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primarysourced Photonics sector Coherent
COHR
~6 min read · 1,342 words ·updated 2026-04-29 · confidence 86%

Silicon carbide (SiC) substrates

Silicon carbide is a wide-bandgap (3.26 eV) compound-semiconductor material whose physical properties — high critical electric field, high thermal conductivity, high saturation electron velocity — make it the dominant choice for high-voltage, high-frequency, high-temperature power-electronic devices. Modern applications include:

  • Electric vehicle traction inverters (Tesla Model 3 was the first major automotive deployment, 2017)
  • EV onboard chargers and DC fast-charge infrastructure
  • Datacenter power supplies and AC-DC stages
  • Industrial motor drives and renewable-energy inverters
  • Aerospace and defense radar and electronic-warfare systems

The SiC franchise is non-photonics but historically the founding business of legacy II-VI Incorporated (Saxonburg, PA — 1971-origin). After the 2022 II-VI/Coherent Inc. combination and the 2022 corporate rename to Coherent Corp., SiC remains a meaningful revenue and margin contributor in the Materials segment of Coherent’s three-segment 10-K disclosure (01_company).

Materials segment context

Coherent’s FY2025 10-K segments revenue across:

SegmentFY2025 trendKey drivers
Networking+49% YoY ✓AI datacenter, 800G/1.6T transceivers, ROADM/WSS
Materials−6% YoY ✓Weakness in automotive electronics and SiC; cyclical
Lasers+3% YoY ✓Display capital equipment recovery

Source: Coherent FY2025 Annual Report ✓.

The Materials-segment FY2025 decline reflects the broader SiC supply-demand reset that has impacted all merchant SiC suppliers in 2024–2025 — slowing EV-volume growth, especially for premium-segment EVs that initially drove SiC inverter adoption, and inventory destocking through Tier-1 power-module assemblers (Infineon, onsemi, ROHM internal, STMicroelectronics internal).

SiC substrate roadmap — 100 mm → 150 mm → 200 mm → 300 mm

The wafer-size race in SiC mirrors what happened in silicon over four decades, compressed into a decade. Coherent’s progression:

Wafer sizeProduction status (2026-Q1)Source
100 mm (4-inch)mature, declining mix ◐legacy II-VI
150 mm (6-inch)mature production ✓legacy II-VI
200 mm (8-inch) bare wafervolume ramp ✓Coherent product portfolio
200 mm SiC epitaxial wafer (350 µm and 500 µm)launched ✓Coherent SiC epi launch (2025)
300 mm next-generation platformintroduced December 2025 ✓Coherent 300 mm SiC platform announcement

The 200 mm SiC epi launch — Coherent announcing 350 µm and 500 µm thickness 200 mm SiC epitaxial wafers — moves the company beyond bare wafers into the more value-added epi step, which is a higher-margin, more-differentiated layer of the SiC value chain ✓. Wolfspeed announced its commercial 200 mm SiC materials portfolio in September 2025 (Wolfspeed PR) — Coherent’s parallel positioning is competitive.

The next-generation 300 mm SiC platform, introduced in December 2025, targets datacenter-AI-power applications where the thermal-density argument for SiC over silicon LDMOS or GaN is strongest ◐. Public detail on Coherent’s 300 mm process maturity, qualified-customer count, and projected volume timing is limited.

SiC competitive landscape

Per industry tracker reporting, the top 5 SiC substrate suppliers — Wolfspeed, Coherent, STMicroelectronics, ROHM, SK Siltron — controlled roughly half of global capacity in 2025 ⚠ (Mordor Intelligence).

SupplierCountryVertical positionNotable
Wolfspeed (WOLF)USAsubstrate + epi + device + moduleFirst to commercial 200 mm (Sep 2025); restructured 2025 (Chapter 11 emergence)
Coherent (COHR)USAsubstrate + epi (no device/module)200 mm epi launched; 300 mm platform Dec 2025 ✓
STMicroelectronics (STM)Italy/Francesubstrate + device + moduleNorstel acquisition; vertically integrated
ROHMJapansubstrate + device + moduleVertically integrated; large EV design-ins
SK Siltron CSSSouth Koreasubstrate + epiAcquired DuPont SiC wafer business 2020
TankeBlueChinasubstrateDomestic-China focus; rapidly scaling
SICCChinasubstrateDomestic-China focus; rapidly scaling ✓
Resonac (Showa Denko)Japanepi-onlyHigh-quality epi merchant supplier
II-VI legacy / Coherent (this entry)USAsubstrate + epi(Same entity as row 2; included for legacy reference)

The Chinese SiC suppliers — TankeBlue (天科合达, founded 2006) and SICC (天岳先进, founded 2010) — are the structural threat to Western merchant SiC pricing. Both have rapidly scaled 6-inch and 8-inch capacity through 2023–2025, driven by domestic-China EV demand and aggressive policy support.

The Wolfspeed restructuring (Chapter 11 filed mid-2025; emergence later in 2025 after capital-structure reset) created near-term uncertainty for Wolfspeed’s customer base and arguably created a window for Coherent to gain share — though Wolfspeed remains the merchant volume leader and was the first to launch commercial 200 mm SiC (Wolfspeed PR Sep 2025).

Coherent’s vertical position vs Wolfspeed

A structural distinction: Coherent supplies substrates and epi only — it does not make SiC MOSFETs, modules, or finished power devices. Wolfspeed, ST, ROHM, and onsemi are vertically integrated downstream into devices and modules.

LayerCoherentWolfspeedSTM/ROHM/onsemi
Crystal growth (PVT/HTCVD)✓✓partial
Wafer slicing/polish✓✓partial
Epi growth✓ (200 mm launched)✓✓
MOSFET/JBS-diode device fab—✓✓
Module assembly—✓✓
Discrete + system integration—partial✓

This means Coherent’s SiC business is more akin to a specialty-materials business (margin profile, capital intensity) than a power-semiconductor device business. Coherent supplies merchant substrates to device-makers including (per public corporate descriptions) a broad set of Tier-1 power-semi customers ◐ — Coherent does not publicly disclose individual customer-mix splits.

SiC sales channels and end markets

Coherent’s SiC franchise serves three end markets:

  1. Automotive (EV inverters, onboard chargers) — historically the dominant growth driver, currently the cyclical headwind
  2. Datacenter power — emerging tailwind from AI-driven kilowatt-per-rack increases (rack power approaching 100 kW + drives demand for SiC-based AC-DC stages and DC-DC conversion)
  3. Industrial / renewable / other — solar inverters, motor drives, rail traction

The datacenter power end market is structurally accretive in 2026+ as AI training racks push to 60 kW–100 kW per rack and operators seek SiC-based power stages with higher efficiency than silicon LDMOS. Coherent has highlighted this end-market tailwind in 2025 management commentary ◐ — though SiC’s near-term mix is still automotive-weighted, so the auto-electronics cycle remains the dominant Materials-segment swing factor.

Manufacturing footprint

Coherent’s SiC fab footprint includes:

  • Easton, PA — legacy II-VI; SiC crystal growth and substrate operations
  • Bridgeport, PA — legacy II-VI; SiC operations
  • Saxonburg, PA — corporate headquarters and historical-origin SiC/optics fab

Coherent does not publicly break out SiC-specific capital investment vs the broader Materials-segment capex. The FY2025 capex was concentrated more heavily on Networking-segment InP capacity (InP EML process) than on SiC capacity expansion, reflecting the segment-mix realities of FY2025.

Risks and counter-positions

  • Chinese competition: TankeBlue and SICC are scaling capacity faster than Western players; Western SiC ASPs faced 30%+ pressure during 2024–2025 ⚠
  • EV cyclicality: SiC demand is significantly correlated to premium-EV unit volume, which de-rated through 2024–2025
  • Wolfspeed restructuring window: created share-gain opportunity, partially offset by Wolfspeed’s emergence with new capital and 200 mm leadership
  • Vertical-integration disadvantage: Coherent does not capture device-margin upside that ST, ROHM, and onsemi capture

Cross-tenant context

The SiC business is largely orthogonal to Coherent’s photonics franchise. Within the LWLG-research-driven KB it is a diversification + exposure topic rather than a load-bearing photonics-thesis input. Cross-links primarily flow within Coherent’s 10-K segment structure (Materials segment vs Networking segment) rather than to other photonics tickers.

Sources