What main properties of semiconductors?
On electrical resistance semiconductors take the intermediate place between conductors and insulators. Point-contact diodes and triodes have the number of advantages: small weight and sizes, considerably bigger service life, big mechanical durability.
Let's consider the main properties and characteristics of poluprovodyonik. Concerning their electrical conductance poluprovodyonik are separated into 2 types: with electronic and hole conductivity.
Semiconductors with electronic conductivity have so nayozyvayemy free electrons which are poorly connected with atomic nuclei. If to put potential difference to this semiconductor, then free electrons will progressively move - in determinate direction, creating thus elektriyochesky current. As in these types of semiconductors electric current represents movement of negatively zaryayozhenny particles, they received the name of conductors like п (from the word negative — negative).
Semiconductors with hole conductivity are called poluyoprovodnik of type р (from the word positive — positive). Passing of electric current in these types of semiconductors can be considered as movement of positive charges. In semiconductors with r-conductivity there are no free electrons; if semiconductor atom under the influence of any reasons poyoteryat 1 electron, then it will be loaded positively.
The lack of one electron in atom causing the polozhiyotelny charge of atom of the semiconductor was called the hole (it znayochit that the empty seat in atom was formed). The theory and experience show that holes behave as elementary polozhitelyyony charges.
Hole conductivity consists that under the influence of priyolozhenny potential difference holes that ravnoyosilno to movement of positive charges move.
In fact, at hole conductivity there is the following. Let's assume that there are 2 atoms, one of which is supplied with the hole (otsutyostvut 1 electron in the external orbit), and another, находящийся on the right, has all electrons on the places (we will call it neyyotralny atom). If the potential difference, then under the influence of electric field the electron from the neutral atom which has all electrons on the places is attached to the semiconductor, will move to the left to the atom supplied with the hole.
Thanks to it the atom which had the hole becomes neutral, and the hole pereyomestitsya to the right on atom which the electron left. In poluprovodyonikovy devices process of "filling" of the hole with the free elektroyon is called the recombination. As a result of the recombination both the free electron, and the hole disappears, and the neutral atom is created. And so movement of holes happens in the direction opposite to the movement of electrons.
In absolutely clean (own) semiconductor under the influence of heat or light electrons and holes are born couples therefore the number of electrons and holes in the intrinsic semiconductor is identical.
For creation of semiconductors with sharply expressed electron concentrations or holes clean semiconductors supply with impurity, forming impurity semiconductors. Impurity happen the donor, giving electrons, and the acceptor, forming holes (i.e. the tearing-off electrons from atoms). Therefore, in the semiconductor with donor impurity the conductivity will be mainly electronic, or n - conductivity. In these semiconductors majority carriers of charges are electrons, and nonbasic - holes. In the semiconductor with acceptor impurity, on the contrary, majority carriers of charges are holes, and nonbasic - electrons; these are semiconductors with r-conductivity.
Serve as the main materials for production of point-contact diodes and triodes germaniye and silicon; in relation to them donors are antimony, phosphorus, arsenic; acceptors - indiya, gallium, aluminum, the pine forest.
Impurity which are usually added to the crystalline semiconductor sharply change the physical picture of passing of electric current.
At formation of the semiconductor with n-conductivity in the poluyoprovodnik donor impurity is added: for example, in the poluproyovodnik of germaniye antimony impurity is added. The antimony atoms which are donor report Germany many free electrons, being loaded at the same time is positive.
Thus, in the semiconductor of n-conductivity, obrazovanyony the following types of electric zaryayod are available impurity:
- mobile negative charges (electrons) which are majority carriers (both from donor impurity, and from sobyostvenny conductivity);
- mobile positive charges (holes) - the minority carriers which arose from own conductivity;
- motionless positive charges - ions of the donor priyomesa.
At formation of the semiconductor with r-conductivity acceptor impurity is added to the semiconductor: for example, India impurity is added to the semiconductor of germaniye. Atoms India being acceptor, tear off from atoms Germany elekyotrona, forming holes. Atoms India at the same time are loaded negatively.
Therefore, in the semiconductor of r-conductivity there are sleyoduyushchy types of electric charges:
- mobile positive charges (holes) - the main noyositel who arose from acceptor impurity and from own proyovodimost;
- mobile negative charges (electrons) - the neosnovyony carriers which arose from own conductivity;
- motionless negative charges - ions of acceptor impurity.
In fig. 1 plates r-Germany (a) and n-Germany (b) with the arrangement of electric charges are shown.Top