JP2014154599A - Semiconductor optical element and integrated semiconductor optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor optical element and an integrated semiconductor optical element which have good reliability and good high-temperature operating characteristics.SOLUTION: A semiconductor optical element using a group III-V compound semiconductor comprises an n-type clad layer, a p-type clad layer and an active region including a multiquantum well structure sandwiched between the n-type clad layer and the p-type clad layer. The active region and the n-type clad layer have group V constituent elements different from each other across a junction boundary. The active region has multiple hole barrier layers which are arranged on the side closer to the n-type clad layer than the multiquantum well structure and become an energy barrier against holes.

Description

  The present invention relates to a semiconductor optical device and an integrated semiconductor optical device.

  As a semiconductor laser element for a 1.3 μm to 1.55 μm wavelength band, an element using an AlGaInAs semiconductor material in an active region is disclosed (Non-patent Document 1). When the quantum well layer is made of AlGaInAs, carriers are unlikely to overflow even in a high temperature environment, and thus a semiconductor laser device using this in the active region is suitable for high temperature operation. Therefore, it is expected that the power for cooling the semiconductor laser element can be reduced and the power consumption can be reduced.

Jen-Wei Pan et al., “Suppression of electron and hole leakage in 1.3 um AlGaInAs / InP quantum well lasers using multiquantum barrier”, Applied Physics Letters, vol.72, No.17, pp.2090-2092, 27 April 1998 .

  However, when the AlGaInAs active region is bonded to a semiconductor layer (for example, a clad layer) made of InP, the group V element as a composition element, one is As and the other is P, and they are completely different. As a result of scrutiny by the present inventors, it has been found that dislocations are generated and spread at the junction interface of semiconductor layers having different V group elements, thereby degrading the semiconductor laser device and reducing the reliability.

  The present invention has been made in view of the above, and an object thereof is to provide a semiconductor optical device and an integrated semiconductor optical device having good reliability and high-temperature operating characteristics.

  In order to solve the above-described problems and achieve the object, a semiconductor optical device according to the present invention is a semiconductor optical device using a III-V compound semiconductor, and includes an n-type cladding layer, a p-type cladding layer, And an active region including a multiple quantum well structure interposed between the n-type cladding layer and the p-type cladding layer, the active region and the n-type cladding layer sandwiching a junction interface And the active region has a multiple hole barrier layer disposed on the n-type cladding layer side of the multiple quantum well structure and serving as an energy barrier against holes. It is characterized by.

  The semiconductor optical device according to the present invention is characterized in that, in the above invention, the active region includes Al in at least the multiple quantum well structure and a region closer to the n-type cladding layer than the multiple quantum well structure. .

  The semiconductor optical device according to the present invention is characterized in that, in the above invention, the multiple quantum well structure is made of AlGaInAs.

  In the semiconductor optical device according to the present invention, in the above invention, the group V composition element on the active region side is As and the group V composition element on the n-type cladding layer side is P across the junction interface. Features.

  In the semiconductor optical device according to the present invention, in the above invention, at least a region of the active region closer to the n-type cladding layer than the multiple quantum well structure is made of AlGaInAs, and the n-type cladding layer is made of InP. Features.

  The semiconductor optical device according to the present invention is characterized in that, in the above invention, the multiple hole barrier layers are arranged adjacent to the junction interface between the active region and the n-type cladding layer.

  The semiconductor optical device according to the present invention is characterized in that, in the above invention, the semiconductor optical device is a semiconductor laser device.

  The semiconductor optical device according to the present invention is characterized in that, in the above invention, the semiconductor optical device is a semiconductor optical amplifier.

  An integrated semiconductor optical device according to the present invention includes a plurality of semiconductor laser devices according to the present invention, an optical combiner capable of combining and outputting laser beams output from the plurality of semiconductor laser devices, and the optical combining device. And a semiconductor optical amplifier that amplifies and outputs the laser beam output from the device.

  The integrated semiconductor optical device according to the present invention is characterized in that, in the above invention, the semiconductor optical amplifier is the semiconductor optical amplifier of the invention.

  An integrated semiconductor optical device according to the present invention is an integrated semiconductor laser device according to the above invention and a semiconductor optical modulator that modulates and outputs a laser beam output from the semiconductor laser device. And

  According to the present invention, there is an effect that it is possible to realize a semiconductor optical device and an integrated semiconductor optical device having good reliability and high-temperature operating characteristics.

FIG. 1 is a schematic cross-sectional view of the semiconductor laser device according to the first embodiment. FIG. 2 is a diagram showing a layer structure of the active region shown in FIG. FIG. 3 is a diagram showing a layer structure of the multiple hole barrier region shown in FIG. FIG. 4 is a diagram showing the energy structure of the valence band of the active region shown in FIG. FIG. 5 is a diagram showing the change over time of the rate of change of the threshold current of the semiconductor laser device of the comparative example in the accelerated reliability test. FIG. 6 is a diagram showing the change with time of the change rate of the threshold current of the semiconductor laser device of the example in the accelerated reliability test. FIG. 7 is a schematic plan view of the integrated semiconductor laser device according to the second embodiment. FIG. 8 is a schematic plan view of the integrated semiconductor laser device according to the third embodiment.

  Embodiments of a semiconductor optical device and an integrated semiconductor optical device according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. Moreover, in each drawing, the same code | symbol is attached | subjected suitably to the same or corresponding component. Also, it should be noted that the drawings are schematic, and the thicknesses and ratios of the layers are different from the actual ones. Moreover, the part from which the relationship and ratio of a mutual dimension differ also in between drawings is contained. Further, in this specification, the semiconductor optical element means a light emitting element such as a semiconductor laser element or a semiconductor optical amplifier.

(Embodiment 1)
FIG. 1 is a schematic cross-sectional view of a semiconductor laser device that is a semiconductor optical device according to Embodiment 1 of the present invention. The semiconductor laser device 10 uses a III-V group compound semiconductor, and includes a substrate 2 having an n-side electrode 1 formed on the back surface, an n-type cladding layer 3 formed on the substrate 2, an active region. 4, a p-type cladding layer 5, a buried semiconductor layer 6, a p-type cladding layer 7, a contact layer 8, and a p-side electrode 9. The semiconductor laser element 10 is an edge-emitting semiconductor laser element, and reflection films that form optical resonators are respectively formed on two end faces of the semiconductor laser element 10 that are substantially parallel to the paper surface.

  The substrate 2 is made of n-type InP. The n-side electrode 1 is configured to make ohmic contact with the substrate 2 and has, for example, an AuGeNi / Au structure.

  The n-type cladding layer 3, the active region 4 and the p-type cladding layer 5 are laminated in this order and form a mesa structure. The embedded semiconductor layer 6 is embedded on both sides of the mesa structure.

  The p-type cladding layer 7 and the contact layer 8 are laminated on the p-type cladding layer 5 and the buried semiconductor layer 6 in this order.

  The n-type cladding layer 3 and the p-type cladding layers 5 and 7 are made of n-type InP and p-type InP, respectively. The contact layer 8 is made of p-type InGaAs doped with a high concentration of p-type dopant. The buried semiconductor layer 6 has a structure in which a lower layer 6a made of p-type InP and an upper layer 6b made of n-type InP are stacked, and functions as a current confinement layer.

  The p-side electrode 9 is formed on the surface of the contact layer 8 so as to be in ohmic contact with the contact layer 8, and is made of, for example, a Ti / Pt / Au structure or Au.

  The active region 4 is interposed between the n-type cladding layer 3 and the p-type cladding layer 5. FIG. 2 is a diagram showing a layer structure of the active region 4. The active region 4 includes a multiple quantum well (MQW) structure in which a plurality of (for example, six) well layers 4a and a plurality of barrier layers 4b are alternately stacked. This multiple quantum well structure is further sandwiched between separate confinement heterostructure (SCH) layers 4c and 4d. As a result, the active region 4 has an MQW-SCH structure.

  Well layer 4a is made of i-type AlGaInAs having a composition capable of emitting light at a desired wavelength in the 1550 nm wavelength band, for example. The barrier layer 4b is made of i-type AlGaInAs having a wider band gap than the well layer 4a and the composition adjusted so as to be an energy barrier with respect to the well layer 4a. The SCH layers 4c and 4d are i whose composition is adjusted so that the band gap is wider than the band gap of the barrier layer 4b and the refractive index is higher than that of the n-type cladding layer 3 and the p-type cladding layer 5. It is made of type AlGaInAs.

  Since the MQW structure of the active region 4 is made of i-type AlGaInAs containing Al, the energy barrier in the conduction band can be increased, so that electron carriers are unlikely to overflow even in a high temperature environment. Therefore, it is suitable for high temperature operation. Here, the high temperature environment means, for example, about 60 ° C to 100 ° C. Furthermore, since the MQW structure made of i-type AlGaInAs can lower the energy barrier in the valence band, hole carriers easily move even during high-speed current modulation, so the active region 4 is an active region suitable for high-speed modulation.

  Furthermore, since the MQW structure of the active region 4 is sandwiched between the SCH layers 4c and 4d, the light confinement factor in the MQW structure can be increased and the threshold current can be decreased.

  Here, the active region 4 has a multiple hole barrier region 4d disposed closer to the n-type cladding layer 3 than the MQW structure. FIG. 3 is a diagram showing a layer structure of the multiple hole barrier region 4d. The multiple hole barrier region 4d has a structure in which a plurality of hole barrier layers 4d1 and a plurality of spacer layers 4d2 are alternately stacked.

  The hole blocking layer 4d1 is made of i-type AlGaInAs or AlInAs whose composition is adjusted so that the band gap is wider than the other layers of the active region 4. The layer thickness of the hole barrier layer 4d1 is, for example, 5 ML (monolayer). The spacer layer 4d2 is made of i-type AlGaInAs whose composition is adjusted to have a narrower band gap than the hole barrier layer 4d1. The composition of the spacer layer 4d2 may be the same as that of the SCH layer 4c. Spacer layer 4d2 has a layer thickness of 12 ML, for example.

  The band gap of the barrier layer 4b having the MQW structure in the 1550 nm wavelength band is, for example, about 1 eV. On the other hand, when AlInAs having the largest band gap is adopted as the constituent material of the hole barrier layer 4d1, the band gap of the hole barrier layer 4d1 is 1.37 eV.

  Next, the operation of the semiconductor laser element 10 will be described. When a voltage is applied between the n-side electrode 1 and the p-side electrode 9 to inject a driving current, holes are injected as carriers from the p-side electrode 9 side, and electrons as carriers from the n-side electrode 1 side. Is injected. Holes flow through the p-type cladding layer 5 through the contact layer 8 and the p-type cladding layer 7 and the current path is narrowed by the buried semiconductor layer 6, and are injected into the active region 4. On the other hand, electrons flow through the substrate 2 and the n-type cladding layer 3 and are injected into the active region 4. Each carrier injected into the active region 4 is combined in the well layer 4a to emit light, and the light emission is laser-oscillated at a predetermined wavelength by the optical amplification action of the well layer 4a and the action of the optical resonator.

  Here, FIG. 4 is a diagram showing the energy structure of the valence band of the active region 4. The solid line indicates the level at the lower end of the valence band in each layer. As described above, the n-type cladding layer is made of n-type InP. On the other hand, the spacer layer 4d2 which is a layer on the active region 4 side of the junction interface between the n-type cladding layer 3 and the active region 4 is made of i-type AlGaInAs. Therefore, the active region 4 and the n-type cladding layer 3 are different from each other in the group V composition element across the junction interface, and are As and P, respectively. As described above, the spike S is generated in the energy structure at the junction interface of the semiconductor layers having different group V elements.

  As described above, the present inventors have discovered that dislocations are generated and spread at the junction interface of semiconductor layers having different group V elements, thereby degrading the semiconductor laser device and reducing reliability. Then, when the cause was scrutinized, at the junction interface of the semiconductor layers having different group V elements, a spike occurred in the energy band, and the holes overflowed from the active layer reached the spike in the n-type region, where they were trapped, It was presumed that heat was generated by non-radiative recombination and dislocations spread by the heat. Such a spike is considered to be particularly steep at the junction interface (As / P interface) between the semiconductor layer of the group V element As and the semiconductor layer of P.

  On the other hand, in the semiconductor laser device 10 according to the first embodiment, the multiple hole barrier layer 4d1 serving as an energy barrier against holes is located closer to the n-type cladding layer 3 side than the MQW structure of the active region 4. Are arranged. As a result, as shown in FIG. 4, the holes h are suppressed or prevented from reaching the spike S at the junction interface between the active region 4 and the n-type cladding layer 3. As a result, the spread of dislocations is suppressed, and the reliability of the element is improved. When the junction interface is an As / P interface, the spike S tends to be particularly steep, and hole trapping and non-radiative recombination are likely to occur. Therefore, it is particularly effective to provide the hole barrier layer 4d1.

  In particular, when the MQW structure is made of AlGaInAs containing Al, the energy barrier in the conduction band can be increased, so that the electron carriers are less likely to overflow even in a high temperature environment and are suitable for high temperature operation, while the energy barrier in the valence band is low. Therefore, the hole carriers are likely to overflow. Similarly, when the active region 4 contains Al in the region closer to the n-type cladding layer 3 than the MQW structure (that is, the interface where the spike S is generated is an As / P interface and the layer containing Al and P In the case of an interface with a layer containing), the energy barrier in the valence band is lowered, so that the hole carriers are likely to overflow. In particular, the overflow of hole carriers becomes more prominent in a high temperature environment.

  On the other hand, in the semiconductor laser device 10 according to the first embodiment, the holes h are prevented from reaching the spike S by the multiple hole barrier layer 4d1, so that MQW made of AlGaInAs suitable for high-temperature operation is used. The characteristics of the structure can be exhibited more effectively. Furthermore, since the semiconductor laser device 10 is suitable for high temperature operation, it can be operated without causing much deterioration of the device characteristics even at high temperatures. Therefore, the power for cooling the element can be reduced, and the power consumption can be reduced in the laser module in which the semiconductor laser element 10 is mounted.

  The number of hole barrier layers 4d1 is not particularly limited, but is about 2 to 10, for example. The position of the hole barrier layer 4d1 may be on the n-type cladding layer 3 side of the MQW structure of the active region 4, but is preferably closer to the junction interface between the active region 4 and the n-type cladding layer 3. It is particularly preferred that they are arranged adjacent to the interface. The distance between the hole barrier layer 4d1 and the bonding interface is preferably 10 nm or less, and particularly preferably 0 nm.

  Next, as an example of the present invention, ten semiconductor laser elements similar to the semiconductor laser element according to the first embodiment shown in FIG. 1 were produced. Further, as a comparative example, five semiconductor laser elements having the same configuration as the semiconductor laser element of the example except that the multiple hole barrier region was not provided were manufactured. Each element has a cavity length of 300 μm, an active layer width of 1.8 μm, and a cleavage structure at both end faces. Then, the semiconductor laser devices of the examples and comparative examples are driven by an ACC (Auto current control) operation with a driving current of 150 mA at an environmental temperature of 120 ° C., and an acceleration reliability test for examining the change rate of the threshold current. Went. Here, the rate of change of the threshold current is a rate of change based on the threshold current before the test.

  FIG. 5 is a diagram showing the change over time of the rate of change of the threshold current of the semiconductor laser device of the comparative example in the accelerated reliability test. FIG. 6 is a diagram showing the change with time of the change rate of the threshold current of the semiconductor laser device of the example in the accelerated reliability test. As shown in FIGS. 5 and 6, it was confirmed that the semiconductor laser device of the comparative example increased in threshold current with time and deteriorated in each sample. On the other hand, in the semiconductor laser device of the example, even in such a high temperature environment, the increase of the threshold current is extremely low as time passes for each sample, and the deterioration of the device is suppressed. It was confirmed that the reliability was higher than that of the device.

(Embodiment 2)
FIG. 7 is a schematic plan view of an integrated semiconductor laser device according to the second embodiment of the present invention. As shown in FIG. 7, the integrated semiconductor laser device 100 includes DFB (Distributed Feedback) lasers 20-1 to 20-n (n is an integer of 2 or more) arranged in an array, and a DFB laser 20-1. ˜20-n is connected to a multi-mode interference (MMI) type optical combiner 40 connected through optical waveguides 30-30 to 2-n and an optical output port 40a of the optical combiner 40. The semiconductor optical amplifier 50 having the optical output end 50a is provided. The integrated semiconductor laser device 100 is configured by monolithically integrating a DFB laser 20-1 to 20-n, an optical combiner 40, and a semiconductor optical amplifier 50 on a substrate.

  The DFB lasers 20-1-20-1 to 1-n have the same semiconductor stacked structure as that of the semiconductor laser device 100 according to the first embodiment shown in FIG. 1, but in the p-type cladding layer near the active region. The difference is that diffraction grating layers having different periods are formed. The DFB lasers 20-1-20-1 to 1-n have laser oscillation wavelengths different from each other at wavelengths of 1530 nm to 1570 nm due to the action of the diffraction grating layer, for example. The optical combiner 40 is capable of outputting a plurality of inputted waveguide lights to one waveguide.

  This integrated semiconductor laser device 100 operates as follows. First, any one of the DFB lasers selected from the DFB lasers 20-1 to 20-n is injected with a current and outputs a laser beam. Of the optical waveguides 30-1 to 30-n, the optical waveguide connected to the DFB laser into which current is injected causes the laser beam to be input to the optical combiner 40. The optical combiner 40 outputs the input laser light from the optical output port 40 a and inputs it to the semiconductor optical amplifier 50. The semiconductor optical amplifier 50 amplifies the input laser beam and outputs it from the optical output end 50a. The integrated semiconductor laser device 100 can control the wavelength by changing the DFB laser selected from the DFB lasers 20-1 to 20-n and changing the temperature of the device. Functions as a light source.

  This integrated semiconductor laser device 100 includes DFB lasers 20-1-20-1 to 1-n having multiple hole barrier regions, similar to the semiconductor laser device 10 according to the first embodiment shown in FIG. . As a result, the integrated semiconductor laser device 100 has good reliability and high-temperature operating characteristics, and the module on which the integrated semiconductor laser device 100 is mounted has low power consumption.

  The semiconductor optical amplifier 50 of the integrated semiconductor laser device 100 may be configured with a semiconductor stacked structure having a multiple hole barrier region, similar to the semiconductor laser device 100 according to the first embodiment shown in FIG. As a result, the reliability and high-temperature operating characteristics of the integrated semiconductor laser device 100 are further improved, and the module on which the integrated semiconductor laser device 100 is mounted further reduces power consumption.

(Embodiment 3)
FIG. 8 is a schematic plan view of an integrated semiconductor laser device according to the third embodiment of the present invention. As shown in FIG. 8, the integrated semiconductor laser device 200 is configured by monolithically integrating a DFB laser 20 and an electroabsorption (EA) modulator 60 on a substrate.

  The DFB laser 20 is a DFB laser having the same configuration as the DFB laser 20-1 of the second embodiment. The EA modulator 60 is for modulating the laser beam output from the DFB laser 20 and outputting it as signal light.

  The integrated semiconductor laser element 200 includes a DFB laser 20 having a multiple hole barrier region, similar to the semiconductor laser element 10 according to the first embodiment shown in FIG. As a result, the integrated semiconductor laser element 200 also has good reliability and high-temperature operating characteristics, and a module equipped with the integrated semiconductor laser element 200 has low power consumption.

  In the above embodiment, the active region includes the SCH layer. However, the present invention can also be applied to a semiconductor optical device having an active region that does not include the SCH layer.

  In the above embodiment, the junction interface between the active region and the n-type cladding layer is an As / P interface, but the V group composition elements are different from each other across the junction interface between the active region and the n-type cladding layer. If so, the effect of the present invention can be achieved even with a combination of other group V composition elements.

  Further, the present invention is not limited by the above embodiment. What was comprised combining each component mentioned above suitably is also contained in this invention. Further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspect of the present invention is not limited to the above-described embodiment, and various modifications can be made.

1 n-side electrode 2 substrate 3 n-type cladding layer 4 active region 4a well layer 4b barrier layer 4c SCH layer 4d multiple hole barrier region 4d1 hole barrier layer 4d2 spacer layer 5, 7 p-type cladding layer 6 buried semiconductor layer 6a lower part Layer 6b Upper layer 8 Contact layer 9 P-side electrode 10 Semiconductor laser device 20, 20-1 to 20-n DFB laser 30-1 to 30-n Optical waveguide 40 Optical combiner 40a Optical output port 50 Semiconductor optical amplifier 50a Optical output End 60 EA modulator 100, 200 Integrated semiconductor laser element h Hole S Spike

Claims (11)

A semiconductor optical device using a III-V compound semiconductor,
an n-type cladding layer;
a p-type cladding layer;
An active region including a multiple quantum well structure, interposed between the n-type cladding layer and the p-type cladding layer;
The active region and the n-type cladding layer are different from each other in the group V composition element across a junction interface, and the active region is disposed on the n-type cladding layer side of the multiple quantum well structure. A semiconductor optical device comprising a plurality of hole barrier layers serving as energy barriers against holes.   2. The semiconductor optical device according to claim 1, wherein the active region includes Al in at least the multiple quantum well structure and a region closer to the n-type cladding layer than the multiple quantum well structure.   The semiconductor optical device according to claim 1, wherein the multiple quantum well structure is made of AlGaInAs.   The group V composition element on the active region side across the junction interface is As, and the group V composition element on the n-type cladding layer side is P. The semiconductor optical device described in 1.   5. The semiconductor optical device according to claim 4, wherein at least a region of the active region closer to the n-type cladding layer than the multiple quantum well structure is made of AlGaInAs, and the n-type cladding layer is made of InP.   6. The semiconductor light according to claim 1, wherein the multiple hole barrier layer is disposed adjacent to the junction interface between the active region and the n-type cladding layer. element.   The semiconductor optical device according to claim 1, wherein the semiconductor optical device is a semiconductor laser device.   The semiconductor optical device according to claim 1, wherein the semiconductor optical device is a semiconductor optical amplifier. A plurality of semiconductor laser devices according to claim 7;
An optical combiner capable of combining and outputting laser beams output from the plurality of semiconductor laser elements;
A semiconductor optical amplifier that amplifies and outputs the laser light output from the optical combiner;
An integrated semiconductor optical device characterized by being integrated.   The integrated semiconductor optical device according to claim 9, wherein the semiconductor optical amplifier is a semiconductor optical amplifier according to claim 8. A semiconductor laser device according to claim 7;
An integrated semiconductor optical device comprising: a semiconductor optical modulator that modulates and outputs laser light output from the semiconductor laser device.

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