Papers by Author: Han Seok Seo

Abstract: We have investigated the electrical and physical properties of the oxidized-SiN with or without post oxidation annealing (POA) in N2 gas. A significant reduction in interface-trap density (Dit) has been observed in the oxidized-SiN with N2 POA for 60 min if compared with other oxides. The reason for this has been explained in this paper.

Abstract: Schottky barrier diode (SBD) was fabricated by MOCVD using bistrimethylsilylmethane (BTMSM, C7H20Si2) precursor. The 4H-SiC substrates which had different crystallographic characteristics were used for the comparison of the crystallinity effect on the electrical properties of the SBDs. From the measurement of the reverse I-V characteristics of the SBDs with micropipes, it is shown that the origin of the main leakage path and early breakdown (or ohmic behavior in reverse bias) in 4H-SiC SBDs is the grain boundaries caused by the inclusions or other defects. The best performance of SBD were shown in the epilayer grown at 1440 oC using high quality substrate, and the breakdown voltage and reverse leakage current were about 450 V and 10-9 A/cm2, respectively.

Abstract: Homoepitaxial growth of 4H-SiC epilayer by hot-wall chemical vapor deposition using bis-trimethylsilylmethane (BTMSM, C7H20Si2) precursor was investigated. The growth rate of 4H-SiC was investigated as a function of the growth temperature and source flow rate. The FWHM values of epilayers as the growth temperature and source flow rate also investigated. The growth rate of 4H-SiC epilayer grown by hot-wall CVD was 3.0 μm/h and the background doping level of 4H-SiC epilayer was mid 1015/cm3.

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: 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.