Infra-red Absorption in Gallium Phosphide-Gallium Arsenide Alloys I. Absorption in n-type Material

Abstract

There is an absorption band at 3 μm in n-type gallium phosphide for which a number of explanations have been advanced. These are discussed, and it is shown that a distinction may be made between them by observing the 3 μm band as a function of composition in GaPxAs1-x alloys. Experimentally it is found that at liquid nitrogen temperatures the band is present only if x > 0.50 ± 0.015, and for phosphorus-rich alloys the magnitude and shape of the band vary little with temperature from room temperature downwards. These facts suggest that the transition involved is one from hydrogen-like donor impurities near the conduction band minima to an upper conduction band which has been split off by the lack of a centre of symmetry in the crystal. Above room temperature transitions from the lowest conduction band to this upper band become important.