WO2017129221A1 - Method for producing an optical semiconductor component and optical semiconductor component - Google Patents

Method for producing an optical semiconductor component and optical semiconductor component Download PDF

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Publication number
WO2017129221A1
WO2017129221A1 PCT/EP2016/051441 EP2016051441W WO2017129221A1 WO 2017129221 A1 WO2017129221 A1 WO 2017129221A1 EP 2016051441 W EP2016051441 W EP 2016051441W WO 2017129221 A1 WO2017129221 A1 WO 2017129221A1
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Prior art keywords
optical
waveguide
layer
optical semiconductor
semiconductor component
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PCT/EP2016/051441
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French (fr)
Inventor
Martin MÖHRLE
Michael THEURER
Ariane Sigmund
Ute Troppenz
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Fraunhofer Gesellschaft zur Foerderung der Angewandten Forschung eV
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Fraunhofer Gesellschaft zur Foerderung der Angewandten Forschung eV
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Priority to PCT/EP2016/051441 priority Critical patent/WO2017129221A1/en
Publication of WO2017129221A1 publication Critical patent/WO2017129221A1/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/16—Window-type lasers, i.e. with a region of non-absorbing material between the active region and the reflecting surface
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
    • H01S5/22—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure
    • H01S5/227—Buried mesa structure ; Striped active layer
    • H01S5/2275—Buried mesa structure ; Striped active layer mesa created by etching
    • H—ELECTRICITY
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    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/02—Structural details or components not essential to laser action
    • H01S5/0201—Separation of the wafer into individual elements, e.g. by dicing, cleaving, etching or directly during growth
    • H01S5/0203—Etching
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/1082—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region with a special facet structure, e.g. structured, non planar, oblique
    • H01S5/1085—Oblique facets
    • H—ELECTRICITY
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    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
    • H01S5/22—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure
    • H01S5/2205—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure comprising special burying or current confinement layers
    • H01S5/2206—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure comprising special burying or current confinement layers based on III-V materials
    • H—ELECTRICITY
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    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
    • H01S5/22—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure
    • H01S5/2205—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure comprising special burying or current confinement layers
    • H01S5/2218—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure comprising special burying or current confinement layers having special optical properties
    • H01S5/222—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure comprising special burying or current confinement layers having special optical properties having a refractive index lower than that of the cladding layers or outer guiding layers
    • H—ELECTRICITY
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    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
    • H01S5/22—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure
    • H01S5/2205—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure comprising special burying or current confinement layers
    • H01S5/2222—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure comprising special burying or current confinement layers having special electric properties
    • H—ELECTRICITY
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    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
    • H01S5/22—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure
    • H01S5/2205—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure comprising special burying or current confinement layers
    • H01S5/2222—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure comprising special burying or current confinement layers having special electric properties
    • H01S5/2224—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure comprising special burying or current confinement layers having special electric properties semi-insulating semiconductors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/30—Structure or shape of the active region; Materials used for the active region
    • H01S5/34—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers
    • H01S5/343—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser
    • H01S5/34346—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser characterised by the materials of the barrier layers
    • H01S5/34366—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser characterised by the materials of the barrier layers based on InGa(Al)AS
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/40—Arrangement of two or more semiconductor lasers, not provided for in groups H01S5/02 - H01S5/30
    • H01S5/4025—Array arrangements, e.g. constituted by discrete laser diodes or laser bar
    • H01S5/4031—Edge-emitting structures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/40—Arrangement of two or more semiconductor lasers, not provided for in groups H01S5/02 - H01S5/30
    • H01S5/4025—Array arrangements, e.g. constituted by discrete laser diodes or laser bar
    • H01S5/4087—Array arrangements, e.g. constituted by discrete laser diodes or laser bar emitting more than one wavelength

Definitions

  • the invention relates to a method for producing an optical semiconductor component according to claim 1 and optical semiconductor component according to claim 12.
  • aluminium-containing semiconductor layers e.g. multi-quantum well - MQW layers such as InGaAIAs-MQW layers
  • These components have the potential for an improved high temperature behavior because of the larger discontinuities of the conduction band and therefore may be op- erated under less power consumption and may not require an active cooling device.
  • the active layers may oxidize because of their aluminum content; for example, during a cleaving or etching step for generating optical input and/or output facets.
  • An oxide layer on the optical facets absorbs light which increases the temperature such that during the operation of the component the optical facets may be damaged or even destroyed.
  • the oxide layer on the laser facets may be removed and the facets may be covered by passiv- ating layers.
  • a protective material may be grown for protecting the facets as disclosed in DE 101 57 233 A1 .
  • this method of protecting the optical facets requires at least one additional epitaxy step, thereby e.g. increasing the fabrication costs.
  • a method for producing a optical semiconductor component comprising the steps of:
  • an optical waveguide strip of an optical waveguide e.g. an optical waveguide layer stack
  • the waveguide strip comprising at least one aluminium-containing active layer
  • At least one aluminium-free optically and/or electrically functional layer in such a way that it comprises a first and a second portion, wherein the first portion extends laterally along and/or above the waveguide strip and the second portion covers at least one face (front and/or rear face) of the waveguide strip at least in the region of the active layer;
  • the second portion of the functional layer protects the face of the waveguide strip against oxidization and thus e.g. avoids aging problems due to an oxidation of waveguide facets.
  • the functional layer in particular is a layer that has an electrical and/or optical function in the completed optical semiconductor component, i.e. a layer which has not only been provided for protecting the face of the of the waveguide strip. That is, instead of generating an additional layer or an additional material region for the only purpose of protecting the face of the waveguide strip, at least one of the component's functional layers, which in any case has to be generated, is modified such as to also cover at least one of the waveguide strip's faces (i.e. the front and/or rear face).
  • the "face” of the waveguide strip is a face that extends with an angle (e.g. perpendicular) with respect to the longitudinal direction of the waveguide strip (at least with respect to the longitudinal direction of the corresponding waveguide strip ending).
  • the optical waveguide comprises two light coupling endings (as e.g. in an optical amplifier) such that the wave- guide strip has a front and a rear face
  • the functional layer i.e. its second portion
  • the optical facet provides an optical interface of the completed optical semiconductor com- ponent via which light is coupled into the optical waveguide and/or light is decoupled from the optical waveguide.
  • the optical facet is created in such a way that the face of the waveguide strip remains covered by the second portion of the functional layer. Accordingly, the second portion of the functional layer may not be removed before generating the optical facet.
  • the optical facet is created in such a way that it is at least partially formed by a face of an aluminum-free material region adjacent the face of the waveguide strip, the material region comprising at least a section of the second portion of the functional layer of the optical semiconductor component.
  • the material region comprises the sec- ond portion of the functional layer and/or a portion of another layer (e.g. of an upper cladding layer) of the optical semiconductor component.
  • the optical facet is generated using an etching (wet or dry etching) or a cleaving method.
  • the method according to the invention may be used for fabricating a buried heterostructure component such as a buried heterostructure laser (e.g.
  • a DFB laser a DBR laser, a horizontal cavity surface-emitting laser - HCSEL or a broad area laser
  • amplifier i.e. a semiconductor optical amplifier - SOA or a reflective semiconductor optical amplifier - RSOA.
  • the method may also be used for fabricating other devices such as photodiodes or arrays of optical semiconductor components (see below). Further, the component might have different active layers (e.g. different InGaAIAs-MQW layers).
  • the functional layer may be an epitaxially grown layer.
  • the functional layer is a blocking layer (in particular, of a buried heterostructure component).
  • at least one cladding layer of the optical waveguide may be generated above the functional layer.
  • the active layer is a layer of a MQW stack such as an InGaAIAs-MQW stack.
  • the invention also relates to a optical semiconductor component, in particular fabricated using the method as described above, the component comprising
  • an optical waveguide that comprises a waveguide strip having at least one aluminium- containing active layer
  • At least one aluminium-free optically and/or electrically functional layer comprising a first and a second portion, wherein the first portion extends laterally to and/or above the active layer and the second portion covers at least one face of the waveguide strip at least in the region of the active layer;
  • the optical semiconductor component may be a buried heterostructure component such as a buried heterostructure laser or amplifier.
  • the optical facet is formed by an aluminum-free material region adjacent the face of the waveguide strip, the material region comprising at least a section of the second portion of the functional layer of the optical semiconductor component.
  • the invention further relates to an array of a plurality of optical semiconductor components according to the invention.
  • the optical semiconductor components of the array may have different active layers (e.g. different MQWs).
  • other layers of the two optical semiconductor components may be identical; e.g. the functional layer and/or an upper cladding layer.
  • the invention relates to an array comprising optical semiconductor components in the form of SOAs, RSOAs, DFB lasers, DBR lasers and/or HCSELs, wherein the active layers of at least some of the optical semiconductor components might be different (e.g. different InGaAIAs-MQW layers) as already mentioned above.
  • at least some of the components may comprise different active layers (e.g.
  • the optical semiconductor components of the array may also comprise identical active layers.
  • the array may have optical faces on front and/or rear sides of the individual waveguide strips (generated by e.g. cleaving or etching) providing optical facets of the semiconductor components.
  • Figures 1 A to 3B illustrate steps during the fabrication of an optical semiconductor component using a method according to an embodiment of the invention
  • Figure 4 shows a lateral view of an optical semiconductor component according to an embodiment of the invention
  • Figure 5 shows a lateral view of an optical semiconductor component according to another embodiment of the invention
  • Figure 6 depicts a front view of an array of optical semiconductor ponents according to an embodiment of the invention
  • FIG. 7 to 9 depicts top views of arrays of optical semiconductor components.
  • Figures 1 A to 3A each show front views of a semiconductor structure during different steps of a method according to an embodiment of the invention. More particularly, the method is used for the production of a optical semiconductor component in the form of a buried heterostructure (BH) component (e.g. a laser or an optical amplifier).
  • Figures 1 B to 3B show the semiconductor structure in corresponding side views.
  • BH buried heterostructure
  • lower cladding layers 1 1 e.g. n-doped Indiumphosphide layers
  • a single lower cladding layer are arranged on a substrate 10 (e.g. an Indiumphosphide - InP substrate).
  • a waveguide strip 12 is produced by arranging and structuring a plurality of lower waveguiding layers 121 , a plurality of active layers in the form of aluminum-containing multi-quantum well layers 122 and upper waveguiding layers 123.
  • the multi-quantum well layers 122 (forming e.g. an InGaAIAs-MQW stack) form both the active region and, together with the waveguiding layers (121 , 123), the core of the optical wave- guide of the optical semiconductor component.
  • the layers 121 - 123 are structured laterally and may also be structured in their front and end regions such that the waveguide strip 12 is formed (which at this stage of the fabrication of the semiconductor component has a ridge shape protruding from the lower cladding layer 1 1 ).
  • blocking layers 13 are epitaxially grown in such a way that they comprises a first portion 131 having subsections 131 a, 131 b extending along opposite longitudinal sidewalls of the waveguide strip 12.
  • the first portion 131 of blocking layers 13 is at least partially arranged on the lower cladding layer 1 1 and also covers the longitudinal sidewalls of the waveguide strip 12.
  • the blocking layers 13 may be formed by p- and n-lnP or a semi-insulating material (e.g. semi-insulating InP). If a DFB laser shall be produced, a Bragg grating will be generated before growing the blocking layers 13.
  • the blocking layers 13 further comprise a second portion 132 which covers a front face 140 of waveguide strip 12 and in particular covers the front face of the active MQW layers 122.
  • the second portion 132 thus prevents oxidization of the front face of the aluminum- containing MQW layers 122.
  • Protecting the face 140 of the waveguide strip 12 e.g. allows to keep the cleaved optical semiconductor component under normal ambient conditions (e.g. in normal ambient air) for a longer period of time.
  • upper (e.g. p-doped) cladding layers 14 are grown such that an optical waveguide 120 is realized comprising at least the lower cladding layer 1 1 , the waveguide strip 12 and at least portions of the upper cladding layers 14.
  • the upper cladding layers 14 comprise a section 145 extending adjacent the second portion 132 of the blocking layers 13.
  • the section 145 of the upper cladding layers 14 and the second portion 132 of the blocking layers 13 thus form an aluminum free material region protecting the front face 140 of waveguide strip 12.
  • Figures 3A and 3B show the completed BH structure.
  • an etching process (such as a wet etching process or dry etching process) is used.
  • the etching process is carried out in such a way that an optical facet 130 is formed in the aluminum-free material region provided by section 145 of the upper cladding layers 14 and the second portion 132 of the blocking layers 13. More particularly, the optical facet 130 is formed by a face 1321 of the second portion 132 of the blocking layers 13 and a face 141 of the upper cladding layer 14.
  • the optical facet 130 extends vertically, i.e.
  • optical facet 130 extends obliquely (with respect to the optical waveguide 120) through the upper cladding layer 14 and the second portion 132 of the blocking layers 13 ( Figures 2B and 5). It is also possible that only section 145 of the upper cladding layers 14 (which also can be regarded as "functional layer") covers the front face 140 of waveguide strip 12 such that the entire optical facet 130 is formed in the cladding layer section 145.
  • the optical facet 130 may be coated, e.g. using a high reflection or anti-reflection coating.
  • Figure 6 relates to an array 200 comprising a plurality of optical semiconductor components 100a - 10Oe according to the invention, wherein each of the components 100a - 10Oe is a buried heterostructure component such as a laser or an amplifier. It is possible that at least some of the components have different active layers such that components with different properties are realized.
  • components 100a and 100b comprise different multi- quantum well layers 122a, 122b.
  • the optical semiconductor components 100a - 100e are arranged on a common substrate 10 and may share some functional layers such as the lower and the upper cladding layers 1 1 , 14. Further, the blocking layers 13a - 13e may be grown simultaneously (i.e. using the same processing step).
  • Figure 7 depicts a top view of an array 200 of optical semiconductor components 100a - 100e (e.g. configured similarly or identically to the array shown in Fig. 6).
  • Each one of the components comprises a front optical facet 130a - 130e and a rear optical facet 1300a - 1300e.
  • the optical facets are created by cleaving the substrate 10 (and the layers arranged on the substrate) perpendicular to the direction of the optical semiconductor strip 100a - 10Oe (i.e. perpendicular to their optical waveguides).
  • the front and rear optical facets 130a - 130e, 1300a - 1300e are generated by means of an etching process (e.g. a wet etching process).
  • the resulting optical facets 130a - 130e, 1300a - 1300b are orientated perpendicular (Fig. 8) or inclined (Fig. 9) with respect to the optical waveguides of the optical semiconductor components 100a - 100e. It is also possible that each one of the components 100a - 100e comprises individual front and/or rear facets.

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  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Optics & Photonics (AREA)
  • Geometry (AREA)
  • Semiconductor Lasers (AREA)

Abstract

The invention relates to a method for producing an optical semiconductor component, comprising the steps of fabricating an optical waveguide strip (12) of an optical waveguide (120), the waveguide strip (12) comprising at least one aluminium-containing active layer (122); generating at least one aluminium-free optically and/or electrically functional layer (13) in such a way that it comprises a first and a second portion (131, 132), wherein the first portion (131) extends laterally along and/or above the waveguide strip (14) and the second portion (132) covers at least one face (140) of the waveguide strip (12) at least in the region of the active layer (122); completing the optical waveguide (120); and generating at least one optical facet (130) for injecting light into or emitting light from the optical waveguide (120). The invention also relates to an optical semiconductor component.

Description

Method for producing an optical semiconductor component and optical semiconductor component
Description
The invention relates to a method for producing an optical semiconductor component according to claim 1 and optical semiconductor component according to claim 12.
It is known to use aluminium-containing semiconductor layers (e.g. multi-quantum well - MQW layers such as InGaAIAs-MQW layers) as active material of semiconductor lasers or amplifiers. These components have the potential for an improved high temperature behavior because of the larger discontinuities of the conduction band and therefore may be op- erated under less power consumption and may not require an active cooling device.
However, the active layers may oxidize because of their aluminum content; for example, during a cleaving or etching step for generating optical input and/or output facets. An oxide layer on the optical facets absorbs light which increases the temperature such that during the operation of the component the optical facets may be damaged or even destroyed. The oxide layer on the laser facets may be removed and the facets may be covered by passiv- ating layers. Further, if the optical facets are generated by means of an etching process, a protective material may be grown for protecting the facets as disclosed in DE 101 57 233 A1 . However, this method of protecting the optical facets requires at least one additional epitaxy step, thereby e.g. increasing the fabrication costs.
It is an object of the invention to protect the optical facets while keeping the fabrication process as simple as possible. According to the invention, a method for producing a optical semiconductor component is provided, comprising the steps of:
- fabricating an optical waveguide strip of an optical waveguide (e.g. an optical waveguide layer stack), the waveguide strip comprising at least one aluminium-containing active layer;
- generating at least one aluminium-free optically and/or electrically functional layer in such a way that it comprises a first and a second portion, wherein the first portion extends laterally along and/or above the waveguide strip and the second portion covers at least one face (front and/or rear face) of the waveguide strip at least in the region of the active layer;
- completing the optical waveguide; and
- generating at least one optical facet for injecting light into or emitting light from the optical waveguide.
The second portion of the functional layer protects the face of the waveguide strip against oxidization and thus e.g. avoids aging problems due to an oxidation of waveguide facets. The functional layer in particular is a layer that has an electrical and/or optical function in the completed optical semiconductor component, i.e. a layer which has not only been provided for protecting the face of the of the waveguide strip. That is, instead of generating an additional layer or an additional material region for the only purpose of protecting the face of the waveguide strip, at least one of the component's functional layers, which in any case has to be generated, is modified such as to also cover at least one of the waveguide strip's faces (i.e. the front and/or rear face). Thus, no additional production step is needed for the protection of the active layer of the waveguide strip. The "face" of the waveguide strip is a face that extends with an angle (e.g. perpendicular) with respect to the longitudinal direction of the waveguide strip (at least with respect to the longitudinal direction of the corresponding waveguide strip ending). If the optical waveguide comprises two light coupling endings (as e.g. in an optical amplifier) such that the wave- guide strip has a front and a rear face, the functional layer (i.e. its second portion) can be formed in such a way that it covers both the front and the rear face of the waveguide strip as mentioned above.
The optical facet provides an optical interface of the completed optical semiconductor com- ponent via which light is coupled into the optical waveguide and/or light is decoupled from the optical waveguide. In particular, the optical facet is created in such a way that the face of the waveguide strip remains covered by the second portion of the functional layer. Accordingly, the second portion of the functional layer may not be removed before generating the optical facet.
For example, the optical facet is created in such a way that it is at least partially formed by a face of an aluminum-free material region adjacent the face of the waveguide strip, the material region comprising at least a section of the second portion of the functional layer of the optical semiconductor component. For example, the material region comprises the sec- ond portion of the functional layer and/or a portion of another layer (e.g. of an upper cladding layer) of the optical semiconductor component. According to another embodiment of the invention, the optical facet is generated using an etching (wet or dry etching) or a cleaving method. The method according to the invention may be used for fabricating a buried heterostructure component such as a buried heterostructure laser (e.g. a DFB laser, a DBR laser, a horizontal cavity surface-emitting laser - HCSEL or a broad area laser) or amplifier (i.e. a semiconductor optical amplifier - SOA or a reflective semiconductor optical amplifier - RSOA). The method, however, may also be used for fabricating other devices such as photodiodes or arrays of optical semiconductor components (see below). Further, the component might have different active layers (e.g. different InGaAIAs-MQW layers).
Further, the functional layer may be an epitaxially grown layer. For example, the functional layer is a blocking layer (in particular, of a buried heterostructure component). Moreover, before generating the optical facet, at least one cladding layer of the optical waveguide may be generated above the functional layer. For example, the active layer is a layer of a MQW stack such as an InGaAIAs-MQW stack.
The invention also relates to a optical semiconductor component, in particular fabricated using the method as described above, the component comprising
- an optical waveguide that comprises a waveguide strip having at least one aluminium- containing active layer;
- at least one aluminium-free optically and/or electrically functional layer comprising a first and a second portion, wherein the first portion extends laterally to and/or above the active layer and the second portion covers at least one face of the waveguide strip at least in the region of the active layer; and
- at least one optical facet for injecting light into or emitting light from the optical waveguide.
The optical semiconductor component may be a buried heterostructure component such as a buried heterostructure laser or amplifier. For example, the optical facet is formed by an aluminum-free material region adjacent the face of the waveguide strip, the material region comprising at least a section of the second portion of the functional layer of the optical semiconductor component.
The invention further relates to an array of a plurality of optical semiconductor components according to the invention. For example, at least some of the optical semiconductor components of the array may have different active layers (e.g. different MQWs). However, other layers of the two optical semiconductor components may be identical; e.g. the functional layer and/or an upper cladding layer. For example, the invention relates to an array comprising optical semiconductor components in the form of SOAs, RSOAs, DFB lasers, DBR lasers and/or HCSELs, wherein the active layers of at least some of the optical semiconductor components might be different (e.g. different InGaAIAs-MQW layers) as already mentioned above. Further, at least some of the components may comprise different active layers (e.g. different InGaAIAs-MQW layers). Of course, the optical semiconductor components of the array may also comprise identical active layers. The array may have optical faces on front and/or rear sides of the individual waveguide strips (generated by e.g. cleaving or etching) providing optical facets of the semiconductor components.
Embodiments of the invention are described hereinafter with reference to the drawings, in which: Figures 1 A to 3B illustrate steps during the fabrication of an optical semiconductor component using a method according to an embodiment of the invention;
Figure 4 shows a lateral view of an optical semiconductor component according to an embodiment of the invention;
Figure 5 shows a lateral view of an optical semiconductor component according to another embodiment of the invention; Figure 6 depicts a front view of an array of optical semiconductor ponents according to an embodiment of the invention;
Figures 7 to 9 depicts top views of arrays of optical semiconductor components.
Figures 1 A to 3A each show front views of a semiconductor structure during different steps of a method according to an embodiment of the invention. More particularly, the method is used for the production of a optical semiconductor component in the form of a buried heterostructure (BH) component (e.g. a laser or an optical amplifier). Figures 1 B to 3B show the semiconductor structure in corresponding side views.
According to Figure 1 A, lower cladding layers 1 1 (e.g. n-doped Indiumphosphide layers) or a single lower cladding layer are arranged on a substrate 10 (e.g. an Indiumphosphide - InP substrate). Further, a waveguide strip 12 is produced by arranging and structuring a plurality of lower waveguiding layers 121 , a plurality of active layers in the form of aluminum-containing multi-quantum well layers 122 and upper waveguiding layers 123. The multi-quantum well layers 122 (forming e.g. an InGaAIAs-MQW stack) form both the active region and, together with the waveguiding layers (121 , 123), the core of the optical wave- guide of the optical semiconductor component.
The layers 121 - 123 are structured laterally and may also be structured in their front and end regions such that the waveguide strip 12 is formed (which at this stage of the fabrication of the semiconductor component has a ridge shape protruding from the lower cladding layer 1 1 ).
In a subsequent production step (Figures 2A and 2B), functional layers in the form of blocking layers 13 are epitaxially grown in such a way that they comprises a first portion 131 having subsections 131 a, 131 b extending along opposite longitudinal sidewalls of the waveguide strip 12. The first portion 131 of blocking layers 13 is at least partially arranged on the lower cladding layer 1 1 and also covers the longitudinal sidewalls of the waveguide strip 12. The blocking layers 13 may be formed by p- and n-lnP or a semi-insulating material (e.g. semi-insulating InP). If a DFB laser shall be produced, a Bragg grating will be generated before growing the blocking layers 13.
The blocking layers 13 further comprise a second portion 132 which covers a front face 140 of waveguide strip 12 and in particular covers the front face of the active MQW layers 122. The second portion 132 thus prevents oxidization of the front face of the aluminum- containing MQW layers 122. Protecting the face 140 of the waveguide strip 12 e.g. allows to keep the cleaved optical semiconductor component under normal ambient conditions (e.g. in normal ambient air) for a longer period of time.
After growing the blocking layers 13, upper (e.g. p-doped) cladding layers 14 (or a single upper cladding layer) are grown such that an optical waveguide 120 is realized comprising at least the lower cladding layer 1 1 , the waveguide strip 12 and at least portions of the upper cladding layers 14. The upper cladding layers 14 comprise a section 145 extending adjacent the second portion 132 of the blocking layers 13. The section 145 of the upper cladding layers 14 and the second portion 132 of the blocking layers 13 thus form an aluminum free material region protecting the front face 140 of waveguide strip 12. Figures 3A and 3B show the completed BH structure. The blocking layers 13 and the upper cladding layers 14 together at least essentially hermitically cover the entire active layers 122 such that a laser 1 (or any other optical semiconductor component produced by means of the method according to the invention) is e.g. suited for an airtight packaging of the optical semiconductor component.
For generating an optical facet of the optical waveguide 120 permitting light produced by the laser 1 to be coupled out of its optical waveguide 120, an etching process (such as a wet etching process or dry etching process) is used. The etching process is carried out in such a way that an optical facet 130 is formed in the aluminum-free material region provided by section 145 of the upper cladding layers 14 and the second portion 132 of the blocking layers 13. More particularly, the optical facet 130 is formed by a face 1321 of the second portion 132 of the blocking layers 13 and a face 141 of the upper cladding layer 14. For example, the optical facet 130 extends vertically, i.e. perpendicular to the optical waveguide 120, through the upper cladding layer 14 and the second portion 132 of the blocking layers 13 (Figures 2B and 4) or the optical facet 130 extends obliquely (with respect to the optical waveguide 120) through the upper cladding layer 14 and the second portion 132 of the blocking layers 13 (Figures 2B and 5). It is also possible that only section 145 of the upper cladding layers 14 (which also can be regarded as "functional layer") covers the front face 140 of waveguide strip 12 such that the entire optical facet 130 is formed in the cladding layer section 145. The optical facet 130 may be coated, e.g. using a high reflection or anti-reflection coating. Figure 6 relates to an array 200 comprising a plurality of optical semiconductor components 100a - 10Oe according to the invention, wherein each of the components 100a - 10Oe is a buried heterostructure component such as a laser or an amplifier. It is possible that at least some of the components have different active layers such that components with different properties are realized. For example, components 100a and 100b comprise different multi- quantum well layers 122a, 122b. However, the optical semiconductor components 100a - 100e are arranged on a common substrate 10 and may share some functional layers such as the lower and the upper cladding layers 1 1 , 14. Further, the blocking layers 13a - 13e may be grown simultaneously (i.e. using the same processing step). Figure 7 depicts a top view of an array 200 of optical semiconductor components 100a - 100e (e.g. configured similarly or identically to the array shown in Fig. 6). Each one of the components comprises a front optical facet 130a - 130e and a rear optical facet 1300a - 1300e. The optical facets are created by cleaving the substrate 10 (and the layers arranged on the substrate) perpendicular to the direction of the optical semiconductor strip 100a - 10Oe (i.e. perpendicular to their optical waveguides).
According to the embodiment of Fig. 8, the front and rear optical facets 130a - 130e, 1300a - 1300e are generated by means of an etching process (e.g. a wet etching process). The resulting optical facets 130a - 130e, 1300a - 1300b are orientated perpendicular (Fig. 8) or inclined (Fig. 9) with respect to the optical waveguides of the optical semiconductor components 100a - 100e. It is also possible that each one of the components 100a - 100e comprises individual front and/or rear facets.

Claims

Claims
A method for producing an optical semiconductor component, comprising the steps of:
- fabricating an optical waveguide strip (12) of an optical waveguide (120), the waveguide strip (12) comprising at least one aluminium-containing active layer (122);
- generating at least one aluminium-free optically and/or electrically functional layer (13) in such a way that it comprises a first and a second portion (131 , 132), wherein the first portion (131 ) extends laterally along and/or above the waveguide strip (12)and the second portion (132) covers at least one face (140) of the waveguide strip (12) at least in the region of the active layer (122);
- completing the optical waveguide (120); and
- generating at least one optical facet (130) for injecting light into or emitting light from the optical waveguide (120).
The method as claimed in claim 1 , wherein the optical facet (130) is created in such a way that the face (140) of the waveguide strip (12) remains covered by the second portion (132) of the functional layer (13).
The method as claimed in claim 1 or 2, wherein the optical facet (130) is created in such a way that it is formed by an aluminum-free material region adjacent the face (140) of the waveguide strip (12), the material region comprising at least a section of the second portion of the functional layer (13) of the optical semiconductor component.
The method as claimed in any of the preceding claims, wherein the optical facet (130) is created in such a way that it is at least partially formed by a face (1321 ) of the second portion (132) of the functional layer (13).
The method as claimed in any of the preceding claims, wherein the optical facet (130) is generated using an etching or cleaving method.
The method as claimed in any of the preceding claims, wherein the method is used for fabricating a buried heterostructure component.
7. The method as claimed in claim 6, wherein the method is used for fabricating at least one buried heterostructure laser or amplifier.
8. The method as claimed in any of the preceding claims, wherein the functional layer (13) is an epitaxially grown layer.
9. The method as claimed in any of the preceding claims, wherein the functional layer (13) is a blocking layer.
10. The method as claimed in any of the preceding claims, wherein before generating the optical facet (130), at least one cladding layer (14) of the optical waveguide (120) is generated above the functional layer (13).
1 1 . The method as claimed in any of the preceding claims, wherein the active layer (122) is a layer of MQWs formed by InGaAsP, InGaAIAs and/or InGaAsP/lnGaAIAs.
12. Optical semiconductor component, in particular fabricated using the method as claimed in any of the preceding claims, comprising
- an optical waveguide (120) that comprises a waveguide strip (12) having at least one aluminium-containing active layer (122);
- at least one aluminium-free optically and/or electrically functional layer (13) comprising a first and a second portion (131 , 132), wherein the first portion (131 ) extends laterally to and/or above the active layer (122) and the second portion (132) covers at least one face (140) of the waveguide strip (12) at least in the region of the active layer (122); and
- at least one optical facet (130) for injecting light into or emitting light from the optical waveguide (120).
13. Optical semiconductor component as claimed in claim 12, wherein the optical facet (130) is formed by an aluminum-free material region adjacent the face (140) of the waveguide strip (12), the material region comprising at least a section of the second portion of the functional layer (13) of the optical semiconductor component.
14. Array comprising a plurality of optical semiconductor components (100a - 100e) as claimed in claim 12.
15. Array as claimed in claim 14, wherein at least two of the optical semiconductor components (100a - 10Oe) have different active layers (122a - 122e).
PCT/EP2016/051441 2016-01-25 2016-01-25 Method for producing an optical semiconductor component and optical semiconductor component Ceased WO2017129221A1 (en)

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