Showing papers by "Jun Suda published in 2011"
TL;DR: In this article, the authors demonstrate 4H-SiC bipolar junction transistors with record current gains by utilizing optimized device geometry and continuous epitaxial growth of the emitter-base junction, combined with an intentional deep-level reduction process based on thermal oxidation.
Abstract: We demonstrate 4H-SiC bipolar junction transistors (BJTs) with record current gains. An improved current gain was achieved by utilizing optimized device geometry and continuous epitaxial growth of the emitter-base junction, combined with an intentional deep-level-reduction process based on thermal oxidation to improve the lifetime in p-SiC base. A current gain (β) of 257 was achieved for 4H-SiC BJTs fabricated on the (0001) Si face. A gain of 257 is twice as large as the previous record gain. We also demonstrate BJTs on the (0001] ) C face that showed the highest β of 335 among the SiC BJTs ever reported.
47 citations
TL;DR: In this article, the improvement of current gain in 4H-SiC bipolar junction transistors (BJTs) by utilizing deposited oxides as a surface passivation layer was reported.
Abstract: We report the improvement of current gain in 4H-SiC bipolar junction transistors (BJTs) by utilizing deposited oxides as a surface passivation layer. Various post deposition annealing processes, including annealing ambient (N2, N2O, and NO) and annealing time, were investigated. We successfully demonstrate SiC BJTs with high current gains (β) of 73 and 102 using deposited oxides annealed in N2O and NO, respectively, whereas BJTs having conventional thermally grown oxides showed a current gain of 50.
40 citations
TL;DR: In this paper, the impact of temperature and injection level on carrier lifetimes in 50 µm thick p-type and n-type 4H-SiC epilayers was investigated.
Abstract: Dependencies of temperature and injection level on carrier lifetimes in 50 μm thick p-type and n-type 4H–SiC epilayers have been investigated. The carrier lifetimes have been measured by differential microwave photoconductance decay measurements at various injection levels and temperatures. In both p-type and n-type epilayers, the carrier lifetimes gradually increased with increasing the injection level, which were naturally expected from the Shockley-Read-Hall (SRH) model, and after taking a maximum, the lifetimes dropped at the very high-injection level. In contrast, the carrier lifetimes exhibited continuous increase with elevating the temperature for both epilayers. In addition, the impact of thermal oxidation process on the carrier lifetimes has been also investigated. The thermal oxidation process, by which the Z1/2 and EH6/7 centers were remarkably reduced that had been observed in n-type 4H–SiC in our previous work, led to the improvement of the carrier lifetimes especially for n-type epilayers. T...
32 citations
TL;DR: In this article, the first layer of 300-nm-thick AlN was grown on 6H-SiC(0001) with six Si-C bilayer-height (1.5 nm) steps by rf-plasma-assisted molecular-beam epitaxy (MBE).
Abstract: 300-nm-thick AlN layers were grown directly on 6H-SiC(0001) with six Si–C bilayer-height (1.5 nm) steps by rf-plasma-assisted molecular-beam epitaxy (MBE). To avoid unintentional active-nitrogen exposure, AlN was grown just after the nitrogen plasma ignition. By combining optimized Ga pre-deposition and no active-nitrogen exposure, layer-by-layer growth was realized from the first layer of AlN. Screw-type and edge-type threading dislocation densities in the AlN layer were reduced to 6×104 and 4×108 cm-2, respectively. Most of the edge-type dislocations were located at the step edge of the SiC substrate. The dislocation density of the AlN grown on the terrace of the SiC substrate was as low as 8×107 cm-2.
31 citations
TL;DR: In this article, threading dislocations in 4H-SiC epilayers were investigated by means of micro-photoluminescence (μ-PL) mapping at room temperature.
Abstract: Threading dislocations (TDs) in 4H-SiC epilayers have been investigated by means of micro-photoluminescence (μ-PL) mapping at room temperature. Enhanced nonradiative recombination at TDs was confirmed experimentally, resulting in a reduced local PL emission intensity in the μ-PL intensity map performed at 390 nm (near band-edge emission). The behavior of nonradiative recombination at TDs depends on the dislocation type: the screw type of TDs shows stronger effect on the nonradiative recombination activity than the edge type, evidencing a larger local reduction of PL emission intensity. Furthermore, the contrast of TDs in the μ-PL intensity map greatly depends on the carrier lifetimes of the 4H-SiC epilayers. Lifetimes longer than 0.5 μs are essential to obtain a discernible contrast for the individual TDs.
29 citations
TL;DR: In this article, the authors investigated the impact of surface passivation on carrier lifetimes in p-type 4H-SiC epilayers and found that surface recombination is a limiting factor of carrier lifetime.
Abstract: Impacts of reduction of deep levels and surface passivation on carrier lifetimes in p-type 4H-SiC epilayers are investigated. The authors reported that the carrier lifetime in n-type epilayers increased by reduction of deep levels through thermal oxidation and thermal annealing. However, the carrier lifetimes in p-type epilayers were not significantly enhanced. In this study, in order to investigate the influence of surface passivation on the carrier lifetimes, the epilayer surface was passivated by different oxidation techniques. While the improvement of the carrier lifetime in n-type epilayers was small, the carrier lifetime in p-type epilayers were remarkably improved by appropriate surface passivation. For instance, the carrier lifetime was improved from 1.4 μs to 2.6 μs by passivation with deposited SiO2 annealed in NO. From these results, it was revealed that surface recombination is a limiting factor of carrier lifetimes in p-type 4H-SiC epilayers.
24 citations
TL;DR: In this paper, the authors theoretically studied the valence band structure and hole effective mass of rectangular cross-sectional Si nanowires (NWs) with the crystal orientation of [110, [111], and [001].
Abstract: The authors theoretically studied the valence band structure and hole effective mass of rectangular cross-sectional Si nanowires (NWs) with the crystal orientation of [110], [111], and [001]. The E–k dispersion and the wave function were calculated using an sp3d5s∗ tight-binding method and analyzed with the focus on the nature of p orbitals constituting the subbands. In [110] and [111] nanowires, longitudinal/transverse p orbitals are well separated and longitudinal component makes light (top) subbands and transverse component makes heavy subbands. The heavy subbands are located far below the top light band when NW has square cross-section, but they gain their energy with the increase in the NW width and come near the band edge. This energy shift of heavy bands in [110] NWs shows strong anisotropy to the direction of quantum confinement whereas that in [111] NWs does not have such anisotropy. This anisotropic behavior and the difference among orientations are understandable by the character of the wave fu...
19 citations
23 May 2011
TL;DR: In this article, the authors demonstrate 4H-SiC bipolar junction transistors (BJTs) with record current gains, using optimized device geometry as well as optimized surface passivation and continuous epitaxial growth of the emitter-base junction.
Abstract: We demonstrate 4H-SiC bipolar junction transistors (BJTs) with record current gains. Improved current gain was achieved by utilizing optimized device geometry as well as optimized surface passivation and continuous epitaxial growth of the emitter-base junction, combined with an intentional deep-level-reduction process based on thermal oxidation to improve the lifetime in p-SiC base. Current gain (β) of 257 was achieved for 4H-SiC BJTs fabricated on the (0001)Si-face. The gain of 257 is twice as large as the previous record gain. We also demonstrate, for the first time, BJTs on the (000–1)C-face that showed the highest β of 335 among the SiC BJTs ever reported.
15 citations
TL;DR: In this article, a density functional theory, tight binding method, and effective mass approximation was used to calculate the bandgap of Si-NW MOSFETs, which showed good agreement with that derived from threshold voltage.
Abstract: Si-nanowire (Si-NW) MOSFETs, the cross-sectional size (square root of the cross-sectional area of NWs) of which was changed from 18 to 4 nm, were fabricated and characterized. Both n- and p-channel MOSFETs have shown a nearly ideal subthreshold swing of 63 mV/decade. The threshold voltage of n-/p-channel MOSFETs has gradually increased/decreased with decreasing the cross-sectional size. The bandgap shift from bulk Si has been derived from the threshold-voltage shift. The bandgap of Si-NWs was calculated by a density functional theory, tight binding method, and effective mass approximation. The calculated bandgap shows good agreement with that derived from threshold voltage. The theoretical calculation indicates that the bandgap is dominated by the cross-sectional size (area) and is not very sensitive to the shape within the aspect-ratio range of 1.0-2.5.
8 citations
10 Feb 2011
TL;DR: In this paper, an electrostatic-actuated suspended bridge structure composed by single-crystalline silicon carbide (SiC) is fabricated by a combination of reactive ion etching (RIE) and doping-selective photoelectrochemical (PEC) etching.
Abstract: An electrostatic-actuated suspended bridge structure composed by single-crystalline silicon carbide (SiC) is fabricated.
The structure is entirely made of homoepitaxially grown single-crystalline 4H-SiC. Electrical isolation between the
suspended bridge and the base plate is established with a pnp junction formed by multiple ion implantation. The structure
is fabricated by a combination of reactive ion etching (RIE) and doping-selective photoelectrochemical (PEC) etching.
The suspended bridge is actuated by applying a voltage between the bridge and the base plate.
6 citations
TL;DR: In this paper, the etch hillocks consist of SiC, indicating slower etching at threading dislocations (TDs) and basalplane dislocation (BPDs).
Abstract: Molten KOH etching of 6H- and 4H-SiC0001 on-axis substrates was investigated. After molten KOH etching, etch pits originating from threading dislocations (TDs) and basal-plane dislocations (BPDs) were observed on (0001) surfaces. On the other hand, large and small hillocks were observed on (0001) surfaces. The etch hillocks consist of SiC, indicating slower etching at TDs. By comparing the (0001) side and (0001) side of the same substrate, it was found that large hillocks correspond to edge-type TDs, while small hillocks correspond to screw-type TDs.
TL;DR: In this article, the reliability of n-and p-type 4H-SiC(0001) MOS devices with N2O-grown oxides and deposited oxides annealed in n2O was investigated.
Abstract: In this paper, we have investigated reliability of n- and p-type 4H-SiC(0001) metal–oxide–semiconductor (MOS) devices with N2O-grown oxides and deposited oxides annealed in N2O. From the results of time-dependent dielectric breakdown (TDDB) tests, it is revealed that the N2O-grown oxides have relatively-high reliability (4–30 C cm-2 for n- and p-MOS structures). In addition, the deposited SiO2 on n- and p-SiC exhibited a high charge-to-breakdown of 70.0 and 54.9 C cm-2, respectively. The n/p-MOS structures with the deposited SiO2 maintained a high charge-to-breakdown of 19.9/15.1 C cm-2 even at 200 °C. The deposited SiO2 annealed in N2O has promise as the gate insulator for n- and p-channel 4H-SiC(0001) MOS devices because of its high charge-to-breakdown and good interface properties.
TL;DR: In this article, post-oxidation annealing in Ar at high temperature has been performed during fabrication of 4H-SiC metal-oxide-semiconductor field effect transistors (MOSFETs).
Abstract: Post-oxidation annealing (POA) in Ar at high temperature has been performed during fabrication of 4H-SiC metal-oxide-semiconductor field-effect transistors (MOSFETs). The gate oxides were formed by thermal oxidation followed by N2O annealing, then annealed in Ar for 30 min or 5 h at 1300 °C. The results of Secondary Ion Mass Spectrometry (SIMS) measurements indicated that the C atoms accumulated at the SiO2/SiC interface by thermal oxidation diffused during the 5h-Ar annealing. The characteristics of n-channel MOSFETs were improved and the peak value of field effect mobility was increased to 33 cm2/Vs from 19 cm2/Vs by extending the Ar annealing time.
TL;DR: In this article, the growth of high-content AlGaN was carried out by molecular-beam epitaxy (MBE) using elemental Al, Ga, and rf-plasma-excited nitrogen under various V/III ratios.
Abstract: Crystalline orientation dependence of Ga incorporation in growth of high Al-content AlGaN was investigated. Growth was carried out by molecular-beam epitaxy (MBE) using elemental Al, Ga, and rf-plasma-excited nitrogen under various V/III ratios. 6H-SiC (0001), 4H-SiC (1100) and 4H-SiC (1120) were used as substrates. Ga incorporation increased with increase of V/III ratio in the layers grown on (0001) and (1100) planes. On the other hand, Ga was not incorporated in the layer grown on (1120) plane even when the layer was grown under a nitrogen rich condition, indicating much lower Ga incorporation on (1120) plane than those of other planes. AlGaN with good quality was successfully grown on (1100) plane. Utilization of (1100) plane is suitable in MBE growth of AlGaN-based deep-ultraviolet light emitting devices.
10 Feb 2011
TL;DR: In this paper, the temperature dependence of the refractive indices of 4H-SiC, GaN and AlN were investigated in a wavelength range from the near band edge (392 nm for SiC, 367 nm for GaN, and 217 nm for AlN) to infrared (1700 nm) and a temperature range from room temperature to 512°C.
Abstract: The temperature dependence of the refractive indices of 4H-SiC, GaN, and AlN were investigated in a wavelength range
from the near band edge (392 nm for SiC, 367 nm for GaN, and 217 nm for AlN) to infrared (1700 nm) and a
temperature range from room temperature to 512°C. Optical interference measurements with vertical incident
configuration were employed to precisely evaluate ordinary refractive indices. In visible region, the thermo-optic
coefficient of GaN has the largest value in these materials. Optical simulation of GaN-based tunable band-pass filter with
AlGaN/GaN distributed Bragg reflectors (DBRs) was also carried out by using the obtained thermo-optic coefficients. It
revealed that 9 nm red-shift can be obtained from room temperature to 500°C.
TL;DR: In this paper, the one-to-one correspondence between the individual dislocations and the micro photoluminescence (PL) mapping contrast has been consistently obtained, and the reduction of the intensity in the -PL mapping image performed at 390 nm (near band-edge emission).
Abstract: Dislocations in 4H-SiC epilayers were imaged nondestructively by means of micro photoluminescence (-PL) mapping at room temperature. The one-to-one correspondence between the individual dislocations and the -PL mapping contrast has been consistently obtained. By analyzing the reduction of the intensity in the -PL mapping image performed at 390 nm (near band-edge emission), we were able to distinguish threading screw dislocations and threading edge dislocations. Furthermore, the contrast of dislocations in PL-intensity mapping image greatly depends on the carrier lifetimes of the 4H-SiC epilayers. Lifetimes longer than 0.5 s are essential to obtain a discernible contrast for the individual dislocations.
TL;DR: In this paper, the improvement of current gain in 4H-SiC bipolar junction transistors (BJTs) by using deposited oxides as a surface passivation layer was reported.
Abstract: We report the improvement of current gain in 4H-SiC bipolar junction transistors (BJTs) by using deposited oxides as a surface passivation layer. Various post-deposition annealing processes were investigated. We successfully demonstrated SiC BJTs with a high current gain (β) of 86 using deposited oxides annealed in NO. This is 70% higher current gain compared with that of BJTs with the same structure with conventional thermally-grown oxides.