Jens-Petter Palmquist

Growth of Ti3SiC2 thin films by elemental target magnetron sputtering

Epitaxial Ti3SiC2(0001) thin films have been deposited by dc magnetron sputtering from three elemental targets of Ti, C, and Si onto MgO(111) and Al2O3(0001) substrates at temperatures of 800–900°C. This process allows composition control to synthesize Mn+1AXn (MAX) phases (M: early transition metal; A: A-group element; X: C and∕or N; n=1–3) including Ti4SiC3. Depositions on MgO(100) substrates yielding the Ti–Si–C MAX phases with (101¯5), as the preferred orientation. Samples grown at different substrate temperatures, studied by means of transmission electron microscopy and x-ray diffraction investigations, revealed the constraints of Ti3SiC2 nucleation due to kinetic limitations at substrate temperatures below 700°C. Instead, there is a competitive TiCx growth with Si segregation to form twin boundaries or Si substitutional incorporation in TiCx. Physical properties of the as-deposited single-crystal Ti3SiC2 films were determined. A low resistivity of 25μΩcm was measured. The Young’s modulus, ascertaine...

Magnetron sputtered epitaxial single-phase Ti3SiC2 thin films

We report on the synthesis and characterization of epitaxial single-crystalline Ti3SiC2 films (Mn+1AXn-phase). Two original deposition techniques are described, (i) magnetron sputtering from Ti3SiC2 compound target and (ii) sputtering from individual titanium and silicon targets with co-evaporated C60 as carbon source. Epitaxial Ti3SiC2 films of single-crystal quality were grown at 900 °C with both techniques. Epitaxial TiC(111) deposited in situ on MgO(111) by Ti sputtering using C60 as carbon source was used to nucleate the Ti3SiC2 films. The epitaxial relationship was found to be Ti3SiC2(0001)//TiC(111)//MgO(111) with the in-plane orientation Ti3SiC2[100]//TiC[101]//MgO[101].

Deposition of Ti2AlC and Ti3AlC2 epitaxial films by magnetron sputtering

Thin films of the Mn+1AXn-phases Ti2AlC and Ti3AlC2 have been deposited by dc magnetron sputtering. In agreement with the Ti–Si–C system, the MAX-phase nucleation is strongly temperature dependent. At 900°C epitaxial films of Ti2AlC and Ti3AlC2 were grown, but at 700°C only a cubic (Ti,Al)C phase was formed. In addition, a perovskite carbide, Ti3AlC was grown at 800°C. A bulk resistivity of 0.51μΩm, 0.44μΩm, and 1.4μΩm was measured for the Ti3AlC2, Ti2AlC, and Ti3AlC films deposited at 900°C, respectively. By nanoindentation the hardness and Young’s module was determined for an epitaxial Ti3AlC2 film to 20GPa and 260GPa, respectively.

Magnetron sputtered W-C films with C60 as carbon source

Thin films in the W–C system were prepared by magnetron sputtering of W with coevaporated C60 as carbon source. Epitaxial deposition of different W–C phases is demonstrated. In addition, nanocrystalline tungsten carbide film growth is also observed. At low C60/W ratios, epitaxial growth of α-W with a solid solution of carbon was obtained on MgO(001) and Al2O3(001) at 400 °C. The carbon content in these films (10–20 at.%) was at least an order of magnitude higher than the maximum equilibrium solubility and gives rise to an extreme hardening effect. Nanoindentation measurements showed that the hardness of these films increased with the carbon content and values as high as 35 GPa were observed. At high C60/W ratios, films of the cubic β-WC1−x (x=0–0.6) phase were deposited with a nanocrystalline microstructure. Films with a grain size <30 A were obtained and the hardness of these films varied from 14 to 24 GPa. At intermediate C60/W ratios, epitaxial films of hexagonal W2C were deposited on MgO(111) at 400 °C. Polycrystalline phase mixtures were obtained on other substrates and hexagonal WC could be deposited as minority phase at 800 °C.

Low resistivity ohmic titanium carbide contacts to n- and p-type 4H-silicon carbide

Abstract Low resistivity Ohmic contacts of epitaxial titanium carbide to highly doped n- ( 1.3×10 19 cm −3 ) and p-(> 10 20 cm −3 ) type epilayer on 4H-SiC were investigated. The titanium carbide contacts were epitaxially grown using co-evaporation with an e-beam for Ti and a Knudsen cell for C60 in a UHV system. A comparison of epitaxial evaporated Ti Ohmic contacts on p+ epilayer of 4H-SiC is also given. The as-deposited TiC Ohmic contacts showed a good Ohmic behavior and the lowest contact resistivity (ρC) was 7.4×10 −7 Ω cm 2 at 200°C for n-type, and 1.1×10 −4 Ω cm 2 at 25°C for p-type contacts. Annealing at 950°C did not improve the Ohmic contact to n-type 4H-SiC, but instead resulted in an increase in ρC to 4.01×10 −5 Ω cm 2 at 25°C. In contrast to n-type, after annealing at 950°C the specific ρC for p-type SiC reached its lowest value of 1.9×10 −5 Ω cm 2 at 300°C. Our results indicate that co-evaporated TiC contacts to n- and p-type epilayers of 4H-SiC should not require a higher post-annealing temperature, contrary to earlier works. Material characteristics, utilizing X-ray diffraction, Low energy electron diffraction, Rutherford backscattering spectrometry, transmission electron microscopy, and X-ray photoelectron spectroscopy measurements are also discussed.

Electronic structure investigation ofTi3AlC2,Ti3SiC2, andTi3GeC2by soft x-ray emission spectroscopy

The electronic structures of epitaxially grown films of Ti3AlC2 , Ti3SiC2 , and Ti3GeC2 have been investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured high-resolution Ti L ...

Electronic structure investigation of Ti3AlC2, Ti3SiC2, and Ti3GeC2 by soft x-ray emission spectroscopy

The electronic structures of epitaxially grown films of Ti3AlC2 , Ti3SiC2 , and Ti3GeC2 have been investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured high-resolution Ti L ...

Electrical characterization of TiC ohmic contacts to aluminum ion implanted 4H-silicon carbide

We report on the investigation of epitaxial TiC ohmic contacts to Al ion implanted 4H–SiC. TiC ohmic contacts were formed by coevaporation of Ti and C60 at low temperature (<500 °C). A sacrificial silicon nitride (Si3N4) layer was deposited on the silicon carbide substrate prior to Al implantation in order to reach a high Al dopant concentration at the surface while maintaining a low dose. The combination of epitaxially grown TiC and the silicon nitride layer resulted in a promising scheme to make low resistivity ohmic contacts. The lowest contact resistivity (ρC) and sheet resistance (Rs) of the implanted layer at 25 °C were as low as 2×10−5 Ω cm2 and 0.6 kΩ/□, respectively.

Low resistivity ohmic contacts on 4H-Silicon carbide for high power and high temperature device applications

We investigated titanium based ohmic contacts using co-evaporated epitaxial titanium carbide (TiC) on highly doped n+-and p+-type epilayers as well as Al ion implanted layers for high power and high temperature device application. Epitaxially grown TiC ohmic contacts on epilayers as well as Al implanted layers of 4H-SiC were formed by UHV co-evaporation with Ti and C60 at low substrate temperature. The specific contact resistance (ρc) was as low as 5 × 10-6, 2 × 10-5, and 2 × 10-5 Ωcm2 for TiC contacts on n+, on p÷ epilayer, and on Al implanted layer, respectively, using a linear TLM measurement. In addition to TiC, we also investigated TiW (weight ratio 30:70) ohmic contacts to p- and n-type 4H-SiC for the purpose of long-term reliability tests at high temperature. The average ρc of sputtered TiW contacts was 4 × 10-5 for p+ and n+ epilayer. We also found that an evaporated top layer (Au or Pt) helps to protect from degradation of the contacts under long-term reliability tests with temperatures of up to 600°C in a vacuum chamber.

Growth and Property Characterization of Epitaxial MAX-Phase Thin Films from the Tin+1(Si, Ge, Sn)Cn Systems

Epitaxial Mn+1AXn phase (n=1, 2 or 3) thin films from the chemically related Ti-Si-C, Ti-Ge-C, and Ti-Sn-C systems were grown on Al2O3(0001) substrates at temperatures in the region of 700-1000 oC, using d.c. magnetron sputtering from individual sources. In addition to growth of the known phases Ti3SiC2, Ti3GeC2, Ti2GeC, and Ti2SnC the method allows synthesis of the new phases Ti4SiC3, Ti4GeC3, and Ti3SnC2 as well as the intergrown structures Ti5A2C3 and Ti7A2C5 in the Si and Ge systems. Characterization by XRD, TEM and nanoindentation show similarities with respect to phase distribution, mechanical, and electrical properties, particularly pronounced when comparing Si and Ge. The Ti-Sn-C system is, however, the most liable system with respect to surface segregation of the A-element. This causes less favorable growth of MAX phases as seen by a preferential growth of the binary carbide TiC and metallic Sn. Nanoindentation on films from the Ti-Si-C and Ti-Ge-C systems shows large plastic deformation with extensive pile up. The typical thin film hardness is 20 GPa, and the Young’s modulus in the region of 320 GPa. The four-point probe resistivity is low for all systems, but differs depending on materials system and phase, with values of 25 μcm for Ti3SiC2, and 17 μcm for Ti2GeC.