GaN Epiwafers — GaN-on-Si, GaN-on-SiC, GaN-on-Sapphire

Gallium nitride (GaN) is a wide-bandgap semiconductor (3.4 eV) that enables fast switching, high breakdown voltage, and high-frequency operation in a thin epitaxial layer grown on a foreign substrate. Unlike SiC, commercial GaN devices are built on epiwafers -- a thin GaN layer and device heterostructure grown by MOCVD onto a substrate of silicon, silicon carbide, or sapphire. The choice of substrate determines the epiwafer's cost, diameter, thermal performance, and addressable application market. GaN devices have bifurcated into two distinct markets with different substrate requirements: power conversion (GaN-on-Si) and RF amplification (GaN-on-SiC).

Substrate Platform Comparison

Platform	Substrate	Max Diameter	Primary Application	Thermal Performance	Cost Position	Key Suppliers
GaN-on-Si	Silicon (200mm / 300mm)	200mm in production; 300mm in development	Power conversion: EV chargers, data center PSUs, consumer adapters, solar inverters, industrial drives	Moderate -- silicon thermal conductivity limits heat extraction from active GaN layer; adequate for power applications below ~650V	Lowest -- leverages existing silicon fab infrastructure; 200mm wafer cost comparable to silicon	EpiGaN/Soitec (BE/FR), IQE (UK), Enkris (CN), Innoscience (CN), SCIOCS/Sumitomo (JP), DOWA (JP); Infineon, STMicroelectronics, Transphorm captive
GaN-on-SiC	Semi-insulating SiC (100mm-150mm)	150mm (6-inch) mainstream; transitioning to 200mm	RF power amplifiers: defense radar, 5G base station power amplifiers, satellite, aerospace	Highest -- SiC thermal conductivity (~490 W/m·K) is 3x silicon; enables high power density at RF frequencies	Highest -- SiC substrate cost, smaller wafer diameter; justified by RF power density and thermal performance premium	Wolfspeed (US, dominant for semi-insulating SiC substrate + GaN epi), Coherent (US), MACOM (post-Wolfspeed RF acquisition), Qorvo (captive), RFHIC (KR)
GaN-on-Sapphire	Sapphire (Al2O3) (100mm-200mm)	200mm	LED production (dominant historical use); some laser diodes and optoelectronics; declining for power and RF	Poor -- sapphire is thermally insulating; unsuitable for high-power density applications	Low-Moderate for LED volumes; sapphire substrate well-established; not competitive for power or RF vs. Si or SiC platforms	Multiple LED IDMs (Nichia, Osram, Epistar, San'an) operate captive GaN-on-sapphire; also Chinese LED epi houses
GaN-on-GaN (bulk)	Bulk GaN (50mm-100mm)	100mm; very limited availability	Vertical GaN power devices (next generation); laser diodes requiring lowest defect density	Excellent for vertical device structures	Very high; bulk GaN crystal growth (ammonothermally or HVPE) is extremely costly and slow	Sumitomo Electric (JP), Mitsubishi Chemical (JP), Sciocs; nascent market

GaN-on-Si: Power Conversion Market

GaN-on-Si is the fastest-growing GaN platform by volume, driven by the transition from silicon MOSFETs to GaN in power conversion applications from 20W consumer adapters to 65kW EV onboard chargers. GaN's high electron mobility transistor (HEMT) structure -- a two-dimensional electron gas (2DEG) at the AlGaN/GaN interface -- enables lower on-resistance and faster switching than silicon at equivalent voltage ratings up to ~650V, reducing switching losses and enabling smaller passive components and higher switching frequencies.

The ability to grow GaN-on-Si using existing silicon MOCVD reactors and process GaN-on-Si epiwafers on 200mm silicon fab lines is the key economic advantage of this platform. Innoscience (China) operates the world's largest dedicated GaN-on-Si fab on 200mm wafers and has pursued an aggressive price-reduction strategy that is reshaping the power GaN cost structure. STMicroelectronics and Infineon are building 8-inch GaN-on-Si capability. EpiGaN (acquired by Soitec) and IQE are the leading merchant epi suppliers outside the Chinese market. The QST (quasi-substrate technology) approach -- engineering a buffer layer to reduce thermal mismatch and improve 200mm GaN-on-Si epitaxial quality -- is an active development area for pushing GaN-on-Si toward higher voltages.

GaN-on-SiC: RF & Defense Market

GaN-on-SiC dominates defense radar, 5G base station power amplifiers, and satellite communication power stages -- applications where output power density, efficiency at high frequency, and thermal management are critical and where substrate cost is a secondary concern. SiC's thermal conductivity (~490 W/m·K) is approximately three times silicon's, enabling heat extraction from the GaN device active layer that silicon substrates cannot provide at the same power density. GaN HEMTs on SiC deliver output power densities of 10-40 W/mm at frequencies from 2 GHz to above 100 GHz.

Wolfspeed has been the dominant supplier of semi-insulating SiC substrates for GaN RF epi, but its RF business was acquired by MACOM in 2023, separating the substrate supply (remaining at Wolfspeed) from the RF device business. Coherent (formerly II-VI) also supplies semi-insulating SiC substrates for GaN RF epi alongside its power SiC business. The transition from 100mm to 150mm SiC for GaN RF is underway; 200mm GaN-on-SiC development is active but not yet in production volume. The RF GaN-on-SiC supply chain is more concentrated and defense-oriented than the power GaN-on-Si supply chain, with significant captive capacity at Qorvo and MACOM.

GaN Epiwafer Supplier Landscape

Supplier	HQ	Platform Focus	Business Model	Key Notes
EpiGaN (Soitec)	Belgium / France	GaN-on-Si (power); GaN-on-SiC (RF)	Merchant epi; acquired by Soitec in 2019	Leading European merchant GaN epi house; Soitec's engineered substrate expertise applied to GaN platforms; serves power and RF customers; QST (quasi-substrate) technology for improved GaN-on-Si quality
IQE	UK (Cardiff, Wales)	GaN-on-Si, GaN-on-SiC; also GaAs, InP epi	Merchant epi; world's largest compound semiconductor epi house	Broadest compound semiconductor portfolio; serves RF GaN, power GaN, GaAs RF, InP photonics, VCSEL markets; MOCVD scale advantage; global fab footprint (UK, US, Singapore, Taiwan)
Wolfspeed	US	GaN-on-SiC (semi-insulating SiC substrate + GaN epi)	Captive + merchant; vertically integrated SiC substrate → GaN epi → RF device	Dominant in semi-insulating SiC substrate for GaN RF; RF device business sold to MACOM (2023); materials business continues supplying GaN epi on semi-insulating SiC
Enkris Semiconductor	China (Suzhou)	GaN-on-Si (power); GaN-on-SiC (RF)	Merchant epi; largest GaN epi producer by volume	Largest producer in GaN epitaxial market (~25% share); primarily serves Chinese power GaN device market; growing RF GaN capability
Innoscience	China (Zhuhai)	GaN-on-Si (power); 8-inch focus	Integrated GaN foundry (epi + device fab); world's largest dedicated GaN power fab	Pure-play GaN power foundry; 8-inch GaN-on-Si at scale; aggressive pricing strategy reshaping global power GaN cost structure; STM partnership for GaN-on-Si supply
SCIOCS (Sumitomo Chemical)	Japan	GaN-on-SiC, GaN-on-Si; also GaAs RF epi	Merchant epi; part of Sumitomo Chemical group	Established compound semiconductor epi supplier; serves RF GaN and power GaN alongside GaAs RF market

Supply Chain Outlook

GaN epiwafer supply is bifurcating clearly by platform. GaN-on-Si for power conversion is on a cost-reduction trajectory driven by 200mm wafer scale and Chinese producer expansion -- Innoscience's fab scale and Enkris's epi volume are putting downward pressure on GaN power device pricing globally, accelerating GaN adoption in consumer and industrial power applications. GaN-on-SiC for RF is constrained by semi-insulating SiC substrate supply and the concentration of qualified RF GaN epi capability at a small number of suppliers with defense qualification histories. The MACOM acquisition of Wolfspeed's RF business in 2023 reshuffled the RF GaN supply chain, separating substrate (Wolfspeed) from devices (MACOM) and creating new sourcing considerations for defense customers. The longer-term platform question -- whether GaN-on-Si can encroach on GaN-on-SiC at sub-6 GHz telecom frequencies where power density requirements are lower -- is an active competitive dynamic between the two ecosystems.

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