Frank-type defects on the basal plane in thick 4H–SiC epitaxial layers have been characterized by photoluminescence (PL) spectroscopy and a PL imaging microscopy. The PL emission wavelength of the three kinds of Frank-type defects were determined at ∼424, 457, and 488 nm at room temperature, respectively. The high-resolution PL imaging of the defects was obtained, and the PL emission at the Frank partial dislocations was confirmed in the near infrared region (>700 nm). Correspondence between the optical properties and the microscopic structures of the defects was clarified.

Transmission electron microscopy and KOH etching were used to determine the structure of the carrot defect in 4H-SiC epilayers. The defect consists of two intersecting planar faults on prismatic {11¯00} and basal {0001} planes. Both faults are connected by a stair-rod dislocation with Burgers vector 1∕n [101¯0] with n>3 at the crossover. A Frank-partial dislocation with b=1∕12[44¯03] terminates the basal fault.

Articles you may be interested inA method to determine fault vectors in 4H-SiC from stacking sequences observed on high resolution transmission electron microscopy images

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Conversion of basal plane dislocations (BPDs) to threading edge dislocations (TEDs) is found in 4H-SiC epilayers after being annealed simply at high temperatures. Grazing incidence reflection synchrotron x-ray topography for the dislocations in the epilayers before and after annealing confirmed that some of the BPDs in the epilayers had converted to TEDs from the epilayer surface by the annealing. Observations on the dislocation behavior during annealing are explained in detail, and the mechanism of BPD conversion is discussed. It is argued that the conversion proceeds through the cross slip of constricted BPD segments towards the surface on the prismatic plane driven by the image force as well as TED glide driven by the line tension. Certain kinetic processes during annealing may facilitate the formation of constriction.

Glycyrrhetic acid 3-O-mono-β-d-glucuronide (GAMG) is an important derivative of glycyrrhizin (GL) and has attracted considerable attention, especially in the food and pharmaceutical industries, due to its natural high sweetness and strong biological activities. The biotransformation process is becoming an efficient route for GAMG production with the advantages of mild reaction conditions, environmentally friendly process, and high production efficiency. Recent studies showed that several β-glucuronidases (β-GUS) are key GAMG-producing enzymes, displaying a high potential to convert GL directly into the more valuable GAMG and providing new insights into the generation of high-value compounds. This review provides details of the structural properties, health benefits, and potential applications of GAMG. The progress in the development of the biotransformation processes and fermentation strategies to improve the yield of GAMG is also discussed. This work further summarizes recent advances in the enzymatic synthesis of GAMG using β-GUS with emphasis on the physicochemical and biological properties, molecular modifications, and enzymatic strategies to improve β-GUS biocatalytic efficiencies. This information contributes to a better framework to explore production and application of bioactive GAMG.

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