If now such p-type material is subjected to an electric field by applying a voltage then the holes move in a valence band and are mainly responsible for the conduction. So the
1.10.1 Conduction in p-Type Semiconductor
Fig. 1.13 Conduction in p-type material
current conduction in p-type material is predominantly due to the holes. The free electrons are also present in conduction band but are very less in number. Hence holes are the majority carriers while electrons are minority carriers in p-type material. The conduction in p-type material is shown in the Fig. 1.13.
1.11 P-N Junction
The two type of materials namely p-type and n-type are chemically combined with a special fabrication technique to form a p-n junction. The p-n junction forms a popular semiconductor device called diode. The diode is the basic element of number of electronic circuits. Hence the knowledge of p-n junction and its behaviour is very important in understanding the operation of number of electronic circuits, applications and devices.
Let us study first the features of unbiased p-n junction.
1.11.1 Unbiased P-N Junction
If in a given material if the doping is not uniform then at one place large number of charge carriers exist while at other place small number of charge carriers exist. In a high charge carrier concentration area, all charge carriers are of similar type, either electrons or holes and hence start repelling each other. Due to this, charge carriers start moving from high cocentration area towards low concentration area, to achieve uniform concentration all over the meterial. This process is called diffusion and exists when there is nonuniform concentration of charge carriers in the material. In a p-n junction, on ท side there are large number of electrons while on p side electrons arc minority in number. So there is high