JP2009038253A - Method of forming iii-v compound semiconductor layer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of forming a III-V compound semiconductor layer capable of reducing a hydrogen concentration in a III-V compound semiconductor crystal containing Ga (group III) and arsenic and nitrogen (group V) and reducing pile-up on a regrowth interface as well. <P>SOLUTION: After elevating the temperature of a substrate 31 to a first temperature T1 in an atmosphere containing AsH<SB>3</SB>, the substrate 31 is thermally cleaned at the first temperature T1 while making the AsH<SB>3</SB>sufficiently smaller than a supply amount 5 to 15 sccm when growing a crystal using the AsH<SB>3</SB>flow. After the thermal treatment, the supply of the AsH<SB>3</SB>is stopped and metal arsenic is supplied. In an MBE apparatus 13, first to third III-V compound semiconductor layers 33, 35 and 37 are grown on the substrate 31 using metal As. The first III-V compound semiconductor layer 33 is GaAs, the second III-V compound semiconductor layer 35 is GaInNAs, and the third III-V compound semiconductor layer 37 is GaAs. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for forming a III-V compound semiconductor layer.

Non-Patent Document 1 describes that GaInNAs is grown by molecular beam epitaxy (MBE). In this growth, solid arsenic was used as the As source. Further, in the GaInNAs growth by the gas source MBE using AsH ₃ , hydrogen at a level of 1 × 10 ¹⁸ cm ⁻³ was taken into GaInNAs. In the gas source MBE, the AsH ₃ flow rate is 5 to 15 sccm.
J. Cryst. Growth, 227-228 (2001), p521-526

Hydrogen is taken into GaInNAs by gas source MBE growth using AsH ₃ . In contrast, in GaInNAs by solid source MBE growth using a solid As source, the hydrogen concentration is below the detection limit of SIMS. However, in MBE using a solid As source, according to the knowledge of the inventors, impurities different from the constituent elements of the III-V compound semiconductor pile up at the regrowth interface.

  The present invention has been made in view of such circumstances, and it is possible to reduce the hydrogen concentration in a III-V compound semiconductor crystal containing Ga as a group III and arsenic and nitrogen as a group V, and regrowth. It is an object of the present invention to provide a method for forming a III-V compound semiconductor layer that can reduce pileup at the interface.

One aspect of the present invention is a method for forming a III-V compound semiconductor layer by molecular beam epitaxy. In this method, (a) a substrate having a surface made of a III-V compound semiconductor containing arsenic as a group V is placed in a molecular beam epitaxy apparatus, and then the temperature of the substrate is set to a first temperature in an atmosphere containing AsH _3. (B) a step of heat-treating the substrate at the first temperature in an atmosphere containing AsH ₃ , (c) a step of stopping the supply of AsH ₃ after the heat treatment, ( d) a step of growing a first III-V compound semiconductor layer at a second temperature using metal As in the molecular beam epitaxy apparatus; and (e) a process using metal As in the molecular beam epitaxy apparatus. A step of growing a second III-V compound semiconductor layer at a third temperature, wherein one of the first and second III-V compound semiconductor layers includes Ga as Group III and arsenic as Group V. 1 semiconductor, the first and The other second III-V compound semiconductor layer is made of a second semiconductor containing arsenic and nitrogen as Ga and group V as a Group III.

According to this invention, since the temperature of the substrate is raised to the first temperature in an atmosphere containing AsH ₃ , arsenic escape from the surface of the III-V compound semiconductor containing arsenic as a V group can be reduced. In addition, since the substrate is heat-treated in an atmosphere containing AsH ₃ and thermal cleaning is performed before growth, contamination on the substrate surface can be removed. Furthermore, since the first and second III-V compound semiconductor layers are grown using metal As in a molecular beam epitaxy apparatus, deterioration in quality due to bonding between hydrogen and nitrogen in the film is suppressed.

In the method according to the present invention, in the step of stopping the supply of AsH _3, after the temperature is lowered to the lower than the first temperature fourth temperature, it is performed stopping supply of AsH _3, the AsH ₃ In the step of stopping the supply, it is preferable to start the supply of the metal As and raise the temperature to the second temperature higher than the fourth temperature after the supply of the metal As. According to the present invention, the roughness of the semiconductor surface due to arsenic loss can be reduced.

In the method according to the present invention, it is preferable that metal As is supplied in addition to AsH ₃ in the step of heat-treating the substrate, and metal As is supplied in the step of stopping the supply of AsH _3. .

According to the present invention, since the arsenic atmosphere is maintained by the metal arsenic when the supply of AsH ₃ is stopped after the heat treatment, the roughness of the semiconductor surface due to arsenic removal can be reduced.

  In the method according to the present invention, the second semiconductor preferably contains Ga and In as a group III and arsenic and nitrogen as a group V. According to this method, in a semiconductor containing Ga and In as group III and arsenic and nitrogen as group V, it is possible to suppress a decrease in optical characteristics due to the bond between hydrogen and nitrogen.

  In the method according to the present invention, the second semiconductor may include any of GaInNAs, GaInNAsSb, GaNAs, and GaNASSb. In the method according to the present invention, the first semiconductor may include any one of GaAs, GaNAs, and GaInNAs. However, the first semiconductor has a band gap energy larger than that of the second semiconductor.

  In the method according to the present invention, the second semiconductor can be used for a well layer of a quantum well structure of a semiconductor optical device. According to the present invention, not only an active layer composed of a single layer film but also an active layer having a single quantum well structure and a multiple quantum well structure can reduce the roughness of the semiconductor surface due to arsenic removal and generate a non-luminescent center. Can be suppressed.

  The above and other objects, features, and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments of the present invention, which proceeds with reference to the accompanying drawings.

  As described above, according to the present invention, a method for forming a III-V compound semiconductor layer is provided. According to this method, a III-V compound semiconductor containing Ga as Group III and arsenic and nitrogen as Group V is provided. It is possible to reduce the hydrogen concentration in the crystal and to reduce pile-up at the regrowth interface.

  The knowledge of the present invention can be easily understood by considering the following detailed description with reference to the accompanying drawings shown as examples. Next, embodiments of the method for forming a III-V compound semiconductor layer of the present invention will be described with reference to the accompanying drawings. Where possible, the same parts are denoted by the same reference numerals.

FIG. 1 is a drawing showing an example of a crystal growth apparatus for manufacturing a semiconductor film. FIG. 2 is a schematic diagram showing main steps of a method for forming a III-V compound semiconductor layer according to the present embodiment. As a crystal growth apparatus, a molecular beam epitaxy (MBE) apparatus 13 as shown in FIG. 1 is used. More specifically, the MBE apparatus 13 includes a chamber 13a, a holder 13b for holding the substrate W, a source 13c, a monitor apparatus 13d such as RHEED, and an exhaust port 13e to which a vacuum pump is connected. The source 13 c includes an AsH ₃ source 17 for heat treatment, a group V source sources 19 and 21, a group III source sources 23 and 25, and other sources 27 and 29. The group V raw material source 19 has a valve cracker cell for supplying metal arsenic. The group V source 21 having a radical gun for supplying nitrogen supplies gallium (Ga), and the group III source 25 supplies indium (In). Other sources 27, 29 are used, for example, for n-type dopants, p-type dopants, or other source sources.

The main steps of the method for forming the III-V compound semiconductor layer will be described with reference to FIG. First, a substrate having a surface made of a III-V compound semiconductor containing arsenic as a group V is arranged in the MBE apparatus 13. A substrate 31 is disposed on the holder 13b. In this embodiment, an n-type GaAs substrate is used as the substrate 31, but a p-type GaAs substrate, a non-doped GaAs substrate, or the like can also be used. However, the substrate 31 is not limited to this, and one or a plurality of III-V compound semiconductor layers are grown on the semiconductor substrate so as to have a surface made of a III-V compound semiconductor containing arsenic as a V group. The formed epitaxial substrate can be used as a substrate. Next, as shown in FIG. 2A, the temperature of the substrate 31 is raised toward the first temperature T1 in an atmosphere containing AsH ₃ . Since the temperature of the substrate 31 is increased in an atmosphere containing AsH ₃ , arsenic escape from the surface of the III-V compound semiconductor can be reduced. As shown in FIG. 2B, the substrate 31 is heat-treated at the first temperature T1 in an atmosphere containing AsH ₃ . When the diffraction pattern is observed using a surface observation device such as RHEED, if a 2 × 4 times diffraction pattern is observed, the natural oxide film is removed. Since thermal cleaning is performed before growth by heat treatment of the substrate 31 in an atmosphere containing AsH ₃ , contamination on the substrate surface can be removed. Therefore, pileup of impurities such as oxygen and carbon on the substrate surface is reduced. The first temperature T1 is, for example, 580 degrees Celsius, and the temperature range may be 550 degrees Celsius to 620 degrees Celsius. For example, thermal cleaning can be performed with a supply amount of AsH ₃ of about 1 sccm. This supply amount is sufficiently smaller than the supply amount (supply amount in the gas source MBE) at the time of crystal growth using AsH ₃ , for example, 5 to 15 sccm. In addition, since the crystal growth is not performed in this heat treatment, hydrogen is not taken up during the growth. Furthermore, the active hydrogen generated during the heat treatment can be sufficiently exhausted before crystal growth is started.

After this heat treatment, the supply of AsH ₃ is stopped. As shown in FIG. 2 (c), metal arsenic is supplied together with this stop. A sufficient period is taken after the supply of AsH ₃ is stopped to ensure a change of atmosphere (eg removal of active hydrogen). This reduces the amount of hydrogen remaining in the chamber.

  Next, the first III-V compound semiconductor layer 33 is grown on the substrate 31 at the second temperature T2 using the metal As in the MBE apparatus 13. The first III-V compound semiconductor layer 33 is made of a first semiconductor containing Ga as a group III and arsenic as a group V, and is made of, for example, GaAs. In this embodiment, GaAs is grown by supplying gallium in addition to supplying metal arsenic. The second temperature T2 is, for example, 580 degrees Celsius, and the temperature range can be 500 degrees Celsius to 600 degrees Celsius. If necessary, the substrate temperature can be gradually changed during the growth from the second temperature T2 to the third temperature T3 for subsequent growth. This is because impurities may pile up at the interface when the growth is interrupted and the temperature is changed.

  Subsequently, the second III-V compound semiconductor layer 35 is grown at the third temperature using the metal As in the MBE apparatus 13. The second III-V compound semiconductor layer 35 is made of a second semiconductor containing Ga as a group III and arsenic and nitrogen as a group V, for example, GaInNAs. In this embodiment, GaInNAs is grown by supplying gallium, indium and nitrogen in addition to metal arsenic. The third temperature T3 is, for example, 450 degrees Celsius, and the temperature range can be 350 degrees Celsius to 480 degrees Celsius.

  Thereafter, a third III-V compound semiconductor layer 37 is grown on the substrate 31 using metal As in the MBE apparatus 13. This growth can be performed at a temperature T5, for example. The third III-V compound semiconductor layer 37 is made of a third semiconductor containing Ga as a group III and arsenic as a group V, for example, GaAs. In this embodiment, GaAs is grown by supplying gallium in addition to supplying metal arsenic. The growth temperature T5 is, for example, 580 degrees Celsius, and the temperature range can be 500 degrees Celsius to 600 degrees Celsius. If necessary, the substrate temperature can be gradually changed from the third temperature T3 to the growth temperature T5 during the growth. This is because impurities may pile up when the growth is interrupted and the temperature is changed.

  Since the first to third III-V compound semiconductor layers 33, 35, and 37 are grown using the metal As in the MBE apparatus 13, the bond between nitrogen and hydrogen in the second III-V compound semiconductor layer 35 is achieved. The resulting deterioration in quality is suppressed.

  The first and third semiconductors can include, for example, any of GaAs, GaNAs, and GaInNAs. However, the first and third semiconductors have a band gap energy larger than that of the second semiconductor. Preferably, the second semiconductor of the second III-V compound semiconductor layer 35 contains Ga and In as group III and arsenic and nitrogen as group V. In a semiconductor containing Ga and In as group III and arsenic and nitrogen as group V, generation of a non-radiative center due to a bond between hydrogen and nitrogen can be suppressed. In addition, the second semiconductor can include, for example, any of GaInNAs, GaInNAsSb, GaNAs, and GaNASSb.

In the step of stopping the supply of AsH ₃ after the heat treatment, it is preferable to stop the supply of AsH ₃ after the substrate temperature is lowered to the fourth temperature T4 lower than the first temperature T1. In this step, it is preferable that the supply of the metal As is started and the substrate temperature is raised to a second temperature T2 higher than the third temperature T3 thereafter. The background H concentration can be lowered by raising the temperature after exhausting AsH ₃ sufficiently. By providing a period during which AsH ₃ and As are not supplied, it is possible to confirm that AsH ₃ has been sufficiently exhausted based on the degree of vacuum before raising the temperature. Therefore, it is preferable to provide a time during which As is not supplied.
According to this method, switching from AsH ₃ to metal As is performed at a temperature lower than the heat treatment temperature and the growth temperature, so that the roughness of the semiconductor surface due to arsenic loss can be reduced. The fourth temperature T4 is, for example, 200 degrees Celsius, and the temperature range may be 100 degrees Celsius to 450 degrees Celsius.

Alternatively, in the heat treatment step, metal As can be supplied in addition to AsH ₃ . Thermal cleaning is performed by the action of active hydrogen generated by the decomposition of AsH ₃ . Further, in the step of stopping supply of AsH _3, it is preferable that supply metal As in addition to AsH _3. Since the arsenic atmosphere is maintained by metal arsenic when the supply of AsH ₃ is stopped after the heat treatment, the roughness of the semiconductor surface due to arsenic removal can be reduced. Further, it is not necessary to raise or lower the temperature in order to switch the arsenic supply source by supplying metal arsenic.

(Example)
A GaAs substrate was introduced into the MBE growth chamber, and the substrate temperature was raised to 580 degrees Celsius while flowing AsH ₃ at a supply rate of 1 sccm. Thermal cleaning was performed by holding at this temperature for 20 minutes. The degree of vacuum of the chamber was 1 × 10 ⁻⁵ Torr (converted to 1 Torr = 133.3 Pa). When the diffraction pattern was observed with RHEED, the natural oxide film was removed and a 2 × 4 times diffraction pattern was observed. After the substrate temperature was lowered to 200 degrees Celsius, the supply of AsH ₃ was stopped and the metal As raw material valve was opened. The flux strength of metal arsenic was set to 2 × 10 ⁻⁵ Torr. The substrate temperature was raised to 580 degrees Celsius while supplying this As flux.

  After the temperature was sufficiently stabilized, in addition to As flux, the Ga shutter was opened and gallium flux was supplied to start the growth of the GaAs buffer. A 0.5 μm GaAs buffer layer was grown. While performing this growth, the substrate temperature was lowered to 450 degrees Celsius at a rate of 1 degree / second per second. After the temperature was sufficiently stabilized, the In cell shutter and the N radical gun shutter were opened, and a 7 nm GaInNAs layer was grown by supplying In flux and N flux. An In-cell shutter and an N radical gun shutter were closed, and a GaAs cap layer of 0.1 μm was grown to prepare an epitaxial substrate A. While performing this growth, the substrate temperature was raised to 580 degrees Celsius at a rate of once per second (1 deg / sec) while performing this growth.

In an experiment different from this experiment, metal arsenic was supplied so that the degree of vacuum in the chamber was 2 × 10 ⁻⁵ Torr, and the substrate was maintained at a substrate temperature of 580 degrees Celsius for 20 minutes for thermal cleaning. . When the RHEED diffraction pattern was observed, the natural oxide film was removed, and a 2 × 4 times diffraction pattern was observed. Thereafter, similarly, a 0.5 μm GaAs buffer layer, a 7 nm GaInNAs layer, and a 0.1 μm GaAs cap layer were grown to produce an epitaxial substrate R.

When the photoluminescence (PL) spectrum by Ar laser excitation was measured, the PL spectrum intensity of the epitaxial substrate A (AsH ₃ cleaning) was 6 times the PL spectrum intensity of the epitaxial substrate R (metal As cleaning). Further, the impurity element at the epitaxial film-substrate interface was investigated by SIMS analysis. The result of the main impurity concentration piled up at the interface is shown.

Epitaxial substrate R Epitaxial substrate A
Oxygen (O): 2.39 × 10 ¹⁹ 4.80 × 10 ¹⁷
Carbon (C): 9.18 × 10 ¹⁸ 2.61 × 10 ¹⁸
Sulfur (S): 8.24 × 10 ¹⁶ 2.30 × 10 ¹⁶
The unit is atoms / cc.
Impurity pileup in the AsH ₃ cleaning epitaxial substrate A is reduced compared to the metal As cleaning epitaxial substrate R.

In the cleaning of the AsH ₃ atmosphere in comparison with the cleaning of the metal As atmosphere, cleaning of the substrate surface is promoted by active hydrogen generated by thermal decomposition of AsH ₃ , impurities such as carbon and oxygen are reduced, and pile-up is reduced. .

  Therefore, impurities piled up at the epitaxial layer-substrate interface generate non-radiative recombination centers, thereby reducing the PL spectral intensity. On the other hand, active hydrogen is taken into the crystal during epitaxial growth, particularly during growth of GaInNAs in which N radicals are present, thereby reducing the optical characteristics of the GaInNAs active layer.

When the AsH ₃ flow rate is reduced to 0 at a high temperature, As is released from the substrate surface and surface roughness occurs. In order to avoid arsenic loss, it is necessary to lower the temperature once prior to crystal growth and switch the supply of AsH _{3 to} the supply of metal As, as in the above example. Alternatively, the supply of AsH ₃ may be stopped after flowing AsH ₃ and metal As and performing thermal cleaning. In order to avoid the active hydrogen from being mixed into the crystal from AsH ₃ remaining in the chamber, it is particularly preferable to allow sufficient time for exhausting after the AsH ₃ supply is stopped before starting crystal growth. preferable.

Further, the growth may be performed in a vacuum chamber different from the processing chamber for surface cleaning with AsH ₃ . Surface cleaning with AsH ₃ has a large cleaning effect with active hydrogen. Although cleaning with H ₂ plasma can achieve the same effect, plasma processing can be adversely affected by plasma damage to the substrate surface (for example, the substrate surface is passivated with hydrogen). It is not easy to set. In addition, since plasma control depends on the state of the apparatus, the plasma state may become unstable. Therefore, the treatment with AsH ₃ gas is excellent in terms of process stability, reproducibility, and maintenance of the apparatus.

  As will be understood from the following description, the second semiconductor can be used for the well layer of the quantum well structure of the semiconductor optical device. In addition to the active layer formed of a single layer film, the active surface of the single quantum well structure and the multiple quantum well structure can reduce the roughness of the semiconductor surface due to arsenic removal and suppress the generation of non-luminescent centers.

  FIG. 3 is a process flow showing the main processes in the method for manufacturing a semiconductor light emitting device. In step S101, a Si-doped GaAs substrate is prepared. For the subsequent crystal growth, a metal organic vapor phase epitaxy (MOVPE) method is used. TEGa is used as the Ga source gas. TMAl (trimethylaluminum) was used as the Al source gas. TMIn is used as the In source gas. TBAs is used as the As source gas. DMHy is used as the N source gas. If necessary, an n-type GaAs buffer layer having a thickness of 200 nm is grown on the GaAs substrate. In step S103, an n-type AlGaAs cladding layer having a thickness of 1.5 μm is grown on the GaAs buffer layer. The product is referred to as the epitaxial substrate W1 through the steps so far.

In step S105, an active layer is grown on the AlGaAs cladding layer of the epitaxial substrate 1. Specifically, after performing the heat treatment already described, an active layer is grown using an MBE apparatus. In step S105-1, after the epitaxial substrate W1 is introduced into the MBE apparatus, the substrate temperature is raised to the heat treatment temperature while supplying AsH ₃ . In step S105-2, heat treatment is performed in an AsH ₃ atmosphere to clean the surface of the epitaxial substrate W1. In Step S105-3, the supply is changed from AsH ₃ supply to metal arsenic supply. In step S105-4, an undoped GaAs guide layer having a thickness of 140 nm is grown while supplying gallium and metal arsenic. In step S105-5, undoped 7 nm in thickness while supplying gallium, indium, nitrogen, and metal arsenic. In Step S105-6, an undoped GaAs barrier layer having a thickness of 8 nm is grown while supplying metal arsenic. In Step S105-7, gallium, indium, nitrogen and metal arsenic are supplied. Then, an undoped GaInNAs well layer having a thickness of 7 nm is grown. In step S105-8, an undoped GaAs guide layer having a thickness of 140 nm is grown while supplying metal arsenic. Thereby, an active layer is formed. The product is referred to as the epitaxial substrate W2 through the steps so far.

  In step S107, a p-type AlGaAs cladding layer having a thickness of 1.5 μm is grown on the active layer of the epitaxial substrate W2 using a metal organic chemical vapor deposition reactor. In step S109, a p-type GaAs contact layer is grown on the AlGaAs cladding layer.

  If necessary, in step S111, annealing is performed for 20 minutes while supplying tertiary butylarsine in a metal organic chemical vapor deposition reactor. The annealing temperature is 650 degrees Celsius.

  In step 113, an anode and a cathode are formed. In this manner, a light emitting diode and a semiconductor laser can be manufactured.

  While the principles of the invention have been illustrated and described in the preferred embodiments, it will be appreciated by those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. The present invention is not limited to the specific configuration disclosed in the present embodiment. In this embodiment, a semiconductor optical element such as a semiconductor laser is described as an example, but it can also be applied to an electronic device such as a HEMT. We therefore claim all modifications and changes that come within the scope and spirit of the following claims.

FIG. 1 is a drawing showing an example of a crystal growth apparatus for manufacturing a semiconductor film. FIG. 2 is a schematic diagram showing main steps of a method for forming a III-V compound semiconductor layer according to the present embodiment. FIG. 3 is a process flow showing the main processes in the method for manufacturing a semiconductor light emitting device.

Explanation of symbols

13 ... molecular beam epitaxy (MBE) device, 13a ... chamber, 13b ... holder, 13c ... source, 13d ... monitor device, 13e ... exhaust port, 17 ... AsH ₃ source for heat treatment, 19, 21 ... V group material source, 23, 25 ... Group III source, 27, 29 ... Other sources, 31 ... Substrate, 33 ... First III-V compound semiconductor layer, 35 ... Second III-V compound semiconductor layer, 37 ... Third III-V compound semiconductor layer

Claims (6)

A method of forming a III-V compound semiconductor layer by molecular beam epitaxy,
Placing a substrate having a surface made of a III-V compound semiconductor containing arsenic as a group V in a molecular beam epitaxy apparatus, and then raising the temperature of the substrate to a first temperature in an atmosphere containing AsH ₃ ;
Heat treating the substrate at the first temperature in an atmosphere containing AsH ₃ ;
After the heat treatment, stopping the supply of AsH ₃ ;
Growing a first III-V compound semiconductor layer at a second temperature using metal As in the molecular beam epitaxy apparatus;
Growing a second III-V compound semiconductor layer at a third temperature using metal As in the molecular beam epitaxy apparatus,
One of the first and second III-V compound semiconductor layers is composed of a first semiconductor containing Ga as group III and arsenic as group V;
The other of the first and second III-V compound semiconductor layers comprises a second semiconductor containing Ga as group III and arsenic and nitrogen as group V. In the step of stopping the supply of AsH _3, after the temperature is lowered to the lower than the first temperature fourth temperature, it is performed stopping supply of AsH _3,
The step of stopping the supply of AsH ₃ starts the supply of metal As and raises the temperature to the second temperature higher than the fourth temperature after the supply of metal As. Item 2. The method according to Item 1. In the step of annealing the substrate, and supplying a metal As in addition to AsH _3, and in the step of stopping the supply of AsH _3, metal As is supplied, it in claim 1, wherein The described method.   4. The method according to claim 1, wherein the second semiconductor includes any one of GaInNAs, GaInNAsSb, GaNAs, and GaNASSb. 5.   The method according to claim 4, wherein the first semiconductor includes any one of GaAs, GaNAs, and GaInNAs.   The method according to claim 4, wherein the second semiconductor is used for a well layer of a quantum well structure of a semiconductor optical device.

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