# What semiconductor materials are used in the 2N3904?

The 2N3904 type transistor is manufactured by a number of companies, using different layouts, but the characteristic requirements are the same for all of them. Do these requirements imply the usage of a particular semiconductor material? For example, simple group IV semiconductor with silicon or more complex materials such as III-V or II-VI materials? One would assume silicon-based material but I am curious if there is a source of information on this?

Sam

• They are silicon NPN transistors, nothing exotic. It would be difficult to make a functional replacement with anything else. Aug 28 '17 at 16:41
• Most production is done on wafers (planar processing.) The wafers are made out of very pure silicon that is pulled (multiple times) from melts in "boules." These boules are sliced into wafers. There are a number of processing steps which then take place to build the devices. Eventually, these are tested on the wafer first and those that pass are cut and packaged and, often, tested again.
– jonk
Aug 28 '17 at 16:44
• (Boules might be pulled with an initial dopant already added to save a processing step. But I think this is done more for larger scale bipolar ICs rather than just for discrete parts.)
– jonk
Aug 28 '17 at 16:52
• In theory, it could be implemented in III/V materials as long as the result met the specifications. In reality, the specs are easy to meet using silicon, and silicon fabrication is much cheaper than other semiconductors, so using anything else would be extremely unlikely (more like "unimaginable"). Aug 28 '17 at 17:20
• In practice, different vendor's '3904's are similar enough that in the surface mount form (MMBT3904) they're used interchangably as temperature sensors. For example, some fan control chips and the LTC2990 are designed to use MMBT3904 as an external temperature sensor. Aug 28 '17 at 20:35

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