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4. materials, ease of preparation and cost of high and low: Taking into account the needs of industrial development, preparation of the substrate material be simple,[link widoczny dla zalogowanych], cost should not be very high. Substrate size is generally not less than 2 inches. GaN-based LED current for more substrate materials, but can be used for commercial substrates are only two, namely sapphire and silicon carbide substrate.
Others, such as GaN, Si, ZnO substrate is still in development stage, some distance away from the industry. GaN: the best substrate for GaN growth is the GaN single crystal material, can greatly improve the crystalline quality of epitaxial films and reduce the dislocation density and improve the working life of the device to improve the luminous efficiency and device operating current density. Preparation of GaN single crystal body, but very difficult, so far there has not been an effective approach.
Zinc oxide: ZnO has become a candidate for GaN epitaxial substrate,[link widoczny dla zalogowanych], because both have very striking similarities. Both the same crystal structure, lattice identify the degree is very small, close to the band gap (the band discontinuity is small and exposure to small barrier). However,[link widoczny dla zalogowanych], ZnO as the Achilles heel of GaN epitaxial GaN epitaxial growth in an atmosphere of temperature and easily decomposed,[link widoczny dla zalogowanych], and corrosion.
Currently, ZnO semiconductor material used to make optoelectronic devices still can not, or high-temperature electronic devices, mainly the material fails to reach the device level and P-type doping problem is not a real solution for the growth of ZnO-based semiconductor equipment had not been developed.