Mutual passivation of electrically active and isovalent impurities

The alloy GaN_xAs_1-x (with x typically less than 0.05) is a novel semiconductor that has many interesting electronic properties because of the nitrogen-induced dramatic modifications of the conduction band structure of the host material (GaAs), Here we demonstrate the existence of an entirely new effect in the Ga_xAs_1-x alloy system in which the Si donor in the substitututional Ga site (Si_Ga) and the isovalent atom N in the As sublattice (N_As) passivate each other's electronic activity. This mutual passivation occurs in Si-doped GaN _xAs_1-x through the formation of nearest-neighbour Si _Ga-N_As pairs and is thermally stable up to 950 °C. Consequently, Si doping in GaN_xAs_1-x under equilibrium conditions results in a highly resistive GaN_xAs_1-x layer with the fundamental bandgap governed by a net 'active' N, roughly equal to the total N content minus the Si concentration. Such mutual passivation is expected to be a general phenomenon for electrically active dopants and localized state impurities that can form nearest-neighbour pairs.