Gallium itself is not a semiconductor; it is classified as a metal. However, it is a foundational component in advanced electronic materials through its chemical compounds. Positioned in Group 13, pure gallium has a remarkably low melting point of about 29.76 degrees Celsius, meaning it liquefies just above room temperature. Its electronic role is defined by the structure gallium forms when bonded with other elements, which creates semiconductor functionality.
The Nature of Elemental Gallium
Elemental gallium is a soft, silvery post-transition metal, and its electrical properties confirm its classification as a conductor, not a semiconductor. Like all metals, it exhibits metallic bonding where outer-shell electrons are delocalized and free to move throughout the crystalline structure. This “sea” of mobile electrons allows for the unhindered flow of electric current, which is the definition of a conductor.
Despite being a metal, pure gallium is not an excellent conductor compared to materials like copper or silver, sometimes being described as a poor metal. Its electrical conductivity is approximately 7.1 million Siemens per meter in the solid state. The complex, orthorhombic crystal structure of solid gallium results in electrical anisotropy, meaning its conductivity varies depending on the direction of current flow. The free movement of charge carriers prevents pure gallium from being electronically controlled as a semiconductor.
Defining Gallium-Based Semiconductors
Gallium transitions from a metal when combined with Group 15 elements, such as arsenic and nitrogen. These resulting materials are known as III-V compound semiconductors, named for the groups from which the constituent elements originate. The most common examples are Gallium Arsenide (GaAs) and Gallium Nitride (GaN).
When gallium (three valence electrons) bonds with a Group 15 element (five valence electrons), the resulting compound creates a stable, crystalline structure. This chemical combination fundamentally alters the material’s electronic band structure, opening a specific energy gap characteristic of a semiconductor. Unlike a metal, the conductivity of these compounds can be precisely controlled by introducing impurities, a process called doping. The ability to engineer this bandgap and control electron flow defines these materials as compound semiconductors.
Performance Advantages Over Silicon
Gallium-based compounds offer distinct performance advantages over traditional silicon, which is the cornerstone material of most computing and general electronics. One of the most significant differentiators is electron mobility, which is a measure of how quickly electrons can move through the material under an applied electric field. Gallium Arsenide, for instance, boasts an electron mobility up to six times greater than silicon, allowing for the creation of devices that operate at much higher speeds and frequencies.
These materials also possess a wider bandgap than silicon, especially Gallium Nitride. A wide bandgap translates directly into higher breakdown voltage, meaning devices can handle more electrical power without damage. This property enables operation at higher temperatures and voltages, making GaN suitable for power electronics. Both GaAs and GaN have a direct bandgap structure, allowing them to convert electrical energy into light efficiently, a capability silicon lacks due to its indirect bandgap.
Essential Applications of Gallium Compounds
The advanced electronic properties of gallium compounds have led to their deployment in specialized, high-performance applications where silicon’s capabilities are insufficient. Gallium Arsenide, due to its superior electron mobility, is widely used in radio frequency (RF) components, such as power amplifiers and low-noise amplifiers, found in satellite communications and cellular phones. Its efficiency in light emission also makes it a foundational material for infrared laser diodes and many types of Light-Emitting Diodes (LEDs).
Gallium Nitride is valued for its wide bandgap, making it the preferred material for high-power and high-frequency systems. It is responsible for the blue and white LEDs ubiquitous in modern lighting and enables the violet laser diodes used in Blu-ray technology. GaN is transforming power electronics, allowing for smaller, faster, and more efficient chargers for consumer devices. It is also a core technology in 5G infrastructure and advanced radar systems due to its high power density.