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The performance of JBS (P, S) structure within threading dislocations-induced (GaN on PSS∼108cm−2) traps and in drift-diffusion simulations, including the critical electric field are studied. As the forward and reverse operation, the pillar-to-pillar of various diode lead to the lower turn-on voltage and high breakdown, respectively. Then, it is important to note that is not punch-through the drift layer to n+-GaN yet because that difference is attributed to whether the intrinsic or extrinsic C-dopants, results in the n−-type drift layer or p+-type with bias-dependent deletion region.

This paper reports on new GaN sensors using a Pd-mixture-Pd triple-layer sensing structure to enhance their sensitivity to hydrogen at the tens of ppm level. The proposed hydrogen sensor biased with a constant voltage produced relatively high sensing responses of ∼4.84 × 10 5 % at 10,100 ppm and ∼8.7 × 10 4 % at 49.1 ppm H 2 in N 2 . The corresponding barrier height variations are calculated to be 220 and 168 mV. When the sensor is biased by a constant current with maximum power consumption of 0.4 mW, a sensing voltage as an output signal showed a voltage shift of more than 17 V (the highest value ever reported) at 49.1 ppm H 2 in N 2 . By comparison to Pd-deposited GaN sensors, the improvement in static-state performance is likely attributed to double dipole layers formed individually at the Pd–GaN interface and inside the mixture. 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.

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.

This paper reports on a new Pd/GaN hydrogen sensor with two multi-finger Schottky contacts (named metal–semiconductor–metal (MSM) hydrogen sensor). Effects of hydrogen absorption on the MSM sensor are investigated. In addition to comparisons of sensing mechanism between metal–semiconductor (MS) and MSM sensors, related current–voltage characteristics, sensor responses, Schottky barrier height variations, response transients, and switching behaviors are included. Experimentally, symmetrically bi-directional sensing performances are obtained in the newly designed MSM sensor, resulting in both widespread forward- and reverse-voltage-operating regimes. When the MSM sensor is measured in a 1080 ppm H2/N2 ambience, the voltage-independent response and barrier-height variation obtained are 51 and 102 mV, respectively. Furthermore, the measured response time is as short as 38 ± 2 s. Together with good switching behaviors, the MSM sensor studied is a promising candidate as a high-performance hydrogen sensor being easily integrated with other devices.

In this paper, the device performance and complementary inverter of the InGaP/InGaAs/GaAs doped-channel field-effect transistors (DCFETs) by two-dimensional semiconductor simulation are demonstrated. Due to the relatively large conduction (valance) band discontinuity at InGaP/InGaAs interface, it provides good confinement effect for transporting carriers in InGaAs channel layer for the n-channel (p-channel) device. The large gate turn-on voltage is achieved due to the employment of the wide energy-gap InGaP material as gate layer. The f t and f max are of 6.5 (2.1) and 25 (5) GHz for the n-channel (p-channel) device. Furthermore, the co-integrated structures, by the combination of n- and p-channel field-effect transistors, could form a complementary inverter and the relatively large noise margins are achieved.

New metal-semiconductor-metal hydrogen sensors are fabricated to take advantages of symmetrically bidirectional detection. Unlike commonly used single catalytic metal layers, a mixture of Pd and SiO2 inserted between Pd and GaN was employed as sensing media. There are three sensing regions (i.e., 2-D dipole, transient, and 3-D dipole regions) observed in static response. Room-temperature sensitivity larger than 107 was obtained in 1080-ppm H2/N2 ambient. The barrier-height variation is as high as 422 mV. To our best knowledge, these are the highest values ever reported. According to transient response, a short response time of 70 s is obtained at room temperature. Thus, a newly developed concept of forming 3-D dipoles is introduced to possibly explain experimental results.

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 junction effectively eliminates the potential spike and increases the confined barrier for electrons, simultaneously. Experimentally, a high current gain of 25 and an offset voltage of 100 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 work, an application of wide-gap updoed-Al0.22Ga0.78As bulk to perform the field-plate gate (FP-gate) on Al0.22Ga0.78As/In16Ga84As/Al0.22Ga0.78As DH-HEMTs was investigated. The simulated FPG-devices with a bulk thickness of 1200 Å, exhibit an excellent dispersing property to the electric field peak under gate electrode near to drain side, hence, the breakdown characteristics were effectively improved. Measured gate-diode performance of FPG-device presents a higher breakdown voltage (VBR) of -25.5 V than devices with single recess (SRG-device). Enhancement of device breakdown is contributive to microwave power performances. At 2.4 GHz load-pull measurement of studied devices which were biased at class AB operation, the saturated output power (POUT), power gain (GP) and power-added efficiency (PAE) were 13.06 dBm (202 mW/mm), 12.8 db and 47.3% for FPG-device. These measured results of SRG-device were 10.3 dBm(107 mW/mm), 13.2 db and 38.5%, According to the simulated results, FPG-devices structuring with a bulk layer exhibit excellent performance for high breakdown and microwave power operation.

To investigate the effects of surface leakage on the temperature-dependent dark and optical performance of a heterojunction phototransistor (HPT), three sets of HPTs were prepared. They were unpassivated (HPT A), passivated with diluted (NH4)2S (HPT B), and passivated with neutralized (NH4)2S (HPT C). Passivation treatment successfully suppresses surface-defect-induced effects. The passivated HPTs exhibit a reduced dark current and an enhanced signal-to-noise ratio (SNR). HPT A exhibits a room-temperature collector dark current (ICdark) of 0.59 nA at a VCE of 1 V, while those of HPTs B and C are 0.03 and 0.89 pA, respectively. The room-temperature SNR values for HPTs A, B, and C at a Pin of 8.3 (107.6) nW are 5.9 (42), 59 (91), and 91 (122) dB, respectively. After a three-week air exposure, the room-temperature SNR at a Pin of 107.6 nW decreases to 25 (67) dB for HPT A (B), while it is 116 dB for HPT C. The decrease for HPT C is only 6 dB. A long-term stable passivation with good thermal stability has been achieved by neutralized (NH4)2S treatment.

In this paper, an investigation of the static/dynamic performance of dual-emitter phototransistors (DEPTs) as an electrooptical switch was made. In the static case, the measured optical gains (the collector photocurrents) of DEPTs operated at a 12.5-muW optical power have been enhanced from 13.7 to 20.2 (88 to 129 muA) due to an emitter-induced gain high (EIGH) from photocurrent modulation. For DEPTs as an electrooptical switch, the EIGH from photocurrent modulation and the emitter-induced gain effect from junction-voltage modulation dominate the dynamic operation. In the case of continuous light input, good bistable-state output characteristics can be realized with an electrical clock signal. When the switch is operated with a 2-V supply voltage and a 10-kOmega load resistance, the stable electrical-logic swing (ELS) is 0.41 V for a 1-V/1-kHz clock signal. Electrical inputs of 5-, 10-, and 50-kHz clock signals are also employed to achieve outputs with increased ELSs of 1.18, 1.19, and 1.3 V, respectively. An optical inverter is realized. When two clock signals, an electrical input and an optical input, are employed, DEPTs are operated as a tristable-state switch.

The influence of gate metal with thermal annealed process adopt to control the distance between gate and channel on pseudomorphic Al0.24Ga0.76As/ In0.22Ga0.78As double heterojunction high electron mobility transistors (DH-HEMTs) were studied. Compared to device with gate-recess process, the distance of gate-to-channel could be controlled through the thermal annealed process and therefore exhibit a lower series resistance. Measured transconductance of 150 mS/mm and an open- drain voltage gain of 136 for the DH-HEMT with an as deposited gate are enhanced to 175 mS/mm and 160 for the DH-HEMT with a 330-{degree sign}C annealed gate. Good device linearity is also obtained with a low second-harmonic to fundamental ratio of 3.55 %. In addition, good microwave performances such as unit-current gain- and maximum power gain- frequency were also obtained from devices with gate-annealed process.

N-p-n InGaP/GaAs Dual-Emitter heterojunction phototransistor (DEPT) with/without InGaP-passivation layer have been fabricated to investigate the influence of surface leakage on the device optical performance. The comparison between DEPT with a voltage-biased emitter and HPT with a voltage-biased base is also included. There are four (three) operating regions appearing in the optical characteristics of the DEPT (HPT): negative-saturation, negative-tuning, positive-tuning, and positive-saturation (cut-off, tuning, and saturation) regions. The InGaP-passivated DEPT with the extrinsic base surface passivated by InGaP, exhibits the maximum optical gains of 46.57, 46.86 and 47.39 while the non-passivated one shows those of 32.02, 33.55 and 33.57 under the optical powers of 8.62, 13.2 and 17.5 μW, respectively. However, the optical gains are only in the range of 0.93~2.0 (0.83~1.64) for the InGaP- passivated HPT (non-passivated HPT) for all the illuminating conditions.

Heterojunction doped-channel field-effect transistors (HDCFETs) with a self-built field-plate gate formation were fabricated and proposed in this work. Arrangement of Schottky metal across a step undercut between the Schottky barrier and the insulator-like layer is the key process to produce a self-built field-plate gate. A controllably reduced gate length and a self-built field plate were simultaneously formed. Effects of gate-metal length, field-plate length and insulator thickness on HDCFET performance were also investigated. Simulated results reveal that higher currents, lower electric fields, better device linearity and larger output power are expected by offsetting the Schottky metal towards the drain side. A HDCFET with gate-metal length of 0.4 µm, field-plate length of 0.6 µm and insulator thickness of 120 nm was successfully fabricated for comparison to that with a 1 µm traditional planar gate. Current density (451 mA mm−1), transconductance (225 mS mm−1), 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 a 1 µm gate device without field plates. At 1.8 GHz and VDS of 4.0 V, maximum power-added efficiency of 36% with output power of 13.9 dBm and power gain of 8.7 dB was obtained. Saturated output power and linear power gain are 316 mW mm−1 and 13 dB, respectively.

The performance of a pin structure diode fabricated on epitaxial layer on a GaN template using re-growth p-type GaN technology by PAMBE. Experimental results show that relatively forward turn-on voltage and on-resistance are 3.1V and 5mΩ-cm2, respectively. Due to the metal-semiconductor interface has the lower p-ohmic contact. On the contrary, the breakdown voltage of the device operating greater than 800V is observed. Furthermore, the pin structure diode within acceptor-type traps using a two-dimensional simulator as GaN bulk within threading dislocations (about ∼108cm−2) was compared to including the electric field different from x and y position. It leads to substantially higher electric field as function of x position between the metal and the p-type GaN when drift layer is not fully depleted.

Depletion-mode Al0.24Ga0.76As/In0.22Ga0.78As double-heterojunction high electron mobility transistors (DH-HEMTs) were fabricated with an as deposited gate to compare with those with a buried gate by annealing. Instead of a recessed gate, a buried gate used to control the distance between the gate and channel (and hence the aspect ratio) improves the series resistance. Measured transconductance of 150 mS mm−1 and an open-drain voltage gain of 136 for the DH-HEMT with an as deposited gate are enhanced to 175 mS mm−1 and 160 for the DH-HEMT with a 330 °C annealed gate. Good device linearity is also obtained with a low second harmonic to fundamental ratio of 3.55%. The measured maximums fts (fmaxs) are 13.5, 13.5 and 14.5 (35, 37, and 37.5) GHz for DH-HEMTs with an as deposited gate, and with 280 °C and 330 °C annealed gates, respectively. At a measured frequency of 2.4 GHz, the DH-HEMT with a 330 °C annealed gate exhibits the highest PAE = 44.8% at VDS = 3 V and VGS = −1.0 V and the lowest Fmin = 1.89 dB at VDS = 3 V and ID = 200 mA mm−1.

Depletion-mode δ-doped In0.5Ga0.5As/In0.5Al0.5As mHEMTs have been metamorphically grown on a GaAs substrate and successfully fabricated with different kinds of gate-metal formation. The gate-metal formations include a combination of mesa- or air-type gate feeder with or without a buried gate (before or after annealing). Only the air-type mHEMT with a buried gate shows no clear kink-effect behaviour. For a 1 µm gate mesa-type (air-type) mHEMT, a maximum extrinsic transconductance of 412 (414) and 535 (472) mS mm−1 is obtained before annealing and after annealing. There is a 207 mV (205 mV) shift in VTH after the mesa-type (air-type) mHEMT is annealed. Experimental results indicate that both the gate-feeder metal and the annealing process have a significant effect on output conductance, gate leakage current, breakdown voltage, high frequency and noise performances. The peak gate leakage current density of 12 (120) µA mm−1 for the air-type (mesa-type) mHEMT before annealing is improved to 8 (55) µA mm−1 after annealing. At 2.4 (5.4) GHz, gain = 23 (20) dB can be obtained at Fmin = 1.27 (1.76) dB for the air-type mHEMT after annealing, while gain = 22 (18.5) dB is obtained at Fmin = 1.36 (2.0) dB before annealing. For the mesa-type mHEMT, these values are gain = 20 (16.5) dB at Fmin = 1.47 (2.25) dB and gain = 19.5 (14) dB at Fmin = 1.68 (3.11) dB.

In this paper, extremely high potential barrier height and gate turn-on voltage in an n+/p+/n+/p+/n GaAs field-effect transistor employing double camel-like gate structures are demonstrated. The gate potential barrier height of the double camel-like gate is substantially enhanced by the addition of another n+/p+ layer in the gate region, as compared with the conventional n+/p+/n single camel-like gate structure. The influence of gate structure layers on the depletion depth, potential barrier height, transconductance and gate voltage swing are addressed. Experimental results show that a relatively high gate turn-on voltage up to +4.9 V is realized because two reverse-biased junctions of the double camel-like gate structures absorb part of the positive gate voltage. In addition, an extremely broad gate voltage swing greater than 4.6 V with the transconductance above 100 mS mm?1 is observed. These results indicate that the studied device is suitable for linear and signal amplifiers and inverter circuit applications.

N–p–n InGaP/GaAs Dual-Emitter HPTs (DEHPTs) with and without extrinsic base surface passivation were fabricated to investigate the influence of the surface leakage on the device’s optical performance. There are four operating regions appearing in the output characteristics of DEHPTs under illumination: negative-saturation, negative-tuning, positive-tuning and positive-saturation regions. The InGaP-passivated DEHPT (P-DEHPT), i.e. DEHPT with the extrinsic base surface passivated by InGaP, exhibits the maximum optical gains of 46.57, 46.86 and 47.39 while the non-passivated one (NP-DEHPT) shows ones of 32.02, 33.55 and 33.57 for optical powers of 8.62, 13.2 and 17.5 μW, respectively. However, the NP-DEHPT exhibits the larger peak gain-tuning efficiencies of 37.35, 41.03 and 44.10 compared to 12.76, 13.72 and 16.01 V −1 for the P-DEHPT for optical powers of 8.62, 13.2 and 17.5 μW, respectively. The better tuning efficiency makes the NP-DEHPT a possible low optical power optoelectronic application.

An InGaP/GaAs dual-emitter heterojunction phototransistor (DEPT) with a voltage-biased emitter is compared with a conventional heterojunction phototransistor (HPT) with a voltage-biased base. There are four (three) operating regions in the photocurrent–voltage characteristics of the DEPT (HPT): negative-saturation, negative-tuning, positive-tuning, and positive-saturation (cutoff, positive-tuning, and positive-saturation) regions. The power- and voltage-tunable optical gains are obtained in the DEPT, while only the voltage-tunable optical gain in the HPT. In addition, the maximum optical gain (32.3) obtained in the DEPT is 20-fold that (1.64) in the HPT. Experimental results show that 1) the voltage-tunable optical gain ranges from 0.8 to 1.64 with a gain-tuning efficiency of only 4.4 V-1 for the HPT and that 2) the DEPT exhibits a voltage-tunable optical gain ranging from 12.9 to 32.3 with a maximum gain-tuning efficiency of 43.4 V-1. Furthermore, a simple circuit model is developed to describe well the optical performance tuned by a voltage for both the DEPT and HPT. Experimental and modelling results indicate that the DEPT is very promising for optoelectronic applications when a low optical power is used.

We report on the InGaP/GaAs dual-emitter heterojunction phototransistors (DEPTs) with an emitter biased using a voltage for comparison to heterojunction phototransistors (HPTs) with a floating base operated in the p-i-n and transistor modes and to the HPTs with a base biased using a voltage. The optical gain of the DEPT is presented to be tunable with both of the voltage applied to the emitter and the incident optical power. On the contrary, a conventional HPT's configuration does not simultaneously exhibit both. The power-tunable optical gain is available when the base of the HPT is floated. Otherwise, the voltage-tunable optical is expected for the HPT with a voltage biased base. Experimental results show that (1) the HPT with a voltage biased base exhibits a gain-tuning efficiency of 4.4 V- 1 and (2) the DEPT with an emitter biased using a voltage exhibits a gain-tuning efficiency of 43.4 V-1.

A novel 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 in the InGaAs quantum well and at InGaP/GaAs heterojunction, respectively, 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 device could be used for signal amplifier under normal operation mode and multiple-valued logic circuit application under inverted operation mode.

In this paper, a functional InGaP/GaAs/InGaAs step-compositional-emitter heterojunction bipolar transistor (SCEBT) is demonstrated. The excellent transistor performance, including a high current gain and a low collector–emitter offset voltage, is achieved under normal operation mode. In particular, an interesting three-state S-shaped negative-differential-resistance (NDR) switch is observed under inverted operation mode at room temperature because of the reduction of base barrier height and discontinuous confinement effects for electrons in a InGaP/GaAs heterojunction and InGaAs quantum well, respectively. The three-terminal base-controlled NDR characteristics and multiple-valued logic applications are also investigated. Consequently, the transistor action and switching characteristics of the studied SCEBT are promising for signal amplifier and logic circuit applications.

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

New hydrogen-sensing amplifiers are fabricated by integrating a GaAs Schottky-type hydrogen sensor and an InGaP-GaAs heterojunction bipolar transistor. Sensing collector currents (ICN and ICH) reflecting to N2 and hydrogen-containing gases are employed as output signals in common-emitter characteristics. Gummel-plot sensing characteristics with testing gases as inputs show a high sensing-collector-current gain (ICH/ICN) of > 3000. When operating in standby mode for in situ long-term detection, power consumption is smaller than 0.4 ?W. Furthermore, the room-temperature response time is 85 s for the integrated hydrogen-sensing amplifier fabricated with a bipolar-type structure.

The dynamic performance of a dual-emitter phototransistor (DEPT) was studied. In the static case of a DEPT under a 12.5 µW optical power, the emitter-induced gain effect from photocurrent modulation improves collector photocurrent (88 to 129 µA). 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.

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 (IDSS=451mA/mm), transconductance (gm,max=225mS/mm), breakdown voltages (VBD(DS)/V BD(GD)=22/-25.5V), gate-voltage swing (GVS=2.24V), cutoff, and maximum oscillation frequencies (ft/fmax=17.2/32GHz) are improved as compared to those of a 1-mum gate device without field plate. At a VDS 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

A high-performance InP/InGaAs -doped pnp heterojunction bipolar transistor (HBT) has been first fabricated and demonstrated. The addition of a -doped sheet between two undoped spacer layers effectively eliminates the potential spike at emitter-base junction, lowers the emitter-collector offset voltage, and increases the barrier for electrons, simultaneously. Experimentally, 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 lowest value for the reported InP/InGaAs pnp HBTs.

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.

The spontaneous surface luminescence properties of InGaN/GaN quantum structure lattice (QSL) are reported. The QSL consists of a two-dimensional array of InGaN/GaN quantum boxes (QBs) arranged in a rectangular pattern of 200 nm periodicity. The measured angular dependent photoluminescence (PL) spectra show a strong dependence on the in-plane Bragg diffractions between QBs. The maximum PL intensity of the InGaN/GaN QSL array that fulfill the Bragg condition points in the normal direction of the sample surface with a narrow radiation angle of ∼ ±12°. In addition, a small side lobe is also shown at ±40°. For the QSL sample that does not fulfill the Bragg diffraction condition, the radiation pattern shows a conventional cosine distribution. The finite-difference time-domain numerical analysis confirms that the lowest order and higher order Bragg diffractions between QBs determine the main and the small side lobe of the radiation pattern measured in QSLs, respectively.

The results of the growth of thin (∼3 nm) InGaN/GaN single quantum wells (SQWs) with emission wavelengths in the green region by plasma-assisted molecular beam epitaxy are present. An improved two-step growth method using a high growth temperature up to 650 °C is developed to increase the In content of the InGaN SQW to 30% while maintaining a strong luminescence intensity near a wavelength of 506 nm. The indium composition in InGaN/GaN SQW grown under group-III-rich condition increases with increasing growth temperature following the growth model of liquid phase epitaxy. Further increase in the growth temperature to 670 °C does not improve the photoluminescence property of the material due to rapid loss of indium from the surface and, under certain growth conditions, the onset of phase separation.

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

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.

Interference fringes are generally found in the photoluminescence (PL) spectrum of heterostructures with large refractive index differences between layers and with a smooth interface. To eliminate the interference effects in an air/GaN/InGaN/GaN/Al2O3 structure, the measured interference fringe wavelengths of the PL spectrum are used to deduce the frequency dependent interference function of the system. This interference function is then used to numerically remove interference fringes from the as-measured PL spectrum. This versatile semiempirical method allows the derivation of the true PL spectrum from the measured data, including angular dependent spectra, without complicated calculations or additional measurements.

The roles of micro-metal–oxide (MO) interfaces inside a sensing metal formed by coevaporating Pd and SiO2 in metal–semiconductor–metal GaN sensors are investigated. The porous property of the Pd and SiO2 mixture together with the presence of micro-MO interfaces gives rise to a highly efficient dissociation of hydrogen molecules and hence an enhanced barrier height variation (ΔB) of a reverse-biased Schottky diode. The measured ΔB increases from 294 to 392 mV at a concentration coefficient of 25 mV/decade as the hydrogen concentration increases from 2.13 to 10100 ppm H2/N2. Therefore, when the sensor is subjected to 0.02 ppm H2/N2, ΔB as high as 245 mV is still expected. The sensor in a 2.13 ppm H2/N2 ambience has a sensing response of 8.7×104. Excellent dynamic responses are demonstrated by switching voltage polarity or continuously changing hydrogen concentration, showing that the proposed structure is a promising hydrogen sensor.

A metal–semiconductor–metal Pd/GaN hydrogen sensor with a porous-like mixture of Pd and SiO2 is investigated. Besides symmetrically bidirectional sensing characteristics with a widespread voltage regime (at least −5–5 V), a high sensing response of 8 × 105 (7.7 × 106) corresponding to a Schottky barrier height variation of 352 (411) meV is obtained in a 4890 ppm H2/N2 ambience at a voltage of −1.5 (−5) V. A highly efficient dissociation of hydrogen molecules due to an enhanced catalytic activity of the mixture explains the improved performance. Furthermore, dynamic responses by alternately switching voltage polarity and introducing and removing hydrogen-containing gases are also included to evaluate the proposed device as a high sensing response and low power sensor.

Pseudomorphic Al0.22Ga0.78As/In0.16Ga0.84As/Al0.22Ga0.78As double heterojunction high electron mobility transistors (DH-HEMTs) fabricated with different gate-formation structures of a single-recess gate (SRG), a double-recess gate (DRG) and a field-plate gate (FPG) were comparatively investigated. FPG devices show the best breakdown characteristics among these devices due to great reduction in the peak electric field between the drain and gate electrodes. The measured gate–drain breakdown voltages defined at a 1 mA mm−1 reverse gate–drain current density were −15.3, −19.1 and −26.0 V for SRG, DRG and FPG devices, respectively. No significant differences in their room-temperature common-source current–voltage characteristics were observed. However, FPG devices exhibit threshold voltages being the least sensitive to temperature. Threshold voltages as a function of temperature indicate a threshold-voltage variation as low as −0.97 mV K−1 for FPG devices. According to the 2.4 GHz load–pull power measurement at VDS = 3.0 V and VGS = −0.5 V, the saturated output power (POUT), power gain (GP) and maximum power-added efficiency (PAE) were 10.3 dBm/13.2 dB/36.6%, 11.2 dBm/13.1 dB/39.7% and 13.06 dBm/12.8 dB/47.3%, respectively, for SRG, DRG and FPG devices with a pi-gate in class AB operation. When the FPG device is biased at a VDS of 10 V, the saturated power density is more than 600 mW mm−1.

This paper reports on a four-terminal dual-emitter heterojunction phototransistor (4T-DEPT) with a base biased by current source in comparison with a three-terminal dual-emitter heterojunction photoreansistor (3T-DEPT) without the additional current bias. While only voltage can be used to tune the optical performance of the 3T-DEPT, two kinds of operation modes, voltage- (VE21) and current- (IBdc) control modes, are considered for the 4T-DEPT. In addition to the power- and voltage-tunable optical gains, current-tunable one is also available in the 4T-DEPT operation. When the 4T-DEPT operates under the incident optical power (Pin) of 0.423 μW, it shows the maximum current-dependent gain-tuning efficiency of 62.66 μA-1 at VE21 = 0.06 V and IBdc = 0.001 μA. However, it is only 45.03 V-1 for the maximum voltage-dependent gain-tuning efficiency at VE21 = 0.06 V and IBdc = 0.25 μA.

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Temperature-dependent dark and optical characteristics of the InGaP/GaAs heterojunction phototransistors (HPTs) with and without sulfur treatment are studied. As compared to the HPT without (NH 4 ) 2 S treatment (HPT A), treatment at 50°C for 20 min leads to a reduced p-i-n dark current (/dark) and a reduced collector dark current (IC dark ) for the HPT (HPT D) in the emitter-floated and base-floated configurations, respectively. Moreover, the effective reduction of the surface defects also induces an enhanced p-i-n photocurrent (I ph ). The enhanced I ph combined with the promoted dc current gain results in an enhanced optical gain (G) and signal-to-noise ratio (SNR). For HPT A (D) under P in = 107.6 nW at 298 K, the G is 1.42 (20.3) while the SNR is 42 (94) dB. Experimental results indicate that the treated HPTs, compared to the untreated one, are more sensitive to low-power illumination.

In this article, high-performance InGaP∕InGaAs∕GaAs δ-doped pseudomorphic modulation-doped field effect transistors (pMODFETs) employing n+-GaAs∕p+-InGaP∕n-InGaP camel-gate structure are characterized. Because of the depleted p-n junction in the gate region and the presence of the large conduction-band discontinuity of the InGaP∕InGaAs heterostructure, a large gate turn-on voltage is obtained. The dc and microwave characteristics of single- and double-δ-doped pMODFETs are demonstrated. The double-δ-doped pMODFET exhibits a higher drain saturation current, a larger transconductance, a broader gate voltage swing, and better high-frequency responses than the single-δ-doped device. The excellent performance of the studied devices is promising for linear and large signal amplifiers and high-frequency circuit applications.

A novel InGaP/InGaAs/GaAs p-channel pseudomorphic modulation-doped field effect transistor based on p+-GaAs/n+-InGaP/p-InGaP camel-like gate structure is reported for the first time. Owing to the p–n depletion of the camel-like gate and the presence of relatively large ΔEv at InGaP/InGaAs heterostructure, an extremely large gate turn-on voltage, greater than 2 V, is measured. For a 1×100 µm2 device, the experimental results show a maximum saturation current density of −345 mA/mm and a widely broad gate voltage swing, greater than 4 V, with 80% maximum transconductance. Furthermore, the fT and fmax values are 3.1 and 4.8 GHz, respectively.