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transparent electrodes on the ways in which current spread, in order to achieve the purpose of uniform light. But the metal transparent electrode generally absorb about 30% to 40% of the light, while the chemical properties of GaN-based materials stability, high mechanical strength, its not easy to etch, so the etching process of the need for better equipment,
This will increase production costs. Very high hardness of sapphire, the hardness of natural materials next to diamond, but in the production process of LED devices is required for thinning and cutting it (from 400nm down to 100nm or so). Additions to complete the process of thinning and cutting equipment, but also a large increase in investment.
Thermal conductivity of sapphire is not very good (at 100 ℃ approximately 25W / (m?; K)). Therefore,[link widoczny dla zalogowanych], the use of LED devices, it will transfer a large amount of heat; particularly for larger power devices,[link widoczny dla zalogowanych], thermal conductivity is a very important consideration.
In order to overcome these difficulties, many people tried to direct the growth of GaN optoelectronic devices on silicon substrate, thereby improving the thermal and electrical conductivity. There are currently part of the silicon substrate LED chip silicon substrate.
Chip silicon substrate electrode can be two kinds of contact methods, namely L exposure (Laterial-contact, the level of exposure) and the V exposure (Vertical-contact, vertical contact), hereafter referred to as L-type electrode and V-type electrode. By these two means of contact,[link widoczny dla zalogowanych], LED chip current flow can be horizontal,[link widoczny dla zalogowanych], or vertical movement. Since current can flow vertically, thus increasing the LED light-emitting area, thereby improving the extraction efficiency of LED.
Because silicon is a good conductor of heat, so the device can be significantly improved thermal performance, thus extending the life of the device. SiC substrate SiC substrates (CREE company specializes in the United States as a substrate material using SiC) LED chip electrode is L-type electrode, current is the longitudinal flow.