Symposium E  "Wide-Bandgap Electronics" of the 2001 MRS Spring Meeting  was held at the Marriott hotel in San Francisco from  April 17 - 20, 2001. Proceedings of this symposium will be published online (only) as Volume 680E of the MRS Symp.

I would like to start the short overview of  SiC related papers with highlighting of the report about aluminium nitride: E2.1 SINGLE-CRYSTAL ALUMINUM NITRIDE SUBSTRATE PREPARATION FROM BULK CRYSTALS. Leo J. Schowaltera, J. Carlos Rojo, and Glen A. Slack.  As a substrate for III-nitrides epitaxy AlN is a strong competitor not only to SiC and sapphire, but to GaN also. AlN is an electrical insulator having a thermal conductivity better than GaN. AlN wafers are more desirable substrate for Al-rich nitride epitaxial layers. AlN boules with 15 mm diameter grown by sublimation-recondensation were reported. Wafers preparation, epitaxy on the wafers with various orientations, measurement of AlN thermal conductivity (2.85 W/K-cm) were reported also.

The measurements of SiC thermal conductivity with spatial resolution of about 3 microns on 2 inch 4H-SiC with (1-3)10¹⁸ cm^-3  and 6H-SiC with (6-9)10¹⁷ cm^-3 wafers from ATMI was reported in E2.4 HIGH SPATIAL RESOLUTION THERMAL CONDUCTIVITY INVESTIGATION OF SiC WAFERS. D.I. Florescu, Fred H. Pollak, G.R. Brandes, B.E. Landini, A.D. Salant. The thermal conductivity from 3 to 3.9 W/cm-K was measured depending on the defect density.

The next interesting report was E5.11 INFRARED ABSORPTION AND ANNEALING BEHAVIOR OF SEMI-INSULATING 4H SiC HTCVD SUBSTRATES. B. Magnusson, A. Ellison, N.T. Son, J. Zhang, and E. Janzén. The authors have investigated the influence of annealing effect on semi-insulating properties of 4H-SiC semi-insulating (SI) substrates grown by HTCVD. The annealing was performed at the temperature of 1600^oC for 10 minutes in H₂. This is typical conditions of CVD process. There were substrates of two kinds - Type A (Si vacancies) and Type B (UD-1 defects). Both types remain semi-insulating after annealing, but Type A has resistivity of 10⁶- 10⁷ Ohm.cm and  Type B  - of 10¹⁰ Ohm.cm.  It was not clear from the report and discussion is it possible to manage by the type ot the substrates during their growth or not. 

Three very interesting reports devoted to the well known contacts formed by Ni annealing on n-type SiC were presented. It was reported in the paper E6.9 CORRELATION BETWEEN MORPHOLOGY AND ELECTRICAL PROPERTIES OF NICKEL SILICIDE CONTACTS ON 6H-SiC. F. Roccaforte, F. La Via, V. Raineri, P. Musumeci, L. Calcagno that nickel silicide starts to form on 6H-SiC during annealing at 600^oC for 20 minutes in N₂ ambient and Ni became completely reacted at the temperature of  800^oC. The authors found that the carbon was distributed in the contact layer. After annealing at 950^oC,  the ohmic contacts with 5e-4 Ohm.cm were formed to 6H-SiC with N_D=3.6e18 cm^-3 and 7e-5 Ohm.cm   to 6H-SiC with N_D=7.4e19 cm^-3. The contacts remained stable after annealing for 5 hours at 950^oC. Also, the authors have investigated the formation of Schottky barriers to low doped SiC. They reported that the Ni layer with Ti flash gave the Schottky barrier (1.17eV and ideality factor n = 1.33) to 6H-SiC with N_D=2e14 cm^-3 after the deposition and (1.4 eV, n = 1.04) after annealing at 600^oC for 60 seconds. In contrary, they had (0.9eV and n = 1.6) after the deposition and (1.07 eV n = 1.36) after annealing at 600^oC and leakage 10⁴ A/cm² at 100 V when the deposition was made in the window in SiO₂. This fact was associated with producing of surface defects in SiC by RIE of SiO₂.

The attempt to discover the role of carbon in formation of ohmic contacts to n-SiC was described in the report E6.10 CARBON GRAPHITIZATION AND ELECTRICAL PROPERTIES ON 4H-SiC. Candis A. Adams, Weijie Lu, W. Eugene Collins, Ravi K. Chanana, Leonard C. Feldman, William C. Mitchel. The authors deposited carbon thin films on Si-face 4H-SiC 8^ooff (N_D=1.3e19, 0.7e19 and 2.0e18 cm^-3)  by RF sputtering. The composition was investigated by XPS after the deposition and after annealing at 750^oC and 950^oC for 30 minutes in Ar. It was found that as deposited carbon was in amorphous  state,  and a graphite state of the carbon appears after annealing and increases at 950^oC. But the I-V characteristics shown at presentation were not linear.

At last, the third report about Ni contacts was E6.11 OHMIC CONTACT FORMATION MECHANISM OF Ni-BASED CONTACT ON N-TYPE 4H-SiC. Sang Youn Han, Ki Hong Kim, Jong Kyu Kim, Ho Won Jang, Kwang Ho Lee, Jong-Lam Lee, Nam-Kyun Kim, E.D. Kim. The authors annealed  Ni (100 nm)  on 4H-SiC ( 4.2e15 cm^-3) up to 1000^oC with 100^oC step for 90 seconds. They discovered, that  the Schottky barrier remained to be stable at annealing up to 600^oC.  The height of the barrier increased from 1.55eV after anneal at 400^oC to 1.75 eV  after  anneal at 600^oC. Ni₂₁Si₁₂ phase formed at annealing the temperature higher than 600^oC  and transferred in Ni₂Si with decreasing of SB height at further increasing of the annealing temperature up to 900^oC. The longer annealing at high temperature led to the diffusion of the carbon from  Ni₂Si/SiC interface to the surface. This process of carbon diffusion and formation of  Ni₂Si/SiC interface free of carbon was discovered by SIMS. It was believed to be responsible for the formation of ohmic contact. 

The theme of SiC device processing was continued by a very interesting report  E7.5 IMPROVEMENT OF CARBON-FACE SiC METAL OXIDE SEMICONDUCTOR STRUCTURES USING LOW TEMPERATURE OXIDATION. Wang Chun and M.E. Zvanut. The authors have discovered that the ratio of Auger pike amplitudes I_Si/I_C remains about 1 after annealing of SiC at temperatures below 1100^oC for Si-face and below 900^oC for C-face. This allowed to conclude that the oxidation of C-face must  be performed at temperatures below 900^oC. The authors reported electrical characteristics of C-face MOS structures and their essential improvement with post oxidation annealing in nitrogen oxide or Ar. 

From poster session, the report E9.2 CHARACTERIZATION OF P-TYPE 4H-SiC EPITAXIAL LAYER GROWN ON (112-0) SUBSTRATE. Kazutoishi Kojima, Toshiyuki Ohno, Mituhiro Kushibe, Koh Masahara, Takaya, Suzuki and Tomoyuki Tanaka, Yuuki Ishida, Tetuo Takahashi and Kazuo Arai must be highlighted. The authors reported  the epitaxy of  p-doped 4H-SiC layers with extremely high acceptor concentrations up to 1e19 cm^-3 on the plane parallel to the c-axis. All Al atoms were found ionized. The hole mobility was measured of 73 cm²/Vs in these layers at acceptor concentration of  7e15 cm^-3.

The Symposium E of  MRS 2001 Spring Meeting was closed with the report  E10.11 X-BAND SILICON CARBIDE IMPATT OSCILLATOR. Konstantin Vassilevski, Alexandr Zorenko, Konstantinos Zekentes. The first experimental observation of microwave oscillation produced by SiC IMPATT diode was described. The oscillator with single-drift n⁺-n-p⁺ 4H-SiC diode produced 300 mW RF power at 10 GHz in pulse mode. The detailed description of the diode and oscillator design, diode fabrication, dc and RF measurements were given in the report.