Gallium phosphide (GaP) is an important semiconductor material used in LED fabrication
CHEMISTRY · Multi-part · IB Diploma Programme · Chemistry · Materials and Bonding Models · Materials and Bonding Models
Problem
Gallium phosphide (GaP) is an important semiconductor material used in LED fabrication. In a proposed modification, a materials scientist suggests substituting 10 % of the Ga atoms with calcium to create Ca0.1Ga0.9P.
(a) Identify the predominant type of chemical bonding in pure GaP and justify your answer by referencing the positions of Ga and P in the periodic table and their qualitative electronegativities.
(b) Explain why GaP exhibits electrical conductivity intermediate between that of metals and of typical covalent molecular solids.
(c) Predict how partial replacement of Ga with Ca is likely to affect (i) the overall bonding character in the solid and (ii) the band gap of the material. Provide reasoning for each prediction.
(d) The scientist also considers replacing Ga with aluminum instead of calcium. Compare the expected effects of Al substitution on bonding character and electrical properties with those predicted for Ca substitution in part (c).