I'm trying to find high-resistivity Ge (100) wafers but the vendors I usually buy from don't offer anything like that.
Does anyone know of a vendor offering such wafers?
Do you know if there are any physical limits or is it just the lack of demand for such wafers?
(I'd assume that due to its higher intrinsic carrier density, Ge would tolerate a much higher defect density than Si, while remaining mostly intrinsic; therefore it should be easier to manufacture an intrinsic wafer, in principle)
Thanks in advance
It's probably the lack of demand. We use high-purity Ge detectors for our gamma spectroscopy. These detectors essentially contai. A hockey-puck sized single crystal (both smaller and larger exist) of Ge at has less than 1 ppt of impurities (i.e., 1e-12). This crystal sustains a bias of several kV, so it's pretty resistive. However, the low bandgap means that the crystal needs to be cooled (usually down to liquid nitrogen temperatures) to avoid thermal noise (leakage current). The bandgap limits the RT resistivity somewhat.
Concerning intrinsic defects (vacancies and interstitials, and combinations thereof): they tend to make germanium p-type (unlike for example Si or GaAs that become semi-insulating upon heavy irradiation). This is because the Ge bands lie quite high compared to the dangling bond energy / branch point energy / Fermi stabilization level (you can google any of these keywords to see more).
Thank you for the interesting comment.
Do you mean that you buy a bulk crystal? (i.e., not a wafer)
Could you please refer me to your vendor?
Actually, we buy complete detectors. Bigger vendors include Canberra, Ortec, Princeton Gamma Tech, smaller include PhDs Co and Baltic Scientific Instruments. I guess the bigger detector manufacturers buy their crystals from elsewhere (possibly even from the same source), the smaller may have some production of their own / have other sources. PhDs Co is located in Knoxville, TN, if I remember correctly.
You can get undoped Ge wafers up to 150 mm in diameter. I'm not sure if the purity is good enough for your purposes:
http://www.waferworld.com/services
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