Resonant type optical semiconductor element and method for manufacturing semiconductor optical semiconductor element

Abstract

To provide: a resonant type optical semiconductor element capable of achieving a central wavelength of 2.0 μm or more in a light emitting / receiving element having a resonant structure on a GaAs or AlGaAs substrate; and a method for manufacturing the resonant type optical semiconductor element.SOLUTION: A resonant type optical semiconductor element according to the present invention includes: a GaAs or AlGaAs substrate; a first Bragg reflector which is formed by alternately stacking AlxGa1-xAs (0≤x≤1) and AlyGa1-yAs (0≤y≤1) on the substrate; an InAs buffer layer formed on the first Bragg reflector; an active layer containing InAs1-zSbz (z≥0) formed on the InAs buffer layer; and a second Bragg reflector formed on the active layer.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a resonant type semiconductor optical element and a method for manufacturing a resonant type semiconductor optical element. [Background technology]

[0002] 2. Description of the Related Art Light-receiving and light-emitting elements having a wavelength band in the mid-infrared region (for example, wavelengths of 3 μm to 5 μm) are widely used in applications such as sensors and gas analysis.

[0003] The active layer of such light-receiving and light-emitting devices uses an InGaAsSb-based III-V group semiconductor containing In, As, and Sb. Conventionally, when epitaxially growing an InGaAsSb-based III-V group semiconductor layer such as an InAsSb layer, an InAs substrate or a GaSb substrate was used as the growth substrate for lattice matching. However, in recent years, the use of an inexpensive GaAs substrate that does not lattice match with the InAsSb layer has also been considered.

[0004] Patent Document 1 describes a surface-type optical semiconductor element having an emission wavelength of about 1.5 μm, in which an InGaAs active layer is formed between a first semiconductor distributed reflector and a second semiconductor distributed reflector made of AlGaAs on a GaAs or AlGaAs substrate, with an InP buffer layer grown at low temperature interposed between them.

[0005] Patent Document 2 describes a method for manufacturing a template substrate in which a lattice-mismatched InAs layer is formed on a GaAs substrate. It describes that a template substrate of relatively high quality can be formed by growing the InAs layer in two steps, a first growth step in which the InAs layer is grown at a growth temperature of 400° C. or more and less than 600° C., and a second growth step in which the InAs layer is grown at a growth temperature of 600° C. or more and less than 750° C. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 05-291698 [Patent Document 2] JP 2022-126520 A Summary of the Invention [Problem to be solved by the invention]

[0007] In an optical semiconductor element having a resonant structure as described in Patent Document 1, an optical receiving and emitting wavelength of 1.7 μm or more or 2.0 μm or more is considered difficult to realize because it is necessary to use an active layer with a composition close to InAs, which is not lattice-matched with the GaAs substrate. Even when a buffer layer made of InP grown at low temperature is used, the occurrence of dislocations or internal stress caused by the lattice constant difference between GaAs and InAs cannot be sufficiently eliminated. Furthermore, good flatness is required to form a resonant structure using a reflecting mirror, but it is difficult to form a layer with a large lattice constant difference with good flatness.

[0008] An object of the present invention is to provide a resonant type optical semiconductor element having a central wavelength of 2.0 μm or more and a resonant structure on a GaAs or AlGaAs substrate, and a method for manufacturing the resonant type optical semiconductor element. [Means for solving the problem]

[0009] In order to achieve the above object, the inventors conducted extensive research and have found that after an InAs buffer layer is grown at low temperature on a GaAs or AlGaAs substrate, an active layer is grown at high temperature, and then in the process of forming the Bragg reflector on the active layer, a two-stage growth process is performed, consisting of a first film formation process in which growth of at least the first layer is started at low temperature, and a second film formation process in which the remaining layers are grown at high temperature, thereby enabling the active layer and second Bragg reflector to be grown with good flatness, thereby obtaining a resonant optical semiconductor element.

[0010] That is, the gist and configuration of the present invention are as follows. (1) A GaAs or AlGaAs substrate and an Al x Ga 1-x As(0≦x≦1) and Aly Ga 1-y a first Bragg reflector in which InAs and InAs (0≦y≦1) are alternately stacked; an InAs buffer layer formed on the first Bragg reflector; and an InAs buffer layer formed on the InAs buffer layer. 1-z Sb z (z≧0) and an Al layer formed on the active layer. v Ga 1-v As(0≦v≦1) and Al w Ga 1-w and a second Bragg reflecting mirror in which As (0≦w≦1) is alternately stacked.

[0011] (2) The resonant type semiconductor optical element according to (1) above, wherein the central received and emitted light wavelength of the active layer is 3 μm or more.

[0012] (3) The resonant cavity type semiconductor optical element according to (1) or (2) above, which has misfit dislocations at an interface between the first Bragg reflector and the InAs buffer layer.

[0013] (4) Al on a GaAs or AlGaAs substrate x Ga 1-x As(0≦x≦1) and Al y Ga 1-y forming a first Bragg reflector in which InAs and InAs (0≦y≦1) are alternately stacked; forming an InAs buffer layer on the first Bragg reflector at a growth temperature of 400° C. or higher and lower than 550° C.; and depositing InAs on the InAs buffer layer. 1-z Sb z forming an active layer containing (z≧0) at a growth temperature of 550° C. or more and less than 750° C.; v Ga 1-v As(0≦v≦1) and Al w Ga 1-wand forming a second Bragg reflector by alternating deposition of W and As (0≦w≦1), wherein the process of forming the second Bragg reflector includes a first deposition process in which deposition of at least a first layer of the second Bragg reflector is commenced at a temperature less than 600° C., and a second deposition process performed after the first deposition process in which remaining layers of the second Bragg reflector are grown at a temperature of 600° C. or higher and 800° C. or lower. Effect of the Invention

[0014] It is possible to provide a resonant type optical semiconductor element having a central wavelength of 2.0 μm or more and a resonant structure on a GaAs or AlGaAs substrate, and a method for manufacturing the resonant type optical semiconductor element. [Brief description of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view illustrating a configuration of a resonant type optical semiconductor element according to a first embodiment. [Diagram 2] FIG. 4 is a cross-sectional view showing a configuration of a resonant type optical semiconductor element according to a second embodiment. [Diagram 3] 4 is a graph showing the relationship between wavelength and reflectance of the first Bragg reflecting mirror in Example 1. [Figure 4] 4 is a graph showing a reflection spectrum of the resonant type optical semiconductor element in accordance with Example 1. [Diagram 5] 13 is a graph showing the reflection spectrum and the PL spectrum of the resonant type optical semiconductor element according to Example 4. [Figure 6] 1 is a graph showing PL spectra of Example 1, Example 2, and an InAs substrate. [Figure 7] 1 is a graph showing the PL spectra of Example 4 and the PL confirmation substrate. [Figure 8] 1 is a cross-sectional SEM image of Example 2. [Figure 9A] 3 is a cross-sectional TEM image showing the interface between an n-type GaAs layer and an i-type InAs buffer layer in Example 1. [Figure 9B] 2 is a cross-sectional TEM image showing the interface between the i-type InAs active layer and the i-type GaAs layer in Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Prior to describing an embodiment of the present invention, the following points will be explained in advance.

[0017] In one embodiment, InAs is a III-V group compound semiconductor mainly composed of In as group III and As as group V. InAs is allowed to contain impurity elements other than In and As within the scope of the effect of the present invention. In this case, even if there is no mention of Ga, which is a group III element, a part of In may be substituted with Ga as long as it is 5% or less. Also, even if there is no mention of P or Sb, which is a group V element, a part of As may be substituted with P or Sb as long as it is 5% or less.

[0018] In one embodiment, "AlGaAs" means Al, where the Al composition ratio is a. a Ga 1―a It means that the Al composition is As. In one embodiment, the value of the Al composition ratio a of AlGaAs is specified from the wavelength observed by photoluminescence measurement performed on the surface of each layer when each layer is grown. The Al composition ratio a is 0 to 1 unless otherwise specified. As a method for specifying the Al composition from the cross section of the light-emitting device, for example, EDS (energy dispersive X-ray spectroscopy) can be used.

[0019] The thickness of each layer formed by epitaxial growth may be measured by SEM (scanning electron microscope). When the composition of adjacent layers is sufficiently different, the thickness can be calculated from cross-sectional observation of the grown layer by SEM or TEM (transmission electron microscope). It is preferable to use SEM when the film thickness is 10 nm or more, and TEM when the film thickness is less than 10 nm. Furthermore, the thickness of each layer can also be calculated from the growth rate calculation results using an optical interference film thickness measuring device attached to the growth apparatus or XRD based on the film thickness measurement results by the above SEM (or TEM).

[0020] In one embodiment, the flatness and dislocation density are evaluated by observing cross-sectional SEM images and cross-sectional TEM images.

[0021] In one embodiment, the reflectance is measured using a microscope FT-IR (Fourier transform infrared spectroscopy) FT / IR-6600ST manufactured by JASCO Corporation.

[0022] In one embodiment, the PL spectrum and PL intensity are measured by a PL evaluation device equipped with an InSb detector, using a 1064 nm laser as an excitation light source.

[0023] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In each drawing, the aspect ratio of the substrate and each layer is exaggerated from the actual ratio for the sake of convenience of explanation.

[0024] [First embodiment] With reference to FIG. 1, an example of a resonant optical semiconductor element 100 which is a first embodiment of a resonant optical semiconductor element according to the present invention will be described together with a manufacturing method.

[0025] Resonant optical semiconductor element 100 includes a substrate 1 made of GaAs or AlGaAs, a first Bragg reflector 2 made of AlGaAs, an InAs buffer layer 3, an active layer 4 containing InAsSb, and a second Bragg reflector 5 made of AlGaAs. In resonant optical semiconductor element 100, first Bragg reflector 2, InAs buffer layer 3, active layer 4, and second Bragg reflector 5 are stacked on substrate 1 in this order.

[0026] First Bragg reflector 2, InAs buffer layer 3, active layer 4 and second Bragg reflector 5 on substrate 1 may be formed in this order by epitaxial growth on substrate 1, for example by MOCVD (Metal Organic Chemical Vapor Deposition) method.

[0027] <Substrate> Substrate 1 is made of GaAs or AlGaAs. Substrate 1 may be a substrate made of GaAs or AlGaAs single crystal, or a template substrate including a layer made of GaAs or AlGaAs formed in a plate shape on the surface. As described later, a first Bragg reflector 2, an InAs buffer layer 3, an active layer 4, and a second Bragg reflector 5 are laminated in this order on substrate 1. Substrate 1 made of GaAs or AlGaAs may be n-type doped.

[0028] <First Bragg reflector> On the substrate 1, Al x Ga 1-x As(0≦x≦1) and Al y Ga 1-y The first Bragg reflector 2 is formed by alternately laminating Al As (0≦y≦1). The values ​​of x and y are different. x Ga 1-x As and Al y Ga 1-y As may be doped as an n-type impurity, and examples of the doping impurity include Se.

[0029] Here, the emission wavelength in air of the active layer 4 described later is λ, Al x Ga 1-x As and Al y Ga 1-y The refractive index of As is n x , n y The Al constituting the first Bragg reflector 2 is x Ga 1-x As and Al y Ga 1-y The thickness of each As layer is λ / (4n x ), λ / (4n y ) is preferable. x Ga 1-x As and Al y Ga 1-y This is because the reflection at each interface due to the difference in the refractive index of As is maximized when the layers are alternately stacked with a film thickness of 1 / 4 wavelength.

[0030] The Al that constitutes the first Bragg reflector 2 x Ga1-x As and Al y Ga 1-y It is preferable that five or more and twenty or less layers of As are alternately stacked respectively.

[0031] <InAs buffer layer> An InAs buffer layer 3 is provided on the first Bragg reflector 2. The growth temperature of the InAs buffer layer 3 is 400 °C or more and less than 550 °C. The film thickness of the InAs buffer layer 3 is preferably 50 nm or more. By making the InAs buffer layer 3 50 nm or more, the surface on the side opposite to the side in contact with the first Bragg reflector 2 is sufficiently flattened. The InAs buffer layer 3 preferably has a film thickness of 80 nm or more and 300 nm or less. Further, the InAs buffer layer 3 is preferably undoped.

[0032] <Active layer> InAs on the InAs buffer layer 3 1-z Sb z (z ≧ 0) is provided with an active layer 4 containing. The growth temperature of the active layer 4 is 550 °C or more and less than 750 °C. The active layer 4 preferably has a wavelength range with an emission and absorption center wavelength of 3 μm or more.

[0033] Further, the active layer 4 preferably has a film thickness of 50 nm or more. By making the active layer 4 50 nm or more, the surface on the side opposite to the side in contact with the InAs buffer layer 3 is sufficiently flattened. The active layer 4 preferably has a film thickness of 80 nm or more and 300 nm or less. Further, the active layer 4 is preferably undoped.

[0034] When the refractive index of InAs is n z the total film thickness of the InAs buffer layer 3 and the active layer 4 is preferably λ / (2n z ). This is to satisfy the resonance condition as a resonant optical semiconductor device.

[0035] By growing the InAs buffer layer 3 at a temperature of 400°C or higher and lower than 550°C, and growing the active layer 4 at a higher temperature of 550°C or higher and lower than 750°C, it is possible to form the InAs buffer layer 3 and active layer 4, which have significantly different lattice constants, on the first Bragg reflector 2 with excellent flatness.

[0036] <Second Bragg reflector> Al on active layer 4 v Ga 1-v As(0≦v≦1) and Al w Ga 1-w Second Bragg reflector 5 is provided by alternately stacking AlAs (0≦w≦1). The values ​​of v and w are different. The process of forming second Bragg reflector 5 includes a first film formation step in which at least the first layer is formed at a temperature of 500° C. or higher and lower than 600° C., and a second film formation step, which is performed after the first film formation step, in which the remaining layers are grown at a temperature of 600° C. or higher and 800° C. or lower. By performing two-stage growth by changing the growth temperature, an annealing effect is generated in active layer 4, improving the crystallinity. v Ga 1-v As and Al w Ga 1-w As may be p-type doped, and the doped impurity may be Zn or the like.

[0037] In the first deposition step, deposition of the first layer of second Bragg reflector 5 may be started at a temperature of preferably 520° C. to 580° C. The first deposition step is preferably carried out for one minute or more. In the subsequent second deposition step, evaporation of As from active layer 4 can be more effectively suppressed.

[0038] Setting the growth temperature of second Bragg reflector 5 in the second film formation step to 600° C. or higher provides the effect of improving the crystallinity by heat treatment of active layer 4. Setting the growth temperature of second Bragg reflector 5 in the second film formation step to 800° C. or lower can suppress evaporation of As from active layer 4 or second Bragg reflector 5 during the second film formation step.

[0039] The second film formation step preferably includes a period during which the growth temperature of second Bragg reflector 5 is set to 650° C. or higher. This may further improve the flatness of each layer of second Bragg reflector 5.

[0040] In the second film formation step, there may be a period during which the growth temperature of second Bragg reflector 5 is constant, or there may be a period during which the growth temperature is increased continuously or stepwise (for example, in a step-like manner). For example, after the growth temperature of second Bragg reflector 5 is increased to a predetermined temperature of 600° C. or more and 800° C. or less following the first film formation step, the predetermined temperature may be maintained until the end of the second film formation step, or the growth temperature of second Bragg reflector 5 may be increased continuously or stepwise within the range of 600° C. or more and 800° C. or less.

[0041] The first and second film formation steps may be performed continuously. For example, the formation of the first layer of second Bragg reflector 5 may be started at a growth temperature below 600° C. (e.g., 500° C. or 550° C.), and the temperature may be continuously increased to a predetermined temperature of 800° C. or lower (e.g., 650° C.) after the start of the film formation.

[0042] Here, Al v Ga 1-v As and Al w Ga 1-w The refractive index of As is n v , n w The Al constituting the second Bragg reflector 5 is v Ga 1-v As and Al w Ga 1-w The thickness of each As layer is λ / (4n v ), λ / (4n w ) is preferable. v Ga 1-v As and Al w Ga 1-w This is because the reflection at each interface due to the difference in the refractive index of As is maximized when the layers are alternately stacked with a film thickness of 1 / 4 wavelength.

[0043] The Al constituting the second Bragg reflector 5v Ga 1-v As and Al w Ga 1-w It is preferable that As has 5 to 20 layers stacked alternately.

[0044] As described above, by providing the first film formation step of low-temperature growth and the second film formation step of high-temperature growth, it is possible to suppress evaporation of Sb or As in InAs buffer layer 3 or active layer 4. In addition, the flatness of each layer of second Bragg reflector 5 is improved, making it possible to form a Bragg reflector with fewer dislocations.

[0045] After the step of forming active layer 4, a heating step may be performed in which the semiconductor laminate consisting of the semiconductor layers laminated up to that point is heated at a temperature of 520°C to 800°C in an arsenic atmosphere. The heating step may be performed separately from the step of forming second Bragg reflector 5, or may be performed simultaneously with the step of forming second Bragg reflector 5. In the heating step, it is preferable that there is a period during which the semiconductor laminate is at a temperature of 550°C or higher, more preferably a period during which the semiconductor laminate is at a temperature of 600°C or higher, and even more preferably a period during which the laminate is at a temperature of 650°C or higher. The heating step is preferably performed for a total of 8 minutes or more. This may improve the light emission output from active layer 4.

[0046] When the heating step is performed separately from the second Bragg reflector 5 forming step, the heating step can be performed before the second Bragg reflector 5 forming step. When the heating step is performed simultaneously with the second Bragg reflector 5 forming step, the heating step can be performed simultaneously with the first and second film forming steps in the second Bragg reflector 5 forming step. For example, when the second Bragg reflector 5 forming step is performed, since an arsenic-containing gas is used as the raw material for AlGaAs constituting the second Bragg reflector 5, the arsenic partial pressure is high, which is equivalent to performing heating in an arsenic atmosphere. Therefore, the first and second film forming steps can include a heating step.

[0047] As described above, the heating step heats the semiconductor laminate in an arsenic atmosphere. One example of the arsenic atmosphere is an AsH3 (arsine) atmosphere. The heating step is performed, for example, by passing AsH3 gas through a space (for example, inside an MOCVD apparatus) containing the semiconductor laminate and setting the temperature of a base (for example, a stage in an MOCVD apparatus) on which the semiconductor laminate is placed to 520°C or higher and 800°C or lower. When the heating step is performed as the second Bragg reflector 5 forming step, the space containing the semiconductor laminate can be further made into a gallium atmosphere. For example, Ga(CH3)3 (triethylgallium, TEG) gas and Al(CH3)3 (trimethylaluminum, TMAl) gas can be passed through the space containing the semiconductor laminate together with AsH3 gas. The heating step may further be performed in an arsenic-antimony atmosphere (for example, a mixed atmosphere of AsH3 gas and Sb(C2H5)3 (triethylantimony, TESb)).

[0048] What is noteworthy in this embodiment is that InAs, which has a significantly different lattice constant, is formed on a GaAs or AlGaAs layer. 1-z Sb z The point is that an active layer including a lattice constant of 0 (z≧0) is formed. Conventionally, it has been considered difficult to form an InAs layer or a layer with a lattice constant close to that of InAs directly on a GaAs or AlGaAs layer due to the large difference in lattice constant between GaAs or AlGaAs and InAs. Even when an InP buffer layer is used, it has been considered impossible to form an active layer with a composition close to that of InAs, since the occurrence of dislocations or internal stress caused by the difference in lattice constant between GaAs or AlGaAs and InAs cannot be sufficiently eliminated. However, the present inventors have found that a high-quality InAs layer that is flat and has few dislocations can be formed by performing two-stage growth, in which an InAs layer on a GaAs or AlGaAs layer is grown at a low temperature and then at a high temperature. This makes it possible to form an InAs layer on a GaAs or AlGaAs layer. 1-z Sb z It was possible to form an active layer containing (z≧0).

[0049] In addition, InAs 1-z Sbz By depositing at least the first layer of an AlGaAs Bragg reflector on an active layer containing (z≧0) at a low temperature and the remaining layers at a high temperature, it has become possible to form a Bragg reflector with excellent flatness and few dislocations without degrading the crystallinity of the InAs layer and active layer.

[0050] The resonant-type optical semiconductor element thus formed is a GaAs or AlGaAs substrate and an Al x Ga 1-x As(0≦x≦1) and Al y Ga 1-y a first Bragg reflector in which InAs and InAs (0≦y≦1) are alternately stacked, an InAs buffer layer is formed on the first Bragg reflector, and an InAs buffer layer is formed on the InAs 1-z Sb z (z≧0) and a second Bragg reflector formed on the active layer. This resonant type optical semiconductor element has good interface steepness between layers and good crystallinity of each layer, making it possible to obtain resonance by RC (resonant) structure. Such a resonant type optical semiconductor element has a small full width at half maximum of the emission spectrum and can be suitably used for sensing applications.

[0051] In particular, in the above-mentioned resonant-type semiconductor optical element, the second Bragg reflector is formed by two-stage growth, and therefore the lattice-mismatched InAs 1-z Sb z (z≧0) can be used for the active layer. Therefore, the central received and emitted light wavelength of the resonant type optical semiconductor element can be set to 2 μm or more, and can also be set to 3 μm or more.

[0052] Although the above-mentioned resonant semiconductor optical element hardly propagates into the InAs layer and hardly generates dislocations inside the layer, misfit dislocations may occur at the interface between the InAs first Bragg reflector and the InAs buffer layer due to lattice mismatch. The above-mentioned resonant semiconductor optical element may also have misfit dislocations at the interface between the active layer and the second Bragg reflector.

[0053] [Second embodiment] In the first embodiment, the resonant optical semiconductor element 100 is described as having the substrate 1, the first Bragg reflector 2, the InAs buffer layer 3, the active layer 4, and the second Bragg reflector 5 stacked in this order, and further described as having the second Bragg reflector 5 formed directly on the surface of the active layer 4. However, the resonant optical semiconductor element 100 can be modified to have an InAs cap layer 6 formed between the active layer 4 and the second Bragg reflector 5 as shown in FIG. 2. The InAs cap layer 6 can reduce the lattice constant difference between the active layer 4 and the second Bragg reflector 5. The InAs cap layer 6 is preferably formed at the same growth temperature as the active layer 4. The InAs cap layer 6 may be p-type doped, and the doped impurity may be Zn or the like. In this case, the second Bragg reflector 5 may be formed on the surface of the InAs cap layer 6.

[0054] It should be noted that the embodiment disclosed in this specification is merely an example, and the embodiment of the present invention is not limited thereto, and can be appropriately modified within the scope of the object of the present invention. For example, not only may InAs cap layer 6 be present between active layer 4 and second Bragg reflector 5 as in the above-mentioned second embodiment, but other layers (not shown) may be inserted between each layer on substrate 1, and an additional layer may be formed on second Bragg reflector 5.

[0055] In the following, examples of a resonant optical semiconductor element and a method for manufacturing a resonant optical semiconductor element according to an embodiment will be described.

[0056] Example 1 First, a Se-doped n-type GaAs substrate (film thickness: 430 μm) was placed on the stage in the chamber of the MOCVD apparatus. Next, the stage temperature was set to 500°C, and the reactor pressure in the chamber was set to 76 Torr.

[0057] (First Bragg reflector forming process) While simultaneously passing TMAl (trimethylaluminum) gas, AsH3 (arsine) gas, TEGa (triethylgallium) gas, and hydrogen as a carrier gas through the chamber, n-type Al was deposited on an n-type GaAs substrate. 0.85 Ga 0.15 The first Bragg reflector was formed by alternately growing 15 layers of As and n-type GaAs. The first Bragg reflector was made an n-type semiconductor by doping with Se. 0.85 Ga 0.15 The thickness of each of the n-type GaAs layers is 281 nm, and the thickness of each of the n-type AlAs layers is 243 nm. 0.85 Ga 0.15 The growth time for each As layer was 350.6 seconds, and the flow rates of TMAl gas, AsH3 gas, TEGa gas, and hydrogen were 50.4 sccm, 150 sccm, 43.3 sccm, and 3 SLM, respectively. The growth time for each GaAs layer was 326 seconds, and the flow rates of TMAl gas, AsH3 gas, TEGa gas, and hydrogen were 0 sccm, 100 sccm, 306.7 sccm, and 3 SLM, respectively. Note that the unit "sccm" is the gas flow rate (cm) converted to a value at 1 atmosphere and 0°C. 3 / min). The unit "SLM" is the gas flow rate (L / min) converted to a value at 1 atmosphere and 0°C.

[0058] (InAs buffer layer formation process) Next, while simultaneously flowing TMI gas, AsH3 gas, and hydrogen as a carrier gas into the chamber, an undoped InAs layer was grown on the first Bragg reflector as an InAs buffer layer to a thickness of 234 nm. The stage temperature was 450°C. The growth time was 677.7 seconds.

[0059] (Active layer formation process) Next, the stage temperature was raised to 550°C, and an undoped InAs layer was grown as an active layer on the InAs buffer layer to a thickness of 234 nm while simultaneously passing TMI gas, AsH3 gas, and hydrogen as a carrier gas. The total thickness of the InAs buffer layer and active layer was 468 nm. The growth time was 677.7 seconds.

[0060] (Second Bragg reflector forming process) After the active layer formation process, an undoped GaAs layer was grown on the active layer for 302.4 seconds until the thickness reached 243 nm while simultaneously flowing AsH3 (arsine) gas, TEGa (triethylgallium) gas, and hydrogen as a carrier gas into the chamber. In the second Bragg reflector formation process, the process of growing the first layer to be formed on the active layer (in this embodiment, an i-type GaAs layer) corresponds to the first film formation process. In the first film formation process, the growth of the i-type GaAs layer was started at a stage temperature of 550°C, and while the i-type GaAs layer was growing, the stage temperature was raised linearly from 550°C to 650°C over 302.4 seconds. After the first film formation process, in the second film formation process, with the stage temperature kept at 650°C, a carbon-doped p-type Al was grown on the i-type GaAs layer formed in the first film formation process. 0.85 Ga 0.15 The As and p-type GaAs layers were grown alternately in five layers. 0.85 Ga 0.15 The thickness of each As layer is 281 nm, and the thickness of each p-type GaAs layer is 243 nm. The growth time of each p-type GaAs layer is 324 seconds, and the flow rates of TMAl gas, AsH3 gas, TEGa gas, and hydrogen are 0 sccm, 100 sccm, 306.7 sccm, and 3 SLM, respectively. 0.85 Ga 0.15 The growth time of each As layer was 325.2 seconds, and the flow rates of TMAl gas, AsH3 gas, TEGa gas and hydrogen were 50.4 sccm, 150 sccm, 43.3 sccm and 3 SLM, respectively. The stack after the formation of the second Bragg reflector was used as the resonant type optical semiconductor element of Example 1.

[0061] FIG. 3 is a graph showing the relationship between wavelength and reflectance of the first Bragg reflector portion of Example 1. 0.85 Ga 0.15 The As layers and n-type GaAs layers are stacked alternately at 15 layers each. 0.85 Ga 0.15 The thickness of each layer of the As layer is 281 nm, and the thickness of each layer of the n-type GaAs layer is 243 nm. The reflectance is measured by a micro FT-IR microscope, and the vertical axis is adjusted so that it is 30% at a wavelength of about 2.4 μm. The reflectance is maximum at a wavelength of about 3.3 μm.

[0062] 4 shows the reflection spectrum of the resonant type optical semiconductor element according to Example 1. A dip in the reflectance can be confirmed at the resonant wavelength of 3.3 μm. This confirms that the resonant type optical semiconductor element according to Example 1 oscillates at a central wavelength of about 3.3 μm.

[0063] Example 2 Second Bragg reflector: p-type GaAs and p-type Al 0.85 Ga 0.15 A resonant type optical semiconductor element according to Example 2 was obtained in the same manner as in Example 1, except that the number of As layers was set to 10 for each layer.

[0064] Example 3 In Example 3, a stack was formed in the same manner as in Example 1 up to the InAs buffer layer formation process. After the InAs buffer layer was formed, the stage temperature was raised to 650° C., and undoped InAs was 0.9 Sb 0.1 Well layer (thickness: 7 nm), InAs intermediate layer (thickness: 3.5 nm), InAs 0.77 P 0.23The formation of the barrier layer (film thickness: 7 nm) was repeated three times to form an active layer of a strain-compensated multiple quantum well layer. After the active layer was formed, an InAs cap layer made of Zn-doped p-type InAs was formed while the stage temperature was kept at 650°C. The thickness of the InAs cap layer was 181.5 nm, and the total film thickness from the InAs buffer layer to the InAs cap layer was 468 nm. The second Bragg reflector formation process was the same as in Example 1. The stack obtained as described above was used as a resonant type optical semiconductor element according to Example 3.

[0065] Example 4 In Example 4, first, a Si-doped n-type GaAs substrate with a thickness of 350 μm was prepared. Next, a first Bragg reflector was formed on the n-type GaAs substrate. The first Bragg reflector was formed by first stacking a Te-doped n-type GaAs (thickness: 316.0 nm) on top of which was also Te-doped n-type Al. 0.9 Ga 0.1 Five layers of As (thickness: 366.1 nm) and n-type GaAs (thickness: 316.0 nm) were alternately stacked in sequence, making 10.5 pairs including the first layer. Next, the stage temperature was set to 500°C, and a Te-doped n-type InAs buffer layer (thickness: 300 nm) was formed on the first Bragg reflector. Furthermore, the stage temperature was set to 650°C, and a Te-doped n-type InAs buffer layer (thickness: 425 nm) was formed. Furthermore, while maintaining the stage temperature at 650°C, an undoped InAs buffer layer (thickness: 75 nm) was formed.

[0066] Next, while keeping the stage temperature at 650° C., an active layer, an electron blocking layer, and an InAs cap layer were formed on the InAs buffer. The active layer was made of undoped InAs. 0.9 P 0.1 Barrier layer (thickness: 30 nm) and InAs 0.9 Sb 0.1 After stacking 10 well layers (thickness: 10 nm) in sequence, InAs 0.9 P 0.1 The barrier layers were stacked to form a multi-quantum well layer with 10.5 pairs of barrier layers, including the last barrier layer. Zn-doped p-type Al 0.3 In0.7 An As electron blocking layer (thickness: 15 nm) was formed, and then a Zn-doped p-type InAs cap layer (thickness: 20 nm) was formed.

[0067] Next, the stage temperature was lowered to 500° C. A C-doped p-type GaAs layer (thickness: 316.0 nm) and a p-type Al 0.9 Ga 0.1 Two layers of As (film thickness: 366.1 nm) were alternately stacked in order, and a p-type GaAs layer was further stacked. Including the last p-type GaAs layer, 2.5 pairs of second Bragg reflectors were formed. Here, the growth temperature of the first p-type GaAs layer of the second Bragg reflector was started at 500°C, and was raised to 650°C during the growth of the first layer. The remaining second Bragg reflectors were grown at 650°C. The stack obtained as described above was used as the resonant type optical semiconductor element of Example 4.

[0068] 5 shows the reflection spectrum and the PL spectrum of the resonant optical semiconductor device of Example 4. The reflection spectrum was measured using a JASCO FTIR-4200, and the PL spectrum was measured using a Horiba PL-M2 infrared photoluminescence measurement device. It can be confirmed that the wavelength at which the reflection spectrum dips coincides with the peak wavelength of the PL spectrum.

[0069] (Comparative Example) In the comparative example, a laminate was formed in the same manner as in Example 1 up to the active layer formation step. After the active layer was formed, the stage temperature was not lowered and was kept at 650° C., and the second Bragg reflector was formed. In addition, the p-type GaAs and p-type Al 0.8 Ga 0.2 The number of As layers was set to 10 for each layer.

[0070] For the resonant semiconductor optical elements according to Examples 1 to 4 and Comparative Example, evaluations were performed on photoluminescence (PL) and on the flatness and dislocation density between layers for comparison. The evaluation of PL is an evaluation item related to light emission output and spectrum, and the higher the PL intensity, the higher the light emission output when used as a resonant semiconductor optical element, and the narrower the PL spectrum width, the more suitable it is for sensing applications. The flatter the surface is, and the lower the dislocation density, the better the abruptness of the interface between layers during epitaxial growth and the crystallinity of each layer are (i.e., the better the quality of epitaxial growth), and the higher the light emission output when used as a resonant semiconductor optical element. These results are shown in Table 1. In Table 1, the item "number of pairs of second Bragg reflector" indicates the number of pairs of p-type GaAs and p-type Al in the second Bragg reflector. 0.8 Ga 0.2 represents the number of each As layer.

[0071] [Table 1]

[0072] The evaluation of photoluminescence (PL) for Examples 1 and 2 was performed by using a light source with a central wavelength of 1064 nm as an infrared light source, irradiating the resonant optical semiconductor element of each Example with light of 1064 nm wavelength from the light source, and measuring the intensity of light emitted by excitation of the resonant optical semiconductor element (active layer). Note that the spectrum was performed using a diffraction grating with 150 lattices and a lattice spacing of 8 μm and a slit with a slit width of 0.3 mm, and the intensity was measured with an InSb photodetector.

[0073] FIG. 6 shows the PL measurement results at room temperature for Example 1, Example 2, and the InAs substrate, measured with a slit width of 0.3 mm. Both the resonant optical semiconductor elements of Example 1 and Example 2 obtained a PL intensity similar to that of the InAs substrate. The full width at half maximum was 57 nm for Example 1, 46 nm for Example 2, and 220 nm for the InAs substrate. Since the greater the number of layers constituting the Bragg reflector, the stronger the light confinement, it can be confirmed that Example 2 has a lower PL intensity than Example 1. On the other hand, the full width at half maximum of the PL spectrum is narrower in Example 2.

[0074] The evaluation of photoluminescence (PL) for Example 4 was performed by using a light source with a central wavelength of 1064 nm as an infrared light source, irradiating the resonant optical semiconductor element according to each Example with light of 1064 nm wavelength from the light source, and measuring the intensity of light emitted by excitation of the resonant optical semiconductor element (active layer). The measurement was performed using a PL-M2 manufactured by Horiba Ltd. as an apparatus, a diffraction grating with 100 lattices and a lattice interval of 10 μm and a slit with a slit width of 0.326 mm, and the intensity was measured with an InSb photodetector. Figure 7 shows the PL measurement results at room temperature for Example 4 and the epitaxial substrate prepared for PL spectrum confirmation (hereinafter abbreviated as PL confirmation substrate). The epitaxial substrate prepared for PL spectrum confirmation was prepared by the following method. The stage temperature was set to 500°C and a Te-doped n-type InAs buffer layer (thickness: 300 nm) was formed on the GaAs substrate, then the stage temperature was set to 650°C and a Te-doped n-type InAs buffer layer (thickness: 4925 nm) was formed. Furthermore, with the stage temperature maintained at 650°C, an undoped InAs buffer layer (thickness: 75 nm) was formed. Next, with the stage temperature maintained at 650°C, an active layer, an electron blocking layer and an InAs cap layer were formed on the InAs buffer. The active layer was undoped InAs. 0.9 P 0.1 Barrier layer (thickness: 30 nm) and InAs 0.9 Sb 0.1 After stacking 10 well layers (thickness: 10 nm) in sequence, InAs 0.9 P 0.1The barrier layers were stacked to form a multi-quantum well layer with 10.5 pairs of barrier layers, including the last barrier layer. Zn-doped p-type Al 0.3 In 0.7 An As electron blocking layer (thickness: 15 nm) was formed, and then a Zn-doped p-type InAs cap layer (thickness: 20 nm) was formed.

[0075] The peak value of the PL intensity of the resonant type optical semiconductor element and the PL confirmation substrate of Example 4 is about twice as large as that of Example 4. This is believed to be because, in Example 4, the number of layers constituting both the first and second Bragg reflectors is smaller than in the other examples, so that the light is less confined within the resonator and a larger proportion of light is emitted to the outside. The full width at half maximum of the PL spectrum is 220 nm in Example 4 and 1350 nm in the PL confirmation substrate, and it can be confirmed that the spectrum width is narrowed by using a resonant structure.

[0076] From the evaluation of these PL spectra, it was confirmed that the resonant optical semiconductor elements of Examples 1 to 4 have no deterioration in PL intensity even when they have a resonant structure, and that the resonant structure enables the production of PL spectra with narrow full width at half maximum.

[0077] The surface flatness was evaluated by taking cross-sectional SEM images of the resonant optical semiconductor elements of each example, such as the interface between the active layer and the second Bragg reflector, the interfaces between the layers of the second Bragg reflector, and the surface of the last grown layer of the second Bragg reflector opposite to the GaAs substrate. The flatness of Examples 1 to 4 was good, and better results were obtained than in the comparative example. Figure 8 shows a cross-sectional SEM image of Example 2.

[0078] The dislocation density on the surface was evaluated by acquiring a cross-sectional TEM image of the resonant optical semiconductor device of each Example. FIG. 9A shows a cross-sectional TEM image of the interface between the n-type GaAs layer (the last layer of the first Bragg reflector) and the i-type InAs buffer layer of Example 1. Furthermore, FIG. 9B shows a cross-sectional TEM image of the interface between the i-type InAs active layer and the i-type GaAs layer (the first layer of the second Bragg reflector) of Example 1. In both FIG. 9A and FIG. 9B, periodic dislocations (misfit dislocations) are observed at the interface. On the other hand, there is little propagation into the InAs buffer layer and the active layer and little dislocation generation inside the layers. In FIG. 9B, although there is room for improvement in the dislocation density of the i-type GaAs layer, a good result was obtained compared to the comparative example.

[0079] The above results demonstrate that by growing the InAs buffer layer at a low temperature, then growing the active layer at a high temperature, and starting the first film formation step of the second Bragg reflector at a low temperature and then raising the temperature to a high temperature before carrying out the second film formation step, it is possible to grow the active layer and second Bragg reflector with good flatness and obtain a resonant optical semiconductor element.

[0080] In this manner, it is possible to provide a resonant type optical semiconductor element having a high light emission output and a narrow spectral width, and a method for manufacturing the resonant type optical semiconductor element. [Explanation of symbols]

[0081] 100 Resonant type optical semiconductor element 1 Board 2. First Bragg reflector 3. InAs buffer layer 4 Active layer 5. Second Bragg reflector 6 InAs cap layer

Claims

1. a GaAs or AlGaAs substrate; The Al on the substrate ｘ G １－ｘ As (0≦x≦1) and Al ｙ G １－ｙ a first Bragg reflector formed by alternately stacking As (0≦y≦1); an InAs buffer layer formed on the first Bragg reflector; An InAs layer formed on the InAs buffer layer １－ｚ Sb ｚ (z≧0), and The Al formed on the active layer ｖ G １－ｖ As (0≦v≦1) and Al ｗ G １－ｗ a second Bragg reflector formed by alternately stacking As (0≦w≦1); Characterized in that it has Resonant optical semiconductor element.

2. The central receiving and emitting wavelength of the active layer is 3 μm or more.

2. The resonant type semiconductor optical element according to claim 1.

3. a first Bragg reflector having misfit dislocations at an interface between the first Bragg reflector and the InAs buffer layer; 2. The resonant type semiconductor optical element according to claim 1.

4. On a GaAs or AlGaAs substrate, A ｘ G １－ｘ As (0≦x≦1) and Al ｙ G １－ｙ forming a first Bragg reflector by alternately stacking As and Y (0≦y≦1); forming an InAs buffer layer on the first Bragg reflector at a growth temperature of 400° C. or more and less than 550° C.; On the InAs buffer layer, １－ｚ Sb ｚ forming an active layer including (z≧0) at a growth temperature of 550° C. or higher and lower than 750° C.; On the active layer, Al ｖ G １－ｖ As (0≦v≦1) and Al ｗ G １－ｗ forming a second Bragg reflector by alternating lamination of As and As (0≦w≦1); Including, The step of forming the second Bragg reflector includes: a first deposition step initiating deposition of at least a first layer of the second Bragg reflector at a temperature less than 600° C.; a second deposition step, which is performed after the first deposition step, of growing remaining layers of the second Bragg reflector at a temperature of 600° C. or more and 800° C. or less; Characterized in that it comprises A method for manufacturing a resonant type optical semiconductor element.

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