I am interested in your InP wafers. What does the A in (111)A stand for? Is this a cubic crystal wafer?
What Do (111)A and (111)B Mean for Indium Phosphide Wafers?
A graduate research associate in materials science and engineering asked about the crystal orientation and polarity of an Indium Phosphide (InP) wafer.
Example wafer specification:
HQ20. 5/10/30 Indium Phosphide wafers,
P/E 2" Ø × 350 ± 25 µm
Undoped InP, (111)B ± 0.5°
Carrier concentration < 3 × 1016 cm−3
Bow < 30 µm, Warp < 30 µm
One-side polished, backside matte etched
Surface roughness < 15 Å
Sealed under nitrogen in a single-wafer cassette
What Is the Difference Between InP (111)A and (111)B?
Indium Phosphide has the zinc-blende crystal structure, which is cubic. Because InP is a binary III-V compound containing indium and phosphorus, the two opposite {111} surfaces are not chemically equivalent.
- InP (111)A: conventionally refers to the group-III, indium-polar surface.
- InP (111)B: conventionally refers to the group-V, phosphorus-polar surface.
The A and B designations therefore describe the polarity of the {111} crystal surface, not a different crystal structure. Surface polarity can affect chemical etching, surface reconstruction, epitaxial nucleation, morphology, and growth behavior.
For wafer specifications, the notation (111)A or (111)B is preferable when referring to the wafer surface orientation. Square brackets, such as [111], are normally used to describe crystallographic directions.
Reference #268498 for specs and pricing.
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Benefits of Indium Phosphide (InP)
Indium Phosphide (InP) is a III-V compound semiconductor valued for high-speed electronics and optoelectronics. It has a direct band gap of approximately 1.34 eV at room temperature and favorable electron transport properties.
Its direct band structure makes InP-based material systems particularly useful for devices that generate, detect, amplify, or modulate light. InP is therefore an important substrate and integration platform for optical-communication and photonic devices.
InP substrates can also support epitaxial heterostructures containing materials such as Indium Gallium Arsenide (InGaAs) , InGaAsP, and related III-V alloys.
Indium Phosphide (InP) Applications
InP substrates and InP-based epitaxial structures are used in a variety of electronic and photonic applications, including:
- Laser diodes
- Photodetectors and optical receivers
- Photonic integrated circuits (PICs)
- Optical modulators
- Semiconductor optical amplifiers
- Fiber-optic communication components
- High Electron Mobility Transistors (HEMTs)
- Heterojunction Bipolar Transistors (HBTs)
- Millimeter-wave and high-frequency electronics
- Terahertz research
- Infrared sensing and spectroscopy
Why Is InP Important for Optical Communications?
InP-based semiconductor systems are particularly important in optical communications because they can be engineered to provide active photonic functions near important fiber-optic telecommunications wavelengths, including approximately 1.3 µm and 1.55 µm.
InP photonic platforms can integrate devices such as lasers, optical amplifiers, modulators, waveguides, and photodetectors on a common semiconductor platform. This ability to integrate active optical functions is one of the major reasons InP remains important for high-speed optical transmitters, receivers, and photonic integrated circuits.
Indium Phosphide for High-Speed Electronics
In addition to photonics, InP-based material systems are important for very-high-frequency electronic devices. InP substrates are used to support epitaxial structures for devices such as HEMTs and HBTs where high carrier transport performance is required.
Device performance depends on the complete epitaxial heterostructure, doping profile, layer composition, device geometry, contacts, and fabrication process. It should therefore not be assumed that an InP substrate alone automatically provides better performance than GaAs or silicon for every application.
How Are InP Wafer Defects Evaluated?
Crystal defects can affect epitaxial growth, device yield, electrical performance, and reliability. An important specification for single-crystal InP substrates is etch-pit density (EPD), which can be used as an indicator of dislocation density after an appropriate selective etching procedure.
Other characterization methods can provide additional information about surface and bulk crystal quality. Depending on the application, these may include:
- Optical microscopy
- Atomic force microscopy (AFM)
- X-ray diffraction and rocking-curve measurements
- Photoluminescence measurements
- Hall-effect measurements
- Surface roughness measurements
- Bow and warp measurements
- Etch-pit density measurements
The appropriate defect specification depends on the epitaxial process and device being fabricated. A low measured defect density does not by itself guarantee a completely defect-free finished device.
Video: Indium Phosphide-Based HEMT
The Importance of Indium Phosphide in Photonics
InP is one of the major III-V semiconductor platforms used for active integrated photonics. Its direct band structure and compatibility with InGaAs, InGaAsP, and related epitaxial alloys allow designers to create semiconductor heterostructures with optical and electronic properties tailored for particular wavelengths and device functions.
A major advantage of an InP-based photonic platform is the ability to integrate multiple active and passive components. Depending on the epitaxial structure and fabrication process, an InP photonic integrated circuit can incorporate functions such as:
- Semiconductor lasers
- Optical amplifiers
- Electro-absorption and other optical modulators
- Photodetectors
- Waveguides
- Splitters and couplers
- Wavelength multiplexing and demultiplexing components
InP and Silicon Photonics
InP and silicon are both important photonic platforms, but they offer different strengths. Silicon benefits from mature semiconductor manufacturing and is widely used for passive and electro-optic photonic circuitry, while InP-based materials provide efficient active functions such as light generation and optical amplification.
Modern photonic systems can combine III-V materials such as InP with silicon or silicon-on-insulator platforms using techniques including wafer bonding, transfer printing, heterogeneous integration, or other advanced integration processes.
InP for Space and Radiation Research
InP materials and devices have also been investigated for space, radiation, and photovoltaic research. Their performance under radiation depends on device architecture, material quality, particle type, radiation dose or fluence, operating temperature, and other conditions.
InP should therefore not be described as universally “radiation-proof” or automatically superior to silicon or GaAs. Material and device selection must be based on the specific radiation environment and application requirements.
Can III-V Semiconductors Be Grown on Silicon Wafers?
A clean-energy technology researcher asked UniversityWafer about using silicon substrates with different surface finishes for III-V epitaxial growth. The researcher wanted to compare as-cut, lapped, single-side-polished, and epi-ready silicon wafers to evaluate substrate-processing costs.
We are investigating III-V growth on silicon wafers and would like to understand how substrate surface preparation affects cost. Can as-cut, lapped, single-side-polished, and epi-ready silicon wafers be compared for research and potential high-volume production?
Growing III-V semiconductor layers directly on silicon is possible, but it presents significant materials-engineering challenges. These can include lattice mismatch, thermal-expansion mismatch, interface defects, threading dislocations, and, for polar III-V compounds grown on nonpolar silicon, antiphase defects.
Surface preparation is also critical. Slicing and lapping can leave subsurface mechanical damage and a relatively rough surface. Chemical etching can remove damaged material, while polishing and final cleaning are normally required when a smooth, well-controlled surface is needed for high-quality epitaxial growth.
The appropriate surface finish depends on the III-V material, growth technique, buffer-layer strategy, orientation, and research objective. A rough or lapped wafer should therefore not be assumed to provide the same epitaxial result as an epi-ready polished wafer.
III-V-on-silicon integration is an active research field. Materials including GaP, GaAs, InP, and related III-V heterostructures have been investigated using direct epitaxy and heterogeneous integration methods.
Reference #225505 for specs and pricing.
Highly Doped Indium Phosphide for Low-Temperature NMR Research
Researchers may require highly doped InP when a high free-carrier concentration is needed for specialized electrical, magnetic, or low-temperature experiments.
A university physics researcher requested highly sulfur-doped n-type InP for use as a low-temperature NMR magnetometer in an antimatter experiment. The experiment required a high carrier concentration and operation near liquid-helium temperature.
Example material previously quoted:
Item #H357
2" n-type InP:S
(100), approximately 400 µm thick
Single-side polished, epi-ready
The certificate of conformance for the referenced material reported a measured carrier concentration of approximately 8.24 × 1018 cm−3.
Actual carrier concentration, dopant concentration, mobility, resistivity, and low-temperature behavior should be verified for the specific wafer or lot being used. Dopant concentration and free-carrier concentration should not automatically be treated as identical quantities.
Reference #226058 for specs and pricing.
Preparing Indium Phosphide Wafers for Epitaxial Growth
Researchers using InP as an epitaxial substrate often require an epi-ready polished surface with tightly controlled surface contamination, roughness, orientation, and defect density.
A postdoctoral researcher asked whether an undoped (100) InP wafer required additional cleaning before epitaxial thin-film growth and whether native surface oxides could be present.
Important: InP surfaces can form native oxides when exposed to air. The previous statement that "There is no native oxide on the InP wafers" should not be used. Surface oxidation and contamination are important considerations when preparing InP for epitaxy.
The appropriate cleaning and oxide-removal procedure depends on the epitaxial technique and device process. Researchers should follow a validated process compatible with their MBE, MOCVD, MOVPE, or other deposition system rather than assuming that rinsing with water or alcohol alone produces an epitaxy-ready atomic surface.
Epi-ready wafers should also be handled carefully to minimize particles, organic contamination, scratches, and unnecessary atmospheric exposure.
Example InP specification:
Item #EF54b — Indium Phosphide wafer
2" Ø × 350 ± 25 µm
(100) ± 0.5°
Carrier concentration < 1 × 1016 cm−3
Electron mobility > 3,500 cm2/V·s
EPD < 5,000 cm−2
One-side polished, backside matte etched
Sealed under nitrogen in a single-wafer cassette
Reference #211633 for additional specifications and pricing.
What Is Indium Phosphide (InP)?
Indium phosphide (InP) is a binary III-V compound semiconductor composed of indium and phosphorus. It crystallizes in the cubic zinc-blende structure under ordinary bulk conditions and has a direct band gap of approximately 1.34 eV at room temperature.
InP is not a metal. Although indium itself is a metallic element, the compound InP is a semiconductor with electronic and optical properties very different from elemental indium.
Its direct band structure and favorable carrier-transport properties make InP important for high-speed electronics and optoelectronics.
InP is particularly important as a substrate and integration platform for epitaxial III-V heterostructures containing materials such as InGaAs, InGaAsP, and related alloys.
What Is the Band Gap of Indium Phosphide?
The band gap is the energy difference between the valence-band maximum and the conduction-band minimum of a semiconductor. InP has a direct band gap of approximately 1.34 eV at room temperature.
Because InP is a direct-band-gap semiconductor, the conduction-band minimum and valence-band maximum occur at the same crystal momentum. This allows efficient optical transitions and makes InP-based material systems useful for light-emitting and light-detecting devices.
The band gap of InP is temperature dependent. As with many semiconductors, its band-gap energy generally decreases as temperature increases.
How Does Doping Affect InP?
Doping changes the electrical properties of InP by introducing electrically active impurities.
Donor dopants can create energy levels near the conduction band and increase electron concentration, producing n-type InP. Sulfur is one dopant that can be used for n-type InP.
Acceptor dopants can create energy levels near the valence band and increase hole concentration, producing p-type InP. Zinc is commonly used as an acceptor dopant in InP.
These donor and acceptor levels are not the band gap. The band gap remains the energy separation between the valence-band maximum and conduction-band minimum.
Doping also changes carrier concentration, resistivity, conductivity, and the position of the Fermi level. At very high dopant concentrations, additional effects such as degeneracy and band-gap narrowing may need to be considered.
Why Is InP Important for Photonics?
InP is an important semiconductor platform for active photonic devices. InP-based epitaxial systems can be engineered to generate, amplify, modulate, guide, and detect light.
This makes InP-based material systems especially useful for optical communication near the important 1.3 µm and 1.55 µm telecommunications windows.
Applications include:
- Laser diodes
- Photonic integrated circuits (PICs)
- Semiconductor optical amplifiers
- Optical modulators
- Photodetectors and avalanche photodiodes
- Fiber-optic transmitters and receivers
- Infrared sensing and spectroscopy
Indium Phosphide vs. Gallium Arsenide
Gallium Arsenide (GaAs) and InP are both III-V compound semiconductors with cubic zinc-blende crystal structures and direct band gaps, but they are different compounds with different lattice constants, band structures, transport properties, and compatible epitaxial material systems.
| Property | InP | GaAs |
|---|---|---|
| Composition | Indium + Phosphorus | Gallium + Arsenic |
| Semiconductor Family | III-V | III-V |
| Band-Gap Type | Direct | Direct |
| Room-Temperature Band Gap | Approximately 1.34 eV | Approximately 1.42 eV |
| Crystal Structure | Zinc blende | Zinc blende |
| Common Research Areas | Photonics, telecom, HEMTs, HBTs, detectors | RF electronics, lasers, LEDs, photovoltaics |
Neither material is universally "better." The appropriate substrate depends on the epitaxial structure, wavelength, device architecture, operating frequency, thermal requirements, cost, and fabrication process.
What InP Substrate Is Suitable for THz Research?
InP and related III-V materials are used in terahertz research, but the correct substrate depends on the specific THz generation, detection, modulation, or transmission mechanism.
For optical photoexcitation, the photon energy must be considered relative to the semiconductor's band gap. At the same time, researchers may need to consider free-carrier absorption, resistivity, carrier lifetime, mobility, substrate thickness, and dielectric properties in the THz frequency range.
Semi-insulating InP can be useful when low electrical conductivity is required from the substrate. Other narrow-band-gap semiconductors such as GaSb and InSb may also be considered when their optical and electronic properties better match the experiment.
In-Stock Indium Phosphide
UniversityWafer supplies InP in multiple conductivity types, dopants, orientations, thicknesses, and surface finishes. Available inventory may include undoped InP, sulfur-doped n-type InP, zinc-doped p-type InP, and semi-insulating InP.
Inventory changes frequently, so researchers should confirm current specifications, carrier concentration, resistivity, orientation, thickness, surface finish, EPD, and availability before designing a process around a particular item.
What Is Semi-Insulating Indium Phosphide?
Semi-insulating InP is high-resistivity InP designed to provide an electrically isolating substrate for electronic and optoelectronic structures.
Iron-compensated InP is commonly used to obtain semi-insulating behavior. Deep levels associated with compensation can reduce the concentration of free carriers and produce high bulk resistivity.
Semi-insulating substrates are useful because they can reduce unwanted substrate conduction, parasitic capacitance, and electrical coupling between devices.
High-Frequency and RF Applications
- HEMTs: InP-based heterostructures are used for extremely high-frequency and low-noise transistor research.
- MMICs: Semi-insulating substrates can provide electrical isolation for microwave and millimeter-wave integrated circuits.
- Low-Noise Amplifiers: InP-based transistor technologies are important for sensitive high-frequency receiver systems, including radio astronomy and communications.
Optoelectronics and Photonics
- Photonic Integrated Circuits: InP platforms can integrate active and passive optical functions.
- Lasers: InP-based heterostructures are widely used for telecommunications laser sources.
- Photodetectors: InP is commonly used with InGaAs and related materials in infrared photodetector structures.
- Optical Modulators: InP-based material systems support high-speed optical modulation.
Terahertz and Advanced Research
InP-based materials and devices are also investigated for terahertz generation and detection, high-speed electronics, quantum photonics, spectroscopy, and other advanced semiconductor applications.
Common Indium Phosphide Wafer Specifications
When requesting an InP substrate, researchers should consider specifying:
- Wafer diameter or sample dimensions
- Crystal orientation, such as (100), (111)A, or (111)B
- Conductivity type
- Dopant species
- Carrier concentration
- Resistivity
- Carrier mobility when required
- Thickness and thickness tolerance
- Single-side or double-side polish
- Surface roughness
- Etch-pit density (EPD)
- Bow and warp
- Epi-ready surface requirements