JPS6146439B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a single crystal of a multi-component semiconductor, particularly a semiconductor made of a lead chalcogen compound.

Lead telluride (PbTe), which is an intermetallic compound of lead (Pb) and tellurium (Te), is used as a substrate for epitaxial growth in the manufacture of semiconductor laser devices that emit infrared rays. This intermetallic compound has properties as a semiconductor, but its conductivity type reverses depending on whether Pb or Te is in excess, especially when Pb and Te are not completely equal in number of atoms. There is.
When it has a completely equiatomic composition, it has the lowest carrier number and has properties almost equivalent to an intrinsic semiconductor, which is preferable as a substrate for epitaxial growth.

However, with normal crystal growth methods, it is difficult to obtain a uniform atomic composition, and a composition deviation of about 0.01% tends to occur. For example, if Te is in excess of about 0.01%, the crystal will exhibit a strong P type, In the reverse case, there was a problem that it would become n-type.

The present invention was developed in view of the above-mentioned points, and consists of stacking and forming multiple semiconductor growth layers each having a different composition on a substrate, and then heating the layers to cause atoms to move between adjacent layers. It is an object of the present invention to provide a novel method for manufacturing a multicomponent semiconductor crystal that forms a single crystal layer having a certain composition.

Embodiments of the present invention will be described in detail below with reference to the drawings. Figures 1 and 2 show cases where the present invention is applied.
FIG. 2 is a schematic cross-sectional view for explaining an example of a PbTe single crystal manufacturing process.

First, prepare a high-quality PbTe single crystal substrate. This substrate 1 may be formed by, for example, selecting and cutting out a relatively good quality portion of a single crystal grown by a conventionally known method.

First, place 0.01% on the substrate 1 above as shown in Figure 1.
An epitaxially grown layer 2 with an excess of about Te is formed. This growth is performed by a liquid phase epitaxial growth method, and obtaining an epitaxially grown layer (hereinafter simply referred to as a grown layer) with a desired composition depends on controlling the composition and temperature of the liquid phase. This will be explained in more detail later in connection with the problem of phase equilibrium.

Then, on the growth layer 2, as shown in FIG.
An excessively grown layer 3 containing about 0.002% Pb is formed. In this embodiment, both grown layers 2 and 3 (hereinafter referred to as first and second grown layers, respectively) have the same thickness. The substrate on which these two growth layers have been formed is
Keep at a constant temperature, for example 550℃, for 0.5 hours. In this way, Te will move from the first growth layer 2 with an excess of Te toward the second growth layer 3 by diffusion, and the second growth layer with an excess of Te will also move from the first growth layer 2 with an excess of Te toward the second growth layer 3.
Pb moves from the grown layer toward the first grown layer 2 by diffusion, and the difference in composition between the two grown layers is reduced. When the compositions of both grown layers become completely equal, the composition will be approximately 50.007% expressed as an atomic ratio of Te, and the composition of the first growth layer (expressed as an atomic ratio of Te) will be approximately 50.007%.
(50.015%), the composition is much closer to stoichiometric composition.

In order to further approximate the stoichiometric composition, the first grown layer, which has a large degree of deviation, may be made thinner than the second grown layer. When the thickness of the first grown layer is set to 1/3 of the thickness of the second grown layer, the theoretical atomic ratio of Te is approximately 50.002%, and a crystal with an almost stoichiometric composition can be obtained. However, increasing the thickness of each growth layer requires a long time to make the composition uniform, so it is difficult to form a thick single crystal with a composition close to the stoichiometric composition using only two layers. In order to overcome this difficulty, a large number of relatively thin growth layers may be laminated, and the laminated growth layers may be heated to cause mutual diffusion in the thickness direction of each layer. In other words, if we represent a grown layer with a certain composition as A and a grown layer with a different composition as B, then
A large number of growth layers are stacked alternately in the process of ABABAB... If the growth layer thus formed is heated, the time required for the composition to become uniform will be approximately the same as in the case of only two layers, and it will not take an unreasonably long time. FIG. 3 shows the state in which six growth layers are formed on the substrate 1, 21a, 21b, 2
1c is a growth layer having a composition corresponding to composition A, and 22a, 22b, and 22c have a composition corresponding to composition B, respectively. Note that the same reference numerals as in the previous figure are attached to the substrate 1. The thickness of each layer and the number of layers are carriers (electrons and holes).
It is determined as appropriate by taking into account the diffusion distance of , the composition of each layer, the time required for uniformization, the number of steps required for lamination, etc.

Next, a method for forming a grown layer having a desired composition will be explained.

Figure 4 is a phase diagram of PbTe, showing curves A,
The region divided by b and c is a liquid phase region,
is a solid phase region, and is a liquid phase-solid phase coexistence region. Also, the vertical dotted line D represents the stoichiometric composition, and the horizontal dotted line E represents the isotherm at 550°C. Furnace and temperature for liquid phase epitaxial growth
If a PbTe single crystal substrate with a composition close to this composition is brought into contact with a liquid phase whose composition is approximately close to the intersection point P of the dotted line E and the curve C in the region while keeping the temperature constant at 550℃, the point P will be reached in an equilibrium state. A grown layer of corresponding composition is formed. Next, this substrate is lifted from the liquid phase and brought into contact with a liquid phase having a composition close to the intersection point Q between the isothermal line E and the curve B, so that a growth layer having a composition corresponding to the point Q is formed. The composition of point P is approximately 50.01% Te in atomic ratio, and the composition of point Q is also approximately Te.
This corresponds to 49.98% respectively. These growth temperatures and compositions are merely examples for convenience;
Curve B in the figure is nearly vertical below 800°C, while curve C becomes oblique from around 600°, so if growth is performed at a temperature close to 500°C, a grown layer with even lower Te content will emerge from the region. Therefore, when the composition is made uniform by heating, a crystal with a composition closer to the stoichiometric composition can be obtained.

FIG. 5 shows an example structure of the above-mentioned epitaxial growth apparatus, which is installed in the furnace core tube 23. As shown in FIG. H is a heater. The structure of the device itself is not particularly different from conventional epitaxial growth devices for manufacturing semiconductor laser devices.
It consists of a port 24 that accommodates the liquid phase and a slider 25 that holds the substrate 1. There are two liquid reservoirs in port 24, each containing a predetermined composition.
PbTe melts 26A and 26B are accommodated therein. By bringing the substrate 1 into contact with the liquid phase in each reservoir, two growth layers as previously shown in FIG. 2 are grown. The subsequent heat treatment for compositional uniformity may be performed in the same furnace, or may of course be performed in a separate furnace dedicated for compositional uniformity. To form multiple growth layers, the above-described operation may be repeated as many times as required. Of course, a plurality of reservoirs containing melts of the same composition may be arranged so that the contents of different compositions are adjacent to each other, and the substrates may be sequentially moved.

In the present invention, the method for forming a growth layer with a predetermined composition is not limited to the liquid phase epitaxial growth method,
An epitaxial growth method from a gas phase may also be used. In particular, the manufacturing method of the present invention is called a hot wall epitaxial growth method. A vapor phase growth method in a vacuum is suitable. In this method, the material to be grown is placed in the bottom of an evacuated cylindrical container, a substrate is placed above the container, and the material is sublimated by heating and solidified as a single crystal on the bottom surface of the substrate. . To form a plurality of growth layers, a plurality of cylindrical containers may be placed in the same exhaust container, materials of different compositions may be placed in each container, and the substrates may be sequentially moved onto each container. Incidentally, such a growth method is well known and is described in an article starting from page 5815 of Volume 50, No. 9, of the Journal of Applied Physics. The present inventors were able to produce a PbTe single crystal with a carrier concentration of ¹⁰¹⁵ pieces/cc using this growth method. This value is about an order of magnitude lower than with conventional methods. Note that the substrate is not limited to PbTe, and other ionic crystals having a similar crystal structure may be used.

The method of the present invention described above has the excellent advantage that a multicomponent semiconductor crystal having a sufficiently close to stoichiometric composition and therefore a sufficiently low carrier concentration can be manufactured through simple steps. Therefore, it is difficult to obtain crystals with stoichiometric composition.
It is extremely advantageous to apply this method to the production of low carrier concentration crystals of original semiconductors.

[Brief explanation of the drawing]

Figures 1 and 2 show PbTe to which the present invention is applied.
A schematic cross-sectional view for explaining an example of a single crystal manufacturing process, FIG. 3 is a schematic cross-sectional view of a substrate after the growth process in another manufacturing process, and FIG.
The phase diagram of PbTe, FIG. 5, is a sectional view showing an example structure of an apparatus for carrying out the method of the present invention. 1: substrate, 2: first growth layer, 3: second growth layer,
21a, 21b, 21c: Growth layer of A composition, 21
a, 22b, 22c: growth layer with B composition, 23: furnace core tube, 24: port, 25: slider, 26A
and 26B: PbTe melts with mutually different compositions.

Claims (1)

[Claims] 1 In a method for manufacturing a multi-component semiconductor crystal, a multi-component semiconductor crystal exhibiting a liquid phase-solid phase coexistence state and a solid phase state at a predetermined temperature in accordance with the composition ratio is manufactured by manufacturing a multi-component semiconductor crystal that exhibits a liquid phase-solid phase coexistence state and a solid phase state in accordance with the composition ratio. Forming a crystal growth layer with a first composition near the boundary of or more times, and by keeping each growth layer at a high temperature, atoms move between the first and second crystal layers to obtain a multicomponent semiconductor crystal having a composition intermediate between the respective crystal layers. A method for manufacturing multi-component semiconductor crystals.