JP2017017284A - Semiconductor optical element and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a high-performance embedded semiconductor optical element having excellent element characteristics by inhibiting overflow of a carrier (electron, hole) and deterioration in current block due to p-type dopant diffusion at the same time.SOLUTION: In an embedded semiconductor optical element where a laminate composed of at least a first conductivity type clad layer, an active region composed of an active layer and a second conductivity type clad layer is processed on a first conductivity type InP substrate in a mesa stripe shape, and semiconductor crystals are embedded in contact with side walls on both sides of the mesa stripe, at least a first layer of the embedded layer in contact with the side walls of the mesa, which is composed of semiconductor crystals contains semiconductor crystals of AlP and AlSb.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an embedded semiconductor optical device in which both sides of an active region are embedded with semi-insulating crystals and a method for manufacturing the same.

  When a high-resistance buried structure using a semi-insulating crystal as a buried layer is used for a semiconductor optical device such as a semiconductor laser, the device capacity is smaller than when a pn buried structure is used, and high-speed modulation is possible. An embedded semiconductor optical device in which both sides are embedded with a high-resistance semi-insulating crystal is an indispensable light source for a large-capacity optical transmission system.

  On the other hand, a semiconductor laser using a quantum well structure made of a semiconductor crystal containing Al (aluminum) in the active layer has a large ΔEc (conduction band energy discontinuity) corresponding to the band energy depth of the quantum well layer. Therefore, there is a feature that a decrease in carrier injection efficiency is small even at a high temperature, and good laser characteristics can be maintained even at a high temperature.

  Therefore, a semiconductor laser in which an active layer made of a quantum well structure of a semiconductor crystal containing Al is buried with a high-resistance buried layer can realize excellent device characteristics even at high temperatures.

  In recent years, semiconductor lasers have a strong market demand for lower prices, so it is essential to reduce the number of Peltier elements to prevent the temperature rise of semiconductor lasers. Al-based semiconductors that can realize sufficient characteristics even at high temperatures The active layer high-resistance buried structure laser can be reduced in price by operation without Peltier.

Japanese Patent No. 5206368

  However, the structure in which the Al-based active layer is buried with the high-resistance buried layer has the following problems.

  The structure of the Al-based active layer suppresses overflow of injected carriers called carrier stop layers (CS layers) on both the p-layer side and n-layer side, which are the upper and lower layers of the quantum well structure, or only on the p-layer side. Layer to be placed. As this CS layer, an InAlAs (indium aluminum arsenide) layer having a large band gap is usually used. By this CS layer, even at a high temperature, the injected carriers (electrons) are prevented from overflowing (overflowing) from the active layer to the upper and lower layers, and excellent high temperature characteristics can be maintained.

  However, in the case of a laser using a high-resistance buried structure, carrier overflow from the active layer to the upper and lower layers can be suppressed by the CS layer, but the high-resistance buried layer on both sides of the active layer having the mesa structure is usually made of InP. Since the crystal is used and the energy level of the conduction band of the InP layer is lower than that of the InAlAs layer, carriers leak from the side walls on both sides of the mesa structure of the active layer to the InP layer side, and the efficiency of carrier injection into the active layer As a result, the device characteristics deteriorated.

  Therefore, a high-resistance buried layer that can suppress the overflow of carriers (electrons and holes) and obtain sufficient device characteristics is required.

  Further, as a second problem, not only the carrier overflow as described above but also a p-type dopant (hole) from the clad layer having the second conductivity type (usually p-type) of the mesa structure laminate. There is also a problem that Zn (zinc) diffuses into the buried layer and deteriorates the current blocking characteristics.

  Conventionally, as disclosed in Patent Document 1, a method of suppressing hole overflow with InGaP and suppressing electron overflow with AlAsSb by laminating InGaP (indium gallium phosphide) and AlAsSb (aluminum arsenic antimony) beside the mesa It was as a technology.

  However, since AlAsSb contains As (arsenic) as a group V element, there is an As / P interface at the interface with the InGaP layer and the interface with the InP buried layer, which makes it difficult to sharply switch the group V element. For this reason, film composition modulation and film quality deterioration are likely to occur at the interface, which causes deterioration of long-term high reliability.

  Since it is generally difficult to improve the quality of a semiconductor crystal containing Sb (antimony), it is essential that there is no As / P interface that causes quality degradation. In addition, when embedding an active layer containing Al that is easily oxidized, it is more effective for improving the reliability to directly grow a buried layer containing Al having an oxygen gettering effect instead of an InGaP film. is there.

  In the semiconductor optical device of the present invention for solving the above-described problems, at least a first conductivity type cladding layer, an active region comprising an active layer, and a second conductivity are provided on an InP substrate having a first plane orientation. A laminate composed of a clad layer is processed into a mesa stripe shape, and has a structure in which both sides of the mesa stripe are embedded with a semi-insulating semiconductor crystal, and at least from the first layer semiconductor crystal in contact with the side wall of the mesa stripe The buried layer is made of a semiconductor crystal containing AlP (aluminum phosphorus) and AlSb (aluminum antimony) semiconductor crystals, so that the overflow of electrons can be suppressed, and at the same time, the overflowing holes are trapped by doping Ti (titanium). In addition, holes due to the p-type dopant diffused in the buried layer are simultaneously trapped. By be so as not to deteriorate the current blocking characteristic.

  Since the energy level of the conduction band of AlP, AlSb, and AlPSb (aluminum phosphorus antimony) is higher than that of generally used InP, InAlAs, InGaAlAs, and InGaAsP, an effect of suppressing the overflow of carriers (electrons) can be expected. Since the energy level of AlP and AlSb conductors is higher than that of AlPSb, the effect of suppressing electron overflow can be expected more. Further, since AlPSb mixed crystal can lattice match with InP of the substrate, there is no problem of crystallinity deterioration due to strain.

  Moreover, the AlP / AlSb multilayer structure can form a strain compensation structure. Furthermore, by using a multilayer structure of AlP / InP / AlSb / InP, the AlSb layer and the AlP layer can be sandwiched between InP layers so that the crystal quality is not deteriorated.

  In order to achieve such an object, the present invention is characterized by having the following configuration.

(Structure 1 of the invention)
On the InP substrate having the first conductivity type, a laminate composed of at least the first conductivity type cladding layer, the active region made of the active layer, and the cladding layer having the second conductivity type is processed into a mesa stripe shape. In an embedded semiconductor optical device in which a semiconductor crystal is embedded in contact with the side walls on both sides of the mesa stripe,
A semiconductor optical device, wherein at least a first layer of a buried layer made of the semiconductor crystal in contact with a side wall of the mesa stripe includes AlP and AlSb semiconductor crystals.

(Configuration 2)
In the first aspect of the invention, the semiconductor crystal including the AlP and AlSb semiconductor crystals in the first layer of the buried layer made of the semiconductor crystal in contact with the side wall of the mesa stripe is an AlPSb single layer film. Semiconductor optical device.

(Structure 3 of the invention)
In the first aspect of the invention, the semiconductor crystal including the AlP and AlSb semiconductor crystals in the first layer of the buried layer made of the semiconductor crystal in contact with the side wall of the mesa stripe is an AlP / AlSb multilayer film. Semiconductor optical device.

(Configuration 4)
In the first aspect of the invention, the semiconductor crystal including the AlP and AlSb semiconductor crystals in the first layer of the buried layer made of the semiconductor crystal in contact with the side wall of the mesa stripe is an AlP / InP / AlSb / InP multilayer film. A semiconductor optical device.

(Structure 5 of the invention)
In the first aspect of the invention, titanium (element symbol: Ti) is doped in a semiconductor crystal including AlP and AlSb semiconductor crystals in the first layer of the buried layer made of the semiconductor crystal in contact with the side wall of the mesa stripe. A semiconductor optical device.

(Structure 6 of the invention)
In the first aspect of the invention, the second layer semiconductor crystal stacked on the semiconductor crystal including the first layer AlP and AlSb semiconductor crystal of the buried layer made of the semiconductor crystal in contact with the side wall of the mesa stripe is provided. A semiconductor optical device characterized by being a semi-insulating InP semiconductor crystal.

(Configuration 7)
Structure 6 of the invention is characterized in that the dopant for semi-insulating the semi-insulating InP semiconductor crystal as the second layer semiconductor crystal is ruthenium (element symbol: Ru) or iron (element symbol: Fe). A semiconductor optical device.

(Configuration 8)
A step of laminating and growing at least a first conductivity type cladding layer, an active region comprising an active layer, and a second conductivity clad layer on an InP substrate having the first conductivity type; In a mesa stripe process and a process of embedding a semiconductor crystal in contact with the side walls on both sides of the mesa stripe,
A step of growing a semiconductor crystal including a first layer of titanium doped AlP and AlSb semiconductor crystals in contact with the side walls of the mesa stripe, and a step of growing a second layer semi-insulating InP semiconductor crystal. A method for producing a semiconductor optical device characterized by the above.

  As described above, in the conventional technique, when an active layer made of a quantum well structure of a semiconductor crystal containing Al is embedded with a high-resistance buried layer, in order to suppress carrier overflow, InGaP / AlAsSb layers, InAlAs crystals, InAlGaAs crystals or InGaAsP crystals were used.

  On the other hand, according to the present invention, by using a semiconductor crystal containing a semiconductor mixed crystal of AlP and AlSb doped with titanium in the first buried layer in contact with the side wall of the mesa, the carrier overflow is more effectively performed. It is possible to suppress the deterioration of the current blocking function due to the diffusion of the p-type dopant, and to realize excellent device characteristics and high reliability.

(A)-(c) is sectional drawing of the order of a manufacturing process of the semiconductor element of Example 1 of this invention. (A)-(c) is sectional drawing of the order of a manufacturing process of the semiconductor element of Example 2 of this invention. (A)-(c) is sectional drawing of the order of the manufacturing process of the semiconductor element of Example 3 of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
In the following, an example in which the present invention is applied to a direct modulation laser will be described.

Example 1
FIG. 1 is a sectional view showing the structure of a semiconductor device according to a first embodiment of the present invention in the order of manufacturing steps. This is a cross-sectional view of a semiconductor laser using MQW as an active layer.

  As shown in FIG. 1A, an n-type InP clad layer (2), an n-type InAlGaAs clad layer (3), an n-type InAlAs carrier stop ( CS) layer (4), non-doped InAlGaAs SCH layer (5, SCH: Separated Confinement Heterostructure), non-doped InAlGaAs / InAlGaAs strained MQW (Multiple Quantum Well) active layer (6), non-doped InAlGaAs SCH layer ( 7), a p-type InAlAs carrier stop (CS) layer (8), a p-type InP clad layer (9), and a p-type indium gallium arsenide phosphorus (InGaAsP) contact layer (10).

  Here, the compound semiconductor other than the active layer has a composition that lattice matches with the InP substrate unless otherwise specified.

  Next, as shown in FIG. 1B, mesa stripes having a width of 2 μm and a height of about 3 μm were formed by RIE (reactive ion etching) using SiO 2 (11) as a mask.

  Next, as shown in FIG.1 (c), it embedded with the semi-insulating semiconductor crystal on both sides of the mesa stripe. The semi-insulating buried layer was grown on a single-layer film of AlPSb (12) doped with Ti (titanium) over the substrate surface in contact with the side walls on both sides of the mesa stripe, and then doped with Ru (ruthenium) A Ru-doped InP buried layer (13) was grown.

  Ti effectively traps both the holes that are overflowing carriers and the holes generated by Zn of the p-type dopant that has diffused into the buried layer, and Ru is both the leaking holes and electrons. Can be trapped.

  Since Ru does not cause mutual diffusion with Zn, abnormal diffusion of Zn can also be suppressed.

  By using the embedded layer structure described above, an embedded semiconductor optical device having extremely excellent current blocking characteristics can be realized.

  As described above, since holes are trapped by basic Ti, Fe (iron) capable of trapping only electrons instead of Ru (ruthenium) can be used as a dopant for the InP buried layer (13).

  As for the small signal modulation characteristics of the semiconductor laser fabricated as a chip, the 3 dB band was about 10 GHz at 85 ° C. The oscillation threshold was about 16.5 mA @ 85 ° C, and the light output efficiency was about 22% @ 85 ° C. Therefore, excellent modulation characteristics and light output characteristics were obtained.

(Example 2)
FIG. 2 is a sectional view showing the structure of a semiconductor device according to the second embodiment of the present invention in the order of the manufacturing process.

  As shown in FIG. 2 (a), an n-type InP clad layer (102), an n-type InAlGaAs clad layer (103), an n-type InAlAs carrier stop ( CS) layer (104), non-doped InAlGaAs SCH layer (105), non-doped InAlGaAs / InAlGaAs strained MQW (multiple quantum well) active layer (106), non-doped InAlGaAs SCH layer (107), p-type InAlAs carrier stop (CS) layer (108) Then, a p-type InP clad layer (109) and a p-type indium gallium arsenide phosphorus (InGaAsP) contact layer (110) were laminated in this order.

  Here, the compound semiconductor other than the active layer has a composition that lattice matches with the InP substrate unless otherwise specified.

  Next, as shown in FIG. 2B, mesa stripes having a width of 2 μm and a height of about 3 μm were formed by RIE (reactive ion etching) using SiO 2 (111) as a mask.

  Next, as shown in FIG. 2C, both sides of the mesa stripe were embedded with a semi-insulating semiconductor crystal. In this Example 2, the semi-insulating buried layer grows a Ti-doped AlP / AlSb multilayer structure (112) over the substrate surface in contact with the side walls on both sides of the mesa stripe, and a Ru-doped InP buried layer thereon. Growing layer (113).

  Similarly to Example 1, Fe (iron) can be used as a dopant in the InP buried layer (113) instead of Ru (ruthenium).

  The AlP / AlSb multilayer structure (112) has a layer structure in which distortion is compensated for InP.

  This is because AlP and AlSb do not lattice match with InP in the case of a single layer and have strain, so the crystal quality may deteriorate, but by using a strain compensation structure that cancels strain, higher quality is achieved. This is because a simple crystal can be grown.

The oscillation threshold of the semiconductor laser fabricated as a chip was about 16 mA at 85 ° C., and the light output efficiency was about 23% at 85 ° C. Therefore, excellent modulation characteristics and light output characteristics were obtained.
In the above embodiments, a single semiconductor laser has been described, but it goes without saying that it is effective for an integrated device in which an optical modulator is integrated in a semiconductor laser.

(Example 3)
FIG. 3 is a sectional view showing the structure of a semiconductor device according to a third embodiment of the present invention in the order of manufacturing steps.

  As shown in FIG. 3A, an n-type InP clad layer (202), an n-type InAlGaAs clad layer (203), an n-type InAlAs carrier stop (on a surface-oriented (100) n-type InP substrate (201)). CS) layer (204), non-doped InAlGaAs SCH layer (205), non-doped InAlGaAs / InAlGaAs strained MQW (multiple quantum well) active layer (206), non-doped InAlGaAs SCH layer (207), p-type InAlAs carrier stop (CS) layer (208) Then, a p-type InP clad layer (209) and a p-type indium gallium arsenide phosphorus (InGaAsP) contact layer (210) were laminated in this order.

  Here, the compound semiconductor other than the active layer has a composition that lattice matches with the InP substrate unless otherwise specified.

  Next, as shown in FIG. 3B, mesa stripes having a width of 2 μm and a height of about 3 μm were formed by RIE (reactive ion etching) using SiO 2 (211) as a mask.

  Next, as shown in FIG. 3C, both sides of the mesa stripe were embedded with a semi-insulating semiconductor crystal. In the third embodiment, the semi-insulating buried layer grows a Ti-doped AlP / InP / AlSb / InP multilayer structure (212) over the substrate surface in contact with the side walls on both sides of the mesa stripe, on which A Ru-doped InP buried layer (213) was grown.

  As in the first and second embodiments, Fe (iron) that traps only electrons can be used as a dopant in the InP buried layer (213) instead of Ru (ruthenium).

  The third embodiment is characterized in that an AlP / InP / AlSb / InP multilayer structure in which an InP layer is inserted between an AlP layer of an AlP / AlSb multilayer structure that is a strain compensation structure for InP and an AlSb layer is used. To do.

  The oscillation threshold of the semiconductor laser fabricated as a chip was about 16 mA at 85 ° C., and the light output efficiency was about 24% at 85 ° C. Therefore, excellent modulation characteristics and light output characteristics were obtained.

  In the above embodiments, a single semiconductor laser has been described, but it is needless to say that the structure is also effective for an integrated device in which an optical modulator is integrated in a semiconductor laser.

  As described in detail in the above embodiments, according to the present invention, when an active layer composed of a quantum well structure of a semiconductor crystal containing Al is embedded with a high-resistance buried layer, a conduction band is formed in the buried layer from an InP crystal. Semiconductor crystal with high energy level and doped with dopant to compensate for p-type dopant, specifically AlPSb doped with Ti (titanium), AlP / AlSb multilayer structure, AlP / InP / AlSb / InP multilayer structure By using this, it is possible to simultaneously suppress overflow of carriers (electrons, holes) and current block deterioration due to p-type dopant diffusion, and to obtain excellent device characteristics.

  Therefore, there is a remarkable effect that a high-performance embedded semiconductor optical device can be obtained.

1,101,201 n-type InP substrate 2,102,202 n-type InP clad layer 3,103,203 n-type InAlGaAs clad layer 4,104,204 n-type InAlAs carrier stop (CS) layer 5,105,205 non-doped InAlGaAsSCH Layers 6, 106, 206 Non-doped InAlGaAs / InAlGaAs strained MQW (multiple quantum well) active layers 7, 107, 207 Non-doped InAlGaAs SCH layers 8, 108, 208 p-type InAlAs carrier stop (CS) layers 9, 109, 209 p-type InP cladding Layer 10, 110, 210 p-type InGaAsP contact layer 11, 111, 211 SiO2 mask 12, 112, 212 Ti-doped AlPSb, AlP / AlSb multilayer structure, or AlP / InP / AlSb / InP multilayer structure 13, 113, 213 Ru Doped semi-insulating InP buried layer

Claims (8)

On the InP substrate having the first conductivity type, a laminate composed of at least the first conductivity type cladding layer, the active region made of the active layer, and the cladding layer having the second conductivity type is processed into a mesa stripe shape. In an embedded semiconductor optical device in which a semiconductor crystal is embedded in contact with the side walls on both sides of the mesa stripe,
A semiconductor optical device, wherein at least a first layer of a buried layer made of the semiconductor crystal in contact with a side wall of the mesa stripe includes AlP and AlSb semiconductor crystals.   2. The semiconductor according to claim 1, wherein the semiconductor crystal including the AlP and AlSb semiconductor crystals in the first layer of the buried layer made of the semiconductor crystal in contact with the side wall of the mesa stripe is an AlPSb single layer film. Optical element.   2. The semiconductor according to claim 1, wherein the semiconductor crystal including the first AlP and AlSb semiconductor crystals of the buried layer made of the semiconductor crystal in contact with the side wall of the mesa stripe is an AlP / AlSb multilayer film. Optical element.   2. The semiconductor crystal according to claim 1, wherein the semiconductor crystal including the AlP and AlSb semiconductor crystals in the first layer of the buried layer made of the semiconductor crystal in contact with the side wall of the mesa stripe is an AlP / InP / AlSb / InP multilayer film. A semiconductor optical device.   2. The semiconductor crystal according to claim 1, wherein the semiconductor crystal including the semiconductor crystal of AlP and AlSb in the first layer of the buried layer made of the semiconductor crystal in contact with the side wall of the mesa stripe is doped with titanium (element symbol: Ti). A semiconductor optical device.   2. The semiconductor crystal according to claim 1, wherein the second layer semiconductor crystal stacked on the semiconductor crystal including the first layer AlP and AlSb semiconductor crystal of the buried layer made of the semiconductor crystal in contact with the side wall of the mesa stripe is a half. A semiconductor optical device comprising an insulating InP semiconductor crystal.   7. The dopant according to claim 6, wherein the dopant for semi-insulating the semi-insulating InP semiconductor crystal as the second layer semiconductor crystal is ruthenium (element symbol: Ru) or iron (element symbol: Fe). Semiconductor optical device. A step of laminating and growing at least a first conductivity type cladding layer, an active region comprising an active layer, and a second conductivity clad layer on an InP substrate having the first conductivity type; In a mesa stripe process and a process of embedding a semiconductor crystal in contact with the side walls on both sides of the mesa stripe,
A step of growing a semiconductor crystal including a first layer of titanium doped AlP and AlSb semiconductor crystals in contact with the side walls of the mesa stripe, and a step of growing a second layer semi-insulating InP semiconductor crystal. A method for producing a semiconductor optical device characterized by the above.