Combined method of axial low-frequency vibrations and axial heat flux for crystal growth from a melt

Abstract

The crystal quality in many respects depends on the conditions of heat-mass transfer forming the concen tration field near the crystallization front and its shape. It is especially difficult to control heat-mass transfer during the growth of large diameter crystals. In the conventional methods of growth of large diameter crystals, the intensity of thermo gravitational convec tion is frequently so high that unsteady and turbulent flows easily arise in the melt. An efficient way of sup pressing thermal convection is growth from a thin layer of the melt used in the axial heating process (AHP) [1] and the allied submerged heater method [2]. The application of the AHP method, a feature of which is the thermal action directly on the crystallization front ( Fig. 1a), showed a high uniformity of the composition of the multicomponent GaInSb and GeSi crystals grown [3,4].However, the use of a weak laminar flow of the melt in this method can result in a considerable inhomoge neity of the composition of the crystal over the cross section [5, 6] because of insufficient mixing of the melt near the crystallization front. The attempts at creation of an additional forced flow and improvement of mix ing in a thin melt layer due to the rotating magnetic field in the AHP method [6] or the submerged heater rotation method [7] led to no positive results.The numerical modeling of the process of growth of semiconductor crystals with a low heat conductivity (GaAs, CdTe) and the diameter exceeding 100 mm by the AHP method in the configuration of the directed crystallization shows that, already at 30 mm crystal length, this method fails to solve the problem of level ing the temperature along the growth cell diameter near the crystallization front with taking into account the crystallization heat.The low frequency axial vibration control (AVC) technique [8] is a method that made a good showing in the control for heat-mass transfer by forming a con trollable forced melt flow near the crystallization front. This technique was successfully applied in the growth of crystals from the melt by various methods [9] including those using the oscillations of an inert baf fle submerged into the melt in the vertical Bridgman [10] and Czochralski [11] configurations (Fig. 1b).In the research, we proposed a new combined method of crystal growth joining the AHP and AVC techniques by means of the vibration of the AHP heater submerged in the melt. It enables us to obtain two independent channels of the heat-mass transfer control near the crystallization front in one method (Fig. 1c): the thermal effect within the framework of the AHP technique and the vibrating activation of the melt by the AVC technique. The application of the AVC technique with using a solid with cylindrical sym metry and special configuration (Fig. 1b) submerged in the melt provides the formation of hot descending vibration flows along the crucible walls, which level the crystallization front [12].We developed a new scheme of controlling the heat-mass transfer in the vertical Bridgman and...

Growing Single Crystals with a Low Melt Height and an Axial Vibration

“…This method is called axial vibrational control (AVC) and has been used in the growth of PbTe, CdTe, and NaNO 3 − crystals in the Cz and VB configurations. The AVC and AHP methods have been recently numerically analyzed for Ge, CdTe, and NaNO 3 .…”