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We present a systematic investigation on growth parameters (the ratio of reactive gases and total flow rate) of silicon nitride (StNx) films by Low-Pressure Chemical Vapor Deposition (LPCVD). The post-growth annealing condition would influence the bonds and electrical properties of the SiN x. When the concentration of SiH 2 Cl2 and NH3 is 20sccm/250sccm and with post-growth annealing in O 2 at 650°C, the electrical performance of SiN x film is the best, which is evaluated by capacitance-voltage, dielectric breakdown and reliability test. Increasing the total flow rate of gas source can improve the reliability of device.

Electric field crowding at the Schottky edge and Schottky barrier lowering induced leakage current are two major problems that limit the performance of GaN-on-GaN vertical SBD. In this paper, we try to solve these issues. On one hand, a planar edge termination method based on high-energy fluorine ion implantation is explored for high voltage vertical GaN SBD. The space charge induced field modulation effect (SCIFM) is discovered in the ion implanted region. The electrons injected in the implanted region could effectively reduce the surface electric field, alleviating the field crowding at the metal edge. The SBD terminated with high-energy fluorine implanted region presents a breakdown voltage of 1300 V. Utilizing the depletion effect of space charges, the leaky path through the implanted region is partially blocked by the high-energy fluorine ion implanted guard rings. The reverse leakage current of SBD with guard rings is reduced by nearly 3 orders at the reverse bias of 300 V without the deterioration of forward characteristics. On the other hand, the fluorine ion implantation based quasi-JBS structure is investigated to shield the electric field seen by the Schottky contact and reduce the Schottky barrier lowering induced leakage current. The turn-on voltage modulation effect and improved breakdown voltage are observed in the fabricated quasi-JBS diodes, confirming the validity of the SCIFM mechanism in the ion implanted region.

In this letter, based on a new growth strategy, we demonstrate a high-performance quasi-vertical GaN Schottky barrier diode (SBD) fabricated on the hetero-epitaxial layer on silicon, with the highest current on/off ratio of 1010, the lowest specific on-resistance of 0.95 mΩ·cm2, and the lowest ideality factor of 1.23 among the GaN quasi-vertical GaN SBD reported until now. It reveals the great potential of the GaN vertical structure device on Si thanks to the novel growth strategy, which is capable of realizing low density of threading dislocation and thick epitaxial layer at the same time.

Robust gate dielectric and dielectric/semiconductor are highly desired for GaN power MOS devices, while the trapping effect of the border traps close to the MOS interface could lead to reliability issues in those devices. In this paper, a complete model for border traps in lateral GaN MOS diode is proposed based on a distributed network of the border traps and channel resistance. We show that excluding the effect of channel resistance is critical for accurate calculating the distribution of border traps in lateral devices with low channel mobility, such as GaN and SiC MOS devices. The proposed model agrees well with the measured frequency dependent capacitance and conductance curves of Al 2 O 3 /GaN MOS diode in a gate recessed normally-off GaN power MOSFET. The new insight derived from the impedance dispersion characteristics of lateral MOS devices is critical for quantitative analysis of the quality of III-V lateral MOS structures.

The radiation dose dependent sensitivity characteristics of bilateral silicon sensors are studied to improve the radiation hardness under neutron irradiation. Sensors with different effective intrinsic base lengths using 1.5mm ultra-thick silicon substrate are fabricated and the effect of structure parameters on neutron detection sensitivity is experimentally investigated. The simulations of devices with different structures are used to study the influence of potential distribution on radiation hardness characteristics. It is found that, increasing the effective intrinsic base length can improve the sensitivity. The effect of radiation does and working current are investigated experimentally.

A new planar MISHEMT structure is proposed with the drain surrounded (D-S) by the gate channel. The gate channel serves as the stop-ring of the drain voltage, eliminating the damages from the high voltage on the mesa edge and isolation area. As a result, the leakage of the D-S MISHEMT is found to be reduced by almost 3 orders comparing with the source surrounded (S-S) MISHEMT. A saturated output current density of 740 mA/mm and an ON-resistance of 13.09 Ω-mm are obtained for device with LG/LGS/LGD/WC = 1.5/5/20/250 μm. Meanwhile, the degradation of dynamic ON-resistance and off-state breakdown performance are investigated in both D-S and S-S MISHEMT, which indicates excellent reliability of the D-S MISHEMT.

This work reports a kilovolt and low current collapse normally-off GaN MOSHEMT on silicon substrate. The device with a drift length of 3 μm features a threshold voltage of 1.7 V and an output current of 430 mA/mm at 8 V gate bias. The off-state breakdown voltage (BV) is as high as 1021 V (800 V) defined at a drain leakage criterion of 10 μA/mm with floating (grounded) substrate. The corresponding breakdown electric field is 3.4 MV/cm and the Baliga's figure-of-merit (BFOM) is 1.6 GW/cm2. A small degradation of the dynamic on-resistance (R on, d ) about 30% is observed with a short pulse width of 500 ns and a quiescent drain bias of 60 V. The record value is supposed to benefit from the intrinsic step-graded field plate, high quality LPCVD SI3N4 passivation and material optimization of 4.5 μm thick epitaxial layer.

A large lattice-mismatch induced stress control technology with a low Al content AlGaN layer has been used to grow high quality GaN layers on Si substrates. The use of this technology allows for high mobility AlGaN/GaN heterostructures with electron mobility of 2240 cm2/Vs. It is demonstrated that the large lattice mismatch between the low Al content AlGaN layer and AlN buffer layer could effectively promote the edge dislocation inclination with relatively large bend angles and therefore significantly reduce the dislocation density in the GaN epilayer.

The paper proposes a design scheme of integrated supervisory control system which is suitable for both 110kV dry-type transformer and intelligent substation. Some special problems such as how to measure temperature in the high voltage winding is discussed in the paper. Fiber grating sensor is used in the system because of its strong anti-interference ability and ac curacy for temperature. The installation method, quantity and trace of fiber are also discussed. The grounded current of core and working current could be monitored through the high precision current transformer. The supervisory and control intelligent electronic device (IED) is used the modular design method based on high-performance ARM processor in order to improve the hardware and software efficiency. It receives the value of winding and core temperature, ambient temperature, grounded current, and analyzes the status of transformer. According to the data the IED could control the cooling fan to reduce the temperature. The IED also can deliver the data to substation control layer using IEC 61850. The comprehensive application server could display the panoramic data such as monitoring and warning data of transformer.

This paper reports a normally-off high voltage hybrid Al 2 O 3 /GaN gate-recessed MOSFET fabricated on silicon substrate. The normally off operation was implemented by digital gate recess using an oxidation and wet etching based AlGaN barrier remove technique. The Al 2 O 3 /GaN MOSFET features a true normally off operation with a threshold voltage of 2 V extracted by the linear extrapolation of the transfer curve. The three terminal off-state breakdown voltage is 1650 V for the device with 30 μm gate-drain distance with floating Si substrate. The breakdown voltage is limited to 1000 V when the Si substrate is grounded. The on-resistance is 7.0 mΩ·cm 2 for the device with 30 μm gate-drain distance and the power figure of merit is 388 MW/cm 2 . The small signal RF performance of the normally-off GaN MOSFET is also evaluated.

In this work, the performance of GaN-based MOS-Channel-HEMTs (MOSC-HEMTs) are shown to be greatly improved by a thin ALD-grown AlN interfacial layer inserted between the amorphous Al 2 O 3 gate dielectric and GaN-channel. The single-crystalline AlN interfacial layer effectively blocks oxygen from the GaN surface and avoids the formation of detrimental Ga-O bonds. Frequency-dispersion in C-V characteristics has been effectively suppressed. The maximum drain current and field-effect mobility are boosted from 410 mA/mm and 98 cm 2 /V·s in a conventional Al 2 O 3 /GaN MOSC-HEMT to 660 mA/mm and 165 cm 2 /V·s in an Al 2 O 3 /AlN/GaN MOSC-HEMT, owing to improved interface quality. The devices also deliver a high ON/OFF current ratio of ~10 10 , and significantly reduced dynamic on-resistance degradation.

In this letter, we have demonstrated that the circular transmission linear model (Marlow's CTLM) is unsuitable for GaN HEMTs structure alloyed ohmic contact resistance evaluation. Very large spread is found in the extracted ohmic resistance values from measured data using the commonly used CTLM test patterns, and some of the contact resistances are found to be negative. We suspect that the stress induced by ohmic contact formation process is the culprit, preventing the use of CTLM test pattern for GaN HEMTs structure ohmic contact resistance evaluation, because of the strong piezoelectric induced polarization property of the hexagonal III-nitride heteroj unction device structure. Meanwhile, measured ohmic contact resistance (Rc) and sheet resistance (Rsq) are found to exhibit good uniformity using a properly prepared linear transmission line model (LTLM) test pattern in which all the Gallium nitride material extended beyond the gaps between the ohmic contact electrodes are removed.

We provide an overview on the underlying physical mechanisms associated with the fluorine plasma ion implantation technology that provides a robust approach to fabricating GaN normally-off transistors. The discussion is based on atomistic modeling and a series of experimental studies including thermal diffusion, positron annihilation spectroscopy, photoconductivity and electroluminescence.

Owing to superior physical properties such as high electron saturation velocity and high electric breakdown field, GaN-based high electron mobility transistors (HEMTs) are capable of delivering superior performance in microwave amplifiers, high power switches, and high temperature integrated circuits (ICs). Compared to the conventional D-mode HEMTs with negative threshold voltages, enhancement-mode (E-mode) or normally-off HEMTs are desirable in these applications, for reduced circuit design complexity and fail-safe operation. Fluorine plasma treatment has been used to fabricate E-mode HEMTs [1], and is a robust process for the channel threshold voltage modulation. However, there is no standard equipment for this process and various groups have reported a wide range of process parameters [1–4]. In this work, we demonstrate the self-aligned enhancement-mode AlGaN/GaN HEMTs fabricated with a standard fluorine ion implantation. Ion implantation is widely used in semiconductor industry with well-controlled dose and precise implantation profile.

A hybrid molecular dynamics (MD)/kinetic Monte Carlo (KMC) model is developed for atomistic modeling of fluorine ion implantation and diffusion in AlGaN/GaN heterostructures. The MD simulation reveals the F distribution profiles and the corresponding defect profiles, and most importantly, the potential energies of fluorine ions in the III-nitride material system. Using the results from the MD simulation, the diffusion process is simulated with KMC method, and the modeling results are validated by the secondary-ion-mass-spectrum (SIMS) measurement. The surface effect on the fluorine's stability and its improvement by passivation are also successfully modeled.

The mechanisms of AlGaN/GaN HEMT's off-state breakdown are investigated. Both the source- and gate-injection induced impact ionizations are identified with the former leading to premature three-terminal breakdown. A 35% improvement of the breakdown voltage could be achieved in an enhanced back barrier HEMT by implanting fluorine ions under the channel region and effectively block the source injection through the buffer layer.

Fluorine plasma ion implantation is a robust technique that enables shallow implantation of fluorine ions into group III-nitride epitaxial structures. This technique has been used to achieve robust threshold control of the AlGaN/GaN high electron mobility transistors (HEMTs) and led to the realization of self-aligned enhancement-mode devices. To reveal the atomic scale interactions and provide a modeling tool for process design and optimization, a molecular dynamics (MD) simulation is conducted for carbon tetrafluoride (CF4) plasma implantation. Specific potential functions are applied to calculate the interactions among atoms and simulate the dynamics process of fluorine ions? penetration and stopping in III-nitride materials. The MD simulation provides accurate information on dopant profiles that are verified by secondary ion mass spectrum (SIMS) measurements. Defect formation and distributions, that are critical in process development, are also investigated. The MD simulation tool is capable of providing 2-dimensional fluorine dopant profiles.

A novel micro controller-based dimmable electronic ballast for HPS lamps is presented in this paper. Power control method is based on the regulation of the average input current of the inverter by varying the switching frequency of the half bridge. Driver signal with low frequency modulation generated from MCU is used to eliminate unstable arc during dimming state. Theoretical analysis is discussed and experimental results based on a 600W HPS lamp show the feasibility of the proposed ballast.