Answer: C, semiconductor.
Answer analysis: First, let's deeply understand the key concepts in the question: LED (light-emitting diode) and the definition of semiconductor devices, and then analyze each option one by one.
LED, or light-emitting diode, is a semiconductor electronic component that can convert electrical energy into light energy. This conversion process is achieved by releasing energy through the recombination of electrons and holes, and this energy is eventually emitted in the form of photons, thereby emitting visible light. The core material of LED is semiconductor, which is the basis for its conversion of electrical energy into light energy.
Now, let's analyze the options one by one:
A. Insulator: Insulators are objects that are not easy to conduct electricity, also called dielectrics. They can hardly conduct current, which is inconsistent with the characteristics of LED as an electronic component, which needs to conduct electricity to realize its function. Therefore, option A is wrong.
B. Conductor: Conductors are objects that are easy to conduct electricity, such as metals, graphite, etc. Although they have good conductivity, they do not have the function of converting electrical energy into light energy, which is inconsistent with the working principle of LED. Therefore, option B is wrong.
C. Semiconductor: Semiconductors are materials with conductivity between conductors and insulators, such as silicon, germanium, selenium, gallium arsenide, etc. Semiconductors can conduct electricity or not under certain conditions, which makes them ideal materials for manufacturing various electronic devices (including LEDs). LEDs use this property of semiconductors to achieve the conversion of electrical energy into light energy. Therefore, option C is correct.
D. Superconductor: Superconductors are conductors with zero resistance at a certain temperature. In the superconducting state, current can flow in the conductor without loss. However, this is completely inconsistent with the function of LED as a light-emitting device, because the key to LED is that it can convert electrical energy into light energy, rather than conduct current without loss. Therefore, option D is wrong.
In summary, LED is a semiconductor device, and the correct answer is C.