mm and an extrinsic transconductance of 166 mS/mm

A newly designed single delta-doped InGaP/InGaAs/GaAs pseudomorphic HEMT with n/sup +/-GaAs/p/sup +/-InGaP/n-InGaP camel gate structure has been first fabricated and demonstrated. For a 1/spl times/100 /spl mu/m/sup 2/ device, the experimental results show an extrinsic transconductance of 85 mS/mm and a saturation current density of 425 mA/mm. Significantly, due to the p-n depletion from p/sup +/-InGaP gate to channel region and the presence of /spl Delta/Ec at InGaP/InGaAs heterostructure, the turn-on voltage of gate is larger than 1.7 V. In addition, an extremely broad gate voltage swing larger than 3 V with above 80% maximum g/sub m/ is obtained. The unit current cutoff frequency f/sub T/ and maximum oscillation frequency f/sub max/ are up to 18 and 30 GHz, respectively.

Novel InGaP/GaAs co-integrated structures consisting of a heterojunction bipolar transistor and a field effect transistor are fabricated and demonstrated. For the HBT, the confinement effect for holes is increased and the potential spike at emitter-base (E-B) heterojunction is reduced significantly owing to the presence of a /spl delta/-doped sheet at the InGaP/GaAs junction. High current gain and low offset voltage are achieved. On the other hand, for a FET, an undoped InGaP gate layer is used to increase gate breakdown voltage, and a thin and heavy-doped GaAs channel is shown to enhance current drivability, transconductance, and linearity. For this structure, a wide gate voltage range larger than 3 V with the transconductance larger 150 mS/mm is obtained.

Sequential resonant tunneling behavior of resonant tunneling bipolar transistor with 5-period i-InP/n-InGaAs superlattice emitter has been demonstrated. An interesting multiple negative-differential-resistance (NDR) phenomena resulting from the creation and extension of high-field domain in superlattice is observed at room temperature. Furthermore, the employing of a thin n-InGaAs emitter layer between InP/InGaAs superlattice and p/sup +/-InGaAs base layer helps to lower the potential spike at base-emitter junction and reduce neutral-emitter recombination current. Experimentally, the transistor performance, incorporating multiple NDR, with a relatively large current gain of 454 and an offset voltage as low as 80 mV is achieved.

A functional InGaP/GaAs double heterostructure-emitter bipolar transistor is fabricated and demonstrated. Due to the large valence band discontinuity to conduction band discontinuity ratio at the InGaP/GaAs heterojunction and the symmetrical structure, excellent transistor performance, with a high current gain of 195 and a low collector-emitter (C-E) offset voltage of 60 mV, is achieved. In particular, attributed to the avalanche multiplication and confinement effect for electrons at the InGaP/GaAs heterojunction, interesting multiple S-shaped negative-differential-resistance switches are observed under large C-E forward voltage.

The authors demonstrate and compare the experimental results of the high-performance InGaP /InGaAs camel-gate n-channel and p-channel /spl delta/-doped pseudomorphic modulation-doped field effect transistors (pMODFETs). For the n-channel device, because of the p-n depletion in the camel-like gate region and the presence of large conduction band discontinuity at InGaP/InGaAs heterostructure, an extremely large gate turn-on voltage than 1.7 V is measured. However, the p-channel device exhibits a larger turn-on voltage than 2 V due to the relatively large valence band discontinuity at InGaP/InGaAs heterostructure.

In this article, high-performance InP/InGaAs heterostructure confinement bipolar transistors, including a /spl delta/-doped heterojunction bipolar transistor (5-HBT) and superlattice-confinement bipolar transistor (SCBT), are successfully fabricated and demonstrated.

An InP/InGaAs /spl delta/-doped pnp heterojunction bipolar transistor (HBT) has been successfully fabricated and demonstrated for the first time. The addition of a /spl delta/-doped sheet between two undoped spacer layers more effectively eliminates the potential spike at the emitter-base junction, lowers the emitter-collector offset voltage, and increases the effective barrier for electrons, simultaneously. A maximum current gain of 50 and a low offset voltage of 70 mV are obtained, respectively. To our knowledge, the offset voltage of the studied device is the best reported for InP/InGaAs pnp HBTs.

A functional InGaP/GaAs/InGaAs step-compositional-emitter heterojunction bipolar transistor (HBT) is fabricated and demonstrated. Due to the avalanche multiplication and discontinuous confinement effects for electrons at InGaP/GaAs heterojunction and InGaAs quantum well, an interesting triple-route S-shaped negative-differential-resistance switch is observed under inverted operation mode at room temperature. In addition, the excellent transistor performances including a high current gain of 220 and a low offset voltage of 60 mV are achieved under normal operation mode. Consequently, the excellent switching characteristic and transistor action of the studied HBT provides a promise for amplifier and multiple-valued logic circuit applications.

A high-performance InGaP/InGaAs/GaAs p-channel pseudomorphic modulation-doped field effect transistor based on p/sup +/-GaAs/n/sup +/-InGaP/p-InGaP camel-like gate structure is demonstrated. Due to the p-n depletion of the camel-like gate and the presence of relatively large /spl Delta/Ev at InGaP/InGaAs heterostructure, an extremely large gate turn-on voltage than 2 V is measured. For a 1/spl times/100 /spl mu/m/sup 2/ device, the experimental results show a maximum saturation current density of -345 mA/mm and a widely broad gate voltage swing than 4 V with 80 % maximum transconductance. Furthermore, the f/sub T/ and f/sub max/ values are 3.1 and 4.8 GHz, respectively.

We demonstrate the effect of recombination current on the electrical properties of heterostructure-emitter bipolar transistors (HEBTs). For comparison, an AlGaAs/GaAs and an AlInAs/GaInAs HEBT are fabricated with the layer structure. For the AlGaAs/GaAs HEBT, the hole diffusion length is larger than the emitter thickness, so that most holes can be reflected back at the confinement layer because the hole recombination current is low in the neutral-emitter region. Thus, high emitter injection efficiency and current gain can be achieved simultaneously. On the other hand, for the AlInAs/GaInAs HEBT, the increase of recombination current in the neutral emitter regime and the existence of a potential spike could reduce the emitter injection efficiency at large V/sub BE/ voltage. Hence, the non-1KT component of collector current is enhanced and the transistor characteristics are degraded. However, a lower offset voltage of 40 mV is obtained attributed to the low base surface recombination current for the AlInAs/GaInAs HEBT.

Two kinds of heterostructure field-effect transistor (FET) with an InGaAs step-doped-channel (SDC) profile have been fabricated and demonstrated. For the 1/spl times/100 /spl mu/m/sup 2/ gated dimension, the maximum drain saturation currents were 735 and 675 mA/mm, the maximum transconductances 200 and 232 mS/mm, the gate breakdown voltages 15 V and 12 V, and the wide gate voltage swing 3.3 and 2.6 V with transconductance g/sub m/ higher than 150 mS/mm. A simple model is employed to analyze the performance of threshold voltage V/sub T/ and values of -3.7 and -1.8 V are obtained. These good performances show that the SDCFET has a good potential for high-speed, high-power circuit applications.

A new functional AlGaAs/InGaAs/GaAs heterostructure-emitter and heterostructure-base transistor (HEHBT) with a pseudomorphic base structure is presented. Due to the insertion of an InGaAs quantum well between the emitter-base (E-B) junctions, the valence band discontinuity can be enhanced and a high emitter injection efficiency may be achieved. In addition, an interesting S-shaped multiple negative differential resistance (MNDR) phenomenon is observed under the inverted operation mode. This may be attributed to an avalanche multiplication and sequential two-stage barrier lowering effect resulting from electron accumulation at the AlGaAs/GaAs heterointerface and InGaAs quantum well, respectively.

We report a new switching device with back-to-back AlGaAs planar-doped barrier and InGaAs/GaAs/InGaAs well grown by molecular beam epitaxy, which exhibits S-shape negative differential resistance (NDR). The device has a large potential barrier between the anode and cathode regions which can be modulated via a third terminal. The NDR phenomenon is attributed mainly to impact ionization within the undoped anode region. Due to the better confinement effect on holes for a double InGaAs/GaAs/InGaAs quantum well, experimental results reveal that good switch behavior and higher turn on current were obtained in our improved device. When external bias is applied to the third electrode, we observe voltage-dependent switching voltage and holding voltage, this introduces multiple stable regimes of the device operation. Therefore, based on a proper design, the studied device has good potential for proposed multiple-valued logic circuit application or acts as an inverter.

In this paper we fabricate a GaAs/n/sup +/InGaAs/GaAs doped-channel FET device with significant transistor performance. The use of the doped-channel structure also has the benefits of: (1) enhanced electron mobility and velocity in the InGaAs channel; and (2) elimination of the undesired DX centers or persistent photoconductivity effect. Study of the structure reveals that it exhibits the anomalous negative differential resistance (NDR) phenomenon. We conclude that the NDR performance is related to the existence of deep-level electron traps and the real-space transfer effect. Because only part of the fabricated devices exhibit NDR phenomena, the nonuniformly distributed deep-level electron traps related to the substrate or MOCVD growth process may be expected. The existence of electron traps enhances the decrease of channel current resulting from the real-space transfer effect. When the channel electrons gain enough energy from the accelerating field (at higher V/sub DS/ regime), they may inject into the neighboring GaAs layers and become trapped in the deep levels. This causes the reduction of conduction current and occurrence of NDR behavior.