Study On Epitaxial Growth At Low Temperature And Annealing Of InP/GaAs Heterostructures

As a direct gap semiconductor,InP material is superior to GaAs material with mature manufacturing technology in terms of solar cell conversion efficiency and radiation resistance.In recent years,many scientists have done a lot of research on InP materials,but the mechanical strength of InP materials is very poor and the price of InP is very expensive,so it is very difficult to get a large size InP.GaAs is the most widely used two-element III-V compound semiconductor material.Its preparation technology and application technology are mature,and its performance is superior.The single junction solar cells fabricated by GaAs materials have high conversion efficiency.If InP film can be grew on GaAs slice,the weaknesses will be avoided and the advantages of two materials will be brought into play.However,there is a lattice mismatch of up to 4% between InP/GaAs heterojunctions.A large number of line dislocations and interface dislocations will be generated during growth.It has become the main obstacle to achieve InP/GaAs with high quality.It has great significance for the development of InP/GaAs materials in the future to carry the work of directly growing InP epitaxial layer on GaAs substrate at low temperature,to clarify the occurrence and distribution of dislocation in InP epitaxial layer,and to discuss the relationship between dislocations and growth conditions as well as that between dislocations and subsequent treatment.In this paper,the InP epitaxial layer was directly grown on the GaAs substrate by metal organic chemical vapor deposition(MOCVD),and the annealing of different temperature,vacuum annealing and the annealing with applied electric field were done for the low temperature growth samples.The influence of thickness,growth temperature and annealing conditions on the structure and properties of InP epitaxial layers in InP/GaAs heterostructures were investigated by atomic force microscopy,Raman spectroscopy,XRD,DCXRD and TEM.The main work of this paper is as follows:(1)The formation mechanism of the antidislocations was discovered and explained.At the low temperature growth conditions,with the increase of the thickness of the epitaxial layer,the crystal quality of the InP epitaxial layer increases and the dislocation density decreased.This phenomenon was caused by the merger of small islands,and its electrical properties were improved.When the thickness of the epitaxial layer reached a specific value,the antidislocation appeared gradually in the GaAs substrate.When the thickness reached the other limit value,the antidislocation would disappear.The appearance of antidislocation was caused by uneven interface.(2)The decomposition phenomenon of InP epilayer during annealing was found and explained.When the annealing temperature exceeded a certain value,the InP epilayer produced a decomposition.A part of InP diffused in the form of In elements and P elements,forming InGaAs and InGaP transition layers.Another part of InP recrystallized,and InP nucleated at the interface and presented island growth.For annealed samples,with the change of annealing temperature and thickness of epitaxial layer,InP had different degrees of decomposition,and the surface morphology,crystal quality,internal structure and electrical properties of InP epitaxial layers had some changes.(3)For the InP/GaAs annealed in the positive and negative electric field,the structure and properties of the InP epitaxial layers had little difference in the structure and properties.The InP layers of annealed samples had higher crystalline quality and better electrical properties than those before annealing.The vacuum annealed InP/GaAs material had a longer annealing time,which led to the complete decomposition of the InP layer.The transition layer was uniform,and the two sides of the transition layer tended to be flat,only a few InP were not decomposed.