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In this letter, we fabricated Schottky barrier diodes (SBDs) using n-type zinc gallium oxide (n-ZnGa2O4) single-crystal substrates, which were grown from the melt by the vertical gradient freeze (VGF) method. X-ray diffraction rocking curve and Laue diffraction results indicate the good crystal quality. The electrical properties of SBDs fabricated on substrates with two doping concentrations are systematically investigated. Heavily-doped (HD) SBDs exhibit lower differential specific on-resistance (~1.13 $\text{m}\Omega \cdot $ cm2) and lower turn-on voltage (~0.16 V) while the lightly-doped (LD) SBDs exhibit better ideality factor (1.17), rectification characteristics (on/off ratio ~1011) and lower reverse leakage. In addition, we separately tested the electrical properties of the two devices at different temperatures (298 K-473 K). The results of varying temperature show that LD-SBDs have better temperature stability in smaller variation of ideality factor and barrier height with temperature. Based on these experimental results, this work demonstrates the great promise of ZnGa2O4 materials to fabricate high-performance power devices. [ABSTRACT FROM AUTHOR]

Selective area doping technique is essential for diversifying semiconductor device structures. In this letter, selective high-resistance zones on $\beta $ -Ga2O3 wafers were successfully achieved by a high-temperature oxygen annealing process. Polysilicon, which proved to have an ideal blocking capability against oxygen annealing ambient, was employed as an annealing cap layer to prevent local carrier concentration changes during annealing. Based on this unique process approach, we further demonstrate a high-resistance anode edge termination of Schottky barrier diodes, which can considerably reduce the leakage current and increase the breakdown voltage of the devices. This research broadens the device manufacturing method and promotes the development of Ga2O3 devices. [ABSTRACT FROM AUTHOR]

A $\beta $ -Ga2O3 MOSFET is fabricated and its threshold voltage $({V}_{\mathrm{TH}})$ instability mechanisms are experimentally investigated under different gate-biased voltages and ambient temperatures. Under the condition of the positive bias stress (PBS) of ${V}_{\mathrm{GS}} = 4$ V for 1000 s at room temperature, the ${V}_{\mathrm{TH}}$ positive shift of 0.61 V is mainly caused by the electrons trapped by border traps in Al2O3. Combining the hysteresis with temperature-dependent performance analysis, the clockwise to anticlockwise hysteresis inversion at 125 °C is discovered in $\beta $ -Ga2O3 MOSFET for the first time, which is probably caused by the activation of deep-level acceptor-type interface states. The deep-level acceptor-type interface states with a fitting activation energy of 114 meV are found, and they also affect the ${V}_{\mathrm{TH}}$ instability at high temperature. With the stress of ${V}_{\mathrm{GS}} =4$ V at 125 °C for 1000 s, ${V}_{\mathrm{TH}}$ is increased by 0.9 V. Analyzing electrical parameters, such as ${V}_{\mathrm{TH}}$ , subthreshold slope (SS), and hysteresis width, can distinguish the quantitative contributions of interface states and border traps to ${V}_{\mathrm{TH}}$ instability under electrical stress and thermal stress (TS). This work reveals an important indication for investigating the ${V}_{\mathrm{TH}}$ instability of $\beta $ -Ga2O3 MOSFET in high-power applications. [ABSTRACT FROM AUTHOR]

In this work, we comprehensively studied the correlation between the electrical characteristics and the gate width (${W}_{G}$) of GaN-based HEMTs. On the one hand, as ${W}_{G}$ is scaled down from 100 $\mu \text{m}$ down to $3~\mu \text{m}$ , the devices exhibit five-times-enhanced on-state drain current density and largely reduced on-resistance, thanks to the increased electron mobility and mitigated self-heating effects in the narrow- ${W}_{G}$ channels. On the other hand, the devices with a wider ${W}_{G}$ exhibit reduced off-state leakage current and enhanced breakdown voltage, thanks to a decreased electric field and increased Schottky barrier height. Further temperature-dependent characterization reveals that the ${W}_{G}$ -modulation behavior on both on- and off-state device properties is still effective at a high temperature of 150°C. These experimental results can provide a straightforward approach for effective channel modulation and device optimization of GaN-based power devices of the future. [ABSTRACT FROM AUTHOR]

This work demonstrates vertical $\boldsymbol {\beta } $ -Ga2O3 Schottky barrier diodes (SBDs) breaking through the power figure of merit of 1 GW/cm2 without edge termination. The unreliable surface on the top of $\sim {1.2}\times {10} ^{{16}}$ cm−3 drift region, which naturally formed in air, was removed by inductively coupled plasma etching. The repaired surface was exposed to ambient air for less than 10 minutes during the entire preparation process. Compared with the excessive air exposure samples, the leakage current was well suppressed for the Ni/ $\boldsymbol {\beta } $ -Ga2O3 SBDs fabricated on a clean surface. Moreover, the blocking voltage reaches a maximum value of 1720 V, and the forward/reverse characteristics of the diodes on the same wafer show good uniformity. These results pave the way for further improving the performance of $\boldsymbol {\beta }$ -Ga2O3 devices and verify the potential of $\boldsymbol {\beta }$ -Ga2O3 SBDs for power applications. [ABSTRACT FROM AUTHOR]

The Ga2O3 solar-blind photodetectors (SBPDs) face the tradeoff between power consumption ($P_{\text {C}}$) and photoresponse performance. Here, an ultrasensitive two-terminal photodetector based on $\boldsymbol {\beta }$ -Ga2O3 microflake with extremely-low working voltage and ${P}_{\text {C}}$ was achieved. At a working voltage of 2 V and ${P}_{\text {C}}$ of 10 fW, the Ga2O3 SBPD exhibits superexcellent photodetection performance, including a responsivity (${R}$) of ${2.3}\,\,\times \,\,{10}^{{5}}\text{A}$ /W, a detectivity (${D}^{ \boldsymbol {\ast }}$) of ${3.5}\,\,\times \,\,{10}^{{18}}$ Jones, a photo-to-dark-current ratio (PDCR) of ${3.2}\,\,\times \,\,{10}^{{8}}$ , and an ultra-low dark current (${I}_{\text {dark}}$) of 5 fA. Strikingly, the device keeps satisfactory performance at ultralow working voltage of 0.01 V, including a ${P}_{\text {C}}$ of 0.05 fW, a ${R}$ of ${2.4}\,\,\times \,\,{10}^{{3}}$ A/W, a ${D}^{ \boldsymbol {\ast }}$ of ${5.6}\,\,\times \,\,{10}^{{16}}$ Jones, and a PDCR of ${3.4}\,\,\times \,\,{10}^{{6}}$. The superior solar-blind sensitivity makes it the most excellent Ga2O3 detector towards high-performance and low- $P_{\text {C}}$ SBPD applications. [ABSTRACT FROM AUTHOR]

In this article, for the first time, a variation of lateral doping (VLD) technique was proposed to improve blocking voltage and ON-resistance properties in the lateral β-Ga2O3 metal–oxide–semiconductor field-effect transistor (MOSFET). Enhancement-mode operation was achieved in the VLD transistor. The maximum transconductance of this new device is more than three times as large as the uniformly doped (UD) transistor. Moreover, the OFF-state electric field at the channel was suppressed compared to the UD transistor, resulting in higher blocking voltage. We also investigated the optimal device properties with changing channel concentration in the drift region of VLD transistor. A power figure of merit of 332.7 MW/cm2 was reached by VLD design. Thus, this proposed structure provides a new design strategy for high-power β-Ga2O3 MOSFETs. [ABSTRACT FROM AUTHOR]

This work reports a $\beta $ -Ga2O3 double-barrier Schottky barrier diode (DBSBD) with both low turn-on voltage and low reverse leakage current by using Ni and PtOx as the anode electrode. The barrier height of PtOx-based diode can be effectively modulated from 1.26 to 1.62 eV by adjusting oxygen pressure during sputtering processes. Combining the maximum work function of PtOx electrode with the optimization of the electrode ratio of Ni and PtOx, the DBSBD with an electrode diameter ratio of $\text{D}_{\text {Ni}} /\text{D}_{\text {PtOx}}= {75}/{150} \mu \text{m}$ not only exhibits a high forward current of 470.9 A/cm2 (at 3.5 V), a low on-resistance of 4.1 $\text{m}\Omega ~\cdot $ cm2 and a low turn-on voltage of 1.13 V, but also possesses a relatively low reverse leakage current of ${1.2}\times {10}^{-{7}}$ A/cm2 (at −100 V), which is more than one order of magnitude lower than that of the Ni-SBD. Silvaco TCAD simulation reveals that such optimization can be attributed to the suppression of edge leakage current due to the double-barrier contact. Therefore, the strategy of double-barrier design can balance the forward and reverse characteristics in SBD, providing a new device structure for advanced power electronics. [ABSTRACT FROM AUTHOR]

This letter reports a high-performance solar-blind phototransistor based on N2-annealed $\beta $ -Ga2O3 microflake for weak light detection. The phototransistor exhibits an ultra-low dark current of 27 fA, a high external quantum efficiency of $8.36\times 10^{7}$ %, a photo-to-dark-current ratio of $1.08\times 10 ^{7}$ , a low power consumption of 2.92 pW, and a narrow-band response with a cut off wavelength of 263 nm. In addition, the spectral selectivity can be well modulated by the gate bias and reaches a maximum ${R} _{240}/{R} _{400}$ ratio of $2.4\times 10 ^{4}$. Especially, an ultra-high responsivity (${R}$) of $1.71\times 10^{5}$ A/W and a record-high detectivity (${D} ^{\ast }$) of $1.19\times 10^{18}$ Jones have been achieved under 254nm illumination of $4.1~\mu \text{W}$ /cm2. The superior weak-light-detection performance of the device makes it one of the best Ga2O3 detectors towards solar-blind photodetection application. [ABSTRACT FROM AUTHOR]

In this article, we performed gated four-probe measurements on amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) to extract their intrinsic mobility and contact resistance as functions of gate voltage and temperature. The abnormal degradation of field-effect mobility was observed in a-IGZO TFTs both at high gate voltage and at high temperature. Results showed that contact resistance played a major role in mobility degradation at high gate bias, whereas band-like transport (phonon scattering) accounts for mobility degeneration at high temperature. We proposed a novel method, which exposed the contact regions to ultraviolet (UV) ozone. The mobility was boosted from 23 to 30 cm2/Vs, nearly 40% increment at high gate bias. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a tunable Schottky diode based on amorphous indium–gallium–zinc–oxide (a-IGZO) film with high performance for rectifying circuit and bipolar one diode-one resistor (1D1R) crossbar applications. By modulating the oxygen content in the a-IGZO film, the device shows adjustable behavior. Under the high oxygen content condition, the device displays outstanding diode features with a large rectification ratio up to 108 at ±1 V and a high forward current density of 100 A/cm2 at ±1 V when used Cu as the top electrode. The thermionic emission model is proposed to explain the Schottky diode behavior. And by utilizing the superior rectifying performance, we successfully demonstrate the dynamic rectifying application. In addition, we combine the optimized Schottky diode device with the bipolar-type resistive random access memory (RRAM) device to investigate the Schottky diode device in 1D1R crossbar application. As a result of its tunable nature and low processing temperature, the a-IGZO Schottky diode is a promising element for rectifying circuit and bipolar 1D1R crossbar applications. [ABSTRACT FROM AUTHOR]

For the first time, in this letter, the anomalous positive bias stress instability of the back gated monolayer polycrystal molybdenum disulfide (MoS2) field-effect transistors with high-hydrogen-concentration SiO2 gate dielectrics is reported. It is found that the threshold voltage shifts exhibit a pronounced turnaround behavior from a positive shift to a negative shift when enlarging the stress voltage and stress time. We relate this anomalous positive bias instability to two physical processes, charge trapping and hydrogen release and migration. [ABSTRACT FROM AUTHOR]

In this paper, a surface potential-based gate-leakage current (GLC) model for organic thin-film transistors is proposed. It is found that the Poole–Frenkel emission is the main mechanism of GLC, which can be well described by our model for both accumulation and depletion modes. In addition, the source and drain partitions of the channel leakage current can be well explained based on our model. Furthermore, the dependence of GLC on drain voltage, temperature, and material disorder has been discussed in detail, which yields perfect agreement with the experimental data. [ABSTRACT FROM PUBLISHER]

An improved cut-off frequency model of a modified equivalent circuit of graphene field-effect transistors, which incorporates the additional capacitive effect physically present due to dipole layer between the metal and the graphene, is proposed. The original equivalent circuit is not accurate for a large separation distance dipole layer. Based on the improved equivalent circuit model, a more accurate parameter extraction by two-port analysis is possible, and the cut-off frequency will be more accurate particularly for largely separated dipole layer near the Dirac point. Considering the dipole layer, the equivalent circuit is never investigated before, and the cut-off frequency model shows good agreement with experiments. [ABSTRACT FROM AUTHOR]

Nucleosomes are basic elements of chromatin structure. The positioning of nucleosomes along a genome is very important to dictate eukaryotic DNA compaction and access. Current computational methods have focused on the analysis of nucleosome occupancy and the positioning of well-positioned nucleosomes. However, fuzzy nucleosomes require more complex configurations and are more difficult to predict their positions. We analyzed the positioning of well-positioned and fuzzy nucleosomes from a novel structural perspective, and proposed WaveNuc, a computational approach for inferring their positions based on continuous wavelet transformation. The comparative analysis demonstrates that these two kinds of nucleosomes exhibit different propeller twist structural characteristics. Well-positioned nucleosomes tend to locate at sharp peaks of the propeller twist profile, whereas fuzzy nucleosomes correspond to broader peaks. The sharpness of these peaks shows that the propeller twist profile may contain nucleosome positioning information. Exploiting this knowledge, we applied WaveNuc to detect the two different kinds of peaks of the propeller twist profile along the genome. We compared the performance of our method with existing methods on real data sets. The results show that the proposed method can accurately resolve complex configurations of fuzzy nucleosomes, which leads to better performance of nucleosome positioning prediction on the whole genome. [ABSTRACT FROM PUBLISHER]