JPH02283695A - Method for growing crystal with molecular beam - Google Patents

Abstract

PURPOSE:To prepare a high quality crystal-growing film preventing the contamination of impurities in the crystal, the generation of defects, etc., by employing a finely inclined surface having a specific angle from the low index surface of a substrate as the crystallizing surface of the substrate used for the growth of the crystal. CONSTITUTION:When a crystal film is formed on a substrate by a molecular beam crystal-growing method, a finely inclined surface is employed as the crystal surface of the substrate. Such an angle that a distance between the molecule steps of the surface substantially coincides with a length integer times larger the period of the long one among the surface reconstitution patterns in the growing crystal is selected as an inclination angle from the low index surface, thereby permitting to give an order to the step distance, reading realize such a growing mode as flowing the step transversely, suppress the contamination of impurities in the crystal and the generation of defects, etc., and further improve the morphology of the surface for the high quality of the crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a molecular beam crystal growth method, and particularly to a molecular beam crystal growth method capable of obtaining a high quality crystal grown film.

[Conventional technology]

When forming a crystalline film on a substrate using the molecular beam crystal growth method, it is known that the quality of the formed crystalline film is influenced by the angle of inclination of the substrate crystal plane from the low index plane.
Examples so far include, for example, C. Rajulescu et al., Journal Op-Applied Physics, 6.
Volume 2, No. 3 (1987).

954 pages (D, C, Radulescu, J, Ap
pl, Phys, 62 (19B?) p, 954
) have been reported. In this example 0°, 2°, 4
A G a As / AI Ga As modulated doped structure was grown on a (100) GaAs substrate with a tilt of 6.5” by molecular beam crystal growth, and the substrate tilt angle affecting the electron transport properties was determined. effects have been reported.

Next, the effects will be explained. Figure 2 is shown in the above-mentioned paper, and shows that G a A s / A I G a A
s The electron mobility of the two-dimensional electron gas existing near the heterojunction and the (111) return from the (100) plane of the substrate.
From this figure, which shows the relationship with the tilt angle in the A-plane direction, it can be seen that the highest mobility is obtained when the tilt angle is 4 degrees.

[Problem to be solved by the invention]

In the conventional molecular beam crystal growth method, the optimal tilt angle was determined empirically as described above. This is because the reason why film quality is improved when using a tilted substrate is not yet well understood.

Therefore, it is necessary to find the best tilt angle depending on differences in the substrate material used, substrate surface orientation used, growing substance, growth conditions, etc.

However, there were no guidelines for this.

This invention was made to solve the above-mentioned problems, and it is possible to provide an optimal substrate inclination angle for molecular beam crystal growth under any substrate material used, substrate surface orientation growth substance used, and growth conditions. With the goal.

[Means to solve the problem]

The molecular beam crystal growth method according to the present invention uses a vicinal crystal plane on the substrate crystal plane used for growth, and the interval between molecular steps on the surface is determined by the angle of inclination from the low-index plane to a long surface reconstruction pattern during crystal growth. This is to ensure that the reconstruction of the surface is not destroyed by the steps.

[Effect]

In this invention, the inclination angle is set so that an integral multiple of the period of surface reconstruction during crystal growth matches the period of steps on the substrate surface caused by the inclination of the substrate. occurs, and as a result, crystal growth tends to be in a lateral growth mode from steps, allowing crystal growth with less crystal defects and impurity incorporation.

〔Example〕

Hereinafter, as an example of the present invention, C,aAs (100
) The case of growing GaAs on a substrate will be explained.

FIG. 1 is a diagram schematically showing the atomic arrangement of a GaAs substrate used in the molecular beam crystal growth method according to an embodiment of the present invention.

Figure 1 (a) is a view seen from the (100) surface, Figure 1 (b)
) is a cross-sectional view seen from the (011) direction. In the figure, 1 is a unit cell with a (2X4) structure, and 2 is a (2x4) unit cell on the crystal growth surface.
100) is the angle with respect to the plane. In this embodiment, this inclination angle is 11.43°.

In the figure, black circles represent arsenic, white circles represent gallium, and to show the difference in the layers of gallium, the white circles, circles with diagonal lines inside the white circles, and circles with an X inside the white circles represent the 171st circle, respectively. It represents gallium in the second and third layers.

Figure 1 shows the literature physical by M, D., Pashley et al.
Review Letters, Volume 60 (1988), 21
76 pages (M, D, Pa5hley, Physica
l Review Letters V.

1.60 (198B), p. 2176) revealed GaA by scanning tunneling microscope observation.
It is drawn based on a reconstruction model of atoms on the s (100) surface. In this surface, the arsenic in the first layer of the surface is [01
1), two of them form a pair in the direction, creating a structure in this direction with 8 members, twice the period of 4 unit cells. on the other hand(
In the 011) direction, every third arsenic atomic row is missing, creating a structure with 4 times the period, 16 atoms, in this direction. This is a unit with a (2×4) structure. , : This is indicated by 1 in the figure. The position of the gallium in the second layer is not directly below the gallium in the first layer, but is shifted by two half grids.

Therefore, as shown in the figure, the (2×4) unit 1 overlaps by two people at a position one molecular layer lower.

Taking this into consideration, FIG. 1 depicts a staircase with a period of 14 people that descends by one molecular layer each time it advances in the (011) direction.

As mentioned above, the distance between the molecular steps on the surface matches the integral multiple of the longer period (here, 4) of the surface reconstruction pattern during crystal growth (here, (2×4)). In the present invention, one of the following three equations is used as a method for calculating the inclination angle from the low index plane.

where a is the thickness of the monoatomic layer or monomolecular layer of the grown film, k
The pattern of surface reconstruction during crystal growth under certain conditions is (
l × m ), then the larger value of 2 and m, b is the size of the unit cell in the direction in which the periodic structure appears twice, α is the larger value of l and m, and k is the smaller value. Let the direction be j, and let n be the unit vector in each direction in which the k times period and double period appear.

Let nJ be the unit vector perpendicular to n, which is in the plane made by nJ and has the smaller angle with , and is the value defined by Amama = α. , N are natural numbers. Also, the direction of inclination is the direction of the helix.

In the case of this embodiment, as described above, the position of the gallium in the second layer is not directly below the gallium in the first layer, but is shifted by two half lattices. In such a case, the optimal equation for calculating the tilt angle is equation (2). In this case, i=2. m=4. ni-4
, α-1, direction of inclination is [011), unit cell 4 people, 1
Since the molecular layer thickness is 2.83, Equation (2) is
N-1), 5.39° (N=2), 3.52" (
N=3).

2.61° (N-4), 2.08° (N=5), 1
．． 72” (N-6).

Surface reconstruction occurs such that any unbound pounds present on the surface are eliminated, lowering and stabilizing the surface energy. Therefore, the surface where the steps are arranged so that the period of reconstruction is preserved as in this embodiment becomes very stable.

When creating a GaAs substrate whose crystal surface has the above-mentioned angle with respect to the (100) plane, although it is possible to set the angle accurately using current technology, errors occur at the atomic level and the step spacing is not necessarily uniform. It is not. However, when molecular beam crystal growth is performed on a substrate surface prepared with the above-mentioned angle, even if the step intervals are not uniform at the beginning, they can be made uniform during annealing or growth. . Therefore, the angle θ
Even if there is some error in , the effect of this embodiment can be obtained. This phenomenon can also be seen when molecular beam crystal growth is performed on a crystal surface with a completely different angle from that described above, but if the error range is set to within ±2%, it is difficult to make the step intervals uniform. The driving force is extremely large, and the effects are clearly different.

In addition, if steps are formed that are arranged in a straight line at equal intervals, by setting the growth conditions appropriately, atoms attached to the surface will always reach the steps and then be incorporated into the crystal, that is, the steps will move laterally. Such a growth mode is easily realized. As a result, the incorporation of impurities into the crystal, the occurrence of defects, etc. can be suppressed, and the quality of the crystal can be improved by improving the surface morphology.

In addition, although the case of N-1 was explained in the said Example, N may be 2 or more. In this case, N quadruple periodic structures are included between steps. Also, by changing the conditions or changing the growth substance during growth (2X4)
When using a pattern from (IX3), it is effective to use the latter part of 3.52@ of N-3, which is commonly applied to both patterns.

In addition, in the above embodiment, the case where two unit units in the first layer and the unit unit in the second layer overlap, that is, the case where equation (2) holds, was explained, but depending on the case, equations (1) and (3)
) formula is appropriate in some cases.

〔Effect of the invention〕

As described above, according to the present invention, the inclination direction and angle of the substrate used are determined so that the atomic steps on the surface are likely to be linear and evenly spaced, so that the steps flow horizontally. This method has the effect of increasing the quality of the crystal by easily realizing a growth mode, suppressing the incorporation of impurities into the crystal, suppressing the generation of defects, and improving the surface morphology. Furthermore, by switching the film to be grown laterally on such evenly spaced linear steps every half of one atomic layer, it is possible to grow ultrafine structures extending parallel to the steps.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the atomic arrangement seen from the surface and cross section of a GaAs substrate tilted by 11.43 degrees in the (011) direction from the (100) plane used in the molecular beam crystal growth method according to an embodiment of the present invention; FIG. 2 is a diagram showing the relationship between the tilt angle and electron mobility obtained by the conventional molecular beam crystal growth method. 1 is the unit cell of the (2x4) structure, and 5 is the angle with the (100) plane. Note that the same reference numerals in the figures indicate the same or the same parts.

Claims (1)

[Claims] (1) In the molecular beam crystal growth method, the inclination angle of the substrate crystal plane used for growth from the low index plane is such that the interval between molecular steps on the surface is an integer of the longer period of the surface reconstruction pattern during crystal growth. A molecular beam crystal growth method characterized by the use of a vicinal slope whose angle is approximately equal to the angle of 2.