G. Gudjonsson

Publications (7)11.16 Total impact

• Article: A strong reduction in the density of near-interface traps at the SiO2/4H-SiC interface by sodium enhanced oxidation

  F. Allerstam, H. O. Olafsson, G. Gudjonsson, D. Dochev, E. O. Sveinbjornsson, T. Rodle, R. Jos
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  ABSTRACT: This paper demonstrates how sodium enhanced oxidation of Si face 4H- Si C results in removal of near-interface traps at the Si O ₂/4H- Si C interface. These detrimental traps have energy levels close to the SiC conduction band edge and are responsible for low electron inversion channel mobilities (1–10 cm ²/ V s ) in Si face 4H- Si C metal-oxide-semiconductor field effect transistors. The presence of sodium during oxidation increases the oxidation rate and suppresses formation of these near-interface traps resulting in high inversion channel mobility of 150 cm ²/ V s in such transistors. Sodium is incorporated by using carrier boats made of sintered alumina during oxidation or by deliberate sodium contamination of the oxide during the formation of the Si C / Si O ₂ interface.
  Journal of Applied Physics 07/2007; · 2.17 Impact Factor
• Article: High-power-density 4H-SiC RF MOSFETs

  G. Gudjonsson, F. Allerstam, H.O. Olafsson, P.A. Nilsson, H. Hjelmgren, K. Andersson, E.O. Sveinbjornsson, H. Zirath, T. Rodle, R. Jos
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  ABSTRACT: The authors have made the first 4H-SiC RF power MOSFETs with cutoff frequency up to 12 GHz, delivering RF power of 1.9 W/mm at 3 GHz. The transistors withstand 200 V drain voltage, are normally off, and show no gate lag, which is often encountered in SiC MESFETs. The measured devices have a single drain finger and a double gate finger, and a total gate width of 0.8 mm. To their knowledge, this is the first time that power densities above 1 W/mm at 3 GHz are reported for SiC MOSFETs.
  IEEE Electron Device Letters 07/2006; · 2.85 Impact Factor
• Article: Stable operation of high mobility 4H-SiC MOSFETs at elevated temperatures

  H.O. Olafsson, G. Gudjonsson, F. Allerstam, E.O. Sveinbjornsson, T. Rodle, R. Jos
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  ABSTRACT: Stable operation of normally-off high mobility 4H-SiC MOSFET transistors from room temperature up to 150°C is reported. The output current in saturation is decreased by about 20% at 150°C as compared to room temperature. This small decrease in current with temperature is attributed to a decrease in the field effect mobility due to phonon scattering.
  Electronics Letters 08/2005; · 0.96 Impact Factor
• Article: High field-effect mobility in n-channel Si face 4H-SiC MOSFETs with gate oxide grown on aluminum ion-implanted material

  G. Gudjonsson, H.O. Olafsson, F. Allerstam, P.-A. Nilsson, E.O. Sveinbjornsson, H. Zirath, T. Rodle, R. Jos
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  ABSTRACT: We report investigations of Si face 4H-SiC MOSFETs with aluminum (Al) ion-implanted gate channels. High-quality SiO₂-SiC interfaces are obtained both when the gate oxide is grown on p-type epitaxial material and when grown on ion-implanted regions. A peak field-effect mobility of 170 cm²/V·s is extracted from transistors with epitaxially grown channel region of doping 5×10¹⁵ cm^-3. Transistors with implanted gate channels with an Al concentration of 1×10¹⁷ cm^-3 exhibit peak field-effect mobility of 100 cm²/V·s, while the mobility is 51 cm²/V·s for an Al concentration of 5×10¹⁷ cm^-3. The mobility reduction with increasing acceptor density follows the same functional relationship as in n-channel Si MOSFETs.
  IEEE Electron Device Letters 03/2005; · 2.85 Impact Factor
• Article: High field effect mobility in Si face 4H-SiC MOSFET transistors

  H.O. Olafsson, G. Gudjonsson, P.-A. Nilsson, E.O. Sveinbjornsson, H. Zirath, T. Rodle, R. Jos
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  ABSTRACT: A report is made on field effect mobility of 150 cm²/Vs in lateral n-channel Si face 4H-SiC MOSFETs made by gate oxidation in N₂O ambient. The high mobility is correlated with a two orders of magnitude reduction in density of interface states near the SiC conduction band edge when compared to gate oxides made in a wet or dry oxygen ambient.
  Electronics Letters 05/2004; · 0.96 Impact Factor
• Article: Sexual adjustment and its predictors after traumatic brain injury.

  M Kreuter, A G Dahllöf, G Gudjonsson, M Sullivan, A Siösteen
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  ABSTRACT: The aim of this study was to investigate the impact of traumatic brain injury (TBI) on sexual ability, activity and satisfaction and to relate the findings to neurological status, functioning and well-being. A total of 92 TBI persons (65 men, 27 women) participated. Their ages ranged from 20-70 years (median 40 years); the median age at injury was 32 years, ranging from 16-56 years. The elapsed time since injury ranged from 1-20 years (median 9 years). The participants were examined according to a procedure including neurological examination, self-assessment of general health status and functioning and mood, and collection of data on social conditions. A structured study-specific questionnaire was developed to assess various aspects of sexuality before and after the injury. Fifty-three of the participants had a stable partner relationship at the time of the investigation. This study showed that a TBI commonly alters sexual functioning as well as desire. Many of the respondents reported decreased ability to achieve an erection, decreased ability to experience organism, decreased sexual desire and diminished frequency of intercourse. A high degree of physical independence and maintained sexual ability were the most important predictors for sexual adjustment. Considering that many TBI persons in this study reported physiological sexual disturbances and decreased sexual ability, it is important to inform patients about possibilities of optimizing their sexual ability. Organized programmes of sexuality education should be an integral component of TBI rehabilitation.
  Brain Injury 06/1998; 12(5):349-68. · 1.36 Impact Factor
• Article: The functional independence measure in Sweden: experience for outcome measurement in rehabilitation medicine.

  G Grimby, G Gudjonsson, M Rodhe, K S Sunnerhagen, V Sundh, M L Ostensson
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  ABSTRACT: The purpose of the study was to describe the Functional Independence Measure (FIM) in Sweden and to analyse some aspects on its structure and the possibility to predict length of stay in a rehabilitation ward. It assesses the degree of dependence with 13 physical and 5 social and cognitive items, using a 7-level ordinal scale. Data are presented from a total of 312 patients and from 267 first admission patients with a mean age of 45 (SD 13) years, 66% being men, in rehabilitation medicine wards in three hospitals in Sweden. The patients were divided into six diagnostic groups. Ratings were made at admission and at discharge. The level of dependence in physical and social cognitive items was reduced during the stay at the ward. Using Rasch analysis, separate physical and social-cognitive items and personal measures were obtained on a linear scale. It was demonstrated that the relative order of the items was similar at admission and discharge. There were minor differences between diagnostic groups for the physical items, whereas more diagnostic-specific differences were seen for the social-cognitive items, for stroke patients with and without aphasia. Individual statistics were used for demonstrating FIM changes during the rehabilitation period. There was a high correlation between admission and discharge FIM values, and the admission FIM (physical items) accounted for up to nearly 50% of the variation in length of stay in a homogeneous sample such as stroke patients, but for less than 40% in the total sample. FIM can be used to follow changes during inpatient rehabilitation and for comparisons between different rehabilitation units.
  Scandinavian Journal of Rehabilitation Medicine 06/1996; 28(2):51-62.