Gallium Nitride Epitaxial Wafers: An Introduction to the Fabrication Process

Gallium Nitride (GaN) epitaxial wafer growth is a complex process, often utilizing a two-step method. This method involves several critical stages, including high-temperature baking, buffer layer growth, recrystallization, and annealing. By meticulously controlling the temperature throughout these stages, the two-step growth method effectively prevents wafer warping caused by lattice mismatch or stress, making it the predominant fabrication method for GaN epitaxial wafers globally.

1. Understanding Epitaxial Wafers

An epitaxial wafer consists of a single-crystal substrate upon which a new single-crystal layer is grown. This epitaxial layer plays a crucial role in determining approximately 70% of the final device’s performance, making it a vital raw material in semiconductor chip manufacturing.

Positioned upstream in the semiconductor industry chain, epitaxial wafers serve as a foundational component, supporting the entire semiconductor manufacturing industry. Manufacturers utilize advanced technologies like Chemical Vapor Deposition (CVD) and Molecular Beam Epitaxy (MBE) to deposit and grow the epitaxial layer on the substrate material. These wafers then undergo further processing through photolithography, thin film deposition, and etching to become semiconductor wafers. Subsequently, these wafers are diced into individual dies, which are then packaged and tested to create the final integrated circuits (ICs). Throughout the entire chip production process, constant interaction with the chip design phase is crucial to ensure the final product meets all specifications and performance requirements.

2. Applications of GaN Epitaxial Wafers

The inherent properties of GaN make GaN epitaxial wafers particularly well-suited for applications requiring high power, high frequency, and medium to low voltage operation. Some key application areas include:

High Breakdown Voltage: The wide bandgap of GaN enables devices to withstand higher voltages compared to traditional silicon or gallium arsenide counterparts. This characteristic makes GaN ideal for applications like 5G base stations and military radar systems.

High Conversion Efficiency: GaN-based power switching devices exhibit significantly lower on-resistance compared to silicon devices, resulting in reduced switching losses and improved energy efficiency.

High Thermal Conductivity: GaN’s excellent thermal conductivity enables efficient heat dissipation, making it suitable for high-power and high-temperature applications.

High Breakdown Electric Field Strength: While GaN’s breakdown electric field strength is comparable to silicon carbide (SiC), factors like semiconductor processing and lattice mismatch typically limit the voltage handling capacity of GaN devices to around 1000V, with a safe operating voltage generally below 650V.

3. Classifying GaN Epitaxial Wafers

As a third-generation semiconductor material, GaN offers numerous advantages, including high-temperature resistance, excellent compatibility, high thermal conductivity, and a wide bandgap. This has led to its widespread adoption in various industries. GaN epitaxial wafers can be categorized based on their substrate material: GaN-on-GaN, GaN-on-SiC, GaN-on-Sapphire, and GaN-on-Silicon. Among these, GaN-on-Silicon wafers are currently the most widely used due to their lower production costs and mature manufacturing processes.**