grade second semiconductor substrate 52 having a much lower defect density than the first semiconductor substrate 40 can be obtained the growth conditions for the second semiconductor substrate 52 are the same as those for the second semiconductor substrate 46 of fig1 in the first embodiment fig1 shows one moment of a process in which the initial second semiconductor substrate 52 a is grown from the second rugged portion 51 of the first semiconductor substrate 40 here the initial second semiconductor substrate 52 a is thinly grown on the entire surface of the second rugged portion 51 meanwhile micro pl mapping was performed to analyze the distribution of crystalline defects within each of the second semiconductor substrates 46 48 and 52 formed according to the first through third embodiments respectively of the present invention the results are shown in fig1 through 20 fig1 is a photograph showing the result of analyzing the crystalline defects of the second semiconductor substrate 46 formed according to the first embodiment fig1 and 20 are photographs showing the results of analyzing the crystalline defects of the second semiconductor substrates 48 and 52 formed according to the second and third embodiments respectively referring to fig1 a bright portion p 1 is a trench portion in which defects are reduced due to a lateral growth and a dark portion p 2 corresponds to a substrate between trenches in fig1 bright and dark lines p 3 and p 4 are shown here bright lines p 3 means that defects are.