Papers by Keyword: Gallium Nitride

Abstract: Lateral GaN devices, with a substantial critical breakdown field and increased mobility of two-dimensional electron gas (2DEG), are particularly promising for future power applications. Despite low power consumption by design, further improvements are required in numerous areas, including reliability concerns and switching loss, usually contributing to significant power loss. The research objective concerns the impact of different notch structures on the transfer characteristics of GaN-based high-electron-mobility transistor (HEMT) devices. Thirteen simulated models were produced using COMSOL Multiphysics, incorporating the electrical, structural, and piezoelectric effects of the device. From the results, notch-structure devices demonstrated better electrical characteristics than devices using conventional architecture, particularly a model with a double-notch design. Higher transconductance and maximum drain current were among the improvements, benefiting from the notch structure at the barrier layer.

Abstract: Synchrotron X-ray topography techniques are used to characterize the microstructures in gallium nitride materials being developed for selective area doping for power electronic applications. Bulk substrates grown by different methods, epitaxial layers that are subject to ion implantation, annealing, etching and regrowth are characterized by X-ray topography in grazing incidence geometry and X-ray rocking curve topography. Strain and tilt maps of ion implanted epitaxial layers and etched and regrown wafers are generated. From the X-ray topographs, it is concluded that ammonothermal grown substrates show the highest quality among other types and most suitable for high-end electronic applications. It is also revealed that epitaxial growth, ion implantation and the annealing process do not change the dislocation distribution, but ion implantation introduces damage, strain and lattice bending effect, which are removed after annealing. Inductively coupled plasma (ICP) etching gives rise to strain variations in the wafer, while using tertiary butyl chloride (TBCl) to etch the wafer does not affect the strain distribution and can remove some damage from a preceding ICP etching process.

Abstract: In this paper, a color-tunable light emitting diode LED with two laterally arranged single quantum wells (SQWs) is designed, and simulated. In this work, III-nitride materials are used. The structure has been numerically investigated using the ATLAS simulation software. The proposed structure has three electrodes. This gives the opportunity to emit violet (420 nm) or green (560 nm) light individually. Furthermore, it can emit simultaneously a mixture of both colors, and at a certain mixture ratio the white light is obtained with chromaticity coordinates ( x = 0.3113, y = 0.3973). The lateral arrangement of the two SQWs reduces the negative effect of photon absorption; which will give good external quantum efficiency (EQE). The structure has a big importance in the application of the solid-state lighting, especially in the white light generation.

Abstract: Advanced power electronic application normally requires high-speed semiconductor switches in a compact design that are capable to transform electrical energy between the sources and the loads with high efficiency. In electronics, inefficiency is a waste that also translated into unnecessarily high costs and limits the device performance. As the number of connected devices increases in modern applications, more efficient power conversion is necessary especially for advanced power electronic systems. Therefore, in this research, on-chip thermal management is designed to improve the power conversion efficiency of Gallium Nitride (GaN) High Electron Mobility Transistor (HEMT). Since the inefficiency in the electronic component is always referred to as losses in the form of heat, proper thermal management is needed to improve the device performance. As nanotechnology promise to be the foundation of the next industrial revolution, the research towards nanoenhanced semiconductor devices has aroused widespread attention from researchers, scientists and engineers. In this research, two-dimensional nanomaterials (2DNMs) are used as heat spreaders to reduce the localized hot spot temperature in GaN HEMT for higher device efficiency. The fabrication process flow, process issues, process characterization, material characterization and thermal performance of the nanomaterial heat spreader are the main topics to be discussed in this paper. Based on the experiment the monolayer graphene can improve the thermal resistance by at least 0.5 K/W. This may help to improve the GaN HEMT device efficiency especially when the device is operated under high power density.

Abstract: GaN based electronic devices have gained great success in the arena of high-frequency and high-power applications. A high-quality GaN MOS structure has the potential to enable new device designs and higher device performance, thereby bringing the success of GaN electronics to a new level. This paper discusses results of the work on GaN MOS structures show that with adequate surface preparation samples featuring interface trap density down to the ~ 10¹⁰ eV^-1cm^-2 range can be formed.

Abstract: Gallium nitride (GaN) and its AlGaN/GaN heterostructures grown on large area Si substrates are promising systems to fabricate power devices inside the existing Si CMOS lines. For this purpose, however, Au-free metallizations are required to avoid cross contaminations. In this paper, the mechanisms of current transport in Au-free metallization on AlGaN/GaN heterostructures are studied, with a focus on non-recessed Ti/Al/Ti Ohmic contacts. In particular, an Ohmic behavior of Ti/Al/Ti stacks was observed after an annealing at moderate temperature (600°C). The values of the specific contact resistance ρ_c decreased from 1.6×10⁴ Ω^.cm² to 7×10⁵ Ω^.cm² with increasing the annealing time from 60 to 180s. The temperature dependence of ρ_c indicated that the current flow is ruled by a thermionic field emission (TFE) mechanism, with barrier height values of 0.58 eV and 0.52 eV, respectively. Finally, preliminary results on the forward and reverse bias characterization of Au-free tungsten carbide (WC) Schottky contacts are presented. This contact exhibited a barrier height value of 0.82 eV.

Abstract: The paper presents the route of manufacturing transistors on gallium nitride. As a result of the work done, prototypes of transistor crystals with a gate length and width of 0.5 μm and 0.8 mm, respectively. The basic static characteristics are presented.

Abstract: As a promising third generation semiconductor material, gallium nitride (GaN) has become a research hotspot in optoelectronic field nowadays. In this paper, GaN thin films were grown by radio frequency (RF) planar magnetron sputtering of a powder GaN target in a pure nitrogen atmosphere at (0.2 – 2.0) Pa, (10 - 100) W onto various substrates such as GaAs (100), Si (100), Si (111), Al₂O₃(0001) and glass without any buffer layer. A clear phase transition from the metastable cubic zinc-blende (c - ZB) to the stable hexagonal wurtzite (h - WZ) dependence on substrates has been found in the GaN thin films. And the phase transition of GaN films were studied by X-ray diffraction (XRD), photoluminescence (PL) and Raman spectroscopy.

Abstract: High temperatures and other harsh environments are domains of predilection for Junction FETs, particularly when wide band-gap semiconductors such as SiC or GaN are used. The present work describes the new compact model of double gate (DG) JFETs which is compared to TCAD simulations of SiC and GaN JFETs over a wide temperature range up to 500oC. The compact model is shown to be predictive of device behavior, for static (current-voltage) as well as dynamic (capacitance-voltage) behavior of long-channel DG JFETs.

Abstract: In this study, TiN anode GaN Schottky barrier diodes (SBDs) with a low access sheet resistance of 28 Ω/□ were fabricated for microwave power transmission application. The performance of the diodes at room temperature (RT) is comparable with the ideality factor n and Schottky barrier height (SBH) were 1.28 and 0.47 eV for the 8-finger SBDs, 1.22 and 0.49 eV for the 16-finger SBDs, respectively. A low on-resistance of 5.71 and 3.58 Ω were obtained for 8-and 16-finger SBD at RT, respectively. The low series resistance induced by larger anode area of 16-finger SBDs results in a lower turn-on voltage of 0.47 V compared with that of 0.68 V for the 8-finger one. Besides, the temperature dependent current-voltage characteristics demonstrate that the TiN anode has a good temperature stability. And the temperature dependent performance of the 16-finger SBDs present a better uniformity than that of the 8-finger SBDs.