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Schottky diodes and the Shockley-Haynes experiment

  1. Oct 30, 2008 #1
    I'm measuring the drift velocity of holes in n-type Germanium using the Shockley-Haynes technique. Two metal point contacts are placed some distance apart on a germanium bar. The collector is negative biased owing to it being connected to a 9V battery. The emitter is connected to a pulse generator and a positive pulse is applied which forward biases the emitter (to emit holes).

    My question is, are the point contacts Schottky diodes? I'm thinking they are just by virtue of there being a metal-semiconductor interface.

    How might I go about measuring the voltage current characteristics of the diode, if indeed the point contacts are Schottky diodes?

    The following report is what has got me thinking about this. Am i automatically setting up a Schottky barrier?

    http://cantab.jkut.com/Mobility of carriers in semiconductors.pdf

    ps. i don't believe this constitutes a 'homework' question but if it needs moving then please do.
  2. jcsd
  3. Oct 30, 2008 #2
    A metal semiconductor interface could produce a Schottky diode, or just an Ohmic contact. It depends on the doping level. When devices are fabricated, heavy doping is used in the region of a conductor to establish an Ohmic, i.e. non-rectifying contact. With light to moderate doping, a Schottky barrier can be created.

    A bjt, for example, uses heavy doping in the silicon regions adjoining the metal leads to avoid rectifying junction behavior. Otherwise, the collector and emitter leads would form Schottkys with the silicon that point in opposite directions. No current would flow as one of the diodes would always be reverse biased.

    Does this help any?

  4. Oct 30, 2008 #3
    There is, soldered to each end of the germanium bar, two OHMIC contacts. A 'sweeping' electric field pulse is applied across the bar using the ohmic contacts. The actual emitter and collector contacts (essentially two metal pins) are partially rectifying and usually represented as diodes. Does 'partially rectifying' constitute a Schottky diode?

    I think that the emitter is forward biased and the collector reversed biased so that we can detect the minority carriers (holes) at the collector.

    I want to measure the current flowing through one of these point contcacts with respect to voltage and probably should see something like the standard voltage-current characteristic diagram for a diode.

    In a similar experiment, you see, someone talks about the contacts being Shottky diodes... i'm wondering if, because i'm reverse biasing one contact with a battery, i have shottky diodes or two pieces of metal which just happen to allow things through in one direction (because of the battery etc.)
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