Barrier height enhancement of Ni/GaN Schottky diode using Ru based passivation scheme
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Wet chemical passivation of n-GaN surface using Ru based solution has been reported. X-ray photoelectron spectroscopy characterization of the GaN surface revealed removal of surface oxides by the introduction of Ru complex species. Ni/n-GaN Schottky barrier diodes were fabricated on passivated GaN and a remarkable improvement in Schottky barrier height from 0.76 eV to 0.92 eV was observed.Keywords:
Passivation
Wide-bandgap semiconductor
The Junction Barrier Schottky (JBS) diode has the advantage of a low forward voltage drop comparable to that of Schottky diodes, as well as a high blocking voltage and low reverse leakage current of a pn diode. This device, originally demonstrated in silicon technology, is especially attractive for wide bandgap materials such as silicon carbide (SiC) in which pn diodes have a large forward voltage drop. Two different JBS designs in 6H SiC have been fabricated, and the electrical characteristics have been compared to Schottky and pn diodes on the same wafer. Although the ion implanted pn diodes had remaining implant damage, the JBS diodes worked well. The JBS diodes were capable of blocking up to 1100 V with a leakage current density of 0.15 A/cm/sup 2/, limited by the leakage when the drift region was fully depleted, or breakdown of the SiC material itself. The forward conduction was limited by an on-resistance of 20 m/spl Omega/ cm/sup 2/.
Reverse leakage current
Metal–semiconductor junction
Wide-bandgap semiconductor
Leakage (economics)
p–n junction
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In recent years, there has been a growing interest in the use of GaAs as a material for high voltage power Schottky diodes. Such devices have been shown to have much lower reverse recovery charge than Si junction diodes and thus to have many potential applications in high-speed switching circuits. However, most Schottky diodes suffer from reverse leakage currents significantly greater than predicted by simple consideration of the Schottky Barrier Height (SBH)-largely as a result of surface leakage. Such problems can be controlled in silicon devices, for which surface passivation methods utilising field oxide and/or electron irradiation are available. By comparison, surface passivation techniques for GaAs devices are relatively undeveloped, although attempts have been made using sulphur and/or selenium coating solutions for low power devices. In this work, we have applied such techniques to power Schottky diodes with the aim of engineering the metal/semiconductor interface to control the forward and reverse characteristics of the device.
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Reverse leakage current
Leakage (economics)
Metal–semiconductor junction
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High-voltage gallium nitride Schottky barrier diodes (SBDs) suffer from large off-state leakage current, which further degrades during operation at high temperatures and limits the device blocking capabilities. The key to achieving low off-state leakage is to protect the Schottky barrier from the high electric field, which is challenging by employing conventional field plate structures due to their large pinch-off voltage. In this work, we propose a simple AlGaN/GaN SBD architecture based on a p-GaN cap layer to achieve excellent off-state performance with a very low leakage current. By properly designing the AlGaN barrier and p-GaN cap, the pinch off-voltage of the p-GaN field plate is carefully controlled and the voltage drop over the Schottky junction is effectively reduced. In addition, a large carrier concentration in the access region is achieved, leading to a reduced sheet resistance. This results in good on-state performance along with a very low leakage current of ∼1 nA/mm at 400 V, which is maintained well below 100 nA/mm up to elevated temperatures of 150 °C. Moreover, the proposed architecture shares the well-established fabrication process of commercial p-GaN HEMTs and, thus, represents a promising and viable solution for future GaN diodes.
Leakage (economics)
Wide-bandgap semiconductor
Reverse leakage current
Saturation current
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Gallium nitride is a highly promising wide band gap semiconductor with applications in high power electronic and optoelectronic devices. Among the devices considered for high power generation is the ubiquitous field-effect transistors which require Schottky barriers for modulating the channel mobile charge. It is in this context that we have undertaken an investigation of likely metal-GaN contacts. Here we report on the electrical conduction and other properties of Pt–GaN Schottky diodes. These Schottky diodes were fabricated using n-GaN grown by the molecular beam epitaxy method. Both capacitance–voltage and current–voltage measurements have been carried out as a function of temperature to gain insight into the processes involved in current conduction. Based on these measurements, physical mechanisms responsible for electrical conduction at low and high voltages and temperatures have been suggested. Schottky barrier height determined from the current–voltage and capacitance–voltage measurements is close to 1.10 eV.
Wide-bandgap semiconductor
Metal–semiconductor junction
Schottky effect
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We designed experiments to investigate the role of dislocation density on the performance of Schottky diodes fabricated on a GaN material grown conventionally and by pendeo-epitaxy. Devices of varying geometries were fabricated on low defect density GaN regions grown selectively via pendeo-epitaxy. In addition, corresponding devices were fabricated on the conventional GaN material with a high density of dislocations. Schottky diodes fabricated on pendeo-material showed nearly two orders of magnitude lower leakage current and displayed improved ideality factor, while diodes built on a conventional material displayed nonideal characteristics.
Wide-bandgap semiconductor
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Wide bandgap semiconductors are an obvious choice for high voltage applications due to their large critical electric field. While both SiC and GaN will support large electric fields, approximately 10x that of the dominant power semiconductor Si, the wide availability of SiC substrates up to 150 mm diameter provides a cost effective platform over GaN for which even 50 mm substrates are in high demand. Besides substrate technology, high growth rate epitaxy, ion implantation and anneal technologies are well established for SiC. The typical insertion path begins with majority carrier devices such as Schottky diodes which are robust and relatively simple to manufacture. Junction barrier Schottky diodes have been shown to be stable at 10kV [1] and are commercially available up to 1.7 kV. The obvious application for JBS diodes is as a substitute for Si PiN diode freewheeling diodes. The key advantage is the transition from the minority carrier Si bipolar device to the majority carrier unipolar SiC device. This transition to the SiC Schottky virtually eliminates the reverse recovery effects typical of Si PiN diodes. Further, the adoption of the junction barrier Schottky structure results in low reverse leakage current and stable blocking voltages. In this work medium voltage, 4.5 kV SiC JBS diodes matched to commercially available 4.5 kV IGBTs are joined to form efficient hybrid modules. Dynamic and static characteristics as well as reliability phenomena are evaluated. Compared to the all-Si module, the hybrid module shows up to a factor of six reduced turn-on loss as is demonstrated in Fig. 1 where 4.5 kV Si PiN diode compared to a SiC JBS diode. The recovery current is shown on the left and the impact on the IGBT turn-on characteristics is shown on the right. Through simulations and hardware testing the modules have been optimized for the IGBT/JBS die are ratio in terms of total power dissipation. Other considerations include surge capability which is limited by the JBS diode and the reverse blocking voltage of the IGBT. An external circuit that clamps the voltage across the diode is developed and demonstrated greatly increasing the surge rating. Reliability considerations such as high temperature dV/dt and HTRB are assessed and will be presented. Overall, the hybrid modules are extremely efficient and robust. Total power losses are reduced by one-half by replacing only the freewheeling Si PiN diode with a SiC JBS diode. The optimized solution reduces the needed SiC die area and thus module costs. Reliability assessments show that the modules are robust. References:[1] Brett A. Hull, Joseph J. Sumakeris, Michael J. O’Loughlin, Qingchun Zhang, Jim Richmond, Adrian R. Powell, Eugene A. Imhoff, Karl D. Hobart, Angel Rivera-López, and Allen R. Heffner, “Performance and Stability of Large-Area 4H- SiC 10-kV Junction Barrier Schottky Rectifiers”, IEEE Transactions on Electron Devices, vol. 55, no. 8, pp.1864-1870 (2008). Figure 1
Wide-bandgap semiconductor
Reverse leakage current
Flyback diode
PIN diode
Leakage (economics)
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The I-V characteristics and S-parameters of AlGaN/GaN on silicon Schottky diodes are investigated. A compact circuit model is constructed for RF application. Simulated results are compared with measured results using AlGaN/GaN on Silicon diodes as RF switches. The simulated and measured results illustrated good agreement within a wide frequency range. The output power from the switch is also measured by sweeping the input power. No suppression is observed when the highest input power equals to 14 dBm at 10 GHz for small device, which proved that the AlGaN/GaN on Silicon devices offer good potential for RF power applications.
Wide-bandgap semiconductor
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SiC Schottky barrier diodes (SBD) are commercially available in the 600 V breakdown voltage range and 1.2 kV SiC SBDs have been announced. In this paper we compare the behavior of recently fabricated high-current 1.2 kV SBD with that of equivalent Si diodes, underlining the high temperature working operation capability (up to 200/spl deg/C), Lower reverse leakage current is obtained using Ni instead of Ti (the most spread solution) for the Schottky contact. The temperature dependence of forward characteristics, reverse leakage current and switching recovery performances have been analyzed.
Reverse leakage current
Metal–semiconductor junction
Wide-bandgap semiconductor
Leakage (economics)
Reverse bias
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Metal–semiconductor junction
Wide-bandgap semiconductor
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The switching characteristics of vertical Gallium Nitride (v-GaN) diodes grown on GaN substrates are reported. v-GaN diodes were tested in a Double-Pulse Test Circuit (DPTC) and compared to test results for SiC Schottky Barrier Diodes (SBDs) and Si PiN diodes. The reported switching characteristics show that GaN diodes, like SiC SBDs, exhibit nearly negligible reverse recovery current compared to traditional Si PiN diodes. The reverse recovery for the v-GaN PiN diodes is limited by parasitics in the DPTC, precluding extraction of a meaningful recovery time. These results are very encouraging for power electronics based on v-GaN and demonstrate the potential for very fast, low-loss switching for these devices.
Parasitic extraction
Wide-bandgap semiconductor
Characterization
PIN diode
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