Conventional gallium nitride (GaN) is grown on the polar plane C plane <0001> of sapphire. C-plane sapphire has a strong polarization effect, and the AlGaN/GaN heterojunction interface produces high-density and high-mobility two-dimensional electron gas (2-DEG) due to the polarization effect, which is beneficial to GaN-based high-electron mobility transistors (HEMT) performance, but this polarization effect is more harmful to optoelectronic devices: the built-in electric field caused by the polarization causes the energy band to bend and tilt, the energy level changes, and the strong polarization electric field makes the positive load current When separated in space, the overlap of the wave functions of electrons and holes becomes smaller, the luminous efficiency of the material is greatly reduced, and the luminous wavelength will also appear red shift.
The GaN grown on A<11-20>, M<1-100>, R<1-102> plane sapphire substrates are polar<0001>, semipolar<1122> and nonpolar<1120, respectively. >Oriented crystals, semi-polar, non-polar gallium nitride materials have good performance in LED device droop effect, wavelength shift and long-wavelength band efficiency, but the crystal quality is poor and the dislocation density is high. Studies have shown that high-temperature AlN nucleation layer and higher AlGaN growth temperature, or the use of multilayer AlGaN with successively decreasing Al composition as a buffer layer can effectively improve the crystal quality of semi-polar AlGaN materials, and Si doping can be effective The crystal quality of polar and semi-polar AlGaN thin films grown on the A-plane and M-plane sapphire substrates are improved.