Role of Impurities in Reducing Grown-In Dislocations in Compound Semiconductor Crystals
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ROLE OF IMPURITIES IN REDUCING GROWN-IN DISLOCATIONS IN COMPOUND SEMICONDUCTOR CRYSTALS KOJI SUMINO Institute for Materials Research, Tohoku University, Sendai 980, Japan
ABSTRACT Impurity effects on the mobility of dislocations and dislocation generation from generation centers in MI- V compound semiconductor crystals are first reviewed on the basis of experimental observations of dynamic behavior of individual dislocations. Dislocation multiplication process is then discussed to account for experimental stress-strain characteristics of these materials obtained in mechanical tests. Using all of such knowledge on dislocation processes in the compound semiconductor crystals, an argument is developed to show how impurities play the role in reducing grown-in dislocations in crystals of these materials. It is shown that immobilization of dislocations caused by impurity gettering plays the decisive role and results in even the growth of dislocation-free crystals. 1. INTRODUCTION Compound semiconductors are widely used as the materials for optoelectronic or high-speed electronic devices. Grown-in dislocations are known to cause spatial nonhomogeneity in the electrical and optical properties of the material. Such non-homogeneity results from the interaction of dislocations with impurities or point defects which play decisive roles in determining the above properties of the materials. Distribution of impurities or point defects in the region in the vicinity of a dislocation is generally different from that in the region far from the dislocation, being determined by the thermal history of the crystal. Homogenization of the electrical or optical properties can be achieved by annealing the crystal at some appropriate temperature. The characteristics in the interaction between dislocations and impurity atoms in a semiconductor crystal have been discussed theoretically in detail by the present author [1-3] and the validity of the discussion has been confirmed by a series of experiments of his group [4-13]. A great deal of efforts have been devoted in the technology of crystal growth to reduce the density of grown-in dislocations. It has been reported that crystals of m - V compound semiconductors with rather low densities of dislocations have been grown with doping certain kinds of impurities. Doping of electrically active Zn, Si, S, Te, Sb impurities or isovalent In impurity is found to be effective in reducing the density of grown-in dislocations in GaAs [14-17]. Recently, dislocation-free crystals of In-doped GaAs crystals as large as 100 mm in diameter are being successfully produced on commercial base by a Japanese company [18,19]. In a similar way, doping of electrically active Zn, S, Te, Sb impurities or isovalent Ga and As impurities is reported to be effective in reducing the density of grown-in dislocations in InP [14,17,20]. There are also many reports showing that the distribution of most grown-in dislocations in a GaAs crystal is well correlated to the distribution of thermal stress within the crystal induced by n
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