Gallium Arsenide (GaAs)

• Chemical Formula: GaAs
• Appearance: Blackish-gray solid
• Melting Point: 1238°C
• Stability: Stable in air below 600°C and resistant to non-oxidizing acids.
• Semiconductor Properties: GaAs is an important semiconductor material, belonging to the III-V group of compound semiconductors. It has a zinc blende crystal structure with a lattice constant of 5.65×10^-10 m, a melting point of 1237°C, and a bandgap of 1.4 eV.
• Advantages: GaAs combines multiple advantages as a semiconductor material. However, transistors made from GaAs have low amplification factors, poor thermal conductivity, and are not suitable for high-power devices. Despite its superior properties, GaAs decomposes at high temperatures, making the production of high-purity single crystals with ideal stoichiometry technically challenging.

• Chemical Formula: GaN
• Structure: GaN is a compound of nitrogen and gallium, a direct bandgap semiconductor commonly used in light-emitting diodes since 1990.
• Properties: GaN has a structure similar to wurtzite and is very hard. It has a wide bandgap of 3.4 eV, making it suitable for high-power, high-speed optoelectronic devices. For example, GaN can be used in violet laser diodes to produce 405 nm violet light without the need for nonlinear semiconductor-pumped solid-state lasers.

• Power Density: GaN devices offer ten times the power density of GaAs devices. The higher power density of GaN devices allows for greater bandwidth, higher amplifier gain, and increased efficiency due to reduced device size.
• Operating Voltage: GaN FETs operate at five times the voltage of their GaAs counterparts. This higher operating voltage makes impedance matching easier in narrowband amplifier designs. "Impedance matching" refers to designing the input impedance of the load to maximize power transfer from the device to the load.
• Current Capability: GaN FETs provide twice the current of GaAs FETs. This higher current capability results in greater intrinsic bandwidth for GaN FETs. The thermal flux of GaN at the device level is five times higher than that of the sun's surface! "Thermal flux" is the rate of heat transfer per unit area. GaN, being a high-power density device, dissipates heat in a very small space, creating high thermal flux. This is why thermal design is so critical for GaN devices. Silicon carbide (SiC) has six times the thermal conductivity of GaAs and three times that of silicon, making it the preferred substrate for high-power density RF applications. The chemical bond strength of GaN is three times that of GaAs, resulting in a larger bandgap that supports higher electric fields and operating voltages. The piezoelectric effect of the GaN—AlGaN structure is five times that of the GaAs—AlGaAs structure. GaN devices have a failure rate of less than 0.002% after operating for 1 million hours at 200°C. TI has extensively validated and tested GaN, confirming its high stability.