JP2010135402A - Semiconductor optical element and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor optical element having the constitution, by which crystallinity of an active layer can be improved by reducing the concentration of hydrogen ions in the active layer, and to provide a method for manufacturing the semiconductor optical element. <P>SOLUTION: The semiconductor optical element 1 includes a first n-type semiconductor layer 13, the active layer 15, a p-type semiconductor layer 17, and a second n-type semiconductor layer 19. The first n-type semiconductor layer 13 is formed on a substrate 11. The active layer 15 is formed on the first n-type semiconductor layer 13 and includes a III-V group compound semiconductor layer including nitrogen and arsenic as V group elements. The p-type semiconductor layer 17 is formed on the active layer 15. The second n-type semiconductor layer 19 is formed between the active layer 15 and the p-type semiconductor layer 17. An n-type dopant is added to the second n-type semiconductor layer 19. Pn junction J is formed by the second n-type semiconductor layer 19 and the p-type semiconductor layer 17. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a semiconductor optical device and a method for manufacturing the semiconductor optical device.

Non-Patent Document 1 describes a semiconductor laser. This semiconductor laser includes a lower cladding layer made of n-type AlGaAs, an active layer made of GaInNAs, and an upper cladding layer made of p-type AlGaAs. These layers are sequentially stacked on the n-type semiconductor substrate. An optical confinement layer made of undoped GaAs is provided between the lower cladding layer and the active layer and between the upper cladding layer and the active layer.
F. Hohnsdorf et al, “Reduced threshold current streams of (GaIn) (NAs) / GaAs single quantum well lasers for emission wavelengths in therange 1.28-1.38μm” Electron. Lett. 1st April 1999, Vol.35, No7.

  The manufacturing process of a semiconductor device described in Non-Patent Document 1 includes a process of growing various semiconductor layers on a GaInNAs active layer by a metal organic vapor phase epitaxy (MOVPE) method. . In these steps, hydrogen ions are contained in the atmosphere or hydrogen ions are generated. The hydrogen ions diffuse into the active layer.

  However, the configuration of the semiconductor optical device described in Non-Patent Document 1 cannot sufficiently suppress the diffusion of hydrogen ions into the active layer in the manufacturing process. Further, nitrogen in the active layer is easily bonded to the diffused hydrogen ions, and crystal defects are formed in the active layer due to the formation of bonds between the hydrogen ions and nitrogen. Formation of crystal defects in the active layer deteriorates the crystallinity of the active layer, and as a result, the light emission characteristics deteriorate.

  Accordingly, an object of the present invention is to provide a semiconductor optical device having a structure capable of improving the crystallinity of the active layer by reducing the concentration of hydrogen ions in the active layer, and a method of manufacturing the semiconductor optical device. To do.

  According to one aspect of the present invention, a semiconductor optical device is provided with a first n-type semiconductor layer provided on a substrate, the first n-type semiconductor layer, and nitrogen as a group V element. And an active layer having a III-V compound semiconductor layer containing arsenic, a p-type semiconductor layer provided on the active layer, and a first layer provided between the active layer and the p-type semiconductor layer. N-type semiconductor layer, and an n-type dopant is added to the second n-type semiconductor layer, and the second n-type semiconductor layer and the p-type semiconductor layer have a pn junction. Form.

  Since the second n-type semiconductor layer is provided between the active layer and the p-type semiconductor layer, a pn junction is formed at the interface between the second n-type semiconductor layer and the p-type semiconductor layer. Due to the electric field (built-in potential) at the pn junction, diffusion of hydrogen ions to the active layer in the manufacturing process is suppressed. Therefore, the generation of crystal defects due to the combination of nitrogen and hydrogen ions in the active layer is suppressed. As a result, this semiconductor optical device has an active layer with good crystallinity.

  In the semiconductor optical device according to the present invention, it is preferable that an undoped semiconductor layer is further provided between the active layer and the second n-type semiconductor layer. According to the configuration of this semiconductor optical device, since the undoped semiconductor layer is between the active layer and the p-type semiconductor layer, absorption loss in the p-type semiconductor layer is suppressed.

In the semiconductor optical device according to the present invention, the second n-type semiconductor layer preferably has a carrier concentration of 1 × 10 ¹⁶ cm ⁻³ or more and 3 × 10 ¹⁸ cm ⁻³ or less. Since the second n-type semiconductor layer has a carrier concentration of 1 × 10 ¹⁶ cm ⁻³ or more, diffusion of hydrogen ions to the active layer in the manufacturing process is sufficiently suppressed. As a result, the crystallinity of the active layer is improved. In addition, since the second n-type semiconductor layer has a carrier concentration of 3 × 10 ¹⁸ cm ⁻³ or less, light absorption by free carriers in the second n-type semiconductor layer 19 is reduced.

  In the semiconductor optical device according to the present invention, it is preferable that the second n-type semiconductor layer has a thickness of 2 nm to 10 nm. Within this range, recombination between carriers (holes) injected from the p-type semiconductor layer and carriers (electrons) in the second n-type semiconductor layer is suppressed in the second n-type semiconductor layer. With the reduction of holes due to this recombination, the generation of reactive current that does not contribute to stimulated emission can be suppressed.

  According to another aspect of the present invention, a method of manufacturing a semiconductor optical device includes a step of forming a first n-type semiconductor layer on a substrate, nitrogen as a group V element on the first n-type semiconductor layer, and Forming an active layer having a group III-V compound semiconductor layer containing arsenic, forming a second n-type semiconductor layer on the active layer, and p-type on the second n-type semiconductor layer A step of forming a semiconductor layer, wherein an n-type dopant is added to the second n-type semiconductor layer, and the second n-type semiconductor layer and the p-type semiconductor layer form a pn junction. Form.

  According to the manufacturing method of the present invention, since the second n-type semiconductor layer is formed after the active layer and prior to the formation of the p-type semiconductor layer, the second n-type semiconductor layer is connected to the p-type semiconductor layer. A pn junction is formed with the interface. The electric field (built-in potential) at the pn junction suppresses the diffusion of hydrogen ions into the active layer during the manufacturing process. As a result, the concentration of hydrogen ions in the active layer can be lowered, and the generation of crystal defects due to the combination of nitrogen and hydrogen ions in the active layer is suppressed.

  ADVANTAGE OF THE INVENTION According to this invention, the semiconductor optical element which has a structure which can improve the crystallinity of an active layer by reducing the density | concentration of the hydrogen ion in an active layer, and its manufacturing method are provided.

  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. Subsequently, embodiments of the semiconductor optical device of the present invention and the manufacturing method thereof will be described with reference to the accompanying drawings. Where possible, the same parts are denoted by the same reference numerals.

(First embodiment)
FIG. 1 is a drawing schematically showing a configuration of a semiconductor optical device 1 according to a first embodiment of the present invention. The semiconductor optical device 1 has a buried ridge structure as will be understood from the following description. When the buried ridge structure is employed, a highly reliable semiconductor optical device can be manufactured by a simple manufacturing process. This embodiment is not limited to the ridge type, and an embedded mesa structure can also be used. The semiconductor optical device can be, for example, a semiconductor laser.

  The semiconductor optical device 1 includes a substrate 11, a first n-type semiconductor layer 13, an active layer 15, a p-type semiconductor layer 17, and a second n-type semiconductor layer 19.

  The first n-type semiconductor layer 13 is provided on the substrate 11 and is, for example, a lower cladding layer. The active layer 15 is provided on the first n-type semiconductor layer 13 and includes a III-V group compound semiconductor layer containing nitrogen and arsenic as group V elements. The III-V compound semiconductor layer is, for example, a well layer having a single quantum well structure. However, the III-V group compound semiconductor layer can have a multiple quantum well structure. The III-V compound semiconductor layer in the active layer 15 is an undoped semiconductor layer or an n-type semiconductor layer to which an n-type dopant is added. The p-type semiconductor layer 17 is provided on the active layer 15 and is, for example, an upper cladding layer. The second n-type semiconductor layer 19 is provided between the active layer 15 and the p-type semiconductor layer 17. The second n-type semiconductor layer 19 is doped with an n-type dopant and is, for example, an upper optical confinement layer. For example, silicon can be used as the n-type dopant. The second n-type semiconductor layer 19 and the p-type semiconductor layer 17 form a pn junction J.

  The pn junction J generates an electric field (built-in potential) E from the second n-type semiconductor layer 19 toward the p-type semiconductor layer 17. The electric field E suppresses diffusion of hydrogen ions into the active layer 15 in the manufacturing process. Therefore, in the present semiconductor optical device 1, the hydrogen concentration in the active layer 15 is low, and generation of crystal defects due to the combination of nitrogen and hydrogen in the active layer 15 is suppressed with a low hydrogen concentration. As a result, the crystal quality of the active layer 15 is excellent.

In the embodiment of the semiconductor optical device 1, the carrier concentration of the second n-type semiconductor layer 19 is 1 × 10 ¹⁶ cm ⁻³ or more. Within this range, the diffusion of hydrogen into the active layer 15 is sufficiently suppressed in the manufacturing process of the semiconductor optical device 1 described later, and as a result, the crystallinity of the active layer 15 is improved. The carrier concentration of the second n-type semiconductor layer 19 is 3 × 10 ¹⁸ cm ⁻³ or less. Within this range, light absorption by free carriers in the second n-type semiconductor layer 19 is reduced.

  The semiconductor optical device 1 can include a buffer layer 23 provided on the semiconductor substrate 21. In the embodiment, a lower optical confinement layer 25 is provided between the first n-type semiconductor layer 13 and the active layer 15. The lower optical confinement layer 25 can be undoped. The semiconductor optical device 1 has a ridge structure in which a p-type semiconductor layer 17 extends along a predetermined axis. N-type buried layers 27 are provided on both side surfaces of the ridge. The semiconductor optical device 1 can include an n-type buried layer 27 and a p-type semiconductor layer 29 (for example, an upper clad layer) provided on the p-type semiconductor layer 17. A contact layer (for example, a p-type contact layer) 31 is provided on the p-type semiconductor layer 29. An electrode (anode) 33 is provided on the contact layer 31. An electrode (cathode) 35 is provided on the back surface of the semiconductor substrate 21.

  The band gap energy of the second n-type semiconductor layer 19 functioning as the optical confinement layer is larger than the band gap energy of the III-V group compound semiconductor layer of the active layer 15 and the first n functioning as the cladding layer. The band gap energy of the p-type semiconductor layer 13 and the p-type semiconductor layer 17 is smaller. The band gap energy of the lower optical confinement layer 25 is larger than the band gap energy of the III-V group compound semiconductor layer of the active layer 15, and the first n-type semiconductor layer 13 and the p-type semiconductor layer function as a cladding layer. It is smaller than 17 band gap energy. Carriers are confined in the active layer 15 by the second n-type semiconductor layer 19 and the lower optical confinement layer 25, and the first n-type semiconductor layer 13 and the p-type semiconductor layer 17.

  The refractive index of the second n-type semiconductor layer 19 is smaller than the average refractive index of the active layer 15 and larger than the refractive indexes of the first n-type semiconductor layer 13 and the p-type semiconductor layer 17. The refractive index of the lower optical confinement layer 25 is smaller than the average refractive index of the active layer 15 and larger than the refractive indexes of the first n-type semiconductor layer 13 and the p-type semiconductor layer 17. With the structure of the semiconductor optical device 1, the first n-type semiconductor layer 13 and the p-type semiconductor layer 17 can confine propagating light in the active layer 15.

An example of the semiconductor optical device 1 is shown below.
Semiconductor substrate 21: n-type GaAs substrate having (100) plane Buffer layer 23: thickness 100 nm, n-type GaAs semiconductor layer first n-type semiconductor layer 13: thickness 1500 nm, n-type Ga _0.51 In _0.49 P semiconductor layer, carrier concentration 7 × 10 ¹⁷ cm ⁻³
Lower optical confinement layer 25: 140 nm thick, i-type GaAs semiconductor layer Active layer 15: 7 nm thick, Ga _0.7 In _0.3 N _0.01 As _0.99 semiconductor layer Second n-type semiconductor layer 19: 140 nm thickness, n-type GaAs semiconductor layer, carrier concentration 1 × 10 ¹⁶ cm ⁻³
p-type semiconductor layer 17: thickness 500 nm, p-type GaInP semiconductor layer, carrier concentration 1 × 10 ¹⁸ cm ⁻³
n-type buried layer 27: thickness 500 nm, n-type AlGaInP semiconductor layer, carrier concentration 1 × 10 ¹⁷ cm ⁻³
p-type semiconductor layer 29: thickness 1000 nm, p-type Ga _0.51 In _0.49 P semiconductor layer contact layer 31: thickness 200 nm, p-type GaAs semiconductor layer. In these layers, for example, Si is used as the n-type dopant, and for example, Zn is used as the p-type dopant.

  Next, a method for manufacturing the semiconductor optical device 1 according to the present embodiment will be described with reference to FIGS. 2-4 is a figure which shows typically each process of the manufacturing method of the semiconductor optical element 1 which concerns on this embodiment. In order to manufacture the semiconductor optical device 1, for example, the following steps are sequentially performed.

(Semiconductor stacking process)
First, the semiconductor substrate 21 is prepared. In the manufacturing method described below, the MOVPE method is used for the growth of a semiconductor crystal. Examples of raw materials for Ga, In, N, As, and P include triethylgallium (TEGa), trimethylindium (TMIn), dimethylhydrazine (DMHy), tertiarybutylarsine (TBAs), and tertiarybutylphosphine (TBP), respectively. ) Is used. For example, tetraethylsilane (TeESi) or diethyl zinc (DEZn) is used as a doping material for Si and Zn. As shown in FIG. 2, a buffer layer 23, a first n-type semiconductor layer 13, a lower optical confinement layer 25, an active layer 15, a second n-type semiconductor layer 19 and a p-type semiconductor layer 17A are formed on a semiconductor substrate 21. Grow sequentially. The second n-type semiconductor layer 19 and the p-type semiconductor layer 17 form a pn junction J. Due to the pn junction J, an electric field E directed upward from the active layer 15 is generated.

For example, the conditions for growing GaInNAs for the III-V compound semiconductor layer of the active layer 15 are as follows:
Growth temperature: 510 ° C.
Growth rate: 0.9 μm / h,
DMHy / V ratio: 0.99
Growth pressure: 76 Torr
It is.

(Embedded layer forming process)
Subsequently, an insulating film 37 is formed on the p-type semiconductor layer 17A. The insulating film 37 is a SiN film, and this SiN film is formed by using, for example, a plasma CVD method. In the formation of the SiN film by the plasma CVD method, a gas containing silane (SiH ₄ ), ammonia (NH ₃ ), and hydrogen (H ₂ ) as main raw materials is used. Thereafter, a photoresist is applied on the insulating film 37 to form a resist layer. Next, a resist mask PM1 is formed by using a photolithography technique. The resist mask PM1 has a stripe mask extending along the direction of a predetermined axis, and the stripe mask width is, for example, 5 μm. The direction of the predetermined axis is the direction of the optical waveguide of the semiconductor optical device.

  Subsequently, the insulating film 37 is etched using the resist mask PM1. Thereby, as shown in FIG. 3, the pattern of the resist mask PM1 is transferred to the etching mask EM1. After the formation of the etching mask EM1, the resist mask PM1 is removed. Thereafter, the p-type semiconductor layer 17A is etched using the etching mask EM1. In the etching step, the p-type semiconductor layer 17A not covered with the etching mask EM1 is removed, so that the ridge-type p-type semiconductor layer 17 is formed. The p-type semiconductor layer 17 has a ridge structure. Thereafter, the n-type buried layer 27 is regrown on both side surfaces of the ridge-type p-type semiconductor layer 17 without removing the etching mask EM1. Thereafter, for example, wet etching is performed to remove the etching mask EM1.

(Other processes)
Subsequently, as shown in FIG. 4, a p-type semiconductor layer 29 and a contact layer 31 are formed on the buried layer 27 and the p-type semiconductor layer 17. Thereafter, an electrode (anode) 33 is formed on the contact layer 31, and an electrode (cathode) 35 is formed on the back surface of the semiconductor substrate 21. Thereby, the semiconductor optical device 1 of FIG. 1 is completed.

  In the manufacturing method described above, examples of the step of placing the active layer 15 in a hydrogen atmosphere include the following. During the formation of the insulating film 37 by the plasma CVD method, the hydrogen concentration in the active layer 15 increases due to the diffusion of hydrogen ions in the plasma gas. Further, during the regrowth of the buried layer 27 and the p-type semiconductor layer 29, hydrogen ions in the MOVPE chamber generated by the thermal decomposition of the organometallic gas (TBP or the like) diffuse to increase the hydrogen concentration in the active layer 15. To do. However, diffusion of hydrogen ions to the active layer 15 is suppressed by the pn junction J formed on the upper side of the active layer 15.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. FIG. 5 is a drawing schematically showing the configuration of the semiconductor optical device 3 according to the second embodiment. The semiconductor optical device 3 is different from the semiconductor optical device 1 according to the first embodiment in that both the second n-type semiconductor layer 19 and the p-type semiconductor layer 17 are embedded by the embedded layer 27. Further, an unembedded semiconductor layer 39 is further provided between the active layer 15 and the second n-type semiconductor layer 19 and the buried layer 27. The semiconductor layer 39 functions as an upper optical confinement layer, and can be undoped, for example. Other configurations are the same as those of the semiconductor optical device 1.

  In this configuration, since the semiconductor layer 39 is between the active layer 15 and the second n-type semiconductor layer 19 and the buried layer 27, the active layer 15 is separated from the p-type semiconductor layer 17. For this reason, the absorption loss in the p-type semiconductor layer 17 is suppressed. In the embodiment of the semiconductor optical device 3, the thickness of the second n-type semiconductor layer 19 is 10 nm. Since the thickness of the second n-type semiconductor layer 19 is 2 nm or more, a barrier against hydrogen diffusion can be provided. In addition, since the second n-type semiconductor layer 19 has a thickness of 10 nm or less, in the second n-type semiconductor layer 19, the majority carriers (electrons) of the second n-type semiconductor layer 19 and the p-type semiconductor layer 17 are injected. Recombination with the formed holes is suppressed. As a result, holes that disappear before reaching the active layer 15 can be reduced.

An example of the semiconductor optical device 3 is shown as follows.
Semiconductor layer 39: 140 nm thick, i-type GaAs semiconductor layer Second n-type semiconductor layer 19: 10 nm thick, n-type Ga _0.51 In _0.49 P semiconductor layer, carrier concentration 1 × 10 ¹⁶ cm ⁻³
p-type semiconductor layer 17: thickness 490 nm, p-type Ga _0.51 In _0.49 P semiconductor layer, carrier concentration 1 × 10 ¹⁸ cm ⁻³
It is.

  Next, a modification of the semiconductor optical device 5 according to the second embodiment of the present invention will be described. FIG. 6 is a drawing schematically showing the configuration of the semiconductor optical device 5. The semiconductor optical device 5 is different from the semiconductor optical device 3 of the second embodiment in the following points. One of them is that the second n-type semiconductor layer 19 is made of the same semiconductor material as that of the semiconductor layer 39, and the other is that the second n-type semiconductor layer 19 is buried by the n-type buried layer 27. This is different from the semiconductor optical device 3 of the second embodiment in that it is not. The second n-type semiconductor layer 19 is provided between the semiconductor layer 39, the p-type semiconductor layer 17, and the n-type buried layer 27.

  Similarly to the semiconductor optical device 3, the semiconductor optical device 5 is provided with the second n-type semiconductor layer 19, and an undoped semiconductor layer 39 is provided between the active layer 15 and the second n-type semiconductor layer 19. It is in. Therefore, the semiconductor optical device 5 can obtain the same effect as the semiconductor optical device 3.

An example of the semiconductor optical device 5 is shown below.
Second n-type semiconductor layer 19: 10 nm thick, n-type GaAs semiconductor layer Semiconductor layer 39: 140 nm thick, i-type GaAs semiconductor layer p-type semiconductor layer 17: 500 nm thick, p-type GaInP semiconductor layer, carrier concentration 1 × 10 ¹⁸ cm ^-3
It is.

  Hereinafter, the effects of the semiconductor optical devices 1, 3 and 5 according to the first and second embodiments will be described in detail in comparison with conventional semiconductor optical devices. FIG. 7 shows a conventional semiconductor optical device 7 to be compared. In the semiconductor optical device 7, an undoped semiconductor layer 39 is provided between the p-type semiconductor layer 17 and the active layer 15. The semiconductor optical device 7 is different from the semiconductor optical device 1 in that it does not include the second n-type semiconductor layer 19. Other configurations are the same as those of the semiconductor optical device 1 for easy comparison.

FIG. 8 is a diagram showing current-light output characteristics in the semiconductor optical devices 1, 3 and 7. In FIG. 8, the horizontal axis represents the applied current (mA), and the vertical axis represents the optical output (mW) at the applied current. FIG. 8 is a graph showing current-light output characteristics PL ₁ , PL ₃ and PL ₇ in the semiconductor optical devices ₁ , ₃ and ₇ . FIG. 8 shows drive current values (threshold currents) I ₁ , I ₃ and I _{7 at} which the semiconductor optical devices 1, 3 and 7 start laser oscillation. As shown in FIG. 8, the semiconductor optical device 7 having the conventional structure has a threshold current I ₇ higher than the threshold currents I ₁ and I _{3 of} the semiconductor optical devices 1 and ₃ , and a light emission efficiency (hereinafter, It can be seen that the slope of the characteristic PL ₇ representing the slope efficiency is smaller than the slopes of the characteristic PL ₁ and the characteristic PL ₃ , respectively.

  First, the cause of the difference between the threshold current and the slope efficiency in FIG. 8 is considered as follows. In the conventional semiconductor optical device 7, unlike the semiconductor optical devices 1 and 3, the second n-type semiconductor layer 19 is not provided between the active layer 15 and the p-type semiconductor layer 17. Therefore, as shown in FIG. 9, when an insulating film 37 is formed by a plasma CVD method on a stacked body that does not include the pn junction J, diffusion of hydrogen ions in the plasma gas to the active layer 15 is not suppressed. Further, when regrowth of the p-type semiconductor layer 29 or the like is performed without forming the pn junction J, hydrogen generated by pyrolysis of organometallic gas TBP in the MOVPE chamber during the regrowth diffuses into the active layer 15. It is not suppressed. As a result, it is considered that a large number of crystal defects are generated due to the combination of hydrogen and nitrogen in the active layer 15, and the crystal defects cause a high threshold current and a low slope efficiency.

  On the other hand, in the first semiconductor optical device 1, a pn junction J is formed on the active layer 15 as shown in FIG. Therefore, an electric field E directed upward from the active layer 15 is generated in the pn junction J, and this electric field prevents hydrogen ions, which are positive ions, from entering the active layer 15 during the manufacturing process. Therefore, the generation of crystal defects due to the combination of nitrogen and hydrogen ions in the active layer 15 is suppressed. As a result, it is considered that the deterioration of the crystallinity of the active layer 15 is suppressed, and a low threshold current and a high slope efficiency are obtained. Also in the semiconductor optical device 3 according to the second embodiment, since the second n-type semiconductor layer 19 is provided between the active layer 15 and the p-type semiconductor layer 17 as in the semiconductor optical device 1. The same effect as the semiconductor optical device 1 can be obtained.

Differences between the characteristic PL ₃ in the property PL ₁ and the semiconductor optical element 3 in the semiconductor optical device 1 will be described with reference to FIGS. 11 and 12. In the semiconductor optical device 1, since the second n-type semiconductor layer 19 is directly provided on the active layer 15, the electrons existing in the second n-type semiconductor layer 19 are shown in FIG. 11. It is considered that part of the holes and holes injected from the p-type semiconductor layer 17 are recombined in the second n-type semiconductor layer 19, thereby reducing the amount of holes injected into the active layer 15 and reducing the light emission efficiency. .

  On the other hand, in the semiconductor optical device 3, the thickness of the second n-type semiconductor layer 19 is 10 nm, which is one digit or more thinner than the thickness 140 nm of the second n-type semiconductor layer 19 of the semiconductor optical device 1. Therefore, as shown in FIG. 12, in the semiconductor optical device 3, the holes from the p-type semiconductor layer 17 and the carriers (electrons) of the second n-type semiconductor layer 19 are compared with those in the semiconductor optical device 1. Less recombination. This is considered to be due to a decrease in the generation of reactive currents that do not contribute to stimulated emission.

In addition, in the semiconductor optical device 3, since the undoped semiconductor layer 39 is between the active layer 15 and the p-type semiconductor layer 29, light propagating through the active layer 15 is absorbed by the p-type semiconductor layer 17. This is considered to have been reduced. For the reasons described above, it is considered that the semiconductor optical device 3 achieved a lower threshold current I ₃ and a higher slope efficiency than the semiconductor optical device 1.

Next, the current-light output characteristics of the semiconductor optical devices 3 and 5 will be described with reference to FIG.
In FIG. 13, the horizontal axis represents the applied current (mA), and the vertical axis represents the optical output (mW) at the applied current. FIG. 13 is a graph showing current-light output characteristics PL ₃ and PL ₅ in the semiconductor optical devices 3 and 5. In FIG. 13, threshold currents I ₃ and I ₅ represent the threshold currents of the semiconductor optical devices 3 and 5, respectively. As shown in FIG. 13, it can be seen that the characteristics PL ₃ and PL ₅ are substantially the same. That is, the semiconductor optical devices 3 and 5 have substantially the same threshold currents I ₃ and I ₅ and substantially the same slope efficiency, respectively. These characteristics are that the semiconductor optical devices 3 and 5 each have an active layer 15, a second n-type semiconductor layer 19, and an undoped semiconductor layer 39 provided between these layers 15 and 19. This is considered due to the structure and the thickness of the second n-type semiconductor layer 19 being about 10 nm.

[Experimental example]
In this experimental example, while making the wafer _{W E1, W E2, W C} in Examples 1 and 2 and Comparative Example 1 respectively corresponding to the semiconductor optical device 1, 3 and 7, the wafer _{W E1, W E2, W C} The hydrogen concentration in the active layer was measured. The MOVPE method was used for manufacturing the wafers W _E1 , W _E2 , and W _C. TEGa, TMIn, DMHy, TBAs, and TBP were used as raw materials for Ga, In, N, As, and P, respectively. TeESi and DEZn were used as doping materials for Si and Zn, respectively.

First, the epitaxial structure S1 was produced as follows. On a Si-doped GaAs (100) substrate, a Si-doped GaAs buffer layer having a thickness of 100 nm, a Si-doped GaInP first n-type semiconductor layer having a thickness of 1500 nm (composition Ga _0.51 In _0.49 P, carrier) Concentration 7 × 10 ¹⁷ cm ⁻³ ), 140 nm thick undoped GaAs lower optical confinement layer, 7 nm thick undoped GaInNAs active layer (composition Ga _0.7 In _0.3 N _0.01 As _0.99 ) 140 nm thick Si-doped GaAs second n-type semiconductor layer (carrier concentration 1 × 10 ¹⁶ cm ⁻³ ) and 500 nm thick Zn-doped GaInP p-type semiconductor layer (composition Ga _0.51 In _{0. 49} P and a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ ) were sequentially formed to produce an epitaxial structure S1.

Epitaxial structure S2 was fabricated as follows. On a Si-doped GaAs (100) substrate, a Si-doped GaAs buffer layer having a thickness of 100 nm, a Si-doped GaInP first n-type semiconductor layer having a thickness of 1500 nm (composition Ga _0.51 In _0.49 P, carrier) Concentration 7 × 10 ¹⁷ cm ⁻³ ), 140 nm thick undoped GaAs lower optical confinement layer, 7 nm thick undoped GaInNAs active layer (composition Ga _0.7 In _0.3 N _0.01 As _0.99 ) 140 nm thick undoped GaAs semiconductor layer, 10 nm thick Si doped GaInP second n-type semiconductor layer (composition Ga _0.51 In _0.49 P, carrier concentration 1 × 10 ¹⁶ cm ⁻³ ) and thickness p-type semiconductor layer of GaInP of 490nm of Zn-doped (composition _Ga 0.51 _{in 0.49} P, a carrier concentration of 1 × ^{10 18} m ^-3) are sequentially formed, and to produce an epitaxial structure S2.

Epitaxial structure S3 was produced as follows. On a Si-doped GaAs (100) substrate, a Si-doped GaAs buffer layer having a thickness of 100 nm, a Si-doped GaInP first n-type semiconductor layer having a thickness of 1500 nm (composition Ga _0.51 In _0.49 P, carrier) Concentration 7 × 10 ¹⁷ cm ⁻³ ), 140 nm thick undoped GaAs lower optical confinement layer, 7 nm thick undoped GaInNAs active layer (composition Ga _0.7 In _0.3 N _0.01 As _0.99 ) Then, an undoped GaAs semiconductor layer having a thickness of 140 nm and a Zn-doped GaInP p-type semiconductor layer having a thickness of 500 nm (composition Ga _0.51 In _0.49 P, carrier concentration 1 × 10 ¹⁸ cm ⁻³ ) are sequentially formed. Thus, an epitaxial structure S3 was produced.

  Next, in order to surely examine the influence of the pn junction J on the hydrogen diffusion in the regrowth, the layers described later were formed simultaneously in the same environment in each of the epitaxial structures S1, S2 and S3. First, the epitaxial structures S1, S2 and S3 were installed in the second MOVPE apparatus, and an undoped GaAs layer having a thickness of 0.1 μm serving as an etching stop layer was formed on the epitaxial structures S1, S2 and S3 together. . Subsequently, a Si-doped AlGaInP layer having a thickness of 500 nm, a Zn-doped GaInP cladding layer having a thickness of 1500 nm, and a Zn-doped GaAs contact layer having a thickness of 200 nm were sequentially formed. In this way, epitaxial structures A, B and C having epitaxial structures S1, S2 and S3 were completed.

Thereafter, in order to increase the depth resolution in the secondary ion mass spectrometry (SIMS) analysis, the epitaxial structures A, B, and C of Examples 1 and 2 and Comparative Example 1 were processed as follows. . First, the GaAs contact layer is removed by wet etching using an etching solution (mixed solution of phosphoric acid, hydrogen peroxide solution, and water), and then wet etching using an etching solution (mixed solution of hydrochloric acid and water). The GaInP cladding layer and the AlGaInP layer were removed. Then, the GaAs etching stop layer was removed using an etching solution (mixed solution of phosphoric acid, hydrogen peroxide solution, and water) to expose the p-type semiconductor layer of GaInP. Wafers W _E1 , W _E2 , and W _C for SIMS analysis having structures equivalent to those in FIGS. 14A, 14 </ b> B, and 14 </ b> _C were manufactured.

A sample for SIMS analysis having a size of about 1 cm square near the center of the wafer was prepared by cleavage. SIMS analysis of these samples was performed using a Q-pole SIMS analyzer. As the primary ions, cesium ions (Cs ⁺ ) having an energy of 2 keV were used, and the incident angle was 60 degrees. Negative ions were detected as secondary ions. In addition, the detection limit of hydrogen in SIMS analysis was about 2 × 10 ¹⁷ cm ⁻³ . Further, in order to calibrate the relationship between the depth from the surface of the sample and the amount of sputtering, the step formed on each sample by sputtering was measured with a step gauge. However, in order to increase the accuracy of depth measurement, the position of the active layer was specified by measuring indium (In) and nitrogen (N) simultaneously with hydrogen. In addition, since the measurement error of In concentration may be large, the value remains as reference data.

(SIMS analysis results)
15 and 16 show the SIMS analysis results of the wafer _{W C} according to Comparative Example 1, FIGS. 17 and 18 show the SIMS analysis results of the wafer _{W E1} of Example 1 and 2, respectively.

In Figure 15, the horizontal axis indicates the depth (nm), and the vertical axis on the left represents the concentration ^{(cm -3)} of the H and N, and the right ordinate in _{Ga 1-X In X N Y} As 1-Y The In content (value of X) is shown. The peaks of the N and In concentration curves at a position of about 560 nm from the surface of the sample correspond to the active layer. FIG. 16 is an enlarged view of a region (near the active layer) from 500 nm to 650 nm from the surface of the sample. Referring to FIG. 16, in the wafer W _C according to Comparative Example 1, it can be seen that the H concentration curves in the active layer is higher than the H concentration value on the layer other than the active layer. Specifically, the layers other than the active layer are a GaAs lower optical confinement layer and an undoped GaAs semiconductor layer. From the difference in H concentration, for example, in the process of forming a p-type semiconductor layer on the active layer, it is considered that hydrogen ions diffuse into the active layer and are trapped in the active layer in a form that combines with nitrogen. It is done.

On the other hand, in FIG. 17, the horizontal axis indicates the depth (nm), and the vertical axis on the left represents the concentration ^{(cm -3)} of the H and N, the right vertical axis _{Ga 1-X In X N Y} As 1- The In content (value of X) in _Y is shown. The peaks of the N and In concentration curves at a position of about 560 nm from the surface of the sample correspond to the active layer. It appears that a large amount of H is detected from the surface of the sample to a depth of about 300 nm, which is due to the influence of contamination on the surface of the sample. FIG. 18 shows an enlarged view of a region (near the active layer) between the position of 500 nm and the position of 650 nm from the surface. As shown in FIG. 18, it can be seen that the concentration of H in the vicinity of the active layer is a value below the detection limit (2 × 10 ¹⁷ cm ⁻³ ). The peak of N and In concentration values near 560 nm on the horizontal axis indicates the position of the active layer, and the H concentration value is below the detection limit in this region. Therefore, it was shown that diffusion of hydrogen ions to the active layer is suppressed in the process of forming the p-type semiconductor layer on the active layer. In addition, in the wafer _{WE2 according} to Example 2, the same result as in Example 1 was obtained.

  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. We therefore claim all modifications and changes that come within the scope and spirit of the following claims.

1 is a drawing schematically showing a configuration of a semiconductor optical device according to a first embodiment. It is a figure which shows the process of manufacturing the semiconductor optical element concerning 1st Embodiment. It is a figure which shows the process of manufacturing the semiconductor optical element concerning 1st Embodiment. It is a figure which shows the process of manufacturing the semiconductor optical element concerning 1st Embodiment. It is drawing which shows schematically the structure of the semiconductor optical element concerning 2nd Embodiment. It is drawing which shows roughly the structure of the semiconductor optical element which concerns on the modification of 2nd Embodiment. 1 is a drawing schematically showing a configuration of a conventional semiconductor optical device. It is a figure which shows the electric current-light output characteristic in each semiconductor optical element shown in FIG.1, FIG5 and FIG.7. FIG. 8 is an energy band diagram in the vicinity of an undoped semiconductor layer, an active layer, and a lower optical confinement layer of the semiconductor optical device in FIG. 7. FIG. 2 is an energy band diagram in a region extending from a lower optical confinement layer to a p-type semiconductor layer of the semiconductor element of FIG. 1. It is a figure for demonstrating the effect of the semiconductor element shown in FIG. It is a figure for demonstrating the effect of the semiconductor optical element shown in FIG. It is a figure which shows the electric current-light output characteristic in each semiconductor optical element shown by FIG.5 and FIG.6. 1 is a view showing wafers according to Examples 1 and 2 and Comparative Example 1. FIG. It is a figure which shows the analysis result by SIMS for showing the hydrogen concentration in the active layer of the wafer which concerns on the comparative example 1. It is a figure which shows the analysis result by SIMS for showing the hydrogen concentration in the active layer of the wafer which concerns on the comparative example 1. It is a figure which shows the analysis result by SIMS for showing the hydrogen concentration in the active layer of the wafer which concerns on Example 1. FIG. It is a figure which shows the analysis result by SIMS for showing the hydrogen concentration in the active layer of the wafer which concerns on Example 1. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,3,5,7 ... Semiconductor optical element, 11 ... Substrate, 13 ... 1st n-type semiconductor layer, 15 ... Active layer, 17 ... p-type semiconductor layer, 19 ... 2nd n-type semiconductor layer.

Claims (5)

A first n-type semiconductor layer provided on the substrate;
An active layer provided on the first n-type semiconductor layer and having a III-V group compound semiconductor layer containing nitrogen and arsenic as group V elements;
A p-type semiconductor layer provided on the active layer;
A second n-type semiconductor layer provided between the active layer and the p-type semiconductor layer;
With
An n-type dopant is added to the second n-type semiconductor layer,
A semiconductor optical device in which the second n-type semiconductor layer and the p-type semiconductor layer form a pn junction.   The semiconductor optical device according to claim 1, further comprising an undoped semiconductor layer between the active layer and the second n-type semiconductor layer. 3. The semiconductor optical device according to claim 1, wherein the second n-type semiconductor layer has a carrier concentration of 1 × 10 ¹⁶ cm ⁻³ or more and 3 × 10 ¹⁸ cm ⁻³ or less.   The semiconductor optical device according to claim 1, wherein the second n-type semiconductor layer has a thickness of 2 nm to 10 nm. A method of manufacturing a semiconductor optical device using metal organic vapor phase epitaxy,
Forming a first n-type semiconductor layer on the substrate;
Forming an active layer having a group III-V compound semiconductor layer containing nitrogen and arsenic as a group V element on the first n-type semiconductor layer;
Forming a second n-type semiconductor layer on the active layer;
Forming a p-type semiconductor layer on the second n-type semiconductor layer;
With
An n-type dopant is added to the second n-type semiconductor layer,
A method of forming a pn junction between the second n-type semiconductor layer and the p-type semiconductor layer.

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