Silicon carbide crystal

Abstract

A silicon carbide crystal includes a seed layer, a bulk layer, and a stress buffering structure formed between the seed layer and the bulk layer. The seed layer, the bulk layer, and the stress buffering structure are each formed with a dopant that cycles between high and low dopant concentration. The stress buffering structure includes a plurality of stacked buffer layers and a transition layer over the buffer layers. The buffer layer closest to the seed layer has the same variation trend of the dopant concentration as the buffer layer closest to the transition layer, and the dopant concentration of the transition layer is equal to the dopant concentration of the seed layer.

What is claimed is: 
     
         1 . A silicon carbide crystal, comprising a seed layer, a bulk layer, and a stress buffering structure formed between the seed layer and the bulk layer, wherein the seed layer, the bulk layer, and the stress buffering structure are each formed with a dopant, and the dopant of the stress buffering structure cycles between high and low dopant concentrations;
 characterized in that the stress buffering structure includes a plurality of stacked buffer layers and a transition layer over the buffer layers, wherein the buffer layer closest to the seed layer has the same variation trend of the dopant concentration as the buffer layer closest to the transition layer, and the dopant concentration of the transition layer is equal to the dopant concentration of the seed layer;   wherein each of the buffer layers has a dopant concentration gradient in its thickness direction;   wherein the dopant of the seed layer has a reference concentration, and the dopant concentration gradient gradually increases or decreases between the reference concentration and a first concentration higher than the reference concentration.   
     
     
         2 . The silicon carbide crystal of  claim 1 , wherein each of the buffer layers has a thickness that is greater than 0 μm and less than 0.1 μm. 
     
     
         3 . The silicon carbide crystal of  claim 2 , wherein the stress buffering structure has a thickness that is less than 0.1 mm. 
     
     
         4 . The silicon carbide crystal of  claim 1 , wherein the dopant of the seed layer has a reference concentration, any one of the buffer layers has a maximum dopant concentration lower than or equal to ten times the reference concentration. 
     
     
         5 . The silicon carbide crystal of  claim 1 , wherein the bulk layer has a micropipe defect density that is less than 0.2 cm −2 . 
     
     
         6 . The silicon carbide crystal of  claim 1 , wherein the bulk layer has a basal plane dislocation density that is 500 cm −2 .