P-type and type N-type material

Pure silicon (intrinsic) is a semiconductor material, has 4 electrons in its valence band atoms bond together by a covalent bond (see fig 1). When we provide heat energy to a semiconductor material such as silicon, some electrons flow from the valence shell and become free electrons, leaving a hole. A hole is then the site leaving an electron leaves the valence shell and become a free electron. A free electron has a higher energy level that an electron orbiting in the valence shell. When a free electron falls into a hole, it releases energy and this process is called recombination.

  • Extrinsic p-type silicon: A P-type material was achieved by replacing some atoms intrinsic semiconductor like silicon, atoms of an element with fewer electrons in its valence shell, usually 3 (trivalent), as the Boro. This process is called doping and manages to increase the number of holes. When atoms replace some intrinsic material other extrinsic material with fewer electrons in the valence shell, a neighboring atom gives up an electron to complete the link, and thus produces a free electron movement within the network.
  • Extrinsic n-type silicon: A N-type semiconductor is achieved through a process of adding some type of doping element usually pentavalent (5 electrons in the valence shell), the semiconductor to increase the number of free electrons. If an atom with five valence electrons such as phosphorus (P), arsenic (As) or antimony (Sb), is incorporated into the lattice in place of a silicon atom, then that atom will have four covalent bonds and an unbound electron. This extra electron results in the formation of free electrons, and the number of free electrons exceeds the number of holes, in this case the holes are minority carriers and electrons are the majority carriers.

The internal barrier potential

By joining material type N and type P, some free electrons recombine N side pockets on P in a phenomenon called diffusion. Upon diffusion appear charges in the joint area, this area is called the internal barrier potential. As the spread increases the potential barrier is widened, and generates an electric field that counteracts the phenomenon of diffusion to stabilize (see fig. 2). This electric field is equivalent to saying that there is a difference in potential between P and N areas, this potential difference (V0) is 0.7 V for silicon and 0.3 V if the crystals are germanium (Ge) (see fig. 3).

Bias the PN junction

For a left-biased PN is, connect the positive pole of a battery to the anode and the negative pole to the cathode. Under these conditions the negative free electron repels the glass N, so that the electrons are directed toward the PN junction. The positive pole attracts the valence electrons of the crystal P, which is to say that drives the holes towards the pn junction.

When the potential difference between terminals of the battery electric field exceeds the potential barrier, the free electrons of the crystal N acquire enough energy to jump into the voids of the crystal P, which previously, as mentioned above, have moved to the pn junction.

 

Figure 1. Silicon crystal structure.
 
 
 

 
Figure 2. Polarized example.
 

 

 
Figura 3. Polarized example.