Blue LEDs Mechanism and Significance

Material Choice 

Light emitting diodes (LEDs) are gadgets that use electric power and are lighted by the motion of electrons in a semiconductor material. They have the capability of emitting light with various wavelengths ranging from infrared to ultraviolet (Chilton, 2014). They are commonly made from a material known as aluminum gallium arsenide (AlGaAs) which when it is pure does not have free electrons to conduct electrical current. With the invention of the blue LEDs, it was easier to make white lights. The initial efforts to make the blue LEDs made use Zinc Selenide and silicon carbide which were characterized by high indirect band gaps and were not able to produce efficient light emission (Chilton, 2014). Gallium nitride (GaN) possible for the development of the blue light emitting diodes. The GaN can be described as a semiconductor that has a Wurtzite crystal structure and also has a direct bandgap which was equivalent to the wavelength in the ultraviolet range. This paper will discuss and a ddress the material choice, critical material properties, manufacturing process and other potential blue LEDs applications. 

The use of GaN in the blue LEDs can be traced to the 1950s. Researchers, from Philips Research Laboratories, had the idea of using it to produce the blue LEDs but they let go that idea due to the obstacles they faced in growing the GaN crystals. In 1986, by using a process known as MOVPE technique, there was the production of high quality and good optical properties GaN. Later, Shuji Nakamura established a way of growing the crystals at low temperatures. There were difficulties in p-doping GaN with exactness hence made it difficult to make the blue LEDs. In the late 1980s, Amano and Akasaki revealed that doping GaN with zinc atoms made it emit more light hence giving a better p-doping. In the early 1990s, Akasaki and Nakamura had research that enabled the use of Heterojunctions (Chilton, 2014). Nakamura, in 1994, employed double Heterojunction InGaN/AlGaN to create a gadget that had the quantum efficiency of 2.7% and helped make way for the production of more efficient blue LEDs easily. 

Properties of Gallium nitride 

GaN is thermodynamically stable, and its alloys are in the hexagonal wurtzite structure. 

Crystal structure 

Wurtzite GaN has two hexagonal closely packed sublattices, and each sublattice contains one set of atoms offset along the c-axis by 5/8. The basic geometric shape of a unit cell of the hcp is a rhomboid, and it has two base atoms that is one at the starting point and the other one at (2/3 1/3 1/2).Gallium has a covalent bond with four tetrahedral bonds in each atom (Pope, 2004). As a result of the huge gap between the electro-negativity of nitrogen and its component, there is a notable ionic assist to the bond. 

Alloys 

In combination with wurtzite III, the nitride material creates a continuous direct band gap alloy arrangement that ranges from 0.9 to 6.2 e V hence giving a basis for the development of light emitting gadgets that ranges from the infrared to the ultraviolet covering the whole of the visible spectrum (Pope, 2004). Alloying is mainly used to enhance the way the device operates or help attain a specific emission wavelength. The alloy composition plays a big part on important parameters such as the band gap energy. 

Strain 

The lattice constants of AIN, GaN, and InN are different hence when these materials are combined in layers; there will be a strain. It affects the valence band structure of the epilayer (Pope, 2004). It shears the arrangements of the semiconductor and separates the quantum levels of light and the whole heavy states. 

Substrates and Buffer Layers 

There are a large number of crystalline layer growth difficulties that are linked to the lack of a single crystalline GaN substrate on the nitrides as a result of the high melting point. Sapphire and silicon carbide are the two main substrates that are employed in case the no crystalline GaN (Pope, 2004). Sapphire is mainly the substrate of choice. However, it has great lattice mismatch with GaN, and if the layers are grown on a sapphire suffer directly, it faces cracking and thread dislocation. High crystalline quality can be attained by making use of InGaN which helps in reducing the defect density by lowering the strain in the GaN layers. 

Manufacturing Process 

In the manufacturing of the GaN substrate, there is the use of other substrates which the thermal expansion coefficient is almost similar to that of GaN. (Motoki) A huge and thick GaN is grown at high speed on a foreign substrate, and the GaN substrate crystals are acquired after the removal of the foreign substrate. The process involves adding the GaN crystals to the foreign substrate and let the crystals grow. Then remove the foreign substrate to obtain your GaN substrate. It should be mechanically flattened. 

Other Uses of Gallium Nitride 

The materials and devices that are generated with the use of GaN can also be used in; Used in ultraviolent devices that are used in sensing systems for airborne and biological factors and also keeping a close look at the ultraviolent reactions (Gila, 2002). They are also used in power amplifiers and monolithic microwave integrated circuits, radar units that have higher performance, communication connections that are wireless and also used in ultra-high power switches. Commonly made from a material known as aluminum gallium arsenide at room temperature, ferromagnetic semiconductors are used in magnetic sensors and actuators that use electric power. 

The aim of this paper was to discuss and address the material choice, critical material properties, manufacturing process and other potential applications of the blue LEDs. The use of GaN in the blue LEDs can be traced to the 1950s. Researchers, from Philips Research Laboratories, had the idea of using it to produce the blue LEDs but they let go that idea due to the obstacles they faced in growing the GaN crystals. Light emitting diodes (LEDs) are gadgets that use electric power and are lighted by the motion of electrons in a semiconductor material. They have the capability of emitting light with various wavelengths ranging from infrared to ultraviolet. They are commonly made from a material known as aluminum gallium arsenide (AlGaAs) which when it is pure does not have free electrons to conduct electrical current. GaN is thermodynamically stable, and its alloys are in the hexagonal wurtzite structure . Wurtzite GaN has two hexagonal closely packed sublattices, and each sublattice contains one set of atoms offset along the c-axis by 5/8. The basic geometric shape of a unit cell of the hcp is a rhomboid, and it has two base atoms that is one at the starting point and the other one at (2/3 1/3 1/2). 

The materials and devices that are generated with the use of GaN can also be used in ultraviolent devices that are used in sensing systems for airborne and biological factors and also keeping a close look at the ultraviolent reactions (Gila, 2002). They are also used in power amplifiers and monolithic microwave integrated circuits, radar units that have higher performance, communication connections that are wireless and also used in ultra-high power switches. At room temperature, ferromagnetic semiconductors are used in magnetic sensors and actuators that use electric power. 

References 

Chilton, A. (2014). Nobel Prize in Physics 2014: Why Were Blue LEDs so Hard to Make?.  Azo Materials . Retrieved from: https://www.azom.com/article.aspx?ArticleID=11451 

Gila. (2002). New applications advisable for gallium nitride.  Materials Today ,  5 (6), 24-31. Retrieved from: https://www.sciencedirect.com/science/article/pii/S1369702102006363 

MOTOKI, K.  Development of Gallium Nitride Substrates . Retrieved from : https://pdfs.semanticscholar.org/9692/f6a5eb0783179ab8d3ef1acb953f4cd08ff1.pdf 

Pope, I. (2004).  The Characterisation of InGaN/GaN Quantum Well Light Emitting Diodes . ProQuest LLC 2013. Retrieved from https://orca.cf.ac.uk/55927/1/U584655.pdf