GaAs Semiconductor: Properties, Applications and Advantages

What is a GaAs Semiconductor?

A GaAs semiconductor is defined as a compound of gallium and arsenic that belongs to the III-V group of semiconductors.

GaAs has a direct band gap of 1.424 eV at 300 K and a zinc blend crystal structure. GaAs semiconductors are widely used to make devices like microwave frequency integrated circuits (MFICs), monolithic microwave integrated circuits (MMICs), infrared light-emitting diodes (LEDs), laser diodes, solar cells, and optical windows.

How is a GaAs Semiconductor Prepared?

There are several methods for producing GaAs semiconductors, depending on the desired purity, quality, and application of the material.

Some of the common methods are:

• The vertical gradient freeze (VGF) process melts a mix of gallium and arsenic in a quartz crucible and cools it slowly from the bottom to form a single crystal. This method produces high-purity GaAs wafers for solar cells and optoelectronic devices.
• The Bridgman-Stockbarger technique involves heating a mixture of gallium and arsenic in a horizontal zone furnace and passing it through a temperature gradient to form a single crystal. This process is suitable for producing low-cost GaAs wafers for MFICs and MMICs.
• The liquid encapsulated Czochralski (LEC) growth, which involves melting a mixture of gallium and arsenic in a quartz crucible surrounded by a layer of molten boron oxide and pulling out a single crystal from the melt using a seed crystal. This process is suitable for producing high-quality GaAs wafers that can exhibit semi-insulating characteristics for MMICs and optoelectronic devices.
• The vapour phase epitaxy (VPE) process, which involves reacting gaseous gallium metal and arsenic trichloride on a heated substrate to form a thin film of GaAs. This process is suitable for producing thin layers of GaAs for LEDs, laser diodes, and solar cells.
• The metalorganic chemical vapour deposition (MOCVD) process, which involves reacting trimethylgallium and arsine on a heated substrate to form a thin film of GaAs. This process is suitable for producing high-quality thin layers of GaAs for LEDs, laser diodes, and solar cells.
• The molecular beam epitaxy (MBE) process involves evaporating gallium and arsenic atoms from separate sources and depositing them on a heated substrate to form a thin film of GaAs. This process is suitable for producing ultra-thin layers of GaAs with precise control over the composition and doping for MMICs, LEDs, laser diodes, and solar cells.

What are the Properties of a GaAs Semiconductor?

GaAs semiconductors have several properties that make them attractive for various electronic and optoelectronic applications.

Some of these properties are:

• High electron mobility: GaAs semiconductors have an electron mobility of 9000 cm²/V·s at 300 K,



which is about five times higher than that of silicon. This means that electrons can move faster and more easily in GaAs than in silicon, resulting in higher speed and lower power consumption of devices.

• Low reverse saturation current: GaAs semiconductors have a reverse saturation current of about 10^-9 A/cm², which is about 1000 times lower than that of silicon. This means that GaAs devices have less leakage current and lower noise than silicon devices, resulting in better performance and reliability.
• Excellent temperature sensitivity: GaAs semiconductors have a temperature coefficient of resistance of about -0.07%/K, which is much lower than that of silicon (-0.2%/K). This means that GaAs devices have less variation in their electrical characteristics with temperature changes than silicon devices, resulting in better stability and accuracy.
• High breakdown voltage: GaAs semiconductors have a breakdown voltage of about 400 V/µm, which is about four times higher than that of silicon (100 V/µm). This means that GaAs devices can withstand higher voltages and currents than silicon devices, resulting in higher power handling capability and efficiency.
• Direct band gap: GaAs has a direct band gap of 1.424 eV at 300 K, allowing it to emit light when an electric current passes through. This property makes GaAs ideal for LEDs, laser diodes, and solar cells operating in the infrared region of the electromagnetic spectrum.

What are the Applications and Advantages of a GaAs Semiconductor?

GaAs semiconductors have various applications and advantages in different fields of electronics and optoelectronics.

Some of these are:

• Microwave frequency integrated circuits (MFICs): GaAs semiconductors are used for making MFICs that operate at frequencies above 1 GHz, such as amplifiers, mixers, oscillators, switches, and filters. These circuits are used for communication systems, radar systems, satellite systems, and wireless systems. The advantages of using GaAs for MFICs are high speed, low noise, low power consumption, high gain, high linearity, and wide bandwidth.
• Monolithic microwave integrated circuits (MMICs): GaAs semiconductors are used for making MMICs that integrate multiple MFICs on a single chip, such as transmitters, receivers, modulators, demodulators, and converters. These circuits are used for communication systems, radar systems, satellite systems, and wireless systems. The advantages of using GaAs for MMICs are high integration density, high performance, low cost, low weight, and small size.
• Infrared light-emitting diodes (LEDs): GaAs semiconductors are used for making LEDs that emit light in the infrared region (700 nm to 1 mm) of the electromagnetic spectrum. These LEDs are used for remote controls, optical sensors, optical communication systems and night vision systems. The advantages of using GaAs for LEDs are high efficiency, long lifetime, low cost and easy fabrication.
• Laser diodes: GaAs semiconductors are used for making laser diodes that emit coherent light in the infrared region (700 nm to 1 mm) of the electromagnetic spectrum. These laser diodes are used for optical communication systems, optical storage systems, and medical applications such as surgery and therapy. The advantages of using GaAs for laser diodes are high power output, high modulation speed, and narrow spectral linewidth.
• Solar cells: GaAs semiconductors are used for making solar cells that convert sunlight into electricity. These solar cells are used for space applications and terrestrial applications such as rooftop panels and concentrator systems. The advantages of using GaAs for solar cells are high efficiency, high radiation resistance, high-temperature tolerance, and wide spectral response.
• Optical windows: GaAs semiconductors are used for making optical windows that transmit light in the infrared region (700 nm to 1 mm) of the electromagnetic spectrum.

  

  These optical windows are used for infrared cameras, thermal imaging systems, and spectroscopy instruments. The advantages of using GaAs for optical windows are high transparency, low absorption, low reflection, and low scattering.

Conclusion

GaAs semiconductor is a compound of gallium and arsenic that has many desirable properties such as high electron mobility, low reverse saturation current, excellent temperature sensitivity, high breakdown voltage, and direct band gap. These properties enable GaAs to be used for various electronic and optoelectronic devices such as MFICs, MMICs, LEDs, laser diodes, solar cells, and optical windows. These devices have various applications and advantages in different fields, such as communication systems, radar systems, satellite systems, wireless systems, remote controls, optical sensors, optical storage systems, medical applications, space applications, and thermal imaging systems.