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Recess structure is one of the main schemes for insulated-gate E-mode GaN transistors. In this work, selective area growth (SAG) is proposed to fabricate damage-free recess-gate device, and related progresses regarding process optimization and structure evolution have been reviewed. Firstly, the SAG process has been optimized by interface separation (conduction interface and regrowth interface) and n-type Si impurity removal to achieve high-quality AlGaN/GaN heterostructure. Compared to the traditional etching method, the feasibility and superiority of SAG scheme are demonstrated for realizing E-mode Al2O3/GaN MISFET with small Vth hysteresis. Then, by inserting an in situ AlN interlayer, the SAG Al2O3/AlN/GaN MISFET yields improved frequency dispersion and gate channel conduction performances. To further enhance the channel conduction, the SAG partially recess-gate Al2O3/AlGaN/GaN MIS-HFET structure is proposed, by which both high Vth and high-field-effect channel mobility have been achieved. Those results indicate that SAG method gives a perspective way for insulated-recess-gate GaN transistors fabrication. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A nonvolatile memory (NVM) based on an amorphous-indium–gallium–zinc oxide (a-IGZO) thin-film transistor (TFT) with defect-engineered gate insulator was demonstrated. The gate insulator was a blocking alumina/storage alumina/tunneling alumina stack structure, which was simply assembled in a single atomic layer deposition step. The memory device showed a positive shift of threshold voltage as large as 14.4 V after +20 V, 1 s programming. In contrast, the memory erasing was not sensitive to negative gate voltage in the dark. Once programmed, the memory can only be light erased. Furthermore, the light combined with a negative bias improved the erasing speed effectively. In addition, a 10-year memory window as large as 7.5 V was extrapolated at room temperature with a charge loss of 34.7%. Based on the observation of blisters in the storage alumina layer after high temperature annealing, Fourier transform infrared spectroscopy measurement and first-principles calculations, the high electron storage capacity can be attributed to the deep defect levels in the storage alumina layer, which were originated from hydrogen impurity. This a-IGZO TFT charge trapping NVM with high performance and simple process is a candidate device for the application of fully functional transparent system on panel. [ABSTRACT FROM AUTHOR]

In this work, the leakage current properties of semi-insulating GaN (SI-GaN) grown on Si(1 1 1) substrate with a low-temperature (LT) AlN interlayer were studied. Two terminal lateral current–voltage measurements revealed an early conduction phenomenon via buffer layers with an LT-AlN interlayer, in which both p- and n-type conduction phenomena were observed from Hall-effect measurement during temperature changing. It is suggested that the p-type conduction existed in the Si substrate due to the diffusion of Al atoms into the Si substrate during the epitaxial growth. The origin of n-type conduction was two-dimensional electron gas (2DEG) in the LT-AlN/GaN interface, which acted as a conduction channel in SI-GaN. Furthermore, the vertical leakage current measurement and the space charge limited current model were used to analyse the impact of the 2DEG conduction channel on the leakage current properties. It is revealed that leakage current properties are very sensitive to the thickness of the GaN layer above the LT-AlN interlayer (Top-GaN). Increasing the thickness of Top-GaN becomes an effective way to suppress leakage current. Therefore, both strain engineering and leakage current properties are essential factors to be considered in the selection of strain compensation interlayer in the growth of SI-GaN on Si substrate for power switching applications. [ABSTRACT FROM AUTHOR]

In this letter, a normally-off GaN recessed-gate MOSFET is demonstrated using a nonplasma gate recess technique, in which the access region with AlGaN/GaN heterostructure was selectively grown on a semi-insulating GaN/Si template to naturally form a recessed gate. The normally-off recessed-gate Al2O3/GaN MOSFET presents a high threshold voltage of 3.5 V and a maximum drain current density of 550 mA/mm (at a positive gate bias of 12 V). A maximum field-effect mobility of 170 cm2 V−1 s−1 and a large on/off current ratio of more than 107 was obtained, which indicates the high quality of the Al2O3/GaN interface. [ABSTRACT FROM AUTHOR]

Graphitic carbon nitride (g-CN), a promising visible-light-responsive semiconductor material, is regarded as a fascinating photocatalyst and heterogeneous catalyst for various reactions due to its non-toxicity, high thermal durability and chemical durability, and "earth-abundant" nature. However, practical applications of g-CN in photoelectrochemical (PEC) and photoelectronic devices are still in the early stages of development due to the difficulties in fabricating high-quality g-CN layers on substrates, wide band gaps, high charge-recombination rates, and low electronic conductivity. Various fabrication and modification strategies of g-CN-based films have been reported. This review summarizes the latest progress related to the growth and modification of high-quality g-CN-based films. Furthermore, (1) the classification of synthetic pathways for the preparation of g-CN films, (2) functionalization of g-CN films at an atomic level (elemental doping) and molecular level (copolymerization), (3) modification of g-CN films with a co-catalyst, and (4) composite films fabricating, will be discussed in detail. Last but not least, this review will conclude with a summary and some invigorating viewpoints on the key challenges and future developments.