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AlGaN/GaN Schottky barrier diode (SBD) temperature sensor with low turn-on voltage was fabricated by employing the recessed anode structure. This AlGaN/GaN SBD demonstrates good rectification in a broad temperature scope from 298 to 473 K. Compared with common planar diode, the recessed anode SBD shows a relatively lower turn-on voltage and better Schottky contact characteristics. The temperature-dependent forward voltage at a fixed current displays great linearity, contributing to a sensitivity of about 1.0 mV/K. The calculated sensitivities exhibit the downtrend by increasing current level, which is in agreement with the thermionic emission (TE) model. The recessed anode AlGaN/GaN SBDs show good potential in temperature sensor application.

High-performance AlGaN/GaN lateral Schottky barrier diodes (SBDs) with recess structure and dual metal nitride anodes were demonstrated. With high work-function and nonrecess structure, a NiN anode enhances the breakdown voltage (BV), while a TiN anode reduces the turn-on voltage ( ${V}_{ \mathrm{\scriptscriptstyle ON}}$ ) due to its low work-function and contact to the two-dimensional electron gas (2DEG) layer directly on a recess structure. As the length of the NiN anode ( ${L}_{r}$ ) on the nonrecess region decreases from 75 to 3 $\mu \text{m}$ , ${V}_{ \mathrm{\scriptscriptstyle ON}}$ is reduced from 0.56 to 0.30 V, while the reverse leakage current slightly increases from ${3} \times {10}^{-{4}}$ to ${2} \times {10}^{-{3}}$ A/cm2 at the bias of −10 V. The lateral AlGaN/GaN SBD with a ${L}_{r}$ of 3 $\mu \text{m}$ at a distance of cathode–anode ( ${L}_{\text {AC}}$ ) of 20 $\mu \text{m}$ achieves a high BV of 1.62 kV, an ultralow ${V}_{ \mathrm{\scriptscriptstyle ON}}$ of 0.30 V and a small capacitance of 6.0 pF at zero bias with little degradation on ON-resistance, indicating superior potential application in high-frequency and high-power devices.

AlGaN/gallium nitride (GaN) ion-sensitive field-effect transistors (ISFETs) were fabricated as pH sensors. The sensitivity of the AlGaN/GaN ISFETs was evolved with gate recess process and ammonium hydroxide (NH4OH) treatment. By performing the gate recess process, the threshold voltage ( ${V}_{\text {T}}$ ) of the ISFET increased from −3.33 to −0.31 V and the maximum conductance ( ${G}_{\text {M}}$ ) of the ISFET increased from 0.8 to 2 mS, with the current sensitivity of the pH sensor improving from 52.25 to $78.86~\mu \text{A}$ /pH. Further, after performing the ammonium hydroxide treatment, the ${V}_{\text {T}}$ of the ISFET increased from −0.33 to −0.14 V, with the current sensitivity of the pH sensor improving from 78.86 to $84.39~\mu \text{A}$ /pH. To characterize the surface conditions the X-ray photoelectron spectroscopy (XPS) was deployed. The results indicated that many nitrogen vacancies ( ${V}_{\text {N}}$ ) were introduced during the recess process, leading to a negative ${V}_{\text {T}}$ shift and a smaller potential sensitivity ( ${S}_{V}$ ), which can be improved by ammonium hydroxide treatment.

This article presents a terahertz integrated cavity bandpass filter based on cyclic etched silicon carbon (SiC) via-holes. Solutions are discussed in detail, including design, fabrication, and optimization. The fabrication procedures of the integrated filters are specially optimized, which are fully compatible with that of the common terahertz monolithic integrated circuit. The cyclic via-hole etching technique based on inductively coupled plasma (ICP) is proposed, which achieves via-holes with a controllable inclination on SiC substrate. Measurements show that the insertion loss of the cavity integrated filter is only 1.55 dB at 185 GHz, with a relative bandwidth of 9.7%. Two transmission zeros are introduced by the over-moded technique, achieving the out-of-band suppression of the filter higher than 40 dB. Compared with the traditional terahertz cavity filters, the integrated cavity on SiC substrate provides similar electric performances and better integration but with the one-thousandth of the volume.

This article presents a finger-type gallium nitride (GaN) Schottky barrier diode (SBD)-based microwave rectifier with medium-power capacity and wide power bandwidth. A complete solution including SBD design and fabrication, model extraction, circuit optimization, and demonstration is proposed. The finger-type anode and critical thickness epitaxial layer techniques are adopted to reduce the GaN SBD resistance to 1.9 $\Omega $ (0.011 $\text{m}\sf \Omega \cdot \text {cm}^{{2}}$ ) and achieve nearly constant junction capacitance over a wide range of voltages (17–25 V). Revised equivalent models including the effects of large pads, critical thickness epitaxial layer, and finger-type layout are proposed to describe the new features of the SBD. A 2.45-GHz microwave rectifier based on the GaN SBD is designed and measured, having a maximum power and an efficiency of 1.91 W and 78.5%, respectively. The high-efficiency power range (≥70% and ≥75%) is significantly extended to 14 and 10.8 dB. Finally, a wireless clinical examination prototype constructed by a rectifier, antennas, biomedical sensors, and a signal processer is proposed for demonstration. The resulting wireless electrocardiogram shown in computer is clear and stable.

TiN/GaN Schottky barrier diodes with different anode diameters are fabricated to investigate the temperature sensing mechanism. All the circular diodes present good stability over a temperature range of 25 °C–200 °C. In the fully turn-on region, the sensitivity increases with the increasing diameter. Furthermore, the highest sensitivity of 1.22 mV/K is obtained for a 300- $\mu \text{m}$ -diameter device at current of 20 mA, taking into account the series resistance. In the subthreshold region, the forward current ( ${I}_{D}$ ) density determines the sensor sensitivity, in which a larger current density corresponds to a lower sensitivity. In addition, the strong dependence of the leakage current on the temperature indicates that the linearity of ln ( ${I}_{r}$ ) versus temperature can be also used for sensor applications.

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.

We fabricated AlGaN/GaN heterostructure field effect transistors (HFETs) with p-GaN substrate layers and p-type ohmic contacts (p-sub HFETs) and measured the substrate-bias (VSUB) -dependent threshold voltage VT variation. From this VT-VSUB characteristic, the acceptor concentration in the buffer layer was determined. This method for doping profile measurement has been widely used for Si MOSFETs. By applying this method to AlGaN/GaN HFETs stressed by negative substrate bias or UV light irradiation, buffer layer deep traps were specifically investigated. The deep traps in the buffer layer were determined to be hole traps with a concentration of 0.5-1 × 1016 cm-3. The energy level was estimated to be approximately 0.71-0.95 eV above the valence band.