Preparation And Characterization Of GaN Based LED On Different Substrates

As the third generation semiconductor material, Gallium nitride(GaN) has excellent physical, chemical, optical and mechanical properties. GaN, which is widely used in the blue green light, ultraviolet LED, LD and high power electronic devices, plays an important role in LED and promote the development of semiconductor lighting industry. The comparatively important technology of GaN based LED device is the epitaxial growth of GaN thin film. The epitaxial growth of GaN in commercial LED is based on the sapphire substrate. Sapphire substrate has been widely used due to its characteristics of mature preparation and low cost. However, there exist some inherent defects of sapphire including poor heat dissipation and the recession of light efficiency under large current. The above problems can be solved by using GaN single crystal as a homogeneous epitaxial substrate material. However, it is unable to grow large size and high quality GaN single crystal at present. So it is critical to find out the suitable substrate material.In this paper, GaN films with the structure of 7 layer InGaN/GaN MQWs were successfully grown on a and c plane sapphire substrates respectively by MOCVD, We found that the prepared GaN thin films on different substrates were all in the (001) orientation. Compared with the GaN on c plane sapphire, the GaN film on a plane sapphire has better crystallization quality, smaller compressive stress and its band gap is closer to the theoretical value (3.4eV). These results indicate that the structure and optical properties of GaN thin films grown on a plane sapphire are much better. In addition, nonpolar (110) plane GaN thin films was successfully prepared by using the same method on r plane sapphire and has good crystalline quality and small stress.In this paper, nonpolar (110) plane GaN thin films with single preferred orientation were successfully grown on lithium aluminate and the compressive stress in films was only 0.46GPa, electroluminescence (EL) peak observed at 480 nm is obtained at an injection current of 20 mA. The successful preparation of nonpolar m plane films solved the problem of the reducing internal quantum efficiency which is caused by the spontaneous polarization and piezoelectric polarization from intrinsic electric field in polar films.