Anomalous
charge-pumping characteristics of 4H-silicon carbide (SiC) MOSFETs were
analyzed. Charge-pumping measurements of n- and p-channel 4H-SiC MOSFETs
with and without NO annealing were performed. Measurements using various pulse
fall times revealed that the geometric component exists in the n-channel 4H-SiC MOSFETs
and is particularly large in the unannealed n-channel 4H-SiC MOSFETs with
low channel mobility. In addition, influence of interface states on the
charge-pumping curves is significant in the unannealed 4H-SiC MOSFETs.
The charge-pumping curves are distorted by these two nonideal effects, making
the analysis of the charge-pumping curves difficult. A sufficiently long pulse
fall time, which is on the order of 1-10 mus for the n-channel 4H-SiC MOSFETs
with a 10-mum gate length, is required to minimize the effect of the geometric
component.
Source:IEEE
DC
and transient test results of high power, fast recovery 4H-SiC MPS
diodes using multi-step junction termination (MJTE) designs are presented. The
MJTE design allows full utilization of the superior breakdown properties of SiC. 4H-SiC MPS
diode DC properties were studied and the transient properties were obtained by
using an inductively-loaded half-bridge inverter circuit at high current and
high temperatures (high-T). Results show that the replacement of Si
freewheeling diodes by SiC diodes results in far less storage charge
in the diodes and substantial reduction in diode turn-off energy loss,
especially at high-T.
Source:IEEE
The development of high-voltage power devices based on wide
bandgap semiconductor such as silicon carbide (SiC) has attracted great
attention due to its superior material properties over silicon for
high-temperature applications. Among the high-voltage SiC power
devices, the 4H-SiC gate turn-off thyristor (GTO) offers excellent
current handling, very high voltage blocking, and fast turn-off capabilities.
The 4H-SiC GTO also exhibits lower forward voltage drop than the
IGBT-based switches, resulting in lower losses during normal operation. It is
an ideal switch for pulsed power applications that require high turn-on di/dt.
In order to achieve a blocking capability of or greater than 20 kV in SiC,
a thick drift epi-layer (> 160 μm) with an improved carrier lifetime (5 ~ 10
μs) is necessary to obtain a full conductivity modulation. In this paper, for
the first time to our knowledge, we report our recently developed 1×2 cm2,
20 kV, 4H-SiC p-GTO using a 160 μm, 2×1014/cm3 doped,
p-type drift layer. The active conducting area of the device is 0.53 cm2.
Due to the limitations of the high-voltage test set-up, the 4H-SiC p-GTO
showed an on-wafer gate-to-anode blocking voltage of 19.9 kV at a leakage
current of 1 μA, which corresponds to a one-dimensional (1D) maximum electrical
field of ~ 1.5 MV/cm at room-temperature. To measure this large area, 4H-SiC,
p-GTO at high current levels (> 100 A/cm2), the forward
characteristics of the device were evaluated using a Tektronix 371 curve tracer
in pulse mode. A differential specific on-resistance of 11 MΩ-cm2 was
obtained at a gate current of 0.35 A and a high current of 300 A/cm2 ~ 400
A/cm2. More results and discussion will be presented at the
conference.
Source:IEEE
Silicon
carbide (SiC) has attracted increasing attention as a promising wide bandgap
semiconductor projected to high-power and high-temperature electronics.
Although SiC MOSFETs are recognized as ideal power switches, SiC MOSFETs
have still suffered from low effective channel mobility. In recent years,
post-oxidation nitridation in an NO ambience is widely used to improve SiO2/4H-SiC(0001)
interface properties and thereby to increase effective channel mobility of
MOSFETs as presented in S. Dimitrijev et al. (1997) and G. Y. Chung et al.
(2001). Direct oxidation with N2O has been also proposed as an
alternative to form the "nitrided" MOS interface for the safety
reason according to L. A. Lipkin et al. (2002). In this study, the interface
state density and MOSFET performance have been investigated on4H-SiC(0001),
(000-1), and (11-20) stated in H. Yano et al. (1999) by using N2O
oxidation. Effects of doping concentration in the p-body on MOSFET performance
are discussed.
Defect and electrical characterization
of bulk semi-insulating (SI) 4H-SiC crystals and SI and
n-type 4H-SiC epitaxial layers grown by chemical vapor deposition
(CVD) on highly doped (0001) 4H-SiCsubstrates is reported. Optical
microscopy, electron beam induced current (EBIC) imaging, current-voltage ($I$–$V$)
measurements, thermally stimulated current (TSC) spectroscopy (94 K–620 K),
Hall effect, and van der Pauw measurements have been conducted for
characterization and defect correlation studies. Both epitaxial layers
exhibited relatively shallow levels related to Al, B, $L$ - and
D-centers. Deep level centers in the n-type epitaxial layer peaked at ${sim}
400$ K ($E_{a} sim 1.1$ eV), and ${sim}
470$ K were correlated with $IL_{2}$ defect and 1.1 eV center in high-purity bulk SI 4H-SiC.
The SI epitaxial layer exhibited peak at ${sim} 290$ K ( $E_{a} = 0.82hbox{--}0.87$ eV) that was attributed to $IL_{1}$ and
HK2 centers, and at ${sim} 525$ K that
was related to intrinsic defects and their complexes with energy levels close
to the middle of the band-gap. Results of EBIC and optical microscopy showed
segregation of threading dislocations around comet tail defects in the n-type
epitaxial layer. The $I$– $V$ characteristics of the devices on SI epitaxial layer exhibited steps
corresponding to the ultimate trap filling of deep centers. The
high-temperature resistivity measurements of bulk SI 4H-SiC sample
revealed resistivity hysteresis that was attributed to the filling of the
deep-level electron trap centers. The responsivity of the n-type
epitaxial 4H-SiC detector in the soft X-ray energy range is reported
for the first time.
Source:IEEE
Nuclear radiation detectors in the energy range of soft
x-rays have been fabricated using bulk semi-insulating (SI) 4H-SiC crystals
and SI and n-type 4H-SiC epitaxial layers grown by chemical vapor
deposition (CVD) on highly doped (0001) 4H-SiC substrates. The
devices have been characterized by optical microscopy, current-voltage (I-V)
measurements, thermally stimulated current (TSC) spectroscopy (94K - 650 K),
Hall effect, van der Pauw measurements, and electron beam induced current
(EBIC) technique. Both epitaxial layers exhibited relatively shallow levels
related to Al, B, L- and D- centers. Deep level centers in the n-type epitaxial
layer peaked at ~ 400 K (Ea ~ 1.1 eV) and ~ 470 K were
correlated with IL2 defect and 1.1 eV center in high purity bulk SI 4H-SiC.
The SI epitaxial layer exhibited peak at ~ 290 K (Ea = 0.82 -
0.87 eV) that was attributed to IL1 and HK2 centers, and at ~ 525 K that
was related to intrinsic defects and their complexes with energy levels close
to the middle of the band gap. Results of EBIC and optical microscopy
characterization showed segregation of threading dislocations around comet tail
defects in the n-type epitaxial layers. The I-V characteristics of the devices
on SI epitaxial layers obtained in wide temperature range (94K - 650 K)
exhibited steps at ~ 1 V and ~ 70 V corresponding to the ultimate trap filling
of deep centers peaked at >; 500 K and at ~ 250 K (Ea ~ 0.57
eV), & ~ 300 K (Ea ~ 0.85 eV) respectively. The high
temperature resistivity measurements of bulk SI 4H-SiC sample
revealed resistivity hysteresis that was attributed to the filling of the deep
level electron trap centers. The responsivity of the n-type epitaxial SiC sensors
to low energy x-rays is reported for the first time.
Source:IEEE
The
large bandgap of 4H-SiC (3.25 eV) makes it a suitable material for
visible-blind UV detection. In the paper, the performance of 4H-SiC avalanche
photodiodes (APDs) with a thin avalanche width of 0.1 μm is evaluated.
Avalanche photodiodes with thin multiplication regions can greatly improve the
signal-to-noise ratio of photoreceiver systems by providing internal gain while
maintaining a high operating speed and low operating voltage. The diodes
exhibit a peak unity-gain responsivity of 144 mA/W at a wavelength of 265 nm.
Photomultiplication measurements carried out on these diodes showed that β>α
in 4H-SiC, where β and α are the hole and electron ionisation
coefficients, respectively. The 4H-SiCAPDs also exhibit very low excess
noise corresponding to k=0.1 (where k=α/β for hole multiplication) in the local
model when illuminated by 325 nm light. This is much lower than that of
commonly used Si APDs with identical thickness and indicates that 4H-SiC is
well suited for high gain, low noise UV detection. In view of the large β/α
ratio measured in these thin 4H-SiC APDs, multiplication must be
initiated by hole injection to ensure a low excess-noise performance.
Source:IEEE
We report on purity improvement effects which recently have been observed when comparing different series of wafers produced in two separate, but basically similar, home-made physical vapor transport (PVT) reactors. Looking in detail for the origin of this phenomenon, we have found a strong influence of the residual purity of the graphite material used to manufacture the crucibles. After proper optimization, a second effect has been found. It manifests when the residual level of impurities in the seed material is high and provides evidence for in situ auto-doping. Finally, quantitative analyses of C(V) characteristics and Raman spectra have been done. In this way we follow the trend in residual carrier concentration and mobility.
Source:
Materials Science and Engineering: B
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effects in bulk 6H and 4H-SiC wafers grown by physical vapor transport, please
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The relationship between the warpage of 4H-SiC CVD grown epi-wafers with crystal bending and substrate properties is investigated. The wafer surface preparation before and after epitaxy is found to affect both long range properties such as the wafer flatness and to some extent local properties such as the epi-substrate interface. Structural characterisation is carried out using X-ray diffraction techniques and KOH etching.
Source:
Diamond and Related Materials
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properties of 4H-SiC epi-wafers, please visit our website:http://www.qualitymaterial.net,
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