Introduction Flashcards
What’s the conductivity of metals?
high (but almost uncontrolled) electrical conductance
What is the conductivity of semiconductors?
easily controlled (over a wide range) electrical conductance.
you can control the properties and they are easily tunable.
what are dielectrics (insulators)?
no electrical conductance
What unit is conductivity measured in?
1/ resistivity = 1/ohm*m
what is an optoelectronics?
both using electricity and light
What is the feasibility of electric current for materials?
metals: yes
insulators: no
semi: yes
What is the feasibility of light for materials?
metals: no
insulators: yes
semi: yes
What is the feasibility of optoelectronics for materials?
metals: no
insulators: no
semi: yes
Explain this image
scan using scanning tunneling microscopy STM represents electron concentration
What is this?
A silicon ingot being pulled from a melt
how are silicon ingots grown?
in labs in crystal drawers
what is GaA used in?
high speed electronic devices and optoelectronics
why isn’t silicon used in fast electronic devices
you can’t use silicon to absorb or emit light
What is used to wire devices within a chip/integrated circuit?
metal interconnects
What was the first commercial transistor?
silicon from Texas Instruments 1954
pocket radio
The Bipolar Junction Transistor BJT
what does this demonstrate
demonstrates quantum nature of light. light is comprised of huge numbers of small particles
why don’t particles have mass
they move with the speed of light
do photons have mass? energy?
no mass, because it moves at the speed of light
yes energy, it has velocity
what’s important about this table?
different materials for light emitting dyads.
the wavelength light column changes the different type of light
new type of material– new wavelength
how do you convert from wavelength to Eg
wavelength = 1.24 /Eg
What does LASER stand for
light amplification by stimulated emission of radiation
what does the light look like in absorption, spontaneous emission, and stimulated emission?
what happens during absorption
electron goes to the next level
what happens during spontaneous emission
electron goes down to a lower level
it happens easily because electrons go down by themselves easily, and it releases a photon
what is the difference in energy in versus out
energy of the photon
what happens during stimulated emission?
it doesn’t dop down by itself, the stimulation is coming from the light
releases 2 photos, one from light one from emission
made by the photon
what are three categories of lasers?
gas lasers
solid-state lasers
semiconductor lasers
why are semiconductor lasers good
- small and compact
- you don’t need to have another source of light
- you inject an electron
- you take out the electron from the lower level and put in the top (introducing a positive charge basically)
where is electrical current injection used
semiconductor lasers
what is the most common pumping scheme
optical pumping
What three categories are semiconductor lasers at the intersection of?
physics
optoelectronics
materials science
