AXT makes specialty semiconductor substrate wafers — the thin crystalline slices on which chips, lasers, and optical devices are fabricated. Silicon can't meet the performance requirements of certain applications, and AXT's wafers fill that gap. AXT's three substrate products are Indium Phosphide (InP), Gallium Arsenide (GaAs), and Germanium (Ge). InP is AXT's fastest-growing product, used to make lasers and photodetectors for high-speed fiber optic networks and data center interconnects — demand driven heavily by AI infrastructure buildout. GaAs is AXT's largest substrate by historical revenue, used in wireless RF amplifiers, LEDs, and optical sensing devices. Ge is the smallest and lowest-margin substrate, used primarily in solar cells for satellites. AXT operates at the very beginning of the semiconductor supply chain: growing single-crystal ingots, slicing them into wafers, and selling to epitaxial layer companies, which apply chemical coatings before passing wafers to chip manufacturers. About two-thirds of revenue comes from substrates; the remainder comes from a raw materials segment that produces purified gallium, crucibles, and InP base material, some of which feeds AXT's own manufacturing and the rest sold externally. Profitability is driven by volume and factory utilization, product mix (InP carries the best margins), wafer yield, and wafer diameter — larger diameters command higher prices. AXT's key growth priority is expanding InP capacity to meet surging AI-driven demand, targeting a doubling of InP production capacity by end of 2026. The primary near-term risk is China's export permit regime, which covers all three of AXT's substrates and has severely constrained shipments to customers outside China.