Papers by Keyword: Threading Dislocation

Abstract: Tilt angles of threading dislocations (TDs) which induce leakage of current on SiC junction barrier schottky diodes (SiC-JBSs) were investigated by two-photon-excited photoluminescence (2PPL) and transmission electron microscopy (TEM). Observation of leakage spots measured by atomic force microscopy (AFM) revealed that pit-like structures were certainly formed but the depths were considerably shallow, indicating that influence of local electric field due to the structures was negligible on our SiC-JBSs. It became clear that tilt angles of the TDs inducing leakage were relatively larger than about 11° by 2PPL and that the TD was the threading mixed dislocation by TEM.

Abstract: We evaluated crystalline quality of SiC p/n column layers over 20 μm thickness formed by trench-filling-epitaxial growth. Although threading dislocation density of trench-filling-epitaxial layer is almost same as flat n-type epitaxial layer, threading dislocations are localized in only trench-filled p-columns. We consider that threading dislocations migrated toward p-columns around trench bottom during trench-filling-epitaxial growth.

Abstract: In this work, the origin of the dielectric breakdown of 4H-SiC power MOSFETs was studied at the nanoscale, analyzing devices that failed after extremely long (three months) of high temperature reverse bias (HTRB) stress. A one-to-one correspondence between the location of the breakdown event and a threading dislocation propagating through the epitaxial layer was found. Scanning probe microscopy (SPM) revealed the conductive nature of the threading dislocation and a local modification of the minority carriers concentration. Basing on these results, the role of the threading dislocation on the failure of 4H-SiC MOSFETs could be clarified.

Abstract: This paper demonstrates high-resolution photoluminescence (PL) imaging and discrimination of threading dislocations in 4H-SiC epilayers. Threading screw dislocations (TSDs) and TEDs are distinguished by differences in PL spot size and spectrum. We found that TEDs are further discriminated into six types according to their Burgers vector directions by the appearance of PL imaging. Cross-sectional PL imaging reveals inclination angles of threading dislocations across a thick epilayer.

Abstract: Nomarski optical microscopic, KOH etching and synchrotron topographic studies are presented of faint needle-like surface morphological features in 4H-SiC homoepitaxial layers. Grazing incidence synchrotron white beam x-ray topographs show V shaped features which transmission topographs reveal to enclose 1/4[0001] Frank-type stacking faults. Some of these V-shaped features have a tail associated with them and are referred to as Y-shaped defects. Geometric analysis of the size and shape of the V-shaped faults indicates that they are fully contained within the epilayer and appear to be nucleated at the substrate/epilayer interface. Detailed analysis shows that the positions of the V-shaped stacking faults match with the positions of c-axis threading dislocations with Burgers vectors of c or c+a in the substrate and thus appear to result from the deflection of these dislocations onto the basal plane during epilayer growth. Similarly, the Y-shaped defects match well with the substrate surface intersections of c-axis threading dislocations with Burgers vectors of c or c+a in the substrate which were deflected onto the basal plane during substrate growth. Based on the observed morphology of these defect configurations we propose a model for their formation mechanism.

Abstract: Studies of threading dislocations with Burgers vector of c+a have been carried out using synchrotron white beam X-ray topography. The nucleation and propagation of pairs of opposite sign threading c+a dislocations is observed. Overgrowth of inclusions by growth steps leads to lattice closure failure and the stresses associated with this can be relaxed by the nucleation of opposite sign pairs of dislocations with Burgers vector c+a. Once these dislocations are nucleated they propagate along the c-axis growth direction, or can be deflected onto the basal plane by overgrowth of macrosteps. For the c+a dislocations, partial deflection can occasionally occur, e.g. the a-component deflects onto basal plane while the c-component continuously propagates along the growth direction. One factor controlling the details of these deflection processes is suggested to be related to the ratio between the height of the overgrowing macrostep and that of the surface spiral hillock associated with the threading growth dislocations with c-component of Burgers vector.

Abstract: We investigated the dislocation behaviors during the solution growth on Si-face and C-face off-axis 4H-SiC seed crystals by using synchrotron X-ray topography. On Si-face, almost all threading screw dislocations (TSDs) and threading edge dislocations (TEDs) are converted into Frank-type defects and basal plane dislocations (BPDs), respectively. On the other hand, on C-face, TSDs were hardly converted. Some of TEDs were converted to BPDs and BPD-TED reconversion was often occurred. Therefore, to reduce density of threading dislocations in the grown crystal, it is better to use Si-face off-axis seed crystal.

Abstract: A review is presented of Synchrotron White Beam X-ray Topography (SWBXT) studies of stacking faults observed in PVT-Grown 4H-SiC crystals. A detailed analysis of various interesting phenomena were performed and one such observation is the deflection of threading dislocations with Burgers vector c/c+a onto the basal plane and associated stacking faults. Based on the model involving macrostep overgrowth of surface outcrops of threading dislocations, SWBXT image contrast studies of these stacking faults on different reflections and comparison with calculated phase shits for postulated fault vectors, has revealed faults to be of basically four types: (a) Frank faults; (b) Shockley faults; (c) Combined Shockley + Frank faults with fault vector s+c/2; (d) Combined Shockley + Frank faults with fault vector s+c/4.

Abstract: Synchrotron White Beam X-ray Topography (SWBXT) imaging of wafers cut parallel to the growth axis from 4H-SiC boules grown using Physical Vapor Transport has enabled visualization of the evolution of the defect microstructure. Here we present observations of the propagation and post-growth mutual interaction of threading growth dislocations with c-component of Burgers vector. Detailed contrast extinction studies reveal the presence of two types of such dislocations: pure c-axis screw dislocations and those with Burgers Vector n₁c+n₂a, where n₁ is equal to 1 and n₂ is equal to 1 or 2. In addition, observations of dislocation propagation show that some of the threading dislocations with c-component of Burgers adopt a curved, slightly helical morphology which can drive the dislocations from adjacent nucleation sites together enabling them to respond to the inter-dislocation forces and react. Since all of the dislocations exhibiting such helical configurations have significant screw component, and in view of the fact that such dislocations are typically not observed to glide, it is believed that such morphologies result in large part from the interaction of a non-equilibrium concentration of vacancies with the originally approximately straight dislocation cores during post-growth cooling. Such interactions can lead to complete or partial Burgers vector annihilation. Among the reactions observed are: (a) the reaction between opposite-sign threading screw dislocations with Burgers vectors c and –c wherein some segments annihilate leaving others in the form of trails of stranded loops comprising closed dislocation dipoles; (b) the reaction between threading dislocations with Burgers vectors of -c+a and c+a wherein the opposite c-components annihilate leaving behind the two a-components; (c) the similar reaction between threading dislocations with Burgers vectors of -c and c+a leaving behind the a-component.

Abstract: The leakage current sources of 4H-SiC Schottky barrier diodes (SBDs) were analyzed using atomic force microscopy (AFM) to determine the surface morphology. Nanosized circular cone shaped pits (nanopits), which depth were distributed from 5 to 70 nm, were observed at the leakage current sources. The leakage currents of 4H-SiC SBDs generate at the nanopits due to the concentration of the electrical field strength. The positions of nanopits correspond to the positions of threading dislocations (TDs), which were identified from molten potassium hydroxide (KOH) etching.