Study On Growth Of High Al Fraction AlGaN And P-type Doping Of AlGaN Materials

With the successful preparation of group III nitride semiconductor material Al GaN,related optoelectronic devices have been extensively studied.AlGaN-based deep-ultraviolet lightemitting diodes(LED)have been widely used in the fields of disinfection and sterilization,skin treatment,air and water purification due to short-wavelength characteristics,and have become one of the most important research topics in semiconductor light-emitting devices.In recent years,with the continuous improvement of the technology of scientific research,the preparation of AlGaN-based deep ultraviolet LEDs has made some important breakthroughs and progress,but its luminous efficiency and power still have a big gap to meet the current standards of commercial LEDs,and there are also technical problems such as high defect density and low hole injection efficiency of high-Al composition AlGaN films that need to be solved urgently.Aiming at the key issues of AlGaN-based deep ultraviolet LEDs,this article will focus on how to improve the quality and hole concentration of highAl composition AlGaN films.The Al N substrate was prepared by sputtered and metal organic chemical vapor deposition(MOCVD),and the Al N film was post-processed by high temperature thermal annealing technology.At the same time,the Al N/sapphire was used as the substrate to homoepitaxially a high Al composition AlGaN layer,and the Mg-doped p-type AlGaN was grown and annealed on the AlGaN layer.The main research results and contents are as follows:A 200 nm thick Al N film was prepared on the c-plane sapphire by magnetron sputtering technology and MOCVD respectively,and the sputtered Al N substrate was thermally annealed at 1680?.The study found that annealing causes the Al N crystal pillars to coalesce,which eliminates the tilt and distortion of the crystal grains in the sputtered Al N film,leading to the annihilation of the crystal domain boundaries,thereby improving the crystallinity of the Al N film.Compared with the unannealed Al N film,the dislocation density of the annealed sputtered Al N film is reduced by an order of magnitude,and finally an Al N film with the(002)crystal face rocking curve FWHM of 70 arcsec is obtained.A high-Al composition AlGaN film was grown on the Al N/sapphire substrate by MOCVD.XRD analysis found that compared to the unannealed AlGaN film on the sputtered Al N substrate,the screw dislocation density of the AlGaN film that was grown on the sputtered Al N substrate after high temperature annealing decreased from 1.4×109 cm-2 to 1.3×108 cm-2,and the edge dislocation density dropped from 3.1×1010 cm-2 to 2.3×109 cm-2.In addition,through XRD and RSM analysis,it is found that different substrates have a significant impact on the stress and strain in the AlGaN film.Among them,the stress of the epitaxial layer grown on the sputter-annealed Al N is the smallest.At the same time,the compressive stress will have a pulling effect on the Ga atoms in AlGaN,causing the Al composition in AlGaN to increase with the increase of the compressive stress.Observation of the TEM image of the cross-section of the epitaxial layer shows that the dislocations in the AlGaN epitaxial layer mainly originate from the Al N layer,and the reduction of the dislocation density of Al N will improve the crystal quality of AlGaN.In addition,The AlGaN epitaxial layer will undergo strain relaxation by tilting dislocations,and the degree of relaxation is proportional to the size of the dislocation tilt angle.In addition,a large dislocation tilt angle will increase the probability of dislocation merging and annihilation,and can effectively reduce the dislocation density in the material.Mg-doped p-type AlGaN was grown by MOCVD,and it was found that the high-quality unintentionally doped AlGaN film played a key role in buffering the lattice mismatch between p-AlGaN and the substrate,reducing the dislocation density of p-AlGaN The study of Mg-doped AlGaN at different annealing temperatures found that 880? is the optimal annealing temperature for p-AlGaN.At the same time,annealing will release the residual stress in the material,and will also lead to an increase in the surface roughness of the epitaxial layer.Annealing above 880? will lead to a decrease in the radiative recombination probability of VN donor and Mg Ga acceptor in the material,and an increase in the radiative recombination probability of deep acceptor(V?3-)and shallow donor(O).