The barrier (built-in) potential of an unbiased silicon p-n junction at room temperature is approximately

1. The barrier (built-in) potential of a p-n junction depends on the band gap of the semiconductor material. 2. For Si, the band gap is $E_g \approx 1.1\,\text{eV}$ and the room-temperature barrier potential is about $0.7\,\text{V}$. 3. For Ge, with band gap $E_g \approx 0.67\,\text{eV}$, the barrier potential is about $0.3\,\text{V}$. 4. These numbers also correspond to the FORWARD-BIAS THRESHOLD voltages: a Si diode needs $\sim 0.7\,\text{V}$ before significant current flows, a Ge diode needs $\sim 0.3\,\text{V}$. NEET-PMT problems often test this knee voltage. 5. Option A is the Ge value. Option C is the barrier for compound semiconductors like GaAs. Option D is an inflated value not consistent with elemental semiconductor band gaps. _Source: NCERT Class 12 Physics Part 2, Ch 14, §14.5.1 + §14.6.1 (barrier potential, diode I-V), p. 11–12._