Large size semiconductor crystals are being requested in several device-oriented technologies. These crystals exhibit various defects (point and extended defects). Indeed, it is well-known in the case of GaAs that the presence of dislocations strongly decreases the life-time of Ga1-xAlxAs/ GaAs lasers. Moreover, it appears now, that the dislocations have a detrimental effect on GaAs integrated circuits. Their presence in LEC (Liquid Encapsulated Czochralski) crystals are mainly due to the thermal stresses occurring during the growth. We present in this paper some experimental results showing that it is possible to strongly reduce (by a factor 10, at least) the dislocation density either by decreasing the thermal stresses level (Liquid Encapsulated Kyropoulos Technique) or by adding an isoelectronic impurity (indium to the melt).
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