Diode is all about insulating layer and switched conductivity, NOT
POTENTIAL HILLS. Voltage barrier, that's thermocouple, not diode. A
potential barrier exists at all junctions, including nonrectifying
contacts between different metals, and between metal terminals and
semiconductor surfaces. Touch metal against silicon and you usually get
thermocouple, not a diode. Same thing if you touch n-doped against
p-doped. To prevent the formation of conductive thermocouples, you need
utterly clean semiconductor surfaces which lack the high doping caused by
contamination. High-doping gives "metallic" conductivity silicon, and no
diode effect. Only low doping creates diodes.
For potential hills, with differing materials in a closed circuit: for
each charge pushed in one end, another charge leaves the other end
~simultaneously. This means that any charge going up a hill is balanced
by another charge going down a different hill, so it takes zero total
energy in order for charges to overcome the hills. That's why "potential
barriers" are not real barriers unless a depletion zone (a diode) forms.
DOPED SILICON IS ELECTRICALLY NEUTRAL, it's charged with particles of
'neutralized charge' which can move around. But every moving charge in
the silicon ends up near an opposite stationary charge (a charged atom, a
doping ion,) so the average charge in the material is smoothed out to
WHY DON'T N AND P CANCEL OUT? Touch N against P, any wandering
charges get trapped. Basically it's a SELF-CHARGING CAPACITOR, where the
conductive plates are being turned into insulating dielectric! Metal
becomes like glass!
CONDUCTIVITY IS ELECTRONS IN ORBIT (a single electron is a conductor)
In metals, electrons orbit all among the atoms, jumping from one to
another, but staying the same distance away from each nucleus. Close
orbit, low energy, yet still orbits all atoms in the material.
HOLES ARE GENUINELY POSITIVE: when a hole first forms, an electron
jumps into an electrically-neutral P-type dopant atom, making it negative
...but that neighboring silicon atom which donated that electron is no
longer cancelled out. It's now a positive ion, and the dopant atom is a
negative ion. A hole is an extra proton. If an electron jumps into the
hole, that electron "reveals" an extra proton behind it. The "extraness"
of the protons can wannder around, even though the protons themselves
POSITIVE CHARGE? IT'S NOT "MISSING ELECTRONS." If we have some
then take them away, have we created any positive charge? Made any
positrons? Nope. Positive charge only appears when electrons were
removed from NEUTRAL MATTER, and neutral matter is full of protons which
had been cancelled-out by nearby electrons. Removing an electron doesn't
create positive particles, instead it "reveals" them, un-cancels them.
TWO KINDS OF CONDUCTIVITY: electrons in close orbits aren't electrons in
high orbits. The high-orbit electrons jump constantly between atoms too.
High electrons can't switch to low orbits unless they emit either light
photons or sound vibrations (phonons, heat.) Low electrons can't switch
to high orbits unless they absorb either light photons or sound vibrations.
So, we can have holes and electrons wandering around in the same piece of
material, because the holes are actually part of the low-orbit population
of electrons, while the free electrons are high-orbit electrons.