WHY SCR not GCR?

Discussion in 'Homework Help' started by extremeads1, Sep 3, 2007.

  1. extremeads1

    Thread Starter Active Member

    Feb 10, 2007
    64
    0
    yesterday we were introduced about SCR and after studying it my colleague asked me why its a silicon controlled rectifier why not germanium controlled when both are semconductors. i have no answer but i wish to know the answer does any one has the answer pls reply.
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    I believe the answer is that the semiconductor properties of silicon are superior to those of germanium. It is for that reason that germanium transistors are no longer the standard they once were.

    hgmjr
     
  3. extremeads1

    Thread Starter Active Member

    Feb 10, 2007
    64
    0
    thanks sir for your immediate response but what are those properties can you provide me those ?
     
  4. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Among the properties that make silicon superior to germanium in the manufacture of semiconductors is the greater temperature stability that silicon provides over the temperature stabilty of germinium.

    hgmjr
     
  5. Gadget

    Distinguished Member

    Jan 10, 2006
    613
    0
    If germanium were still in common use for semiconductors, then I can see no reason why not a GCR, but as hgmjr has already stated, silicon is now used as it has superior characteristics, and not prone to thermal runaway.
     
  6. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    145
    If you want to know why germanium has worse thermal properties than silicon in semi-conductor applications, it is because of the relative different in the band-gaps for these two materials - germanium has a much smaller band gap than silicon.

    How does this translate into the thermal runaway effects described above? Well, the band gap defines the energy required to promote electrons (the source/constituent of current flow) from the valence band (where they do not contribute to current flow) to the conduction band (where they do contribute to current flow). Since germanium has a small band gap, only a small amount of energy - which can be supplied by thermal energy, amongst other sources - is required to promote electrons to the conduction band. This increases the net current flow, which in turn increases the temperature, and we get more electrons promoted to the conduction band, which increases temperature, and so on - this is thermal runaway. Given the amount of heat generated by electronic devices, this is very important, and the net result for semiconductor devices is that they eventually destroy themselves.

    Silicon on the other hand has a large band-gap and the above thermal runaway scenario is generally not as significant.

    Dave
     
  7. Dave

    Retired Moderator

    Nov 17, 2003
    6,960
    145
    A further point here is that the decision to use silicon against germanium is largely down to economics - including availability, cost per unit, and the processing capabilities.

    Dave
     
  8. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
  9. nanovate

    Distinguished Member

    May 7, 2007
    665
    1
    But the lower bandgap can be an advantage in some cases when you want a lower forward voltage drop. One other consequence of the lower bandgap is a higher leakage current. Germanium does have its uses in photovoltaic applications. But in most cases silicon is superior.
     
Loading...