Papers by Author: Erik Janzén

Abstract: The deep levels ON₁ and ON_2a/b introduced by oxidation into 4H-SiC are characterized via standard DLTS and via filling pulse dependent DLTS measurements. Separation of the closely spaced ON_2a/b defect is achieved by using a higher resolution correlation function (Gaver-Stehfest 4) and apparent energy level, apparent electron capture cross section and filling pulse measurement derived capture cross sections are given.

Abstract: Well addressable and controllable point defects in device friendly semiconductors are desired for quantum computational and quantum informational processes. Recently, such defect, an ultra-bright single photon emitter, the antisite carbon carbon vacancy pair, was experimentally investigated in 4H-SiC. In our theoretical work, based on ab initio calculation and group theory analysis, we provide a deeper understanding of the features of the electronic structures and the luminescence process of this defect.

Abstract: We calculated the hyperfine structure and the zero-field splitting parameters of divacancies in 3C, 4H and 6H SiC in the ground state and in the excited state for 4H SiC within the framework of density functional theory. Besides that our calculations provide identification of the defect in different polytypes, we can find some carbon atoms next to the divacancy that of the spin polarizations are similar in the ground and excited states. This coherent nuclear spin polarization phenomenon can be the base to utilize ¹³C spins as quantum memory.

Abstract: The growth of 4H-SiC epilayers on 1.28^o off-cut substrates is reported in this study and comparison when using standard 4^o and 8^o off-cut substrates is added. Growth at high temperature is needed for the polytype stability, whereas low C/Si is requested to decrease both triangular defects density and roughness of the grown surface. An in-situ etching with Si rich ambient allows the growth of epilayers with specular surface. The formation of Si droplets can be observed on the grown surfaces when lowering the growth temperature and appears first for the high off-cut angle.

Abstract: In freestanding n-type 4H-SiC epilayers irradiated with low-energy (250 keV) electrons at room temperature, the electron paramagnetic resonance (EPR) spectrum of the negative carbon vacancy at the hexagonal site, VC- (h), and a new signal were observed. From the similarity in defect formation and the spin-Hamiltonian parameters of the two defects, the new center is suggested to be the negative C vacancy at the quasi-cubic site, VC- (k). The identification is further supported by hyperfine calculations.

Abstract: Homoepitaxial layers of 4H-SiC were grown with horizontal hot-wall CVD on 2˚ off-cut substrates, with the purpose of improving the surface morphology of the epilayers and reducing the density of surface morphological defects. In-situ etching conditions in either pure hydrogen or in a mixture of silane and hydrogen prior to the growth were compared as well as C/Si ratios in the range 0.8 to 1.0 during growth. The smoothest epilayer surface, together with lowest defect density, was achieved with growth at a C/Si ratio of 0.9 after an in-situ etching in pure hydrogen atmosphere.

Abstract: The optical properties of isotope-pure ²⁸Si¹²C, natural SiC and enriched with ¹³C isotope samples of the 4H polytype are studied by means of Raman and photoluminescence spectroscopies. The phonon energies of the Raman active phonons at the Γ point and the phonons at the M point of the Brillouin zone are experimentally determined. The excitonic bandgaps of the samples are accurately derived using tunable laser excitation and the phonon energies obtained from the photoluminescence spectra. Qualitative comparison with previously reported results on isotope-manipulated Si is presented.

Abstract: The effect of process parameters such as growth temperature, C/Si ratio, etching time, and Si/H₂ ratio on dislocation density was investigated by performing KOH etching on 100 μm thick epitaxial layers grown on 4° off axis 4H-SiC substrates at various growth conditions by a chemical vapor deposition (CVD) process using a chloride-based chemistry to achieve growth rates exceeding 100 μm/h. We observe that the growth temperature and the growth rate have no significant influence on the dislocation density in the grown epitaxial layers. A low C/Si ratio increases the density of threading screw dislocations (TSD) markedly. The basal plane dislocation (BPD) density was reduced by using a proper in-situ etch prior to growth.

Abstract: Simulations of SiC chemical vapor deposition is an excellent tool for understanding, improving and optimizing this complex process. However, models used up to date have often been validated for one particular set of process parameters, often in the silicon limited growth regime, in one particular growth equipment. With chlorinated precursors optimal growth condition is often found to take place at the border between carbon limited and silicon limited regimes. At those conditions the previous models fail to predict deposition rates properly. In this study we argue that molecules like C₂H₂, C₂H₄ and CH₄, actually might react with the surface with much higher rates than suggested before. Comparisons are made between the previous model and our new model, as well as experiments. It is shown that higher reactivities of the hydrocarbon molecules will improve simulation results as compared to experimental findings, and help to better explain some of the trends for varying C/Si ratios.

Abstract: The growth of 3C-SiC on hexagonal polytype is addressed and a brief review is given for various growth techniques. The Chemical Vapor Deposition is shown as a suitable technique to grow single domain 3C epilayers on 4H-SiC substrate and a 12.5 µm thick layer is demonstrated; even thicker layers have been obtained. Various characterization techniques including optical microscopy, X-ray techniques and photoluminescence are compared for the evaluation of the crystal quality and purity of the layers.