The luminous efficiency of LED is a main factor to measure whether the photoelectric convertor is efficiency. How to improve the luminaries efficiency.The transparent substrate technology is one of the effect ways to improve the luminaries efficiency of LED.
InGaAIP LED is usually manufactured on the GaAs substrate epitaxial growth of InGaAIP luminous zone of Gap window area. Compared with InGaAIP, the material of GaAs has a much smaller forbidden bandwidth,therefore, when the light of short wavelength rejects into the substrate of GaAs from the surface of luminous zone and window area, it will be absorbed by all, which becomes the primary cause of low luminous efficiency of the device.
A bragg reflection area that develops between substrate and confinement layer,which can reflect the light in the substrate vertically to the luminous zone or the window area, improves the optical properties of the device partly. A more efficiency way is to wipe off the substrate of GaAs, instead of transparent crystal of GaP. Because the chip removes the substrate absorption area, makes quantum efficiency from 4% to 25% to 30%.
Three years before,in order to reduce the absorption of electrode area, someone made the device of transparent substrate InGaAIP into the shape of a cutting angle of cone, which makes quantum efficiency a larger increase.Obviously, this device that has the shape of a cutting angle of cone makes the transparent area larger, in red light district, the external quantum efficiency of this kind of device can exceed 50%.