InP技术初探
发布时间：2003-11-13 19:10:25 热度：2127
Indium Phosphide (InP) is a member of the III-V family of semiconductors. III-V materials are binary crystals with one element from the metallic group 3 of the periodic table, and one from the non-metallic group 5. The family includes GaAs, InP, GaN, InSb and InAs. Some of these binary compounds are known for their high mobility of electrons and holes, which in the case of the best known example - gallium arsenide - facilitates the operation of very high speed electronics.
InP has been a focus of development since the early 1980s, and today the material is being used as a platform for a wide variety of fiber communications components, including lasers, LEDs, semiconductor optical amplifiers, modulators and photo-detectors.
III-V compounds have a cubic lattice-like structure with atoms in each corner. InP, for example, features alternate indium and phosphorous atoms. Being a semiconductor, InP has an energy bandgap, which makes it opaque for light energy that is higher than the bandgap, and transparent for light energy levels that are below. The bandgap of many III-V materials, including InP, is also known as 'direct'. This means that the quantum transitions which take place when a photon is absorbed or emitted do not require any quantum change in the momentum of carriers, i.e. they occur much more readily, making the material highly suitable for fabricating devices such as lasers or LEDs. This direct bandgap supports optical gain as required for lasers, and also very high absorption (photons can be absorbed within very short distances) - making functions such as data modulators or fast photo-detectors easy to implement.
A family of materials - including InGaAs and InGaAsP - share the same 5.87Å lattice constant as InP, allowing epitaxial processing on top of the basic InP wafer. These materials may be used to provide attributes such as electrical confinement to improve laser efficiency, and optical confinement to provide active (gain or absorption) and passive (transparent) optical waveguide functions. Other non-matched materials may also be grown in thin layers to add useful properties such as quantum effects and strain. In the case of InP these allow the fabrication of high-efficiency quantum well lasers.
One of the key advantages of InP is device size. Because the refractive indices of InP and its ternary (InGaAs) and quaternary (InGaAsP) derivatives are relatively higher than for other optical materials, bends can be made much sharper and smaller. As the energy bandgap is also closer to light energy, electro-optical effects are stronger than in other materials (which again translates into shorter distances, and lower drive voltages). A downside of these smaller geometries is that it becomes more difficult and lossy to couple to optical fiber. This is overcome by means of taper structures at the interfaces, to match the optical mode size at the InP chip facets with the fiber ends.
The result is extremely small devices - die sizes are typically less than 5mm, and for the simple types of functions discussed in this article (lasers, modulators) they are considerably less than that (1mm or smaller). InP processing complexity compares favorably with commodity silicon chips, with under 16 stages of photolithography.
As a semiconductor, InP has a very strong potential for creating integrated devices. This includes combining different active optical elements together, such as lasers, modulators and amplifiers, and optical switches and interferometers - along with passive waveguides. Moreover, current development work on HBTs (heterojunction bipolar transistors) holds out a strong promise of combining optical elements with electrical drive circuitry, providing very powerful and cost effective solutions for implementing high speed DWDM and OTDM systems.
InP has been a focus of development since the early 1980s, and today the material is being used as a platform for a wide variety of fiber communications components, including lasers, LEDs, semiconductor optical amplifiers, modulators and photo-detectors.
III-V compounds have a cubic lattice-like structure with atoms in each corner. InP, for example, features alternate indium and phosphorous atoms. Being a semiconductor, InP has an energy bandgap, which makes it opaque for light energy that is higher than the bandgap, and transparent for light energy levels that are below. The bandgap of many III-V materials, including InP, is also known as 'direct'. This means that the quantum transitions which take place when a photon is absorbed or emitted do not require any quantum change in the momentum of carriers, i.e. they occur much more readily, making the material highly suitable for fabricating devices such as lasers or LEDs. This direct bandgap supports optical gain as required for lasers, and also very high absorption (photons can be absorbed within very short distances) - making functions such as data modulators or fast photo-detectors easy to implement.
A family of materials - including InGaAs and InGaAsP - share the same 5.87Å lattice constant as InP, allowing epitaxial processing on top of the basic InP wafer. These materials may be used to provide attributes such as electrical confinement to improve laser efficiency, and optical confinement to provide active (gain or absorption) and passive (transparent) optical waveguide functions. Other non-matched materials may also be grown in thin layers to add useful properties such as quantum effects and strain. In the case of InP these allow the fabrication of high-efficiency quantum well lasers.
One of the key advantages of InP is device size. Because the refractive indices of InP and its ternary (InGaAs) and quaternary (InGaAsP) derivatives are relatively higher than for other optical materials, bends can be made much sharper and smaller. As the energy bandgap is also closer to light energy, electro-optical effects are stronger than in other materials (which again translates into shorter distances, and lower drive voltages). A downside of these smaller geometries is that it becomes more difficult and lossy to couple to optical fiber. This is overcome by means of taper structures at the interfaces, to match the optical mode size at the InP chip facets with the fiber ends.
The result is extremely small devices - die sizes are typically less than 5mm, and for the simple types of functions discussed in this article (lasers, modulators) they are considerably less than that (1mm or smaller). InP processing complexity compares favorably with commodity silicon chips, with under 16 stages of photolithography.
As a semiconductor, InP has a very strong potential for creating integrated devices. This includes combining different active optical elements together, such as lasers, modulators and amplifiers, and optical switches and interferometers - along with passive waveguides. Moreover, current development work on HBTs (heterojunction bipolar transistors) holds out a strong promise of combining optical elements with electrical drive circuitry, providing very powerful and cost effective solutions for implementing high speed DWDM and OTDM systems.
