Preparation And Characterization Of AlInn/GaN Heterojunctions

In recent years, devices base on GaN have attracted more and more attention. Great progress has made on the research of AlGaN/GaN HEMT, while the piezoelectric effect caused by stress limits the progress.Compared with AlGaN, Al1-xInxN can perfectly match GaN films when x takes0.17. Therefore, the heteroj unctions can eliminate the stress effect, avoid the piezoelectric polarization and have few interface defects, high carrier density and high reliability. Meanwhile, A1N has a high Curie temperature (>1000℃), which predicts AlInN/GaN heterojunctions has a higher thermal stability than AlGaN/GaN. So AlInN/GaN can improve the surface instability and reduce the polarization dipole induced channel.Although compared with the mature study of AlGaN materials, the AlInN materials have better characters, it’s difficult to grow high-quality AlInN films and there are few studies on AlInN materials. In this paper, the AlInN/GaN heterojunctions were prepared with MOCVD method, and the structural, the surface morphology and the composition of heterojunctions were researched.The major work and results are as follows:1. GaN films were fabricated on sapphire (0001) with MOCVD method. High purity trimethyl gallium Ga(CH3)3(TMGa) was employed as Ga organometallic(OM) source, NH3as nitridizing agent and N2as carrier gas. The growth temperature was varied from900℃to1050℃, the time of buffer was varied from1min to5min, and the N/Al supply ratio was from1000to1800. The structural properties of samples were investigated in detail by x-ray diffraction. When the time of buffer is5min, the temperature is1050℃, the N/Al supply ratio is1800, and we get the best crystalline quality. A thick buffer layer provides the nucleation with the same orientation as substrate so that the stress generated by the lattice mismatch between GaN and the substrate is released. Meanwhile, with N/Al supply ratio increasing, the horizontal/vertical growth rate ratio increases, so that we can get GaN films with better quality. 2. Al1-xInxN films with high-In were fabricated on sapphire (0001) with MOCVD method. High purity trimethyl aluminum Al(CH3)3(TMA) was employed as Al organometallic(OM) source, trimethyl indium In(CH3)3(TMIn) as In organometallic(OM) source, NH3as nitridizing agent and N2as carrier gas. The growth temperature was varied from500℃to700℃and the composition x was varied from0.5to0.8. The structural properties of samples were investigated in detail by x-ray diffraction. With temperature increasing, the crystalline quality gets better and the lattice constant increases. The orientation of the film depends on temperature. The composition of films was investigated in detail by X-ray Photoelectron Spectroscopy. The In content was decreased with growth temperature increasing. Perhaps In can improve the growth of films; therefore with composition x decreasing the growth rate of films was decreased.3. Al1-xInxN films with high-In were fabricated on GaN (0002) with MOCVD method. High purity trimethyl aluminum Al(CH3)3(TMA) was employed as Al organometallic(OM) source, trimethyl indium In(CH3)3(TMIn) as In organometallic(OM) source, NH3as nitridizing agent and N2as carrier gas. The growth temperature was varied from500℃to700℃, the composition x was varied from0.2to0.4and the N/Al supply ratio was from1000to2000. The structural properties of samples were investigated in detail by x-ray diffraction. The composition of films was investigated in detail by X-ray Photoelectron Spectroscopy. With the N/Al supply ratio decreasing, the In content increased. Perhaps In can improve the growth of films; therefore with composition x decreasing the growth rate of films was decreased.