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This study investigates how ambient/carrier gases affect the material characteristics of amorphous indium–gallium–zinc oxide (a-InGaZnO) thin films deposited using the ultrasonic spray pyrolysis deposition (USPD) method. Nitrogen and air are used as the ambient/carrier gases in this study. The crystallinity, oxygen deficiency, energy bandgap, and trap level in the a-InGaZnO thin films are analyzed. The performance of the thin-film transistors (TFTs) based on a-InGaZnO with different ambient/carrier gases is investigated as well. It is found that oxygen deficiency is suppressed when air is used as the ambient/carrier gas. When nitrogen is used as the ambient/carrier gas to deposit a-InGaZnO thin film, the TFT shows higher field-effect mobility and saturation mobility. However, when the a-InGaZnO thin film is deposited with air as the ambient/carrier gas, the subthreshold swing, ON-/ OFF-current ratio, interface trap density, and stability of the TFT are improved. This study demonstrates how ambient/carrier gases in the USPD system affect the performance of a-InGaZnO TFT.

A new leakage-prevention pixel circuit is proposed to maintain the driving capability of its driving thin-film transistors (TFTs) at a low frame rate of 15 Hz for use in active-matrix organic light-emitting diode (AMOLED) displays. The proposed leakage-prevention mechanism generates a compensating leakage current that reduces the source-to-drain voltage of the switching TFT, thereby lessening the fluctuation of the stored driving voltage when the frame rate is reduced from 60 to 15 Hz. Moreover, the proposed circuit can compensate for the threshold voltage variation in low-temperature polycrystalline silicon TFTs (LTPS TFTs) and current–resistance drops in VDD lines. To validate the performance of the compensation and leakage prevention, simulation models based on the measurement of the fabricated LTPS TFTs and an organic light-emitting diode (OLED) are established. The experimental results confirm that the leakage current of the gate node is successfully suppressed from 50.34 to 1.25 pA by the proposed leakage-prevention mechanism. Also, within the long emission period, the highly uniform OLED currents at low, medium, and high gray levels are achieved, verifying the feasibility of the proposed pixel circuit.

In this study, we fabricate a counter electrode by coating a Pt ribbon onto a fluorine-doped tin oxide glass substrate with a Pt layer. The Pt ribbon gives rise to a protrusive structure of the counter electrode, produced by photolithography, sputtering and lift-off processes. The experimental results reveal that the photoelectric efficiency of the dye-sensitized solar cell (DSSC) with the Pt ribbon (5.32%) is 21% higher than that of the DSSC without a Pt ribbon (4.38%). This infers that Pt ribbons can increase the photoelectric efficiencies of DSSCs. The DSSC with the Pt ribbon has a large photoelectric efficiency of 5.32%, not only because the protrusive structure has specific channels for directional electron transport, but also because of its large surface area. The method that is proposed herein has the advantages of a low production cost and easy fabrication that can be applied to various electrode structures.

Widegap-channel Al0.65Ga0.35N/Al0.3Ga0.7N/AlN/SiC metal-oxide-semiconductor heterostructure field-effect transistors (MOS-HFETs) with ultrasonic spray pyrolysis deposition (USPD) grown Al2O3 gate-oxide demonstrating enhancement-mode (E-mode) operation are investigated for the first time. The E-mode operation was achieved by using fluorine ions (F−) implantation. In comparison, conventional Schottky-gate device (sample A) and MOS-HFET (sample B) showing depletion-mode (D-mode) operation were fabricated on the same epitaxial structure. The device characteristics with respect to different gate-to-drain spacings ( $L_{GD}$ ) of $6~\boldsymbol {\mu }\text{m}$ and 14 $\boldsymbol {\mu }\text{m}$ have also been studied. The present E-mode Al0.65Ga0.35N/Al0.3Ga0.7N/AlN MOS-HFET (sample C) with $L_{GD} =6$ (14) $\boldsymbol {\mu }\text{m}$ has demonstrated improved maximum drain-source current density ( $I_{DS,max}$ ) of 206.3 (163.5) mA/mm at $V_{DS} =20$ V, maximum extrinsic transconductance ( $\text{g}_{m,max}$ ) of 32.9 (22.0) mS/mm, on/off-current ratio ( $I_{on}/I_{off}$ ) of 3.7 ${\times }\,\,10^{9}$ ( $1.8\,\,{\times }\,\,10^{9}$ ), two-terminal off-state gate-drain breakdown voltage ( $BV_{GD}$ ) of −370 (−475) V, and three-terminal on-state drain-source breakdown voltage ( $BV_{DS}$ ) of 330 395 V.

In this work, an effective bilayer modulation is achieved for the multilayer hexagonal boron nitride (hBN) resistive random-access memory (RRAM) by an insertion of intentionally oxidized titanium oxide layer. The controllable multiple resistance states can be achieved by setting stop voltage of gradual RESET and compliance current during SET, which is beneficial for multilevel storage and neuromorphic application. The switching uniformity and the endurance of memory window are both improved by the effective bilayer modulation. Through experimental data and ab-initio calculation, both the switching and modulation mechanisms are clarified. The effective modulation can be attributed to the multiple thin conductive filaments with dual vacancies within the bilayer stacks of the multilayer hBN and titanium oxide. A significant formation energy difference between the two kinds of vacancy defects existing in bilayer stacks plays the key role for the filament formation through the fixed paths which benefits the switching uniformity. The findings gained from this work can help promote hBN in RRAM application.

We demonstrate a high-performance normally-OFF AlGaN/GaN fin metal–insulator–semiconductor high electron mobility transistor (fin-MISHEMT) on silicon with a low work function metal-source contact ledge (LWFM-SCL). In order to realize the normally-OFF operation, an optimized gate-recessed fin structure is used. The fin structure inherently containing a gate-connected field plate (FP) design improves the breakdown voltage ( ${V}_{\text {BD}}$ ). Moreover, the LWFM-SCL can improve the device overall ON-resistance ( ${R}_{ \mathrm{ON}}$ ) by lowering the gate–source access resistance ( ${R}_{\text {a}}$ ). The proposed device with a gate–drain length ( ${L}_{\text {GD}}$ ) of 7 $\mu \text{m}$ exhibits superior characteristics such as a threshold voltage ( $V_{\text {TH}}$ ) of +1.2 V, maximum drain current ( ${I}_{\text {D, max}}$ ) of 825 mA/mm, ON-state/OFF-state current ( ${I}_{ \mathrm{ON}}/{I}_{ \mathrm{OFF}}$ ) ratio of 109–1010, subthreshold swing (SS) of 76 mV/decade, ${V}_{\text {BD}}$ of 810 V, and specific ${R}_{ \mathrm{ON}}$ ( ${R}_{\text {on, sp}}$ ) of 0.63 $\text{m}\Omega \cdot $ cm2. It also possesses excellent ${V}_{\text {TH}}$ hysteresis, temperature stability, and dynamic ${R}_{ \mathrm{ON}}$ characteristics. These results suggest that the proposed device is very suitable for high power switching applications.

This study demonstrates an enhancement-mode (E-mode) InAlN/GaN MOSHEMT on a silicon substrate with a Schottky tri-drain extension (STDE) to yield a large breakdown voltage ( $\text{V}_{\text {BD}}$ ) while maintaining a low on-resistance ( $\text{R}_{\text {on}}$ ). The E-mode operation is realized by a recessed tri-gate nanowire structure. The STDE functions as a drain-connected field plate (FP) to effectively distribute the electric field (E-field) around the drain contact edge, improving the $\text{V}_{\text {BD}}$ . Moreover, through the metal of the STDE directly contacting the 2-D electron gas (2-DEG) from the sidewalls, a low specific $\text{R}_{\text {on}}$ ( $\text{R}_{\text {on, sp}}$ ) is achieved. The proposed device with a gate-to-drain length ( $\text{L}_{\text {GD}}$ ) of $5~\mu \text{m}$ exhibits a threshold voltage ( $\text{V}_{\text {TH}}$ ) of +0.9 V, large maximum drain current ( $\text{I}_{\text {D, max}}$ ) of 815 ± 27 mA/mm, high $\text{I}_{\text {on}}/\text{I}_{\text {off}}$ ratio of 1010, steep subthreshold swing (SS) of 67 mV/decade, superior $\text{V}_{\text {BD}}$ of 830 V, and low $\text{R}_{\text {on, sp}}$ of 0.74 ± 0.04~\text{m}\Omega \cdot cm2. With $\text{L}_{\text {GD}}$ of $10~\mu \text{m}$ , a $\text{V}_{\text {BD}}$ of 1190 V is achieved, corresponding to a $\text{R}_{\text {on, sp}}$ of 1.39 ± $0.07~\text{m}\Omega \cdot$ cm2. These results reveal great potential for future E-mode power device applications.

This study demonstrates an amorphous indium–tin–zinc–oxide (a-ITZO) thin-film transistor (TFT) using an ultrasonic spray pyrolysis deposition (USPD) method. X-ray diffraction, X-ray photoelectron spectroscopy, Tauc plot, and photoluminescence spectrum are used to confirm the crystal structure, oxygen contents, energy bandgap, and the existence of oxygen deficiencies. Besides, these material characteristics are compared with a sputter-deposited ITZO film. The TFT based on the USPD-deposited ITZO shows better electrical performance than the TFT based on the sputter-deposited ITZO. In addition, the negative- /positive-bias illumination stress results indicate that the TFT based on the USPD-deposited ITZO film is more stable than the one based on the sputter-deposited ITZO.

Novel Al 0.75 Ga 0.25 N/Al x Ga 1-x N/Al 0.75 Ga 0.25 N/AlN metal-oxide-semiconductor heterostructure field-effect transistors (MOS-HFETs) with symmetrically-graded widegap Al x Ga 1-x N channel (x = 0.75 → 0.25 → 0.75) grown on a SiC substrate are investigated. Al 2 O 3 was devised as the gate dielectric by using a non-vacuum ultrasonic spray pyrolysis deposition (USPD) technique. Device characteristics with respect to different etch depths of the source/drain recesses were studied. For a 2-μm gate length (L G ), the present widegap V-shape-channel MOS-HFET has shown improved maximum drain-source current density (I DS,max ) of 299.3 A/mm at V DS = 20 V, I DS density at V GS = 0 V (I DSS0 ) of 153.9 mA/mm, on/off-current ratio (I on /I off ) of 1.4 × 10 7 , extrinsic transconductance (g m , max ) of 16.7 mS/mm, two-terminal off-state gate-drain breakdown voltage (BV GD ) of -379 V, and three-terminal on-state drain-source breakdown voltage (BV DS ) of 339 V. Besides, superior deep-UV sensing performance with high spectral responsivity (SR) of 1780 (810.2) A/W at wavelength λ = 250 (300) nm are also achieved.

This letter demonstrates a novel enhancement-mode (E-mode) tri-gate nanowire InAlN/GaN MOSHEMT with ultrasonic spray pyrolysis deposition (USPD) deposited Al2O3 as the gate dielectric layer. The proposed device reveals a threshold voltage ( ${V}_{\text {TH}}$ ) of +2.3 V and a maximum drain current ( ${I}_{D, \text {max}}$ ) of 705 mA/mm. It also exhibits superior electrical performances, including a high ON-state/ OFF-state current ( ${I}_{ {{ \scriptscriptstyle {\text {ON}}}}}/{I}_{ {{ \scriptscriptstyle {\text {OFF}}}}}$ ) ratio of 109–1010, a steep subthreshold swing (SS) of 65 mV/decade, and a large breakdown voltage (BV) of 800 V with a leakage current of 0.7 $\mu \text{A}$ /mm while keeping a low-specific ON-resistance ( ${R}_{ {{ \scriptscriptstyle {\text {ON}}}}, \text {sp}}$ ) of 1.04 $\text{m}\Omega \cdot \text {cm}^{\text {2}}$ . This novel E-mode device presents a great potential for power device applications.

Al05Ga0.5N/n-Al0.3Ga0.7N/AlN metal-oxide-semiconductor heterostructure field- effect transistors (MOS-HFETs), grown on a SiC substrate, with composite Al2O3/in situ SiN passivation and Al2O3 gate dielectric are investigated. 20 nm thick high-k Al2O3 was deposited by using a non-vacuum ultrasonic spray pyrolysis deposition (USPD) method. Comparative studies between an in situ SiN-passivated Schottky-gate HFET (sample A) and a composite Al2O3/SiN-passivated MOS-HFET were made. Besides, electrical and deep-UV sensing characteristics for devices with different gate-drain separations (L GD ) of 6 μm and 14 μm were also studied. Improved device performances have been obtained for the present sample B (A) with L GD = 6/14 μm separately, including maximum drain-source current density (I DS, max) of 634.4/463.1 (421.8/301.1) mA mm−1, maximum extrinsic transconductance (g m, max) of 25.2/17.9 (19.1/15.2) mS mm−1, on/off-current ratio (I on /I off ) of 7.4 × 107/5.4 × 107 (4.5 × 105/5.4 × 104), two-terminal off-state gate-drain breakdown voltage (BV GD ) of −420/−480 (−320/−390) V, and three-terminal on-state drain-source breakdown voltage (BV DS ) of 310/380 (220/300) V at 300 K. Superior spectral responsivity (SR) of 885.6 A W−1 under 250 nm deep-UV radiation has also been achieved for the present MOS-HFET.

An interesting device design including a zirconium oxide (ZrO2) current blocking layer (CBL) and a ZrO2 surface passivation layer (SPL) is employed to manufacture a GaN/InGaN light-emitting diode (LED). Based on the inherently good performance of ZrO2, the current spreading effect and the undesired surface leakage are efficiently enhanced and suppressed, respectively. Energy-dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) are used to study the relevant properties. It is found that by series calibration, 50 nm is the proper thickness of the ZrO2 CBL and SPL. The peak emission wavelength of the proposed LEDs is around 452 nm. Experimentally, at the operating condition of 110 A cm−2, the proposed Device L3 with a 50 nm-thick ZrO2 CBL and a 50 nm-thick ZrO2 SPL demonstrates improvements of 66.1% in light output power (LOP) and 64.5% in wall plug efficiency (WPE) as compared to a traditional Device L1 without the specific design. Furthermore, the proposed Device L3 presents a notable enhancement in the light emission mapping image in comparison to the traditional LED. So, the proposed device design which incorporates a proper ZrO2 CBL and ZrO2 SPL, is beneficial for manufacturing GaN/InGaN LEDs.

GaN-based HEMTs feature a lot of superior material properties, including high electron mobility, wide band-gap, and large breakdown field. These properties are very suitable for power electronic applications. However, due to the high two dimensional electron gas (2DEG) density, a conventional GaN HEMT is an inherently normally-on device. Considering safety design in the power electronic systems, high performance normally-off GaN HEMT s are needed [1] . FinFet (tri-gate) structure has recently been applied to GaN HEMTs for the normally-off operation. However, a conventional FinFet (tri-gate) GaN HEMT requires very small channel widths to achieve the normally-off operation. This needs very critical process conditions and could cause the on-resistance (R on ) to be obviouslhy degraded [2] . In this study, an InAlN/GaN fin-MOSHEMT combined with fluorine treatment is demonstrated. It doesn’t require very small channel widths to achieve a normally-off HEMT while having excellent performances.

Novel Al2O3-dielectric InAlN/AlN/GaN Γ-Gate metal-oxide-semiconductor heterostructure field-effect transistors (MOS-HFETs) with composite Al2O3/TiO2 passivation oxides formed by using ultrasonic spray pyrolysis deposition/RF sputtering, respectively, are investigated. The r-gate includes a 1-μm long active gate on the Al2O3 dielectric and a 1-μm long field-plate on the composite Al2O3/TiO2 oxides. The present Γ-Gate MOS-HFET has demonstrated excellent on/off current ratio (Ion/Ioff) of 8.2 x 1010, subthreshold swing of 102.3 mV/dec, maximum extrinsic transconductance of (gm,max) of 210.1 mS/mm, maximum drain-source saturation current density (IDS,max) of 868.3 mA/mm, two-terminal off-state gate-drain breakdown voltage (BVGD) of -311.2 V, three-terminal drain-source breakdown voltage (BVDS) of 237 V at VGS = -10 V, and power-added efficiency of 39.9% at 2.4 GHz. A conventional Schottky-gate HFET and TiO2-dielectric MOS-HFET were also prepared in comparison. The present design has shown superior dc/RF device performance. It is suitable for high-power RF circuit applications.

This work used mist chemical vapor deposition to deposit an in-situ Cl— doped Al2O3 film. 0.05 vol%, 0.1 vol%, and 0.15 vol% HCl were added to the precursor solutions for Cl— doping. The recess and Cl— doped Al2O3 gate dielectrics were used to form enhancement-mode AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors. The Cl— doping was confirmed by X-ray photoelectron spectroscopy and the negative charge concentration was extracted by capacitance-voltage method. It was found that the doping concentration affects the gate leakage performance and the carrier transportation mechanisms of the gate leakage were investigated. By using the Cl— doped Al2O3 as the gate dielectric layer, the device performance was improved, including more positive threshold voltage, higher output current at the same overdrive voltage, and over 600 V off-state breakdown voltage. In addition, the temperature-dependent threshold voltage characteristics were investigated to estimate the Cl— dopant runaway.

Systematic designs to achieve normally-off operation and improved device performance for Al0.26Ga0.74N/AlN/GaN high electron mobility transistors (HEMTs) grown on a Si substrate are investigated in this work. The step-by-step approach includes: (1) devising a thin AlGaN/AlN composite barrier, (2) introducing fluoride ions within the active region by using CF4 plasma treatment, (3) growing the Al2O3 oxide passivation layers within gate-drain/source regions by using a cost-effective ozone water oxidization technique, and (4) integrating a metal-oxide-semiconductor gate (MOS-gate) design with high-k Al2O3 gate dielectric. Devices with four different evolutionary gate structures have been compared and studied. Variations of threshold voltage (Vth), Hooge coefficients (αH), maximum drain-source current density (IDS, max), maximum extrinsic transconductance (gm, max), gate-voltage swing (GVS) linearity, two-terminal gate-drain breakdown/turn-on voltages (BVGD/Von), on/off current ratio (Ion/Ioff), and high-temperature characteristics up to 450 K are also investigated.

This letter presents amorphous TiO2-based thin-film phototransistors whose structures are designed for front-side and back-side illumination. The channel and gate dielectric layers are deposited by ultrasonic spray pyrolysis deposition, which is a non-vacuum, cost-effective, thin-film deposition technique similar to chemical vapor deposition. The material structure, chemical composition, and optical characteristics of the amorphous TiO2 thin film are analyzed. The phototransistor shows the typical current–voltage ( ${I}$ – ${V}$ ) characteristics of field-effect transistors. It demonstrates a UV-to-visible rejection ratio of approximately 70 –80, a high responsivity of 13.64 A/W, and a high detectivity of $1.64\times 10^{12}$ Jones. The phototransistor can be operated in the high-photo-responsivity and high-detectivity modes by biasing at different quiescent points.

The letter reports normally-off device characteristics of Al0.26Ga0.74N/AlN/GaN oxide-passivated high electron mobility transistors (HEMTs) and metal-oxide-semiconductor HEMTs (MOS-HEMTs) grown on a Si substrate. Al2O3 was formed as the surface passivation oxide or gate dielectric on a thin AlGaN barrier layer by using a cost-effective ozone water oxidization technique. CF4 plasma was used to enable normally-off operation. For the gate dimensions of 1×100 µm2, the present oxide-passivated HEMT and MOS-HEMT (a control Schottky-gate HEMT) have demonstrated superior on/off-current ratio (Ion/Ioff) of 2.5×106 and 1×107 (3.9×103), maximum extrinsic transconductance (gm, max) of 154 and 175 (120) mS/mm, maximum drain-source current density (IDS, max) of 312 and 349 (300) mA/mm, two-terminal gate-drain breakdown voltage (BVGD) of −80 and −140 (−36) V, turn-on voltage (Von) of 1.2 and 1.3 (1) V, and three-terminal on-state breakdown voltage (BVDS) of 93 and 109 (48) V. Excellent BVGD and BVDS enhancements of 122% (288%) and 94% (127%) are achieved in the present oxide-passivated HEMT (MOS-HEMT) design.

This letter demonstrates an integration process of in situ Cl− doped Al2O3 and gate recess technique to fabricate the enhancement mode AlGaN/GaN MOSHEMTs. The Cl− doped Al2O3 thin film is deposited by the ultrasonic spray pyrolysis deposition and characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. The relative permittivity of Cl− doped Al2O3 is higher than the pure Al2O3 and the output current is enhanced. The threshold voltage of the enhancement mode AlGaN/GaN MOSHEMT with the Cl− doped Al2O3 gate dielectric layer rose from 0.2 to 1.3 V. Furthermore, the breakdown voltage of present enhancement mode AlGaN/GaN MOSHEMT reached 650 V. It was also found that the MOSHEMT with Cl− doped Al2O3 has higher gate leakage than that with pure Al2O3. The thermal stability of threshold voltage and current collapse phenomenon is described in this letter.

Hexagonal boron nitride (hBN) has recently become a promising material for being utilized as switching layer while resistive random-access memory (RRAM) continues to emerge. In this work, the insertion of intentionally oxidized titanium oxide between multilayer hBN and top electrode modulates the RESET characteristic into gradual RESET, which can promote the reliability for multilayer-hBN RRAM. The consistency of high resistance state (HRS) can be improved by preventing the RRAM devices from abrupt RESET, and then the good uniformity of SET and RESET voltages can be obtained. The effective modulation can be attributed to the multiple thin conductive filaments, and the inhibition for Ti penetration. Significant reliability improvement for multilayer-hBN RRAM is achieved through the demonstrated simple process control.

Al0.75Ga0.25N/n-AlxGa1-xN/Al0.75Ga0.25N/AlN metal-oxide-semiconductor heterostructure field-effect transistors (MOS-HFETs), grown on a SiC substrate, with step-graded Si-doped (n = 3 × 1018 cm-3) widegap AlxGa1-xN channel and Al2O3 gate-dielectric are investigated. Increased Al-compositions with x = 0.25, 0.5, and 0.75 towards the buffer were devised in the composite widegap channel. The high-k Al2O3 dielectric/passivation layer was grown by using a non-vacuum ultrasonic spray pyrolysis deposition (USPD) method. Experimental comparisons were made with respect to a conventional Schottky-gate HFET. The epitaxial structure of the studied Al2O3-dielectric Al0.75Ga0.25N/n-AlxGa1-xN/Al0.75Ga0.25N/AlN MOS-HFET (sample A) and Schottky-gate HFET (sample B). Both devices have the identical epitaxial structure grown on a SiC substrate by using a low-pressure metal-organic chemical vapor deposition (LP-MOCVD) system. The layer structure includes an undoped AlN buffer, a 20-nm undoped Al0.75Ga0.25N barrier, a 150-nm step-graded Si-doped (n = 3 × 1018 cm-3) AlxGa1-xN channel (x = 0.25, 0.5, and 0.75), and a 20-nm undoped Al0.75Ga0.25N barrier. Standard photolithography and lift-off techniques were used for device processing. For sample B, mesa etching was performed with respect to a 100-nm thick Ni barrier by using an inductively coupled-plasma reactive ion etcher (ICP-RIE). Flow rates were tuned and set at 10 sccm and 20 sccm for the mixed etching gases of BCl3 and Cl2, respectively. The 20-nm undoped Al0.75Ga0.25N barrier was etched away before deposition of source/drain electrodes. Ti (10 nm)/Al (50 nm)/Ni (10 nm)/Au (50 nm) were evaporated. The source/drain ohmic contacts were formed by annealing the sample for 25 seconds at 900°C by using a rapid thermal annealing (RTA) system (ULVAC MILA-5000). Then, 30-nm thick Al2O3 layer was deposited on the Al0.75Ga0.25N barrier by using the USPD technique. Finally, gate electrode of Ni (100 nm)/Au (50 nm) was evaporated after gate photolithography. As for sample A, the gate electrode was formed directly on the surface of Al0.75Ga0.25N barrier without oxide deposition. Improved device performance of the present MOS-HFET design have been obtained, including maximum drain-source current density (IDS, max ) of 130.1 A/mm at VGS = 10 V and VDS = 20 V, IDS at VGS = 0 V (IDSS0 ) of 83.1 mA/mm, on/off-current ratio (Ion /Ioff ) of 1.4 × 107, maximum extrinsic transconductance (gm, max ) of 11.8 mS/mm, two-terminal off-state gate-drain breakdown voltage (BVGD ) of -404 V, and three-terminal on-state drain-source breakdown voltage (BVDS ) of 364 V at 300 K. The present MOS-HFET design has also shown high spectral responsivity (SR) of 737 A/W under 250-nm deep-UV radiation at 300 K.

This paper demonstrates an AlGaN/GaN ion-sensitive heterostructure field-effect transistors (ISHFETs)-based pH sensors with an aluminum oxide (Al2O3) to serve as a passivation layer and a sensing membrane at the same time. Al2O3 was deposited by the ultrasonic spray pyrolysis deposition (USPD) method. It was found that the ISHFET with Al2O3 showed a higher pH sensitivity of 55.6 mV/pH, a faster response speed of 3 s (from pH 4 to pH 7) and 7 s (from pH 7 to pH 10), a lower hysteresis voltage of 4.3 mV, and a smaller drift rate of 1.25 mV/h (at pH 7) compared with the ISHFET without passivation. In addition, the ISHFET with an Al2O3 passivation layer exhibited significant surface potential variation and low degradation rate. These results suggest that the performance of ISHFET improved using USPD-grown Al2O3.