As, we know that the diode only works in forward biased, so the output is obtained only when positive input is given, so the output waveform is

In CE transistor amplifier, the power gain is very high. In this circuit, the extra power required for amplified output is obtained from DC source. Thus, the circuit used does not violate the law of conservation of energy.

The given combination consists of NOR gate and NOT gate, so equivalent gate is OR gate.
Truth Table

From the truth table, it is clear that the output is 1 only when atleast one of the inputs is at the high state(i.e.1).

A material is a conductor, if in its energy band diagram, there is no energy gap between conduction band and valence band. For insulator, the energy gap is large and for semiconductor, the energy gap is moderate. The energy gap for Sn is 0 eV, for C is 5.4 eV, for Si is 1.1 eV and for Ge is 0.7 eV, related to their atomic size. Therefore, Sn is a conductor, C is an insulator and Ge and Si are semiconductors.

The size of the dopant atom should be such that their presence in the pure semiconductor does not distort the semiconductor but easily contribute the charge carriers on forming covalent bonds with Si or Ge atoms, which are provided by group XIII or group XV elements.