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Mar17-10, 05:12 PM
P: 38
Background: I have a BS in CompSci, not Physics, so if this question stuns you in its naivete, please forgive me. In the last couple weeks, I have been reading up on PN junctions and how they work. I've also seen the standard Si/Ge (Group IV) + Tri/Penta-valent (Group III/V) doping examples.

Despite their efforts to escape I think I have those basics trapped within my brain.

Wikipedia has a nice "list of semiconducting materials" list, and I was perusing that, and some oddities stuck out: mostly about how the overall size/atomic-weight/periodic-row affect how semiconductors are fashioned and doped. My questions stem from there.

Tin and Lead for instance, are in the same column as Silicon, but I don't ever hear about them being used as semiconductors by themselves. Tin and Lead are metallic/oid, of course, while carbon and silicon are not, but Germanium, which is also frequently used as a semiconductor, seems to be a metal as well, or at least as "metallic" as Tin and Lead.

Observation 1: The Group "III-IV-V" examples in the all textbooks don't seem to hold as the period increases.

Q1: Why?

Observation 2: Larger/heavier elements from group IV are sometimes paired with Sulfur or Selenium from Group VI to turn them into semiconducting strata, but not with Oxygen (also from Group VI)

Q2: Why?
Q3: Do they "dope" these semiconductors with the same group III/V elements to make them P and N? (I seem to find that the answer is YES, but I'm asking anyway)

Observation 3: Even stranger (3-and-4-element) combinations, (CuInGaSe) are also used.

Q4: What's the underpinning logic/science of choosing these compounds?

Metaquestion: All the textbooks seem to make these bright-shiny-clean generalizations about 4 valence electrons in their explanations, but that seems to fall well short of the actual physics, possibly TOO far to warrant such inaccurate explanations. Is there a slightly less general description of semiconductor structure which might prepare the dilettante such as myself for the realities of semiconductors?

I thank you for your patience,
-Jeff Evarts
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