Optical, Electrical Properties And Stress Of GaN Based LED Wafers

GaN based LEDs on the market are c plane GaN based LEDs currently, all of them are polar GaN based LEDs. However, along the (001) direction, atomic number is not equal in wurtzite structure, so spontaneous polarization and piezoelectric polarization will produce polarization electric field, and thus the energy band of multiple quantum wells will be inclined. Electrons and holes are confined in the triangular potential well of the heterojunction interface. This phenomenon stops the recombination of some electrons and holes, which will reduce the performance and efficiency of LEDs:On one hand, the band bending reduce the effective width of band gap, so luminescence of electron hole recombination has the phenomenon of redshift, namely the production of quantum confined Stark effect; On the other hand, the lowly recombination efficiency of electrons and holes greatly limit the luminescence efficiency of devices.In this paper, the polar LEDs have been studied. The optical properties of m plane LEDs are better than a plane LEDs'. The results show that the patterned substrate can improve the crysal quality of (102) plane, but this is not the reason of better optical properties. The real reason are the stress and the direction of the light in the films, and the the direction of the light is the main reason. Since the patterned substrate can greatly improve the optical efficiency, we have launched a series of experiments on the surface of the substrate. The experimental conditions show that the etching conditions of c plane sapphire are the most critical. At same time, the nonpolar m plane and a plane LEDs were successfully obtained by MOCVD on the substrates of (100) plane LiAIO2 and (302) plane surface LiAlO2, respectively. The both LEDs can be lighted up by 10 mA, but the luminous efficiency of m plane LEDs is much better than a plane LEDs, and the wavelength appears redshift. The carrier density in the films is the reason of higher luminous efficiency, and the higher content of indium in the m plane LEDs the longer wavelength.