haha a legit question, but i guess you got downvoted because you could have researched it and shared it? dunno.

anyway. not a chem dude at all, but it appears III-V semis are when you combine: "III-V compound semiconductors obtained by combining group III elements (essentially Al, Ga, In) with group V elements (essentially N, P , As, Sb). This gives us 12 possible combinations; the most important ones are probably GaAs, InP GaP and GaN." [1]

In other words, the materials in general are: Nitrogen, Phosphorus, Antimony, Arsenic, Bismuth, Boron, Aluminum, Gallium, Indium and Thallium.

I imagine nitrogen, phosphorus and aluminum are the easiest to find generally throughout the world.

China appears to control 90% of antimony [2] and its price seems to have gone up 700% over the last decade.

Arsenic seems to have major supply issues, one of the most critical in terms of scarcity according to [3] and [4]. Nevertheless, the price has gone down over the last 100 years significantly and according to this source is less scarce than it was a century ago: [5]

Bismuth is "relatively rare" but doesn't appear to be scarce. it is found mostly in Peru Japan Mexico, Canada, Bolivia and not in the USA. [6]

remaining elements are left as an exercise to the reader.

[1] http://www.tf.uni-kiel.de/matwis/amat/semitech_en/kap_2/back... [2]http://www.tf.uni-kiel.de/matwis/amat/semitech_en/kap_2/back... [3]http://www.acs.org/content/acs/en/pressroom/presspacs/2012/a... [4]http://environment.yale.edu/news/article/arsenic-supply-at-r... [5]http://theunbrokenwindow.com/2010/03/08/running-out-of-resou... [6]http://www.carondelet.pvt.k12.ca.us/Family/Science/Nitrogen/...

That is the question. All of the materials are expensive themselves (gallium, indium) or expensive to process ( silicon) - which means these cells will never scale and replace oil.

Which is why dye-sensitized solar cells are such a promising alternative, despite their lower single module efficiencies of ~15% (20-30% for the expensive semiconductors discussed in OP). http://en.wikipedia.org/wiki/Dye-sensitized_solar_cell