Growth and characterization of 3C–SiC and 2H–AlN/GaN films and devices produced on step-free 4H–SiC mesa substrates

Abstract

While previously published experimental results have shown that the step-free (0 0 0 1) 4H–SiC mesa growth surface uniquely enables radical improvement of 3C–SiC and 2H–AlN/GaN heteroepitaxial film quality (>100-fold reduction in extended defect densities), important aspects of the step-free mesa heterofilm growth processes and resulting electronic device benefits remain to be more fully elucidated. This paper reviews and updates recent ongoing studies of 3C–SiC and 2H–AlN/GaN heteroepilayers grown on top of 4H–SiC mesas. For both 3C–SiC and AlN/GaN films nucleated on 4H–SiC mesas rendered completely free of atomic-scale surface steps, TEM studies reveal that relaxation of heterofilm strain arising from in-plane film/substrate lattice constant mismatch occurs in a remarkably benign manner that avoids formation of threading dislocations in the heteroepilayer. In particular, relaxation appears to occur via nucleation and inward lateral glide of near-interfacial dislocation half-loops from the mesa sidewalls. Preliminary studies of homojunction diodes implemented in 3C-SiC and AlN/GaN heterolayers demonstrate improved electrical performance compared with much more defective heterofilms grown on neighbouring stepped 4H–SiC mesas. Recombination-enhanced dislocation motion known to degrade forward-biased 4H–SiC bipolar diodes has been completely absent from our initial studies of 3C–SiC diodes, including diodes implemented on defective 3C–SiC heterolayers grown on stepped 4H–SiC mesas.

Source:IOPscience

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Cree Offers 4H Silicon Carbide Epitaxial Wafers Featuring Very Low Basal Plane Dislocation

Cree,Inc,announces its latest silicon carbide (SiC) offering with low basal plane dislocation (LBPD) 100-mm 4H SiC epitaxial wafers.
 This LBPD material exhibits a total BPD density of < 1 cm-2 in the epitaxial drift layer, with BPDs capable of causing Vf drift as low as < 0.1 cm-2.
 
This low BPD material further demonstrates Cree’s long-standing commitment to continuous improvement and investment in SiC materials technology.

“Bipolar devices in SiC have long been held back by forward voltage degradation caused by the presence of BPDs,” said John Palmour, CTO, Cree Power & RF. “This Low BPD material enables very high voltage bipolar devices such as IGBTs (insulated-gate bipolar transistors) and GTOs (gate turn-off thyristor) to have improved stability over time. This recent development helps remove roadblocks to commercialization of these extremely high power devices.

SiC is a high-performance semiconductor material used in the production of a broad range of lighting, power and communication components, including light-emitting diodes(LEDs), power switching devices and RF power transistors for wireless communications. 

Keywords:SiC Epitaxial Wafer,North America,Cree,

Source:IOPscience

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Size effect on high temperature variable range hopping in Al+ implanted 4H-SiC

Abstract

The hole transport properties of heavily doped 4H-SiC (Al) layers with Al implanted concentrations of 3  ×  1020 and 5  ×  1020 cm−3 and annealed in the temperature range 1950–2100 °C, have been analyzed to determine the main transport mechanisms. This study shows that the temperature dependence of the resistivity (conductivity) may be accounted for by a variable range hopping (VRH) transport into an impurity band. Depending on the concentration of the implanted impurities and the post-implantation annealing treatment, this VRH mechanism persists over different temperature ranges that may extend up to room temperature. In this framework, two different transport regimes are identified, having the characteristic of an isotropic 3D VRH and an anisotropic nearly 2D VRH. The latter conduction mechanism appears to take place in a rather thick layer (about 400 nm) that is too large to induce a confinement effect of the carrier hops. The possibility that an anisotropic transport may be induced by a structural modification of the implanted layer because of a high density of basal plane stacking faults (SF) in the implanted layers is considered. The interpretation of the conduction in the heaviest doped samples in terms of nearly 2D VRH is supported by the results of the transmission electron microscopy (TEM) investigation on one of the 5  ×  1020 cm−3 Al implanted samples of this study. In this context, the average separation between basal plane SFs, measured along the c-axis, which is orthogonal to the carrier transport during electrical characterization, appears to be in keeping with the estimated value of the optimal hopping length of the VRH theory. Conversely, no SFs are detected by TEM in a sample with an Al concentration of 1  ×  1019 cm−3 where a 3D nearest neighbor hopping (NNH) transport is observed.

Source:IOPscience

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