In the band diagram of a semiconductor, the Fermi level represents the energy level at which the probability of finding an electron is 50%. It plays a crucial role in determining the electrical and optical properties of the semiconductor. Let's analyze the given information and understand why the correct answer is option 'C', which represents the donor level.

1. Understanding the Fermi Level:
The Fermi level is an energy reference point that lies within the energy band gap of a semiconductor. It separates the energy levels occupied by electrons (valence band) from the energy levels that are unoccupied (conduction band). The position of the Fermi level is determined by the doping concentration and temperature of the semiconductor.

2. Intrinsic Level and Fermi Level:
In an intrinsic semiconductor, the Fermi level is located at the middle of the energy band gap. This is because there are equal numbers of electrons in the valence band and holes in the conduction band, resulting in a balanced state with no net charge. In this case, the Fermi level is equal to the intrinsic level.

3. Fermi Level Position in Doped Semiconductors:
When a semiconductor is doped with impurities, the Fermi level shifts either towards the conduction band (for n-type doping) or towards the valence band (for p-type doping). This shift occurs due to the introduction of extra electrons or holes in the semiconductor.

4. Given Information:
According to the given information, the Fermi level is 0.3 eV above the intrinsic level. This implies that the semiconductor is n-type doped, as the Fermi level has moved closer to the conduction band.

5. Donor Level in N-Type Doped Semiconductor:
In n-type doped semiconductors, the dopant atoms introduce extra electrons into the conduction band, which increases the electron concentration. These dopant atoms are called donors. The energy level associated with these donor atoms is known as the donor level.

6. Conclusion:
Based on the given information, the Fermi level being 0.3 eV above the intrinsic level indicates n-type doping. Therefore, the correct answer is option 'C', which represents the donor level. This energy level represents the energy required for an electron to transition from the donor level to the conduction band, thus contributing to the increased electron concentration in the semiconductor.