LED epitaxial wafer related knowledge teach you to read

1. What is epitaxial and epitaxial wafers?
Epitaxy, also known as epitaxial growth, is a process for making high purity microelectronic composites by depositing a thin layer of single crystal (or compound) on a single crystal (or compound) substrate material. The newly deposited layer is called an epitaxial layer. The substrate material on which the epitaxial layer is deposited is called an epitaxial wafer.
2. Which materials can be used as substrate materials for growing epitaxial layers? What are their respective advantages and disadvantages?
The most widely used substrate material is gallium arsenide, which can be used to grow epitaxial layers of GaAs, GaP, GaAlAs, InGaAlP. The advantage is that the dislocation-free single crystal can be made due to the comparative matching of lattice constants of GaAs, and the processing is convenient. Cheaper. The disadvantage is that it is a kind of light-absorbing material, which absorbs more light from the PN junction and affects the luminous efficiency.
The gallium phosphide can grow the top layer of GaP:ZnO, GaP:N, GaAs, GaAlAs:N, and InGaAlP. The advantage is that it is a transparent material and can be made into a transparent substrate to improve the light extraction efficiency.
The substrates for growing InGaN and InGaAlN are mainly sapphire (Al2O3), silicon carbide, and silicon. The advantage of the sapphire substrate is its transparency, which is beneficial to improve the luminous efficiency. It is still the main substrate for epitaxial growth of InGaN. The disadvantage is that there is a large lattice mismatch; the hardness is high, resulting in high processing costs; the thermal conductivity is low, which is not conducive to the device's heat dissipation, and is unfavorable for manufacturing power LEDs. Silicon carbide substrate has a small lattice mismatch, low hardness, easy processing, high thermal conductivity, and is conducive to the production of power devices.
3, LED light emitting active layer? PN junction is made of? Which are the semiconductor materials commonly used to make LEDs?
The substantial structure of the LED is a semiconductor PN junction. The PN junction refers to a structure having adjacent P and N regions in a single crystal. It usually generates a thin layer of another conductivity type by diffusion, ion implantation or growth on a conductive type crystal. To be made.
Commonly used to manufacture LED semiconductor materials are gallium arsenide, gallium phosphide, gallium aluminum arsenic, phosphorous gallium arsenide, indium gallium nitrogen, indium gallium aluminum phosphorus and other III? V compound semiconductor materials, and other group IV compound semiconductor carbonization Silicon, II-VI compounds such as zinc selenide.
What is MOCVD?
MOCVD is the abbreviation for MetEL-Organic Chemical Vapor Deposition, ie, chemical vapor deposition of metal organic materials. It is a technology for epitaxial growth. It uses special equipment and uses a metal organic source (MO source) as a raw material, using hydrogen gas or nitrogen gas. As a carrier gas, the vapor is carried into the liquid, mixed with the hydride of the group V, passed into the reaction chamber, reacted on the surface of the heated substrate, and a compound crystal film is epitaxially grown. Since the MOCVD crystal growth reaction is performed in thermal decomposition, it is also called thermal decomposition. The utility model shows that this is a method with high reliability, precise control thickness, high composition doping concentration accuracy, good verticality, and great flexibility, and is very suitable for epitaxial growth of III-V compound semiconductors and solid solutions thereof. It can also be applied to the growth of materials such as II-VI compounds, and is currently an industrial method for producing AlGaInP red and yellow LEDs and InGaN blue, green and white LEDs. Nowadays, this special equipment is also commonly referred to as MOCVD.
5. What is the MO source?
The MO source is Metel Organic, a source of metal organics, which is a raw material for MOCVD epitaxial growth. The Group II and Group III metal organic compounds are usually methyl or ethyl compounds such as Ga(CH3)3, In(CH3)3, Al(CH3)3, Ga(CH3)3, Zn(CH3)3, etc. Most are high vapor pressure liquids or solids.
What is the process of MOCVD epitaxial growth?
6. What is the internal quantum efficiency of an LED?
When a forward voltage is applied to the PN junction of the LED, a current flows through the PN junction. The electrons and holes recombine in the PN transition layer will generate photons, but not every pair of electrons and hole pairs will generate photons. Due to the PN junction of the LED, as an impurity semiconductor, there are material quality defects, dislocations and other factors , And various defects in the process, will produce impurity ionization, intrinsic excitation scattering and lattice scattering problems, so that when the electron transitions from the excited state to the ground state, it will exchange energy with the lattice atoms or ions and generate no radiation transition, that is, No photons are generated. This part of energy is not converted into light energy and converted into thermal energy and lost in the PN junction. Therefore, there is a problem that the conversion efficiency of composite carriers into photons exists. Equation 1 can be used to express this conversion efficiency, and The symbol ηint represents.
Ηint = (number of photons generated by composite carriers / total number of composite carriers) × 100? (1)
We cannot count the total number of composite carriers and the total number of photons generated in (1). This efficiency is typically evaluated by measuring the optical power of the LED output, which is called internal quantum efficiency.
7. Can a photon emitted by an LED PN junction 100 escape to the air?
8. What are the epitaxial methods for growing active layers of LEDs? What are their characteristics?
There are vapor phase epitaxy (VPE), liquid phase epitaxy (LPE), metal organic chemical vapor deposition (MOCVD), and molecular beam epitaxy (MBE). Their active materials for the growth of the LED layer are vapor phase epitaxial GaAsP, GaP, liquid phase epitaxy GaP, GaAlAs, metal organic chemical vapor deposition InGaAlP, IganN, molecular beam epitaxy ZnSe and so on.
Vapor-phase epitaxy is relatively simple, and PN junctions are often made by diffusion after epitaxial growth, so the efficiency is low. Liquid phase epitaxy has been able to grow 60-100 pieces in one furnace, and the production efficiency is high. The re-use cost through helium has dropped very low, and high-luminance GaP green light-emitting devices and general brightness GaP red light-emitting devices can also be manufactured. Ultra-high brightness GaAlAs light emitting devices. Metalorganic chemical vapor deposition is currently the main method for producing ultra-high brightness InGaN blue, green LED and InGaAlP red and yellow LEDs. It can not only precisely control the thickness but also precisely control the composition of the epitaxial layer. Molecular beam epitaxy is currently mainly used for the development of white light-emitting diodes. It works well and can grow epitaxial layers less than 10 angstroms. The disadvantage is that the growth rate is slow, about 1 micrometer per hour, and the loading capacity is also quite low, resulting in low production efficiency.
9. At present, there are several major methods for the production of super bright LEDs.
At present, there are mainly two types of epitaxial methods for producing ultra-bright LEDs, namely, liquid phase epitaxy production of AlGaAs LEDs and metal organic chemical vapor deposition (MOCVD) to produce AlGaAs, AlGaInP, and InGaN LEDs. Among them, the MOCVD method is the main method.
10. What innovation is currently in place for the epitaxial layer structure of high-efficiency LEDs used as semiconductor light sources?
In order to improve the luminous efficiency of LEDs, many improvements have been made to their epitaxial structures, which have been applied to products at present, and have played an extremely important role in improving the luminous efficiency of LEDs. Are: 1 single quantum well (SQW) structure; 2 multiple quantum well (MQW) structure; 3 distributed Bragg reflector (DBR) structure; 4 transparent substrate technology (TS); 5 mirror substrate method (MS); 6 transparent Glial bonding type; 7 texture surface structure.

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