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The application fields of infrared photodetectors are quite extensive. Compared with traditional infrared photodetection materials such as IV and III–V semiconductors, newly emerging low‐dimensional materials and quantum materials (e.g., 2D materials and quantum wells) have many advantages in different aspects, such as wide spectral range, low dark current, room temperature operation, and high processing compatibility. However, the performance of photodetectors based on low‐dimensional materials is limited by the ultra small thicknesses, polarization selectivity, and the poor absorption efficiency. Therefore, improving the performance of infrared photodetectors based on low‐dimensional materials has been a focus research task in recent years. The integration of photonic structures can improve the performance of infrared photodetectors, such as enhancing absorption efficiency, reducing the volume of active materials, and increasing polarization selectivity. Herein, different kinds of photonic structure integrated infrared photodetectors, roughly divided into two categories, namely, dielectric photonic structure integrated ones and metallic photonic structure integrated ones, are reviewed. The active materials include 2D materials, quantum wells, quantum dots, and carbon nanotubes.

In this work, H2O-Al2O3/O3-Al2O3 insulating bilayers were grown on GaN by atomic-layer deposition (ALD) technique using H2O vapor and O3 as oxidants. The electrical and material properties show that the H2O-Al2O3/O3-Al2O3 stack structure appeared to be an appropriate dielectric for GaN MOS devices that had low leakage current densities, high breakdown voltages, and good capacitance–voltage (C–V) curves. The H2O-Al2O3 interlayer between the O3-Al2O3 and GaN efficiently prevented the GaN surface from oxidizing by ozone oxidant by its strong oxidizing power. By taking photo-assisted C–V measurements, it was found that the deep interface state densities at the Al2O3/GaN interface reduced, while increasing the thicknesses of the H2O-Al2O3 interlayer restricted the “Vth shift” phenomenon and improved the stability and reliability of the GaN MOS devices.

We present an explicit numerical analysis on GaN-based multi-quantum-well planar Gunn diodes. The simulation demonstrates that Gunn oscillations generated in the multi-channel can be self-synchronized to each other, which significantly improves the output characteristics of planar Gunn diode due to the superposition of the dipole domain in each channel. The optimized output characteristics are obtained in the triple-channel Gunn diode, where the RF output power is about 6.45 mW and the DC-to-RF conversion efficiency is about 2.39% at the fundamental frequency of 216.05 GHz, more than three times larger than that of the single-channel AlGaN/GaN Gunn diode. The proposed GaN HEMT-like multi-channel planar Gunn diode with higher level of output characteristics shows great potential as a solid-state radiation source of millimeter-wave and sub-terahertz.

A five-stage monolithic Cockcroft-Walton voltage multiplier is reported which uses metal-insulator-metal capacitor and Schottky diode based on AlGaN/GaN heterostructure field-effect transistor (HFET) structure. The voltage multiplier includes 5 capacitors and 5 Schottky diodes. AlGaN/GaN HFET with L/W = 1 μm/10 μm is used as the Schottky diode, where the gate made of Ni/Au/Ti is used for the anode and the ohmic contact is used for the cathode. The size of the chip is 0.567 mm×0.445 mm. The breakdown voltage of the capacitor is around 40 V and the diode breakdown voltage in reverse direction is more than 100 V. At input AC peak to peak voltage of 20 V under frequency of 10 MHz, the measured output voltage is about 40 V with the output impedance less than 1 MΩ. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A highly sensitive UV phototransistor was developed using AlGaN/GaN heterojunction field effect transistor (HFET) technology. The phototransistor consisted of a thin undoped GaN layer added on top of a conventional AlGaN/GaN HFET structure. In such a structure, holes generated in the surface i-GaN layer are accumulated at the GaN/AlGaN interface, and they modulate the electrons in the FET channel. Due to this charge modulation effect, high photocurrent can be obtained. In the structure under study, hole life time was so long that a hole-evacuating refresh operation was required for fast response and linear sensitivity. When irradiated with UV light of 360 nm, a device with 6x10 -4 mm 2 active area produced two hundred times higher photocurrent than a commercial Si UV diode with a much larger area.

The thermal stability of copper (Cu)-gate AlGaN/GaN high electron mobility transistors (HEMTs) was investigated by annealing the devices at 300 °C and 500 °C for 1 h, and at 700 °C for 30 min, respectively. The current–voltage performance of the devices such as drain current, transconductance, threshold voltage and gate leakage current has no obvious degradation up to an annealing temperature of 500 °C and a time of 1 h. Up to 500 °C and 1 h annealing, no Cu diffusion was found at the Cu and AlGaN interface by secondary ion mass spectrometry determination. At an annealing temperature of 700 °C and a time of 30 min, the devices failed due to Cu diffusion into the 2DEG channel. These results indicate that the Schottky contact and the device performance of a Cu-gate AlGaN/GaN HEMT are stable up to an annealing temperature of at least 500 °C and a time of 1 h. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Design and fabrication of monolithic blue LED series arrays that can be operated under high ac voltage are described. Several LEDs, such as 3, 7, and 20, are connected in series and in parallel to meet ac operation. The chip size of a single device is 150 μm x 120 μm and the total size is 1.1 mm x 1 mm for a 40 (20 + 20) LED array. Deep dry etching was performed as device isolation. Two-layer interconnection and air bridge are utilized to connect the devices in an array. The monolithic series array exhibit the expected operation function under dc and ac bias. The output power and forward voltage are almost proportional to LED numbers connected in series. On-wafer measurement shows that the output power is 40 mW for 40 (20 + 20) LED array under ac 72 V.

Oxygen vacancy on semiconductor has been usually considered as donor contributor which can improve the charge transfer capacity of the photoanode. However, oxygen vacancy has also been found to perform as recombination center for the photogenerated charges. Herein, electrochemical reduction method is employed to treat the surface of Mo-doped BiVO4 (BiMoVO) photoanode. Experimental data indicate that when the reduction potential is located at −0.8 V (vs Ag/AgCl), quasioxygen vacancy is formed on the (020) facet (only BiO bonds crack), the electron mobility and photo-electrochemical (PEC) current density of the BiMoVO photoanode are increased dramatically. However, with the reduction potential increasing to −1.2 V, oxygen vacancy is formed on the surface of (020) facet (both BiO and VO bonds crack simultaneously), the PEC current density is decreased obviously. Further density functional theory calculation data point out that a moderate level of reduction is a key factor for the adjustment of photoanode performance. Thus, these results demonstrate first that oxygen vacancy actually is not the positive factor to improve the PEC performance of a BiVO4 photoelectrode, but the quasioxygen vacancy forming on the surface of the active facet is.

Monolayer WxMo1−xS2-based field effect transistors are demonstrated for the first time on the monolayer WxMo1−xS2 flake, which is grown by the chemical vapor deposition method under an atmospheric pressure. Detailed material studies using Raman and photoluminescence measurements have been carried out on the as-grown monolayer WxMo1−xS2. Electronic band structure of monolayer WxMo1−xS2 has been calculated using first-principle theory. The thermal stability of monolayer WxMo1−xS2 has been evaluated using Raman-temperature measurement. Carrier transport study on the fabricated WxMo1−xS2 FETs has been analyzed using temperature-dependent current measurement, and a field effect mobility of ≈30 cm2 V−1 s−1 at 300 K is obtained.