Gap Band

Factors Affecting the

Band Gap of LEDs

By Mohammad Reza Farham

Chemistry 222 Thursday 08.02.2012

Lab Partner: Thanh Nguyen ANALYSIS ANSWERS
Factors Affecting the Band Gap of LEDs

1. Based on your observations in Experiments 1 and 2, prepare a single table listing an approximate band gap energy, Eg compared to composition of the LEDs, as well as the voltage across each LED. Recall that Eg = hc/λ.

Composition
Color
Wavelength λ
Band Gap Eg
Voltage
GaP0.40As0.60
Red
653.6 nm
0.0304*10-17J
1.394 V
GaP0.65As0.35
Orange
625.3 nm
0.0318*10-17J
1.544 V
GaP0.85As0.15
Yellow
594.1 nm
0.0335*10-17J
1.573 V
GaP1.00As0.00
Green
563.2 nm
0.0353*10-17J
1.625 V
Blue LED
Blue
427.0 nm
0.0466*10-17J
2.339 V
Clear LED
Clear
463.3 nm
0.0428*10-17J
2.325 V

2. Which compound has the larger bond length, GaP or GaAs? - GaAs
3. Which compound has the greater bond strength, GaP or GaAs?
-GaP
4. Which compound has the greater ΔGaP or GaAs?
-GaP
5. Which compound has the greatest degree of ionic character, GaP or GaAs? (You may wish to use a bond-type triangle to discuss this point.)
-GaP
6. Rank the following LEDs that you used in lab in terms of increasing lattice spacing. (Lattice spacing reflects the average bond length between the III-V type atoms in the solid.) 

GaP0.40As0.60,