Tetra valent semiconductor is to be doped with ---------------valent element to achieve -----------------type extrinsic semiconductor.

 When a semiconductor having 4 valence electrons is doped with an element having 3 valence electrons, then an excess hole is generated and the semiconductor becomes p-type extrinsic semiconductor. When a semiconductor having 4 valence electrons is doped with an element having 5 valence electrons, then an excess electron becomes available and the semiconductor becomes n-type extrinsic semiconductor.