For the given pairs, CdS, GaN, and GaAs have the larger band gaps when compared to CdTe, InP, and InAs respectively, because elements higher in the periodic table generally contribute to larger band gaps in semiconductors.
The question asks which of the given pairs of semiconductors have the larger band gap.
The band gap is the energy difference between the top of the valence band and the bottom of the conduction band in semiconductors.
This gap determines the electrical conductivity of the material.
Generally, when comparing semiconductors within the same group of the periodic table and with similar structures, the material with the heavier element (further down the periodic table) will have a smaller band gap due to more closely spaced energy levels.
- CdS has a larger band gap than CdTe because sulfur is above tellurium in the periodic table.
- GaN has a larger band gap than InP because gallium is above indium in the periodic table and nitrogen is above phosphorus.
- GaAs has a larger band gap than InAs because gallium is above indium in the periodic table.