Hey guys.

I'm a little confused as to how my teacher came in his conclusion on these question.

Question:
Silicon is doped with 5 × 10^16 arsenic atoms/cm3. (a) Is the material n- or p-type? (b) Calculate the electron and hole concentrations at T = 300 K

Ans
a)
n-type
b)
ni = 1.5 x 10^10
no = Nd = 5 × 10^16 cm^-3
po = 4.5 x 10^3 cm^-3


I understand how to do part b), but its determining if its n-type or p-type thats got me confused.
From what I understand
if no<po, then it is p-type
if no>po then it is n-type
but we only have ni and (Nd or Na)...

Question:
A silicon semiconductor material is to be designed such that the majority carrier electron concentration is no = 7 × 10^15 cm^−3 . Should donor or acceptor impurity atoms be added to intrinsic silicon to achieve this electron concentration?
What concentration of dopant impurity atoms is required?

Ans:
Donor
Nd = 7 × 10^15 cm^−3

Is this because an intrinsic material requires no = po = ni?

thanks guys

 

Arsenic is a Group V element (donor), so doping with it creates n-type Silicon.

 

ah cool. So what is the result of doping with Group III or IV?

 

ah cool. So what is the result of doping with Group III or IV?

Group III are acceptors - the missing 4th valence electron creates an extra hole per each dopant atom added. So it would be p-type.

I don't know what the benefit of doping with Group IV atoms would be as this wouldn't change the balance of electrons/holes in the semiconductor (silicon itself is Group IV.) But, I'm far from an expert, so maybe another member can chime in here.