Hi, Dr. Topp,
I was wondering if you could take a look at something I'm thinking of
putting in my e-portfolio as an entry about how I've improved my use of
accurate scientific language.... I wanted to discuss my use of
terminology related to diode lasers. I think I may be confusing
myself, but could you tell me if this sounds correct? I though I
understood it in Spec, but I'm having my doubts....
- diode: a device that contains two electrodes (a
cathode and anode), made of positively (p-) and negatively (n-) doped
semiconductors
- p-doped semiconductor: a
semiconductor that has positively charged "holes" that act as positive
charge carriers (producing positive current); this can occur by
replacing atoms in the semiconductor matrix with electron deficient
atoms (e.g. replacing tetravalent Ge with trivalent Ga)
- n-doped semiconductor:
a semiconductor which has an overabundance of electrons which act as
negative charge carriers (producing negative current); this can occur
by replacing atoms in the semiconductor matrix with more electron rich
atoms (e.g. replacing tetravalent Ge with pentavalent As)
(IS THERE ANY OTHER WAY TO CREATE P- AND N- DOPED SEMICONDUCTORS--I.E.
BY APPLYING A VOLTAGE?)
- conduction band: in a
diode laser, the conduction band is the energy level of the excited
electrons in the semiconductor. This band does not have
the same
energy level throughout the diode. The conduction band is lower
energy
in the n-doped semiconductor (which is easier to excite because of the
extra electrons) than in the p-doped semiconductor. The energy level
of the conduction band in the n-doped semiconductor is therefore close
(can be higher or lower) to the valence band energy level for the
p-doped semiconductor
- valence band: in a diode
laser, the valence band is the energy level of the non-excited valence
electrons. This band does not have the same energy level
throughout
the diode. The
valence band of the p-doped semiconductor is higher
energy than the valence band of the n-doped semiconductor, and it is
therefore easy to achieve a population inversion by exciting electrons
from the p-doped semiconductor's valence band to the n-doped
semiconductor's conduction band.
- band gap: the energy
difference between the conduction band (i.e. excited state or energy
level) and the valence band (i.e. ground state or energy level) in a
semiconductor
- pumping by electrical current:a
diode laser is pumped with an electrical current so that the number of
electrons in the conduction band exceeds the number of electrons in the
valence band. Electrons from the valence p-type semiconductor are
excited into the conduction band of the n-type semiconductor.
This
creates a voltage in which the p-type semiconductor develops more
"positive holes" as the conduction band of the n-type semiconductor
gets more populated with electrons until there is a population
inversion that can sustain lasing action (as long as the electrical
current, or voltage, is maintained).
When the
critical voltage is applied, electrons move from the n-type
semiconductor's conduction band to the p-type semiconductor's conduction band
(first fast transition), which decreases the
difference betewen the p-type and n-type semiconductor energy levels
(conduction and valence band). The second, lasing
transition occurs as electrons relax from the conduction band to the
valence band.
Thanks!
-Grace
|
|