Hiroshi Kambayashi

Normally Off n-Channel GaN MOSFETs on Si Substrates Using an SAG Technique and Ion Implantation

We have demonstrated n-channel gallium nitride (GaN) MOSFETs using a selective area growth (SAG) technique and ion implantation on a silicon substrate. Both MOSFETs realized good normally off operations. The MOSFET using the SAG technique showed a large drain current of 112 mA/mm, a lower leakage current, and a high field mobility of 113 cm2/V . s, which is, to our knowledge, the best for a GaN MOSFET on a silicon substrate.

High-Temperature Operation of AlGaN/GaN HFET With a Low on -State Resistance, High Breakdown Voltage, and Fast Switching

Improved characteristics of an AlGaN/GaN HFET are reported. In this paper, the authors introduce a new ohmic electrode of Ti/AlSi/Mo and a low refractive index SiNx to decrease the contact resistance and gate leakage current. The AlGaN/GaN HFET showed a low specific resistance of 6.3 mOmega middot cm2 and a high breakdown voltage of 750 V. The switching characteristics of an AlGaN/GaN HFET are investigated. The small turn-on delay of 7.2 ns, which was one-tenth of Si MOSFETs, was measured. The switching operation of the HFET showed no significant degradation up to 225 degC

Enhancement-mode GaN hybrid MOS-HFETs on Si substrates with Over 70 A operation

We report on the demonstration of enhancement-mode n-channel GaN-based hybrid MOS-HFETs realized on AlGaN/GaN heterostructure on silicon substrates with a large drain current operation. The GaN-based hybrid MOS HFETs realized the threshold voltage of 2.8 V, the maximum drain current of over 70 A with the channel width of 340 mm. This is the best value for an enhancement-mode GaN-based FET. The specific on-state resistance was 16.5 mΩcm2. The breakdown voltage was over 500 V. These results suggest that this structure is a good candidate for power switching applications.

Fabrication of AlGaN/GaN HFET with a High Breakdown Voltage on 4-inch Si (111) Substrate by MOVPE

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.

High Power AlGaN/GaN Schottky Barrier Diode with 1000 V Operation

We investigated an AlGaN/GaN Schottky barrier diode (SBD) with a field plate structure for a high breakdown voltage. The AlGaN/GaN heterostructure was grown by MOCVD. The AlGaN buffer was grown on the Si (111) substrate and Al0.25Ga0.75N (25 nm)/ GaN (1000 nm) was grown on the buffer layer. The AlGaN/GaN heterostructure without any crack was obtained. After that, a Schottky barrier diode was fabricated using an AlGaN/GaN heterostructure. In order to obtain a high breakdown voltage, a gate field plate structure was used. SiO 2 was formed on the AlGaN layer using a plasma chemical vapor deposition. The Schottky electrode of Ni/Au was partially deposited on the SiO 2 film towards the ohmic region. The length of field plate structure was also changed to investigate the effect. Ti/Al-silicide was used for an ohmic electrode of SBD. The contact resistance of ohmic electrodes was 8E-6 ohmcm 2 . The current-voltage characteristics of an AlGaN/GaN SBD were measured. The reverse breakdown voltage of the diode was also over 1000 V and the reverse leakage current was below 1.5E-6 A/mm.

500 K operation AlGaN/GaN HFETs with a large current and a high breakdown voltage

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.