Question

please say why you have chosen this answer in details also please clear hand writing thanks in advance

(v) When doping a semiconductor p type, the bulk of the material has:

      A positive charge

       A negative charge

       Is neutral

        Will only get a positive charge when we apply a voltage

Explain why you chose this answer:      

(vi) In order to generate free charge carriers by optical excitation, the wavelength of the incident light needs to be:   

      Monochromatic (single wavelength)

       Longer than the cut-off wavelength of the material

       Shorter than the cut-off wavelength of the material

        Of a very high intensity to penetrate the material

Explain why you chose this answer:

(vii) Light of the correct wavelength to produce optical excitation is incident on a piece a p-type Si. This will produce:

      A greater number of holes than electrons

       A greater number of electrons than holes

       A greater change in the number of holes relative to the number before illumination

        A greater change in the number of electrons relative to the number before illumination.  

Explain why you chose this answer:

(viii) Compared to silicon, compound semiconductors such as GaAs will always:

      Have a direct bandgap

       Be more expensive to produce

       Be easier to dope  

       Allow us to easily vary the bandgap.   

Explain why you chose this answer:

Answer 1

1-

Answer is (c) : is Neutral

p-type material by itself has mainly positive charge carrier (holes) which are able to move relatively freely, but it is still neutral because the fixed acceptor atoms, having accepted electrons, are negative.

2-(C)

3-(D) A greater change in the number of electrons relative to the number before illumination.

Because in p type semiconductor, holes are already in excess. So when you grant optical excitation, then the new electron gap pairs are generated in equal numbers. But we already had holes in excess, so the newly generated holes will no longer have any considerable effect. But on the other hand, as we solely had a few electrons earlier than illumination, so after illumination the electrons quantity will extend to a an awful lot larger extent.

4-Compound Semiconductors are usually made up of various columns or periodic table classes e.g. Group III (Ga and V (As) elements & Group II (Zn) and VI (Se) elements.

• Compound semiconductor can be direct band gap as well as indirect bandgap semiconductors.
  • Examples
  • compound Direct bandgap:  GaAs, GaN, ZnSe and GaP.
  • compound indirect bandgap: SiC.

1st option is wrong as compound SiC ( Semiconductor) can be direct as well as indirect band-gap.

In comparison to Si semiconductors, the Compound SC is usually high in cost and difficult to process. The difficulties inherent in handling the compound SC products are attributed to the large prices.

option 2nd " Be more expensive to produce" is right option.  

Doping elementary SC Silicon as compound SC is always easy, because we only have to deal with one type of SC in the elementary SC.

So option 3 " Easier to dope" is wrong

One can change the compound SC's band gap by adjusting the composition. Through modifying a compound SC 's composition, one may build new SC itself whose band gap is specific yet set. Therefore, by adjusting the composition of compound SC i.e. with specific composition, we may adjust the bandgap. It is not quite simple, and the band gap is fixed at that composition.

So Last option 4, " Allow us to easily vary band gap" is also wrong.