JPH05326922A - Semiconductor crystal growth - Google Patents

Abstract

PURPOSE:To improve flatness in the plane on the substrate crystal surface by controlling the height of step on the grown crystal surface to the single atom layer and the width of terrace with the equal interval. CONSTITUTION:A vertical type semiconductor superlattice is formed through the processes that a GaAs buffer layer 5 is brown by the organic metal vapor growth method in the thickness of about 600Angstrom on a substrate crystal surface of a GaAs inclined substrate 1, thereafter a superlattice is grown in the 20 periods, each period thereof including formation of three-atom layers of AlAs crystal layer 10 and three-atom layers of GaAs crystal layer 11 on this GaAs buffer layer 5, next a semiconductor superlattice is grown for 900 periods, each period thereof including formation of 0.5 atom layer of AlAs and next 0.5-atom layer of GaAs on this superlattice.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor crystal growth method applied to the formation of, for example, an ultrafast low-dimensional electron transistor, a quantum well having a low oscillation threshold, or a quantum well thin-line structure laser, and more particularly to a substrate crystal. The present invention relates to an in-plane flatness control method on a surface.

[0002]

2. Description of the Related Art GaAs (001) is formed by using a crystal growth method (MOCVD method) in which a plurality of raw materials such as organometallic compound gases are sequentially introduced into a heating furnace and deposited on a substrate crystal surface according to the raw materials. Using the atomic step formed along the [110] direction on the substrate crystal surface tilted from the plane toward the [Bar 110] direction, the lateral growth is preferentially performed from that step, and the vertical semiconductor as shown in FIG. Superlattice structure 4
When a quantum wire structure is to be formed, the step (step) 2 on the substrate crystal surface of the GaAs tilted substrate 1 is the width of one atomic layer or the terrace 3 (interval between steps).
Must be evenly spaced.

However, GaAs used for crystal growth
On the substrate surface of the inclined substrate 1, there are many steps having processing damage and steps of several tens of atomic layers, and the terrace intervals are also non-uniform. Therefore, several hundred Å or more of GaAs is formed as a buffer layer on the substrate crystal, or GaA
An attempt has been made to control a monatomic step and a terrace width by inserting a superlattice in which s and AlAs are alternately formed with 40 to 100Å as one cycle for 20 to 100 cycles between the substrate crystal and the vertical semiconductor superlattice. It was being appreciated.

[0004]

However, even in the above-described conventional semiconductor crystal growth method, since the flatness on the surface of the grown crystal is not controlled, as shown in FIG.
On the growth surface of the GaAs buffer layer 5 formed on the As-graded substrate 1, there are irregularities whose step 6 has a height of several atomic layers or more, and the terraces 7 are not evenly spaced but wide (several hundreds). Å) Terrace 7a and narrow width (40-50 Å or less)
The terrace 7b is mixed. Therefore, when the vertical semiconductor superlattice 4 is formed, there are problems that the period is nonuniform and the superlattice interface is mixed. In addition, there is a problem in that the in-plane dimension of the thin line width in the quantum thin line structure is not uniform, and the variations in the characteristics increase.

Therefore, the present invention has been made to solve the above-mentioned conventional problems, and its purpose is to control the height of steps on the surface of a grown crystal by one atomic layer and the terrace width at equal intervals. Another object of the present invention is to provide a semiconductor crystal growth method capable of improving in-plane flatness on the surface of a substrate crystal.

[0006]

In order to achieve such an object, the present invention is directed by sequentially switching a plurality of raw materials such as organometallic compounds, and depositing a semiconductor according to the raw materials on the crystal surface of the substrate. GaAs (00
1) Two kinds of semiconductors, for example, GaAs and AlAs are alternately supplied every one atomic layer or several atomic layers on the surface of the substrate crystal inclined in the [Bar 110] direction from the plane, and one atomic layer or several atomic layers are supplied. A superlattice having a layer as one period is formed for ten to several tens of periods.

[0007]

In the present invention, even when the substrate crystal surface inclined from the GaAs (001) plane in the [Bar 110] direction has many steps (steps) and uneven terraces, the growth surface is Have steps of one atomic layer and are formed with evenly spaced terrace widths.

[0008]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic diagram for explaining an embodiment of a semiconductor crystal growth method according to the present invention, and the same parts as those in the above-mentioned drawings are designated by the same reference numerals. In the figure, 8 indicates a step and 9 indicates a terrace. Here, GaA
The angle θ = with respect to the [bar 110] direction of the s (001) plane
A GaAs tilted substrate 1 having a crystal surface tilted at an angle θ of 0.1 degree with respect to [110] in the in-plane vertical direction was used. First, as the first step, GaAs is formed on the substrate crystal of the GaAs inclined substrate 1 by metal organic vapor phase epitaxy.
The buffer layer 5 was grown to about 600Å to eliminate the influence of processing damage on the substrate surface. Next, as the second step, AlA
The s crystal layer 10 and the GaAs crystal layer 11 were grown as a triatomic layer and a triatomic layer, and 20 cycles of a superlattice were grown. After that, as a third step, 0.5 atomic layer of AlAs as shown in FIG.
A vertical semiconductor superlattice 4 was formed by growing 900 cycles of a semiconductor superlattice having an atomic layer as one cycle.

In such a method, the height of the step 8 and the width of the terrace 9 on the surface of the superlattice grown in the second step were observed by TEM. As a result, the step was one atomic layer and the terrace was wide and narrow. The difference in the width of the terrace is 10
It was Å or less (about 3 atomic layers), and it was confirmed that the growth surface was completely controlled. The same effect was obtained when the AlAs crystal layer 10 and the GaAs crystal layer 11 in FIG. 1 were grown for about 60 cycles with one atomic layer or two atomic layers as one cycle.

FIG. 2 shows the relationship between the superlattice period and the terrace width on the surface according to the present invention. In the figure, the horizontal axis represents the thickness (ML: monolayer) of the atomic layer of one period of the AlAs crystal layer and the GaAs crystal layer, and the vertical axis represents the terrace of the wide terrace (Tw) and the narrow terrace (Tn). The width difference (Å) is shown. As can be seen from the figure, the 26-atom superlattice period has a terrace width variation of 150 Å or more, while the 6-atom layer has a terrace width of 10 Å or less.
As described above, according to this example, it is understood that the uniformity of the terrace width on the growth surface is improved by about 15 times.

Next, the details of the above-mentioned crystal growth conditions will be described. Approximately 76 torr using horizontal furnace of high frequency heating
The crystal was grown under reduced pressure. As a raw material, triethylaluminum (TEAl), triethylgallium (TEGa),
Arsine (AsH ₃ ) was used. The partial pressures in the reaction tube are 5.9 × 10 ⁻⁴ torr and 5.8 × 10 ⁻⁴ torr, respectively.
r, 5.3 × 10 ⁻¹ torr, and the total gas flow rate including the hydrogen carrier gas is 4 liters / minute. The growth temperature is about 600 ° C. The growth rate under this condition is
0.47Å / sec, and terrace (flat part) 9 in about 6 seconds
The front surface of is covered and corresponds to exactly one atomic layer thickness.

FIG. 3 is a schematic view showing a case where the semiconductor superlattice formed by the semiconductor crystal growth method according to the present invention is applied to a quantum wire laser having an active layer of InAs as an application to an optical element. In the figure, 21 is an n-GaAs substrate corresponding to the GaAs tilted substrate 1 described above, and 22
Is n- (AlAs) ₃ (GaAs) ₃ superlattice, and 23 is Ga
As layer, 24 is InAs active layer, 25 is p-AlGaA
s clad layer, 26 is a p-GaAs cap layer, 27 electrodes, 28 are electrodes.

According to this structure, the electrode 27 is positive,
By applying a negative voltage to the electrode 28, p-AlGa
From the As clad layer 25, holes, n- (AlAs) ₃ (Ga
In) InAs in which electrons have a fine wire structure from the As) ₃ superlattice 22.
When the density of states of electrons and holes supplied to the active layer 24 becomes one-dimensional, they become discontinuous, the oscillation threshold is lowered, and the temperature is stabilized with respect to temperature.

[0014]

As described above, according to the present invention,
Even when there are a large number of steps (steps) on the substrate crystal surface tilted from the GaAs (001) plane in the [bar 110] direction and there is a non-uniform terrace width, the step heights (steps) are It is possible to control the monolayer and the terrace width at equal intervals. Therefore, the uniformity of the period and the interface of the vertical semiconductor superlattice are improved, and an excellent effect is obtained in the fabrication and improvement of characteristics of ultrafast low-dimensional electron transistors or quantum wells or quantum wire lasers with a low oscillation threshold. is there.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a superlattice period and a terrace width.

FIG. 3 is a schematic view of a quantum wire laser showing an application example of the present invention.

FIG. 4 is a schematic diagram showing a configuration of a conventional (AlAs) _1/2 (GaAs) _1/2 vertical semiconductor superlattice.

FIG. 5 is a schematic diagram showing the surface of a GaAs buffer layer when the step height and the terrace width in the conventional vertical semiconductor superlattice are not controlled.

[Explanation of symbols]

1 GaAs inclined substrate 2 step 3 terrace 4 vertical semiconductor superlattice 5 GaAs buffer layer 6 step 7 terrace 7a wide terrace 7b narrow terrace 7 8 step 9 terrace 10 AlAs crystal layer 11 GaAs crystal layer 21 n-GaAs inclination Substrate 22 n- (AlAs) ₃ (GaAs) ₃ Superlattice 23 GaAs Layer 24 InAs Active Layer 25 p-AlGaAs Clad Layer 26 p-GaAs Cap Layer 27 Electrode 28 Electrode

Claims (1)

[Claims] 1. Crystal growth in which a plurality of source atoms or source compounds are sequentially switched to deposit at least two kinds of semiconductors according to the source material on a substrate crystal surface inclined from the GaAs (001) plane in the [bar 110] direction. In a method for growing a semiconductor crystal of a vertical type semiconductor using a vertical method, prior to forming the vertical type semiconductor superlattice, two kinds of semiconductors, one atomic layer or several atomic layers, are formed on the surface of the substrate crystal. A method for growing a semiconductor crystal, which comprises forming several tens of superlattices each having a periodicity.