Growth And P-type Doping Of AlGaN/GaN Superlattices On Sapphire Substrate

Group Ⅲ nitrides and their compound materials play an increasingly important role in many fields.The third generation semiconductor with Gan as the core is setting off a new commercial revolution,which has been widely used in many fields,such as white lighting,landscape lamp,medical sterilization,printing and curing,backlight and so on.In order to improve the luminous intensity of UV LED devices,GaN based materials with high crystal quality,low dislocation density and p-type structure with high doping efficiency are needed.This paper focuses on how to improve the quality of AlGaN/GaN superlattice materials and the performance of p-type structure.In this paper,GaN thin films were prepared on sapphire substrate by c-deflection m-plane angle（C→m）,and then epitaxial AlGaN/GaN superlattice（SLs）structure.A series of characterization methods were used to test the crystal quality and doping ability.The main results and contents of this paper are as follows:By using MOCVD technology,at 850℃,the temperature of c→m 0°、c→m 1.5°、c→m 4°Epitaxy on sapphire substrateμGaN thin films were then epitaxed for 30 cycles with 2.5 nm AlGaN/2.5 nm Gan superlattices.The surface morphology,crystal quality,stress-strain,cross-section microstructure and electrical properties of GaN thin films and AlGaN/GaN superlattices grown on different oblique cutting substrates were analyzed by characterization.It is found that the growth mode of GaN crystal is changed from 2D to 3D by cutting the substrate obliquely,and the stacking structure is formed to block the continuation of dislocations.As a result,the dislocation density of 002 edge of Gan sample is reduced by 25%,and the line defects are obviously reduced.Compared with different oblique cutting angles,c→m4°.The E2（high）peaks of the GaN and AlGaN/GaN superlattices grown on the substrate are the smallest,which indicates that the oblique cutting of the substrate can adjust the substrate stress.Hall measurements of AlGaN/GaN superlattices show that c→m 4°.The epitaxial superlattice structure does increase the carrier concentration and decrease the resistivity.TEM shows that the line defects in the cross section of the sample will form ring dislocations in the superlattice layer and eventually annihilate.The influence of AlGaN/GaN superlattice structure on p-type layer is investigated.The test data show that the structure of the superlattice prepared by oblique cutting is in the range of c→m4°.The electrical performance is the best.Although compared with the traditional p-type structure,the hole concentration and mobility increase,but did not achieve the desired effect,the analysis is due to the poor ratio of well barrier.It is predicted that when the barrier becomes wider and thicker,the barrier will hold more electrons,and the holes and electrons in the superlattice p-layer structure will keep dynamic equilibrium.When the electrons are held by the superlattice barrier,the electron concentration will decrease and the hole concentration will increase.This prediction is proved by APSYS simulation software.By comparing the hole mobility and hole concentration of the simulation structure,it is determined that the best barrier/well thickness ratio is 4.5nm/2.5nm.The simulation hole concentration of this structure is 10¹⁸cm^-3,and the mobility is 2300 cm²/vs.The new structure was epitaxial prepared on sapphire substrates with different bevel angles,and the electrical properties were tested.The results show that the new structure can improve the performance of p-type structure.It is found that c→m 4°.The hole concentration and mobility of the epitaxial superlattice structure on the substrate are still the best°.The hole concentration increases by 2.6 times,the mobility increases by 1.78times,and the resistivity decreases by 626Ω/sq;Compared with the original structure,the new structure is c→m 4°.The hole concentration increases by 2.32 times,the mobility reaches 814.38cm²/Vs,and the resistivity decreases by 533Ω/sq。...