Min Woo Ha

Effects of nitride-based plasma pretreatment prior to SiNx passivation in AlGaN/GaN high-electron-mobility transistors on silicon substrates

The effects of nitride-based plasma pretreatment on the output characteristics of AlGaN/GaN high-electron-mobility transistors (HEMTs) on silicon substrates are investigated. N2 and NH3 plasma pre-treatment methods are studied to overcome the RF dispersion phenomenon caused by nitrogen-vacancy (VN)-related defect reduction. It is found that the nitride-based plasma pretreatment is effective to overcome the RF dispersion in AlGaN/GaN HEMTs on Si. The NH3 plasma pretreatment markedly reduced RF dispersion from 63 to 1%. This is considered to be attributable to the reduction of the effective VN-related defect density and elimination of carbon/oxide residuals on the surface of AlGaN/GaN HEMTs. A NH3 plasma pretreatment prior to SiNx 100 nm passivation in the AlGaN/GaN HEMTs on Si markedly improves the total output power from 15 to 18.1 dBm under the operating conditions of VDS = 15 V/VGS = -1 V.

Hydroquinone-ZnO nano-laminate deposited by molecular-atomic layer deposition

In this study, we have deposited organic-inorganic hybrid semiconducting hydroquinone (HQ)/zinc oxide (ZnO) superlattices using molecular-atomic layer deposition, which enables accurate control of film thickness, excellent uniformity, and sharp interfaces at a low deposition temperature (150 °C). Self-limiting growth of organic layers is observed for the HQ precursor on ZnO surface. Nano-laminates were prepared by varying the number of HQ to ZnO cycles in order to investigate the physical and electrical effects of different HQ to ZnO ratios. It is indicated that the addition of HQ layer results in enhanced mobility and reduced carrier concentration. The highest Hall mobility of approximately 2.3 cm2/V·s and the lowest n-type carrier concentration of approximately 1.0 × 1018/cm3 were achieved with the organic-inorganic superlattice deposited with a ratio of 10 ZnO cycles to 1 HQ cycle. This study offers an approach to tune the electrical transport characteristics of ALD ZnO matrix thin films using an organ...

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.

AlGaN/GaN Schottky Barrier Diode on Si Substrate Employing NiOx/Ni/Au Contact

We proposed and fabricated an AlGaN/GaN lateral Schottky barrier diode (SBD) employing nickel oxide (NiOx)-based double metal contacts, which showed a highly stable reverse blocking capability, by improving the reliability in the high-temperature reverse bias condition. The leakage current of the proposed device was decreased by three orders of magnitude. The measured leakage current of the diode, fabricated using a NiOx (oxidized at 500 °C)–Ni/Au contact as an anode was 236 pA at room temperature while that of the conventional diode was 2.6 µA. The barrier height of the proposed device measured at 200 °C was 0.84 eV while that of conventional one was 0.69 eV. We have also obtained a high breakdown voltage of 1200 V without any additional structure to mitigate the field concentrated at the anode. The highly rectifying contact of the proposed device was attributed to the increment in the barrier height owing to a stoichiometric change at the surface of the device.

7-Octenyltrichrolosilane/trimethyaluminum hybrid dielectrics fabricated by molecular-atomic layer deposition on ZnO thin film transistors

We demonstrate the fabrication of 7-octenytrichlorosilane (7-OTS)/trimethylaluminum (TMA) organic–inorganic hybrid films using molecular-atomic layer deposition (MALD). The properties of 7-OTS/TMA hybrid films are extensively investigated using transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), and electrical measurements. Our results suggest that uniform and smooth amorphous hybrid thin films with excellent insulating properties are obtained using the MALD process. Films have a relatively high dielectric constant of approximately 5.0 and low leakage current density. We fabricate zinc oxide (ZnO) based thin film transistors (TFTs) using 7-OTS/TMA hybrid material as a back gate dielectric with the top ZnO channel layer deposited in-situ via MALD. The ZnO TFTs exhibit a field effect mobility of approximately 0.43 cm2 V−1 s−1, a threshold voltage of approximately 1 V, and an on/off ratio of approximately 103 under low voltage operation (from −3 to 9 V). This work demonstrates an organic–inorganic hybrid gate dielectric material potentially useful in flexible electronics application.

Fabrication of single TiO2 nanotube devices with Pt interconnections using electron-and ion-beam-assisted deposition

Device fabrication using nanostructured materials, such as nanotubes, requires appropriate metal interconnections between nanotubes and electrical probing pads. Here, electron-beam-assisted deposition (EBAD) and ion-beam-assisted deposition (IBAD) techniques for fabrication of Pt interconnections for single TiO2 nanotube devices are investigated. IBAD conditions were optimized to reduce the leakage current as a result of Pt spreading. The resistivity of the IBAD-Pt was about three orders of magnitude less than that of the EBAD-Pt, due to low carbon concentration and Ga doping, as indicated by X-ray photoelectron spectroscopy analysis. The total resistances of single TiO2 nanotube devices with EBAD- or IBAD-Pt interconnections were 3.82 × 1010 and 4.76 × 108 Ω, respectively. When the resistivity of a single nanotube is low, the high series resistance of EBAD-Pt cannot be ignored. IBAD is a suitable method for nanotechnology applications, such as photocatalysis and biosensors.

The field modulation effect of fluoride plasma treatment on blocking characteristics of AlGaN/GaN HEMT

We proposed and fabricated AlGaN/GaN HEMTs with highly stable reverse blocking characteristics by employing fluoride plasma treatment using CF4 gas. The plasma treatment with various RF power was performed selectively on drain side gate edge region where electric field was concentrated. Unlike a 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 simulated energy band structure and the change of off-state gate drain capacitance. Expanded gate depletion spread E-field more uniformly with reducing field intensity and prevented surface potential from dropping drastically at the gate edge under 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 was1400 V while that of untreated sample was 900 V. The leakage current of plasma treated device was 9.5 nA.