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1.	Buono, Benedetto, et al. (författare) Current Gain Degradation in 4H-SiC Power BJTs 2011 Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 679-680, s. 702-705 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.
2.	Buono, Benedetto, et al. (författare) Influence of Emitter Width and Emitter-Base Distance on the Current Gain in 4H-SiC Power BJTs 2010 Ingår i: IEEE Transactions on Electron Devices. - 0018-9383 .- 1557-9646. ; 57:10, s. 2664-2670 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.
3.	Buono, Benedetto, et al. (författare) Investigation of Current Gain Degradation in 4H-SiC Power BJTs 2012 Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 717-720, s. 1131-1134 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.
4.	Buono, Benedetto, et al. (författare) Modeling and Characterization of Current Gain Versus Temperature in 4H-SiC Power BJTs 2010 Ingår i: IEEE Transactions on Electron Devices. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9383 .- 1557-9646. ; 57:3, s. 704-711 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.
5.	Buono, Benedetto, et al. (författare) Modeling and Characterization of the ON-Resistance in 4H-SiC Power BJTs 2011 Ingår i: IEEE Transactions on Electron Devices. - 0018-9383 .- 1557-9646. ; 58:7, s. 2081-2087 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.
6.	Buono, Benedetto, et al. (författare) Simulations of Open Emitter Breakdown Voltage in SiC BJTs with non Implanted JTE 2009 Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 615-617, s. 841-844 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.
7.	Buono, Benedetto, et al. (författare) Temperature Modeling and Characterization of the Current Gain in 4H-SiC Power BJTs 2010 Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 645-648, s. 1061-1064 Tidskriftsartikel (refereegranskat)abstract The current gain of 4H-SiC BJTs has been modeled using interface traps between SIC and SiO2 to describe surface recombination, by a positive temperature dependence of the carrier lifetime in the base region and by bandgap narrowing in the emitter region. The interface traps have been modeled by one single level at 1 eV above the valence band, with capture cross section of 1 x 10(-15) cm(2) and concentration of 2 x 10(12) cm(-2). The temperature behavior of SiC BJTs has been simulated and the results have been compared with measurements. An analysis of the carrier concentration has been performed in order to describe the mechanisms for fall-off of the current gain at high collector current. At room temperature high injection in the base 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 only acting mechanism for the current gain fall-off at high collector current. This mechanism and the negative temperature dependence of the carrier mobility can also explain the reduction of the knee current for gain fall-off with increasing temperature. Simulations with different emitter widths have been also performed and analyzed to characterize the emitter size effect. Higher current density caused by reducing the emitter width introduces higher carrier recombination in the emitter region, leading to a reduction of the current gain.
8.	Cho, H., et al. (författare) Ultradeep, low-damage dry etching of SiC 2000 Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 76:6, s. 739-741 Tidskriftsartikel (refereegranskat)abstract The Schottky barrier height (Phi(B)) and reverse breakdown voltage (V-B) of Au/n-SiC diodes were used to examine the effect of inductively coupled plasma SF6/O-2 discharges on the near-surface electrical properties of SiC. For low ion energies (less than or equal to 60 eV) in the discharge, there is minimal change in Phi(B) and V-B, but both parameters degrade at higher energies. Highly anisotropic features typical of through-wafer via holes were formed in SiC using an Al mask.
9.	Dahlquist, Fanny, et al. (författare) 2.8 kV, forward drop JBS diode with low leakage 2000 Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 338-342, s. 1179-1182 Tidskriftsartikel (refereegranskat)abstract High voltage Schottky-, Junction Barrier Schottky (JBS)- and PiN-diodes with an implanted JTE termination have been fabricated on the same 4H-SiC wafer. Blocking voltages of 2.5-2.8 kV were reached for JBS and PiN diodes while the Schottky diodes reach about 2.0 kV. It is shown that the JBS design increases the blocking voltage effectively compared to the Schottky device with less than 10% increase in on-state static losses. Also, a comparison of static losses to a PiN diode gives a decrease of 40% for the JBS. The leakage current is also lowered by two decades compared to the Schottky device at its blocking voltage. Temperature measurements show that the low leakage current is maintained up to at least 225 Â°C.
10.	Dahlquist, Fanny, et al. (författare) Junction barrier Schottky diodes in 4H-SiC and 6H-SiC 1998 Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 264-268:PART 2, s. 1061-1064 Tidskriftsartikel (refereegranskat)abstract The Junction Barrier Schottky (JBS) diode in silicon carbide is a promising candidate for a low-leakage power rectifier for high switching frequencies and elevated temperature operation. It has the advantage of a low forward voltage drop while keeping a low leakage current at high blocking voltage. JBS devices have been fabricated in 4H SiC and 6H SiC and then electrically characterised in comparison with pn and Schottky diodes on the same wafer. The JBS devices reached blocking voltages up to 1.0 kV at a leakage current density of 13 ÎŒA/cm2 and the forward conduction was limited by an on-resistance close to the theoretical value.
11.	Danielson, E., et al. (författare) Investigation of thermal properties in fabricated 4H-SiC high power bipolar transistors 2003 Ingår i: Solid-State Electronics. - 0038-1101 .- 1879-2405. ; 47:4, s. 639-644 Tidskriftsartikel (refereegranskat)abstract Silicon carbide bipolar junction transistors have been fabricated and investigated. The transistors had a maximum current gain of approximately 10 times, and a breakdown voltage of 450 V. When operated at high power densities the device showed a clear self-heating effect, decreasing the current gain. The junction temperature was extracted during self-heating to approximately 150 degreesC, using the assumption that the current gain only depends on temperature. Thermal images of a device under operation were also recorded using an infrared camera, showing a significant temperature increase in the vicinity of the device. The device was also tested in a switched setup, showing fast turn on and turn off at 1 MHz and 300 V supply voltage. Device simulations have been used to analyze the measured data. The thermal conductivity is fitted against the self-heating, and the lifetime in the base is fitted against the measurement of the current gain.
12.	Danielsson, Erik, et al. (författare) A 4H-SiC BJT with an epitaxially regrown extrinsic base layer 2005 Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 483, s. 905-908 Tidskriftsartikel (refereegranskat)abstract 4H-SiC BJTs were fabricated using epitaxial regrowth instead of ion implantation to form a highly doped extrinsic base layer necessary for a good base ohmic contact. A remaining p(+) regrowth spacer at the edge of the base-emitter junction is proposed to explain a low current gain of 6 for the BJTs. A breakdown voltage of 1000 V was obtained for devices with Al implanted JTE.
13.	Danielsson, E., et al. (författare) Characterization of heterojunction diodes with hydride vapor phase epitaxy grown AlGaN on 4H-SiC 2002 Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 91:4, s. 2372-2379 Tidskriftsartikel (refereegranskat)abstract AlGaN/4H-SiC heterojunction diodes with varying composition of Al have been fabricated. Five different compositions were investigated, GaN, Al0.1Ga0.9N, Al0.15Ga0.85N, Al0.3Ga0.7N, and Al0.5Ga0.5N, along with a 4H-SiC homojunction diode for comparison. The turn on voltage was around 1 V, and the ideality factor between 1 and 2 for all heterojunction diodes except for the Al0.3Ga0.7N diode. This diode had an ideality factor between 2 and 3, and also showed a much lower series resistance, indicating a change in transport mechanism across the junction. A tunnel assisted recombination model was analyzed and compared to the extracted values of the GaN diode. The model agreed well with both current-voltage and capacitance-voltage measurements for this diode. This model was not applied to the other samples, since their characteristics could not be explained by a simple mechanism.
14.	Danielsson, Erik, et al. (författare) Dry etching and metallization schemes in a GaN/SiC heterojunction device process 2000 Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 338-342, s. 1049-1052 Tidskriftsartikel (refereegranskat)abstract Dry etching and metallization schemes are described for a GaN/SiC heterojunction. GaN was reactive ion etched in a chlorine based chemistry (Cl2/Ar), and an ICP etch was used on 4H-SiC using a fluorine based chemistry (SF6/Ar/O2). The etch rates obtained on GaN was above 400 nm/min. High sample temperature from self heating and large dc-bias was the probable cause for the high etch rate. The ICP etch rate on SiC approached 320 nm/min, and the etch selectivity to GaN was >100. The metallization was based on Ti for both n-GaN and p-SiC. TLM and Kelvin structures were used to extract the specific contact resistivity, ÏC. After a 950 Â°C anneal in N2 ÏC on the GaN samples were below 1Â·10-6 Î©cm2 for sputtered contacts in room temperature, and an order of magnitude higher with evaporation. On p-SiC no ohmic behavior was found with a doping of 4Â·1018 cm-3, but the same contact metallization on highly doped areas (>1020 cm-3) showed ohmic behavior with ÏC below 10-4 Î©cm2.
15.	Danielsson, Erik, et al. (författare) Extrinsic base design of SiC bipolar transistors 2004 Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 457-460:II, s. 1117-1120 Tidskriftsartikel (refereegranskat)abstract The SiC npn bipolar junction transistor (BJT) is a very promising device for high voltage and high power switches. The SiC BJT has, due to junction voltage cancellation, potentially a low on-resistance. However, the high resistivity in the base layer can induce a locally forward biased base collector junction and a premature current from the base to collector at on-state. In this work we propose a new technique to fabricate the extrinsic base using regrowth of the extrinsic base layer. This technique can put the highly doped region of the extrinsic base a few tenths of a micron from the intrinsic region. We also propose a new mobility model in our simulations to correctly account for the ionized impurities in minority carrier transport and elevated temperature.
16.	Danielsson, E., et al. (författare) Fabrication and characterization of heterojunction diodes with HVPE-Grown GaN on 4H-SiC 2001 Ingår i: IEEE Transactions on Electron Devices. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9383 .- 1557-9646. ; 48:3, s. 444-449 Tidskriftsartikel (refereegranskat)abstract GaN/SiC heterojunctions can improve the performance considerably for BJTs and FETs. In this work, heterojunction diodes have been manufactured and characterized. The fabricated diodes have a GaN n-type cathode region on top of a JH-SIC p-type epi layer. The GaN layer was grown with HVPE directly on off-axis SiC without a buffer layer. Mesa structures were formed and a Ti metallization was used as cathode contact to GaN, and the anode contact was deposited on the backside using sputtered Al. Both current-voltage (I-V) and capacitance-voltage (C-V) measurements were performed on the diode structures. The ideality factor of the measured diodes was 1.1 and was constant with temperature. A built in potential of 2.06 V was extracted from I-V-measurements and agrees well with the built in potential from C-V-measurements. The conduction band offset was extracted to 1.1 eV and the heterojunction was of type II. The turn on voltage for the diodes is about 1 V lower than expected and a suggested mechanism for this effect is discussed.
17.	Danielsson, E., et al. (författare) Inductively coupled plasma etch damage in 4H-SiC investigated by Schottky diode characterization 2001 Ingår i: Journal of Electronic Materials. - : Springer Science and Business Media LLC. - 0361-5235 .- 1543-186X. ; 30:3, s. 247-252 Tidskriftsartikel (refereegranskat)abstract Ti Schottky diodes have been used to investigate the damage caused by inductively coupled plasma (ICP) etching of silicon carbide. The Schottky diodes were characterized using TV and CV measurements. An oxidation approach was tested in order to anneal the damage, and the diode characterization was used to determine the success of the annealing. The barrier height, leakage current, and ideality factor changed significantly on the sample exposed to the etch. When the etched samples were oxidized the electrical properties were recovered and were similar to the unetched reference sample (with oxidation temperatures ranging from 900 degreesC up to 1250 degreesC). Annealing in nitrogen at 1050 degreesC did not improve the electrical characteristics. A low energy etch showed little influence on the electrical characteristics, but since the etch rate was very low the etched depth may not be sufficient in order to reach a steady state condition for the surface damage.
18.	Danielsson, Erik, et al. (författare) Investigation of thermal properties in fabricated 4H-SiC high-power bipolar transistors 2002 Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 389-393:2, s. 1337-1340 Tidskriftsartikel (refereegranskat)abstract Silicon Carbide bipolar junction transistors have been fabricated and investigated. The transistors had a maximmn current gain of approximately 10 times, and a breakdown voltage of up to 600 V. When operated at high power densities the device showed a clear self-heating effect, decreasing the current gain. The junction temperature was extracted during self-heating to approximately 150 Â°C, using the assumption that the current gain only depends on temperature. Thermal images of a device under operation were also recorded using an infrared camera, showing a significant temperature increase in the vicinity of the device. Physical device simulations have been used to analyze the measured data. The thermal conductivity is fitted to model the measured self-heating, and the lifetime in the base is fitted against the measurement of the current gain.
19.	Danielsson, Erik, et al. (författare) Simulation and electrical characterization of GaN/SiC and AlGaN/SiC heterodiodes 1999 Ingår i: Materials Science & Engineering. - 0921-5107 .- 1873-4944. ; 61-62, s. 320-324 Tidskriftsartikel (refereegranskat)abstract Heterojunctions on SiC is an area in rapid development, especially GaN/SiC and AlGaN/SiC heterojunctions. The heterojunction can improve the performance considerably for BJTs and FETs. In this work heterojunction diodes have been manufactured and characterized. The structure was a GaN or AlGaN n-type region on top of a 6H-SiC p-type substrate. Two different approaches of growing the n-type region were tested. The GaN was grown with the MBE technique using a polycrystalline GaN buffer, whereas the AlGaN was grown with CVD and an AlN buffer. The AlGaN had an aluminum mole fraction of around 0.1. Mesa structures were formed using Cl2 RIE of GaN/AlGaN, which showed good selectivity on 6H-SiC (about 1:6). A Ti metallization with subsequent RTA was used as contact to GaN and AlGaN, and the contact to 6H-SiC was liquid InGa. Both I-V and C-V measurements were performed on the heterojunction diode. The ideality factor of the diodes, doping concentration of the SiC, and the band alignment of the heterojunction were extracted. Â© 1999 Elsevier Science S.A.
20.	Danielsson, Erik, et al. (författare) Simulation Study of on-state Losses as Function of Carrier Life-time for a GaN/SiC High Power HBT Design 1999 Ingår i: Physica scripta. T. - 0281-1847. ; 79, s. 290-293 Tidskriftsartikel (refereegranskat)abstract SiC has several properties that makes it more suitable than silicon for high power devices. One problem with SiC bipolar devices is the short carrier life times, and this problem becomes more severe when designing devices for high voltage applications since the dimensions are larger. This work investigates how the Shockley-Read-Hall lifetime influences the on-state characteristics of a HBT or BJT switch in 4H-SiC. The on-state characteristics were simulated with varying SRH lifetimes in the base and drift region. Comparisons were made at 100 A/cm2 collector current density, Jc, and at the base current density, JB, where the total on-state power loss of the design is at minimum. The SRH lifetime in the drift region is the dominant parameter for on-state performance, whereas the SRH lifetime in the base is of much less importance. The simulations showed that to reach an acceptable JC/JB-ratio of 100 at power minimum a SRH lifetime of at least 100 ÎŒs in the drift region was needed for the HBT design. This lifetime is far from the experimental values reported for 4H-SiC. The advantages of the heterojunction in comparison to ordinary BJTs decreases with shorter SRH lifetimes, but an improvement could always be seen.
21.	Danielsson, E., et al. (författare) The influence of band offsets on the IV characteristics for GaN/SiC heterojunctions 2002 Ingår i: Solid-State Electronics. - 0038-1101 .- 1879-2405. ; 46:6, s. 827-835 Tidskriftsartikel (refereegranskat)abstract GaN/SiC heterojunctions can improve the performance considerably for bipolar transistors based on SiC technology. In order to fabricate such devices with a high current gain, the origin of the low turn-on voltage for the heterojunction has to be investigated, which is believed to decrease the minority carrier injection considerably. In this work heterojunction diodes are compared and characterized. For the investigated diodes, the GaN layers have been grown by molecular beam epitaxy (MBE), metal organic chemical vapor deposition, and hydride vapor phase epitaxy. A diode structure fabricated with MBE is presented here, whereas others are collected from previous publications. The layers were grown either with a low temperature buffer, AIN buffer, or without buffer layer. The extracted band offsets are compared and included in a model for a recombination process assisted by tunneling, which is proposed as explanation for the low turn-on voltage. This model was implemented in a device simulator and compared to the measured structures, with good agreement for the diodes with a GaN layer grown without buffer layer. In addition the band offset has been calculated from Schottky barrier measurements, resulting in a type II band alignment with a conduction band offset in the range 0.6-0.9 eV. This range agrees well with the values extracted from capacitance-voltage measurements.
22.	Danielsson, Erik, et al. (författare) Thermal stability of sputtered TiN as metal gate on 4H-SiC 1998 Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 264-268:PART 2, s. 805-808 Tidskriftsartikel (refereegranskat)abstract MOS-structures were made with TiN as metal gate on 4H-SiC. The thermal stability and electrical properties of this gate was determined by CV-measurements. Comparison with Al gates showed that TiN worked well as a gate metal on 4H-SiC. The hysteresis and density of the interface states were comparable for the two gate types. The n-type samples had low leakage and a flatband voltage of a few volts, while the p-type samples had high leakage and a fiatband voltage of around -20 V. The structure showed poor characteristics after a 700Â°C anneal for one hour, which is probably caused by the formation of titanium silicide. The TiN films had a lower content of nitrogen than expected, which could influence the stability.
23.	Domeij, Martin, et al. (författare) Analysis of the base current and saturation voltage in 4H-SiC power BJTs 2007 Ingår i: 2007 European Conference On Power Electronics And Applications. - 9789075815115 ; , s. 2744-2750 Konferensbidrag (refereegranskat)abstract Silicon carbide (SiC) power bipolar junction transistors are interesting competitors to Si IGBTs for 1200 V power electronics applications. Advantages of SiC BJTs are low collector-emitter saturation voltages, little stored charge and high temperature capability. In this work, SiC NPN power BJTs with common emitter current gains of 40 have been fabricated and characterized. Electrical measurements for BJTs with different emitter widths indicate that the current gain is limited by surface recombination. A low value of V-CESAT=0.9 V at J(C)=100 A/cm(2) was obtained for small and large area (3.4 mm(2)) BJTs and correlated with the formation of low-resistive ohmic contacts to the base. Large area BJTs were shown to operate with a current gain of 48 in pulsed mode at a collector current of 12 A corresponding to J(C)=360 A/cm(2).
24.	Domeij, Martin, et al. (författare) Current gain dependence on emitter width in 4H-SiC BJTs 2006 Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. - 9780878494255 ; 527-529, s. 1425-1428 Tidskriftsartikel (refereegranskat)abstract This paper reports the fabrication of epitaxial 4H-SiC bipolar junction transistors (BJTs) with a maximum current gain beta = 64 and a breakdown voltage of 1100 V. The high beta value is attributed to high material quality obtained after a continuous epitaxial growth of the base-emitter junction. The current gain of the BJTs increases with increasing emitter width indicating a significant influence of surface recombination. This "emitter-size" effect is in good agreement with device simulations including recombination in interface states at the etched termination of the base-emitter junction.
25.	Domeij, Martin, et al. (författare) Current gain of 4H-SiC bipolar transistors including the effect of interface states 2005 Ingår i: Materials Science Forum. - ZURICH-UETIKON : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. - 0878499636 ; 483, s. 889-892 Tidskriftsartikel (refereegranskat)abstract The current gain (β) of 4H-SiC BJTs as function of collector current (I-C) has been investigated by DC and pulsed measurements and by device simulations. A measured monotonic increase of β with I-C agrees well with simulations using a constant distribution of interface states at the 4H-SiC/SiO2 interface along the etched side-wall of the base-emitter junction. Simulations using only bulk recombination, on the other hand, are in poor agreement with the measurements. The interface states degrade the simulated current gain by combined effects of localized recombination and trapped charge that influence the surface potential. Additionally, bandgap narrowing has a significant impact by reducing the peak current gain by about 50% in simulations.

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