Measurement of diffrent parameters in semiconductor material
Measurement of conductivity : four Probe method
Four Probe method is used to measure the conductivity, non destructively and accurately. The conductivity of ingot / slides both thick or thin of semiconductor crystal. The arrangement of four point probe method is shown in above figure. The probe head basically implies four spring loaded dimensions needle which may contact with plane flat surface of sample.
The stabilized current is passed through the outer pair of probe that is one and four. And voltage V is applied across other to probe two and 3 .
The voltmeter drop small current through it. the sample dimension is to be very large in comparison to the separation between two Probe that is "d".
Hot probe method
The parameters like impurity concentration, mobility of charge carrier of crystalline semiconductor can be easily determined by the conventional method like four point probe method.
However hot point probe method is a fast and efficient way to find the type of semiconductor whether it is P type or N type with the help of multimeter.
Pair of cold probe and hot attached to semiconductor. The hot Probe is connected to positive terminal of multimeter and cold probe is connected to negative terminal of multimeter. The heat from probe will create and increased number of higher energy carrier which then diffuse away from the contact point. This will cause potential difference in tern electric current.
Example if heat source is placed on the positive lead and voltmeter attached to N type semiconductor, a positive voltage reading will result as area around hot Pro becomes positively charged.
The hot point Pro can be described in 3 step process..
- The hot probe excites free charge carrier of two type
- The hot majority career begin to leave hot part of semiconductor by a diffusion process where builtin electric field is created between the electrode at the same time second electron also get warmed. This process is called warming of the cold probe and this warming process and built in electric field prevent diffusion process up to steady state condition. The study state condition exist until we switch off the heating source.
- At the end the recombination of excited charge carrier take place.
