The present invention is effective if any one of the following gas or their mixture gas is introduced at the time of forming the surface layer: raw material gas containing nitrogen atoms, such as nitrogen or ammonia gas; raw material gas containing oxygen atoms, such as oxygen , nitrogen monoxide , nitrogen dioxide , {HEAD ~ dinitrogen monoxide} , carbon monoxide or carbon dioxide gas; and dopant gas such as diborane , boron fluoride or {TAIL ~ phosphine gas} 
The present invention is effective if any one of the following gas or their mixture gas is introduced at the time of forming the surface layer : raw material gas containing nitrogen atoms , such as nitrogen or ammonia gas ; raw material gas containing oxygen atoms , such as oxygen , nitrogen monoxide , nitrogen dioxide , { HEAD ~ dinitrogen monoxide } , carbon monoxide or carbon dioxide gas ; and dopant gas such as diborane , boron fluoride or { TAIL ~ phosphine gas }
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