Arrange the following materials with respect to their relative dielectric constants in descending orders : (A) Ge Choose the most appropriate answer from the options given below :
(B) C
(C) CdS
(D) TiO2
(D), (A), (C), (B)
The descending order is TiO2, Ge, CdS, C — option 2.
| Material | Relative permittivity | Kind |
|---|---|---|
| (D) TiO2 | ~80 – 100 | Ionic ceramic |
| (A) Ge | 16 | Narrow-gap semiconductor |
| (C) CdS | ~8.9 | Wide-gap compound semiconductor |
| (B) C (diamond) | 5.7 | Very wide-gap insulator |
The physical trend behind the numbers. Permittivity measures how readily a material's charge redistributes under an applied field, and two mechanisms contribute.
Electronic polarisation — the displacement of the electron cloud relative to the nucleus — dominates in covalent semiconductors, and it is larger when the electrons are less tightly bound. That means permittivity rises as the band gap falls, and the ordering of the three covalent materials follows exactly:
| Material | Band gap | εr |
|---|---|---|
| Ge | 0.67 eV | 16 |
| CdS | 2.4 eV | 8.9 |
| Diamond | 5.5 eV | 5.7 |
Diamond's electrons are held in extremely strong, short covalent bonds, so the cloud barely shifts and the permittivity is the lowest of the four.
Ionic polarisation is what puts TiO2 far ahead. In an ionic crystal whole ions — not merely electron clouds — are displaced by the field, and in titanium dioxide the Ti ion sits in a large, easily distorted oxygen cage. That gives a permittivity an order of magnitude above any of the semiconductors, which is why titanates are the basis of ceramic capacitors.
A useful check on any candidate ordering : TiO2 must be first by a wide margin and diamond last, since the two mechanisms place them at opposite extremes. Options 1, 3 and 4 all misplace one of the remaining pair; only option 2 also puts germanium, the narrowest-gap material, above the two wide-gap ones.
Hence, the descending order is (D), (A), (C), (B).
Similar Questions
The most common kind of area defect found in silicon is the ________ and it always occur along ________ plane.
Atomic numbers for the following semiconducting and doping materials like Ga, In, As, Sb are respectively :
A. 33
B. 49
C. 31
D. 51
Choose the correct answer from the options given below :
Arrange the following materials in ascending order based on their mobility of electrons at 300 K :
(a) Germanium (b) Silicon (c) Gallium Arsenide (d) Gallium Nitride
Codes :
Energy bands of a material is decided by :
(a) The atomic number
(b) Relative spacing of atoms in the solids
(c) Melting point of the material
(d) Hardness of the materialWhich of the following is correct ?
Important Questions from Semiconductor Materials
Which of the following is NOT an advantage of a hot carrier diode?
Silicon Controlled Rectifier (SCR) is usually turned on by
The forbidden energy gap for germanium is
Which of the following is NOT an example of a semiconductor material?
In an N-type semiconductor, there are
