Substrates for Epitaxial Deposition

Epitaxial wafers combine a crystalline substrate with one or more carefully controlled crystalline layers for semiconductor devices, photonics, RF electronics, power devices, LEDs, sensors, MEMS, and advanced materials research. UniversityWafer supplies epitaxial silicon wafers, GaN-based heterostructures, epi-ready substrates, and custom wafer configurations for CVD, MOCVD, MBE, and related epitaxial growth processes.

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Epitaxial Wafers for Semiconductor Research

UniversityWafer supplies standard and custom epitaxial wafers for semiconductor research, prototype fabrication, device development, materials characterization, MEMS, photonics, RF electronics, power devices, sensors, and university laboratories.

Available materials and structures may include epitaxial silicon wafers , multilayer silicon structures, GaN on SiC , GaN on sapphire , and epi-ready crystalline substrates for MBE, MOCVD, CVD, and related epitaxial growth processes.

Research Example: Two-Layer Silicon Epi Wafer

A university researcher requested a custom silicon structure combining a heavily doped substrate with a more lightly doped epitaxial device layer for subsequent semiconductor fabrication.

Requested specifications:

  • Wafer diameter: 100 mm
  • Substrate: Approximately 500 µm n+ silicon
  • Substrate dopant: Phosphorus
  • Substrate dopant concentration: Approximately 1 × 1019 cm−3
  • Epitaxial layer: Approximately 10 µm p-type silicon
  • Epi dopant: Boron
  • Epi dopant concentration: Approximately 7 × 1015 cm−3
  • Front surface: Polished for additional device processing
  • Optional backside metallization: Approximately 1.5 µm aluminum
  • Quantity: 1–25 wafers

The researcher also requested guidance on whether epitaxial growth, ion implantation, or a combination of processes would be appropriate for achieving the required layer structure and doping profile.

Reference #210870

How to Specify an Epitaxial Wafer

Providing complete specifications helps determine whether an existing epi wafer can meet the application requirements or whether a custom epitaxial structure is needed.

  • Substrate material
  • Wafer diameter or dimensions
  • Crystal orientation and offcut, if required
  • Substrate conductivity type
  • Substrate resistivity or dopant concentration
  • Epitaxial material and layer sequence
  • Epi-layer thickness
  • Epi conductivity type
  • Dopant species and concentration
  • Target epi-layer resistivity
  • Surface polish requirements
  • Buffer, nucleation, oxide, nitride, or metal layers
  • Required quantity

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Sapphire Substrates for Epitaxial Growth

Sapphire wafers are important crystalline substrates for heteroepitaxial growth because they provide high-temperature stability, chemical durability, electrical insulation, and commercially available crystallographic orientations.

Sapphire is widely used as a substrate for III-nitride materials such as GaN, AlN, AlGaN, and InGaN. It is also investigated as a crystalline substrate for selected oxide and other thin-film material systems. Growth methods can include MOCVD , MBE , and other deposition techniques depending on the material system.

Crystal orientation is important because the sapphire surface affects nucleation, epitaxial relationship, film orientation, strain, and resulting material properties.

Research Example: Epi-Ready A-Plane Sapphire

A university postdoctoral researcher requested cleanroom-packed, A-plane sapphire substrates for MBE research.

Requested specifications:

  • Material: A-plane sapphire
  • Nominal orientation: (11-20)
  • Orientation tolerance: ±0.1°
  • Diameter: 1 inch
  • Thickness: Approximately 0.3–0.8 mm
  • Surface finish: Single-side polished
  • Packaging: Epi-ready and cleanroom packed
  • Quantity: 10 wafers

The researcher also requested:

  • 20 × 20 mm A-plane sapphire pieces
  • Thickness of approximately 0.3–0.8 mm
  • Single-side-polished surfaces
  • Quantity: 10 pieces

A primary requirement was obtaining surfaces suitable for the intended vacuum-growth process while minimizing additional handling and preparation before loading into the research system.

Reference #101799

What Is Epitaxial Growth?

Epitaxial growth is the growth of a crystalline layer on a crystalline substrate in which the deposited material maintains a defined crystallographic relationship with the underlying surface.

Unlike an amorphous film or a randomly oriented polycrystalline coating, an epitaxial layer has an ordered crystal structure whose orientation is influenced by the crystalline substrate. This allows engineers to design semiconductor layers with controlled electrical, optical, structural, and compositional properties.

Epitaxial layers are used in semiconductor devices including integrated circuits, transistors, LEDs, laser diodes, photodetectors, RF devices, power electronics, solar cells, sensors, and quantum and nanoscale structures.

Homoepitaxy and Heteroepitaxy

  • Homoepitaxy: The epitaxial layer and substrate consist of the same semiconductor material, such as single-crystal silicon grown on silicon.
  • Heteroepitaxy: The epitaxial layer and substrate are different materials but maintain a defined crystallographic relationship, such as GaN grown on sapphire or GaN grown on SiC.

Heteroepitaxial growth requires careful management of factors such as lattice mismatch, thermal-expansion mismatch, substrate orientation, interface chemistry, strain, and dislocation formation.

Why Epitaxial Layer Quality Matters

Device performance depends strongly on the structural and electrical quality of the epitaxial layer. The most important specifications vary by material system and application, but commonly include:

  • Layer thickness and thickness uniformity
  • Crystal orientation and epitaxial relationship
  • Composition and alloy uniformity
  • Dopant concentration and carrier concentration
  • Electrical resistivity
  • Interface abruptness and quality
  • Defect and dislocation density
  • Surface morphology and roughness
  • Residual strain and wafer bow

Precise control of these parameters allows epitaxial wafers to be engineered for applications ranging from power electronics and RF devices to LEDs, photonics, MEMS, sensors, integrated circuits, and advanced materials research.

Applications of Epitaxial Wafers

Epitaxial growth enables device engineers to create semiconductor regions with properties that cannot always be achieved using the bulk substrate alone. Depending on the material system, epitaxial wafers support applications such as:

  • Power electronics – engineered drift layers and wide-bandgap structures for high-voltage devices
  • RF and microwave electronics – GaN and III-V heterostructures for high-frequency transistors
  • LEDs and lasers – multilayer III-V structures with engineered active regions
  • Photodetectors and photonics – controlled optical absorption and carrier-transport layers
  • Integrated circuits – controlled silicon doping, resistivity, and junction structures
  • MEMS and sensors – crystalline device layers with controlled thickness and electrical properties

What Is an Epitaxial Wafer?

An epitaxial wafer, often called an epi wafer, contains one or more crystalline semiconductor layers grown on a crystalline substrate. During epitaxial growth, the growing layer maintains a defined crystallographic relationship with the underlying substrate.

Epitaxy enables precise control of semiconductor properties such as layer thickness, composition, conductivity type, dopant concentration, resistivity, and heterostructure design. These capabilities make epitaxial wafers important for integrated circuits, power devices, RF electronics, LEDs, lasers, photodetectors, sensors, MEMS, and advanced semiconductor research.

UniversityWafer supplies epitaxial silicon wafers, GaN on SiC wafers, GaN on sapphire wafers, epi-ready substrates, and custom semiconductor structures for research, device development, and fabrication.

Epitaxial wafer applications including power electronics, RF devices, LEDs, photonics, integrated circuits, MEMS and sensors

Homoepitaxy vs. Heteroepitaxy

Epitaxial structures are commonly classified as either homoepitaxial or heteroepitaxial.

  • Homoepitaxy: The epitaxial layer and substrate are the same semiconductor material. A common example is single-crystal silicon grown epitaxially on a silicon wafer.
  • Heteroepitaxy: The epitaxial layer and substrate are different materials but maintain a defined crystallographic relationship. Examples include GaN on SiC and GaN on sapphire.

In heteroepitaxy, lattice mismatch, thermal-expansion mismatch, surface preparation, buffer-layer design, and growth conditions can strongly influence strain, dislocation density, interface quality, and device performance.

Common Epitaxial Growth Methods

The appropriate epitaxial growth technique depends on the substrate, semiconductor material, required layer thickness, composition, interface quality, throughput, and intended device.

  • Chemical Vapor Deposition (CVD): Uses gaseous precursors to form crystalline films and is widely used for silicon epitaxy and selected compound-semiconductor processes.
  • Metal-Organic Chemical Vapor Deposition (MOCVD): Widely used for III-V semiconductor heterostructures, including GaN, AlGaN, InGaN, GaAs, and related materials used in LEDs, RF electronics, lasers, and power devices.
  • Molecular Beam Epitaxy (MBE): Uses controlled molecular or atomic beams under ultra-high-vacuum conditions to grow crystalline layers with precise control of thickness, composition, doping, and interfaces.
  • Liquid Phase Epitaxy (LPE): Grows crystalline material from a liquid phase and remains useful for selected semiconductor and optoelectronic material systems.

GaN/AlN/SiC Epitaxial Wafers

GaN/AlN/SiC epitaxial structures combine gallium nitride device layers with an AlN nucleation or buffer layer on a silicon carbide substrate. AlN can assist GaN nucleation and interface engineering, while SiC provides high thermal conductivity and is well suited to high-power and high-frequency semiconductor structures.

GaN/AlN/SiC structures are investigated and used for:

  • High-electron-mobility transistors (HEMTs)
  • RF and microwave electronics
  • High-power semiconductor devices
  • GaN materials and interface research
  • Surface-science and synchrotron studies
  • Advanced wide-bandgap semiconductor development

Research Example: GaN/AlN Epitaxial Structures

A chemical-physics researcher requested 50 mm, on-axis, n-type GaN/AlN structures on SiC or sapphire for synchrotron radiation research.

  • Structure: GaN/AlN/SiC or GaN/AlN/Al2O3
  • Diameter: 50 mm
  • Orientation: On-axis
  • Conductivity: N-type
  • GaN thickness: Approximately 0.5–0.8 µm
  • AlN thickness: Approximately 0.1 µm
  • Quantity: 1 or 5 wafers

Reference #91327

Gallium Nitride Epitaxial Wafers

GaN on SiC combines wide-bandgap GaN device layers with a substrate that offers high thermal conductivity. This material platform is important for high-frequency and high-power electronic devices, including GaN HEMT structures.

GaN on sapphire is widely used for optoelectronics, particularly LED structures, and is also used for photodetectors, materials research, and GaN process development.

Research Example: GaN on SiC and Sapphire

A semiconductor company requested:

  • GaN on 6H-SiC, 50 mm, on-axis, n-type, with approximately 0.5 µm GaN
  • GaN on sapphire, 50 mm, on-axis, n-type, with approximately 0.5–10 µm GaN
  • Two-inch 6H-SiC substrates with SSP or DSP surfaces
  • Two-inch p-type silicon substrates with double-side polish

Reference #90172

Epitaxial Silicon Wafers

Epitaxial silicon wafers contain a single-crystal silicon layer grown on a single-crystal silicon substrate. The epitaxial layer and substrate can be engineered with different dopant species, conductivity types, concentrations, and resistivities.

Common silicon epi configurations include:

  • N-type epi on an n+ substrate
  • P-type epi on a p+ substrate
  • P-type epi on an n-type substrate
  • N-type epi on a p-type substrate
  • Lightly doped or nominally undoped epi layers
  • Single-layer and multilayer epitaxial structures

Important specifications include wafer diameter, crystal orientation, epi-layer thickness, substrate and epi resistivity, dopant species and concentration, surface finish, layer uniformity, and allowable defect levels.

Research Example: Thin N/N+ Silicon Epi

  • Orientation: <111>
  • Structure: N-type epi on n+ silicon
  • Epi thickness: 500 nm–1 µm
  • Target epi resistivity: Approximately 0.1 Ω·cm
  • Target substrate resistivity: Less than 0.01 Ω·cm
  • Priority: In-stock material and short lead time

Reference #103430

Epitaxial Silicon on SOI Wafers

An epitaxial silicon layer can be grown on the exposed crystalline device layer of a silicon-on-insulator (SOI) wafer when the surface, crystal orientation, thermal budget, and process conditions are compatible with epitaxial growth.

Epitaxy can increase the crystalline silicon device-layer thickness or create controlled doping profiles while retaining the buried oxide beneath the device layer. Such structures may be useful in MEMS, sensors, photonics, specialized integrated devices, and semiconductor process research.

A researcher requested:

  • Approximately 2–4 µm of crystalline silicon
  • P-type or n-type conductivity
  • An electrically insulating underlying structure
  • Small research quantities
  • Evaluation of epitaxial growth on silicon-based samples

Reference #94309

PN Junctions in Epitaxial Silicon

A PN junction can be created near the interface between an epitaxial layer and substrate when the two regions have opposite conductivity types. For example, p-type silicon can be grown epitaxially on an n-type substrate, or n-type silicon on a p-type substrate.

Epitaxial layer thickness and doping can be engineered to influence the junction's depletion behavior, electric-field distribution, breakdown characteristics, and series resistance.

A microstructure-physics researcher requested four-inch silicon wafers with oppositely doped substrate and epitaxial regions to form a PN junction near the substrate/epi interface.

Reference #106430

Epitaxial Layers for Transistors and Electronic Devices

Epitaxy is widely used to engineer semiconductor regions for bipolar transistors, MOSFETs, power devices, HEMTs, RF electronics, and integrated circuits. Depending on the device architecture, epitaxial layers can provide controlled doping profiles, composition, thickness, strain, and electrical properties.

Cross-sectional diagram of an epitaxial transistor showing emitter, base, collector and epitaxial regions

Benefits of properly engineered epitaxial structures can include:

  • Controlled doping: Dopant concentration and conductivity type can be tailored across different regions of the device.
  • Engineered active layers: Epitaxy allows device layers to be grown with controlled thickness, composition, and electrical properties.
  • Voltage management: Lightly doped epitaxial drift regions are commonly used in power devices to support high electric fields.
  • Heterostructure engineering: Compound-semiconductor epitaxy enables interfaces such as AlGaN/GaN and other structures used to control carrier confinement and transport.

Semiconductor Materials Used in Epitaxial Devices

  • Silicon: Used extensively for integrated circuits, bipolar devices, CMOS-compatible structures, sensors, and power electronics.
  • Silicon-Germanium (SiGe): SiGe epitaxy enables band-structure and strain engineering and is widely used in high-speed SiGe heterojunction bipolar transistors and RF devices.
  • Gallium Arsenide (GaAs): Used in RF electronics, lasers, LEDs, photodetectors, and other optoelectronic devices.
  • Gallium Nitride (GaN): Important for high-power and high-frequency electronics as well as optoelectronic devices.

Multilayer Epitaxial and Coated Wafer Structures

Semiconductor wafers may combine one or more epitaxial crystalline layers with separately deposited or grown dielectric, conductive, or functional films. Not every layer in a multilayer wafer stack is epitaxial; materials such as SiO2 are typically amorphous rather than epitaxial.

These engineered wafer stacks can provide controlled electrical, optical, mechanical, and surface properties at different depths within the structure.

A researcher requested a structure consisting of:

  1. Bulk p-type silicon substrate, approximately 0.5 mm thick
  2. Approximately 2 µm of higher-conductivity p-type epitaxial silicon
  3. Approximately 3.6 µm of silicon dioxide

Reference #103963

LED Epitaxial Wafers

An LED epitaxial wafer contains multiple semiconductor layers engineered to inject electrons and holes into an active region, where radiative recombination generates light.

Blue and green LEDs commonly use GaN-based heterostructures containing InGaN active regions grown on substrates such as sapphire or silicon carbide. Other III-V material systems based on GaAs and related III-V semiconductors are used for other wavelength ranges.

Typical GaN LED Epitaxial Structure

  1. Substrate: Provides mechanical support and the crystalline template for the epitaxial stack.
  2. Nucleation or buffer layers: Help establish the desired crystal structure and accommodate material mismatch.
  3. N-type GaN: Provides the electron-injection side of the LED structure.
  4. InGaN/GaN multiple quantum wells: Form the active light-emitting region in many blue and green LEDs.
  5. P-type GaN: Provides the hole-injection side of the device.

A postdoctoral researcher requested blue or green LED epi wafers with p-GaN/MQW/n-GaN/u-GaN/sapphire structures, along with undoped and n-type GaN-on-sapphire materials.

Layer structure of blue and green GaN LED epitaxial wafers

How to Specify an Epitaxial Wafer

Providing complete specifications helps determine whether an existing epi wafer is suitable or whether a custom epitaxial structure is required.

  • Substrate material
  • Wafer diameter or dimensions
  • Crystal orientation and required offcut
  • Substrate conductivity type and resistivity
  • Epitaxial material and complete layer sequence
  • Individual epitaxial-layer thicknesses
  • Dopant species, conductivity type, and concentration
  • Target layer resistivity where applicable
  • Surface finish and polish requirements
  • Buffer, nucleation, dielectric, or other additional layers
  • Required quantity

UniversityWafer supplies standard and custom epitaxial wafers and substrates for university research, semiconductor process development, prototype fabrication, device research, and industrial R&D.

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