Resistance of semiconductors is interesting as in respect of an intermediate position in the size between metals and dielectrics, and in respect of distinctive dependence on temperature.
It is required to you
- The textbook on electrical equipment, a pencil, the sheet of paper
Instruction
1. Master the main data on the structure of semiconductors from textbooks on electrical equipment. The fact is that all regularities characteristic of semiconductors are explained by the nature of their internal building. The explanation of this nature is based on the so-called zonal theory of solid bodies. This theory explains the principles of the organization of conductivity of macrobodies by means of power charts.
2. Draw the vertical axis designated by energy on the sheet of paper. On this axis energy (power levels) of electrons of atoms of substance will be designated. Each electron has a set of possible power levels at which it can be. It is worth noticing that only power levels of electrons of external orbitals of atoms because they affect conductivity of substance will be designated in this case. It is known that atoms in a firm macrobody a huge number. It leads to the fact that on the power chart of this body there is a huge number of lines of power levels which almost continuously fill out the chart.
3. However, if you correctly draw all these lines, then will notice that in some area there is a gap, that is there is such interval of the power chart in which there are no lines. Thus, all chart is divided into three parts: a valent zone (lower), forbidden zone (there are no levels) and a conductivity zone (top). The zone of conductivity answers those electrons which wander in free space and can participate in conductivity of a body. The electrons having energy of a valent zone do not participate in conductivity, they are strictly attached to atom. The power chart of semiconductors in this context differs in the fact that width of the forbidden zone is rather small. It leads to an opportunity for transition of electrons from a valent zone in a conductivity zone. The usual conductivity of the semiconductor at the room temperature is caused by the fluctuations throwing electrons in a conductivity zone.
4. Present that semiconductor substance heats up. Heating leads to the fact that electrons of a valent zone receive enough energy to pass into a conductivity zone. Thus, more and more electrons have an opportunity to participate in conductivity of a body, and in an experiment it becomes visible that at increase in temperature the conductivity of the semiconductor increases.