We demonstrated the operation of GaN-on-Si metal–oxide–semiconductor field effect transistors (MOSFETs) for power electronics components. The interface states at SiO2/GaN were successfully improved by annealing at 800°C for 30min in N2 ambient. The interface state density was less than 1×1011cm–2eV−1 at Ec−0.4eV. The n+ contact layers as the source and drain regions as well as the reduced surface field (RESURF) zone were formed using a Si ion implantation technique with the activation annealing at 1200°C for 10s in rapid thermal annealing (RTA). As a result, we achieved an over 1000V and 30mA operation on GaN-on-Si MOSFETs. The threshold voltage was +2.6V. It was found that the breakdown voltage depended upon the RESURF length and nitride based epi-layer thickness. In addition, we discussed the comparison of each performance of GaN-on-Si with -sapphire devices.

In this paper, GaN-based HFET devices on 4-inch Si substrates were fabricated, and the device characteristics were examined. As a result, the maximum drain current was estimated to be over 115 A using MIS-structures. A trade-off between the specific on-resistance (RonA) and the breakdown voltage (Vb) was improved using carbon doped buffer layers, resulting in obtaining RonA=3D 5.9 mΩcm2 and Vb=3D 1730 V simultaneously with the gate-width of a 340 mm. Furthermore, the gate field-plate structure was introduced into MIS-HFET structures. We have examined the suppression of a current collapse phenomenon owing to the combination of the gate field-plate structure and a conductive Si substrate with MIS-HFET devices.

In this paper, we successfully demonstrate an AlGaN/GaN HFET with a high breakdown voltage on 4-inch Si substrates. In order to obtain the high breakdown voltage and to improve the crystalline quality of GaN layers, a thick GaN epitaxial layer including a buffer layer was grown. The breakdown voltage and the maximum drain current were achieved to be over 1.3 kV and 120 A, respectively. Furthermore, the suppression of a current collapse phenomenon was examined. The on-resistance was not significantly increased up to a high drain off-bias-stress of 900 V. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

A normally off AlGaN/GaN Hetero-junction Field Effect Transistor (HFET) structure is proposed. Two dimensional electron gas (2DEG) of more than 1x10(13) cm(-2), which a AlGaN/GaN HFET generally has, can be compensated completely by the negative charge in a floating gate or in a SiO2 layer on the AlGaN. Computer simulation showed that the threshold voltage was shifted from -3 V to -15 V with 20 nm SiO2 layer between the control gate and the AlGaN layer, but it was also shifted to +5V with 5x10(13) cm(-2) electrons (negative charge) in the middle of the SiO2 layer (a floating gate) or minus ions in the SiO2 layer itself. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

In this paper, GaN-based MIS-HFET devices on 4-inch Si substrates were fabricated, and the device characteristics were examined. As a result, the breakdown voltage was improved to be over 2.45 kV using high-resistive carbon doped buffer layers with a larger thickness of over 7.3 mum. The maximum drain current was estimated to be over 115 A using MIS-structures. A trade-off between the specific on-resistance (RonA) and the breakdown voltage (Vb) was improved using carbon doped buffer layers, resulting in obtaining RonA = 5.9 mOmegacm2 and Vb = 1730 V simultaneously with the gate-width of a 340 mm. Furthermore, the field-plate structure was introduced into MIS-HFET structures. We have examined the suppression of a current collapse phenomenon owing to the combination of the gate field-plate structure and a conductive Si substrate with MIS-HFET devices.

We report on the 288 V-10 V DC- DC converter circuit using AlGaN/GaN HFETs for the first time. The AlGaN/GaN HFET with a large current and a high breakdown voltage operation was fabricated. That is, the maximum drain current was over 50 A, and the minimum on-resistance was 70 mohm. The breakdown voltage was over 600 V. A DC-DC down-converter from input DC 288 V to output DC 10 V was fabricated using these HFETs. It was confirmed that the switching speed of the AlGaN/GaN HFET was faster than that of Si MOSFET. The DC-DC down-converter was fabricated using these HFETs. This converter was composed of a full bridge circuit using four n-channel AlGaN/GaN HFETs. In the case of AlGaN/GaN HFET, a gate switching wave (Vgs) and source-drain wave (Vds) were abrupt compared with those of using Si MOSFETs. In both cases, a stable and constant output DC 10V was also obtained and the conversion efficiency of the converters with AlGaN/GaN HFETs was 84%.

In this paper, we successfully demonstrate an AlGaN HFET with a high breakdown voltage of over 1.8 kV on 4 inch Si substrates. In order to obtain the high breakdown voltage and to improve the crystalline quality of GaN layers, a thick GaN epitaxial layer including a buffer layer with a total thickness of over 6 mum was grown. The breakdown voltage and the maximum drain current were achieved to be over 1.8 kV and 120 A, respectively. Furthermore, the suppression of the current collapse phenomenon is examined. The on-resistance is not so significantly increased up to the high drain off-bias-stress of 1.0 kV.

We have studied the activation of Si ion implanted un- and Mg-doped gallium nitride (GaN) for the fabrication of reduced surface field (RESURF) metal-oxide-semiconductor field-effect transistors (MOSFETs). By annealing at 1260 degrees C for 30s by using rapid thermal annealing (RTA), the activation ratios of un- and Mg-doped GaN with Si doses of 3 x 10(15) cm(-2) were similar to 100 and 73%, respectively, These values are sufficient for application some semiconductor devices. Hardly any diffusion of the Si atoms implanted in GaN was observed by secondary ion mass spectrometry (SIMS). The activation ratio between un- and Mg-doped GaN was markedly different at low doses. The cause of the difference appears to be Mg compensation in GaN. In addition, we fabricated GaN MOSFETs with ion implanted RESURF zones. We also monitored the field-effect transitor (FET) operation and high breakdown voltage of the GaN MOSFETs. The threshold voltage was +2 V. An enhancement mode operation and a breakdown voltage higher 1500 V at a RESURF length of 20 mu m were achieved.

AlGaN/GaN HFETs with a large current and a high breakdown voltage were fabricated. We examined the switching characteristics and capacitance parameters such as an input capacitance (C-iss), a reverse transfer capacitance (C-rss), a gate to a source charge (Q(gs)) and a gate to a drain charge (Q(gd)), using the GaN HFET devices. An order to confirm the advantage for the high-frequency switching operation of the GaN HFETs compared with Si devices, capacitance parameters and the figure of merit (FOM) Vb/(Ron) for a switching capability were examined. As a result, a law Ciss, Crss, and Qg were obtained and the FOMs of GaN HFETs have one order of magnitude larger than those of Si power devices.

tion as an alternative to Si as a semiconductor material for ultra-low-loss power devices. Early development of GaN was carried out in the area of light-emitting devices—green LEDs, lasers, etc.—but its superior performance as noted above and the needs of society led to R&D work for electronic devices being conducted world-wide. Specifically, the AlGaN/GaN HFET structure permits the formation of a high-density electron layer known as a two-dimensional electron layer on an AlGaN/GaN hetero interface by adding impurities to the carrier supply layer of AlGaN. Thus this AlGaN/GaN HFET structure holds out the possibility of achieving a high-frequency output device surpassing the characteristics of existing devices. Furukawa Electric has been involved in this development from the earliest stages, and has reported the world's first prototype inverter circuit using an AlGaN/GaN HFET. This inverter is made up of a DC converter using an AlGaN/GaN HFET and an AC inverter. Its operating output power was 50 W and maximum output power was 200 W 7). More recently a device with an output power in excess of 200 W has been reported 8), and its application as a high-output power device is anticipated. In this paper we describe the results of investigations in an AlGaN/GaN HFET, of, first of all, a Ti/AlSi/Mo structure for a unique ohmic electrode having reduced on-state resistance. We also describe how this ohmic electrode evolved into a larger device (gate width: 200 mm) and mounted in a package designed for operation in a hightemperature environment, and its characteristics at 500 K

We developed new ohmic electrodes combined with an Al-silicide and a molybdenum for AlGaN/GaN HFETs to realize a high power switching application. As a result, the maximum drain current of the HFET was over 55 A and the breakdown voltage was about 800 V. The specific on-state resistance of the HFET was smaller than that of a Si Cool MOSFET. Furthermore, we examined the dynamic characteristics. The turn-off and turn-on delay time were 14.8 nsec. and 8.4 nsec. at the condition of 100 V, respectively. These values were considerbly smaller compared with those of Si Cool MOSFETs. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

In this paper, we report the development of a high breakdown voltage InGaP/GaAs HBT process for low-to-mid power and high-voltage power amplifier operation. To achieve the high-breakdown InGaP HBT, two different collector designs and collector-etch processes were investigated. The first device process approach uses a thick GaAs collector with low n doping. The process challenges and considerations of this long collector approach are briefly discussed. An alternative approach uses wide band gap InGaP material as part of the collector design. High breakdown voltage can be obtained from both material design approaches. However, to fully leverage the existing process modules of our high volume HBT production line and allow the re-use of our current HBT design rules and libraries, our high voltage HBT (HV-HBT) development efforts focus on HBTs with InGaP in the collector (either composite collector, CCHBT, or double heterojunctions, DHBTs). Using a slightly modified process, InGaP DHBT devices have been demonstrated with BVceo and BVcbo values of 40 V and 56 V, respectively. A cut off frequency, ft, of 40 GHz has also been obtained at a current density of Jc=0.3 mA/μm by using this process. Preliminary circuit level performance results are also presented and discussed.

We investigated an AlGaN/GaN heterostructure field effect transistor (HFET) on Si substrates using a multi-wafer metalorganic vapor phase epitaxy (MOVPE) system. It was confirmed that a GaN film with smooth surface and without any crack was obtained. To increase a resistance of a GaN buffer layer, the carbon (C) -doping was carried out by controlling the V/III ratio and the growth pressure. The breakdown voltage of the buffer layer was dramatically improved by introducing the C. As a result, the breakdown voltage was about 900 V when the C concentration was about ∼8×10 18 cm −3 . After while, an AlGaN/GaN heterojunction FET (HFET) on a C-doped GaN buffer layer was fabricated. We achieved the breakdown voltage of over 1000 V and the maximum drain current of over 150 mA/mm, respectively. It was found that the C doped buffer layer is very effective for improving the breakdown voltage of AlGaN/GaN HFETs.

It is reported that we demonstrated a large current operation AlGaN/GaN HFET with a low-on state resistance and a high breakdown voltage operation at room temperature and 500 K. We developed our unique ohmic electrode using Ti/AlSi/Mo. In addition, we investigated the dependence between the distance from the gate electrode to the drain electrode and the off-state breakdown voltage. As a result, the breakdown voltage of a unit HFET was over 1100 V. Furthermore, on the large scale HFET with the gate width of 240 mm, the maximum drain current of over 50 A was obtained at room temperature and also, that of over 25 A was obtained at 500 K. The off-state breakdown voltage was obtained about 800 V at room temperature and about 600 V at 500 K, although Si-based FETs can not operate in such a high temperature.

In order to obtain a high quality thick GaN layer on a 2‐inch Si substrate without any crack, we investigated three kinds of buffer layer (AlGaN graded structure, AlN/GaN super lattice (SL) structure, and AlN/thick GaN/AlN structure) using a metal‐organic chemical vapor deposition (MOCVD). As a result, we obtained a crack‐free AlGaN/GaN hetero‐structure with a smooth surface using three kinds of buffer structure. We also observed the cross‐sectional TEM image of three kinds of buffer structures. In the case of using an AlGaN graded buffer on the AlN buffer, the number of surface defect with the size of 10000 nm was comparatively larger compared with the other buffer structures. In the case of using an AlN (18 nm)/GaN (5 nm) super‐lattice (SL) buffer, a 1000 nm‐thick GaN was grown without crack. In the case of using three AlN (50 nm)/two thick GaN (200 nm) buffer structure, the threading dislocation using this buffer was 1.5 × 109 cm–2 and the value was smaller compared with the other buffer structures. This reduction effect of dislocation was larger than the other buffer structures. We also fabricated a HFET using the AlGaN/GaN heterostructure using three AlN/two thick GaN buffer. It was confirmed that the breakdown voltage of FET was over 400 V. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

GaN electron devices are expected to contribute significantly toward efficiency improvement and downsizing of power supplies since the devices have the potential of realizing higher breakdown voltages and lower on-state resistances in comparison to Si electron devices conventionally used. The authors have investigated, by thinning the AlGaN layer and simultaneously inserting an AlN layer, GaN/AlGaN heterojunction Field Effect Transistor (HFET) structures aimed at realization of normally-off type devices that are high in breakdown voltage yet comparatively low in on-state resistance characteristics. And, using AlGaN/GaN heterostructure epitaxial layers on a Si substrate-- one of the prerequisites for cost reduction, normally-off operation with a threshold voltage of 0 V has been achieved. A proprietary diode structure has also been proposed to enable loss reduction, and operation with a low on-state voltage has been confirmed where a current begins to flow at approximately 0 V. Moreover, an epitaxial AlGaN structure with a reduced thickness has been applied to this structure, and a diode featuring low leakage current as well as low on-state voltage operation has been obtained.