Vantagens e Desvantagens

Question 1

LEDs performance issues

Answer 1

-Light-current characteristics:the light-current of the LED is essentially linear except for high drive current when the light output saturated.
- poor Spectral purity
-Temporal response
-Temperature dependance.

Question 2

Problems of the homojunction LED

Answer 2

-Strong non-radiative recombination via high density
states at the emitting surface
-Low carrier injection efficiency

Question 3

Advantages of a heterojunction LED

Answer 3

-higher quantum and coupling efficiency
-Do not suffer from poor surface conditions since the active region is not near the surface..
-Increased carrier injection efficiency due to the low doping active layer.
-The photons emitted are also not absorbed in the top or bottom region because the photon energy is smaller than the bandgap of the n- or p-region.

Question 4

p-i-n photodiodes drawbacks:

Answer 4

-Depletion layer capacitance is not sufficiently small to allow photodetection at high modulation frequencies
-Narrow SCL

Question 5

vantagens APD

Answer 5

– vary large internal current gain
– fast response to the light modulated at microwave frequencies
– high sensitivity to low-level optical signals with about 1 ns response time, particular useful in fiber optic communication.

Question 6

vantagens APD

Answer 6

– Breakdown voltage : VB
– Ionization rate (coefficient) : The number of EHPs generated by an
electron (or hole) per unit distance.
– Multiplication factor : M
The ratio of the number of electrons leaving the junction to those entering it.

Question 7

Avalanche vs. p-i-n photodiodes

Answer 7

-APDs have greater sensitivity for a given material
-APDs have higher dark current.
-PIN diode may have greater sensitivity for long wavelength detection than an APD.
-PIN diodes are easier to fabricate.
-PIN diodes are easier to integrate (with amplifiers)
-APDs are very temperature sensitive for dark current and multiplication factor.
-APDs require a high operating voltage.