JPH10326749A - Manufacture of compound semiconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a compound semiconductor by which a mixed crystal layer of highly nitrogenated composition can be obtained without degrading crystallinity, when forming the mixed crystal layer of a III-V group compound semiconductor including at least one more V group element together with nitrogen by a molecular beam epitaxial growth process. SOLUTION: In a method for manufacturing a compound semiconductor, a crystal of a III-V group compound semiconductor including at least one mope V group element together with nitrogen is grown by radiating a molecular beam of raw materials to a substrate in a crystal growth chamber exhausted to a vacuum, so that the mean free path of molecules of the ray materials can be longer than the distance between the substrate and a molecular beam source. In that case, a nitrogen compound is used as a raw material of nitrogen, and molecules of the nitrogen compound is decomposed after reaching the substrate surface to incorporate only nitrogen atoms into a semiconductor crystal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a molecular beam epitaxial growth (MBE) method, a gas source MBE (GSMB)
E) evacuation such that the mean free path of the source molecules is larger than the distance between the substrate and the molecular beam source as in the method E, the actinic beam epitaxial growth (CBE) method, the metalorganic molecular beam epitaxial growth (MOMBE) method, and the like. The present invention relates to a method for producing a group III-V compound semiconductor containing at least another group V element together with nitrogen by irradiating a substrate with a source molecular beam in a crystal growth chamber.

[0002]

2. Description of the Related Art In recent years, a group III-V compound semiconductor containing at least one other group V element together with nitrogen has attracted attention as a material for optoelectronics. This is because the crystal lattice constant and the energy band gap of the group III-V compound semiconductor can be controlled in a wide range by changing the composition of the mixed crystal. Above all, a GaInNAs-based semiconductor is 1.3 μm or 1.55 μm in a composition that enables lattice matching with GaAs.
having a band gap desired for an active layer of an optical fiber communication laser for transmitting light in a band including a wavelength of m,
In addition, since a large band offset of a conduction band can be obtained by combination with an AlGaAs-based or InGaP-based semiconductor, a communication semiconductor laser having an improved temperature characteristic that a required current does not increase much even when the temperature rises. (For example, see Applied Physics, Vol. 65 (1996), p. 148).

Conventionally, a molecular beam epitaxial growth (MBE) method, a gas source MBE (GSMBE) method, and an actinic ray have been used for forming a III-V compound semiconductor containing another group V element together with nitrogen, such as a GaInNAs-based semiconductor. In crystal growth by an epitaxial growth (CBE) method, a metalorganic molecular beam epitaxial growth (MOMBE) method or the like (hereinafter, these methods are collectively referred to as an MBE method), from the viewpoint of the efficiency of incorporating nitrogen into the crystal, Active nitrogen (nitrogen radical) obtained from (N ₂ ) or ammonia (NH ₃ ) plasma is used (see JP-A-6-334168).

[0004]

However, according to the MBE method using a nitrogen radical as a nitrogen source, in the crystal growth of a group III-V compound semiconductor containing another group V element together with nitrogen, the growth of the nitrogen concentration increases. There is a problem that the crystallinity of the semiconductor is reduced. For example, Ga
In a semiconductor laser in which a mixed crystal of _0.75 In _0.25 N _0.005 As _0.995 is used as an active layer of a single quantum well (SQW), a semiconductor laser having a thickness of 7
Laser oscillation of light having a wavelength of 1.113 μm at 7K has been reported (Electronics Letters, Vol. 32, 1996, p. 158).
5), and laser oscillation of light in a band including a wavelength of 1.3 μm or 1.55 μm used for optical fiber communication has not been realized.

That is, Ga which can be lattice-matched to GaAs
In order to obtain an energy band gap corresponding to an oscillation wavelength of 1.3 μm or more in an InNAs-based mixed crystal, V
The nitrogen content in the group III element must be about 2.5 atomic% or more, which is larger than 0.5 atomic% in the conventional example described above. It has been found that in a semiconductor, the crystallinity decreases as the nitrogen content increases.

It is considered that this is because, when a nitrogen radical is used as a nitrogen source, a crystal defect is induced due to a high reactivity or a high energy of the nitrogen radical. That is, based on the reactivity of nitrogen radicals, nitrogen easily forms bonds with group III elements and is taken into the crystal with high efficiency. At the same time, nitrogen bonded with group V elements other than nitrogen Compound molecules are also formed, and these nitrogen compound molecules are also incorporated into the crystal to form antisite group V elements (group V elements that occupy lattice positions to be occupied by group III elements) and interstitial atoms such as It is thought to induce crystal defects. At this time, even if N—N bonds were formed, the N ₂ molecules had a high vapor pressure, the incorporation rate into the crystal was small, and bonds between nitrogen and Group V elements other than nitrogen were formed. In such a case, a problem of deterioration in crystallinity occurs.

Further, the energy released from the nitrogen radical causes the III near the crystal growth surface already formed to be formed.
Bonding between group V elements and group V elements other than nitrogen (for example, Ga
-As bond) is dissociated, and V having a relatively high vapor pressure
It is conceivable that a group element is desorbed to generate vacancies. At this time, since the bond between the group III element and nitrogen is strong and stable, the crystallinity is particularly high in a group III-V compound semiconductor containing another group V element whose bond strength with the group III element is smaller than that of nitrogen. The problem of degradation occurs.

Therefore, MBE using nitrogen radical
III-V containing other group V elements together with nitrogen by the method
When growing a crystal of a group III compound semiconductor, there is a problem that it is difficult to obtain a high-quality crystal if the supply amount of nitrogen radicals is increased to increase the nitrogen concentration in the crystal.

In view of the above problems in the prior art, the present invention provides a method of manufacturing a compound semiconductor which can realize excellent crystallinity even in a III-V compound semiconductor containing at least another group V element together with nitrogen. It is intended to provide.

[0010]

According to one aspect of the present invention, there is provided a method of manufacturing a compound semiconductor, comprising: evacuation of a crystal so that a mean free path of a source molecule is larger than a distance between a substrate and a molecular beam source. When a group III-V compound semiconductor crystal containing at least one other group V element together with nitrogen is grown by irradiating a substrate with a source molecular beam in a growth chamber, a nitrogen compound is used as a source of nitrogen. It is characterized in that the molecules of the nitrogen compound decompose after reaching the surface of the substrate and only nitrogen atoms are taken into the semiconductor crystal.

That is, nitrogen atoms are incorporated into the crystal by dissociation and adsorption of the nitrogen compound on the crystal growth surface. Therefore, by using a stable nitrogen compound instead of a nitrogen radical as a nitrogen source, it is possible to suppress a reaction between a group V element other than nitrogen and nitrogen at the time of decomposition of the nitrogen compound. Also, the energy released by the reaction when nitrogen is taken into the crystal by the decomposition of the nitrogen compound on the crystal growth surface can be made smaller than the energy released by the nitrogen radicals. It is possible to suppress the dissociation of the bond with any other group V element, and to realize stable crystal growth.

As the nitrogen compound, a hydride of nitrogen can be preferably used. Since the bond dissociation energy of nitrogen hydride is smaller than that of N ₂ molecules, dissociation of hydride and adsorption of nitrogen on the crystal growth surface can be performed at a relatively low temperature. Therefore, it is easy to control the composition ratio of nitrogen and other group V elements in the compound semiconductor to be grown. In addition, since H ₂ molecules generated by dissociation of hydrides of nitrogen are easily desorbed from the crystal growth surface, unnecessary impurities are not taken into the crystal. Further, when impurities such as carbon (C) are present on the crystal growth surface, an effect of cleaning can be expected by the impurities forming hydrides and being eliminated from the crystal growth surface.

As the nitrogen hydride, NH ₃ can be preferably used. NH ₃ is the most stable of the hydrides of nitrogen, and minimizes the generation of crystal defects due to the interaction between nitrogen and other Group V elements when nitrogen atoms are incorporated into the crystal by dissociation and adsorption. Can be minimized.

When a hydride of nitrogen is used as the nitrogen compound, the substrate is kept at 500 to 750 ° C. during the crystal growth.
Is preferably maintained at a temperature within the range described above. When NH ₃ is used as the nitrogen compound, it is preferable to irradiate the substrate after heating the NH ₃ to a temperature in the range of 350 to 500 ° C.

As a nitrogen hydride, hydrazine (N ₂ H ₄ ) can be preferably used similarly to NH ₃ .

Further, as the nitrogen compound, a nitrogen alkyl compound can be preferably used. Alkyl compounds of nitrogen generally have lower bond dissociation energies than hydrides of nitrogen. As a result, the dissociation of the nitrogen compound on the crystal growth surface becomes easy, and the efficiency of taking nitrogen into the crystal can be increased. In addition, since the alkyl group generated by the decomposition of the alkyl compound of nitrogen is a hydrocarbon having a high vapor pressure, a high-purity crystal is obtained because it is not easily desorbed from the crystal growth surface and taken into the crystal. be able to.

Incidentally, as the nitrogen alkyl compound, an alkylated product of hydrazine can also be preferably used.

Further, an alkylamine compound may be preferably used as the nitrogen alkyl compound. When a stable alkylamine compound is used, when nitrogen atoms are incorporated into the crystal by dissociation and adsorption on the crystal growth surface, the generation of crystal defects due to the interaction between nitrogen and other Group V elements is minimized. Can be suppressed. When an alkylamine compound is used as the nitrogen compound, the substrate is preferably maintained at a temperature in the range of 400 to 750 ° C. during crystal growth.

The substrate is preferably a compound semiconductor having a zinc blende type crystal structure, and its surface is {100}
It is preferable to have a predetermined off angle from the surface toward the {111} A surface direction. Decomposition of the nitrogen compound is promoted on the surface of such a compound semiconductor substrate, and even if a nitrogen compound having lower reactivity than nitrogen radicals is used, a high efficiency of taking in nitrogen into the crystal can be realized. In particular, the off angle of the surface of the compound semiconductor substrate is preferably in the range of 5 to 15 °.

When the group V element is supplied onto the substrate, the step of irradiating the substrate with nitrogen compound molecules and the step of irradiating the substrate with another group V element are preferably performed alternately without overlapping. By separately and independently supplying the nitrogen source and the other group V element source to the substrate, the interaction between nitrogen and the other group V element can be reduced. Accordingly, the efficiency of taking nitrogen into the crystal is improved, and the reaction between nitrogen and other group V elements, which cannot be sufficiently suppressed by using a nitrogen source that is not a nitrogen radical, can be sufficiently suppressed.

As the nitrogen source, a nitrogen compound having a Gibbs energy of formation smaller than 100 kJ / mol can be more preferably used. By using a nitrogen compound having a Gibbs energy of formation smaller than 100 kJ / mol, a reaction between a group V element other than nitrogen and nitrogen can be more effectively suppressed during decomposition of the nitrogen compound.
Further, on the crystal growth surface, III is caused by a reaction when nitrogen is taken into the crystal by decomposition of the nitrogen compound.
Dissociation of the bond between the group V element and the group V element other than the nitrogen element is more effectively suppressed, and a high-quality crystal can be obtained.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following, embodiments of the present invention will be described in detail through various examples.

(Embodiment 1) In the first embodiment of the present invention,
GaInNAs and AlGaAs having a composition lattice-matched to a GaAs substrate by MBE using NH ₃ as a nitrogen source and a solid source as a source of other elements.
To form a single quantum well (SQW) structure.

In FIG. 1, such GaInNAs
The quantum well structure composed of / AlGaAs-SQW is shown in a schematic sectional view. In this quantum well structure, on a GaAs substrate 1 having a just {100} crystal surface, a lower cladding layer 2 of Al _0.3 Ga _0.7 As and a thickness of 1 μm and a thickness of 6 n of a GaInNAs mixed crystal are formed.
An m quantum well layer 3, a 0.2 μm thick upper cladding layer 4 made of Al _0.3 Ga _0.7 As, and a 0.1 μm thick cap layer 5 made of GaAs were sequentially grown by MBE.

Each of Al, Ga and In as MBE raw materials
For each, the solid metal raw materials are converted using Knudsen cells.
By heating, the molecular beam is irradiated on the substrate surface
Was. As for As, the solid As raw material is cracked
By heating with_TwoBeam is a substrate
Irradiated on the surface. As a nitrogen raw material, 100% N
H_ThreeGas was used. NH_ThreeIs not broken down 3
Heated to 50 ° C by a gas source cell, the gas source
From cell to NH_ThreeThe beam was irradiated on the substrate surface. N
H_ThreeThe crystal growth by heating
NH on the surface _ThreeThe diffusion of molecules is promoted and the crystal growth surface
Is improved. However, NH_ThreeThe gas source cell
Heating to 500 ° C. or more by_ThreeGrows crystal
Pyrolysis before reaching the surface_TwoProduces and crystal
The efficiency of nitrogen uptake is reduced. Therefore, NH
_ThreeIs heated to a temperature within the range of 100 to 500 ° C
Is preferred.

During the growth of the AlGaAs layers 2, 4 and the GaAs layer 5, the substrate is kept at a temperature of 580 ° C., and the molecular beam intensity is Al = 2 × 10 ⁻⁷ Torr (this is unnecessary in the case of forming a GaAs layer). ), Ga = 5 × 10 ⁻⁷ Torr, and As = 5 × 10 ⁻⁶ Torr. The crystal growth rate in this case was about 0.5 μm / h in the thickness direction.

In forming the GaInNAs mixed crystal layer 3, the substrate is maintained at a temperature of 580 ° C., and crystal growth is performed using a molecular beam intensity almost proportional to a target composition as exemplified in Table 1. Was.

[0028]

[Table 1]

[0029] In FIG. 2, the nitrogen composition dependency of PL (photoluminescence) emission intensity in the quantum well structure composed of the first examples fabricated GaInNAs / AlGaAs-SQW is nitrogen instead of NH ₃ in the MBE method This is shown in comparison with a quantum well structure fabricated using radicals. In the graph of FIG. 2, the horizontal axis represents the nitrogen content (atomic%) in the group V element contained in the GaInNAs active layer 3, and the vertical axis represents the PL emission intensity (arbitrary unit). Curve 2A including the black circle is the first curve.
The PL light emission intensity in the quantum well structure according to the embodiment is shown, and a curve 2B including a white square mark represents the PL light emission intensity in the conventional quantum well structure formed using nitrogen radicals.

As is apparent from FIG. 2, in the quantum well structure manufactured by using NH ₃ , PL light emission of sufficient intensity is obtained even with a high nitrogen content of about 3.5 atomic%. It was confirmed that it could occur. On the other hand, in the quantum well structure manufactured using the nitrogen radical, the PL emission intensity sharply decreased when the nitrogen content exceeded about 2 atomic%. Further, even in a low nitrogen concentration range of about 2 atomic% or less, the PL emission intensity of the quantum well structure manufactured using NH ₃ is improved as compared with that manufactured using nitrogen radicals. It became clear.

As is clear from the above results in the first embodiment, according to the present invention, a GaInNAs mixed crystal of high quality can be obtained up to a relatively high nitrogen concentration range. In addition, high quality GaI containing such a high concentration of nitrogen
By manufacturing a semiconductor laser using an nNAs layer as an active layer, light in a band including a wavelength of 1.3 μm or 1.55 μm can be emitted with a low current, and a long-life and high-performance optical communication A semiconductor laser can be provided.

In FIG. 2, NH ₃ of nitrogen hydride is used as a nitrogen source, but hydrazine (N ₂ H ₄ ) and hydrogen azide (N ₃ H) are used as other hydrides of nitrogen. Can also be used. As shown in Table 2, hydrazine and hydrogen azide have a smaller bond dissociation energy than NH ₃ and are easily decomposed on the crystal growth surface, so that the efficiency of nitrogen uptake into the crystal is improved. Can be

[0033]

[Table 2]

However, as shown in Table 3, NH 3
₃ has the lowest Gibbs energy of formation among nitrogen hydrides and is stable. Therefore, from the viewpoint of obtaining high-quality crystals, NH ₃ suppresses generation of crystal defects due to the interaction between nitrogen and other Group V elements when nitrogen atoms are taken into the crystal by dissociation and adsorption. This is preferable in that it can be minimized.

[0035]

[Table 3]

In FIG. 2, the substrate temperature is 580 ° C.
However, when NH ₃ is used as a nitrogen source, a substrate temperature in the range of 500 to 750 ° C. can be used. If the substrate temperature is lower than 500 ° C., the decomposition efficiency of NH ₃ on the crystal growth surface sharply decreases, and it becomes difficult to grow a mixed crystal containing nitrogen. On the other hand, if the substrate temperature exceeds 750 ° C., the desorption of group V elements other than nitrogen, such as As and P, generally increases, crystal defects increase and the crystal surface becomes rough, and high-quality crystals are obtained. It becomes difficult.

In FIG. 2, an Al _0.3 Ga _0.7 As layer was used as the cladding layer of the SQW structure.
An InGaP cladding layer lattice-matched to the aAs substrate may be used. Further, although a GaAs substrate having a just {100} plane is used as the substrate, a substrate surface having a predetermined off angle with respect to the {100} plane may be used.

(Embodiment 2) In the second embodiment of the present invention, as shown in FIG. 1, as in Embodiment 1, except that the formation conditions of the quantum well layer 3 are changed. Quantum well structure was fabricated.

That is, in the second embodiment, dimethylamine was used instead of NH ₃ as the nitrogen source. The dimethylamine vapor, as in the case of NH ₃ ,
Irradiation was performed on the substrate surface using a gas source cell. The gas source cell was heated to a temperature in the range of 50-150C to prevent re-condensation of dimethylamine vapor on the cell. The dimethylamine vapor emitted from the gas source cell heated to a temperature within this range is not decomposed before reaching the substrate surface.

During the formation of the quantum well layer 3, the substrate is 50
The temperature was maintained at 0 ° C., and the molecular beam intensity was Ga = 5 × 10 ^−7.
Torr, In = 3.8 × 10 ⁻⁷ Torr, As = 2.
5 × 10 ⁻⁶ Torr and dimethylamine = 2.1 ×
It was set to 10 ^-7 Torr. In the quantum well layer 3 thus formed, the In content in the group III element is 7.1 atomic%, and the nitrogen content in the group V element is 2.5 atomic%.
Atomic%.

FIG. 3 shows the PL emission spectrum intensity of the quantum well structure according to the second embodiment in comparison with a quantum well structure manufactured using nitrogen radicals. That is, the horizontal axis of FIG. 3 represents the wavelength (nm) of light emitted from the quantum well structure, and the vertical axis represents PL emission intensity (arbitrary unit). Curve 3A corresponds to a quantum well structure made using dimethylamine,
Curve 3B corresponds to a quantum well structure manufactured using nitrogen radicals.

As is clear from FIG. 3, the quantum well structure including the quantum well layer 3 formed by MBE using dimethylamine instead of nitrogen radical has a high peak intensity and a small half-width near a wavelength of 1.3 μm. , Which can emit PL light having high quality
An s / AlGaAs-SQW structure can be obtained. That is, high quality Ga can also be obtained by the MBE method using dimethylamine as the nitrogen source as in the second embodiment.
An InNAs mixed crystal can be obtained.

Incidentally, although in the above description of the second embodiment dimethylamine was used as alkylation containing nitrogen, NH ₃ mentioned in Example 1 In addition, hydrazine, such as hydrogen azide Alkylated compounds such as methylamine, methylhydrazine, methyl azide, and the like, in which a hydrogen atom in a nitrogen hydride is substituted with an alkyl group, can also be used. By substituting a hydrogen atom in a nitrogen hydride with an alkyl group, as illustrated in Table 4, the bond dissociation energy of the nitrogen compound can be reduced with almost no change in Gibbs energy generated as compared with the nitrogen hydride. It becomes possible to make it smaller. As a result, the efficiency of dissociation of the nitrogen compound can be improved without increasing the reaction between nitrogen and other group V elements on the crystal growth surface, and the efficiency of incorporation of nitrogen into the crystal is improved, It becomes possible to lower the crystal growth temperature.

[0044]

[Table 4]

Among the nitrogen-containing alkylated compounds, alkylamine compounds are stable compounds like NH _3, and when nitrogen atoms are taken into the crystal by dissociation and adsorption, nitrogen and other group V elements Can be minimized.

In FIG. 3, the substrate was kept at 500 ° C. during the formation of the quantum well 3 using dimethylamine. However, when an alkylamine-based compound was used as a nitrogen raw material, the substrate was heated to 400 to 750. By maintaining the temperature in the range of ° C., it is possible to grow the quantum well layer 3 of high quality. That is, when an alkylamine-based compound is used, the quantum well layer 3 can be grown on the substrate surface at a relatively low temperature because it is easily decomposed as compared with NH ₃ , On the substrate surface at the same temperature, higher incorporation efficiency of nitrogen into the crystal can be obtained.

In FIG. 3, although the Al _0.3 Ga _0.7 As layers are used as the cladding layers 2 and 4 in the SQW structure, InGaP lattice-matched to the GaAs substrate may be used. Furthermore, just # 1 is used as the substrate surface.
Although a 00 crystal plane was used, a substrate surface having a predetermined off angle with respect to the {100} plane may be used.

(Embodiment 3) In a third embodiment of the present invention, GaIn is placed on the just {100} plane of a GaP substrate.
An NP mixed crystal layer was grown. The substrate was maintained at a temperature of 550 ° C., PH ₃ was cracked at 800 ° C. in a gas source cell, and a P ₂ beam was irradiated on the substrate surface. For Ga, In, and N of other elements, the same raw materials and cells as in Example 1 were used.

This GaInNP mixed crystal layer is grown to a thickness of 1 μm with a composition (In = 5 at% in group III element, N = 3 at% in group V element) that can lattice match with the GaP substrate. Was. The condition of the molecular beam at this time is Ga =
5.0 × 10 ⁻⁷ Torr, In = 2.6 × 10 ⁻⁸ Torr
r, P ₂ (PH ₃ ) = 5.0 × 10 ⁻⁶ Torr, and NH ₃ = 3.9 × 10 ⁻⁷ Torr.

The obtained GaInNP layer was evaluated by X-ray diffraction. As a result, the half width of the {400} diffraction spectrum was 15 seconds, which is an extremely small and good value. Thus, according to the present invention, a high-quality GaInNP mixed crystal layer can be obtained.

In the above description of the third embodiment, NH ₃ is used as a nitrogen source. However, it goes without saying that other nitrogen raw materials exemplified in the first and second embodiments can be used. No.

(Embodiment 4) In the fourth embodiment of the present invention, the GaAs substrate having a zinc blende type crystal structure has various off angles from the just {100} plane toward the {111} plane. 1 μm thick GaInN on the surface
An As mixed crystal layer was grown under condition 2 in Table 1. In the obtained GaInNAs mixed crystal layer, the relationship between the off-angle of the substrate surface and the nitrogen content in the group V element is PL
Investigation was performed using the peak energy of the light emission and the X-ray diffraction peak position, and the results are shown in FIG.

In the graph of FIG. 4, the horizontal axis represents <0> from the just {100} plane of the GaAs substrate through the {111} plane.
11> represents the off-angle (degree) toward the direction, and the ordinate represents the nitrogen composition (atomic%) in the group V element in the GaInNAs mixed crystal layer. As can be seen from FIG. 4, the nitrogen content in the obtained GaInNAs mixed crystal layer increases when the substrate surface has an off-angle toward the {111} A plane, but the off-axis toward the {111} B plane. It does not increase when it has a corner. The reason for this is probably
The decomposition efficiency of the nitrogen compound in the step consisting of group III atoms formed on the substrate surface when the off angle is directed to the {111} A plane direction is higher than that formed on the substrate surface when the off angle is directed to the {111} B plane direction. This is considered to be higher than that in the step consisting of the group V atom.

The {111} A plane means a {111} plane terminated by a cation atom, and the {111} B plane means a {111} plane terminated by an anion atom. Here, in the case of a group III-V compound semiconductor, a cation atom means a group III element, and an anion atom means a group V element.

From the results shown in FIG.
By using a substrate surface having an off angle of 3 to 20 ° toward the 1｝ A plane, an improvement in the efficiency of nitrogen incorporation into the grown mixed crystal layer can be expected. In particular, 5-1
With a 5 ° off angle, higher nitrogen uptake efficiency can be expected.

Next, except that the off angle of the GaAs substrate surface was variously changed, the quantum well structure as shown in FIG. 2 was made. FIG. 5 shows the relationship between the PL emission intensity and the off angle of the quantum well structure thus obtained.

In FIG. 5, the horizontal axis represents the off-angle of the substrate surface as in FIG. 4, while the vertical axis represents the PL emission intensity (arbitrary unit). As shown in FIG. 5, when the off angle of the substrate surface is in the range of 5 to 15 °, an increase in PL emission intensity is obtained. It is considered that the reason for this is that the effect of the off-angle of the substrate surface improves the nitrogen uptake efficiency during the growth of the mixed crystal layer and the crystallinity of the mixed crystal layer. On the other hand, when the off-angle of the substrate surface becomes 20 ° or more, the PL of the quantum well structure becomes
Conversely, the emission intensity tends to decrease. It is considered that the reason for this is that when the off angle of the substrate surface becomes 20 ° or more, the substrate surface becomes rough. From the above, it is possible to improve the PL emission intensity of the quantum well structure by setting the off angle of the substrate surface in the range of 5 to 15 ° from the {100} plane to the {111} A plane.

In the fourth embodiment, it goes without saying that, other than NH _3, other nitrogen compounds exemplified in the first and second embodiments can be used in the same manner as in the fourth embodiment.

(Embodiment 5) In the fifth embodiment of the present invention,
During the growth of the quantum well layer 3, a nitrogen source (NH _Three)When
Arsenic raw material (As_Two) Is simultaneously provided on the substrate surface at 500 ° C.
Implemented except that it was supplied alternately without being paid
Quantum well as shown in FIG. 1 as in Example 1.
The structure was created. FIG. 6 shows a GaAs substrate {100}.
Timing chart showing the sequence of material supply on the surface
It is. As can be seen from FIG. 6, the GaInNAs quantum
During the growth of the well layer 3, the group III elements Ga and In
In this case, the molecular beam was constantly irradiated on the substrate surface. Only
However, as for the group V element, the arsenic raw material (As
_Two) Is supplied for 11.5 seconds and then 1 second interval
Nitrogen material (NH_Three) Supplied for 3.3 seconds
This sequence is repeated at intervals of 1 second.
Repeated several times.

At this time, the intensity of the raw material molecular beam is Ga = 2.
5 × 10^-7Torr, In = 2.5 × 10^-8Torr,
As_Two= 2.5 × 10^-6Torr, and NH_Three= 5 ×
10 ^-6Set to Torr. With such molecular beam intensity
Therefore, one cycle of the supply sequence of the nitrogen raw material and the arsenic raw material
During the process, almost three molecular layers of GaInNAs layer were grown.
It is.

In the raw material supply as shown in FIG. 6, Ga, In and nitrogen are taken into the crystal during the supply of the nitrogen raw material, and Ga, In and As are supplied between the supply of the arsenic raw material.
Is incorporated into the crystal. At this time, if the thickness of the mixed crystal layer grown in one cycle of the raw material supply sequence is set within a range of about 0.5 to 5 molecular layers, a mixed crystal having a substantially uniform composition can be obtained. In addition, it is possible to control the mixed crystal composition by appropriately adjusting the molecular beam intensity and the supply time of the nitrogen source and the arsenic source.

According to the raw material supply method as in the fifth embodiment, since the nitrogen raw material and the raw material of the group V element other than nitrogen are supplied independently, the other group V element is incorporated with respect to the incorporation of nitrogen into the crystal. Competition with nitrogen can be avoided, and the efficiency of nitrogen incorporation into the crystal can be improved. As a result, in the quantum well structure according to the fifth embodiment, PL is higher than that including a quantum well layer manufactured by simultaneously supplying nitrogen and other group V elements onto the substrate surface.
The emission intensity is increased, ie, high quality GaInNAs /
An AlGaAs-SQW structure was obtained.

In the fifth embodiment, it goes without saying that other nitrogen compounds exemplified in the first and second embodiments can be used besides NH ₃ using nitrogen as a raw material.
Also, in the fifth embodiment, the substrate just
It goes without saying that a substrate surface having an off angle other than the 0 ° surface can be used.

(Embodiment 6) In the sixth embodiment of the present invention, as shown in FIG. 1, as in the case of Embodiment 1, except that the heating temperature of NH _{3 in} the gas cell was changed variously. A quantum well structure was fabricated as described. NH ₃ supplied from the gas supply line to the gas cell was supplied to the crystal growth surface after being heated to a desired temperature through a heating portion inside the gas cell. GaInNAs layer 3
The intensity of each molecular beam during growth, NH ₃ in the original conditions of the heating temperature of the gas is 350 ° C., a nitrogen-containing group V element in our 7.1 atomic% content of In in the III group elements The amount was fixed at 2.5 atomic%. FIG. 7 shows the relationship between the heating temperature of the NH ₃ gas and the PL emission characteristics in the quantum well structure manufactured as described above.

In the graph of FIG. 7, the horizontal axis represents the heating temperature (° C.) of the NH ₃ gas, the left vertical axis represents the PL emission intensity (arbitrary unit), and the right vertical axis represents the PL emission peak. It represents the wavelength (nm). Also,
The broken line curve 7A represents the PL emission wavelength, and the solid line curve 7A.
B represents the PL emission intensity.

As can be seen from the curve 7A, when the heating temperature of the NH ₃ gas is 500 ° C. or higher, the wavelength at the emission intensity peak becomes shorter. This is because, at a heating temperature of 500 ° C. or more, NH ₃ is decomposed to form stable N ₂ molecules, so that the amount of nitrogen atoms taken up on the crystal growth surface is reduced, and the nitrogen in the GaInNAs layer is reduced. It is considered that the content is reduced.

On the other hand, as can be seen from the curve 7B, NH ₃
By heating the gas to 100 ° C. or higher, the PL emission intensity increases, and in particular, a remarkable increase in the emission intensity is obtained within a heating temperature range of 350 to 500 ° C. But N
If the H ₃ gas is heated to a temperature of 500 ° C. or higher, the PL emission intensity sharply decreases as the temperature increases.

The reason that the emission intensity is increased due to the heating of the NH ₃ gas is probably because the thermal energy of the NH ₃ molecule is increased and the migration of the NH ₃ molecule on the crystal growth surface is promoted. It is believed that there is. In particular, it is considered that when the heating temperature of the NH ₃ gas is in the range of 350 to 500 ° C., the effect due to the migration of NH ₃ molecules becomes significant. On the other hand, NH ₃
The reason that the emission intensity decreases when the gas heating temperature is 500 ° C. or higher is that crystal defects caused by deviation from lattice matching conditions with the GaAs substrate are accompanied by a decrease in the rate of incorporation of nitrogen into the crystal. It is considered that this occurs.

To summarize the above, the PL emission wavelength and the GaI
From the viewpoint of the crystallinity of the nNAs layer, the heating temperature of the NH ₃ gas is preferably 500 ° C. or less. GaIn
From the viewpoint of the crystallinity of the NAs layer, the heating temperature of the NH ₃ gas is preferably 100 ° C. or higher, more preferably 350 ° C. or higher.

In the above description of the sixth embodiment, a solid material was used as a material other than nitrogen.
Tertiary butylarsine (TBAs), trisdimethylaminoarsine (TDMAAs), or the like can be used as a raw material, and Ga or In can be used as a group III element raw material.
And the like can also be used.

(Embodiment 7) In the seventh embodiment of the present invention, a mixed crystal layer of a III-V compound semiconductor containing another group V element together with nitrogen uses monomethylhydrazine (MMHy) as a nitrogen source. Grew up.

First, on the {100} plane of the GaAs substrate,
By growing a GaAsN mixed crystal layer using MMHy under various substrate temperatures, the substrate temperature dependence of the nitrogen content in the mixed crystal layer was investigated. At this time, G
Raw material a was supplied in the same manner as in Example 1, but As raw material was tertiary butyl arsine (TBAs) at 600 ° C.
Was supplied as an As ₂ molecular beam by heating. The other crystal growth conditions were set so that the efficiency of nitrogen incorporation into the GaAsN layer was the highest, and the nitrogen content in the group V element became 10 atomic%, which was almost saturated. Also,
Except for the use of NH ₃ instead of MMHy was GaAsN layer was is grown even under the same conditions. FIG. 8 shows the relationship between the nitrogen content in the GaAsN layer thus obtained and the substrate temperature.

In the graph of FIG. 8, the horizontal axis represents the substrate temperature (° C.), and the vertical axis represents the nitrogen composition (atomic%) in the group V element in the GaAsN layer. The solid curve 8A and dashed curve 8B represents a nitrogen composition of GaAsN layer in the case of using the case and NH ₃ with MMHy respectively.

As can be seen from the curve 8A, the MMHy
If the substrate temperature is about 350 ° C or higher and the GaAsN layer
Grow and the nitrogen content increases with increasing substrate temperature.
At about 600 ° C. or more. On the other hand, the curve
As can be seen from FIG. 8B, NH _ThreeWhen using, about 4
The GaAsN layer grows at 50 ° C or higher, and the substrate temperature rises.
Accordingly, the nitrogen content increases and tends to saturate at about 700 ° C.
There is a direction. That is, from the results of FIG.
Of a mixed crystal layer of a group III-V compound semiconductor containing a group V element
In growth, using MMHy as a nitrogen source
Therefore, NH_ThreeAt a lower temperature than when using
It can be seen that a crystal layer can be grown.

FIG. 8 shows the case where TBAs is used to exemplify that various arsenic raw materials can be used. However, the case where a solid raw material is used as in the case of Example 1 as the arsenic raw material is shown. However, the tendency as shown in FIG. 8 hardly changes.

Next, NH ₃ or MMH was used as a nitrogen raw material.
500 ° C. during the growth of quantum well layer 3 using y
A quantum well structure as shown in FIG. 1 was produced in the same manner as in Example 1 except that the quantum well structure was retained. At this time, the composition of the GaInNAs layer 3 is 1.3 μm
In order to obtain the emission wavelength of the above, the In content in the group III element is 7.1 atomic% and the N content in the group V element is 2.5 atomic%.
The conditions of each raw material molecular beam were optimized so as to become atomic%. FIG. 9 shows the PL emission intensity of the quantum well structure thus obtained. In the graph of FIG. 9, the horizontal axis represents the PL emission wavelength (nm) of the quantum well structure, and the vertical axis represents the PL emission intensity (arbitrary unit). And
The solid curve 9A and the dashed curve 9B are respectively MMH
The PL emission intensity when y is used and when NH ₃ is used are shown. As is apparent from the results of FIG.
At a substrate temperature of 00 ° C., MMHy is used instead of NH _3.
PL emission having a high peak and a narrow half width is obtained in a quantum well structure manufactured using
It can be seen that the nNAs quantum well 3 is formed. However, under the condition that the substrate temperature is about 600 ° C. or more, M
A semiconductor laser fabricated using NH ₃ instead of MHy exhibited better PL emission characteristics.

As described above, the reason why the effects of NH ₃ and MMHy are different is that when the substrate temperature is low, the decomposition efficiency of NH ₃ on the crystal growth surface decreases.
It is considered that undecomposed NH ₃ molecules inhibit crystal growth and cause a decrease in crystallinity. On the other hand, under the condition that the substrate temperature is high and both NH ₃ and MMHy can be easily decomposed, when NH ₃ having relatively low reactivity and hardly causing defects on the crystal growth surface is used, This is because good crystallinity can be obtained.

In the above description of the seventh embodiment, MMHy is used as a hydrazine-based compound. However, hydrazine (N ₂ H ₄ ) or dimethylhydrazine (D
MHy) can be used as a preferable nitrogen source in the same substrate temperature range. However, when DMHy is used, carbon may be taken into the crystal as an impurity. Therefore, MMHy containing an alkyl group less than DMHy and N ₂ H ₄ containing no alkyl group are used as impurities in the crystal. It is more preferable in that the uptake of carbon can be suppressed.

(Eighth Embodiment) An eighth embodiment of the present invention is shown in FIG. 1 similarly to the first embodiment, except that the formation conditions of the quantum well layer 3 are changed. Such a quantum well structure was manufactured. That is, in the eighth embodiment, various raw materials having different generation energies as shown in Table 5 are used as the nitrogen raw material, and the substrate uses the respective nitrogen raw materials while the quantum well layer 3 is formed. Optimum temperature was maintained when used. In content in the group III element in the quantum well layer 3 is 7.1 atomic%.
The molecular beam intensity of Ga, In, As, and the nitrogen source was set such that the nitrogen content in the group V element was 2.5 atomic%.

[0080]

[Table 5]

FIG. 10 shows the relationship between the PL emission spectrum intensity and the Gibbs energy of the nitrogen source in the quantum well structure according to the eighth embodiment. That is, the horizontal axis in FIG. 10 indicates the Gibbs energy (kJ / kJ /) of the nitrogen source used for forming the quantum well layer 3 at 298 K.
mol), and the vertical axis represents PL emission intensity (arbitrary unit). As is clear from FIG. 10, the PL emission intensity tends to increase by using a nitrogen source having a smaller Gibbs energy of formation than nitrogen radicals. In particular, by using a nitrogen source having a Gibbs energy of formation smaller than about 100 kJ / mol, a high quality GaInNAs / AlG having a high PL emission intensity can be obtained.
An aAs-SQW structure can be obtained.

In the above description of the eighth embodiment, the just {100} crystal plane is used as the substrate surface. However, even when a substrate surface having an off-angle is used, as shown in FIG. The tendency to stay is almost the same.
Further, as the cladding layers 2 and 4, Al _0.3 Ga _0.7 As
Although a layer was used, Ga could be lattice matched to the GaAs substrate.
Even when InP is used, the tendency shown in FIG. 10 hardly changes.

(Embodiment 9) In the ninth embodiment of the present invention, as in Embodiment 1, MBE using NH ₃ as a nitrogen source and a solid source as a source of other elements is used.
A semiconductor laser including an active layer of GaInNAs-SQW formed by the method was manufactured.

In FIG. 11, such a GaInNA
A semiconductor laser including an s-SQW structure is shown in a schematic sectional view. In this semiconductor laser, on an n-type GaAs substrate 1 having a just {100} crystal surface,
a 0.5 μm thick buffer layer 6 made of n-type GaAs,
n-type cladding layer 7 of n-type Al _0.3 Ga _0.7 As having a thickness of 1 μm, n-type guide layer 8 of n-type GaAs having a thickness of 0.15 μm, undoped Ga _0.929 In _0.071 N
SQW layer 9 of _0.025 As _0.975 , p-type guide layer 10 of p-type GaAs having a thickness of 0.15 μm, p-type Al
0.5 μm thick p-type cladding layer 11 made of _0.3 Ga _0.7 As and 0.1 μm thick made of p-type GaAs
Were sequentially grown by MBE. In growing these layers, the substrate temperature, NH
_3. The same conditions as in Example 1 were used for the gas heating temperature and the like. Ga _0.929 In _0.071 N
_In the growth of _0.025 As _0.975 -SQW layer 9, Table 1
The growth condition shown in Condition 2 in the middle was adopted.

After the respective semiconductor layers are grown and laminated in this way, a part of the p-type Al _0.3 Ga _0.7 As clad layer 11 and a part of the p-type GaAs contact layer 12 are etched into a mesa stripe by wet etching. The insulating layer 13 made of polyamide was removed so as to cover the etched portion. further,
The upper electrode 14 and the lower electrode 15 were formed, and a ridge stripe type semiconductor laser as shown in FIG. 11 was manufactured.

In this semiconductor laser, λ /
1.3 μm at room temperature with coating applied
Continuous oscillation of light having a wavelength of m was confirmed. The oscillation threshold was 15 mA, and the efficiency was 0.35 W / A. Also,
The characteristic temperature of the conventional semiconductor laser is about 50K, but in the semiconductor laser of this embodiment, the characteristic temperature has been improved to 170K in the range from room temperature to 85 ° C (that is, the characteristic temperature required for the laser oscillation accompanying the temperature rise). Current increase is reduced). Furthermore, a reliability test was performed by driving the semiconductor laser of this example at 60 ° C. with an output of 10 mW. As a result, a life of 5000 hours or more (time until the drive current increases by 20% from the initial current)
Was confirmed.

As described above, by using the method of manufacturing a compound semiconductor according to the present invention, a semiconductor laser for optical communication having a high characteristic temperature, a low oscillation threshold, and high reliability and high performance can be obtained. . In the ninth embodiment, NH ₃ was used as a nitrogen source. However, as in the other embodiments, dimethylamine, MMHy, etc.
Even when a nitrogen compound having a Gibbs energy of formation smaller than kJ / mol is used, a semiconductor laser having similar performance can be obtained. Further, by changing the composition of the GaInNAs active layer, a semiconductor laser having similarly excellent performance even in a wavelength band of 1.55 μm can be obtained.

It should be noted that M described in the above embodiment has been described.
The BE method includes the GSMBE method, the CBE method, and the MO method as described above.
It is used as a broad concept including the MBE method, etc.
A gas such as AsH ₃ can also be used as a group III element material, and trimethyl gallium (TMGa), trimethyl aluminum (TMAl),
Alternatively, an organic metal such as trimethylindium (TMIn) can be used. In short, a compound semiconductor crystal is grown by irradiating a substrate with a source molecular beam in a crystal growth chamber evacuated so that the mean free path of the source molecule is equal to or longer than the distance between the substrate and the molecular beam source. If the MBE method described above is used, each raw material molecule causes a reaction only on the crystal growth surface, so that various raw materials can be applied to the present invention.

In each of the various embodiments described above, as the III-V compound semiconductor containing nitrogen and other group V elements, the N concentration in the group V element is equal to or less than 3.5 atomic% and the GaAs
GaInNAs mixed crystal and N concentration that can be lattice-matched to the s substrate =
GaIn which is 3 atomic% and can be lattice-matched to a GaP substrate
Although NP mixed crystals were used, the present invention is not limited to GaInNAs and GaInNP mixed crystals having various other nitrogen concentrations, as well as nitrogen and other group V elements A
s, at least one of P, Sb, and Bi;
The present invention can be applied to the growth of a mixed crystal layer of a III-V compound semiconductor containing at least one of B, Al, Ga, In, and Tl as a group II element.

[0090]

As described above, according to the present invention, III-III containing at least one or more other group V elements together with nitrogen.
In MBE growth of a mixed crystal layer of a group V compound semiconductor, a high-quality mixed crystal layer can be obtained without generating crystal defects. Therefore, it is possible to provide a high-performance optoelectronic device by utilizing such a high-quality mixed crystal layer.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view for explaining a quantum well structure manufactured in Example 1 of the present invention.

FIG. 2 is a graph showing a relationship between a nitrogen concentration in a quantum well layer and a PL emission intensity in the quantum well structure manufactured in Example 1 of the present invention.

FIG. 3 is a graph showing a PL emission spectrum of a quantum well structure manufactured in Example 2 of the present invention.

FIG. 4 shows GaIn fabricated in Example 4 of the present invention.
4 is a graph showing a relationship between a nitrogen composition of an NAs film and an off angle from a {100} plane of a substrate surface.

FIG. 5 is a graph showing the relationship between the PL emission intensity and the off-angle of the substrate surface in the quantum well structure manufactured in Example 4 of the present invention.

FIG. 6 is a timing chart for explaining a raw material supply sequence in growing a GaInNAs mixed crystal layer according to a fifth embodiment of the present invention.

FIG. 7 is a graph showing the relationship between the heating temperature of NH ₃ source gas and the wavelength and intensity of PL emission in the quantum well structure according to Example 6 of the present invention.

FIG. 8 shows GaAs formed in Example 7 of the present invention.
4 is a graph showing a relationship between a nitrogen composition contained in an N layer and a substrate temperature.

FIG. 9 is a graph showing the relationship between wavelength and intensity of PL light emission in a quantum well structure manufactured according to Example 7.

FIG. 10 is a graph showing a relationship between PL emission intensity of a quantum well structure manufactured in Example 8 of the present invention and Gibbs energy of generation of a nitrogen source.

FIG. 11 is a schematic sectional view showing a semiconductor laser manufactured in Example 9 of the present invention.

[Explanation of symbols]

 Reference Signs List 1 GaAs substrate 2 AlGaAs lower cladding layer 3 GaInNAs-SQW layer 4 AlGaAs upper cladding layer 5 GaAs cap layer 6 n-type GaAs buffer layer 7 n-type AlGaAs cladding layer 8 n-type GaAs guide layer 9 GaInNAs quantum well layer 10 p-type GaAs guide Layer 11 p-type AlGaAs cladding layer 12 p-type GaAs contact layer 13 polyamide insulating layer 14 upper electrode 15 lower electrode

Claims (14)

[Claims] At least one additional source of nitrogen along with nitrogen is applied to the substrate by irradiating the source molecular beam to the substrate in a crystal growth chamber evacuated so that the mean free path of the source molecule is larger than the distance between the substrate and the molecular beam source. II containing two Group V elements
When a group IV compound semiconductor crystal is grown, a nitrogen compound is used as a source of nitrogen, and the molecules of the nitrogen compound decompose after reaching the surface of the substrate so that only nitrogen atoms are present in the semiconductor crystal. A method for producing a compound semiconductor, which is incorporated. 2. The method according to claim 1, wherein a hydride of nitrogen is used as the nitrogen source. 3. The method according to claim 2, wherein ammonia is used as the hydride of nitrogen. 4. The method according to claim 3, wherein the substrate is kept at a temperature in the range of 500 to 700 ° C. during the growth of the semiconductor crystal. 5. The method according to claim 3, wherein the substrate is irradiated with the ammonia after being heated to a temperature in the range of 350 to 500 ° C. 6. The method according to claim 2, wherein hydrazine is used as the hydride of nitrogen. 7. The method according to claim 1, wherein an alkylated nitrogen is used as the nitrogen source. 8. The method according to claim 7, wherein an alkylamine compound is used as the alkylated nitrogen. 9. The method according to claim 8, wherein the substrate is kept at a temperature in a range of 400 to 750 ° C. during the growth of the semiconductor crystal. 10. The method according to claim 2, wherein an alkylated hydrazine is used as the nitrogen source. 11. The substrate according to claim 1, wherein the substrate is made of a compound semiconductor having a zinc blende type crystal structure, and the substrate has a predetermined off angle from a {100} plane toward a {111} A plane. Item 10. The method for producing a compound semiconductor according to any one of Items 1 to 10. 12. The method according to claim 11, wherein the off-angle is in a range of 5 ° to 15 °. 13. When supplying a group V element onto the substrate, the step of irradiating the substrate with a nitrogen source and the step of irradiating the substrate with a group V element other than nitrogen are alternately performed without overlapping. The method for producing a compound semiconductor according to claim 1, wherein: 14. The method according to claim 1, wherein the nitrogen material is 100 kJ / m
14. The method of manufacturing a compound semiconductor according to claim 1, wherein a nitrogen compound having a Gibbs energy of formation smaller than ol is used.