Quiz 12 potential problems ChE 350 sp10 - Sample question...

Sample question for ChE 350 Spring 2010
Quiz 12 Name:________________________
1
1. An example of a high brightness blue LED device is shown below [From Gee et al., “Flip-
Chip Light Emitting Diode with Resonant Optical Microcavity,” US Patent 6,969,874 B1]
The “MQW” layer is composed of In
x
Ga
1-x
N. The band gap energies of GaN and InN are 3.44
eV and 1.89 eV, respectively.
(a) It is desired that the LED will emit a blue color with a peak emission wavelength of 425 nm.
What is the necessary In
x
Ga
1-x
N composition to achieve this color?
(b) Sketch the band structure of the device (GaN/In
x
Ga
1-x
N/GaN) layers placing the p-side on the
left of your diagram. You need to show the Fermi level and a reasonably accurate estimation of
the relative band gaps of the layers, taking into consideration the answer provided in (a). [Note
that the In
x
Ga
1-x
N layer is the emitting “MQW” layer in the device.]
(c) Sketch the band structure of a device with the MQW layer replaced with AlN (band gap
energy is 6.2 eV). Would it still emit light?