Jiyong Lim

High breakdown voltage GaN Schottky barrier diode employing floating metal rings on AlGaN/GaN hetero-junction

We have reported a lateral GaN SBDs on AlGaN/GaN hetero-junction employing floating metal rings (FMRs) which exhibit a very high breakdown voltage, a low leakage current and a low on-state voltage. We have obtained a very high breakdown voltage of 930V without any additional process step. We have also optimized design parameters of FMR, such as the space between main junction and FMR and the number of rings. Our experimental results show that FMR which is rather simple may be suitable for lateral GaN SBD.

Suppression of Leakage Current of Ni/Au Schottky Barrier Diode Fabricated on AlGaN/GaN Heterostructure by Oxidation

We have proposed and fabricated a lateral GaN Schottky barrier diode (SBD) that increases the breakdown voltage and decreases the leakage current by the oxidation of a Ni/Au Schottky contact. After an oxidation, the anode current was increased under a high anode bias, whereas the turn-on voltage was slightly increased. The leakage current was considerably decreased to less than 1 nA after the oxidations of 5 and 10 min. A high breakdown voltage of 750 V was measured in the proposed GaN SBD when multiple floating metal rings (FMRs) were used for edge termination and oxidation was employed. We have also measured the reverse recovery waveforms at room temperature and 125 °C and the fabricated GaN SBDs show very fast reverse recovery characteristics.

Increase of Breakdown Voltage on AlGaN/GaN HEMTs by Employing Proton Implantation

The breakdown voltage of new AlGaN/GaN high electron mobility transistors (HEMTs) was increased considerably without sacrificing any other electrical characteristics by proton implantation. The breakdown voltage of proton-implanted AlGaN/GaN HEMTs with 150 KeV 1 times 1014 -cm-2 fluence after thermal annealing at 400 degC for 5 min under N2 ambient was 719 V, while that of conventional device was 416 V. The increase of the breakdown voltage is attributed to the expansion of the depletion region under the 2-D electron gas (2-DEG) channel. The depletion region expanded downward into the GaN buffer layer because implanted protons acted as positive ions and attracted electrons in the 2-DEG channel.

SiO2 Passivation Effects on the Leakage Current in AlGaN/GaN High-Electron-Mobility Transistors Employing Additional Schottky Gate

The leakage current of AlGaN/GaN high-electron-mobility transistors employing the additional Schottky gate before and after SiO2 passivation is investigated. The SiO2 passivation successfully decreases the drain leakage current from 1.70 µA to 88.05 nA due to the suppressed conduction of surface trap states. The leakage current injection from additional-gate to main-gate is observed in the unpassivated device while no leakage current injection at additional-gate is observed in the passivated device. The measured leakage current at additional-gate in the unpassivated device and passivated one are 15.58 µA and 7.10 pA respectively. The measured leakage current at main-gate in those devices are -50.72 µA and -91.10 nA respectively. The SiO2 passivation for AlGaN/GaN HEMT employing additional Schottky gate successfully decreases the leakage current through surface trap states as well as the undesirable leakage current between Schottky contacts.

An AlGaN/GaN HEMT power switch employing a field plate and a floating gate

We have proposed and fabricated AlGaN/GaN high electron mobility transistors (HEMTs) which increase the gate-drain breakdown voltage by employing a floating gate and a field plate. Experimental results show that the breakdown voltage of the proposed devices was successfully increased compared with that of the devices which employ only the floating gate in our previous report. High breakdown voltage of 484 V is obtained while the breakdown voltage of the conventional devices is 250 V. The leakage current is reduced considerably from 88 to 8.5 μA by employing the additional field plate. Measurement of dynamic characteristics shows that the proposed devices operate under high frequency inductive load switching without any current dispersion.

Hot-Carrier-Stress-Induced Degradation of 1 kV AlGaN/GaN HEMTs by Employing SiO2 Passivation

High-voltage AlGaN/GaN HEMTs (high-electron-mobility transistors) are fabricated by employing SiO2 passivation and the degradation due to the hot carrier stress has been investigated. Our experimental result shows that the SiO2 passivation of AlGaN/GaN HEMT successfully achieves the breakdown voltage of 1 kV without any field plate design. The pulsed I-V measurement for AlGaN/GaN HEMT shows that the SiO2 passivation suppresses the frequency dispersion and decreases the on-resistance from 2.46 to 1.38 mOmega-cm2. The hot carrier stress degrades the electric characteristics of AlGaN/GaN HEMT because the high field increases the trapping at the surface and the interface. However, the SiO2 passivation of AlGaN/GaN HEMT decreases the surface trapping and 2DEG depletion during the hot carrier stress, so that a passivated device exhibits less degradation than an unpassivated one. After the hot carrier stress with VDS=30 V and VGS=10 V is applied to the device for 5times104 sec, the SiO2 passivation decreases the stress-induced degradation of forward drain current from 30.4 to 24.5 %.

High breakdown voltage AlGaN/GaN HEMT by employing selective fluoride plasma treatment

We proposed and fabricated AlGaN/GaN HEMT with high stable reverse blocking characteristics employing fluoride plasma treatment using CF 4 gas. The plasma treatment with various rf power was performed selectively on drain-side gate edge region where electric field was concentrated. Unlike normally-off process, fluoride plasma treatment with attenuated RF power expanded gate depletion region in the direction of drain electrode. Expansion of depletion was confirmed by the change of measured off-state gate-drain capacitance. Expanded gate depletion spread E-field more uniformly with reducing peak of field intensity and prevented from drastic surface potential drop at the gate edge under large reverse bias condition. By the mitigation of field concentration and gradual potential change due to plasma treatment, was leakage current reduced and high breakdown voltage achieved. The breakdown voltage of plasma treated device with optimized rf power was 1400 V while that of untreated sample was 900 V. The leakage current of plasma treated device was 9.5 nA.

Suppression of the leakage current of a Ni/Au Schottky Barrier Diode fabricated on AlGaN/GaN hetero-structure by oxidation

We have proposed and fabricated a lateral GaN Schottky barrier diode (SBD) that increases the breakdown voltage and decreases the leakage current by the oxidation of a Ni/Au Schottky contact. After an oxidation, the anode current was increased under a high anode bias, whereas the turn-on voltage was slightly increased. The leakage current was considerably decreased to less than 1 nA after the oxidations of 5 and 10min. A high breakdown voltage of 750V was measured in the proposed GaN SBD when multiple floating metal rings (FMRs) were used for edge termination and oxidation was employed. We have also measured the reverse recovery waveforms at room temperature and 125 C and the fabricated GaN SBDs show very fast reverse recovery characteristics. [DOI: 10.1143/JJAP.45.3398]

High-Voltage Schottky Barrier Diode on Silicon Substrate

New GaN Schottky barrier diodes (SBDs) on Si substrates are proposed to achieve a high-breakdown voltage. We have fabricated GaN SBDs using doped GaN/unintentionally doped (UID) GaN because doped GaN with the thickness of 200 nm is suitable for high-current operation. The 1-µm-deep mesa and low-temperature annealing of ohmic contacts suppress the leakage current of GaN SBDs. Annealing of Schottky contacts also improves the interface between a Schottky contact and GaN. Annealing of ohmic contacts at 670 °C yields the low leakage current of 2.8 nA through the surface and the buffer. When the anode–cathode distance is 5 µm, the fabricated GaN SBD successfully achieves a low forward voltage drop of 1.3 V at 100 A/cm2, low on-resistance of 4.00 mΩ cm2, and the low leakage current of 0.6 A/cm2 at -100 V. The measured breakdown voltage of GaN SBDs is approximately 400 V.

New AlGaN/GaN HEMTs employing both a floating gate and a field plate

We designed and fabricated AlGaN/GaN high-electron-mobility transistors (HEMTs) employing both a floating gate (FG) and a field plate (FP), which increase the breakdown voltage of AlGaN/GaN HEMTs significantly without sacrificing forward electric characteristics. The electric field strength at the gate–drain region of the proposed AlGaN/GaN HEMT was reduced successfully due to an increase in the number of depletion region edges. The breakdown voltage of the proposed AlGaN/GaN HEMT was 1106 V, while those of the conventional devices with only an FP or FG were 688 and 828 V, respectively. The leakage current of the proposed AlGaN/GaN HEMTs was 1.68 μA under a reverse bias of −100 V while those of the conventional devices with only an FP or FG were 3.21 and 1.91 μA, respectively, under the same condition. The forward electric characteristics of the proposed and conventional AlGaN/GaN HEMTs are similar. The maximum drain current of the proposed AlGaN/GaN HEMTs was 344 mA mm−1 while those of the conventional devices with only an FP or FG were 350 and 357 mA mm−1, respectively. The maximum transconductance of the proposed device was 102.9 mS mm−1, while those of the conventional devices were 97.8 and 101.9 mS mm−1. The breakdown voltage and the leakage current of the proposed device were improved considerably without sacrificing the forward electric characteristics. It should be noted that there were no additional processing steps and mask levels compared to the conventional FP process.