Papers by Author: Jawad ul Hassan

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Authors: Pierre Brosselard, Nicolas Camara, Jawad ul Hassan, Xavier Jordá, Peder Bergman, Josep Montserrat, José Millan
Abstract: An innovative process has been developed by Linköping University to prepare the 4HSiC substrate surface before epitaxial growth. The processed PiN diodes have been characterized in forward and reverse mode at different temperature. The larger diodes (2.56 mm2) have a very low leakage current around 20 nA @ 500V for temperatures up to 300°C. A performant yield (68%) was obtained on these larger diodes have a breakdown voltage superior to 500V. Electroluminescence characteristics have been done on these devices and they show that there is no generation of Stacking Faults during the bipolar conduction.
Authors: Jawad ul Hassan, Peder Bergman, Anne Henry, Henrik Pedersen, Patrick J. McNally, Erik Janzén
Abstract: We report on the growth of 4H-SiC epitaxial layer on Si-face polished nominally on-axis 2” full wafer, using Hot-Wall CVD epitaxy. The polytype stability has been maintained over the larger part of the wafer, but 3C inclusions have not been possible to avoid. Special attention has given to the mechanism of generation and propagation of 3C polytype in 4H-SiC epilayer. Different optical and structural techniques were used to characterize the material and to understand the growth mechanisms. It was found that all 3C inclusions were generated at the interface between the substrate and the epitaxial layer, and no 3C inclusions were initiated at later stages of the growth.
Authors: Michael Winters, Mattias Thorsell, Jawad ul Hassan, Niklas Rorsman, Erik Janzén, Herbert Zirath
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.
Authors: Y. Shishkin, Shailaja P. Rao, Olof Kordina, I. Agafonov, Andrei A. Maltsev, Jawad ul Hassan, Anne Henry, Catherine Moisson, Stephen E. Saddow
Abstract: Crystal growth of 6H-SiC in two non-basal directions is reported. The two explored surfaces are the {1-103} plane, named qC-face, and the {1-10-3} plane, named qSi-face. The asgrown bulk surfaces exhibit a smooth structure with a small ridging effect originating from the miscut of the seed crystals. Layers, epitaxially grown on the chemically-mechanically polished qCface, nicely replicate the original crystal structure and show no sign of polytype mixing. Lowtemperature photoluminescence measurements collected on the epilayers exhibit near bandedge spectral characteristics indicative of good quality 6H-SiC.
Authors: Henrik Pedersen, Anne Henry, Jawad ul Hassan, Peder Bergman, Erik Janzén
Abstract: Epitaxial layers were grown in a horizontal hot-wall CVD reactor and intentionally doped with aluminium in a wide concentration range by varying the flow of aluminium into the reactor. The layers were grown on 4H and 6H SiC substrates on both Si and C face. Low temperature photoluminescence (LTPL) has been used to characterize the layers; 6H-SiC show differences in the structure of the Al bound-exciton (Al-BE) between the two faces, suggesting that the site preference is face dependent. From the LTPL spectra the Al concentration in the layers can be estimated.
Authors: Jawad ul Hassan, Peder Bergman, Justinas Palisaitis, Anne Henry, Patrick J. McNally, S. Anderson, Erik Janzén
Abstract: Homoepitaxial growth has been performed on 3” Si-face on-axis 4H–SiC substrates using standard gas system in a horizontal Hot-wall chemical vapor deposition system. Substrate surface damages are found to act as preferential nucleation sites for 3C inclusions also, the surface morphology after in-situ etching is found to largely influence the polytype stability in the epilayer. Different in-situ etching conditions were studied where Si-rich conditions are found to be better. Growth parameters and starting growth conditions are refined to obtain stable polytype in the epilayer. High quality homoepitaxial layers with 100% 4H–SiC are obtained on 3” substrates. Different optical and structural techniques are used to characterize the layers and to understand the growth mechanisms. The layers are found to be of high quality and no epitaxial defects typically found on off-axis epitaxial layers are observed. A high surface roughness is observed in these layers, however higher growth rate significantly lowers the surface roughness without affecting the polytype stability in the epilayer.
Authors: Jawad ul Hassan, Peder Bergman, Anne Henry, Erik Janzén
Abstract: The effect of different C/Si ratio on the surface morphology has been studied to optimize the on-axis homoepitaxial growth conditions on 4H-SiC substrates to improve the surface roughness of epilayers. The overall surface roughness is found to decrease with decreasing C/Si ratio. An order of magnitude lower surface roughness has been observed using C/Si ratio = 0.8 without disturbing the polytype stability in the epilayer. A high growth rate of 10 µm/h was achieved without introducing 3C inclusions. The epilayers grown at higher growth rate with C/Si ratio = 1 also had improvements in the surface roughness. 100% 4H polytype was maintained in the epilayers grown with C/Si ratio in the range of 1.2 to 0.8 and with high growth rate of 10 µm/h.
Authors: Jawad ul Hassan, Peder Bergman
Abstract: Thick 4H-SiC epitaxial layers have been characterized using high-resolution lifetime mapping. The lifetime maps are obtain by the detection of photoluminescence decay of the band gap emission. Full wafers mappings with 200 m resolution reveal lifetime variations that can be associated with structural defects replicated from the substrate, and variations in epitaxial growth conditions due to the susceptor design. High resolution mapping over smaller regions with down to 20 m step size, reveals local lifetime reductions associated with different structural defects in the epitaxial layer. Identified defects that influence the lifetime are the carrot defect, different types of in-grown stacking faults, and an unidentified defect associated with a pair of basal plane dislocations on the surface. Also clusters of threading screw dislocations, probably originating from a dissociated micropipe in the substrate, are found to reduce the lifetime.
Authors: Hervé Peyre, J.W. Sun, Jude Guelfucci, Sandrine Juillaguet, Jawad ul Hassan, Anne Henry, Sylvie Contreras, Pierre Brosselard, Jean Camassel
Abstract: Focusing on the change in aluminium-related photoluminescence lines in 4H-SiC versus doping concentration, we have used a combination of LTPL (Low Temperature PhotoLuminescence) and secondary ion mass spectrometry measurements to set new calibration curves. In this way, one can probe the change in aluminum concentration in the range 1017 to 1019 cm-3. When applied to LTPL maps collected on full 3-inch wafers, we show that such abacuses constitute a powerful tool to control efficiently the doping level of as-grown p+ (emitters) and p++ (contact) layers for power device applications.
Authors: Nicolas Dheilly, Dominique Planson, Pierre Brosselard, Jawad ul Hassan, Pascal Bevilacqua, Dominique Tournier, Josep Montserrat, Christophe Raynaud, Hervé Morel
Abstract: This paper reports on the influence of temperature on the electrical carrier lifetime of a 3.3 kV 4H-SiC PiN diode processed with a new generation of SiC material. The Open Circuit Voltage Decay (OCVD) is used to evaluate ambipolar lifetime evolution versus temperature. The paper presents a description of the setup, electrical measurements and extraction fittings. The ambipolar lifetime is found to rise from 600 ns at 30 °C to 3.5 μs at 150 °C.
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