Papers by Author: Erik Janzén

Abstract: 3C-SiC epilayers grown on Si-face nominally on-axis 4H-SiC substrate are characterized with X-ray diffraction techniques. The aim was to investigate if these 3C-SiC epilayers were grown by single domain growth. The results show that all samples start by having several nucleation centers all over the substrate surface and the growth continues with two domain formations. As the growth proceeds one domain overtakes the growth and single domain crystal growth occurs. This single domain was further investigated and the results show that it seems to contain many sub-domains with same lattice constant but slightly tilted.

Abstract: A set of lines in the photoluminescence spectra of 4H-, 6H-, and 15R-SiC in the near-infrared are attributed to Nb-related defects on the ground of doping experiments conducted with 4H-SiC. A model based on a an exciton bound at the Nb-centre in an asymmetric split vacancy configuration at a hexagonal site is proposed, which explains the structure of the luminescence spectrum and the observed Zeeman splitting of the lines.

Abstract: Carrier lifetime and formation of defects have been investigated as a function of growth temperature in n-type 4H-SiC epitaxial layers, grown by horizontal hot-wall CVD. Emphasis has been put on having fixed conditions except for the growth temperature, hence growth rate, doping and epilayer thickness were constant in all epilayers independent of growth temperature. An increasing growth temperature gave higher Z1/2 concentrations along with decreasing carrier lifetime. A correlation between growth temperature and D1 defect was also observed.

Abstract: Results of surface preparation on Si-face 4° off-cut 4H-SiC substrates are presented in this paper. The influences of two types of etchants, i.e. hydrogen chloride (HCl) and only hydrogen (H2), were investigated by Nomarski microscopy and AFM. The experiments were performed in a hot wall CVD reactor using a TaC coated susceptor. Four etching temperatures, including 1580 °C, 1600 °C, 1620 °C and 1640 °C, were studied. In-situ etching with only H2 as ambient atmosphere is found to be the optimal way for the SiC surface preparation. Using HCl at temperature higher than 1620 °C could degrade the substrates surface quality.

Abstract: This paper deals with electrical characterization of PiN diodes fabricated on an 8° off-axis 4H-SiC with a p⁺⁺ localized epitaxial area grown by Vapour-Liquid-Solid (VLS) transport. It provides for the first time evidence that a high quality p-n junction can be achieved by using this technique followed by a High Temperature Annealing (HTA) process.

Abstract: 8H-SiC epilayers grown on small 8H-SiC Lely platelets are investigated optically using photoluminescence spectroscopy. At low temperature the near band gap emission detected in the 2.78 to 2.67 eV range contains sharp lines associated to nitrogen-bound-exciton recombination. Three different no-phonon lines are detected accompanied by their phonon replicas. Free-exciton replicas are also observed which allows the determination of the excitonic band gap. The binding energy of the bound excitons can thus be determined and the ionization energies of the three nitrogen levels in 8H-SiC are estimated and found to be rather shallow compared to the values for other hexagonal polytypes. Additional bound-exciton lines are observed when the experimental photoluminescence temperature is increased.

Abstract: Epitaxial growth of about 200 µm thick, low doped 4H-SiC layers grown on n-type 8° off-axis Si-face substrates at growth rates around 100 µm/h has been done in order to realize thick epitaxial layers with excellent morphology suitable for high power devices. The study was done in a hot wall chemical vapor deposition reactor without rotation. The growth of such thick layers required favorable pre-growth conditions and in-situ etch. The growth of 190 µm thick, low doped epitaxial layers with excellent morphology was possible when the C/Si ratio was below 0.9. A low C/Si ratio and a favorable in-situ etch are shown to be the key parameters to achieve 190 µm thick epitaxial layers with excellent morphology.

Abstract: Abstract. The aim of this study is to compare DC characteristics of ‘as-grown’ and hydrogen (H)-intercalated epitaxial graphenes on SiC substrates [1,2]. Epitaxial graphene is grown on SiC at 1400-1600C, and H-intercalation is performed via in-situ introduction of Hydrogen during the graphitization process [6]. The fabrication processing steps used to define test structures are identical for the two materials. Results on the DC behaviour and uniformity issues with respect to both materials are reported. As-grown material behaves as a linear resistance, while H-intercalated demonstrates a non-linear characteristic. Hysteresis effects and time dependent behaviors are also observed in both materials. Extensive Hall measurements are performed on both materials with the aim of providing a qualitative understanding of material uniformity in both epi-graphenes.

Abstract: InGaN quantum dots (QDs) formed on top of GaN pyramids have been fabricated by means of selective area growth employing hot wall MOCVD. Upon regrowth of a patterned substrate, the growth will solely occur in the holes, which evolve into epitaxially grown wurtzite based pyramids. These pyramids are subsequently overgrown by a thin optically active InGaN well. The QDs are preferably nucleating at the apices of the pyramids as evidenced by the transmission electron microscopy (TEM). The emission from these QDs have been monitored by means of microphotoluminescence (μPL), in which single emission lines have been detected with a sub-meV line width. The μPL measurements undoubtedly reveal that the QDs are located in the apexes of the pyramids, since the sharp emission peaks can only be monitored as the excitation laser is focused on the apices in the µPL. It is also demonstrated that the emission energy can be changed in a controlled way by altering the growth conditions, like the growth temperature and/or composition, for the InGaN layers. The tip of the GaN pyramid is on the nm scale and can be made sharp or slightly truncated. TEM analysis combined with µPL results strongly indicate that the Stranski-Krastanow growth modepreferably is taking place at the microscopic c-plane truncation of the GaN pyramid. Single emission lines with a high degree of polarization is a common feature observed for individual QDs. This emission remains unchanged with increasing the excitation power and sample temperature. An in-plane elongated QD forming a shallow potential with an equal number of electrons and holes is proposed to explain the observed characteristics of merely a single exciton emission with a high degree of polarization.

Abstract: Epitaxial growth of 4H-SiC on 8º off-axis substrates has been performed under different condition during the temperature ramp up in order to study the effect on the carrot defect. The study was done in a hot wall chemical vapor deposition reactor using the single molecule precursor methyltrichlorosilane (MTS). During the temperature ramp up, a small flow of HCl or C2H4 was added to the H2 ambient to study different surface etching conditions. The best result was obtained when HCl was added from 1175 to 1520 °C during the ramp up to growth temperature (1575 °C).