Papers by Author: Hoon Joo Na

Abstract: Planar MESFETs were fabricated on high-purity semi-insulating (HPSI) 4H-SiC substrates. The saturation drain current of the fabricated MESFETs with a gate length of 0.5 μm and a gate width of 100 μm was 430 mA/mm, and the transconductance was 25 mS/mm. The maximum oscillation frequency and cut-off frequency were 26.4 GHz and 7.2 GHz, respectively. The power gain was 8.4 dB and the maximum output power density was 2.8 W/mm for operation of class A at CW 2 GHz. MESFETs on HPSI substrates showed no current instability and much higher output power density in comparison to MESFETs on vanadium-doped SI substrates.

Abstract: We have investigated the electrical properties of metal-oxide-semiconductor (MOS) capacitors with atomic-layer-deposited La2O3, thermal-nitrided SiO2, and atomic-layer-deposited La2O3/thermal-nitrided SiO2 on n-type 4H-SiC. A significant reduction in leakage current density has been observed in La2O3 structure when a 6-nm thick thermal nitrided SiO2 has been sandwiched between the La2O3 and SiC. However, this reduction is still considered high if compared to sample having thermal-nitrided SiO2 alone. The reasons for this have been explained in this paper.

Abstract: The authors attempted to grow a semi-insulating SiC epitaxial layer by in-situ vanadium doping. The homoepitaxial growth of the vanadium-doped 4H-SiC layer was performed by MOCVD using the organo-silicon precursor, bis-trimethylsilylmethane (BTMSM, [C7H20Si2]) and the metal-organic precursor, bis-cyclopentadienylvanadium (Verrocene, [C10H10V]). Vanadium doping effect on crystallinity of epilayer was very destructive. Vanadium-doped epilayers grown on normal condition had various surface or crystal defects such as micropipes, polytype inclusions. But this crystallinity degradation was overcome by high growth temperature. For the measurement of the resistivity of the highly resistive vanadium-doped 4H-SiC epilayers, the authors used the on-resistance technique. Based on the measurements of the on-resistance of the epilayers using the current-voltage technique, it is shown that the residual donor concentration of the epilayers was decreased with increasing partial pressure of verrocene. The resistivity of the vanadium-doped 4H-SiC epilayer was about 107 /cm.

Abstract: 4H-SiC planar MESFETs were fabricated using ion-implantation on high-purity semi-insulating substrate, and their DC and RF performances were characterized. A modified RCA method was used to clean the substrate before each procedure. Sacrificial oxide was grown after channel layer etching to eliminate plasma damage to the gate region. A thin, thermal oxide layer was grown to passivate the surface and then a thick field oxide was deposited by CVD. The maximum oscillation frequency of 26.4 GHz and the cut-off frequency of 7.2 GHz were obtained. The power gain was 8.4 dB and the output power was 2.8 W/mm at 2 GHz.

Abstract: The La2O3 and Al2O3/La2O3 layers were grown on 4H-SiC by atomic layer deposition (ALD) method. The electrical properties of La2O3 on 4H-SiC were examined using metal-insulator-semiconductor (MIS) structures of Pt/La2O3(18nm)/4H-SiC and Pt/Al2O3(10nm)/La2O3(5nm)/4H-SiC. For the Pt/La2O3(18nm)/4H-SiC structure, even though the leakage current density was slightly reduced after the rapid thermal annealing at 500 oC, accumulation capacitance was gradually increased with increasing bias voltage due to a high leakage current. On the other hand, since the leakage current in the accumulation regime was decreased for the Pt/Al2O3/La2O3/4H-SiC MIS structure owing to the capped Al2O3 layer, the capacitance was saturated. But the saturation capacitance was strongly dependent on frequency, indicating a leaky interfacial layer formed between the La2O3 and SiC during the fabrication process of Pt/Al2O3(10nm)/ La2O3(5nm)/ 4H-SiC structure.