Fabricate two semiconductor Hall samples (one p-type and one
n-type) and one copper sample. On each
sample, measure resistivity and Hall voltages by following the instructions in
the NIST manual and filling out the handy worksheet from the NIST manual. You may
want to perform the sequence of Hall voltage measurements for different values
of current and magnetic field.
Making a good metal-semiconductor contact is not
trivial. The contact resistance may be
high, or worse, the contact may act as a diode to some degree. Feel free to experiment with modifications to
this procedure; it was developed largely through trial and error.
the hot plate to the highest setting.
a razor blade, slice off four small pieces of indium to serve as
contacts. You may want to discard
the top slice that was exposed to air.
the native oxide (the ~10Å of SiO2 that forms on silicon in
air) by pressing Scotch tape onto the silicon wafer and removing it. (The standard procedure for removing the
native oxide is to dip the wafer in a solution of HF. You may do this if you choose, but be
aware that HF can kill you by interfering with the calcium channels in your
the metal tweezers, press the pieces of indium onto the silicon so that
the wafer on the hot plate; the indium should melt instantly.
- I have
no idea what this does, but I can't make good contacts without it: Dip the metal tweezers into each molten
indium dot and stir it around a little, gently scraping the silicon
the wafer sit on the hot plate for about three minutes.
the sample cools, attach wires using one of these techniques: sandwich the wire between the indium on
the silicon and another piece of indium, and press with the metal
tweezers; or use regular solder to attach the wires to the indium.
metallic thin films:
Hall voltages are proportional to the sheet resistance (RS
of a sample. Whereas semiconductor
resistivity is sufficiently high to permit measurements of sizeable Hall
voltages (0.01-0.1 mV) on thick samples (~0.03 cm), the resistivity of metals
is so low that similar voltages can only be measured on thin films. We use the evaporator to produce thin films
of metal on a glass substrate.
the bell jar after opening the venting valve. Place your substrate above the boat and
place the copper evaporation source in the boat. The best sample I've made so far came
from using about 60 mg of copper.
the bell jar and close the venting valve.
on the water, which cools the evaporator.
on the mechanical pump.
the valve between the mechanical pump and the bell jar.
- When the
pressure in the bell jar drops below 20 mm
of mercury, close the valve between the mechanical pump and the bell jar,
and the open the valve between the mechanical pump and the back of the
the pressure at the back of the diffusion pump drops below 20 mm
of mercury, turn on the diffusion pump.
the valve between the diffusion pump and the bell jar. THE DIFFUSION PUMP WILL BE DESTROYED
UNLESS TWO CONDITIONS ARE SATISFIED:
the pressure in the bell jar must be previously lowered below 20 mm
of mercury, and the pressure behind the diffusion pump must be constantly
maintained at a similar level by the mechanical pump.
ionization gauge, used to read very low pressures, may be turned on when
the diffusion pump is evacuating the bell jar. THE IONIZATION GAUGE WILL BE DESTROYED
UNLESS THE PRESSURE IN THE BELL JAR IS FAR BELOW 20 mm
the pressure has fallen below about 10-5 torr,
you may begin evaporation. Turn on
the evaporation power. Turn the
dial until the copper melts, then leave it at that setting (usually about
33) for two minutes. Then increase
slowly to a higher setting, perhaps 48, and the
copper should rapidly evaporate.
remove the sample: turn off the
evaporation power, wait 15 minutes for the sample to cool, close the valve
between the diffusion pump and the bell jar, turn off the ionization
gauge, and open the vent valve.
When the pressure in the bell jar reaches atmosphere, you can lift
the bell jar.
make contacts to the thin film, you can press indium onto the thin film
and sandwich a wire under another piece of indium.
Always turn the water on before the power supply. Always adjust the current slowly, and reduce
it to zero before shutting off the power supply. Wait some time before turning off the water,
but remember to turn it off before you leave for the day.
Your lab reports should address all of the following (and
may, of course, include additional information and analysis):
the Hall effect in words.
explain the difference between metals and semiconductors.
explain the difference between p-type and n-type semiconductors.
Figure 3, explain why V24P would have a different sign for
p-type and n-type carriers (assuming a perfectly square sample). For which carrier type is V24P
positive? For which type is it
define any terms that may be new to you (sheet resistance, bulk carrier
density, sheet carrier density, etc.).
the purpose of making all the measurements on the worksheet.
Eq. (12) from Eq. (1).
Specifically, where does the factor of 8 x 10-8 come
discuss your data. Do your
measurements satisfy Eqs. (8) and (9)?
If not, what does this imply?
each of your silicon samples, what resistivity, bulk carrier density, and
carrier type are indicated by your data?
Are the resistivity and carrier density values consistent with
theory? (See www.solecon.com/sra/rho2ccal.htm.) Can you speculate as to the cause of any
- Do you
observe a Hall voltage in your copper sample? Using the resistivity of copper (1.7 x
10-6 W-cm) and your measured sheet
resistance, what is the expected thickness of your copper film? Using this thickness and other
parameters from your measurements, what is the expected Hall voltage? What do you conclude?
the carrier density for copper from its mass density (8.92
g/cm3) and atomic mass (63.5 g/mol). How does this compare with the carrier
densities in your silicon samples?