JP2010109237A - Optical phase control element and semiconductor light-emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical phase control element and a semiconductor light-emitting element, for reducing the power consumption by suppressing recoupling of carriers in a phase control region and an optical gain due to recoupling. <P>SOLUTION: The optical phase control element includes a semiconductor substrate 11 comprising n-type InP, an n-type clad layer 12 formed on the semiconductor substrate 11 and comprising Si-doped n-type InP, an active waveguide layer 13 formed on the n-type clad layer 12 and changing the phase of impinging light, and a p-type clad layer 14 formed on the active waveguide layer 13 and comprising Zn-doped p-type InP. The active waveguide layer 13 has a structure wherein an electron trapping layer 131 comprising GaInAs and a hole trapping layer 132 comprising AlGaInAs are alternately laminated 4 times. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical phase control element and a semiconductor light emitting element having a phase control region for continuously changing an oscillation wavelength by changing the phase of light, and in particular, an active waveguide based on a plasma effect of injected carriers. The present invention relates to an optical phase control element and a semiconductor light emitting element using a change in refractive index.

  2. Description of the Related Art Conventionally, as a light source used for optical communication, a semiconductor laser capable of varying an oscillation wavelength by providing a light emitting region that emits light and a phase control region that changes the phase of light emitted by the light emitting region has been proposed. (For example, refer to Patent Document 1).

  FIG. 8 is a cross-sectional view along the light guiding direction of a conventional semiconductor laser. The semiconductor laser shown in FIG. 8 includes a semiconductor substrate 101, a distributed Bragg reflector (DBR) 102 (light emitting region) having optical gain and wavelength selectivity, and a waveguide layer 103 (phase control region) having no optical gain. , A light emitting region electrode 104, a phase control region electrode 105, a back electrode 106, an antireflection film 107, and a waveguide end surface 108.

  Since the DBR 102 has both optical gain and wavelength selectivity, the DBR 102 amplifies only light in a specific wavelength band centered on the Bragg wavelength of the DBR 102 and determined by the stop bandwidth of the DBR 102.

  The oscillation wavelength is present in the specific wavelength band among the longitudinal mode wavelengths determined based on the resonator length of the laser resonator constituted by the DBR 102, the waveguide layer 103, and the waveguide end face 108. .

  Here, when carriers are injected into the waveguide layer 103 as a phase control region having no gain, the effective refractive index of the waveguide layer 103 is reduced due to the plasma effect, so that the phase of light transmitted through the waveguide layer 103 is reduced. Changes, and the wavelength and spacing of the longitudinal mode changes.

In the conventional semiconductor laser shown in FIG. 8, the interval between the longitudinal modes is wider than the stop band width of the DBR 102, and there is only one longitudinal mode in the stop band. Therefore, the semiconductor laser can continuously change the oscillation wavelength in a specific wavelength band determined by the stop bandwidth by controlling the current injected into the waveguide layer 103.
JP 2004-273644 A ([0055])

  However, in the semiconductor laser disclosed in Patent Document 1, since recombination occurs between carriers in the phase control region, the current injected into the phase control region must be increased in order to compensate for the decreased carriers due to the recombination. There was a problem of not becoming.

  In addition, in order to obtain a particularly large phase change, a larger current is injected into the phase control region. In this case, the carrier density of the waveguide layer in the phase control region is increased, which causes carrier recombination. The resulting optical gain is generated. As a result, there has been a problem that the reduction of carriers becomes remarkable and a desired phase change cannot be obtained unless the current injected into the phase control region is further increased.

  The present invention has been made to solve such conventional problems, and can suppress optical gain caused by carrier recombination and recombination in the phase control region, thereby reducing power consumption. An object is to provide an optical phase control element and a semiconductor light emitting element.

  The optical phase control element of the present invention includes an active waveguide layer that changes the phase of incident light on a substrate, and the active waveguide layer includes a staggered band structure including an electron confinement layer and a hole confinement layer. And having a configuration in which the layers are alternately stacked.

  With this configuration, since the electron confinement layer and the hole confinement layer form a staggered band structure, optical recombination and recombination of carriers in the active waveguide layer can be suppressed, and power consumption can be reduced. it can.

The optical phase control element of the present invention has a configuration in which the electron confinement layer has a larger thickness than the hole confinement layer.
With this configuration, an overflow current due to electrons is suppressed, so that power consumption can be significantly reduced.

  The semiconductor light-emitting device of the present invention is a semiconductor in which a light-emitting region that emits light and a phase control region that changes the phase of light emitted by the light-emitting region are arranged in series in a light guiding direction on a substrate. In the light emitting device, the phase control region includes an active waveguide layer in which an electron confinement layer and a hole confinement layer are alternately stacked in a staggered band structure.

  With this configuration, since the electron confinement layer and the hole confinement layer form a staggered band structure, optical recombination and recombination of carriers in the active waveguide layer can be suppressed, and power consumption can be reduced. it can.

In addition, the semiconductor light emitting device of the present invention has a configuration in which the thickness of the electron confinement layer is larger than the thickness of the hole confinement layer.
With this configuration, an overflow current due to electrons is suppressed, so that power consumption can be significantly reduced.

  The present invention provides an optical phase control element and a semiconductor light emitting element that have an effect of suppressing optical gain resulting from carrier recombination and recombination in a phase control region and reducing power consumption. .

  Hereinafter, embodiments of an optical phase control element and a semiconductor light emitting element according to the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 shows a first embodiment of an optical phase control element according to the present invention. FIG. 1A is a cross-sectional view of the optical phase control element of the present embodiment along the light guiding direction, and FIG. 1B is a partially enlarged view of FIG.

  That is, the optical phase control element of the first embodiment includes a semiconductor substrate 11 made of n-type InP, an n-type cladding layer 12 made of Si-doped n-type InP formed on the semiconductor substrate 11, and an n-type. An active waveguide layer 13 formed on the clad layer 12 and changing the phase of incident light; a p-type clad layer 14 made of Zn-doped p-type InP formed on the active waveguide layer 13; Is provided.

  A p-type contact layer 15 is formed on the upper surface of the p-type cladding layer 14, and a p-type electrode 16 is provided on the upper surface of the p-type contact layer 15. An n-type electrode 17 is provided on the lower surface of the semiconductor substrate 11.

  Furthermore, the optical phase control element of the first embodiment includes one end face 18a and the other end face 18b.

  As shown in the partially enlarged view of FIG. 1B, the active waveguide layer 13 has a structure in which, for example, four electron confinement layers 131 and four hole confinement layers 132 are alternately stacked. The electron confinement layer 131 and the hole confinement layer 132 are lattice-matched to InP.

Here, the electron confinement layer 131 is made of non-doped Ga _0.067 In _0.933 As _0.144 P _0.856 and has a layer thickness of 0.1 μm. The hole confinement layer 132 is made of non-doped Al _0.468 Ga _0.012 In _0.52 As and has a layer thickness of 0.1 μm. The n-type cladding layer 12 is made of Si-doped n-type InP, and the p-type cladding layer 14 is made of Zn-doped p-type InP.

  FIG. 2 is a diagram schematically showing a band structure of the active waveguide layer 13 of the optical phase control element of the present embodiment. The conduction band edge of the electron confinement layer 131 exists at an energy position lower than that of the hole confinement layer 132. On the other hand, the hole band edge of the hole confinement layer 132 exists at a lower energy position for the hole than that of the electron confinement layer 131.

  Such a band structure is called a staggered band structure or a type II band structure. Note that since both the electron confinement layer 131 and the hole confinement layer 132 are lattice-matched to InP, the heavy hole band and the light hole band are degenerated. Also, the heterobarriers against electrons and holes in the active waveguide layer 13 are about 286 meV and 108 meV, respectively.

  When a direct current (hereinafter referred to as a phase control current) is applied to the active waveguide layer 13 having a staggered band structure through the p-type electrode 16 and the n-type electrode 17, as shown in FIG. Electrons are accumulated in the electron confinement layer 131, and holes are accumulated in the hole confinement layer 132. Thus, since electrons and holes are spatially separated in the active waveguide layer 13, recombination of electrons and holes is suppressed.

At this time, the effective refractive index n _p of the active waveguide layer 13 decreases due to the plasma effect of electrons and holes that are spatially separated and accumulated in the active waveguide layer 13. The absolute value of the reduction amount Δn _p (<0) of the effective refractive index n _p is increased by increasing the phase control current. However, in this embodiment, since recombination of electrons and holes is suppressed, A reduction amount Δn _p that brings about a desired phase change can be obtained with less current than in the past.

An antireflection film (not shown) is formed on the other end face 18b of the optical phase control element of the present embodiment configured as described above, and the light is emitted from a semiconductor light emitting element (not shown) such as a semiconductor laser via the one end face 18a. When the incident light enters the active waveguide layer 13, the phase of the light incident on the active waveguide layer 13 is advanced according to the effective refractive index n _p of the active waveguide layer 13 changed by the phase control current. . The light whose phase has been advanced in the active waveguide layer 13 is emitted from the other end face 18b on which the antireflection film is formed.

  As described above, the optical phase control element of this embodiment suppresses the optical gain caused by recombination current and recombination because electrons and holes are spatially separated in the active waveguide layer. Power consumption can be reduced.

  In addition, since the hetero barriers for electrons and holes in the active waveguide layer of the optical phase control element of this embodiment are as large as about 286 meV and 108 meV, respectively, the current flowing due to the overflow of electrons or holes can be reduced.

(Second Embodiment)
FIG. 3 shows a second embodiment of the optical phase control element according to the present invention. FIG. 3 is a partially enlarged view of the vicinity of the active waveguide layer of the optical phase control element of this embodiment. The description of the same configuration as that of the first embodiment is omitted.

  That is, the optical phase control element of the present embodiment is an active conducting layer formed between the n-type cladding layer 12 made of Si-doped n-type InP and the p-type cladding layer 14 made of Zn-doped p-type InP. A waveguide layer 23 is provided.

  As shown in the partially enlarged view of FIG. 3, the active waveguide layer 23 has a structure in which, for example, four electron confinement layers 231 and four hole confinement layers 232 are alternately stacked one by one. Both layers are lattice-matched to InP.

  Here, the composition of the electron confinement layer 231 and the hole confinement layer 232 is the same as that of the first embodiment, but the electron confinement layer 231 is thicker than the layer thickness of the hole confinement layer 232. The thickness is 0.05 μm, and the electron confinement layer 231 is 0.15 μm.

  FIG. 4 is a diagram schematically showing a band structure of the active waveguide layer 23 of the optical phase control element of the present embodiment. Similar to the optical phase control element of the first embodiment, when a phase control current is applied to the active waveguide layer 23, electrons are accumulated in the electron confinement layer 231 and holes are accumulated in the hole confinement layer 232.

  Since the charge neutrality condition is satisfied in the active waveguide layer 23, the layer thickness of the electron confinement layer 231 in the optical phase control element of the present embodiment in which the layer thickness of the electron confinement layer 231 is larger than the layer thickness of the hole confinement layer 232. Compared with the first embodiment in which the layer thickness of the hole confinement layer 232 is equal, the electron density of the electron confinement layer 231 decreases.

  In general, electrons having a lighter effective mass than holes tend to cause a so-called overflow current that leaks from the confinement layer across the hetero barrier. However, since the overflow current is suppressed as the electron density is lower, the optical phase control element of this embodiment can further reduce the power consumption than the first embodiment.

  The phase change amount in the first embodiment and the phase change amount in the optical phase control element of the present embodiment are the same because the thicknesses of the electron confinement layer and the hole confinement layer are inversely proportional to the carrier density in each layer. . That is, in the operation of the optical phase control element, the structure of this embodiment that can greatly reduce the power consumption is further advantageous.

(Third embodiment)
An embodiment of a semiconductor light emitting device according to the present invention is shown in FIG. FIG. 5A is a cross-sectional view taken along the light guiding direction of the semiconductor light emitting device of the third embodiment, and FIG. 5B is a partially enlarged view of FIG.

  That is, in the semiconductor light emitting device of the third embodiment, the light emitting region 1 having optical gain and the phase control region 2 for changing the phase of light emitted from the light emitting region 1 are arranged in series in the light guiding direction. It has the structure which was made.

  In addition, the semiconductor light emitting device of the third embodiment includes a semiconductor substrate 31 made of n-type InP, an n-type cladding layer 32 made of n-type InP formed on the semiconductor substrate 31, and an upper side of the n-type cladding layer 32. A p-type cladding layer 33 made of p-type InP, and a p-type contact layer 34 formed on the p-type cladding layer 33.

  The light emitting region 1 is formed between the n-type cladding layer 32 and the p-type cladding layer 33 on the optical separation and confinement (SCH) layer 35 made of GaInAsP and the SCH layer 35, and has a multiple quantum well (MQW) structure. And an MQW layer 36 for emitting light, and an SCH layer 37 made of InGaAsP formed on the MQW layer 36.

  On the other hand, the phase control region 2 is a region corresponding to the optical phase control element of the first or second embodiment, and between the n-type cladding layer 32 and the p-type contact layer 34, n-type InP doped with Si. An n-type cladding layer 38, an active waveguide layer 39 for changing the phase of incident light, and a p-type cladding layer 40 made of Zn-doped p-type InP.

  Further, on the upper surface of the p-type contact layer 34, a light-emitting region p-type electrode 41 and a phase control region p-type electrode 42 are provided in the light-emitting region 1 and the phase control region 2, respectively. An n-type electrode 43 common to the light emitting region 1 and the phase control region 2 is provided on the lower surface of the semiconductor substrate 31.

  Furthermore, the semiconductor light emitting device of this embodiment includes one end face 44a and the other end face 44b, and an antireflection film 45 is provided on the other end face 44b.

  As shown in the partially enlarged view of FIG. 5B, the MQW layer 36 has an MQW structure in which four well layers 361 and three barrier layers 362 are alternately stacked. From the semiconductor substrate 31 side, layers are stacked in the order of a well layer 361, a barrier layer 362, and a well layer 361.

The well layer 361 is made of non-doped Ga _0.2 In _0.8 As and has a thickness of 3 nm. On the other hand, the barrier layer 362 is made of non-doped Ga _0.282 In _0.718 As _0.612 P _0.388 and has a layer thickness of 20 nm. Here, for example, the well layer 361 may have compressive strain, and the barrier layer 362 may have tensile strain.

The SCH layer 35 and the SCH layer 37 are made of non-doped Ga _0.282 In _0.718 As _0.612 P _0.388 , have a band gap wavelength of 1.3 μm, a layer thickness of 40 nm, and are lattice-matched to InP. The n-type cladding layer 32 is made of Si-doped n-type InP, and the p-type cladding layer 33 is made of Zn-doped p-type InP.

  As in the active waveguide layer in the optical phase control element of the first or second embodiment, the active waveguide layer 39 includes, for example, four electron confinement layers (not shown) and four hole confinement layers alternately. A staggered band structure laminated on the substrate. The electron confinement layer and the hole confinement layer are lattice-matched to InP.

Here, like the optical phase control element of the second embodiment, the electron confinement layer is made of non-doped Ga _0.067 In _0.933 As _0.144 P _0.856 and has a layer thickness of 0.15 μm. The hole confinement layer is made of non-doped Al _0.468 Ga _0.012 In _0.52 As and has a layer thickness of 0.05 μm. Also, the heterobarriers against electrons and holes in the active waveguide layer 39 are about 286 meV and 108 meV, respectively.

  As a result of the simulation of the element structure of the present invention by the present applicant, the optical coupling efficiency between the light emitting region 1 and the phase control region 2 is as high as about 96%, and the active waveguide in the phase control region 2 About 48% was obtained as the TE mode light confinement factor in the layer 39, and it was found that the phase control efficiency was good.

  In addition, the semiconductor light emitting element of this embodiment was provided with the aspect provided with the diffraction grating in at least one part of the light emission area | region 1, the aspect provided with the DBR area | region (light emission area | region-phase control area | region-DBR area), and also the light emission area | region. A mode (light emission region-phase control region-light emission region) may be used. Further, as described below, it may be applied as a semiconductor laser for an external resonator type laser having a wavelength selection mechanism such as a diffraction grating having a rotation mechanism or a liquid crystal filter.

  FIG. 6 is a top view showing a configuration of an external cavity laser to which the semiconductor light emitting device of this embodiment is applied. The external resonator type laser shown in FIG. 6 has a semiconductor light emitting element 3, a lens 4 for making light emitted from the other end face 44b of the semiconductor light emitting element 3 into parallel light, and an oscillation wavelength for selection. And a rotatable diffraction grating 5.

The oscillation wavelength is determined by [Expression 1] based on the resonator length of the laser resonator constituted by one end face 44a of the semiconductor light emitting element 3, the phase control region 2, the light emitting region 1, and the diffraction grating 5. The mode wavelength is selected by the diffraction grating 5. Here, m is the order of the longitudinal mode, n ₁ and L ₁ are the effective refractive index and length of the phase control region 2, n ₂ and L ₂ are the effective refractive index and length of the light emitting region 1, n ₃ and L ₃ Is the refractive index of the atmosphere and the length from the other end face 44 b of the semiconductor light emitting element 3 to the diffraction grating 5.

At this time, the longitudinal mode interval Δλ is given by [Equation 2].

By applying a current to the light emitting region 1 through the p-type electrode 41 for the light emitting region, light is emitted from the MQW layer 36 in the light emitting region 1. Further, when a phase control current is applied to the phase control region 2 via the phase control region p-type electrode 42, the effective refractive index n ₁ of the active waveguide layer 39 is decreased by Δn ₁ .

Therefore, the phase of the light emitted from the MQW layer 36 in the light emitting region 1 and incident on the active waveguide layer 39 in the phase control region 2 changes according to the phase control current, and accordingly, the longitudinal mode wavelength λ and The interval Δλ changes. The amount of change Δλ ′ of the longitudinal mode wavelength at this time is given by [Equation 3].

  Therefore, the oscillation wavelength can be continuously changed by continuously changing the phase control current until the longitudinal mode wavelength variation Δλ ′ becomes larger than the longitudinal mode interval Δλ. In the present embodiment, since the recombination of electrons and holes is suppressed in the phase control region 2, the oscillation wavelength can be changed with a smaller current than in the prior art.

  Hereinafter, an example of the manufacturing method of the semiconductor light emitting device of this embodiment will be described. FIG. 7 is a cross-sectional view taken along the light guiding direction, showing a part of the manufacturing process of the semiconductor light emitting device of this embodiment.

First, an n-type cladding layer 32 made of n-type InP is formed on a semiconductor substrate 31 made of n-type InP by using a metal organic chemical vapor deposition (MOVPE) method. Next, a Ga _0.282 In _0.718 As _0.612 P _0.388 layer (layer thickness: 40 nm / non-doped) having a band gap wavelength of 1.3 μm and lattice-matched to InP is formed as the SCH layer 35.

Next, on the SCH layer 35, a well layer 361 of Ga _0.2 In _0.8 As (layer thickness: 3 nm / number of layers: 4 / non-doped) and Ga _0.282 In _0.718 As _0.612 P _0.388 (layer thickness: 20 nm / number of layers) : MQ / non-doped) barrier layer 362 is formed to form an MQW layer 36 having an MQW structure.

On the MQW layer 36 thus formed, a Ga _0.282 In _0.718 As _0.612 P _0.388 layer (layer thickness: 40 nm / non-doped) having a band gap wavelength of 1.3 μm as the SCH layer 37 and lattice-matching to InP. Form.

  Next, a p-type cladding layer 33 made of p-type InP is formed on the SCH layer 37, and a p-type contact layer 34 made of p-type GaInAsP is formed to produce a multilayer structure substrate having the light emitting region 1. (FIG. 7 (1)).

  Next, the multilayer substrate is etched by wet etching or the like so as to include a part of the n-type cladding layer 32, and the n-type cladding layer made of n-type InP doped with Si in the etched part. 38 are stacked (FIG. 7B).

From the n-type cladding layer 38 side, an electron confinement layer (layer thickness: 0.1 μm / non-doped) of Ga _0.067 In _0.933 As _0.144 P _0.856 (not shown), a hole confinement layer of Al _0.468 Ga _0.012 In _0.52 As (layer thickness: 0) ... 1 μm / non-doped), for example, four layers are repeatedly stacked to form the active waveguide layer 39, and a butt joint junction with the MQW layer 36 in the light emitting region 1 already formed is formed. In this step, it is important to perform the growth so that the stacking center of the MQW layer 36 in the light emitting region 1 and the stacking center of the active waveguide layer 39 in the phase control region 2 coincide.

  Next, a p-type cladding layer 40 made of Zn-doped p-type InP is laminated on the active waveguide layer 39 in the phase control region 2, and a p-type contact layer 34 of p-type GaInAsP is laminated again. A double heterostructure substrate having the light emitting region 1 and the phase control region 2 is formed (FIG. 7C).

  Subsequently, the n-type cladding layer 32 is arranged so that the light emitting region 1 having the MQW layer 36 and the phase control region 2 having the active waveguide layer 39 are arranged in series with respect to the double heterostructure substrate. Mesa etching is performed so as to include a part of the semiconductor substrate 31 deeper.

  The mesa etching substrate formed in this way is sequentially buried and grown by p-type InP and n-type InP (not shown). After this burying growth, an n-type electrode 43 is formed on the n-type InP semiconductor substrate 31 side, a p-type electrode 41 for the light emitting region and a p-type electrode 42 for the phase control region are formed on the p-type contact layer 34 side of the p-type GaInAsP, The semiconductor light emitting device of the present invention is completed.

  As described above, the semiconductor light emitting device of this embodiment has an optical gain due to recombination current and recombination because electrons and holes are spatially separated in the active waveguide layer of the phase control region. It can be suppressed and power consumption can be reduced.

  Further, in the semiconductor light emitting device using the second embodiment of the present invention, the heterobarrier to electrons and holes in the active waveguide layer in the phase control region is large as about 286 meV and 108 meV, respectively, and the electron density of the electron confinement layer Therefore, power consumption can be further reduced by suppressing the overflow current.

So far, the present invention has been described with respect to a structure in which AlGaInAs (hole confinement layer) and GaInAsP (electron confinement layer) are combined as a mixed crystal material for forming an active waveguide in the phase control region. However, since the electron confinement layer and the hole confinement layer constituting the active waveguide only need to be a staggered band lineup in the essence of the present invention, as an active waveguide in the phase control region, for example, Al _0.45 Ga _0.55 As (Hole confinement layer) and AlAs (electron confinement layer), Al _0.35 Ga _0.15 In _0.5 P (hole confinement layer) and AlInP (electron confinement layer), GaAsSb (hole confinement layer) and GaInAs (electron confinement layer) ) And the like are also applicable to the present invention.

Sectional drawing and the elements on larger scale which show the optical phase control element of the 1st Embodiment of this invention Schematic diagram showing the band structure of the optical phase control element of the first embodiment of the present invention The elements on larger scale which show the optical phase control element of the 2nd Embodiment of this invention The schematic diagram which shows the band structure of the optical phase control element of the 2nd Embodiment of this invention Sectional drawing and the elements on larger scale which show the semiconductor light-emitting device of the 3rd Embodiment of this invention The top view which shows the structure of the external resonator type laser to which the semiconductor light-emitting device of the 3rd Embodiment of this invention was applied. Sectional drawing which shows a part of manufacturing process of the semiconductor light-emitting device of the 3rd Embodiment of this invention. Sectional view showing a conventional semiconductor laser

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light emission area | region 2 Phase control area 13, 23, 39 Active waveguide layer 131,231 Electron confinement layer 132,232 Hole confinement layer

Claims (4)

An active waveguide layer that changes the phase of incident light is provided on a substrate,
An optical phase control element, wherein the active waveguide layer is formed by alternately stacking an electron confinement layer and a hole confinement layer in a staggered band structure. The optical phase control element according to claim 1, wherein a layer thickness of the electron confinement layer is larger than a layer thickness of the hole confinement layer. In a semiconductor light emitting device in which a light emitting region that emits light and a phase control region that changes a phase of light emitted by the light emitting region are arranged in series in a light guiding direction on a substrate,
The semiconductor light emitting device according to claim 1, wherein the phase control region includes an active waveguide layer in which an electron confinement layer and a hole confinement layer are alternately stacked in a staggered band structure. The semiconductor light-emitting element according to claim 3, wherein the electron confinement layer has a thickness greater than that of the hole confinement layer.

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