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GALLİUM ARSENİDE (GaAs) WAFER: STRUCTURE, PROPERTİES, USES

Gallium arsenide (GaAs) is a compound of gallium and arsenic. It is a vital semiconductor and is commonly used to manufacture devices such as infrared emitting diodes, laser diodes, integrated circuits at microwave frequencies, and photovoltaic cells.

Structure of Gallium arsenide (GaAs) Wafer

In the Gallium arsenide (GaAs) Wafer, each gallium atom is bordered by arsenic atoms. 5 valence electrons of arsenic atoms and 3 valence electrons of gallium atoms share each other. So, each of the gallium and arsenic atom gets 8 valence electrons in the outer shell. It is also to be noted that a covalent bond exists between gallium and arsenic atom in the GaAs Wafer. The covalent bonds despite being strong can be broken with an enough amount of external energy.

Properties of GaAs Wafer

The main properties of gallium arsenide (GaAs) are given below:

  • The Molar mass of Gallium arsenide (GaAs) is 144.64 g/mol.
  • Gallium arsenide (GaAs) has the Melting point of 1238 °C.
  • The density of Gallium arsenide (GaAs) is 5.32 g/cm3.

Use of GaAs Wafers

The main use of gallium arsenide (GaAs) is found in:

  • Computers
  • Photovoltaic cells
  • Optoelectronic communications
  • Laser diodes and infrared emission

GaAs Wafers’ Use in Transistors & Computers

The physical and chemical properties of GaAs complicate its use in the manufacturing of transistors by being a binary composite with a lower thermal conductivity and a higher coefficient of thermal expansion (CTE), while silicon and germanium are elementary semiconductors. In addition, failures in devices based on GaAs are more difficult to understand than those in silicon and can be more expensive, due to its recent use. But comparing the relationship, quality, and price, the added value of GaAs offsets manufacturing costs. The indicated markets are in continuous growth, which demand the technology that allows higher frequencies, which help reducing the costs.

GaAs Wafers’ Use in Defense & Aerospace

Gallium arsenide has been incorporated into commercial markets since its use began for the military and aerospace field. It belongs to the semiconductor materials group in the periodic table. The width of the band gap is greater than in silicon or germanium. The mobility of the electrons is also greater than in silicon or germanium, and that of the holes similar to those of silicon.

To impurify the type p, materials such as zinc, cadmium or copper are used since they introduce permitted levels in the range of 0.08 to 0.37 eV above the valence band of GaAs. The donor materials are sulfur, selenium and the elements of group IV of the periodic table, in small concentration, if they replace gallium atoms.

The GaAs is used for photoelectric cells, tunneling diodes, lasers, semiconductors and MESFET transistors.

The GaAs has several circuit topologies and device types. The most dominant and commercially available is the FET logic directly coupled with DCFL (Direct Coupled FET Logic), although BFL logic (Buffered FET Logic) and SDFL logic (Schottky Diode FET Logic) are also available.

 

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GaAs Wafers in high frequency technologies

The effective mass of the electric charge of the doped N-type GaAs is lower than in the silicon of the same type, so the electrons in GaAs Wafers are accelerated at higher speeds, taking less time to cross the transistor channel. This is very useful at high frequencies, since a higher maximum operating frequency will be reached.

This possibility and need to work with circuits that allow to act at higher frequencies has its origin in the defense and space industries, in the use of radars, secure communications and sensors. After development by federal programs, GaAs soon expanded to new commercial markets, such as wireless local area networks (WLAN), personal communication systems (PCS), live satellite transmission (DBS), transmission and reception by the consumer, global positioning systems (GPS) and mobile communications. All these markets required working at high and low frequencies that could not be achieved with silicon or germanium.

In addition, this has affected the philosophy of manufacturing semiconductors, now using statistical methods to control uniformity and ensure the best possible quality without seriously affecting the cost. All this also made possible the creation of new digital transmission techniques with higher radio frequency power and low voltage amplifiers to maximize the operation and standby time in battery powered devices.

Advantages of Gallium Arsenide (GaAs) Wafers

The advantage of gallium arsenide wafers over solar-grade silicon wafers is that it offers almost twice the efficiency. Another advantage of GaAs wafer refers to the increase in efficiency. Usually the gallium arsenide is deposited in a single thin layer on a small sheet, but at the University of Illinois, multiple layers of material have been deposited on the wafers, obtaining a higher yield. Multiple layers eliminate the limitations in the area of work, something very important in the case of solar cells, which require a wide coverage area to capture as much light as possible. Thus, a greater area of coverage is achieved, generating more energy and lower cost. The use of arsenide in solar cells is not new. It has been used for many years in the multi-junction cells.

Disadvantages of Gallium Arsenide (GaAs) Wafers

The devices manufactured with GaAs wafers can work at temperatures of up to 450 °C. But despite this advantages, its use poses some difficulties, compared with that of silicon. For example, unlike silicon, there is no natural oxide that acts as a mask to produce simple elements of the CMOS logic style.

The big disadvantage, which explains its low utilization, is the price. To solve this dilemma, engineers and researchers say they have achieved new methods of manufacturing thin films of low cost gallium arsenide, which would create devices that would replace silicon, hence increasing the efficiency of photovoltaic cells.

Conclusion

Gallium arsenide (GaAs) contains an atom of Gallium and another atom of Arsenide. Its use is commonly found in electronics, such as in the manufacturing of semiconductors. The compound has some advantages and disadvantages, as described above. The work is underway to regulate the price of this compound and there is much more that Gallium arsenide (GaAs) Wafers can offer in other sectors also. Therefore, the research must be continued to discover its exceptional uses.

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