Study On Solid-liquid Interface During VGF Growth Process Of 3 Inch GaAs Single Crystal

The CGSim numerical simulation package was used in this paper to simulate and analysis the solid-liquid interface shape and the thermal stress during VGF growth process of 3 inch GaAs single crystal.The reasons of formulation and change of solid-liquid interface shape and the effect of the solid-liquid interface shape on thermal stress were studied.The chemical preferential etching technology was used to test the distribution of dislocation density of GaAs crystal,which the test result was compared with the thermal stress distribution achieved by numerical simulation to prove the accuracy of numerical model.Hall Effect was used to test the distribution of carrier concentration of the crystal.The effect of solid-liquid interface shape on the distribution of carrier concentration was studied.Finally,we got the conclusions as follows:(1)The growth rate of any one position on solid-liquid interface depends linearly on its net heat flux ?q,which means the growth rate will increase when the net heat flux?q increase,and vice versa.The growth rate of any one position on solid-liquid interface depends on the net heat flux?q of the position,which means the growth rate increase or decrease with the ?q.Under the effect of different rates and their changes at different positions of the solid-liquid interface,the solid-liquid interface shape is formed.(2)The distribution of thermal stress presents a shape with a typical characteristic "W",and it is obviously seen at the begin of equal-diameter stage.The "W-type"distribution became less obvious with the growth of the crystal,which means the radial distribution became more homogeneous.(3)The thermal stress of crystal near the solid-liquid interface not only depends on the solid-liquid interface shape which means the thermal stress would decrease when the interface deflection decrease,but also depends on the heat dissipation,namely net heat flux ?q which the thermal stress would decrease when the ?q increase.(4)Dislocation distribution in the head and tail area of the crystalline are tested by chemical preferential etching method.The results were compared with numerical simulation.It turned out that thermal stress increase near the radial edge,especially in the head area.In the etching test,the pattern of distribution were totally different,which can be attribute to the simplification in the model building,where the thermal stress generated by the different of expansion coefficient between crystal and crucible.(5)Dislocation were found where the thermal stress reach over critical resolved shear stress(0.7MPa).Radical distribution of dislocation out of experiment was highly consistent with the calculating result.The model of GaAs single crystal growth turns out to be accurate.The deviation,often found near the edge,between thermal stress and dislocation density caused by simplification when building the calculating model.(6)Radical distribution of carrier concentration was characterized.It turned out that the axial density of carriers in the crystalline increase during the growth.Density of carrier concentration increase from center to edge in the case with convex interface,while decrease from center to edge in that with concave interface.And the uniformity of radical carrier distribution rise with larger interface deflection.