Nature of the fundamental band gap in GaNxP1-x alloys

The optical properties of GaNxP1-x alloys (0.007 less than or equal to x less than or equal to 0.031) grown by gas-source molecular-beam epitaxy have been studied. An absorption edge appears in GaNxP1-x at energy below the indirect Gamma(V)-X-C transition in GaP, and the absorption edge shifts to lower energy with increasing N concentration. Strong photomodulation signals associated with the absorption edges in GaNxP1-x indicate that a direct fundamental optical transition is taking place, revealing that the fundamental band gap has changed from indirect to direct. This N-induced transformation from indirect to direct band gap is explained in terms of an interaction between the highly localized nitrogen states and the extended states at the Gamma conduction-band minimum. (C) 2000 American Institute of Physics. [S0003-6951(00)01922-7].