Gallium nitride (GaN) epitaxial growth on silicon substrates presents a compelling opportunity for the semiconductor industry due to the cost advantages of silicon and its compatibility with existing fabrication infrastructure. However, the process is fraught with challenges stemming from lattice and thermal mismatch, which lead to high defect densities, wafer bowing, and cracking. Addressing these issues requires careful engineering of buffer layers, strain management techniques, and growth optimization to enable high-performance devices for power electronics, RF applications, and optoelectronics.

One of the primary challenges in GaN-on-Si epitaxy is the significant lattice mismatch between GaN (a = 3.189 Å) and silicon (a = 5.431 Å), which exceeds 16%. This mismatch induces high threading dislocation densities (TDD) in the GaN layer, degrading device performance. Additionally, the thermal expansion coefficient of GaN (5.59 × 10⁻⁶ K⁻¹) differs substantially from that of silicon (2.59 × 10⁻⁶ K⁻¹), leading to tensile stress during cooling from growth temperatures, often resulting in crack formation.

To mitigate these issues, buffer layer engineering is critical. A common approach involves using an aluminum nitride (AlN) nucleation layer, which provides a transition between the silicon substrate and the GaN layer. The AlN layer reduces lattice mismatch at the interface and helps in dislocation filtering. However, AlN alone is insufficient for complete strain compensation. Multilayer buffer structures, such as AlGaN/GaN superlattices or step-graded AlGaN layers, are employed to gradually adjust the lattice constant and thermal expansion mismatch. These buffers distribute strain more evenly and reduce TDD to the range of 10⁸–10⁹ cm⁻², compared to 10¹⁰ cm⁻² or higher in unoptimized growth.

Strain management is another key consideration. Compressive strain during growth can counteract the tensile strain induced during cooling, reducing crack formation. Techniques such as low-temperature AlN interlayers or in-situ silicon nitride (SiNx) masking have been shown to bend threading dislocations and promote lateral over vertical growth, further reducing defect densities. Additionally, optimizing growth parameters like temperature, pressure, and V/III ratio can influence strain accumulation and defect propagation.

Crack prevention is essential for achieving high-quality GaN layers, particularly for thick epitaxial films required in power devices. Cracks typically form due to excessive tensile stress exceeding the fracture toughness of GaN. Strategies to prevent cracking include using compliant substrates, such as patterned silicon or porous silicon layers, which absorb strain. Another method involves growing thin GaN layers with intermediate annealing steps to relieve stress. Some processes employ carbon doping in the buffer layers to pin dislocations and reduce wafer bowing.

The economic benefits of GaN-on-Si technology are substantial. Silicon substrates are significantly cheaper than native GaN or SiC substrates, reducing manufacturing costs by up to 80% for large-area wafers. This cost advantage enables scalable production for high-volume applications like power transistors and LEDs. Furthermore, silicon’s high thermal conductivity and compatibility with CMOS processes allow for monolithic integration of GaN devices with silicon-based control circuitry, simplifying system design.

GaN-on-Si devices find applications in multiple domains. In power electronics, high-electron-mobility transistors (HEMTs) benefit from GaN’s wide bandgap (3.4 eV), enabling high breakdown voltages and low on-resistance. These devices are used in electric vehicles, renewable energy systems, and data center power supplies. RF applications leverage GaN’s high electron saturation velocity for 5G base stations and radar systems. Optoelectronic devices, such as micro-LEDs and UV photodetectors, also utilize GaN-on-Si platforms due to their superior performance and integration potential.

Despite progress, challenges remain in achieving defect densities comparable to GaN-on-sapphire or GaN-on-SiC systems. Advanced techniques like epitaxial lateral overgrowth (ELO) or nano-patterning of silicon substrates show promise in further reducing TDD. Additionally, optimizing post-growth annealing and defect passivation methods can enhance device reliability.

In summary, GaN epitaxial growth on silicon substrates requires a multifaceted approach to address lattice and thermal mismatch. Through innovative buffer layer designs, strain management, and crack prevention strategies, high-quality GaN layers can be realized at a fraction of the cost of alternative substrates. These advancements pave the way for integrated GaN-Si devices that combine performance, scalability, and cost-efficiency across power, RF, and optoelectronic applications. Future research will focus on further defect reduction and large-wafer uniformity to unlock the full potential of GaN-on-Si technology.