# Semiconductor Doping

Discussion in 'Homework Help' started by Jess_88, Oct 18, 2011.

1. ### Jess_88 Thread Starter Member

Apr 29, 2011
174
1
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

2. ### Zazoo Member

Jul 27, 2011
114
43
Arsenic is a Group V element (donor), so doping with it creates n-type Silicon.

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3. ### Jess_88 Thread Starter Member

Apr 29, 2011
174
1
ah cool. So what is the result of doping with Group III or IV?

4. ### Zazoo Member

Jul 27, 2011
114
43
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.

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