Abstract: The amount of Group-V element included in a melt 6 has the close relationship with the oxygen concentration of the melt 6. This relationship is utilized for controlling the oxygen concentration of a single crystal 8 at a high level. The content of Group-V element is calculated from the weight of the melt 6 gauged by a gravimeter 11 and compared with a preset value in a control unit 12. When the calculated content is smaller than the preset value, the control signal to additionally supply Group-V element to the melt 6 is outputted from the control unit 12 to a feeder 14. When the calculated content is larger than the preset value, the control signal to supply a raw material to the melt 6 is outputted to another feeder 13.

Abstract: The density of a melt precisely represents the stability of the melt, so that the initiation of pulling-up operation can be determined on the basis of the changing rate of the density. The pulling-up operation may be started when the density becomes constant, or when the changing rate of the density with respect to the temperature becomes smaller. Since the melt or clusters do not include different minute structures, an obtained single crystal is of high quality free from minute faults or dislocations.

Abstract: The measuring device has bobs 10, 17 suspended from a weight 12 with wires 11, 16. The hook 13 of the weight 12 is hung from a suspensor thread 15 extending downwards from a balance 14. The weight 12 may be omitted by using the upper bob 10 for dead weight. The bobs 10, 17 and the wires 11, 16 may be coated with a coating layer unreactive to the melt 19 whose density is to be measured. The weights of the measuring device is measured by the balance 14 under the first condition that the lower bob 17 is immersed in the liquid 19 and the second condition that the bobs 10, 17 are both immersed in the liquid 19. The density of the liquid 19 is calculated from the two measured values without the influence of the surface tension of the liquid 19 applied to the wires 11, 16.