CA1070029A - Methods for forming semiconductor waveguide devices - Google Patents
Methods for forming semiconductor waveguide devicesInfo
- Publication number
- CA1070029A CA1070029A CA267,912A CA267912A CA1070029A CA 1070029 A CA1070029 A CA 1070029A CA 267912 A CA267912 A CA 267912A CA 1070029 A CA1070029 A CA 1070029A
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- Prior art keywords
- layer
- groove
- refractive index
- growth
- higher refractive
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/122—Basic optical elements, e.g. light-guiding paths
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/02104—Forming layers
- H01L21/02365—Forming inorganic semiconducting materials on a substrate
- H01L21/02367—Substrates
- H01L21/0237—Materials
- H01L21/02387—Group 13/15 materials
- H01L21/02395—Arsenides
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/02104—Forming layers
- H01L21/02365—Forming inorganic semiconducting materials on a substrate
- H01L21/02367—Substrates
- H01L21/02428—Structure
- H01L21/0243—Surface structure
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/02104—Forming layers
- H01L21/02365—Forming inorganic semiconducting materials on a substrate
- H01L21/02518—Deposited layers
- H01L21/02521—Materials
- H01L21/02538—Group 13/15 materials
- H01L21/02546—Arsenides
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/02104—Forming layers
- H01L21/02365—Forming inorganic semiconducting materials on a substrate
- H01L21/02612—Formation types
- H01L21/02617—Deposition types
- H01L21/02623—Liquid deposition
- H01L21/02625—Liquid deposition using melted materials
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/02104—Forming layers
- H01L21/02365—Forming inorganic semiconducting materials on a substrate
- H01L21/02612—Formation types
- H01L21/02617—Deposition types
- H01L21/02623—Liquid deposition
- H01L21/02628—Liquid deposition using solutions
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- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Microelectronics & Electronic Packaging (AREA)
- General Physics & Mathematics (AREA)
- Computer Hardware Design (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- Manufacturing & Machinery (AREA)
- Power Engineering (AREA)
- Chemical & Material Sciences (AREA)
- Materials Engineering (AREA)
- Optics & Photonics (AREA)
- Semiconductor Lasers (AREA)
- Optical Integrated Circuits (AREA)
Abstract
METHODS FOR FORMING
SEMICONDUCTOR WAVEGUIDE DEVICES
Abstract of the Disclosure Methods are provided for making buried rib and buried heterostructure waveguides by liquid phase epitaxy, The provision of a groove in -the substrate layer results in the preferential growth of new material without intermediate etching procedures.
SEMICONDUCTOR WAVEGUIDE DEVICES
Abstract of the Disclosure Methods are provided for making buried rib and buried heterostructure waveguides by liquid phase epitaxy, The provision of a groove in -the substrate layer results in the preferential growth of new material without intermediate etching procedures.
Description
~ P~ul A. Kirby - 2 f'' (~evision~
~ ~7~Zc3 Fie].d oE the I~ven~.ion __. ___ __ This inve~ticn relates to heterostructure sem.iconductor wavegu.ide structures.
Back~round of the Invèntion ____ __ .
S . Heterostructure rib waveguide i.njection lasers such as that described by T. P. Lee et al. in a paper entitled 'AlGaAs Double Heterostructure Rib WavecJuide Injection Lasers' appearing in the XEEE Journal of Quantum El2ctronics Spec~al lssue Vol. 11 No. 7 pp ~32 - 43S (July 1975~ are known.
L0 disadvantage o that structure is howeve.~ that its method of construction involves halting the e~i~axy at an interrnediate sta~e, removing the device from the epitax~ furnace, and masking and etching the device before returning it to the furnace for the . completi.on of the epitaxy. This interruption of the epitaxy is very lLable to produce a poor quality interface between ' the later grown matexial and the earlier grown material. "
: Problems are encountered with the later grown material fail,ing ` to nucleate properly un].ess there is less than about 0.8% AlAs ,in ;, the materia]. upon whi.ch tlle later qrown materlal is to be '20 deposited. Th.is is attributed to effects of ex.idation of the ,, - 's~rface while it is removed from the furnace. .' One'example of a known buried heterostructure injec~ion laser is that describecl by T. Tsukada in a paper en-titled 5Ga,~s Ga~ As Buried Heterostructure Injection Lasers' appearirlg i.n the Journal of Applied Physics Vol. 45 pp 4899-49~6 : , (Nov. 1974). ~owever that structure is like the one descri~ed' in the IEEE Journal ref~rre'~ to previously, in that its manu-factur~ involves halting the epitaxy at an i,ntermedi.ate stage t r~moving the device from the ep.itaxy ~urnace, and masking and ,30 , etching th~ device ~efore returning it to the furnace fc~r com-pletion of the epitaxy~ ,' , .
~6~76~
S ary o:E the Inventi.on Acco~ling to the present invention there is provided a method of heterostruc-turc semiconductor waveguide manufacture wherein a first COII-tinuous layer o:~ semiconductive material is grown by liquid phase epitaxy upon a substTate surface having one or more grooves extending therein, the thickness of the layer and the conditions of growth being such that a groove is formecl in the exposed surface of the first layer overlying the groove in the substrate, wherein semi.conductive material of higher refrac-tive index is gro~n by liquid phase pitaxy in said groove in the exposed surface of the first layer and wherein the epitaxially deposited higher refractive index material is covered by the growth by liquid phase epitaxy of a further layer of semiconductive material which further layer has a refractive index less than that of said higher refractive index material.
The first epitaxially deposited layer may be of opposite conduc-tivity type to each succeeding epitaxially deposited layer, and the higher reractive index material may consist of or include a region forming the active material of an injection laser or light amplifier.
According to the present invention there is also provided a semi-conductor light emitting device comprising: a substrate having a surface with a first groove provided.therein; a first layer of low refractive index material of one conductivity type provided on the surface, said first layer having a surface wi~h a second groove provided therein overlying the first groove; an active layer of higher refractive index material provided in ~he second groove; a second layer of low refractive index material of the other conductivity type provided over said active layer and said first layer; and an electrode layer provided over said second layer.
Description of the Invention ., ~ .
T~e invention relies upon the tendency for grooves in a substrate ~ ~ to become preferentially filled when l.ayers are grown on ~he subs~rate by :.~ 30 liquid phase epitaxy~ Thus if a groove of depth _ is provided in the surface of a substrate on which material is grown by liquid phase epit~xy, the depth a of the groove in the surface of grown material approximately .. :, .
~' ~
~7~ 9 follows the relationship a = aO exp-t/c, where t i9 the thickness of the grown material covering a p:Lane part of the substrate, cmd c is a decay constant dependent upon the melt composition and the conditions oE the growth. ~le decay constant has been found to be particularly small for growth on a substrate whose surface i9 closely aligned w:Lth one of the low index 3a-Paul A. Kirby - 2 ,~t~Z9 ( Revision~
p~anes, such as a {100~ plan~ in GaAlAs. In this i.ns-tance however, the decay constant is si~nificantly increased when the --. ancJle bet~een the substrate surface and the {100} plane is f increased to greater than 1/2 Thus, Eor instance, it is Eound -that when a suhstrate surace, that is tilted by betweenl ~2~nd 3 about a<100> direction from a {100~ plane, is provided with a 51,m width Vee-shaped g:roove extending in a direction at right angles to the ti.lt axis, the groove profile in the surface of the grown material is reduced to 1.5~1m under typical growth conditions when the depth o the grown material in plane regions near the groove has a -thi.ckness of about 2.5~m. Thus any epitaxially deposited layer has a region of increased thickness that follows the track o the groove in the surface of the underlying substrate. ~y lS arranging that the material bounding this layer is of lower refractive index than the layer, this ].ayer is provided with the optical guiding properties of a 'rib' waveguide.
For certain applications use may also be made of the fact that in liquid phase epitaxy the equilibrium saturation temperature of a melt in contact with a solid surface is a function o:~ the curvature of tne interface between them. In particular the equilibrium saturation -temperature is higher where the solid is convex and lower where it is concave, and, for surfaces having a curvature in one direction only, sati6fies the equationo-Tr = T~ y L 1 r~l) where Tr is the equilibrium temperature in a region where the surface has a radius of curvature r, T~ is the equilibrium temperature in a region where the surface is planar, y ls the free surEace energy at the liquid solid interface, ancl F' Paul ~. Kirby - 2 tRevis.ion) ~t7 L is the latent heat o~ Eusi.c-n per Ul):it vol~lme.
Thereore by choosing to perform a liquid phase epitaxy und~r condi-t.iolls in which the melt is sli.ghtly undersa-turated wi.th respec~ -to a plane surface, the epitaxial growth can be S confined to a strip along the bottom of the groove where the solid surface is concave. By ar:ran~ing for the growth of the g strip to be on lower refractive index material, and by arranging for the strip to be covered by the growth of a layer of lower refractive index material the s*rip is provided with the optical guidi.ng properties of a 'clad' wav`eguide.
This selectivity of deposition arising from curvature ~~~ differences may also be used to make complex integrated optics st.ructures incorporating active elements, lasers or light ampli--fiers, wi.th passive waveguides. For this purpose the profile of the groove or grooves is arranged to be different in different parts o~ the substra-te so that an epitaxy can be performed which will result in the deposition of the active material required for 1`
the lasers or light amplifiers to occur in one groove but not t another, or to occur in a po.rtion of a groove, but not over the ~20 whole of its l.ength. .
There follows a description of -the methods of manufacture of constructions of ~aAlAs heterostructure laser embodying the invention in preferred forms. The description refers to the accom~anying drawings in which:-Brie~ Description o the_Drawings I
~ igure 1 is a transverse section through a buried 'rib' injection laser a~cording to the inven-tion.
Figure 2 depicts a transverse section through an isolated ~ stripe heterostructure injection laser, according to the ~.
lnvention, and - S
' , , Paul A. Kirby 2 (Revision) ~t7~
Figure 3 depicts a transverse section through a buried heterostructure injection laser according to the invention.
Descript,ion of the Preferred Embodiment S Referriny to Figure 1 a substrate 10 has a Vee-shaped groove 11 e~tending substantially in a <110> direction along t.he substrate surface. This surface exten'ds in a {100} plane, but - is tilted b~ between 1/2 and 3 about an axis substantially perpendicu],ar to the groove direction. The substrate is placed .
10 - in a mul-ti-well liquid phase epitaxy graphite boat (not shown) provided with melts for growing three layers 12, 13 and 14 on the substrate. The boat is placed in an epitaxy furnace and the three layers are grown withou-t interruption. Layers 12 and 14 are constructed of GaAlAs of opposite conductivity type. ~;
Normally the substrate is n-type, and hence layer 12 is n-type and layer 14 p-type. Layer 13 is grown in lower band gap higher refractive index material than the other two layers, ~
and contains either a reduced AlAs content or substantially no ~, AlAs. Layers 12 and 14 are of opposite polarity type in order to form a p~n junction near ~he surface of or within layer 13, , which is the ac-tive layer, and which may be o~ either conductivity type, but is usually grown p-type. Typically the doping levels used for these layers lie in the region of 5 x 1017 carriers cm 3-Typically layer 13 is about 0.2 ~m thick, and in order to 3 provide adequate lateral optical guidance, is required to have its centre about 0.02~m thicker than its edges. The amount of thickening can readily be controlled by adjusting the thickness of the underlying layer 12 because the depth of the groove in ita , ~-surface varies substantially exponentially with thickness. It is also possible to control the exponential decay constant by varying the growth conditions, in particular -to speed up the ,.
r Paul ~. Kirby - 2 ~7~ ( Revision) "
growth rate so as to reduce the rate of (lecay w:ith depth.
After the growth of the three ep.itaxial layers, the st.ructure is prov,ided with an insulator layer 16. This i9 ca:refully masked fnr etching a channel throu~h i~ which will accurately register with the underl.ying buried ri.b. Then, a~ter the etchi.ng, a ,' metal elect.rode layer 17 is prov.ided over the insulator layer 16 ~.;
to make a stripe electrical contact with the exposed portio.n of layer 14.
The structure of figure 1 provides more lateral optical guidance tllan a conventional stripe double heterostructure laser employing p:Lane layers because the pr.imary lateral optical guidarlce ." ~
in the onventional stripe laser is that provided by gain guiding.
The basic structure of figure 1 is progressively modified ~'~ in the structure now to be described with reference to f.igures
~ ~7~Zc3 Fie].d oE the I~ven~.ion __. ___ __ This inve~ticn relates to heterostructure sem.iconductor wavegu.ide structures.
Back~round of the Invèntion ____ __ .
S . Heterostructure rib waveguide i.njection lasers such as that described by T. P. Lee et al. in a paper entitled 'AlGaAs Double Heterostructure Rib WavecJuide Injection Lasers' appearing in the XEEE Journal of Quantum El2ctronics Spec~al lssue Vol. 11 No. 7 pp ~32 - 43S (July 1975~ are known.
L0 disadvantage o that structure is howeve.~ that its method of construction involves halting the e~i~axy at an interrnediate sta~e, removing the device from the epitax~ furnace, and masking and etching the device before returning it to the furnace for the . completi.on of the epitaxy. This interruption of the epitaxy is very lLable to produce a poor quality interface between ' the later grown matexial and the earlier grown material. "
: Problems are encountered with the later grown material fail,ing ` to nucleate properly un].ess there is less than about 0.8% AlAs ,in ;, the materia]. upon whi.ch tlle later qrown materlal is to be '20 deposited. Th.is is attributed to effects of ex.idation of the ,, - 's~rface while it is removed from the furnace. .' One'example of a known buried heterostructure injec~ion laser is that describecl by T. Tsukada in a paper en-titled 5Ga,~s Ga~ As Buried Heterostructure Injection Lasers' appearirlg i.n the Journal of Applied Physics Vol. 45 pp 4899-49~6 : , (Nov. 1974). ~owever that structure is like the one descri~ed' in the IEEE Journal ref~rre'~ to previously, in that its manu-factur~ involves halting the epitaxy at an i,ntermedi.ate stage t r~moving the device from the ep.itaxy ~urnace, and masking and ,30 , etching th~ device ~efore returning it to the furnace fc~r com-pletion of the epitaxy~ ,' , .
~6~76~
S ary o:E the Inventi.on Acco~ling to the present invention there is provided a method of heterostruc-turc semiconductor waveguide manufacture wherein a first COII-tinuous layer o:~ semiconductive material is grown by liquid phase epitaxy upon a substTate surface having one or more grooves extending therein, the thickness of the layer and the conditions of growth being such that a groove is formecl in the exposed surface of the first layer overlying the groove in the substrate, wherein semi.conductive material of higher refrac-tive index is gro~n by liquid phase pitaxy in said groove in the exposed surface of the first layer and wherein the epitaxially deposited higher refractive index material is covered by the growth by liquid phase epitaxy of a further layer of semiconductive material which further layer has a refractive index less than that of said higher refractive index material.
The first epitaxially deposited layer may be of opposite conduc-tivity type to each succeeding epitaxially deposited layer, and the higher reractive index material may consist of or include a region forming the active material of an injection laser or light amplifier.
According to the present invention there is also provided a semi-conductor light emitting device comprising: a substrate having a surface with a first groove provided.therein; a first layer of low refractive index material of one conductivity type provided on the surface, said first layer having a surface wi~h a second groove provided therein overlying the first groove; an active layer of higher refractive index material provided in ~he second groove; a second layer of low refractive index material of the other conductivity type provided over said active layer and said first layer; and an electrode layer provided over said second layer.
Description of the Invention ., ~ .
T~e invention relies upon the tendency for grooves in a substrate ~ ~ to become preferentially filled when l.ayers are grown on ~he subs~rate by :.~ 30 liquid phase epitaxy~ Thus if a groove of depth _ is provided in the surface of a substrate on which material is grown by liquid phase epit~xy, the depth a of the groove in the surface of grown material approximately .. :, .
~' ~
~7~ 9 follows the relationship a = aO exp-t/c, where t i9 the thickness of the grown material covering a p:Lane part of the substrate, cmd c is a decay constant dependent upon the melt composition and the conditions oE the growth. ~le decay constant has been found to be particularly small for growth on a substrate whose surface i9 closely aligned w:Lth one of the low index 3a-Paul A. Kirby - 2 ,~t~Z9 ( Revision~
p~anes, such as a {100~ plan~ in GaAlAs. In this i.ns-tance however, the decay constant is si~nificantly increased when the --. ancJle bet~een the substrate surface and the {100} plane is f increased to greater than 1/2 Thus, Eor instance, it is Eound -that when a suhstrate surace, that is tilted by betweenl ~2~nd 3 about a<100> direction from a {100~ plane, is provided with a 51,m width Vee-shaped g:roove extending in a direction at right angles to the ti.lt axis, the groove profile in the surface of the grown material is reduced to 1.5~1m under typical growth conditions when the depth o the grown material in plane regions near the groove has a -thi.ckness of about 2.5~m. Thus any epitaxially deposited layer has a region of increased thickness that follows the track o the groove in the surface of the underlying substrate. ~y lS arranging that the material bounding this layer is of lower refractive index than the layer, this ].ayer is provided with the optical guiding properties of a 'rib' waveguide.
For certain applications use may also be made of the fact that in liquid phase epitaxy the equilibrium saturation temperature of a melt in contact with a solid surface is a function o:~ the curvature of tne interface between them. In particular the equilibrium saturation -temperature is higher where the solid is convex and lower where it is concave, and, for surfaces having a curvature in one direction only, sati6fies the equationo-Tr = T~ y L 1 r~l) where Tr is the equilibrium temperature in a region where the surface has a radius of curvature r, T~ is the equilibrium temperature in a region where the surface is planar, y ls the free surEace energy at the liquid solid interface, ancl F' Paul ~. Kirby - 2 tRevis.ion) ~t7 L is the latent heat o~ Eusi.c-n per Ul):it vol~lme.
Thereore by choosing to perform a liquid phase epitaxy und~r condi-t.iolls in which the melt is sli.ghtly undersa-turated wi.th respec~ -to a plane surface, the epitaxial growth can be S confined to a strip along the bottom of the groove where the solid surface is concave. By ar:ran~ing for the growth of the g strip to be on lower refractive index material, and by arranging for the strip to be covered by the growth of a layer of lower refractive index material the s*rip is provided with the optical guidi.ng properties of a 'clad' wav`eguide.
This selectivity of deposition arising from curvature ~~~ differences may also be used to make complex integrated optics st.ructures incorporating active elements, lasers or light ampli--fiers, wi.th passive waveguides. For this purpose the profile of the groove or grooves is arranged to be different in different parts o~ the substra-te so that an epitaxy can be performed which will result in the deposition of the active material required for 1`
the lasers or light amplifiers to occur in one groove but not t another, or to occur in a po.rtion of a groove, but not over the ~20 whole of its l.ength. .
There follows a description of -the methods of manufacture of constructions of ~aAlAs heterostructure laser embodying the invention in preferred forms. The description refers to the accom~anying drawings in which:-Brie~ Description o the_Drawings I
~ igure 1 is a transverse section through a buried 'rib' injection laser a~cording to the inven-tion.
Figure 2 depicts a transverse section through an isolated ~ stripe heterostructure injection laser, according to the ~.
lnvention, and - S
' , , Paul A. Kirby 2 (Revision) ~t7~
Figure 3 depicts a transverse section through a buried heterostructure injection laser according to the invention.
Descript,ion of the Preferred Embodiment S Referriny to Figure 1 a substrate 10 has a Vee-shaped groove 11 e~tending substantially in a <110> direction along t.he substrate surface. This surface exten'ds in a {100} plane, but - is tilted b~ between 1/2 and 3 about an axis substantially perpendicu],ar to the groove direction. The substrate is placed .
10 - in a mul-ti-well liquid phase epitaxy graphite boat (not shown) provided with melts for growing three layers 12, 13 and 14 on the substrate. The boat is placed in an epitaxy furnace and the three layers are grown withou-t interruption. Layers 12 and 14 are constructed of GaAlAs of opposite conductivity type. ~;
Normally the substrate is n-type, and hence layer 12 is n-type and layer 14 p-type. Layer 13 is grown in lower band gap higher refractive index material than the other two layers, ~
and contains either a reduced AlAs content or substantially no ~, AlAs. Layers 12 and 14 are of opposite polarity type in order to form a p~n junction near ~he surface of or within layer 13, , which is the ac-tive layer, and which may be o~ either conductivity type, but is usually grown p-type. Typically the doping levels used for these layers lie in the region of 5 x 1017 carriers cm 3-Typically layer 13 is about 0.2 ~m thick, and in order to 3 provide adequate lateral optical guidance, is required to have its centre about 0.02~m thicker than its edges. The amount of thickening can readily be controlled by adjusting the thickness of the underlying layer 12 because the depth of the groove in ita , ~-surface varies substantially exponentially with thickness. It is also possible to control the exponential decay constant by varying the growth conditions, in particular -to speed up the ,.
r Paul ~. Kirby - 2 ~7~ ( Revision) "
growth rate so as to reduce the rate of (lecay w:ith depth.
After the growth of the three ep.itaxial layers, the st.ructure is prov,ided with an insulator layer 16. This i9 ca:refully masked fnr etching a channel throu~h i~ which will accurately register with the underl.ying buried ri.b. Then, a~ter the etchi.ng, a ,' metal elect.rode layer 17 is prov.ided over the insulator layer 16 ~.;
to make a stripe electrical contact with the exposed portio.n of layer 14.
The structure of figure 1 provides more lateral optical guidance tllan a conventional stripe double heterostructure laser employing p:Lane layers because the pr.imary lateral optical guidarlce ." ~
in the onventional stripe laser is that provided by gain guiding.
The basic structure of figure 1 is progressively modified ~'~ in the structure now to be described with reference to f.igures
2 and 3.
The only modification required to make the structure of ',~
f.i.gu~e 2 involves making a slight change to the melt conditions employed in the growth of the active material 13'. The supe.r-saturation of the melt is reduced so that, while the melt is still super saturated with respect to plane surfaces and concave ¦.
suxfaces, i.t is unsaturated with respect to the concave surfaces 1-that occur at the si.des of the groove in layer 12. The result is that layer 13' is interrupted by two reyions 20 where no active I ' materlal is deposited. In between these two regions 20 there is a stripe o active material 21 encircled by the lower refract.ive index material of layers 12 and 14. The optical guiding provided by this stripe 21 is thus not that of a 'rib' structure, but instead that ~f a 'core surrounded by lower.refractive index claddingl structure.
In a particular exa~lple of this ~ype of structure the ,.
~...................................................................... i stripe 2~ was found to be approximately 17~m wide. The stripe '. ' Il . ~ I
Paul ~. Kirby - 2 ~Revision) was appr~:~in~ate:ly 0,28~m thiclc alony its cent:r~ lire ~rlc' amooth~y tapered to nothin~ at the sides. In the Elanking reylons 23 of layer 1~' o~tsicle the regions 20 the thickrless of tlle active material was found to increase again to a maximum of about 0.15~m.
In this st.ructure there will be substant:ially no current ~low across the pn junction in -the regions 20 because here the junction is bounc3ed on both sides by the higher band-gap materia]. of layers 12 and 14, whereas in ~the strlpe 21 it is bounded on at least one side by the lower band-gap act,:ive material.
A stripe contact top electrode is however still necessary in order to reduce the current flow across the pn junction in the regions 23 outside the strips 20.
In the str~lcture of E.igure 3 the modification of the figure 2 construction is taken a stage fur-ther with the melt ~~' -- 15 cond.itions used for growing the active material 13" arranged f so that the melt is unsaturated with respect to a plane, and f . supersaturated only with respect to the concave surface at the bottom of the groove in the surface of layer 12. As a result the growth of the active material is confined to the stripe 31.
In a particular example of this type of structure the stripe 31 was found to be about 9~m w.ide and about 0.15~m thi.ck along its centre line, the thickness smoothly tapering to nothing at the sides.
In this structure there is suhstant.ially no current flow across the pn junction outside the region of the stripe because outside this region the junction is bounded on both s.ides by the h,igher band-gap material of layers 12 and '14 whereas inside the region it is bounded on at least one side by the lower band-gap material 13". As a resu1t there is no need' to use a stripe electr.ical contact, and hence the steps of depositing the insulating layer, masking it, and etchin~ it~ may be omit~ed~
.~ : . . . . : - ,. ~
Paul K. Kir~ly ~ 2 (Revision) ~ 3~
It is to be ullclerstooc1 that the invention is not limitec1 to the construc1;on oE lasers ancl light an1F)Lifiers, bnt i~ appll~
cable also to ~he construction of inteqratecl circuit structures.
For example a directional coupler is Eormecl by ùsing the invention to form waveguiding on a substrate provided with two grooves, which, over a portion of their length, exltend side ~y side in close proxim:ity. If a pn junction is ~or1ned in the region of the waveguides the structure can be arranged to be an active device in which the coupling between the guides is capable of l~ bein-~ varied electrically. This is achievable by reverse biasing the junction to establish a depletion region in which the re- ~-fractive index is changed in part as a result of the extraction `- o~ free carriers and in part by the electro-optic light effect produ~ed by the field extending in the depletion region. More complex integrated optics structures may be produced by having i diferent profiles o groove so that liquid phase epitaxy can be used to deposite~ active material in one portion of the groove s-tructure but not another. This is then followed by an additional li~uid phase epitaxy preceding the deposition of the lower refractive index material. This additional expi~y is used to deposit passive material along the entire length o the groove structure. In this way there is produced a waveguide structure of passive material under which there are locali%ed regions of active material. The passive material has a larger band-gap than the active material and hence current across the pn junction ~s substantially conined to the active regions which thereby provi~e optical gain for the structure by skimulated emission.
It will be appreciated ~hat the control of the saturation o~ the melt from which the higher refractive index material is grown is a particularly critical matter when structures of the - type~ illustrated in figures 2 and 3 are being made. In _ 9 _ Paul ~. Kirby - 2 ~l~evis.ion) In particl1lar account has to be tak~n of the rapid in:itial growth -that is l:i.ablt? to occur when a melt first comes :into conl:act ' with the surface upon which ex~taxi~ growth is required. Good contIol oE this rap:icl initlal g.rowth phenor~e1lon is ach.ievable by use of an epitaxy furnace with a controllable vextical temper~
a-ture gradient. The appropri.ate vertical. temperature gradier1t for a par-ti.cular material and structu~e will depend upon cooli.ng rate.
In the laser structures of figure l and 2 t.he current flow across the pn junctior1 is substantially confined to the requireA
region by use of a stripe contac-t. Current flow across the junction outside -the required region is effectively a leakage ~1;
current. Such leakage can be reduced or eliminated by mesaing away the junctions in -the leakage regions or by converting lS these regions to semi-insulating material for instance by t proton bombardment. If either of these expedients are adopted it i.s not necessary Eor the insulating layer ~o be provided which defines the stripe contact.
It is to be understood that the foregoing description of speciic examples of this invention is made by way of example only and is not to be considered as a limitation on its scope. ' RA~:sq October 26, 1976 --- .
- , . ' , . . ::, ~. : , .
The only modification required to make the structure of ',~
f.i.gu~e 2 involves making a slight change to the melt conditions employed in the growth of the active material 13'. The supe.r-saturation of the melt is reduced so that, while the melt is still super saturated with respect to plane surfaces and concave ¦.
suxfaces, i.t is unsaturated with respect to the concave surfaces 1-that occur at the si.des of the groove in layer 12. The result is that layer 13' is interrupted by two reyions 20 where no active I ' materlal is deposited. In between these two regions 20 there is a stripe o active material 21 encircled by the lower refract.ive index material of layers 12 and 14. The optical guiding provided by this stripe 21 is thus not that of a 'rib' structure, but instead that ~f a 'core surrounded by lower.refractive index claddingl structure.
In a particular exa~lple of this ~ype of structure the ,.
~...................................................................... i stripe 2~ was found to be approximately 17~m wide. The stripe '. ' Il . ~ I
Paul ~. Kirby - 2 ~Revision) was appr~:~in~ate:ly 0,28~m thiclc alony its cent:r~ lire ~rlc' amooth~y tapered to nothin~ at the sides. In the Elanking reylons 23 of layer 1~' o~tsicle the regions 20 the thickrless of tlle active material was found to increase again to a maximum of about 0.15~m.
In this st.ructure there will be substant:ially no current ~low across the pn junction in -the regions 20 because here the junction is bounc3ed on both sides by the higher band-gap materia]. of layers 12 and 14, whereas in ~the strlpe 21 it is bounded on at least one side by the lower band-gap act,:ive material.
A stripe contact top electrode is however still necessary in order to reduce the current flow across the pn junction in the regions 23 outside the strips 20.
In the str~lcture of E.igure 3 the modification of the figure 2 construction is taken a stage fur-ther with the melt ~~' -- 15 cond.itions used for growing the active material 13" arranged f so that the melt is unsaturated with respect to a plane, and f . supersaturated only with respect to the concave surface at the bottom of the groove in the surface of layer 12. As a result the growth of the active material is confined to the stripe 31.
In a particular example of this type of structure the stripe 31 was found to be about 9~m w.ide and about 0.15~m thi.ck along its centre line, the thickness smoothly tapering to nothing at the sides.
In this structure there is suhstant.ially no current flow across the pn junction outside the region of the stripe because outside this region the junction is bounded on both s.ides by the h,igher band-gap material of layers 12 and '14 whereas inside the region it is bounded on at least one side by the lower band-gap material 13". As a resu1t there is no need' to use a stripe electr.ical contact, and hence the steps of depositing the insulating layer, masking it, and etchin~ it~ may be omit~ed~
.~ : . . . . : - ,. ~
Paul K. Kir~ly ~ 2 (Revision) ~ 3~
It is to be ullclerstooc1 that the invention is not limitec1 to the construc1;on oE lasers ancl light an1F)Lifiers, bnt i~ appll~
cable also to ~he construction of inteqratecl circuit structures.
For example a directional coupler is Eormecl by ùsing the invention to form waveguiding on a substrate provided with two grooves, which, over a portion of their length, exltend side ~y side in close proxim:ity. If a pn junction is ~or1ned in the region of the waveguides the structure can be arranged to be an active device in which the coupling between the guides is capable of l~ bein-~ varied electrically. This is achievable by reverse biasing the junction to establish a depletion region in which the re- ~-fractive index is changed in part as a result of the extraction `- o~ free carriers and in part by the electro-optic light effect produ~ed by the field extending in the depletion region. More complex integrated optics structures may be produced by having i diferent profiles o groove so that liquid phase epitaxy can be used to deposite~ active material in one portion of the groove s-tructure but not another. This is then followed by an additional li~uid phase epitaxy preceding the deposition of the lower refractive index material. This additional expi~y is used to deposit passive material along the entire length o the groove structure. In this way there is produced a waveguide structure of passive material under which there are locali%ed regions of active material. The passive material has a larger band-gap than the active material and hence current across the pn junction ~s substantially conined to the active regions which thereby provi~e optical gain for the structure by skimulated emission.
It will be appreciated ~hat the control of the saturation o~ the melt from which the higher refractive index material is grown is a particularly critical matter when structures of the - type~ illustrated in figures 2 and 3 are being made. In _ 9 _ Paul ~. Kirby - 2 ~l~evis.ion) In particl1lar account has to be tak~n of the rapid in:itial growth -that is l:i.ablt? to occur when a melt first comes :into conl:act ' with the surface upon which ex~taxi~ growth is required. Good contIol oE this rap:icl initlal g.rowth phenor~e1lon is ach.ievable by use of an epitaxy furnace with a controllable vextical temper~
a-ture gradient. The appropri.ate vertical. temperature gradier1t for a par-ti.cular material and structu~e will depend upon cooli.ng rate.
In the laser structures of figure l and 2 t.he current flow across the pn junctior1 is substantially confined to the requireA
region by use of a stripe contac-t. Current flow across the junction outside -the required region is effectively a leakage ~1;
current. Such leakage can be reduced or eliminated by mesaing away the junctions in -the leakage regions or by converting lS these regions to semi-insulating material for instance by t proton bombardment. If either of these expedients are adopted it i.s not necessary Eor the insulating layer ~o be provided which defines the stripe contact.
It is to be understood that the foregoing description of speciic examples of this invention is made by way of example only and is not to be considered as a limitation on its scope. ' RA~:sq October 26, 1976 --- .
- , . ' , . . ::, ~. : , .
Claims (15)
1. A method of heterostructure semi-conductor waveguide manufacture comprising:
growing a first continuous layer of semiconductive material by liquid phase epitaxy upon a substrate surface having at least one groove extending therein, the thickness of the layer and the conditions of growth being such that a corresponding groove is formed in the exposed surface of the first layer overlying the groove in the substrate;
growing semiconductive material of higher refractive index by liquid phase epitaxy in said corresponding groove in the exposed surface of the first layer;
and growing a further layer of semiconductive material of refractive index less than said higher refractive index material by liquid phase epitaxy on the epitaxially deposited higher index material.
growing a first continuous layer of semiconductive material by liquid phase epitaxy upon a substrate surface having at least one groove extending therein, the thickness of the layer and the conditions of growth being such that a corresponding groove is formed in the exposed surface of the first layer overlying the groove in the substrate;
growing semiconductive material of higher refractive index by liquid phase epitaxy in said corresponding groove in the exposed surface of the first layer;
and growing a further layer of semiconductive material of refractive index less than said higher refractive index material by liquid phase epitaxy on the epitaxially deposited higher index material.
2. The method of claim 1 wherein the substrate is GaAs and the epitaxially deposited material is GaxAll-xAs (x>o).
3. The method of claim 1 wherein the conditions of growth of said material of higher refractive index are such that each side of the corresponding groove in the surface of the first layer includes a convex surface upon at least a portion of which none of the higher refractive index material remains after said growth of said higher refractive index material.
4. The method of claim 1 wherein the conditions of growth of said material of higher refractive index are such that none of said higher refractive index material remains after said growth of said higher refractive index material except in the corres-ponding groove in the surface of the first layer.
5. The method of claim 1 wherein said first and further layers are grown of opposite conductivity type material.
6. The method of claim 1 wherein the first and further layers are grown of opposite conductivity type material, and wherein a portion of a pn junction on either side of the groove is removed by etching.
7. The method of claim 6 wherein a portion of a pn junction on either side of the groove is eliminated by the formation of a semi-insulating material.
8. The method of claim 4 wherein in the length of said groove in the substrate surface there are portions of different profiles such that the growth of said material of higher refractive index occurs in one portion of the corresponding groove in the surface of the first deposited layer but not in another of the groove in the surface of the first deposited layer, and wherein said growth of the further layer is preceded by the additional growth by liquid phase epitaxy of material having a higher refractive index than that of said further layer and said additional growth is arranged to occur over the entire length of the groove in the surface to which the additional growth is exposed.
9. A semiconductor light emitting device comprising:
a substrate having a surface with a first groove provided therein;
a first layer of low refractive index material of one conductivity type provided on the surface, said first layer having a surface with a second groove provided therein overlying the first groove;
an active layer of higher refractive index material provided in the second groove;
a second layer of low refractive index material of the other conductivity type provided over said active layer and said first layer; and an electrode layer provided over said second layer.
a substrate having a surface with a first groove provided therein;
a first layer of low refractive index material of one conductivity type provided on the surface, said first layer having a surface with a second groove provided therein overlying the first groove;
an active layer of higher refractive index material provided in the second groove;
a second layer of low refractive index material of the other conductivity type provided over said active layer and said first layer; and an electrode layer provided over said second layer.
10. The device of claim 9 wherein said active layer is further provided between said first and second layers in a region flanking both sides of the second groove.
11. The device of claim 10 wherein said first and second layers provide a pn junction in the region between the flanking region and the second groove such that said active layer within the second groove is surrounded by low refractive material.
12. The device of claim 9 further including an insulating layer between said electrode layer and said second layer, said insulating layer having a channel therethrough such that said electrode layer is in contact with said second layer in a region overlying said active layer in the second groove.
13. The device of claim 12 wherein said active layer is further provided over the entire surface of said first layer so as to separate said first and second layers.
14. The device of claim 9 wherein the substrate surface is tilted from 1/2° - 3° about a <100> direction from a {100}
plane.
plane.
15. The device of claim 9 wherein the first groove extends in a <110> direction along the substrate surface.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB5249075A GB1530323A (en) | 1975-12-22 | 1975-12-22 | Semiconductor waveguide structures |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1070029A true CA1070029A (en) | 1980-01-15 |
Family
ID=10464116
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA267,912A Expired CA1070029A (en) | 1975-12-22 | 1976-12-15 | Methods for forming semiconductor waveguide devices |
Country Status (6)
| Country | Link |
|---|---|
| AU (1) | AU500265B2 (en) |
| CA (1) | CA1070029A (en) |
| CH (1) | CH609488A5 (en) |
| DE (1) | DE2656532A1 (en) |
| FR (1) | FR2336797A1 (en) |
| GB (1) | GB1530323A (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4166253A (en) * | 1977-08-15 | 1979-08-28 | International Business Machines Corporation | Heterostructure diode injection laser having a constricted active region |
| CA1127282A (en) * | 1978-05-22 | 1982-07-06 | Takashi Sugino | Semiconductor laser and method of making the same |
| JPS5522807A (en) * | 1978-06-30 | 1980-02-18 | Hitachi Ltd | Semiconductor laser element and manufacturing of the same |
| GB2029083B (en) * | 1978-08-18 | 1982-08-11 | Standard Telephones Cables Ltd | Semiconductor waveguide devices |
| GB2046983B (en) * | 1979-01-18 | 1983-03-16 | Nippon Electric Co | Semiconductor lasers |
| GB2123604B (en) * | 1982-06-29 | 1985-12-18 | Standard Telephones Cables Ltd | Injection laser manufacture |
| FR2548220B1 (en) * | 1983-07-01 | 1987-07-31 | Labo Electronique Physique | LIGHT WAVEGUIDE ON SEMICONDUCTOR MATERIAL |
| WO1995005616A1 (en) * | 1993-08-13 | 1995-02-23 | Telstra Corporation Limited | A method of forming an optical waveguide device |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA1065460A (en) * | 1975-06-23 | 1979-10-30 | Robert D. Burnham | Buried-heterostructure diode injection laser |
-
1975
- 1975-12-22 GB GB5249075A patent/GB1530323A/en not_active Expired
-
1976
- 1976-12-07 AU AU20316/76A patent/AU500265B2/en not_active Expired
- 1976-12-14 DE DE19762656532 patent/DE2656532A1/en not_active Withdrawn
- 1976-12-15 CA CA267,912A patent/CA1070029A/en not_active Expired
- 1976-12-17 CH CH1589176A patent/CH609488A5/en not_active IP Right Cessation
- 1976-12-22 FR FR7638714A patent/FR2336797A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| DE2656532A1 (en) | 1977-07-07 |
| GB1530323A (en) | 1978-10-25 |
| FR2336797A1 (en) | 1977-07-22 |
| AU500265B2 (en) | 1979-05-17 |
| FR2336797B1 (en) | 1982-05-21 |
| CH609488A5 (en) | 1979-02-28 |
| AU2031676A (en) | 1978-06-15 |
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