JPH06183873A - Method for growing semimagnetic compound semiconductor single crystal - Google Patents

Abstract

PURPOSE:To provide a method for growing the semimagnetic IIB group element-VIB group element compound semiconductor single crystal in which a 3d transition metal element is contained in an uniform concentration distribution. CONSTITUTION:A flux is produced from a IIB group element and a VIB group element, either of the elements being more excessive than their stoichiometric composition. The IIB group element, the VIB group element and a fine amount of a 3d transition metal element are vacuum-sealed in the same closed tubular crucible, and the IIB group element and the VIB group element are melted. A strong magnetic field is applied to the crucible to float the 3d transition metal element in the melted liquid. The crucible or the strong magnetic field-generating device is vertically transferred to change the relative position of the 3d transition metal element in the melted liquid, and the 3d transition metal element is simultaneously perfectly dissolved in the melted liquid of the IIB group element-VIB group element. The application of the magnetic field is subsequently stopped, and all of the melted liquid is uniformly mixed by the utilization of the natural convection. The melted liquid is gradually cooled from the bottom of the crucible to deposit a desired single crystal by a monodirectional coagulation method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for growing a semi-magnetic compound semiconductor single crystal, and more specifically, it uses a vertical Bridgman furnace installed in a cylindrical longitudinal magnetic field space and a trace amount of 3d transition metal by a flux method. The present invention relates to a method for growing a IIB group element-VIB group element compound semiconductor single crystal containing an element as a substituting element by unidirectionally solidifying, and using a strong magnetic field to obtain a uniform melt.

[0002]

2. Description of the Related Art Conventionally, as a method for growing a single crystal of a semi-magnetic compound semiconductor, one of the IIB group element and the VIB group element is used in excess of the stoichiometric composition to form a flux, and a small amount of substitution is performed together with the flux. A method is adopted in which an additive element (3d transition metal element) is vacuum-sealed in a transparent quartz tube (crucible), these elements are melted in an electric furnace, and directly synthesized. That is, a vacuum-sealed quartz crucible is placed in an electric furnace and first preheated at several 100 ° C. to completely melt the IIB group element and the VIB group element. However, since a small amount of the substitutional additive element has a high melting point, it does not dissolve in the IIB group element-VIB group element melt at this point. Next, the temperature of the entire crucible is raised to near 1150 ° C. to promote the mixing of the melt, and at the same time, a small amount of the substitutional additive element is gradually dissolved in the melt of the IIB group element-VIB element melt. When all the elements are considered to be completely melted, the crucible is slowly lowered (moved to a low temperature region) to start crystal precipitation from the bottom of the crucible. This method is called a solution growth method and is usually adopted to obtain a bulk crystal of a semimagnetic compound semiconductor. IIB group element-VI
The main reasons for adopting this solution growth method for growing a crystal of a group B element compound semiconductor are that the crystal can be grown at a relatively low temperature, a high melting point of a group IIB element-VIB element compound semiconductor, It is possible to avoid the problem of high vapor pressure as much as possible. However, in such a conventional method, it is sometimes seen that a trace amount of the substitutional additive element is present in the grown crystal in a non-uniform concentration distribution. In extreme cases,
The crystal growth may end in a state where the additive element is not completely melted and at least a part is deposited on the bottom of the crucible.

[0003]

As described above, in the conventional method, a trace amount of the substitutional additive element is not completely dissolved in the IIB group-VIB group element melt, and at least a part of the element is formed in the bottom of the crucible. Even if it remains or melts, it is difficult to grow a desired crystal because it brings a non-uniform concentration distribution into the crystal.

The object of the present invention is to provide 3d in a IIB group element-VIB group element compound semiconductor single crystal containing a trace amount of 3d transition metal element (Mn, Fe, Co, Ni, etc.) as a substitution element.
It is to provide a method for growing a semi-magnetic compound semiconductor single crystal in which a transition metal element exists in a uniform concentration distribution.

[0005]

In order to achieve the above object, it is necessary to prepare a uniform melt consisting of a IIB group element, a VIB group element and a trace amount of a 3d transition metal element before growing a crystal. . As a result of various studies on a method for obtaining such a uniform melt, 1T (Tesla) was added to the IIB group-VIB group element melt already well mixed at high temperature (1150 ° C).
As described above, preferably a strong static magnetic field of 5 to 10 T (this is referred to as a strong magnetic field in the present specification) is applied to suspend a trace amount of the undissolved 3d transition metal element at a predetermined position in the melt, By changing the relative position between the undissolved 3d transition metal element and the melt over a long period of time, that is, either the undissolved 3d transition metal element or the surrounding melt is moved vertically. As a result, it was found that the concentration gradient was increased and the 3d transition metal element was completely dissolved. Next, the applied magnetic field is released to induce natural convection (natural convection was blocked by the applied magnetic field), and stirring by this causes the melt to have a more uniform concentration distribution.

That is, the method for growing a semi-magnetic compound semiconductor single crystal of the present invention uses a vertical Bridgman furnace installed in a cylindrical vertical magnetic field space, and a trace amount of a 3d transition metal element is used as a substitution element by a flux method. Group IIB element contained-VIB
In a method of unidirectionally solidifying and growing a group element compound semiconductor single crystal, one of the group IIB element and the group VIB element is used in excess of the stoichiometric composition to form a flux, and the group IIB element, VIB A group 3 element and a trace amount of 3d transition metal element are vacuum sealed in the same closed tube crucible,
The IIB group element and the VIB group element are melted, and then a strong magnetic field is applied to suspend the 3d transition metal element having a high melting point in the melt, and the crucible or the strong magnetic field generator is moved vertically to melt the melt. The 3d transition metal element is changed to the IIB group element-VIB while changing the relative position of the 3d transition metal element in
It is completely dissolved in the group element melt, then the applied magnetic field is released, the entire melt is uniformly mixed by utilizing natural convection in the melt, and then the melt is gradually cooled from the bottom of the crucible. The desired single crystal is deposited by the unidirectional solidification method.

A method of growing a semi-magnetic compound semiconductor single crystal according to the present invention will be described below in which Mn or Co is used as a small amount of a substitution additive element in a Cd-Se compound semiconductor which is a IIB group element-VIB group element compound semiconductor. Will be described. Mn
Alternatively, a semi-magnetic semiconductor obtained by substituting a part of the constituent elements of a Cd—Se compound semiconductor by using Co as a trace substitution additive element is _{x such as} Cd _1-x Mn _x Se and Cd _1-y Co _y Se. Alternatively, it can be represented by using y.

Since Mn and Co as substitutional additive elements are magnetic materials, they feel a magnetic field gradient in an applied magnetic field and receive a force, and are pushed toward a position without a magnetic field gradient. Therefore, under the applied magnetic field, the magnetic field tends to stay at the strongest position. In the longitudinal magnetic field used in the present invention, this position corresponds to just the center of the magnetic field generating coil. Therefore, a small amount of M
n or Co can be kept in this position by the force of the applied magnetic field. Therefore, the relative position of Mn or Co in the melt is changed by moving the Cd-Se melt or the strong magnetic field generator up and down, that is, M in the undissolved state.
It is possible to efficiently dissolve Mn or Co by increasing the concentration gradient around Mn or Co in an undissolved state and promoting diffusion while vertically moving either n or Co or the surrounding melt. it can. Crystals having a uniform concentration distribution can be obtained from the melt having a uniform concentration distribution thus obtained.

[0009]

EXAMPLE An outer diameter of 15 mm and a wall thickness of 2.5 mm, which is suitable for growing a single crystal in a vertical Bridgman furnace, and an inner wall is covered with a carbon film to prevent the reaction between the crucible and the raw material. Using a transparent quartz crucible (quartz ampoule), the raw materials are packed from the bottom in the order of Cd and Se.
e Mn or Co, which is a substitution additive element, was placed at the boundary of the raw material.

In order to eliminate residual gas from the quartz crucible packed with the raw materials in the above order, the temperature is 10 ^-6 Torr at room temperature.
I evacuated until. Next, while continuing evacuation, the temperature around the crucible was raised to about 200 ° C. and maintained at this temperature, the gas was eliminated, and then the crucible was vacuum-sealed. Since the crystal is grown by adopting the flux method (solution growth method), the composition of the melt should be 10% Se excess from the stoichiometric composition (melting at 1400 to 1500 ° C.) (melting point: The operation of lowering), the composition of the raw material was adjusted from the beginning.

A quartz crucible filled with raw materials and sealed in vacuum was placed in the center of a vertical Bridgman furnace placed in a vertical magnetic field, and first preheated at 600 ° C. for 3 hours. At this point, Cd having a melting point of 321 ° C. and Se having a melting point of 221 ° C. were completely melted. However, Mn (melting point 1244) which is a trace substitutional additive element
C.) or Co (melting point 1495.degree. C.) remained unmelted due to their high melting point. Next, the temperature of the electric furnace was slowly raised to 1150 ° C., and the temperature was maintained for 5 hours to completely mix the Cd—Se mother melt with the help of natural convection. (As a comparative example, at this point,
When crystal growth is attempted by a unidirectional solidification method without a magnetic field, it sometimes happens that crystal growth ends in a state where at least a part of Mn or Co, which is a substitutional additive element, remains undissolved on the bottom of the crucible. In order to avoid such a situation and grow a crystal, the present invention employs the following means. ) Applying a magnetic field of 8T with the furnace temperature maintained at 1150 ° C,
Mn or Co, which is a trace replacement additive element, was kept at the center position of the magnetic field coil. This state corresponds to the substitutional additive element floating in the melt due to the applied magnetic field. Next, by slowly moving the crucible up and down, the substitutional additive element was slowly and efficiently dissolved while moving relatively from the lower end to the upper end of the melt. The movement speed of the quartz crucible at this time was 10 mm / hr, and the movement was repeated for 8 hours to make two reciprocations (the movement speed of the quartz crucible is not fixed, for example, one reciprocation is 5 mm / hr. May be 10 round trips at 50 mm / hr). After continuously applying a strong magnetic field for 8 hours, the applied magnetic field was released (returning to the magnetic field 0) to cause thermal convection again, thereby stirring the entire melt. During this time, the quartz crucible was returned to the initial set position to prepare for the unidirectional solidification experiment. Crystal growth was started 1 hour after the applied magnetic field was released. The unidirectional solidification method was adopted for crystal growth, and the quartz crucible was moved downward at a constant speed of 5 mm / hr so that the desired single crystal was precipitated from the Se-excess solution from the bottom of the crucible.

As described above, a high concentration of Mn or Co
Semi-magnetic compound semiconductor containing Cd _1-x Mn _x Se or C
It was possible to obtain d _1-y Co _y Se (where x is 0.01 to 0.50 and y is 0.001 to 0.05) as a single crystal. Regarding the size of the single crystal, Cd _1-x Mn _x Se had a diameter of 10 mm and a length of 10 mm, and Cd _1-y Co _y Se had a size of about 5 mm × 5 mm × 5 mm. M in these single crystals
The concentration distribution of n or Co can be obtained with considerable accuracy by measuring the magnetization in a strong magnetic field. That is,
Magnetization measurement samples were respectively obtained from the lower end portion, the central portion and the upper end portion of each single crystal, and the magnetization curve was measured at 4.2 K (liquid helium temperature). The magnetic efficiency per Mn or Co atom obtained from these magnetization curves is upper, middle,
5μ _B / Mn · atom, 3μ _B / Co for each bottom
・ It was the same as atom, and the measurement accuracy was 0.2% or less. These values are very close to the theoretical values of Mn ²⁺ or Co ²⁺ , and the concentration of Mn or Co at each site of the single crystal is the same within the measurement error range, so that the concentration distribution is uniform over the entire grown crystal. It was fully guaranteed that

As is clear from the above examples, a semi-magnetic compound semiconductor Cd _1-x Mn _x Se or Cd is prepared by adding a magnetic material such as Mn or Co as a slight amount of a substitution additive element.
_When growing _1-y Co _y Se as a single crystal having a uniform concentration distribution, it is important to keep the concentration of the melt of these compounds uniform. It is effective to use a strong magnetic field as the means, which leads to effective utilization of the applied magnetic field.

The method according to the invention is also suitable for other Group IIB elements-VI.
The present invention is also applicable to obtain a single crystal having a uniform concentration distribution by adding a small amount of a magnetic material such as Mn, Fe, Co, or Ni as a substitution additive element to a group B element compound semiconductor. Can be reliably and stably manufactured (improved productivity).

[0015]

According to the method for growing a semi-magnetic compound semiconductor single crystal of the present invention, a trace amount of 3d transition metal element (Mn, Fe,
It is possible to obtain a semi-magnetic IIB group element-VIB group element compound semiconductor single crystal containing Co, Ni, etc.) as a substitution element in a uniform concentration distribution.

Claims (1)

[Claims] 1. A group IIB element-VIB containing a trace amount of a 3d transition metal element as a substitution element by a flux method using a vertical Bridgman furnace installed in a cylindrical vertical magnetic field space.
In a method of unidirectionally solidifying and growing a group element compound semiconductor single crystal, one of the group IIB element and the group VIB element is used in excess of the stoichiometric composition to form a flux, and the group IIB element, VIB A group 3 element and a trace amount of 3d transition metal element are vacuum sealed in the same closed tube crucible,
The IIB group element and the VIB group element are melted, then a high magnetic field is applied to suspend the 3d transition metal element having a high melting point in the melt, and the crucible or the strong magnetic field generator is moved vertically to melt the melt. The 3d transition metal element is changed to the IIB group element-VIB while changing the relative position of the 3d transition metal element in
It is completely dissolved in the group element melt, then the applied magnetic field is released, the entire melt is uniformly mixed by utilizing natural convection in the melt, and then the melt is gradually cooled from the bottom of the crucible. A method for growing a semi-magnetic compound semiconductor single crystal, which comprises depositing a desired single crystal by a unidirectional solidification method.