What is Gallium Arsenide?
Gallium Arsenide is a compound of elements Gallium and Arsenide. The atomic number of Gallium is 31 and it belongs to IIIrd group and atomic number of Arsenide is 33 and it belongs to Vth group.
The GaAs and Silicon have similar crystalline structure. Gallium is not found naturally, but it is found in bauxite and zinc. Arsenide is found in many minerals like sulphur and it is toxic. It is used as a strengthener in alloys.
Why Gallium Arsenide is used?
The advantages of Gallium Arsenide are electron mobility is 30 % higher than silicon, efficiency is higher, better heat and moisture resistance, direct band gap and high breakdown voltages. So it is widely used in high frequency applications. But silicon is much cheaper than the Gallium Arsenide devices, so only in special application like aerospace technology, medical devices, solar cells GaAs is used.
Energy band gap of Gallium Arsenide
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| Energy band gap of GaAs |
Band gap is the minimum energy difference between the top of the valence band and the bottom of the conduction band. But mostly the top of the valence band and bottom of the conduction band does not happen at the same value of electron momentum. Gallium Arsenide have direct band gap, so the top of the valence band and the bottom of the conduction band happens at the same value of electron momentum.
Types of Gallium Arsenide devices:
There are three types of electron devices where Gallium Arsenide is used. They are the diodes, bipolar junction transistor and Field effect transistor.
Gallium Arsenide Photonic devices:
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| Gallium Arsenide PIN Diode |
Because of its optical properties Gallium Arsenide is used in Light Emitting Diodes(LED), Laser diodes, photo detectors, solar cells and waveguides. The advantage over the other semiconductor devices is lower leakage current
Gallium Arsenide Heterojunction Bipolar Transistor(HBT)
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| GaAs HBT |
Heavily doped n+ layer is used for emitter and collector contact, p+ layer is used for base layer. This forms low resistance Ohmic contacts. This improves the movement of electrons from emitter to the base. The capacitance between the emitter and base is reduced. The operation of HBT is similar to the BJT. The emitter base junction is forward biased and collector base junction is reverse biased. Electrons move from emitter to base and then to collector. This forms the base current and collector current. This HBTs are used in microwave applications.
Gallium Arsenide Field Effect Transistor:
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| GaAs FET |
GaAs FET performs better than the other types of FETs. It is a type of FET used in amplifier circuits at very high, ultra high and microwave radio frequencies which operates with less noise. Because of its small size, weight, radiation hardness and reliability it is used in radio astronomy and space applications like phase array radars, signal processors, space based electronic detection systems, tracking devices and digital transmitter receivers.
Advantages of Gallium Arsenide:
- Flexible and light weight
- UV and moisture resistant
- Highly efficient
- In solar cells it performs at low light.
- Very high electron mobility
- Lower noise
Disadvantages of Gallium Arsenide:
- Production cost is high
- More brittle compared to silicon
Applications:
- Used in microwave applications in consumer applications to warfare electronics.
- Used in optoelectronics including LED, Laser diode and Solar cells
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