Propagation and Density Reduction of Threading Dislocations in SiC Crystals during Sublimation Growth

Abstract

SiC single crystal wafers grown by sublimation exhibit relatively high dislocation densities. While it is generally known that the overall dislocation density tends to decrease throughout crystal growth, there has been a limited quantitative analysis of such trend. In this study, we measured the density of threading dislocations in the wafers sliced from several SiC boules. Although the dislocation density in the wafers sliced from different boules could differ by orders of magnitude, a consistent empirical relationship was found between the dislocation density (ρ) and the axial wafer position within the crystal (w):Monte Carlo simulations were performed based on two assumptions: (i) during growth the threading dislocations move randomly in the lateral directions, and (ii) two dislocations of opposite sign annihilate when they come within a critical distance between them. Good agreement was achieved between the model and experimental results. The critical distance determined from the simulations was in the range between a few hundred Ă and a micron.

A Follow-up Study on Bauschinger’s Effect in Bidirectional Wear of Cu-40%Zn against Different Types of Counter-Face

“…At the microscopic level, Bauschinger's effect could be attributed to local reversible movement of dislocations [9][10][11] and annihilation of dislocations with opposite signs [12][13][14] as the applied stress is reversed. These decrease the rate of dislocation accumulation and consequently lower the strain-hardening rate [9,[15][16][17][18]. It is expected that Baushinger effect should also play a role in wear processes involving wearing stress reversal such as cyclic abrasion and saw cutting processes.…”