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  • 1.
    Abdalla, Munir
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Dubaric, Ervin
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Fröjdh, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Petersson, Sture
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    A scintillator-coated phototransistor pixel sensor with dark current cancellation2001In: cecs2001: 8th IEEE international conference on electronics, circuits and systems, Vols. I-III, Conference Proceedings, 2001, p. 663-667Conference paper (Other academic)
  • 2.
    Bertilsson, Kent
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Dubaric, Ervin
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Hjelm, Mats
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Petersson, Sture
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Monte Carlo simulation of vertical MESFETs in 2H, 4H and 6H-SiC2001In: Diamond and related materials, ISSN 0925-9635, E-ISSN 1879-0062, Vol. 10, no 3-7, p. 1283-1286Article in journal (Refereed)
    Abstract [en]

    The 4H-SiC static induction transistor (SIT) is a very competitive device for high frequency and high power applications (3-6 GHz range). The large breakdown voltage and the high thermal conductivity of 4H-SiC allow transistors with extremely high current density at high voltages. The SIT transistor shows better output power capabilities but the unity current-gain frequency is lower compared to a MESFET device. In this work we show, using a very accurate numerical model, that a compromise between the features given by the SIT structure and the ordinary MESFET structure can be obtained using the vertical MESFET structure. The device dimension has been selected very aggressively to demonstrate the performance of an optimized technology. We also present results from drift-diffusion simulations of devices, using transport parameters obtained from the Monte Carlo simulation. The simulations indicate that 2H-SiC is superior to both 4H and 6H-SiC for vertical devices. For lateral devices, 2H-SiC is slightly faster compared to an identical 4H-SiC device

  • 3.
    Bertilsson, Kent
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Dubaric, Ervin
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Thungström, Göran
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Petersson, Sture
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Simulation of a low atmospheric-noise modified four-quadrant position sensitive detector2001In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 466, no 1, p. 183-187Article in journal (Refereed)
    Abstract [en]

    A modified four-quadrant position sensitive detector (PSD) is developed. This structure is less sensitive to atmospheric turbulence that is a major drawback with the traditional four-quadrant detector. The inter-electrode resistance is as high as for the four-quadrant detector, which is an advantage compared to the lateral effect PSD. The linearity for the modified four-quadrant detector is good in the whole active range of sensing. The structures are limited to small sensing areas with well focused beams and are suitable for use in detectors up to 1 mm in size.

  • 4.
    Dubaric, Ervin
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Simulations of Submicron MOSFETs in 2H, 4H and 6H-SiC2002In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 101, p. 14-17Article in journal (Refereed)
    Abstract [en]

    In this paper, we present numerical studies of the high frequency performance of a submicron MOSFET in 2H-, 4H- and 6H-SiC. The studies are based on simulations where commercial two-dimensional drift-diffusion and hydrodynamic carrier transport models have been used. The results have been compared with those obtained from full band Monte Carlo simulations. The Monte Carlo carrier transport model is based on data from a full potential band structure calculation using the Local Density Approximation to the Density Functional Theory. In 6H-SiC the bulk transport properties in the direction perpendicular to the c-axis, are slightly lower than in 2H- and 4H-SiC. However, in the direction parallel to the c-axis the transport properties are considerably less favourable than in the other two polytypes. The effects of these differences, on surface mobility device performance and carrier energy, have been studied.

  • 5.
    Dubaric, Ervin
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Fröjdh, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Hjelm, Mats
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Abdallah, Munir
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Pettersson, C.S.
    Monte Carlo simulations of the imaging properties of scintillator coated X-ray pixel detectors2000In: IEEE Nuclear Science Symposium and Medical Imaging Conference: vol. 1, IEEE conference proceedings, 2000, Vol. 1, p. 6/282-6/285Conference paper (Refereed)
    Abstract [en]

    The imaging properties of X-ray pixel detectors depend on the quantum efficiency for X-rays, the generated signal for each X-ray photon and the distribution of the generated signal between different pixels. In a scintillator coated device the signal is generated both by X-ray photons captured in the scintillator and by X-ray photons captured directly in the semiconductor. Hence, the signal-to-noise ratio (SNR) in the image is then a function of the number of photons captured in each of these processes, and the yield of each process, in terms of electron-hole pairs (EHPs) produced in the semiconductor. The full process from the absorption of the X-ray photon to the final signal read out from the detector has been simulated with a combination of the Monte Carlo program MCNP and the commercial carrier transport simulation tool MEDICI. An in house program calculating the light transport between the scintillator and the semiconductor serves as a link

  • 6.
    Dubaric, Ervin
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Fröjdh, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Petersson, Sture
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Resolution and Noise Properties of Scintillator Coated X-ray Detectors2001In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 466, no 1, p. 178-182Article in journal (Refereed)
    Abstract [en]

    The imaging properties of X-ray pixel detectors depend on the quantum efficiency of X-rays, the generated signal of each X-ray photon and the distribution of the generated signal between pixels. In a scintillator coated device the signal is generated both by X-ray photons captured in the scintillator and by X-ray photons captured directly in the semiconductor. The Signal-to-Noise Ratio in the image is then a function of the number of photons captured in each of these processes and the yield, in terms of electron-hole pairs produced in the semiconductor, of each process. The spatial resolution is primarily determined by the light spreading within the scintillator. In a pure semiconductor detector the signal is generated by one process only. The Signal-to-Noise Ratio in the image is proportional to the number of X-ray photons captured within the sensitive layer. The spatial resolution is affected by the initial charge cloud generated in the semiconductor and any diffusion of carriers between the point of interaction and the readout electrode. In this paper we discuss the theory underlying the imaging properties of scintillator coated X-ray imaging detectors. The model is verified by simulations using MCNP and by experimental results. The results from the two-layer detector are compared with those from a pure semiconductor X-ray detector.

  • 7.
    Dubaric, Ervin
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Hjelm, Mats
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Petersson, Sture
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Kackell, P
    The effect of different transport models in simulations of a 4H-SiC ultra short channel MOSFET1999In: Proceedings of International Conference on Microelectronics (ICM'99), 22-24 Nov. 1999 , Kuwait, 1999, p. 247-250Conference paper (Other academic)
  • 8.
    Dubaric, Ervin
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Fröjdh, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Norlin, Börje
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Monte Carlo simulation of the response of a pixellated 3D photodetector in silicon2002In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 487, no 1-2, p. 136-141Article in journal (Refereed)
    Abstract [en]

    The charge transport and X-ray photon absorption in three-dimensional (3D) X-ray pixel detectors have been studied using numerical simulations. The charge transport has been modelled using the drift-diffusion simulator MEDICI, while photon absorption has been studied using MCNP. The response of the entire pixel detector system in terms of charge sharing, line spread function and modulation transfer function, has been simulated using a system level Monte Carlo simulation approach. A major part of the study is devoted to the effect of charge sharing on the energy resolution in 3D-pixel detectors. The 3D configuration was found to suppress charge sharing much better than conventional planar detectors.

  • 9.
    Dubaric, Ervin
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Petersson, Sture
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Numerical modelling of the floating body enhanced breakdown in ultra small non-fully depleted SOI MOSFETs1999In: Physica scripta. T, ISSN 0281-1847, Vol. T79, p. 311-313Article in journal (Refereed)
  • 10.
    Hjelm, Mats
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Dubaric, Ervin
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Kackell, P
    Petersson, Sture
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Full band Monte Carlo simulation of a 100 nm 4H-SiC high frequency MOSFET1998In: Compound Semiconductors 1998. Proceedings of the Twenty-Fifth International Symposium on Compound Semiconductors 12-16 Oct. 1998 , Nara, Japan, 1998, p. 273-278Conference paper (Other academic)
  • 11.
    Hjelm, Mats
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Dubaric, Ervin
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Persson, C
    Käckell, P.
    Pettersson, C. S
    Full band Monte Carlo simulation of short channel MOSFETs in 4H and 6H-SiC1999In: Proceedings of Wide-Bandgap Semiconductors for High-Power, High-Frequency and High-Temperature Applications: Symposium held April 5-8, 1999, San Francisco, California, U.S.A., Warrendale, Pa.: Materials Research Society , 1999, p. 559-Conference paper (Refereed)
  • 12.
    Nilsson, Hans-Erik
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Dubaric, Ervin
    Hjelm, Mats
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Numerical simulation of field effect transistors in 4H and 6H-SiC2001Conference paper (Other academic)
    Abstract [en]

    Silicon Carbide is a very interesting semiconductor material for high temperature, high frequency, and high power applications. The main reasons are its high saturation velocity, large thermal conductivity, high Schottky barriers, and high breakdown voltages. High quality 4H-SiC and 6H-SiC polytype substrates and epitaxial layers are commercially available today. An additional advantage of SiC is the native oxide that allows fabrication of MOS devices. A large effort has been devoted towards the development of high performance devices in SiC. The largest success has been for unipolar devices like Schottky diodes and different kinds of MESFETs. MOSFETs have also been fabricated in both 4H- and 6H-SiC. Unfortunately, the MOSFET performance was found to be much worse than expected, due to a very low surface mobility. Nevertheless, the technology developed is very interesting and includes possible large scale integration of digital circuits operating at very high temperatures. In this work we present numerical simulations of the device performance of different Field Effect Transistors (FETs). Both full band Monte Carlo simulations and macroscopic modeling using the drift-diffusion approach have been utilized in this work. The Monte Carlo simulations have been used to extract transport parameters and to evaluate the macroscopic models in a device configuration

  • 13.
    Nilsson, Hans-Erik
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Hjelm, Mats
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Dubaric, Ervin
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Numerical Simulation of Field Effect Transistors in 4H- and 6H-SiC2002In: Journal of Wide Bandgap Materials, ISSN 1524-511X, E-ISSN 1530-8081, Vol. 9, no 4, p. 293-305Article in journal (Refereed)
    Abstract [en]

    Numerical simulations of microscopic and macroscopic device properties of field effect transistors in 4H- and 6H-SiC are presented. The microscopic properties have been simulated using a full band (ab initio method) Monte Carlo simulation model and the macroscopic properties have been simulated using a drift-diffusion model with transport parameters obtained from the Monte Carlo simulations. Different models for the SiC/SiO2 interface in SiC MOSFETs have been evaluated and compared with experimental data. Finally, we present a comparison of simulated device performance for MOSFETs and MESFETs in 4- and 6H-SiC technologies. Both vertical (SIT) and lateral MESFET structures have been considered

  • 14.
    Nilsson, Hans-Erik
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Dubaric, Ervin
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Hjelm, Mats
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Simulation of photon and charge transport in X-ray imaging semiconductor sensors2002In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 487, no 1-2, p. 151-162Article in journal (Refereed)
    Abstract [en]

    A fully stochastic model for the imaging properties of X-ray silicon pixel detectors is presented. Both integrating and photon counting configurations have been considered, as well as scintillator-coated structures. The model is based on three levels of Monte Carlo simulations; photon transport and absorption using MCNP, full band Monte Carlo simulation of charge transport and system level Monte Carlo simulation of the imaging performance of the detector system. In the case of scintillator-coated detectors, the light scattering in the detector layers has been simulated using a Monte Carlo method. The image resolution was found to be much lower in scintillator-coated systems due to large light spread in thick scintillator layers. A comparison between integrating and photon counting readout methods shows that the image resolution can be slightly enhanced using a photon-counting readout. In addition, the proposed model has been used to study charge-sharing effects on the energy resolution in photon counting detectors. The simulation shows that charge-sharing effects are pronounced in pixel detectors with a pixel size below 170 * 170 mu m2. A pixel size of 50 * 50 mu m2 gives a highly distorted energy spectrum due to charge sharing. This negative effect can only be resolved by introducing advanced counting schemes, where neighbouring pixels communicate in order to resolve the charge sharing.

  • 15.
    Nilsson, Hans-Erik
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Dubaric, Ervin
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Hjelm, Mats
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Englund, U.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Monte Carlo simulation of the transient response of single photon absorption in X-ray pixel detectors2003In: Mathematics and Computers in Simulation, ISSN 0378-4754, E-ISSN 1872-7166, Vol. 62, p. 471-478Article in journal (Refereed)
    Abstract [en]

    A Monte Carlo study of the transient response of single photon absorption in X-ray pixel detectors is presented. The simulation results have been combined with Monte Carlo simulation of the X-ray photon transport and absorption, and used to estimate the image properties of a detector system, including the pixel array and readout electronics. The study includes several different simulation challenges, such as full band Monte Carlo simulation of charge transport in large devices (300 mu m * 100 mu m), modelling of three-dimensional electrostatic effects using cylindrical coordinates, Monte Carlo simulation of photon transport and absorption, and a system level Monte Carlo simulation of the entire pixel detector and readout

  • 16.
    Nilsson, Hans-Erik
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Fröjdh, Christer
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Dubaric, Ervin
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Monte Carlo simulation of charge sharing effects in silicon and GaAs photon-counting X-ray imaging detectors2004In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 51, no 4, p. 1636-1640Article in journal (Refereed)
    Abstract [en]

    In this work we present a numerical study of charge sharing in photon counting X-ray imaging detectors. The study is based on charge transport simulations combined with a system level Monte Carlo simulation code to calculate the energy resolution of different pixel detector configurations. Our simulations show that the charge sharing is very sensitive to the electric field distribution in the device, and that the higher doping levels used in GaAs detectors reduce the effect of charge sharing significantly. Our study concludes that one of advantage's in using very heavy semiconductor materials in X-ray imaging detectors is the possibility to suppress charge sharing utilizing structures with much higher electric field. A 100 mum thick epitaxial GaAs detector absorbs 52% of the photons, while a 300 pin thick Silicon detector absorbs only 8% of the photons (30keV source). In addition to the superior stopping power, the GaAs detector has 5 times lower charge diffusion, resulting in superior spatial and energy resolution.

  • 17.
    Thungström, Göran
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Dubaric, Ervin
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Svensson, B.G.
    Royal Institute of Technology, Dept. Electronics, Electrum 229, S., Stockholm.
    Processing of silicon UV-photodetectors2001In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 460, no 1, p. 165-184Article in journal (Refereed)
    Abstract [en]

    UV-enhanced photodetectors of both n+-p and p+-n type have been processed in silicon. Photodetectors of the p+-n type display a responsivity close to the theoretical limit with an antireflective coating of either thermally grown dry silicon dioxide or deposited oxide (TEOS), followed by a short wet oxidizing step. This holds, irrespective of whether the detector window is doped by boron through ion implantation or diffusion from a solid source. However, for p+-n photodiodes with a TEOS-oxide in the as-deposited state the responsivity decreases substantially for wavelenghts below 500 nm compared to the theoretical predictions. This is attributed to a high recombination velocity at the silicon dioxide/silicon interface, as supported by computer simulations of the detector performance. In contrast, n+-p photodiodes are found to be rather insensitive with respect to the properties of the silicon dioxide/silicon interface. These results provide the first experimental demonstration that high built in electric fields, caused by abrupt dopant profiles, can suppress the influence of a high interface carrier recombination velocity.

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