Ki-Se Kim

Temperature dependence of current-voltage characteristics of Ni–AlGaN/GaN Schottky diodes

Ni–AlGaN/GaN Schottky barrier diodes (SBDs) with lateral geometry were fabricated on sapphire substrates. At 300 K, devices with 500-μm-diameter Schottky contacts exhibited breakdown voltage (VB) of 765 V, forward current (IF) of 0.065 A at 1.5 V, and specific on-resistance (Ron) of 81.3 mΩ cm2, producing a figure-of-merit (VB2/Ron) of ∼7.2 MW cm−2. Measured in multifinger patterns, the same parameters were 420 V, 3.2 A, 4.6 mΩ cm2, and 38.4 MW cm−2, respectively, at 300 K. With the increase in measurement temperature from 300 to 450 K, SBDs with dimensions of 3000×3000 μm2 showed larger effective barrier heights (0.8 eV at 300 K and 1.27 eV at 475 K) and a slightly negative temperature coefficient (−0.48 V K−1) for reverse breakdown voltage, while there was a little change in reverse leakage current. These results show the strong influence of barrier height inhomogeneity on the temperature dependence of apparent barrier heights obtained through current-voltage measurements.

Variation in the properties of the interface in a CoFeB∕MgO∕CoFeB tunnel junction during thermal annealing

Variation in the quality of the interface in a CoFeB∕MgO∕CoFeB tunnel junction during thermal annealing was investigated using x-ray photoemission spectroscopy. The formation of B oxide and the reduction of Fe oxide at the bottom interface after thermal annealing near Ta=300°C were found to enhance the tunneling magnetoresistance ratio significantly. At the same time, an asymmetry of the conductance (dV∕dI) in the bias polarity and a local minimum of conductance in a positive bias state were measured which were attributed to the presence of a minority state at the bottom interface. The authors believe that the existence of the Bloch state was also responsible for the failure of the application of the Brinkman-Dynes-Rowell or Simmons models to the CoFeB∕MgO∕CoFeB junction.

Analysis of the reverse leakage current in AlGaN/GaN Schottky barrier diodes treated with fluorine plasma

The carrier transport mechanism of CF4 plasma-treated AlGaN/GaN Schottky barrier diodes (SBDs) under reverse bias is investigated. The reverse leakage current is reduced by ∼2 orders of magnitude after the CF4 plasma treatment, but increases exponentially with increasing temperature, indicating that a thermally activated transport mechanism is involved. Based on the activation energy estimated from temperature-dependent current-voltage characteristics and the emission barrier height extracted from Frenkel-Poole emission model, it is suggested that the dominant carrier transport mechanism in the CF4 plasma treated SBDs is the Frenkel-Poole emission from fluorine-related deep-level states into the continuum states of dislocations.

Reduction in Shottky barrier height of AlGaN-based SBD with in-situ deposited silicon carbon nitride (SiCN) cap layer

AlGaN/GaN Schottky barrier diodes (SBDs) with and without in-situ silicon carbon nitride (SiCN) cap layer were investigated. The fabricated SBD with SiCN cap layer exhibited improved electrical characteristics, such as the forward turn on voltage of about 0.7 V, the forward current of 4.1 A at 1.5 V, and the reverse breakdown voltage of 630 V, compared to the corresponding values of 0.8 V, 3.8 A, and 580 V for the reference SBD without the SiCN cap layer. This improvement in the device performance of the SiCN-SBD is because the in-situ SiCN cap layer not only lowers the barrier height, but also effectively passivates the surface of the device with better surface morphology.

Improved Electrical Characteristics of AlGaN/GaN HEMT with In-situ Deposited Silicon Carbon Nitride Cap Layer

1 School of Electrical Engineering and Computer Science, Seoul National University, Republic of Korea San 56-1 Shillim-dong Gwanak-gu Seoul 151-742, Republic of Korea Phone: +82-2-877-0298, Fax: +82-2-887-6575, E-mail: elengine@snu.ac.kr 2 Semiconductor Business, Samsung Electronics Co., Ltd, Suwon, 443-743, Republic of Korea 3 School of Electronic and Electrical Engineering, Hongik University, Seoul 121-791, Korea

Characteristics of AlGaN/GaN heterostructure field effect transistor grown on 4 inch Si (111) substrate using formation of dot-like AlSi x C 1−x interlayer

Group III-nitride semiconductors and their ternary solid solutions are very promising as the candidates for both short wavelength optoelectronics and power electronic devices [1]. The AlGaN/GaN heterostructure field-effect transistors (HFETs) have a great potential for future high-frequency and high-power applications because of the intrinsic advantages of materials such as wide band gap, high breakdown voltage, and high electron peak velocity [2–4]. Si substrate is considered as a promising candidate to replace expensive and small wafers such as sapphire and SiC, even though the GaN layer grown on Si substrate has a large strain and dislocation due to a large lattice mismatch and thermal expansion coefficient difference between the grown GaN layer and the Si substrate. The mismatch between thermal expansion coefficients is about 56%, which induces a large tensile stress and may cause a severe crack generation in the grown GaN films during the cooling process after growth. In this work, for the purpose of reducing the crack density in the AlGaN/GaN heterostructure grown on Si substrate, we have grown dot-like AlSixC1−x interlayer in inital growth state between AlN and Si substrate and demonstrated successful normally-on/off GaN HFET grown on silicon substrate.