Gap Band

Topics: Atomic radius, Light, Electronegativity Pages: 9 (2343 words) Published: October 28, 2013
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, GaP0.65As0.35, GaP0.85As0.15, GaP1.00.As0.00 Increasing from right to left

7. Rank the following LEDs in terms of increasing bond strength. GaP0.40As0.60, GaP0.65As0.35, GaP0.85As0.15, GaP1.00.As0.00

Increasing from left to right
8. Rank the following LEDs that you used in lab in terms of increasing (∆EN reflects the average difference in electronegativity between the III-V type atoms in the solid.) 
 GaP0.40As0.60, GaP0.65As0.35, GaP0.85As0.15, GaP1.00.As0.00 Increasing from left to right

9. Rank the following LEDs in terms of increasing ionic character of the bonds. GaP0.40As0.60, GaP0.65As0.35, GaP0.85As0.15, GaP1.00.As0.00

Increasing from left to right

10. Based on your lab data and answers to Questions 1-8, explain how varying the lattice spacing (bond length) affects the band gap energy. Be sure to support your explanation with data. 
 According to data Greater bond length = LOWER Eg .For Example: GaP1.00As0.00 has the shortest wavelength and the shortest bond length (P1.00 has the shortest bond length) as a result it has the largest band gap energy as we are going up we can see the change in wavelength that it’s getting larger and bonds are getting longer so the band gap energy is getting smaller. Composition

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

11. Based on your lab data and answers to Questions 1-8, explain how bond strength is related to the band gap energy. Be sure to support your explanation with data. Data shows that 
Greater bond strength = GREATER Eg

The above Table shows GaP1.00As0.00 has the highest bond strength. The reason is that P1.00 has the shortest atomic radius which allows the length of the unit cell edge to...
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