91Ó°ÊÓ

The band gap generally increases with increasing atomic number within a given period (row) and decreases with increasing period number (column) in the periodic table. Additionally, the band gap decreases as we move down a group, due to an increase in the atomic radius and the shielding effect from inner electrons. Step 2: Determine the larger band gap for each pair of semiconductors

(a) InP or InAs: Comparing the group and period of the main elements in these semiconductors (In and P in InP and In and As in InAs), we see that phosphorus (P) is above arsenic (As) in the same group of the periodic table. The periodic trend suggests that InP will have a larger band gap than InAs. Therefore, InP has the larger band gap. (b) Ge or AlP: Comparing the main elements in these semiconductors (Ge in Ge and Al and P in AlP), we see that Ge is in the same period as Al but in a different group, while P is in the same group as Ge but in a different period. According to the periodic trend, the band gap generally increases with increasing atomic number within a given period. Therefore, AlP will have a larger band gap than Ge. Thus, AlP has the larger band gap. (c) AgI or CdTe: Comparing the main elements in these semiconductors (I in AgI and Cd and Te in CdTe), we see that iodine (I) is below tellurium (Te) in the same group of the periodic table. The periodic trend suggests that the band gap will decrease as we move down a group. Therefore, the semiconductor with Te (CdTe) will have a larger band gap than the one with I (AgI). Thus, CdTe has the larger band gap. To summarize, the semiconductors with larger band gaps are: (a) InP, (b) AlP, and (c) CdTe.