P-N Junction Diode question from NEET 2014 (AIPMT)

Answer: (d)

1. (1) Material: Ge ($\approx 0.3\text{ V}$) and Si ($\approx 0.7\text{ V}$) have different barriers.
2. (2) Doping: heavier doping gives a larger barrier potential.
3. (3) Temperature: barrier falls by about $2\text{ mV/}^\circ\text{C}$.
4. So the answer is (d) (1), (2) and (3).