Chemical Forums

Specialty Chemistry Forums => Materials and Nanochemistry forum => Topic started by: BluePill on September 10, 2011, 02:49:29 AM

Title: n-type vs p-type
Post by: BluePill on September 10, 2011, 02:49:29 AM

I am confused with the idea of n-type and p-type semiconductors.

If you dope Si with P, it becomes an n-type while Si with Al becomes a p-type. What I don't get is that ZnO thin films would become n-type if doped with Al³⁺. Wouldn't that make it p-type? Moreover, why is Cu⁺ less effective in transforming it to n-type?

Much I've read has been telling me that n-type are electron conducting and p-type are hole conducting. This doesn't make sense.

Title: Re: n-type vs p-type
Post by: Enthalpy on October 14, 2011, 07:14:28 PM

I too learnt that story or Al and P in silicon, with electron and holes conduction, and didn't feel it so senseless. At least, it could explain much of what I experimented. And since this very theory is applied with success to produce chips, there must be some truth in it.

I haven't studied ZnO, but if comparing with GaAs, I suppose the effect of a dopant depends on what atom it replaces... Al replacing Zn would bring one more electron, making it N-type. Within the crystal, Al would become Al³⁺, replacing Zn²⁺. And if Cu has a valence of 2, it won't dope anything by replacing Zn. As well, a dopant level must be near enough to the conduction or the valence band, or it will  be a recombination centre instead of a dopant.

A dopant tends to replace the bigger ion in the crystal, which must be Zn²⁺ rather than O^2-. But in a thin film, which uses to be polycrystalline or amorphous, these simple reasons that work for single-crystals can be very wrong, as grain joints determine most properties and suck impurities.