The University of Cambridge and the two semiconductor companies have recently collaborated on the use of cubic GaN (3C GaN) materials as green LED luminescent materials, which can solve the problem of conversion efficiency of green light materials. The green gap (greengap) problem that has emerged.
The Electronics Weekly website reported that the partnership included two semiconductor companies, including Cambridge University, Plessey Semi Semiconductor and Anvil Semi.
According to Dave Wallis, manager of Plessey, the traditional 6-sided GaN, the electric field will appear on the c-plane of the crystal. Although it is beneficial to manufacture transistors, the electrons that form photons are separated from the holes when manufacturing LEDs. Form the so-called Quantum Confine Stark Effect. Moreover, once the amount of indium increases, the effect is exacerbated, but since the mechanism for increasing indium is to lengthen the GaN LED wavelength, in other words, this effect has become a major obstacle to the effective emission of photons by green GaN LEDs.
However, Wallis pointed out that if cubic GaN is changed because its symmetry will change, the electric field will disappear, so that the effect will not continue to hinder the manufacture of photons. Whether this effect is the only culprit in the green divide is currently inconclusive, but the green LED with cubic GaN has better internal and external quantum efficiency, and more photons can be formed per unit of electron.
Wallis also pointed out that another benefit of using cubic GaN is that the green LED energy gap is 200mV lower than that of hexagonal GaN, so it can save the use of indium, but it also has its shortcomings. Because in GaN, the 3C crystal lattice is thermodynamically unstable, only hexagonal crystals can be formed at the temperature at which epitaxial growth can be achieved, unless the energy balance can be adjusted manually. Fortunately, Anvil Semiconductor has been developed. method. Using the cubic silicon carbide method invented by the company, its lattice constant is quite close to that of cubic GaN, allowing cubic crystals to grow smoothly.
Wallis revealed that the University of Cambridge has successfully grown GaN with a cubic structure of less than 99% and grown quantum wells on the material. In the future, the school will continue to grow N and P-type layers near the quantum wells in order to form a transmissive bias to convert electrons. A photon diode.
The commentary pointed out that another benefit of the Anvil process is the ability to grow cubic silicon carbide on lower cost wafers, and the University of Cambridge's well-known wafer growth hexagonal GaN technology has also been sold to Plessey, which is also used in the manufacture of blue light. With white light on the LED. In the future, when the N and P layers are integrated at Cambridge University, the wafers are sent to the Plessey plant and electrodes are deposited to form a green LED that can be operated. At present, the three-party cooperation has entered the third month, and it is expected that green-light cubic GaN LEDs will be produced in September 2016.
As for the luminous efficiency, Wallis expects green light efficiency to be consistent with blue light. He also pointed out that because the alliance uses 6-inch wafers, it will be able to use the 150mm green LED process.
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