Section 1:
Claim:
Observable factors that affect the composition of LEDs

During our research of gallium arsenide phosphide (GaPxAs1-x), which is a semi-conducting material in the form of light emitting diodes, we observed how properties of the data collected directly correlated to the composition of the LED. The observed and measured properties we were able to notice and calculate during our research were wavelength, color, voltage, and temperature. Using a diffraction grating we first tested the different compositions for which color of light was emitted. Our data as can be seen in appendix 1, on pg. L93 table 1, shows that as the composition shifted from GaP0.40As0.60 to GaP1.00As0.00 the colors emitted, shifted from those associated with longer wavelengths to those of shorter wavelengths. (Red to green) We then set up a scanning spectrometer in order to measure the wavelengths, and as can be seen in our data in appendix 1, on pg. L94 table 2, as well as on the graph in appendix 2, we were able to measure the wavelength of each LED with varying composition. According to our data it can be said that greater bond length equals lower Eg, since lower Eg will result in longer wavelength. For example, GaP1.00As0.00 has the shortest wavelength and the shortest bond length, and as a result has the largest band gap energy. From the same data we can also conclude that greater bond strength equals greater Eg due to the fact that GaP1.00As0.00 has the highest bond strength. The reason for this is because phosphorus has a shorter atomic radius then arsenic, allowing the length of the unit cell edge to decrease, enhancing the orbital overlap, which results in greater Eg. We then measured the voltage out put of each LED composition and as can be seen from our data in appendix 1, on pg. L94 table 3. As the composition shifted from higher levels arsenic to phosphorus we saw an increase in voltage, which suggests an increase in Eg since more electrons were able to cross from the valence band to the conduction band. We then tested two of the LED compositions by placing them in a cup of liquid nitrogen, bringing them to a temperature of roughly 77 kelvin. Our data in appendix a, pg. L95 table 4 shows that when cooled wavelength decreases and voltage increases, suggesting that when cooled, Eg increases. This is due to the fact that cooling the compounds decreases kinetic energy allowing the atoms to move closer together, creating a shorter stronger bond.

Section 2:

Claim:
Factors affecting band gap energy in LEDs

Evidence:
Band gap energy (Eg) is the energy needed to promote an electron from the lower energy valence band into the higher energy conduction band. The color of the light emitted depends on the size of the band gap. There are a few ways to change the band gap energy. The most important way is changing the composition of the LED by varying the ratio of the elements. As can be seen in appendix 1, pg. L94 table1, samples of four different GaPxAsx-1 compositions were examined. GaP0.40As0.60 with a mole ratio of 1:1 (1mole of Ga = 0.40 mole of P +0.60 mole of As) is red in color, which has the largest wavelength (656.6 nm) and the lowest band gap energy 3.027*10^-17J which can be seen in appendix 1, pg. L97. By increasing the mole ratio of phosphorus atoms, the wavelength decreases and the color changes, from red to orange for GaP0.65As0.35, yellow for GaP0.85As0.15 and green for GaP1.00As0.00. The color change is corresponding with lower wavelengths as the mole ratio of P atoms increase. The reason why increasing the mole ratio of phosphorus atoms affects the band gap energy, is because the phosphorus atom is more electronegative than the arsenic atom, it also has a smaller atomic radius enabling shorter stronger bonds, which in turn enhances the orbital overlaps. As a result more phosphorus in the GaPxAsx-1 composition will result in larger band gap energy. Another factor, which can also affect band gap energy, is temperature change, as can be seen in appendix 1, pg. L95 table 4. Two different compositions one being GaP0.40As0.60 and the other being GaP0.65As0.35 were dipped into a foam cup of liquid nitrogen. As the temperature-lowered data shows that their wavelength became shorter as well as having an increase in voltage out put, suggesting the band gap energy increased, compared to their wavelength and voltage measurements at room temperature. The reason being as temperature is lowered, atoms have less kinetic energy resulting in them contracting and being able move close together which in turn enables them to form shorter stronger bonds and more molecular orbital overlap.

Section 3:

Claim: It’s not possible to modify the composition of semiconductors in the family GaPxAsx-1 (tune them) in order to produce a semiconductor that produces blue light.

Evidence:
Data in appendix 1, pg. L94 table 2 shows that the lowest wavelength associated with GaPxAsx-1 is 564.4 nm. Since GaP1.00As0.00 recorded this wavelength we know that it would be impossible to modify the composition anymore then it already has been for this family of semiconductors. In order to produce a blue light the wavelength must be between 480nm and 500nm. Even when looking at data collected for temperature and emitted color in appendix 1, pg. L95 table 4, we can see that the drop in wavelength would not be significant enough produce a blue light.

Section 4:

Claim:
Modifying the composition of GaN can increase its wavelength from 480nm to 490nm.

Evidence: In order to increase the wavelength of GaN permanently, the band gap energy has to be lowered by changing its composition. (Mole ratio between Ga and N) As can be seen in appendix 1, pg. L94 table 2, the data clearly shows the relation between the mole ratios and the wavelength. Changing the mole ratios of GaPxAsx-1 affected its wavelength, which it increased, by lowering the ratio for the smaller and more electronegative phosphorus atom, and increasing the ratio for the larger and less electronegative arsenic atom. In order to increase the wavelength of GaN, the same method has to be used as in the GaPxAsx-1 composition. In which the ratio of the smaller nitrogen atom needs to be lowered to less than 1 mole, and the ratio of the larger gallium atom needs to be increased to more than 1. With this change in composition the band gap energy will decrease and as a result its wavelength will increase. Another important factor for increasing the wavelength (not permanently) is changing the temperature; In this case the GaN temperature has to increase because when temperature goes up a material will expand (the atoms have more kinetic energy) which will cause the atoms to be farther away from each other resulting in longer and weaker bonds (smaller orbital overlap). Weaker bonds mean the Eg will decrease so its wavelength will increase.

Section 5:
Claim:
Blue light lasers have more advantages and benefits over LEDs that are only colored between red and green.

Evidence:
The technology utilizes a "blue" (actually blue-violet) laser diode operating at a wavelength of 405 nm to read and write data. Conventional DVDs and CDs use red and infrared lasers at 650 nm and 780 nm respectively. The blue-violet laser has a shorter wavelength than CD or DVD systems, and this shrinking makes it possible to store more information on a 12 cm (CD/DVD size) disc. The minimum "spot size" that a laser can be focused is limited by diffraction, and depends on the wavelength of the 11 light and the numerical aperture (NA) of the lens used to focus it. By decreasing the wavelength (moving toward the violet end of the spectrum), using a higher NA (higher quality) dual-lens system, and making the disk thinner (to avoid unwanted optical effects), the laser beam can be focused much tighter at the disk surface. This produces a smaller spot on the disc, and therefore allows more information to be physically contained in the same area. In addition to optical movements, Blu-ray Discs feature improvements in data encoding, closer track and pit spacing, allowing for even more data to be packed in. Based on these factors, the company should invest money and resources to research and start blue LED production. This would lend to an increase in overall sales while staying competitive in the market.

Ravi Kumar, and R.V. Krishnaiah, Dr. "Optical Disc with Blue-Ray Technology." International Journal Of Computer Engineering & Applications, Vol. III Issue II/III, Sept. 2013. Web. 8 Feb. 2016. <http://arxiv.org/pdf/1310.1551.pdf>.