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The adaptability of living organisms to dynamically adjust their biological behavior in response to fluctuating surroundings is a prerequisite for their evolutionary success. However, artificially‐synthesized materials, especially semiconductors, have not been able to replicate such adaptability due to their inherent physical rigidity and lack of intrinsic structural responsiveness to external stimuli. Herein, an adaptive structural evolution in group‐III‐nitride semiconductors is demonstrated by constructing an AlGaN‐nanowire/Ni(OH)2 symbiotic‐system, resulting in self‐improved optoelectronic characteristics. The mutualistic interplay between AlGaN and Ni(OH)2 nanostructure leads to the adaptive evolution of crystalline‐facets of AlGaN‐nanowires, along with self‐optimization of Ni(OH)2 nanocrystals upon photon‐irradiation during its operation. Specifically, the nanowire‐surfaces dynamically evolve during Ni(OH)2 photo‐deposition, removing the (0001¯$\bar{1}$) plane while exposing the (101¯1¯$\bar{1}\bar{1}$), which facilitates carrier transport at AlGaN/Ni(OH)2 interface. Moreover, light‐induced electrons generated from AlGaN‐nanowires then partially reduce Ni2+ ions in the Ni(OH)2 nanostructure into Ni0 nanometals, which further boosts the proton reduction thermodynamics, generating an unusual self‐improving photocurrent from −59.6 to −101.6 µA cm−2. Such a "symbiotic system," which is barely observed in conventional semiconductors, provides a promising avenue toward realizing smart adaptive semiconductors that are capable of dynamic structural evolution to fully unleash their potential for emerging optoelectronic and artificial‐photocatalysis applications. [ABSTRACT FROM AUTHOR]

Underwater optical communication (UOC) has attracted considerable interest in the continuous expansion of human activities in marine/ocean environments. The water‐durable and self‐powered photoelectrodes that act as a battery‐free light receiver in UOC are particularly crucial, as they may directly face complex underwater conditions. Emerging photoelectrochemical (PEC)‐type photodetectors are appealing owing to their intrinsic aqueous operation characteristics with versatile tunability of photoresponses. Herein, a self‐powered PEC photodetector employing n‐type gallium nitride (GaN) nanowires as a photoelectrode, which is decorated with an iridium oxide (IrOx) layer to optimize charge transfer dynamics at the GaN/electrolyte interface, is reported. Strikingly, the constructed n‐GaN/IrOx photoelectrode breaks the responsivity‐bandwidth trade‐off limit by simultaneously improving the response speed and responsivity, delivering an ultrafast response speed with response/recovery times of only 2 µs/4 µs while achieving a high responsivity of 110.1 mA W−1. Importantly, the device exhibits a large bandwidth with 3 dB cutoff frequency exceeding 100 kHz in UOC tests, which is one of the highest values among self‐powered photodetectors employed in optical communication system. [ABSTRACT FROM AUTHOR]

The elementary electronic‐logic‐gates, performing basic logic functions using electric signals as input, act as a building block of modern digital circuits. Intriguingly, the optoelectronic‐logic‐gates (OLGs), composed of optical devices, are emerging as a new logic platform which enables faster and large‐capacity data transmission and processing by using photons as input. However, the strict operation principle of classic optical devices, for example, the unidirectional photoresponse of the photodetector, restricts the functional enrichment of OLGs. Herein, reprogrammable OLGs in a photoelectrochemical (PEC)‐environment are reported by employing gallium‐nitride semiconductor p–n nanowires as photoelectrodes where bidirectional photocurrent is achieved, leading to the demonstration of various binary OLGs including "NOT", "XOR", and "OR". Strikingly, thanks to the versatile tunability of PEC‐photoelectrodes, the logic function of these OLGs is switchable by simply adjusting programming inputs including light intensity, bias voltage, electrolyte condition, and the physicochemical properties of the nanowire surface. Most importantly, unique ternary OLGs, for example, ternary "OR" gates, can also be realized based on binary ones by just tuning their applied bias for higher logic complexity applications, without changing the device architecture. Such reprogrammable binary and ternary OLGs could provide a new avenue toward next‐generation logic circuits for fast computing and data‐processing in the future. [ABSTRACT FROM AUTHOR]

The carrier transport dynamics at the surface/interface of semiconductors determine the electronic and optical properties of devices. Thus, precise control of their dynamic processes while understanding the nature of these characteristics is crucial for modulating device functionalities. Here, a photoelectrochemical‐type photosensor is built using monocrystalline p‐GaN nanowires on the Si platform, which unambiguously exhibits either positive or negative photocurrent upon different light illumination. Such dual‐polarity photocurrents are attributed to photogenerated‐carrier‐transport competition at two interfaces: the GaN/electrolyte and GaN/Si interface. Particularly, a rational Pt decoration successfully accelerates the carrier migration at the GaN/electrolyte interface that breaks the original balance of carrier transport. This mechanism is further elaborated by Kelvin‐probe‐force‐microscopy characterization, which intuitively reveals the impact of Pt decoration on modulating nanowires' surface band bending and the consequent carrier dynamics at the interfaces. These insights into the control of carrier dynamics shed light on achieving multi‐functional PEC devices built upon simple semiconductor architectures. [ABSTRACT FROM AUTHOR]

Temperature sensor using series GaN Schottky barrier diode (SBD) with TiN anode was fabricated and evaluated extensively. The diode presents good characteristics in a wide temperature range from 25 °C to 200 °C. The temperature dependent forward voltage of the conventional 8-finger SBD at a fixed current shows good linearity, resulting in a sensitivity of approximately 1.14 mV/K. On the other hand, the series SBD with two 8-finger diodes enhances the sensitivity by nearly two times. The enhancement in temperature sensitivity is interpreted using a series model, with the obtained parameters are comparable with the 8-finger SBD. [ABSTRACT FROM AUTHOR]

Highlights • Transparent NiO is adopted as the gate electrode for HFET fabrication by sputtering. • The NiO gated device presents good electrical and thermal stability. • The hole tapping is detected by conductance measurement due to the type-II staggered band configuration. Abstract In the present study, the reliability of transparent NiO gated AlGaN/GaN heterostructure field-effect transistors have been investigated. Compared with the TiN Schottky gated device, the p-NiO electrode can suppress the gate leakage and shift the threshold voltage positively. Pulse-mode and temperature-dependent current-voltage measurements demonstrate that both kinds of devices present good stability. The frequency-dependent conductance measurement confirms that only fast trap is detected for the TiN gated device while both fast and slow traps for the NiO gated one. The slow trap is ascribed to the hole trapping in the type-II staggered band configuration between NiO and AlGaN/GaN, which is also confirmed from the obvious threshold voltage instability in high frequency loop scan curves. [ABSTRACT FROM AUTHOR]

In this letter, AlGaN/GaN heterojunction metal–insulator-semiconductor field-effect transistors with gate-first process were developed for normally-off operation with p-GaN cap layers and SiNx dielectrics. To avoid the effect of the annealing process on the gate, a low-temperature ohmic contact technique was developed at an annealing temperature of about 500 °C for 20 min in N2 ambient. With the assistance of inductively coupled plasma dry etching, a contact resistance of $1.45~\Omega \cdot \textsf {mm}$ and sheet resistance of $1080.1~\Omega /\Box $ were obtained in the recessed region. Owing to the inset of the SiNx layer, the threshold voltage of the fabricated device was enhanced to approximately 2 V, and good pinch-off was observed with the gate voltage up to 16 V. Compared with the conventional high-temperature ohmic annealing process, the gate leakage current was suppressed significantly in both reverse and forward directions. Good device performance was confirmed with a maximum channel electron field-effect mobility of 1500 cm $^{\textsf {2}}\text{V}^{-\textsf {1}}\text{s}^{-\textsf {1}}$. [ABSTRACT FROM AUTHOR]

Abstract The characteristics of GaN Schottky barrier diodes fabricated with TiN and Ni anodes were evaluated in the temperature range from 25 to 175 °C. The Schottky barrier height (ideality factor) increases (decreases) with increasing temperature for both kinds of diodes owing to the barrier height being nonhomogeneous. The GaN diode with TiN anode presents better interface quality and thermal stability is adopted for temperature sensing application. It demonstrated that the sensitivity of the TiN diode is approximately 1 mV/K and varies only slightly for all current levels. Highlights • Thermal stable TiN is synthesized to alternate Ni metal for GaN SBD fabrication. • The GaN diode with TiN anode presents better interface quality and thermal stability. • The TiN SBD demonstrates excellent potential for temperature sensing application. [ABSTRACT FROM AUTHOR]

In this letter, partial recessed-gate AlAl2O3/AlGaN/GaN MISFET is experimentally demonstrated based on selective-area growth. The device features different contents of Al in the AlGaN barriers that were grown in the recessed and accessed regions that contributed to a higher $\text{V}_{\textsf {th}}$ and lower ON-resistance. As a result, it achieves a positive shift in ${V}_{\textsf {th}}$ as compared to the reference (from 1.8 to 2.5 V). Besides, this method accomplished the highest reported peak $\mu _{\textsf {FE}}$ value of 2033 cm2/ $\textsf {V}\cdot \textsf {s}$ and a lower gate channel sheet resistance of $519~\Omega /\Box $ (access region, ${R}_{\textsf {sh}} $ of $418~\Omega /\Box $) owing to reserving damage-free AlGaN/GaN hetero-structure in the recessed-gate. Notably, the formed device also exhibits a low hysteresis, low gate leakage, and a slight current collapse. [ABSTRACT FROM AUTHOR]

Combining the p-NiO gate electrode and the stack barrier structure with unintentionally doped GaN insertion layer (serves as etching termination layer) is promising for achieving normally-off GaN power device. The band alignment and band offsets at the interface of NiO and GaN insertion layer play a crucial role in determining the performance of GaN device. In this letter, the p-NiO thin film/unintentionally doped GaN heterojunction was fabricated through a simple thermal oxidation method. The p-NiO thin film presents face-centered cubic crystalline structure with a band gap of approximately 3.69 eV. The interfacial band alignment of the heterojunction is characterized by X-ray photoelectron spectroscopy. Based on core-level binding energies and valence band maximum values, the valence and the conduction band offsets were determined to be 1.16 eV and 1.45 eV, respectively. The NiO/GaN heterojunction is concluded to be type-II staggered band configuration. [ABSTRACT FROM AUTHOR]

In this study, titanium nitride (TiN) is synthesized using reactive sputtering for a self-aligned gate process. The Schottky barrier height of the TiN on n-GaN is around 0.5 to 0.6 eV and remains virtually constant with varying nitrogen ratios. As compared with the conventional Ni electrode, the TiN electrode presents a lower turn-on voltage, while its reverse leakage current is comparable with that of Ni. The results of annealing evaluation at different temperatures and duration times show that the TiN/W/Au gate stack can withstand the ohmic annealing process at 800°C for 1 or 3 min. Finally, the self-aligned TiN-gated AlGaN/GaN heterostructure field-effect transistors are obtained with good pinch-off characteristics. [ABSTRACT FROM AUTHOR]

GaN MOSFETs were developed on an AlGaN/GaN heterostructure in which the drain and source ohmic contacts were fabricated on the AlGaN/GaN heterostructure, and the electron channel was formed on the GaN buffer layer by removing the AlGaN barrier layer. For devices with different types and sizes, discrepant field-effect mobilities were observed and the origins of the discrepancy were analyzed. One reason causing the discrepancy is the discrepancy of gate dimension between the design and fabrication. In devices with only mesa as the device isolation, the real channel width would be larger than the mesa width because a parallel channel might have formed in the isolation region just outside the device mesa. Boron ion implantation was found to be effective to cutoff the current path in the isolation region. Another reason causing the discrepancy is that the real channel length would be larger than the designed one owing to the lithography and gate dry recess process. To extract the correct mobility and effective channel length of the GaN MOSFET fabricated on AlGaN/GaN heterostructure with variation in the channel dimensions, several methods were proposed and compared basing on ring-type MOSFETs. [ABSTRACT FROM PUBLISHER]

• Impact of recess GaN lattice damage on MOS interface and device behaviors is studied. • Quality of the regrown AlGaN/GaN heterostructure is evaluated. • ICP GaN MOS-FET suffers from degradating performances compared to SAG MOS-FET. • Higher D it is deduced in ICP MOS interface than SAG MOS interface. • Etching GaN shows rough/disorder morphology and increment of N-vacancy/Ga O bonds. We correlate electical behaviors of recessed-gate Al 2 O 3 /GaN MOS-FETs with the lattice damage at MOS interface region by directly comparing plasma-etching (inductively coupled plasma, ICP) and regrown (selective-area-growth, SAG) methods. Firstly the regrown AlGaN/GaN heterostructure are evaluated, showing high crystal quality and good 2 DEG transport properties and reaching the level of as-grown one. Then based on the as-grown and regrown heterostructures, ICP and SAG E-mode MOS-FETs were fabricated, respectively. ICP MOS-FET suffers from negative shift of V th , leaky gate current, large V th hysteresis and current dispersion, while SAG MOS-FET demonstrates stable and nondegradating device performances. Compared to SAG MOS interface, high interface-traps-density is deduced in ICP MOS interface which causes serious electron trapping effects. These traps are found to be related to the lattice damage of plasma-etching GaN accompanying a rough and disorder surface morphology and the increase of nitrogen-vacancy and Ga O bonds, responsible for the degenerated device behaviors. Step-flow surface morphology is preserved for SAG sample, which results in the high-quality MOS interface. The results reveal the impacts of lattice damage at MOS interface on GaN device behaviors and also provide a pathway to settle them down. [ABSTRACT FROM AUTHOR]

Abstract Nickel nitride (Ni x N) films were deposited by magnetron reactive sputtering under varying N 2 partial pressure (P(N 2)) conditions range from 0.005 to 0.184 Pa. With the increasing P(N 2), the deposition rate decreased while the resistivity and root mean square roughness increased. X-ray diffraction (XRD) and X-ray photoelectron spectra (XPS) indicate that Ni 4 N and Ni 3 N phases dominate the films at low and medium P(N 2), respectively. In addition, Ni 2 N phase can be also obtained at high P(N 2). The Ni/N ratio evaluated from the energy dispersive X-ray spectrum is consistent with the Ni x N phases showed in the XRD spectra of different P(N 2). Compared with the GaN diodes with Ni anode, the Schottky barrier height and turn-on voltage of the Schottky barrier diodes with Ni x N anode were increased by 0.03–0.18 eV and 0.03–0.15 V, respectively. Capacitance-voltage curves demonstrated that good interface quality with no obvious hysteresis was realized. Ni 3 N anode diodes obtained at medium P(N 2) possess a high barrier height and a low reverse leakage current are regarded as a promising anode material. Highlights • Ni x N films were deposited by sputtering under P(N 2) from 0.005 to 0.184 Pa. • Ni 4 N, Ni 3 N and Ni 2 N phases were observed and analyzed. • SBH of the Ni x N-GaN SBDs were 0.03–0.18 eV higher than Ni. • Ni 3 N was regarded as a promising anode material. [ABSTRACT FROM AUTHOR]

In this study, normally-off AlGaN/GaN heterostructure junction field-effect transistors (HJFETs) with p-GaN cap layer were reported, in which intrinsic GaN were proposed as blocking layers between the p-GaN cap layer and the AlGaN layer to alleviate the Mg diffusion. It demonstrates that the p-GaN gated devices present negative shift in the threshold voltage but larger output current density with the increasing thickness of the blocking layer. We found that a 20 nm blocking layer can efficiently block the Mg diffusion into the AlGaN/GaN heterostructure and a channel mobility of 1200 cm 2 V −1 s −1 was obtained. This value is comparable to the result obtained from a conventional AlGaN/GaN heterostructure, which means that the p-GaN cap shows no obvious degradation on channel mobility owing to the introduction of the blocking layer. The electrical performance of the recess region (without p-GaN cap) also confirm the channel degradation which can mainly ascribed to the Mg diffusion. [ABSTRACT FROM AUTHOR]

• A novel normally-off MIS-HEMT structure combining by p-GaN/AlGaN/GaN and SiN x insulator layer was fabricated. • Due to the MIS gate structure, devices demonstrate a higher V th , and the effect of insulator layer on V th was also investigated. • The gate leakage current is limited a relatively low level. And the breakdown voltages of the gate stacks with different SiN x thicknesses are evaluated. • The electron mobility of the 2DEG channel based on the C-V measurements is calculated which can confirm that the SiN x as gate insulator has few effects on channel mobility by varied thickness. In this study, a normally-off AlGaN/GaN metal–insulator-semiconductor high electron mobility transistors (MIS-HEMTs) with p-GaN layer were processed, which possess a high threshold voltage and a low gate leakage current due to metal–insulator-semiconductor (MIS) gate structure. A SiN x layer as the insulator layer was deposited between p-GaN layer and gate electrode. The dependent of device performance on SiN x thickness was investigated. Moreover, the threshold voltage of normally-off MIS-HEMT was emphatically discussed with different insulator layer thickness. It demonstrates that obviously positive shifting for threshold voltage from 1.5 to 6 V was achieved by increasing the SiN x thickness from 0 to 20 nm, while the channel mobility was comparable for all samples. Besides, the introduction of MIS gate structure is also beneficial for suppressing the gate leakage current and improving the maximum gate voltage swing owing to the high breakdown field of approximately 8.3 MV/cm. [ABSTRACT FROM AUTHOR]

In this study, a novel quasi-vertical GaN-on-sapphire MPS diode is fabricated by using the p-NiO/n-GaN heterojunction. The sputtered NiO covers the bottom and sidewall of trench region perfectly, presenting a hole concentration 2.2 × 1018 cm−3 and a mobility of 0.1 cm2/V•s. Compared with the Ni-anode SBD, the SBD and NiO/GaN heterojunction parts in the MPS diode turn on consecutively, resulting in a higher turn-on voltage of about 1.6 V (at the current of 1 A/cm2) and on-resistance of 3.5 mΩ·cm2. On the other hand, the depletion regions at the heterojunction interface suppress the electric field crowding and enhance the reverse breakdown voltage effectively. The TCAD simulation shows that the electric field modulation becomes weak slightly with the increasing p-NiO interval, resulting in the increasing electric field as well as the leakage current. Those results are beneficial to realize a high-performance GaN MPS diode for power electronic device applications. • A novel quasi-vertical GaN-on-sapphire MPS diode is fabricated by using the p-NiO/n-GaN heterojunction. • The SBD and NiO/GaN PND in the MPS turn on consecutively. • The depletion regions at the heterojunction suppress the electric field crowding effectively. • Those results are beneficial to realize a high-performance GaN MPS diode. [ABSTRACT FROM AUTHOR]

• A novel p-GaN/AlGaN/GaN HFET with re-grown AlGaN is designed by using Silvaco TCAD. • The thin AlGaN barrier beneath the p-GaN positively shifts the threshold voltage. • The regrown AlGaN barrier in the access regions can recover the 2DEG concentration. • The field plate structure is beneficial to suppress the electric filed crowding. In this paper, a novel p-GaN/AlGaN/GaN HFET with re-grown AlGaN is designed by using Silvaco TCAD. It demonstrates that a thin AlGaN barrier with relatively small Al content beneath the p-GaN positively shifts the threshold voltage and helps to obtain normally-off operation, while it also degrades the drain current obviously due to the low 2DEG concentration. On the other hand, the re-grown AlGaN barrier in the access regions can recover the 2DEG concentration and enhance the drain current partially. In addition, the field plate structure formed during the AlGaN re-growth process is beneficial to suppress the electric filed crowding and premature breakdown effectively under forward gate bias. By optimizing the device parameters, normally-off p-GaN/AlGaN/GaN HFET with balanced output current, threshold voltage and breakdown voltage is designed. [ABSTRACT FROM AUTHOR]

• GaN SBDs on a -plane, m -plane, and s5 -plane GaN bulk substrates are investigated. • The barrier inhomogeneities of the a -, m -, and s5 -plane Ni/GaN Schottky contacts are evaluated. • XPS spectra show discrepancy in the distribution of GaO x on the GaN with different planes. This work focuses on the electrical properties of Ni/n-GaN Schottky barrier diodes (SBDs) fabricated on GaN bulk substrates with different crystal orientations. For the SBDs on a -plane, m -plane, and s5 -plane GaN, the Schottky barrier heights (SBHs) exhibited magnitudes of 0.65 eV, 0.69 eV, and 0.75 eV, respectively. The relatively small SBH of a -plane devices results in a relatively larger reverse leakage current than that of m -plane and s5 -plane. In addition, the carrier concentrations extracted by C – V characteristics are comparable for the GaN substrates with different crystal orientations. The temperature-dependent I – V characteristics indicate how the barrier inhomogeneity of the Ni/GaN Schottky contacts on the a -plane GaN is smaller than the others. Based on the XPS spectra results, the discrepancy in Schottky contact characteristics stems from the different polarization charges and/or surface oxides of the different crystal planes. The low GaOx density on a -plane GaN surface contributes to the minimum barrier inhomogeneity of the corresponding SBD devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • AlGaN/GaN ISFET with high Al-content AlGaN barrier was fabricated to evaluate the sensing ability and surface reliability. • The AlGaN/GaN ISFET presents a sensitivity of approximately 55.5 mV/pH. • Threshold voltage shifting and output current decreasing are observed after worked in alkaline solution. • The degradation of electrical performances is attributed to the surface oxide as well as the followed dissolution in alkaline solution. As pH sensors, AlGaN/GaN ion-sensitive field-effect transistors (ISFETs) with stacked and high Al-content AlGaN barrier have been fabricated to evaluate the sensing ability and surface reliability. It demonstrates that the stacked barrier shows mild influence on the two-dimensional electron gas channel. In addition, the AlGaN/GaN ISFETs present good pinch-off characteristics in three kinds of solutions with different pH values, showing a sensitivity of approximately 55.5 mV/pH. However, threshold voltage shifting as well as the output current decreasing were observed after worked in alkaline solution. The surface analysis results confirm that the surface was electrochemical etched into many voids, resulting in a positive shift on the threshold voltage. This etching process is related to the surface oxide and dislocation on the high Al-content AlGaN barrier layer. Therefore, the degradation in electrical performances can be attributed to the transformation of AlGaN into surface oxide as well as the followed dissolution in alkaline solution. [ABSTRACT FROM AUTHOR]

In this work, a vertical GaN Schottky barrier diode with a bevel junction termination extension termination was designed by Silvaco TCAD. The effect of drift layer doping concentration, p-GaN doping concentration and bevel angle are evaluated extensively. With the optimum parameters, the bevel junction termination extension provides conduction path in the forward bias region to reduce the on-resistance and suppresses the electric field crowding in the reverse bias region. Furthermore, the Schottky contact characteristics are not affected in the relatively low bias region. The bevel junction termination extension is promising to achieve low turn-on voltage, low on-resistance and high breakdown voltage. • Bevel junction termination extension termination was designed for vertical GaN SBDs. • The bevel termination suppresses the electric field crowding under reverse bias. • The proposed structure is promising to achieve low turn-on voltage, low on-resistance and high breakdown voltage. [ABSTRACT FROM AUTHOR]

In this study, p-NiO deposited by magnetron reactive sputtering was adopted to fabricate NiO/GaN heterojunction and edge termination structure for vertical GaN Schottky barrier diodes. The contact properties of the NiO/GaN heterojunction were evaluated through a vertical pn diode. Turn-on voltage and specific on-resistance are approximately 2.27 V and 1.42 mΩ cm2, respectively. Temperature-dependent current-voltage and low-frequency noise measurements confirm that good interface and thermal stability of NiO/GaN heterojunction are obtained. The leakage current of the NiO pn diode is approximately four orders of magnitude lower than that of Schottky barrier diode, leading to an enhanced breakdown voltage. The p-NiO was selectively deposited as an edge termination structure to alleviate the electric field crowding of Schottky barrier diode, which is beneficial for enhancing the breakdown voltage. [ABSTRACT FROM AUTHOR]