| 1. |
- Badel, Xavier, et al.
(författare)
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Doping of electrochemically etched pore arrays in n-type silicon : processing and electrical characterization
- 2005
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 152:4, s. G252-G258
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Tidskriftsartikel (refereegranskat)abstract
- Silicon p-n diodes formed in the walls of deep pores have been electrically characterized. The pores were electrochemically etched in low-doped n-type silicon substrates, and the entire pore array was doped p(+) by boron diffusion at 1050 degrees C. Two different process flows were investigated to disconnect the p(+) layers from one pore to another. The first consists of removing a few micrometers of silicon at the top of the sample using reactive ion etching after diffusion while the second enables the prevention of doping at the top of the pore walls with an oxide, acting as a barrier during diffusion. Current-voltage and capacitance-voltage characteristics of p-n junctions are presented and related parameters, such as the serial resistance and the ideality factor are discussed. The results show good rectifying behavior of the diodes with a reverse current about four to five decades smaller than the forward current. Measurements with two pores connected in a transistor-like configuration (p(+)/n(-)/p(+)), were also performed. Device simulations were used to examine the device behavior. Finally, our results demonstrate that pores could work as individual detector pixels for moderate reverse voltages, suitable for radiation imaging applications.
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| 2. |
- Buchholt, Kristina, et al.
(författare)
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Growth and characterization of epitaxial Ti3GeC2 thin films on 4H-SiC(0001)
- 2012
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Ingår i: Journal of Crystal Growth. - : Elsevier. - 0022-0248 .- 1873-5002. ; 343:1, s. 133-137
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial Ti3GeC2 thin films were deposited on 4 degrees off-cut 4H-SiC(0001) using magnetron sputtering from high purity Ti, C, and Ge targets. Scanning electron microscopy and helium ion microscopy show that the Ti3GeC2 films grow by lateral step-flow with {11 (2) over bar0} faceting on the SiC surface. Using elastic recoil detection analysis, atomic force microscopy, and X-Ray diffraction the films were found to be substoichiometric in Ge with the presence of small Ge particles at the surface of the film.
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| 3. |
- Buchholt, Kristina, et al.
(författare)
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Ohmic contact properties of magnetron sputtered Ti3SiC2 on n- and p-type 4H-silicon carbide
- 2011
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 98:4, s. 042108-
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial Ti3SiC2 (0001) thin film contacts were grown on doped 4H-SiC (0001) using magnetron sputtering in an ultra high vacuum system. The specific contact resistance was investigated using linear transmission line measurements. Rapid thermal annealing at 950 degrees C for 1 min of as-deposited films yielded ohmic contacts to n-type SiC with contact resistances in the order of 10(-4) Omega cm(2). Transmission electron microscopy shows that the interface between Ti3SiC2 and n-type SiC is atomically sharp with evidence of interfacial ordering after annealing. (c) 2011 American Institute of Physics.
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| 4. |
- Buono, Benedetto, et al.
(författare)
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Current Gain Degradation in 4H-SiC Power BJTs
- 2011
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Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 679-680, s. 702-705
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Tidskriftsartikel (refereegranskat)abstract
- SiC airs are very attractive for high power application, but long term stability is still problematic and it could prohibit commercial production of these devices. The aim of this paper is to investigate the current gain degradation in BJTs with no significant degradation of the on-resistance. Electrical measurements and simulations have been used to characterize the behavior of the BJT during the stress test. Current gain degradation occurs, the gain drops from 58 before stress to 43 after 40 hours, and, moreover, the knee current shows fluctuations in its value during the first 20 hours. Current gain degradation has been attributed to increased interface traps or reduced lifetime in the base-emitter region or small stacking faults in the base-emitter region, while fluctuations of the knee current might be due to stacking faults in the collector region.
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| 5. |
- Buono, Benedetto, et al.
(författare)
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Influence of Emitter Width and Emitter-Base Distance on the Current Gain in 4H-SiC Power BJTs
- 2010
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Ingår i: IEEE Transactions on Electron Devices. - 0018-9383 .- 1557-9646. ; 57:10, s. 2664-2670
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the emitter-base geometry on the current gain has been investigated by means of measurements and simulations. Particular attention has been placed on the emitter width and on the distance between the emitter edge and the base contact. When the emitter width is decreased from 40 to 8 mu m, the current gain is reduced by 20%, whereas when the distance between the base contact and the emitter edge is decreased from 5 to 2 mu m, the current gain is reduced by 10%. Simulations have been used to investigate the reasons for the current gain reduction. The reduction of the emitter width induces two mechanisms of current gain reduction: earlier forward biasing of the base-collector junction and higher recombination in the emitter region. Both mechanisms result from the higher current density flowing under the emitter region. Placing the base contact very close to the emitter edge increases the base current by increasing the gradient of the electron concentration toward the base contact. The effect of increasing the base doping in the extrinsic region has been simulated, and the results demonstrate that the current gain can be improved if a high doping concentration in the range of 5 x 10(18) cm(-3) is used.
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| 6. |
- Buono, Benedetto, et al.
(författare)
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Investigation of Current Gain Degradation in 4H-SiC Power BJTs
- 2012
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Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 717-720, s. 1131-1134
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Tidskriftsartikel (refereegranskat)abstract
- The current gain degradation of 4H-SiC BJTs with no significant drift of the on-resistance is investigated. Electrical stress on devices with different emitter widths suggests that the device design can influence the degradation behavior. Analysis of the base current extrapolated from the Gummel plot indicates that the reduction of the carrier lifetime in the base region could be the cause for the degradation of the gain. However, analysis of the base current of the base-emitter diode shows that the degradation of the passivation layer could also influence the reduction of the current gain.
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| 7. |
- Buono, Benedetto, et al.
(författare)
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Modeling and Characterization of Current Gain Versus Temperature in 4H-SiC Power BJTs
- 2010
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Ingår i: IEEE Transactions on Electron Devices. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9383 .- 1557-9646. ; 57:3, s. 704-711
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Tidskriftsartikel (refereegranskat)abstract
- Accurate physical modeling has been developed to describe the current gain of silicon carbide (SiC) power bipolar junction transistors (BJTs), and the results have been compared with measurements. Interface traps between SiC and SiO2 have been used to model the surface recombination by changing the trap profile, capture cross section, and concentration. The best agreement with measurement is obtained using one single energy level at 1 eV above the valence band, a capture cross section of 1 x 10(-15) cm(2), and a trap concentration of 2 x 10(12) cm(-2). Simulations have been performed at different temperatures to validate the model and characterize the temperature behavior of SiC BJTs. An analysis of the carrier concentration at different collector currents has been performed in order to describe the mechanisms of the current gain fall-off at a high collector current both at room temperature and high temperatures. At room temperature, high injection in the base ( which has a doping concentration of 3 x 10(17) cm(-3)) and forward biasing of the base-collector junction occur simultaneously, causing an abrupt drop of the current gain. At higher temperatures, high injection in the base is alleviated by the higher ionization degree of the aluminum dopants, and then forward biasing of the base-collector junction is the acting mechanism for the current gain fall-off. Forward biasing of the base-collector junction can also explain the reduction of the knee current with increasing temperature by means of the negative temperature dependence of the mobility.
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| 8. |
- Buono, Benedetto, et al.
(författare)
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Modeling and Characterization of the ON-Resistance in 4H-SiC Power BJTs
- 2011
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Ingår i: IEEE Transactions on Electron Devices. - 0018-9383 .- 1557-9646. ; 58:7, s. 2081-2087
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Tidskriftsartikel (refereegranskat)abstract
- The ON-resistance of silicon carbide bipolar transistors is characterized and simulated. Output characteristics are compared at different base currents and different temperatures in order to validate the physical model parameters. A good agreement is obtained, and the key factors, which limit the improvement of R-ON, are identified. Surface recombination and material quality play an important role in improving device performances, but the device design is also crucial. Based on simulation results, a design that can enhance the conductivity modulation in the lowly doped drift region is proposed. By increasing the base doping in the extrinsic region, it is possible to meet the requirements of having low voltage drop, high current density, and satisfactory forced current gain. According to simulation results, if the doping is 5 x 10(18) cm(-3), it is possible to conduct 200 A/cm(2) at V-CE = 1 V by having a forced current gain of about 8, which represents a large improvement, compared with the simulated value of only one in the standard design.
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| 9. |
- Buono, Benedetto
(författare)
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Simulation and Characterization of Silicon Carbide Power Bipolar Junction Transistors
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The superior characteristics of silicon carbide, compared with silicon, have suggested considering this material for the next generation of power semiconductor devices. Among the different power switches, the bipolar junction transistor (BJT) can provide a very low forward voltage drop, a high current capability and a fast switching speed. However, in order to compete on the market, it is crucial to a have high current gain and a breakdown voltage close to ideal. Moreover, the absence of conductivity modulation and long-term stability has to be solved. In this thesis, these topics are investigated comparing simulations and measurements. Initially, an efficient etched JTE has been simulated and fabricated. In agreement with the simulations, the fabricated diodes exhibit the highest BV of around 4.3 kV when a two-zone JTE is implemented. Furthermore, the simulations and measurements demonstrate a good agreement between the electric field distribution inside the device and the optical luminescence measured at breakdown. Additionally, an accurate model to simulate the forward characteristics of 4H-SiC BJTs is presented. In order to validate the model, the simulated current gains are compared with measurements at different temperatures and different base-emitter geometries. Moreover, the simulations and measurements of the on-resistance are compared at different base currents and different temperatures. This comparison, coupled with a detailed analysis of the carrier concentration inside the BJT, indicates that internal forward biasing of the base-collector junction limits the BJT to operate at high current density and low forward voltage drop simultaneously. In agreement with the measurements, a design with a highly-doped extrinsic base is proposed to alleviate this problem. In addition to the static characteristics, the comparison of measured and simulated switching waveforms demonstrates that the SiC BJT can provide fast switching speed when it acts as a unipolar device. This is crucial to have low power losses during transient. Finally, the long-term stability is investigated. It is observed that the electrical stress of the base-emitter diode produces current gain degradation; however, the degradation mechanisms are still unclear. In fact, the analysis of the measured Gummel plot suggests that the reduction of the carrier lifetime in the base-emitter region might be only one of the causes of this degradation. In addition, the current gain degradation due to ionizing radiation is investigated comparing the simulations and measurements. The simulations suggest that the creation of positive charge in the passivation layer can increase the base current; this increase is also observed in the electrical measurements.
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| 10. |
- Buono, Benedetto, et al.
(författare)
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Simulations of Open Emitter Breakdown Voltage in SiC BJTs with non Implanted JTE
- 2009
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Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 615-617, s. 841-844
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Tidskriftsartikel (refereegranskat)abstract
- Ion implantation for selective doping of SiC is problematic due to damage generation during the process and low activation of dopants. In SiC bipolar junction transistor (BJT) the junction termination extension (JTE) can be formed without ion implantation using instead a controlled etching into the epitaxial base. This etched JTE is advantageous because it eliminates ion implantation induced damage and the need for high temperature annealing. However, the dose, which is controlled by the etched base thickness and doping concentration, plays a crucial role. In order to find the optimum parameters, device simulations of different etched base thicknesses have been performed using the software Sentaurus Device. A surface passivation layer consisting of silicon dioxide, considering interface traps and fixed trapped charge, has been included in the analysis by simulations. Moreover a comparison with measured data for fabricated SiC BJTs has been performed.
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