JP2008198942A - Semiconductor photo element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor photo element which can control an overflow of electrons. <P>SOLUTION: The semiconductor photo element 10 includes an active layer 15 which contains a well layer 31 and barrier layer 32 having a quantum well structure, an offset layer 35 (a first clad layer) which is located on the barrier layer 32 and is composed of a semiconductor material of group III-V compound, an electron stopper layer 17 which is located on the offset layer 35 and contains a p-type impurity, and a second clad layer 18 which is located on the electron stopper 17, is composed of the same material to the offset layer 35, and contains a p-type impurity of a concentration lower than the concentration of the p-type impurity of the electron stopper layer 17. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a semiconductor optical device.

  A semiconductor laser element used for optical communication generates laser light having a wavelength of 1.25 μm to 1.65 μm. In such a laser element, a quantum well structure using a GaInAsP-based quaternary mixed crystal material is mainly used as an active layer, and InP is used as a material for a cladding layer.

  One factor that degrades the current-light output characteristics of the semiconductor laser device at high temperature is the overflow of electrons. This is because electrons injected from the n-type cladding layer into the active layer pass through the p-type cladding layer, or electrons in the active layer or the optical confinement layer are thermally excited and leak into the p-type cladding layer. This phenomenon does not contribute to light emission due to recombination at.

  In order to prevent the overflow of electrons, it is conceivable to provide an electron stopper layer between the active layer and the p-type cladding layer.

Non-Patent Documents 1 and 2 below disclose an electronic stopper layer inserted between an active layer and a p-type cladding layer. As a material for the electron stopper layer, a material such as GaInP or AlGaInAs having a larger band gap energy than InP is used.
Hiroshi Wada et al., “Effects of well Number on Temperature Characteristics in 1.3-μm AlGaInAs-InPQuantum-Well Lasers”, IEEE Journal of Selected Topics in Quantum Electronics, Vol. 5, No. 3, pp. 420-427, 1999 Piprek J. et al., "Effects of Quantum Well Recombination Losses on the Internal Differential Efficiency of Multi-Quantum-Well Lasers", Conference Digest. ISLC1998 NARA. 1998 IEEE 16th International Semiconductor LaserConference, pp. 167-168, 1998

  By the way, the present inventor has found that when the p-type impurity is doped at a high concentration on the active layer side of the p-type cladding layer, the electron injection efficiency can be increased, and there is an effect as an electron stopper layer.

  However, as shown in FIG. 6, it was found that when the concentration of the p-type impurity is high, holes ionized from the p-type impurity in the electron stopper layer 117 move to the active layer side in the thermal equilibrium state. . This is probably because the hole energy of the valence band 126 of the optical confinement layer 116 located on the active layer side is significantly lower than the hole energy of the valence band 126 of the electron stopper layer 117. FIG. 6 is a band diagram of a semiconductor optical device in which an electron stopper layer is doped with p-type impurities at a high concentration.

  When holes in the electron stopper layer 117 move to the light confinement layer 116, positive charges are generated in the light confinement layer 116. On the other hand, a negative charge corresponding to the charge amount of the transferred holes is generated in the electron stopper layer 117. As a result, an electric field is generated from the optical confinement layer 116 to the electron stopper layer 117. In accordance with the strength of the electric field, the band (conduction band 127 and valence band 126) on the side of the optical confinement layer 116 in the electron stopper layer 117 bends in the direction in which the electron energy decreases, as shown in FIG. End up. As a result, more electrons pass through the electron stopper layer 117.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a semiconductor optical device capable of suppressing an overflow of electrons.

  In order to solve the above-described problems, a semiconductor optical device of the present invention includes a first active layer including a well layer and a barrier layer and having a quantum well structure, and a first layer made of a III-V group compound semiconductor material provided on the barrier layer. A clad layer, an electron stopper layer containing a p-type impurity provided on the first clad layer, and made of the same material as the first clad layer provided on the electron stopper layer. and a second cladding layer containing a p-type impurity having a lower concentration than the p-type impurity concentration.

  In the semiconductor optical device of the present invention, the number of holes moving to the barrier layer side among the holes in the electron stopper layer is reduced in the thermal equilibrium state as compared with the case where the first cladding layer is not provided. This is because (1) the hole energy in the valence band of the first cladding layer is relatively large, and (2) the electron stopper layer is separated from the barrier layer by the first cladding layer. And so on. When the number of holes moving from the electron stopper layer to the barrier layer side is small, the change in the charge of the electron stopper layer is small, and the electric field applied between the electron stopper layer and the barrier layer is small. Therefore, the conduction band bending of the electron stopper layer is also reduced, so that the overflow of electrons can be suppressed.

  The semiconductor optical device further includes an optical confinement layer provided between the barrier layer and the first cladding layer, and the band gap energy of the optical confinement layer is greater than the band gap energy of the barrier layer. And is preferably smaller than the band gap energy of the first cladding layer.

  In this case, the first cladding layer reduces the number of holes that move to the optical confinement layer among the holes in the electron stopper layer. Further, since the light is easily confined in the active layer by the light confinement layer, it is possible to suppress the light from reaching the electron stopper layer and being absorbed by the electron stopper layer.

  The first clad includes a p-type impurity, the optical confinement layer includes a p-type impurity, and the p-type impurity concentration of the first clad is higher than the p-type impurity concentration of the optical confinement layer, And it is preferable that it is lower than the p-type impurity concentration of the electron stopper layer.

  In this case, since the difference in the p-type impurity concentration between the electron stopper layer and the first cladding layer is reduced, the diffusion movement of holes from the electron stopper layer is reduced, and the bending of the band is reduced. In addition, the electron energy in the conduction band of the first cladding layer becomes relatively large. Therefore, since the first cladding layer serves as a barrier against electrons, movement of electrons from the optical confinement layer to the first cladding layer is suppressed.

  ADVANTAGE OF THE INVENTION According to this invention, the semiconductor optical element which can suppress the overflow of an electron is provided.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same reference numerals are used for the same or equivalent elements, and duplicate descriptions are omitted.

(First embodiment)
FIG. 1 is a cross-sectional view schematically showing a semiconductor optical device according to the first embodiment. Examples of the semiconductor optical device 10 shown in FIG. 1 include a semiconductor laser and a semiconductor amplifier. The semiconductor optical device 10 includes an n-type semiconductor substrate 12, an n-type cladding layer 13 provided on the semiconductor substrate 12, and an n-type (or non-doped) optical confinement layer (SCH) provided on the cladding layer 13. 14, an active layer 15 provided on the optical confinement layer 14, a p-type (or non-doped) optical confinement layer 16 provided on the active layer 15, and an optical confinement layer 16. Offset layer 35 (first cladding layer), p-type electron stopper layer 17 provided on offset layer 35, and p-type cladding layer 18 (second layer) provided on electron stopper layer 17 Clad layer). An n electrode 22 is provided on the back surface of the semiconductor substrate 12. For example, the n-electrode 22 is formed on the entire back surface of the semiconductor substrate 12. A p-electrode 21 is provided on the cladding layer 18. The p electrode 21 is formed in a stripe shape, for example. Alternatively, the p-electrode 21 may be formed on a current confinement structure in which both sides of the active layer etched in a stripe shape are filled with a current blocking layer. The semiconductor substrate 12 and the cladding layer 13 may be integrated. Further, the semiconductor optical device 10 may not include the optical confinement layers 14 and 16.

  The semiconductor substrate 12 is made of a III-V group compound semiconductor material such as InP. The cladding layers 13 and 18 are made of a III-V group compound semiconductor material such as InP, AlGaInAs, and GaInAsP. The active layer 15 has a quantum well structure in which a plurality of well layers 31 and a plurality of barrier layers 32 are alternately stacked (multiple quantum well structure). A barrier layer 32 is disposed on the outermost layer of the active layer 15. Therefore, the optical confinement layer 14 is disposed between the cladding layer 13 and the barrier layer 32. The optical confinement layer 16 is disposed between the offset layer 35 and the barrier layer 32. The active layer 15 may have one well layer 31 (single quantum well structure). The well layer 31 is made of a III-V group compound semiconductor material such as AlGaInAs and GaInAsP. The barrier layer 32 is made of a III-V group compound semiconductor material such as AlGaInAs and GaInAsP. The wavelength of the light output from the semiconductor optical device 10 is, for example, 1.25 to 1.65 μm.

The optical confinement layers 14 and 16 are made of a III-V group compound semiconductor material such as AlGaInAs and GaInAsP, for example. The offset layer 35 is made of a III-V group compound semiconductor material such as InP, AlGaInAs, GaInAsP, or InGaP. The offset layer 35 may or may not include a p-type impurity. When the offset layer 35 includes a p-type impurity, the p-type impurity concentration of the offset layer 35 is, for example, 1 × 10 ¹⁷ to 1 × 10 ¹⁸ cm ⁻³ . The offset layer 35 preferably contains a p-type impurity having a concentration lower than the p-type impurity concentration of the electron stopper layer 17. The thickness of the offset layer 35 is preferably 10 to 500 nm.

The electron stopper layer 17 is made of a III-V group compound semiconductor material such as InP, GaInP, AlGaInAs, or GaInAsP. The electron stopper layer 17 is doped with a high-concentration p-type impurity. The p-type impurity concentration of the electron stopper layer 17 is, for example, 7 × 10 ¹⁷ to 2 × 10 ¹⁹ cm ⁻³ . The thickness of the electronic stopper layer 17 is preferably 2 to 100 nm.

The clad layer 18 is made of the same material as the offset layer 35. The clad layer 18 includes a p-type impurity having a concentration lower than the p-type impurity concentration of the electron stopper layer 17. The p-type impurity concentration of the cladding layer 18 is, for example, 1 × 10 ¹⁷ to 1 × 10 ¹⁸ cm ⁻³ .

  FIG. 2 is a band diagram of the semiconductor optical device according to the first embodiment. In FIG. 2, 26 represents a valence electron, 27 represents a conduction band, a black circle represents an electron, and a white circle represents a hole. Arrows 28 and 29 indicate the directions of holes and electrons injected into the semiconductor optical device 10, respectively. An arrow 25 indicates a transition of electrons accompanying stimulated emission in the active layer 15.

  As shown in FIG. 2, the band gap energy of the well layer 31 is smaller than the band gap energy of the barrier layer 32. The band gap energy of the optical confinement layers 14 and 16 is larger than the band gap energy of the barrier layer 32 and smaller than the band gap energy of the offset layer 35. The band gap energy of the cladding layers 13 and 18 and the electron stopper layer 17 is larger than the band gap energy of the optical confinement layers 14 and 16. The electron stopper layer 17 forms a potential barrier against electrons. The conduction band lower end of the electron stopper layer 17 is higher than the conduction band lower ends of the offset layer 35 and the cladding layer 18. The upper end of the valence band of the electron stopper layer 17 is higher than the upper ends of the valence bands of the offset layer 35 and the cladding layer 18. The valence band upper end of the electron stopper layer 17 may be lower than the valence band upper ends of the offset layer 35 and the cladding layer 18.

  In the semiconductor optical device 10 of the present embodiment, holes that move to the light confinement layer 16 side by diffusion or the like among the holes in the electron stopper layer 17 in a thermal equilibrium state as compared with the case where the offset layer 35 is not provided. The number of This is because (1) the hole energy in the valence band of the offset layer 35 is relatively large, and (2) the electron stopper layer 17 is separated from the optical confinement layer 16 by the offset layer 35. Etc. When the number of holes moving from the electron stopper layer 17 to the light confinement layer 16 side is small, the change in the charge of the electron stopper layer 17 becomes small, so that the charge is applied between the electron stopper layer 17 and the light confinement layer 16. The electric field is reduced. Therefore, since the bending of the conduction band of the electron stopper layer 17 is also reduced, the overflow of electrons can be suppressed. Furthermore, since the valence band of the electron stopper layer 17 can be prevented from bending in the direction of large hole energy, the efficiency of hole injection into the active layer 15 can be improved. Therefore, when the semiconductor optical device 10 is a light emitting device, the optical output of the semiconductor optical device 10 can be increased. The optical output of the semiconductor optical device 10 is unlikely to decrease even under a high temperature environment of 85 ° C.

  Further, when the semiconductor optical device 10 includes the light confinement layers 14 and 16, the light confinement layers 14 and 16 make it easy to confine light in the active layer 15, so that the light reaches the electron stopper layer 17 and is caused by the electron stopper layer 17. Absorption can be suppressed.

  The offset layer 35 contains p-type impurities, and the p-type impurity concentration of the offset layer 35 is higher than the p-type impurity concentration of the optical confinement layer 16 and lower than the p-type impurity concentration of the electron stopper layer 17. preferable. In this case, since the difference in the p-type impurity concentration between the electron stopper layer 17 and the offset layer 35 is reduced, the diffusion and movement of holes from the electron stopper layer 17 are reduced, and the bending of the band is reduced. In addition, the electron energy in the conduction band of the offset layer 35 is relatively greater than when the offset layer 35 is non-doped. Therefore, since the offset layer 35 becomes a barrier against electrons, the electrons are suppressed from moving from the light confinement layer 16 to the offset layer 35.

  Further, the thickness of the offset layer 35 is preferably 10 to 500 nm. When the thickness of the offset layer 35 is less than 10 nm, holes in the electron stopper layer 17 tend to move to the light confinement layer 16, and the conduction band of the electron stopper layer 17 tends to bend. On the other hand, when the thickness of the offset layer 35 exceeds 500 nm, carrier recombination occurs in the offset layer 35, and thus the light emission efficiency of the semiconductor optical device 10 tends to decrease.

FIG. 3 is a graph schematically showing an example of current-light output characteristics (IL characteristics) of the semiconductor optical device according to the first embodiment. In FIG. 3, the vertical axis represents the light output, and the horizontal axis represents the current. In FIG. 3, the solid line G <b> 1 indicates the IL characteristic of the semiconductor optical device 10. Practice G2 shows IL characteristics of a semiconductor optical device having the same configuration as that of the semiconductor optical device 10 except that the offset layer 35 is not provided. As shown in FIG. 3, the threshold current I _th is greater than the current of laser oscillation, the optical output of the semiconductor optical element is can be seen that large by providing the offset layer 35.

  Configuration examples 1 and 2 of the semiconductor optical device according to this embodiment are shown below.

(Configuration example 1)
Cladding layer 18: p-InP layer Electron stopper layer 17: p-InP layer or p-AlGaInAs layer Offset layer 35: p-InP layer Optical confinement layer 16: p-AlGaInAs layer Well layer 31: AlGaInAs layer Barrier layer 32: AlGaInAs layer Optical confinement layer 14: n-AlGaInAs layer Clad layer 13: n-InP layer Semiconductor substrate 12: n-InP substrate

(Configuration example 2)
Clad layer 18: p-InP layer Electron stopper layer 17: p-InP layer Offset layer 35: p-InP layer Optical confinement layer 16: p-GaInAsP layer Well layer 31: GaInAsP layer Barrier layer 32 GaInAsP layer / light confinement layer 14: n-GaInAsP layer / cladding layer 13: n-InP layer / semiconductor substrate 12: n-InP substrate

(Second Embodiment)
FIG. 4 is a cross-sectional view schematically showing a semiconductor optical device according to the second embodiment. FIG. 5 is a band diagram of a semiconductor optical device according to the second embodiment. As the semiconductor optical device 10a shown in FIG. The semiconductor optical device 10a includes a p-type semiconductor substrate 12a, a p-type cladding layer 18 (second cladding layer) provided on the semiconductor substrate 12a, and a p-type electronic stopper provided on the cladding layer 18. Layer 17, offset layer 35 (first cladding layer) provided on electron stopper layer 17, p-type (or non-doped) light confinement layer 16 provided on offset layer 35, and light confinement layer 16 The active layer 15 provided above, the n-type (or non-doped) light confinement layer 14 provided on the active layer 15, and the n-type cladding layer 13 provided on the light confinement layer 14 are provided. A p-electrode 21 is provided on the back surface of the semiconductor substrate 12a. The p electrode 21 is formed on the entire back surface of the semiconductor substrate 12a, for example. An n electrode 22 is provided on the cladding layer 13. The n electrode 22 is formed in a stripe shape, for example. The semiconductor substrate 12a and the cladding layer 18 may be integrated. Further, the semiconductor optical device 10a may not include the optical confinement layers 14 and 16. The semiconductor substrate 12a is made of a III-V group compound semiconductor material such as InP, for example.

  In the semiconductor optical device 10a of the present embodiment, the same effects as the semiconductor optical device 10 can be obtained. Therefore, in the semiconductor optical device 10a, the overflow of electrons can be suppressed.

  As mentioned above, although preferred embodiment of this invention was described in detail, this invention is not limited to the said embodiment.

1 is a cross-sectional view schematically showing a semiconductor optical device according to a first embodiment. 1 is a band diagram of a semiconductor optical device according to a first embodiment. It is a graph which shows typically an example of the current-light output characteristic (IL characteristic) of the semiconductor optical element concerning a 1st embodiment. It is sectional drawing which shows typically the semiconductor optical element which concerns on 2nd Embodiment. It is a band figure of the semiconductor optical element concerning a 2nd embodiment. FIG. 5 is a band diagram of a semiconductor optical device in which an electron stopper layer is doped with a p-type impurity at a high concentration.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10, 10a ... Semiconductor optical element 14, 16 ... Optical confinement layer, 15 ... Active layer, 17 ... Electron stopper layer, 18 ... 2nd cladding layer, 31 ... Well layer, 32 ... Barrier layer, 35 ... Offset layer ( First cladding layer).

Claims (3)

An active layer having a quantum well structure including a well layer and a barrier layer;
A first cladding layer provided on the barrier layer and made of a III-V compound semiconductor material;
An electronic stopper layer provided on the first cladding layer and containing p-type impurities;
A second clad layer provided on the electron stopper layer and made of the same material as the first clad layer, and containing a p-type impurity at a concentration lower than the p-type impurity concentration of the electron stopper layer;
A semiconductor optical device comprising: An optical confinement layer provided between the barrier layer and the first cladding layer;
2. The semiconductor optical device according to claim 1, wherein a band gap energy of the optical confinement layer is larger than a band gap energy of the barrier layer and smaller than a band gap energy of the first cladding layer. The first cladding includes a p-type impurity;
The optical confinement layer includes a p-type impurity;
3. The semiconductor optical device according to claim 2, wherein the p-type impurity concentration of the first cladding is higher than the p-type impurity concentration of the optical confinement layer and lower than the p-type impurity concentration of the electron stopper layer.

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