Papers by Author: Amitesh Shrivastava

Abstract: The temperature dependence of the carrier lifetime was measured in n-type 4H-SiC epilayers of varying Z1/2 deep defect concentrations and layer thicknesses in order to investigate the recombination processes controlling the carrier lifetime in low- Z1/2 material. The results indicate that in more recently grown layers with lower deep defect concentrations, surface recombination tends to dominate over carrier capture by other bulk defects. Low-injection lifetime measurements were also found to provide a convenient method to assess the surface band bending and surface trap density in samples with a significant surface recombination rate.

Abstract: In this work we report the measurement of minority carrier lifetimes using the time resolved photoluminescence technique. It was found that 4H-SiC homo-epilayers grown using chlorine-based precursors have longer carrier lifetimes if used in conjunction with a tantalum carbide coated (TaC-coated) graphite susceptor rather than a SiC-coated graphite susceptor. Longer carrier lifetimes were obtained by optimal combinations of precursor gases and susceptor type. The controllable variation in lifetime from 250 ns to 9.9 s was demonstrated.

Abstract: In this work we identified the nucleation sites of inverted pyramid defects in 4H-SiC epilayers using AFM and KOH etching and proposed a mechanism for its formation. Partial dislocations, bounding the stacking faults, mostly aligned along the <11-20> directions, were found at the base of the inverted pyramid defects. It is shown that the basal plane dislocations, serve as nucleation centers for stacking faults, and eventually the formation of inverted pyramid defects. A geometrical model is formulated to explain the formation mechanism of inverted pyramid defects.

Abstract: The effects of measurement technique and measurement conditions (injection level, temperature) on the measured carrier lifetimes in n- 4H-SiC epilayers are investigated. For three optical measurement techniques, it is shown that the high and low injection lifetimes can vary dramatically. Differences in the lifetime for varying injection level and temperature are approached both experimentally and via carrier dynamics simulations, assuming Z1/Z2 as the dominant defect. Reasonable agreement between measured and calculated behavior is obtained, as is insight into the recombination kinetics associated with the lifetime limiting defect.

Abstract: Triangular defects and inverted pyramid type defects formed during homoepitaxial growth on 4H-SiC Si face, 4° off-cut towards [11-20] direction have been investigated. Growth parameters responsible for triangular defect formation were identified and optimized for its reduction in this study. It was found that although the high temperature reduces the density of inverted pyramid type defects, it is not the only remedy for reducing their density and cleanliness of susceptor along with the initial growth condition plays a major role in the formation of these defects.

Abstract: Dislocations were tracked from 4H-SiC epilayer to the substrate by a new method based on combination of molten KOH etching and Reactive Ion Etching. It was found that basal plane dislocations (BPDs) with dislocation lines parallel (or approximately parallel) to the off-cut direction might propagate as BPDs into the epilayer, while those with dislocation lines forming large angles (>10º) with the off-cut direction will get converted to threading edge dislocations (TEDs). A model is proposed to explain the observations.