| CPC H01L 29/2003 (2013.01) [H01L 21/02145 (2013.01); H01L 21/0254 (2013.01)] | 18 Claims | 

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               1. A semiconductor structure, comprising: 
            a substrate; 
                a first nitride layer formed on the substrate; 
                a polarity inversion layer formed at a surface of the first nitride layer to convert a non-metallic polar surface of the first nitride layer into a metallic polar surface of the polarity inversion layer; 
                a second nitride layer formed on the polarity inversion layer; and 
                a third nitride layer formed on the second nitride layer. 
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