Semiconductor resistivity

Since the 1950s, semiconductor materials have revolutionized electronics, computing and optoelectronics, enabling the production of a huge variety of discrete components and integrated circuits. They owe their success to their extremely rich electronic properties, and in particular to the fact that by doping (i.e. introducing suitable impurities into the material in controlled quantities) :

• to obtain either free-electron conduction (as in metals), or free-hole conduction (a hole being the absence of an electron);

• control the resistivity of the material in a range of values between 10 ^{– 5} and 10 ² Ω · m, through the concentration of doping impurities.

The resistivity of these materials is therefore extremely sensitive:

• the material's crystalline state (amorphous, polycrystalline, monocrystalline) ;

• the level of doping (concentration of electrically active impurities present in the material).

We therefore distinguish four types of material:

• undoped single-crystal material or intrinsic material ;

• doped single-crystal material or extrinsic material (virtually all semiconductor components are made of doped single-crystal material);

• polycrystalline material [MOS (Metal Oxide Semiconductor) gate] ;

• amorphous material (solar cells, flat screens, etc.).

To comply with standardization rules, all quantities have been expressed in the units of the international system. However, it must be recognized that this system is not at all used by specialists in semiconductor materials and components, who prefer a system where lengths are in centimetres and energies in electronvolts (eV). Table 1 gives the conversion factors to be used.