N-type 3C-SiC Research Articles

Nickel and platinum ohmic contacts to polycrystalline 3C-silicon carbide

Nickel and platinum contacts to n-type doped polycrystalline 3C-SiC (poly-3C-SiC) were characterized by the circular transmission line method (CTLM) at room temperature and 300 °C. The poly-3C-SiC films were deposited at 800 °C using 1,3-disilabutane single precursor in a low-pressure chemical vapor deposition (LPCVD) reactor, and were in situ nitrogen doped using NH 3. Nickel contacts to poly-3C-SiC showed ohmic characteristics at room temperature, with contact resistivity varying with the doping content of poly-3C-SiC films and reaching the minimum value of 1.6 × 10 −6 Ω cm 2. The contact resistivity increased to 1.3 × 10 −5 Ω cm 2 after the contact was annealed at 300 °C in air. Platinum contact to poly-3C-SiC was also ohmic with an as-deposited contact resistivity of 1.2 × 10 −5 Ω cm 2, but better thermal stability. A stable ohmic contact at 300 °C was achieved with a contact resistivity of about 3.6 × 10 −5 Ω cm 2 on Pt contacts to poly-3C-SiC films.

Evaluation of Schottky Barrier Height of Al, Ti, Au ,and Ni Contacts to 3C-SiC

The Schottky barrier height (SBH) of Al, Ti, Au, and Ni contacts to n- and p-type 3C-SiC is investigated by means of I-V and C-V measurements. All metal contacts to n- (net donor concentration: 1.0 x 1016 /cm3) and p-type (net acceptor concentration: 4 x 1016 /cm3) 3C-SiC show the rectifying I-V characteristics except for Al contact to n-type 3C-SiC. Only Al contact to n-type 3C-SiC shows the ohmic characteristics. As the work function of metal is increased from 4.3 (Ti) to 5.2 (Ni) eV, SBH for n-type 3C-SiC is increased from 0.4 to 0.7 eV and SBH for p-type 3C-SiC is decreased from 2.2 to 1.8 eV. The small change of SBH for 3C-SiC may be correlated to the crystal orientation and the defects on the surface of 3C-SiC.

초고온 MEMS용 단결정 3C-SiC의 Ohmic Contact 형성

This paper describes the ohmic contact formation of single crystalline 3C-SiC thin films heteroepitaxially grown on Si(001) wafers. In this work, a TiW (Titanium-tungsten) film as a contact matieral was deposited by RF magnetron sputter and annealed with the vacuum and RTA (rapid thermal anneal) process respectively. Contact resistivities between the TiW film and the n-type 3C-SiC substrate were measured by the C-TLM (circular transmission line model) method. The contact phases and interface the TiW/3C-SiC were evaulated with XRD (X-ray diffraction), SEM (scanning electron microscope) and AES (Auger electron spectroscopy) depth-profiles, respectively. The TiW film annealed at <TEX>$1000^{\circ}C$</TEX> for 45 sec with the RTA play am important role in formation of ohmic contact with the 3C-SiC substrate and the contact resistance is less than <TEX>$4.62{\times}10^{-4}{\Omega}{\cdot}cm^{2}$</TEX>. Moreover, the inter-diffusion at TiW/3C-SiC interface was not generated during before and after annealing, and kept stable state. Therefore, the ohmic contact formation technology of single crystalline 3C-SiC using the TiW film is very suitable for high temperature MEMS applications.

Determination of densities and energy levels of donors in free-standing undoped 3C–SiC epilayers with thicknesses of 80μm

The densities and energy levels of donors in free-standing undoped 3C–SiC epilayers with the thicknesses of ∼80μm are investigated from the temperature dependence of the electron concentration n(T) obtained by Hall-effect measurements. Although in the analysis of n(T) many researchers usually assume that only one type of donor species is included in n-type 3C–SiC, no one knows whether this assumption is correct or not. In order to determine the densities and energy levels using n(T) without any assumptions regarding donor species, the graphical peak analysis method called free carrier concentration spectroscopy is applied. Three types of donor species are detected in these epilayers. These donor densities can be reduced to &amp;lt;5×1015cm−3 by growing 3C–SiC epilayers on undulant Si substrate. Moreover, the dependence of each donor level on a total donor density is investigated, which is used in 3C–SiC device simulation.

In Situ Doping of 3C-SiC Grown on (0001) Sapphire Substrates by LPCVD

The heteroepitaxial growth of n-type and p-type 3C-SiC on (0001) sapphire substrates has been performed with a supply of SiH4+C2H4+H-2 system by introducing ammonia (NH3) and diborane (B2H6) precursors, respectively, into gas mixtures. Intentionally incorporated nitrogen impurity levels were affected by changing the Si/C ratio within the growth reactor. As an acceptor, boron can be added uniformly into the growing 3C-SiC epilayers. Nitrogen-doped 3C-SiC epilayers were n-type conduction, and boron-doped epilayers were p-type and probably heavily compensated.

Slow photoconductivity decay in 3C-SiC on Si substrates

N-type 3C-SiC layers grown on p-type (001) Si substrates were characterized by the conventional photoconductivity decay method. A N2 laser (337 nm wavelength) was used as the excitation source. A very slow component with a time constant larger than 1 ms was observed in the photoconductivity decay curves. A numerical simulation considering a trap with a very small capture cross section for electrons (&amp;lt;1×10−21 cm2) was able to reproduce main qualitative features of the experimental results. From comparison of the experimental decay curves with the theoretical ones, the following conclusions were drawn about the trap in 3C-SiC. (1) The trap level Et is close to the conduction band edge Ec(Ec−Et=0.1–0.15 eV). (2) The concentration is considered to decrease with increasing donor concentration.

Temperature dependence of the Hall mobility of n-type 3C-SiC

The Hall mobility of n-type 3C-SiC has been calculated employing a set of hydrodynamic balance equations. The acoustic, polar optical, piezoelectric, and intervalley optical lattice scattering, as well as the ionized and neutral impurity scattering are considered in the transport study. The calculated Hall mobility is in good agreement with the experimental data from 70 K to 1000 K. The Hall factor is shown to be less than unity, due to the nonparabolicity of the energy bands.

Characterization of homoepitaxial SiC layers

An n-type 3C-SiC MBE layer is grown on an off-oriented p-type 6H-SiC substrate with alternating supply of gas sources at a growth temperature of 1100°C. The crystalline quality of the 3C-SiC layer is characterized by high resolution transmission electron microscopy and the electrical properties of this layer are investigated by a series of analytical techniques (current-voltage measurement, capacitance-voltage measurement, deep level transient spectroscopy).

Ohmic contacts to n-type polycrystalline SiC for high-temperature micromechanical applications

Highly doped n-type polycrystalline 3C-SiC films were examined for further use in high-temperature applications. The specific contact resistance of TiW contacts was determined using the circular transmission line method by Marlow and Das. The TiW-SiC interface was investigated by means of auger electron spectroscopy (AES) depth-profiles and atomic force microscopy (AFM) surface scans. In addition n-type 6H-SiC was used for reference purposes. It was found that these polycrystalline films were extremely rough (up to 70 nm) and therefore have a wide metal SiC interface, so that no certain statement about interface reaction could be made. The reference samples showed no interface reaction. TiW shows a good ohmic contact behaviour with a specific contact resistance of ρ c = 7.8 × 10 −5 Ω cm 2 to polycrystalline 3C-SiC and with a ρ c = 3.4 × 10 −4 Ω cm 2 to 6H-SiC.

Photocurrent Sensitivities, Surface Color, and Auger Spectroscopy of Silicon Carbide (siC) by Photoelectro-Chemical (Pec) Etching

AbstractThis novel technique involves the ultraviolet (UV) lamp-assisted photoelectrochemical etching of n-type 3C- and 6H-SiC for device processing. In order for this method to be effective, the UV light must be able to enhance the production of holes in the SiC during the etching process thus providing larger currents with light from the photocurrents generated than those currents with no light. Otherwise dark methods would be used as in the case of p-type 3C-SiC.Experiments have shown that the I/V characteristics of the SiC-electrolyte interface reveal a minimum etch voltage of 3 V and 4 V for n- and p-type 3C-SiC, respectively. Hence, it is possible for etch-stops to occur. From Auger spectroscopy, an oxide formation is present on n-type 3C-SiC where after etching a yellowish layer corresponds to a low silicon to carbon (Si/C) ratio with large photocurrents and a white layer corresponds to a high Si/C ratio with small photocurrents. P-type 3C-SiC shows a grayish or silver layer with a high Si/C ratio and a green layer with a low Si/C ratio. Additionally, n-type 6H-SiC shows a brown or blue layer with a minimum etch voltage of 3 V.The colors of the etched regions of SiC represent layers that have some degree of porousity formed by the electrochemical process. As a result, the photo-excitation allows control of the porousity and changes the electrical properties of SiC. The nature of these porous layers with its increased resistivity can lead to the formation of devices.

Low resistivity as-deposited ohmic contacts to 3C-SiC

The contact resistivities of Al and Ti ohmic contacts to n-type 3C-SiC were measured using the circular TLM method. The surface doping concentration under the contact was increased by ion-implantation of nitrogen into SiC. The contact resistivity was observed to decrease with increasing surface doping concentration for both Al and Ti contacts. The minimum value for the contact resistivities for Aland Ti contacts was 1.4x 10-5and 1.5 x 10-5 ω cm2, respectively, at the surface doping concentration of 3 x 1020 cm-3 without any annealing of the contacts. These values are an order of magnitude lower than previously reported minimum values for as-deposited ohmic contacts on n-type 3C-SiC.

Low Temperature - High Pressure Oxidation of 3C-SiC

AbstractSingle crystal films of n-type 3C-SiC were hydrothermally processed at pressures ranging from 10 to 70 MPa at 550°C. To study the effects of initial thin film microstructure on hydrothermal processing, two different samples of CVD-grown SiC were studied: one, 200 nm thick, contained low angle boundaries and a high density of planar defects; the other, 3500 nm thick, was planar and contained relatively few defects. Raman Spectroscopy, X-Ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) were used to study the chemistry and microstructure of the SiC material both before and after hydrothermal treatment. This study reveals that low temperature (T=550°C) oxidation of single crystal epitaxial SiC is possible but that the resulting oxide film microstructure is strongly dependent on the initial film microstructure and oxidation is greatly enhanced along low angle grain boundaries and on planar defects.

Operation of Schottky-barrier field-effect transistors of 3C-SiC up to 400 °C

Schottky-barrier field-effect transistors have been fabricated from 3C-SiC and transistor operation has been studied at temperatures up to 400 °C. B-doped high-resistivity and undoped n-type 3C-SiC epilayers were successively grown on p-type Si substrates by chemical vapor deposition. Au and Al electrodes were used for Schottky-barrier gate contacts and source and drain contacts for n-type 3C-SiC, respectively. Transconductances of 1.7 and 0.15 mS/mm were obtained at room temperature and 400 °C, respectively.

Temperature dependence of electrical properties of n- and p-type 3C-SiC

Electrical properties of unintentionally doped n-type and Al-doped p-type 3C-SiC layers, epitaxially grown on Si by chemical vapor deposition, have been investigated at temperatures between 10 and 1000 K. Activation energies of Al acceptors and residual donors obtained from the temperature dependence of carrier density are 160 and 18 meV, respectively. 40%–60% of Al acceptors in the p-type epilayers are compensated, and hole mobility is limited by acoustic phonon scattering above 300 K and by ionized impurity scattering below 250 K.

Electrical Properties of 3C-SiC and its application to FET

ABSTRACTElectrical and luminescent properties of nondoped, and N-doped n-type 3C-SiC layers epitaxially grown on Si(100) by chemical vapor deposition were studied. Nondoped n-type epilayers with carrier concentration of 1×1016cm−3 and the Hall mobility of 750cm2/Vs at room temperature have the activation energy of donors, Ed=2OmeV, which is different from that of the donors in the N-doped layers. The photoluminescence spectra of nondoped layers are different from those of N-doped ones. These results suggest that the donors in the unintentionally doped n-type 3C-SiC are not due to N impurities. 45–70 % of N-donors in the N-doped epilayers are compensated.Schottky-barrier and MOS-type field-effect transistors have been fabricated from 3C-SiC. The transistor operations of MESFETs and MOSFETs were studied at elevated temperatures up to 440°C. Transconductances of 1.7mS/mm and 0.15mS/mm for MESFET and 0.8 and 0.05mS/mm for MOSFET at room temperature and 440°C, respectively, were obtained. The drain currentvoltage characteristics of both the FETs at room temperature did not change in the least after heating up to 440°C in the air.

Schottky-barrier field-effect transistors of 3C-SiC

Schottky-barrier field-effect transistors have been fabricated first from 3C-type SiC. Al-doped p-type and nondoped n-type 3C-SiC epilayers were successively grown on p-type Si substrates by chemical vapor deposition. Au and Al electrodes were used for Schottky-barrier gate contacts and ohmic (source and drain) contacts for n-type SiC. Transistor operation was observed for the first time for the field-effect transistors of 3C-SiC.

Schottky barrier diodes on 3C-SiC

Schottky barrier contacts have been made on n-type 3C-SiC epitaxially grown by chemical vapor deposition, and their characteristics were studied by the capacitance and photoresponse measurements. By evaporating Au onto chemically etched surfaces of 3C-SiC, good quality Schottky barrier junctions have been obtained. The barrier height determined by the capacitance measurements is 1.15 (±0.15) eV, while the height by the photoresponse measurements is 1.11 (±0.03) eV. These values are about a half of the energy band gap Eg at room temperature.