JPH0752719B2 - Method for manufacturing vertical semiconductor superlattice - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a vertical semiconductor superlattice used for ultra-high-dimensional one-dimensional electron transistors, quantum well thin-line structure lasers having a low oscillation threshold, and the like. The present invention relates to a manufacturing method.

[Conventional technology]

FIG. 3 (a) shows an idealized AlAs-GaAs vertical semiconductor superlattice. In the figure, the substrate surface S is tilted by an angle θ with respect to (100) in the [011] direction. Further, FIG. 6B shows the X-ray diffraction position of the vertical semiconductor superlattice, and when an ideal vertical semiconductor superlattice structure as shown in FIG. , Superlattice diffraction is seen at the positions indicated by A and B in the figure.

Attempts to fabricate such vertical semiconductor superlattices have already been made by molecular beam epitaxial growth (MBE) (Applied Physics Letters, Vol. 45, No. 6, 620).
−622 (1984): PM Petroff et al.). In this conventional method by the MBE method, a substrate tilted from the [011] direction of the GaAs (100) crystal by 1 to 5 degrees is used. We are trying to fabricate an AlAs-GaAs vertical semiconductor superlattice by alternately supplying the amount equivalent to that on the substrate.

[Problems to be solved by the invention]

However, as a result of investigating the crystal produced by this MBE method by electron beam diffraction, an ideal structure as shown in FIG. 3 (a) was not obtained. As a result of diligent research by the inventor of the present invention, it was found that the reason is that the surface diffusion distance l of the atoms adsorbed on the crystal surface is small according to the MBE method.

That is, as shown in FIG. 8 (a), first, AlAs 2 is adsorbed to an arbitrary position on the terrace portion (horizontal portion of the substrate crystal surface) 1 of the substrate crystal surface by the beam irradiation and tries to move laterally. However, since the surface diffusion distance l is small,
As shown in FIG. 2B, most of AlAs does not reach the atomic step (stepped portion on the crystal surface of the substrate) 3. Since GaAs4 is continuously adsorbed from this state, two-dimensional nucleation occurs on the terrace as shown in FIG.
As a result, uniform nucleation is not performed in the lateral direction from the atomic step, and the vertical semiconductor superlattice as shown in FIG. 3A is not formed.

[Means for solving problems]

The method for manufacturing a vertical semiconductor superlattice of the present invention is made in view of the above problems, and sequentially switches and guides a plurality of organometallic compound gases on the substrate crystal surface tilted in a predetermined direction from the crystal plane, One molecule of two or more kinds of semiconductors formed according to the organometallic compound gas is used by using a metalorganic vapor phase epitaxy method (MOCVD method) in which a semiconductor according to the organometallic compound gas is deposited on the substrate crystal surface. During the formation of layers, they are sequentially deposited to form a superlattice.

[Action]

In the MBE method, the state of the crystal surface is considered to be active due to the high vacuum in the growth system, but in the MOCVD method, the crystal surface state is stabilized by hydrogen adsorption because the pressure in the system is high and the crystal growth is performed in a hydrogen atmosphere. , The supplied atoms move while substituting with hydrogen already adsorbed on the surface, so the atoms adsorbed on the crystal surface move easily, and the surface diffusion distance 1 becomes sufficiently large compared to the case of the MBE method, and the lateral direction Uniform nucleation occurs.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to Examples.

FIG. 1 is a schematic view showing an embodiment of the present invention.
On a substrate crystal tilted by θ = 2 degrees to the [011] direction of the (100) plane
An example is shown in which AlAs0.5 molecular layers and GaAs0.5 molecular layers are alternately deposited. As shown in FIG. 3A, the AlAs2 atoms adsorbed at arbitrary positions on the terrace 1 of the substrate crystal surface move leftward, that is, toward atomic step 3 on each terrace. Then, as shown in FIG.
Uniform nucleation is carried out laterally from atomic step 3. When this nucleation reaches 1/2 of the step interval d as shown in FIG. 7C, GaAs4 is continuously replaced with AlAs2.
Is deposited to form a layer as shown in FIG.

Details of the crystal growth conditions of the examples are shown below. Growth was carried out at a reduced pressure of 0.1 atm using a horizontal furnace of high frequency heating. Triethylaluminum, triethylgallium and arsine were used as raw materials. The partial pressure in the reaction tube is 4.
7 × 10 ⁻⁷ atm, 1.3 × 10 ⁻⁶ atm and 4.7 × 10 ⁻⁴ atm,
The total gas flow rate including the hydrogen carrier gas is 3 liters / minute. The growth temperature is 650 ° C. Then, under these conditions, the raw material triethylaluminum and triethylgallium were alternately switched for 3 seconds each. The growth rate was 0.47Å / sec for both AlAs and GaAs, and they were deposited alternately in 6 seconds.
The amount of AlAs and GaAs deposited is 2.82Å / sec, which corresponds to the thickness of one monolayer. A crystal having a growth layer thickness of 0.5 μm was produced with a total growth time of 3 hours.

The X-ray diffraction of the vertical semiconductor superlattice thus produced is shown in FIG. The diffractions A and B in the figure are diffractions due to the superlattice structure. It can be seen from the diffraction angle of the superlattice that the superlattice period matches the interval of atomic steps, and it is clear that the ideal vertical semiconductor superlattice shown in FIG. 3 has been realized.

In this embodiment, the substrate is tilted by 2 degrees from (100) to the [011] direction. However, even when a substrate tilted by 0.2 to 4.0 degrees in the same direction is used, an ideal vertical semiconductor superlattice is similarly obtained. It was realized. The relationship between the inclination θ and the step interval d is represented by d = h / tan θ (where h is the thickness of one molecular layer as shown in FIG. 1 (d)). So, for example, (100)
When tilted 0.2 degrees from the plane, d = 811Å, and when tilted 4.0 degrees, d = 40Å.

Regarding the substrate plane orientation, as in the present embodiment, [0] of the (100) plane
A vertical semiconductor superlattice is formed when tilted in the [11] orientation, but a good vertical semiconductor superlattice cannot be obtained when tilted in the [010] orientation or the [001] orientation. This is because the unpaired bond (dangling bond) in the atomic step is [01
1] because it extends in the direction. In addition, a good vertical semiconductor superlattice is obtained on a substrate crystal inclined in the [111] direction of the (111) plane and the [11] direction of the (110) plane.

Further, when the deposition amount when two types of semiconductors forming the superlattice are deposited alternately deviates from the equivalent amount of one molecular weight, the vertical semiconductor superlattice is greatly inclined. That is, as shown in FIG. 4, when the inclination angle of the superlattice is β and the inclination angle of the substrate is θ, tan β = {1- (m + n)} / tan θ. Here, m and n are the indices m and n of (AlAs) m (GaAs) n, and indicate m atomic layer and n atomic layer. Therefore, when m = 0.5 and n = 0.5, β = 0 degrees. However, when a thickness equivalent to 1.1 molecular layers is deposited in one cycle, that is, when an atomic layer of m + n = 1.1 is obtained, θ = 2
At the same time, β = 70 degrees, which is close to a parallel superlattice. Therefore, the growth rate of one cycle needs to be accurately adjusted to one molecular layer. For that purpose, the raw material supply amount may be adjusted so that the superlattice diffraction can be seen at the positions indicated by points A and B in the X-ray diffraction of the idealized vertical semiconductor superlattice shown in FIG. 3 (b). .

Further, FIG. 5 shows the relationship between the growth rate and the superlattice diffraction intensity of X-rays. As can be seen from the attached figure, at a high growth rate of 2Å / sec or more, the attached atoms cannot sufficiently diffuse on the crystal surface, and the growth from the atomic step does not occur.

In addition, in the present embodiment, two kinds of semiconductors are alternately deposited during the formation of one molecular layer, but a vertical semiconductor superlattice composed of three or more kinds of semiconductors is formed by sequentially depositing three or more kinds of semiconductors. It can also be formed.

Next, FIGS. 6 and 7 show specific examples of devices utilizing the vertical semiconductor superlattice manufactured in this way.
What is shown in FIG. 6 is a one-dimensional electron FET (field effect transistor) having a modulation doping structure. A vertical semiconductor superlattice having a thickness of about 100 Å is sandwiched between buffer layers (or clad layers) to form a one-dimensional electronic structure. The electrons become one-dimensional, and the probability of scattering due to impurities decreases, resulting in high movement. Degree Transistor (Javanese Journal of Applied Physics
Vol. 19, No. 12, L735-738 1980: H. Sakaki). In the figure, 11 is a source, 12 is a gate, 13 is a drain, and 14 is
Si-doped Al _r Ga _1-r As layer, 15 was fabricated according to this example
AlAs-GaAs vertical semiconductor superlattice, 16 is one-dimensional electron gas, 17
Is an undoped GaAs layer, and 18 is a semi-insulating GaAs substrate.

In addition, as an application to an optical device, a quantum well wire structure laser is shown in FIG. When the density of states of electrons and holes becomes one-dimensional, they become discontinuous, and the oscillation threshold value stabilizes with temperature (Applied Physics Letters 40
Volume 11, pages 939-941 1982: Y. Arakawa et al.). Where 21
Is a p-GaAs cap layer, 22 is a p-GaAs clad layer, 23 is an AlAs-GaAs vertical semiconductor superlattice manufactured by this embodiment, 24 is an n-AlGaAs clad layer, and 25 is an n-GaAs substrate.

〔The invention's effect〕

As described above, according to the method for manufacturing a vertical semiconductor superlattice of the present invention, since the MOCVD method is used, the atoms adsorbed on the crystal surface are easily moved, and the surface diffusion distance is longer than that in the case of the MBE method. l is sufficiently large. Therefore, nucleation occurs uniformly in the lateral direction from the atomic step of the substrate crystal, and an ideal vertical semiconductor superlattice can be formed.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an embodiment of the present invention, FIG. 2 is an X-ray diffraction diagram of a vertical semiconductor superlattice produced by this embodiment, and FIG. 3 (a) is an ideal vertical semiconductor superlattice. Structural diagram showing the lattice,
FIG. 3 (b) is its X-ray diffraction diagram, FIG. 4 is a configuration diagram showing a vertical semiconductor superlattice under different conditions, and FIG. 5 is a relation between crystal growth rate and X-ray superlattice diffraction intensity. FIG. 6, FIG. 6 and FIG. 7 are views showing specific examples of devices using a vertical semiconductor superlattice, and FIG. 8 is an explanatory view showing a conventional method. 1 ... Terrace, 2 ... AlAs, 3 ... Atomic step, 4 ...
… GaAs.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical indication H01S 3/18

Claims (2)

[Claims] 1. A plurality of organometallic compound gases are sequentially switched and guided on a substrate crystal surface tilted in a prescribed direction from a prescribed exponential plane, and a semiconductor corresponding to the organometallic compound gas is deposited on the substrate crystal surface. Using metalorganic vapor phase epitaxy
A method for manufacturing a vertical semiconductor superlattice, comprising forming two or more kinds of semiconductors formed according to the organometallic compound gas in order while forming one molecular layer to form a superlattice. 2. The substrate crystal surface has low index planes of (100) and (1
11. The vertical semiconductor superstructure according to claim 1, wherein when it is 11) or (110), it is tilted from [011] orientation, [11] orientation or [11] orientation by 0.2 to 4.0 degrees. Lattice manufacturing method.