Jan 15, 2014

LED wafer and LED wafer templates

What is LED?
A light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for general lighting. Appearing as practical electronic components in 1962, early LEDs emitted low-intensity red light, but modern versions are available across the visible, ultraviolet, and infrared wavelengths, with very high brightness.
When a light-emitting diode is switched on, electrons are able to recombine with holes within the device, releasing energy in the form of photons. This effect is called electroluminescence, and the color of the light (corresponding to the energy of the photon) is determined by the energy band gap of the semiconductor. An LED is often small in area (less than 1 mm2), and integrated optical components may be used to shape its radiation pattern. LEDs have many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved physical robustness, smaller size, and faster switching. However, LEDs powerful enough for room lighting are relatively expensive, and require more precise current and heat management than compact fluorescent lamp sources of comparable output.
LED wafer substrate
Current substrate for GaN based LED materials more, but can be used for commercialization of substrate only two, namely, Sapphire and silicon carbide substrates. Others such as GaN, Si, ZnO substrates in the research and development stage, there is still some distance away from industrialization.
Blue-Green LED
Substrates for gallium nitride research more, but can be used in the production of substrates at present, only two, namely Sapphire Al2O3 and silicon carbide SiC substrates.
1, gallium nitride substrates:
For GaN growth of gallium nitride single crystal is the most ideal substrate of natural material, such a mechanism can greatly enhance the quality of epitaxial film, reducing the bits wrong density, improve the working life, enhance luminous efficiency, increase device operating current density. However, the preparation of gallium nitride single crystal materials very difficult, yet effective way. Researchers in other substrates by HVPE method (such as Al2O3, SiC, and LGO) growth of gallium nitride thick film and substrate by stripping technology and isolation of gallium nitride thick film, after the separation of gallium nitride thick film can be used as extension of the substrate. Advantages obtained by gallium nitride thick film is clear, namely to substrate-Epitaxial gallium nitride thin film bits wrong density, Al2O3, SiC epitaxy on gallium nitride films by low densities significantly wrong, but expensive. Gallium nitride thick film used as a substrate for semiconductor lighting is restricted.
2, Sapphire Al2O3 substrates:
Currently for nitride gallium growth of most General of lined end of is Al2O3, its advantages is chemical stability good, and does not absorption visible, and price moderate, and manufacturing technology relative mature; insufficient area while many, but are one by one is overcome, as is large of lattice lost distribution is transition layer growth technology by overcome, conductive performance poor through with side p, and n electrode by overcome, machinery performance poor easily cutting through mine shot is zoned tablets by overcome, is large of hot lost paired extension layer formed pressure stress thus does not cracked.However, the difference of thermal conductivity in the device under low current work does not expose a manifestly inadequate, are power-type devices under high current work issues are highlighted.
3, SiC substrates:
Besides Al2O3 substrates, currently for GaN growth substrates is SiC, its market share was 2nd, yet there is a third type of substrate for gallium nitride LED commercial production. It has a number of distinct advantages, good chemical stability, good thermal conductivity, electrical conductivity does not absorb visible light, but also prominent, such as the price is too high, the quality is difficult to reach the Al2O3 and Si so good, machine performance is poor. In addition, the SiC substrate absorption below 380nm ultraviolet light, is not suitable to develop below 380nm ultraviolet LED. Due to excellent electrical conductivity and thermal conductivity of SiC substrate properties, you do not need to power of gallium nitride LED devices on the Al2O3 substrates using flip chip technology to solve thermal problems, instead of using the top and bottom electrode structure, better resolving power of gallium nitride LED devices thermal issues.
Red and yellow light LED
Red LED to GaP (binary) and AlGaAs (ternary) and AlGaInP (four dollars), mainly using GaP and GaAs substrates without industrialization and Sapphire Al2O3 and SI substrates.
1, GaAs substrate: LPE growth when the red LED, the general use of AlGaAs epitaxial layers, when you use the MOCVD growth LED red, yellow, light, general growth AlInGaP Epitaxial structure. Epitaxial layers grown on GaAs substrates, because the lattice match, easy to grow good materials, but the disadvantage is their absorption of a photon of wavelength, mirrors, Prague or wafer bonding technology is used to eliminate this additional technical problems.
2, and GaP lined end of: in using LPE growth red yellow light LED Shi, General using GaP extension layer, wavelength range more wide 565-700nm; using VPE growth red yellow light LED Shi, growth GaAsP extension layer, wavelength in 630-650nm Zhijian; and using MOCVD Shi, general growth AlInGaP extension structure, this structure is good of address has GaAs lined end of sucking light of shortcomings, directly will LED structure growth in transparent lined end of Shang, but shortcomings is lattice lost distribution, Using buffer layer growth of InGaP and AlGaInP structure is required. In addition, GaP base of III-N-V material system has raised wide interest, this material not only can change the bandwidth, you can also add 0.5% nitrogen cases only, from indirect to direct band gap change, and in the Red region has a strong glow effect (650nm). Adopting the structural manufacturing LED, by the GaNP heterostructure lattice matching, one formation LED epitaxial structure and eliminating the need for removal of GaAs substrate wafer bonding and transparent substrate complex processes.
Wafers for LED application
Apparently LED wafer is for LED application, however don't forget LED template is also main application for LED.Currently there are two templates, GaN on sapphire template and GaN on silicon template.
The GaN on sapphire template consists of an n-type GaN layer grown on a sapphire substrate. Using a GaN-template means LED manufacturers do not need to grow an n-type GaN buffer layer and this reduces the time required for growth by about half compared with conventional methods. The GaN-templates from PAM-XIAMEN are also suitable for high-output LEDs which require large currents because they allow both low resistance and high crystal formation.
GaN-on-silicon template have comparable efficiency to GaN-on-sapphire.But growing an LED on silicon is not easy, because there are lattice and thermal mismatches between the substrate and epitaxial layers that can cause the wafer to bow, or even crack. It is also not possible to grow GaN directly onto silicon
Source:PAM-XIAMEN
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