JPH03183683A - Electric furnace - Google Patents

Abstract

PURPOSE:To allow stable temp. control and to prevent the fluctuation in compsn. of a single crystal by connecting two pieces of specific heaters in series so as to avoid the thermal interference thereof with each other and disposing these heaters in an electric furnace for growing the single crystal by a floating zone method. CONSTITUTION:The 1st heater 14a for forming the melt zone having a heating temp. range of a narrow peak characteristic is provided in the electric furnace for growing the single crystal by the floating zone method. Further, the 2nd heater 14b for temp. control having a broad and flat heating temp. range is provided. The 1st heater 14a and the 2nd heater 14b are so disposed that the heaters are not thermally interfered with each other and are connected electrically in series. The raw materials 1 in a quartz ampoule 7 are heated and melted by the heater 14a to form the melt zone 3 and while the temp. is controlled by the heater 14b, the single crystal 2 is grown by the floating zone method.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention relates to an electric furnace, and more particularly to an electric furnace used for growing single crystals by the floating zone method.

[Prior Art] Electric furnaces used to grow single crystals by the floating zone method are classified into high frequency furnaces and resistance furnaces depending on the bO heating method. High frequency furnaces require an expensive power source and a rather large space. Resistance furnaces have the advantage that experimenters can make them by hand according to their own plans, the power supply is cheap, and they do not require a large space.

The outline of the electric furnace using the floating zone method is shown in Figure 3.As shown in Figure 3(a), raw material 1 and single crystal 2 are
A heater 4 is provided to form a melt zone 3 between the two, but the temperature distribution formed by this heater is in a heating range A with a narrow peak as shown in FIG. 3(b).

[Problems to be Solved by the Invention] In order to make the composition of the grown crystals uniform, the temperature of the melt zone created by heating the heater must be maintained at a predetermined value for a long time. Furthermore, the temperature distribution must also have a narrow peak. In the case of a resistance furnace, a thermocouple 5 is installed for this temperature control.

However, since the temperature distribution has peaks and no flat parts, the allowable range of the time constant of the temperature controller becomes narrow and it is difficult to obtain an accurate time constant, resulting in so-called hunting in the output and making it unstable. As a result, there was a drawback that the temperature of the melt zone was not stabilized at a predetermined value.

In order to stabilize this, there is a method to make the temperature distribution flat, but this requires increasing the width of melt zone 3 (the length in the vertical direction in Figure 3), which means that the crystal composition This will lead to misalignment. Incidentally, the width of the melt zone is generally set to be approximately the same as or less than the diameter of the zone.

The present invention has been made in order to solve the conventional problems as described above, and provides an electric furnace for growing single crystals in which the temperature of the melt zone is stable and a single crystal with extremely little compositional fluctuation can be obtained. The purpose is to

[Means for Solving the Problems] The present invention provides an electric furnace used for single crystal growth by the 70-ting zone method, which includes: a first heater for a melt zone forming phase having a narrow peak heating temperature range; and a second heater for temperature control having a wide flat heating temperature range, and the first heater and the second heater are arranged so as not to interfere thermally and to be electrically connected in series. This electric furnace is characterized by:

[Function] FIG. 1 shows the structure of the electric furnace of the present invention, which also serves as an embodiment. As shown in the figure, in the electric furnace of the present invention, the heater configuration consists of two heaters 14a and 14b, of which the first heater 14
The heater 14a is for zone melting and has a narrow peak heating range A for forming the melt zone 3 between the single crystal 2 and the raw material 1 as before, and the other second heater 14b is for temperature control and has a wide heating range A. The heater 14a has a flat heating range B.
and are placed in series with a sufficient distance to avoid thermal interference. The thermocouple 15b for temperature control is the heater 14b.
A monitoring thermocouple 15a is also installed near the heater 14a.

Crystal growth using the electric furnace configured as described above is performed as follows. The temperature control heater 14b is connected to the monitor thermocouple 15a so that the melt zone 3 reaches a predetermined temperature.
When the temperature of the melt zone 3 reaches a predetermined temperature, single crystal growth can be carried out using the floating zone method as usual.

Since the heater 14b has a wide and flat heating range B, the allowable range of the time constant of the temperature controller is wide, and extremely stable temperature control is performed. Therefore, the current flowing through the heater 14b is stable, and therefore the current flowing through the heater 14a during the melt zone formation phase is also stable.
An extremely stable temperature can also be ensured.

[Example] Next, embodiments of the present invention will be described in detail.

The target for single crystal growth was mercury cadmium telluride (g08Cd□, 2Te), which is an n-Vl group compound semiconductor. As a raw material, mercury telluride (Te) and cadmium telluride (CdTe) were mixed and melted in a molar ratio of 4=1 to form polycrystals. The material for the melt zone was mercury cadmium telluride with an excess of tellurium, and the composition was adjusted to have a melting temperature of 500'C. Further, as a seed crystal, a crystal of cadmium telluride (CdTe) adjusted so that the (111) plane was a horizontal plane was used. As shown in Figure 2, these three are placed in a quartz ampoule 7 with an inner diameter of 10 mm and a length of 150 mm.
Seed crystal 6, melt zone material 13, and raw material 1 were layered in this order and vacuum sealed.

The ampoule prepared in this manner is suspended in a resistance type electric furnace consisting of two heaters 14a and 14b as shown in FIG. controlled. At this time, the control thermocouple 15b indicates 515°C, and the temperature stability is ±0.1°.
C was extremely stable. The monitor thermocouple 15a is ±0.
There was a fluctuation of 4°C, or the stability was lower than 1710 of the conventional method. This fluctuation is thought to be due to air convection near the heater.

Single crystal growth is achieved through the movement of the melt zone or at 0.00% per hour.
Ampoule 7 was slowly suspended at an astounding speed of 3mm. Raw material length 60 non melt zone 3
The process was continued until the melt had completely passed through, that is, until the melt zone 3 reached the upper end of the raw material.

After the cultivation, the grown single crystal was removed from the ampoule, sliced, and examined for changes in composition (changes in the molar ratio of mercury and cadmium) in the length direction. It turned out that it was getting smaller.

From this, it became clear that the effect was due to the provision of a heater for temperature control in addition to the heater for heating.

[Advantageous Effects of the Invention 1] As detailed above, when a single crystal is grown by the resistance floating zone single crystal growth method using the electric furnace of the present invention, stable temperature control becomes possible, and as a result, the melt zone The temperature becomes stable and a single crystal with very little compositional fluctuation can be obtained.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of an embodiment of the electric furnace of the present invention and a temperature distribution diagram in the furnace, Fig. 2 is a diagram of the composition of raw materials in a quartz ampoule, and Fig. 3 is an example of an electric furnace according to the prior art. They are a schematic configuration diagram and a temperature distribution diagram inside the furnace. 1... Raw material 2... Single crystal 3... Melt zone 4, 14a, 14b - L-ta 5, 15a, 15b -... Thermocouple 6... Seed crystal 7... Quartz ampoule 13.・・Melt zone material

Claims (1)

[Claims] (1) In an electric furnace used for single crystal growth using the floating zone method, a first heater for forming a melt zone has a narrow peak heating temperature range, and a first heater for temperature control has a wide flat heating temperature range. An electric furnace comprising: a second heater; the first heater and the second heater are arranged so as not to thermally interfere with each other and to be electrically connected in series.