Coupled donor states in InP by Sn doping

Coupled donor states induced by Sn doping into InP and their behaviors were studied by employing photoluminescence (PL) measurements and first-principles calculations. InP: Sn crystals were grown in the [100] orientation by a modified liquid-encapsulated vertical Bridgman technique. The PL data show a donor-acceptor recombination line and its phonon replica at 898 nm and 926 nm, respectively, and another recombination line around 800 nm, which uniquely appears at the top in high Sn concentration. The first-principles calculations for the InP:Sn system support these results by observing two separate donor levels below (DSn1) and above (DSn2) the bottom of the conduction band, which are responsible for the recombination lines. They deviate from the bottom of the conduction band with the increase of Sn concentration. A peak at 879 nm from the band-to-band transition could only be visible at room temperature. The PL mapping of this line shows the increase of Sn concentrations with the crystal growth, which helps to reduce the dislocation density and increase the lifetime of excess carriers.