Hello Sona,

I assume, we have to discuss unipolar transistors. Then, we must know something about the purpose of such a transistor.

An unipolar transistor controls the conductivity sigma = e*n*µ (if n-type] or sigma = e*p*µp for p-type material.

In p-type material, the conductivity takes place in the valence band. The properties of the band of conductivity here are rather not from interest and therefore not the kind of gap.

For n-type material we discuss the purpose of the transistor. For high frequency applications (amplifier for sattelite TV) the mobility µ must be high. The mobility µ = e*tau/m* (tau lifetime, m* effective electron mass) is high for low effective masses. Here, a direct gap is beneficial, like GaAs.

For power electronic, high temperatures must be withstanded. This requires "high" gaps, but regardless of which type.

With Regard

R. Mitdank

Dear Sona,

welcome,

The direct gap is not a necessary condition for making good transistors. Till now the best transistors are built from silicon which is a indirect gap material. Also good transistors are built from GaAs material which is a direct gap material.

I would like to direct you to my book on electronic devices where you will find clear operating principles of the transistors and how they are ideally constructed.

To get the book please follow the link: Book Electronic Devices

Best wishes

to get perfect and good transistor I advice you to use nanomaterials

warmest reqards