as an n type impurity however the concentration of sb could not be more than 5 u00d7 10 18 cm 3 owing to its limitation of solution the inventors have solved this problem by including as in the silicon substrate 1 as the n type impurity as has a higher limitation of solution than sb and therefore solves this problem the concentration of as is set within a range between 7 u00d7 10 18 cm 1 u00d7 10 21 cm 3 therefore the contact resistance between the silicon substrate 1 and the ohmic electrode 26 can be reduced sufficient to avoid a schottky contact and get an ohmic contact since the concentration of as is more than 7 u00d7 10 18 cm 3 a good ohmic contact can be obtained for almost all electrode materials moreover the resistivity of the silicon substrate 1 is also diminished because of the higher concentration of as included in the silicon substrate 1 as an impurity consequently the resistance r3 of the silicon substrate 1 is also reduced the ground surface 22 has been ground to have a concavo convex surface which has many coarse surface irregularities therefore the ohmic electrode 26 can be firmly adhered to the ground surface 22 because the ground surface 22 has a suitable concavo convex surface the process of forming the aforementioned.