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The realization of depletion-mode planar and both enhancement- and depletion-mode tri-gate high electron mobility transistors (HEMTs) based on Al0.2Ga0.8N/AlN/GaN heterostructures grown on silicon substrates using an ultrathin 3C-SiC transition layer is presented. This substrate configuration simplifies heterostructure growth compared to SiC and thick 3C-SiC substrates. The threshold voltage of the tri-gate devices strongly depends on the AlGaN/GaN body (fin) width. A transition from depletion-mode to enhancement-mode operation occurred at 110 nm body width for tri-gate devices without Si3N4 passivation, and is expected to occur at 75 nm for devices with Si3N4 passivation. Threshold voltages of −0.25/0.35 V were achieved at fin widths of 82/100 nm with/without Si3N4 passivation, respectively, for the tri-gate HEMTs in comparison to −3.5 V for the planar HEMTs. Cutoff frequencies fT of 45 GHz and maximum frequencies of oscillation fmax of 50 GHz have been measured for our best 100-nm tri-gate enhancement-mode HEMTs, while depletion-mode planar HEMTs with the same gate length showed 110 GHz for both fT and fmax. This demonstrates the applicability of the developed substrate configuration for high-performance device applications. [ABSTRACT FROM AUTHOR]

AlxGa1-xN solid solutions were heteroepitaxially grown on 3C-SiC(111)/Si(111) pseudo substrates fabricated by low pressure chemical vapour deposition. Free standing doubly-clamped resonator bars and cantilevers were fabricated from these AlxGa1-xN layers. The resonance frequencies of the microelectromechanical structures were measured using electrostatic excitation and vibrometry at ambient conditions. The obtained resonance frequencies allowed a self consistent determination of the Young's modulus of the AlxGa1-xN layers and the residual strain in the free standing structures. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Abstract: The polarity of the 3C–SiC epitaxial layers grown on 3C–SiC(111)/Si(111) pseudosubstrates formed by carbonization using the deposition of elemental carbon under ultra-high vacuum conditions and alternatively at atmospheric pressure in a rapid thermal chemical vapour deposition reactor were studied with different diffraction and electron spectroscopy methods. It is unambiguously shown that the conversion under CVD conditions and the chosen heating-up rate led to the formation of C-face , where as for lower heating-up rates and carbon fluxes Si-face 3C–SiC(111) was obtained. The crystallographic polarity of the carbonized layers is then reproduced during epitaxial growth. Comparing the measurement results of different techniques available to detect the absolute crystallographic orientation it is shown that X-ray diffraction can be used routinely for the determination of the crystallographic polarity, even if the layers are much thinner then the penetration depth of the X-ray radiation. A model, which is based on the formation of energetically or kinetically favoured surface reconstructions at the early stages of the Si to SiC conversion process, is proposed to explain the formation of the different crystallographic polarities of 3C–SiC on a nonpolar Si(111) substrate. [Copyright &y& Elsevier]

Silicon carbide is a material with a multistable crystallographic structure, i.e., a polytypic material. Different polytypes exhibit different band gaps and electronic properties with nearly identical basal plane lattice constants, making them interesting for heterostructures without concentration gradients. The controlled formation of this heterostructure is still a challenge. The ability to adjust a defined temperature–time profile using rapid thermal processing was used to imprint the polytype transitions by controlling the nucleation and structural evolution during the temperature ramp-up and the steady state. The influence of the linear heating-up rate velocity during ramp-up and steady-state temperature on the crystal structure of amorphized ion-implanted silicon carbide layers was studied and used to form heteropolytype structures. Integrating the structural selection properties of the non-isothermal annealing stage of the ion-implanted layers into an epitaxial growth process allows the imprinting of polytype patterns in epitaxial layers due to the structural replication of the polytype pattern during epitaxial growth. The developed methodology paves the way for structural selection and vertical and lateral polytype patterning. In rapid thermal chemical vapor deposition, the adjustment of the process parameters or the buffer layer allowed the nucleation and growth of wurtzite silicon carbide. [ABSTRACT FROM AUTHOR]

In this work, we report on the addition of GeH4 gas during homoepitaxial growth of 4H-SiC by chemical vapor deposition. Ge introduction does not affect dramatically the surface morphology and defect density though it is accompanied by Ge droplet accumulation at the surface. The Ge incorporation level inside the 4H-SiC matrix, ranging from a few 1017 to a few 1018 at. cm-3, was found to be mainly affected by the growth temperature and GeH4 flux. Other growth parameters, such as C/Si ratio, polarity or off-orientation, did not show any significant influence. The Ge incorporation inside SiC was determined to occur at Si sites. On the other hand, adding GeH4 led to an increase in the intentional n-type doping level by a factor of 2-5 depending on the C/Si ratio in the gas phase. [ABSTRACT FROM AUTHOR]