CA1150388A - High power diode lasers - Google Patents
High power diode lasersInfo
- Publication number
- CA1150388A CA1150388A CA000401935A CA401935A CA1150388A CA 1150388 A CA1150388 A CA 1150388A CA 000401935 A CA000401935 A CA 000401935A CA 401935 A CA401935 A CA 401935A CA 1150388 A CA1150388 A CA 1150388A
- Authority
- CA
- Canada
- Prior art keywords
- laser
- substrate
- heterostructure
- channels
- active layer
- 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.)
- Expired
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Classifications
-
- 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
- H01S5/223—Buried stripe structure
- H01S5/2232—Buried stripe structure with inner confining structure between the active layer and the lower electrode
-
- 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
- H01S5/223—Buried stripe structure
- H01S5/2232—Buried stripe structure with inner confining structure between the active layer and the lower electrode
- H01S5/2234—Buried stripe structure with inner confining structure between the active layer and the lower electrode having a structured substrate 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
- H01S5/223—Buried stripe structure
- H01S5/2232—Buried stripe structure with inner confining structure between the active layer and the lower electrode
- H01S5/2234—Buried stripe structure with inner confining structure between the active layer and the lower electrode having a structured substrate surface
- H01S5/2235—Buried stripe structure with inner confining structure between the active layer and the lower electrode having a structured substrate surface with a protrusion
Landscapes
- Physics & Mathematics (AREA)
- Geometry (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Optics & Photonics (AREA)
- Semiconductor Lasers (AREA)
Abstract
HIGH POWER DIODE LASERS
Abstract of the Disclosure A high power diode laser has a double heterostructure epitaxially grown on a channeled substrate. The substrate has three channels, a central one being shallower than two flanking channels.
The heterostructure, in a region extending between the two outer channels is essentially planar except where a first confining layer of the heterostructure is locally thickened owing to the presence of the central channel. During laser operation, unwanted side bands in the far field light output which are apparent at low power are found to reduce, the laser output concentrating in the desired Gaussian profile at high power. The laser is superior in this respect to known single and double channeled double heterostructure lasers.
-i-
Abstract of the Disclosure A high power diode laser has a double heterostructure epitaxially grown on a channeled substrate. The substrate has three channels, a central one being shallower than two flanking channels.
The heterostructure, in a region extending between the two outer channels is essentially planar except where a first confining layer of the heterostructure is locally thickened owing to the presence of the central channel. During laser operation, unwanted side bands in the far field light output which are apparent at low power are found to reduce, the laser output concentrating in the desired Gaussian profile at high power. The laser is superior in this respect to known single and double channeled double heterostructure lasers.
-i-
Description
This invention relates to double heterostructure diode lasers suitable for high power applications. The invention is particularly concerned with laser devices in which a double hetero-structure is epitaxially grown on a IrI-V channeled substrate.
High power diode lasers, ha~ing outputs ideally limited to a single Gaussian mode are needed in applications such as optical recording.
Suitable semiconductor lasers deYeloped for these applications are con~entionally of the double heterostructure type.
Typifying such a structure is the GaAs/GaAlAs double heterostructure which has a planar n-type GaAs substrate on which is grown a first confining layer, an active layer, a second confining layer, and a capping layer. The confining layers are of higher bandgap material than the active layer, and one of the confining layers has a pn ~ heterojunction with the active layer. Carriers are injected into the - active layer at the pn junction via metal contacts on the crystal top and bottom surfaces. These injected carriers lose energy by means of photon emission which in turn stimulates further photon emission resulting in a propagating and amplified photon field. This field i`~ 20 is forced into a resonant condition by positi~e feedback provided by means of opposed mirror-flat facets extending perpendicularly to the i active layer.
Channeled substrate lasers are a development of planar heterostructure lasers. Single channel devices are disclosed by Scifres et al, U.S. Patent No. 4,280,I06 and Burnham et al, U.S. Patent No. 4,249,142. Double channel structures are described by Botez in articles entitled "Constricted Double Heterojunction AlGaAs Diode Lasers;
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Structures and Electro-optical Characteristics", IEEE Journal of Quantum Electronics, Volume QE-17, number 12, December 1981, and "High-Power Single-Mode Semiconductor Diode Lasers" in IEDM 81, page 447.
The presence of a channel in the substrate has a number of effects, most of them deriving from the nature of epitaxial growth over a channeled substrate. Growth occurs at a far greater rate into a concave surface formation then over a convex surface formation. In fact, at a sharp convex corner there may be initial melt-etch of the substrate before epitaxial growth begins.
Consequently the form of the heterostructure junctions generally follow the configuration of the substrate surface but have slope changes which are less severe. The structural and operational consequences of this are many and interactive.
Firstly, current confinement is not determined merely by the position of the top and bottom contacts. Since the substrate is more highly conducting than the heterojunction layers, current passage tends to localize along the least resistive route between the top contact and the substrate, this usually being guaranteed by making the lateral current spreading resistance in the capping and confining layers higher than the pn junction resistance when the device is biased in the carrier injection regime.
The second effect is to alter the effecti~e refracti~e index of the active layer at different positions along the layer.
The substrate, in comparison with the heterostructure layers, is a lower band gap material and tends to absorb light. If the substrate is very close to the active layer, then it lowers the effective
High power diode lasers, ha~ing outputs ideally limited to a single Gaussian mode are needed in applications such as optical recording.
Suitable semiconductor lasers deYeloped for these applications are con~entionally of the double heterostructure type.
Typifying such a structure is the GaAs/GaAlAs double heterostructure which has a planar n-type GaAs substrate on which is grown a first confining layer, an active layer, a second confining layer, and a capping layer. The confining layers are of higher bandgap material than the active layer, and one of the confining layers has a pn ~ heterojunction with the active layer. Carriers are injected into the - active layer at the pn junction via metal contacts on the crystal top and bottom surfaces. These injected carriers lose energy by means of photon emission which in turn stimulates further photon emission resulting in a propagating and amplified photon field. This field i`~ 20 is forced into a resonant condition by positi~e feedback provided by means of opposed mirror-flat facets extending perpendicularly to the i active layer.
Channeled substrate lasers are a development of planar heterostructure lasers. Single channel devices are disclosed by Scifres et al, U.S. Patent No. 4,280,I06 and Burnham et al, U.S. Patent No. 4,249,142. Double channel structures are described by Botez in articles entitled "Constricted Double Heterojunction AlGaAs Diode Lasers;
., ;
~:`
.," - 1 - *
, - .
. ` `
11~038~
Structures and Electro-optical Characteristics", IEEE Journal of Quantum Electronics, Volume QE-17, number 12, December 1981, and "High-Power Single-Mode Semiconductor Diode Lasers" in IEDM 81, page 447.
The presence of a channel in the substrate has a number of effects, most of them deriving from the nature of epitaxial growth over a channeled substrate. Growth occurs at a far greater rate into a concave surface formation then over a convex surface formation. In fact, at a sharp convex corner there may be initial melt-etch of the substrate before epitaxial growth begins.
Consequently the form of the heterostructure junctions generally follow the configuration of the substrate surface but have slope changes which are less severe. The structural and operational consequences of this are many and interactive.
Firstly, current confinement is not determined merely by the position of the top and bottom contacts. Since the substrate is more highly conducting than the heterojunction layers, current passage tends to localize along the least resistive route between the top contact and the substrate, this usually being guaranteed by making the lateral current spreading resistance in the capping and confining layers higher than the pn junction resistance when the device is biased in the carrier injection regime.
The second effect is to alter the effecti~e refracti~e index of the active layer at different positions along the layer.
The substrate, in comparison with the heterostructure layers, is a lower band gap material and tends to absorb light. If the substrate is very close to the active layer, then it lowers the effective
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. - 1-~5~3813 refractive index in the region of the actiYe layer so making it lossy. However, in the channel substrate lasers, the first confining layer of higher refractive index is made relatively thick both within a channel and, in the case of the double channel substrate, above the mesa extending between the two channels. Consequently? when lasing action occurs, there îs a tendency for the lasing light to localize due to index guiding in the region of the channel or the mesa centre depending on the device in question.
A further effect of the growth conditions of a channeled substrate laser is that the thickness of the active layer can vary from a minimum adjacent the channel shoulders. The constricted part of the active layer due to less perpendicular confinement, presents a lossy region discouraging lasing activity.
The structural and operational effects of channeled substrate lasers are optimized in a laser according to the present invention which comprises a double heterostructure epitaxially grown on a substrate, the substrate ha~ing three channels in a top surface thereof, a central channel being shallower than two flanking channels, and electrical contact means on top and bottom surfaces of the laser for directing current across a pn heterojunction within the hetero-; structure along a current path generally centered on the central channel.
The flanking channels are preferably 5~m in depth and the central channel is preferably about 2~m in depthl. The substrate can be a GaAs substrate having an epitaxially grown GaAs/GaAlAs heterostructure or alternatively an InP substrate having an epitaxially grown InP/InGaPAs heterostructure.
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. - 1-~5~3813 refractive index in the region of the actiYe layer so making it lossy. However, in the channel substrate lasers, the first confining layer of higher refractive index is made relatively thick both within a channel and, in the case of the double channel substrate, above the mesa extending between the two channels. Consequently? when lasing action occurs, there îs a tendency for the lasing light to localize due to index guiding in the region of the channel or the mesa centre depending on the device in question.
A further effect of the growth conditions of a channeled substrate laser is that the thickness of the active layer can vary from a minimum adjacent the channel shoulders. The constricted part of the active layer due to less perpendicular confinement, presents a lossy region discouraging lasing activity.
The structural and operational effects of channeled substrate lasers are optimized in a laser according to the present invention which comprises a double heterostructure epitaxially grown on a substrate, the substrate ha~ing three channels in a top surface thereof, a central channel being shallower than two flanking channels, and electrical contact means on top and bottom surfaces of the laser for directing current across a pn heterojunction within the hetero-; structure along a current path generally centered on the central channel.
The flanking channels are preferably 5~m in depth and the central channel is preferably about 2~m in depthl. The substrate can be a GaAs substrate having an epitaxially grown GaAs/GaAlAs heterostructure or alternatively an InP substrate having an epitaxially grown InP/InGaPAs heterostructure.
;,
- 3 -' ~15~38~3 An e~bodimen.t of the inven.tion. will noW be described by way of example with reference to the accompanying drawings in which:-Figure 1 marked PRIOR ART shows in. section a knownsingle channeled substrate double heterostructure la.ser;
Figure 2 marked PRIOR ART shows in section a known double channeled substrate double heterostructure laser,, Figure 3 shows in section a triple channeled substrate double heterostructure laser according to the in~entioni and Figure 4 is a graph comparing the far field light output of the Figure 3 laser at high and lo~ operating powers.
; Referring to Figures 1 and 2, these drawings show respectively single and double channeled substrate lasers which have been discussed in the introduction to this specification.
Referring in detail to Figure 3, there is shown a , double heterostructure laser having a substrate ~0, a, first confining layer 12, an active layer 14, a second confining layer 16, and a ', ca,pping layer 18. The compositions of these four layers are as follows:
, First confining l.ayer - tellurium doped n-type ., 20 GaO 63Alo ~7As i; Active layer . - germanium doped p-type GaO 95Alo o5As Second confining layer- germanium doped p-type GaO.63AlO.37As ,-' Capping layer - tellurium doped n-type ., - 4 -.
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133~38 The substrate has three channels 20? 22 and 24.
The central channel 24 is 2.5~m wide and 2~m deep. The flanking channels 22 and 24 are 5~m wide, 5~m deep and have a centre-to-centre separation of 36~m~ The channel form of the substrate 1`0 is followed in the overlaying layers 12, I4, 16 and 18 but the upper layers have slope changes which are less abrupt than those of the lower layers and of the substrate top surface. Also, the active laYer 14 is slightly reduced in thickness where it overlays the shoulder 26 of a central mesa 28. The active layer 14 has dips 30 corresponding to channels 20 and 22 but is essentially planar over the central channel 24, epitaxial growth being such that the influence here of the shallow ; central channel 24 is negligible. The crystal has top and bottom metal chromium - gold contacts 32 and 34 which are centrally aligned with the channel 24.
To fabricate the laser, starting with an n-type GaAs wafer, a series of the channels 24 are first etched into the substrate surface. Etching is performed using SiO2 window masks and an etchant solution consisting of H2S04, H202, and H20 in a volume ratio of 1:8:8 at 20C. The SiO2 film is subsequently removed with buffered HF at the intended sites of channels 20 and 22 throughout the wafer and a layer of SiO2 is deposited over the formed channels 24 to passivate their surfaces. Under similar conditions, channels 20 and 22 are then etched, the channels of each laser being on 36~m centers.
The two flanking channels 20, 22 are etched for twice as along as the central channel 24 to give a cross sectional area of approximately 5~m x 5~m. The remaining SiO2 film is then removed with buffered HF
and the whole surface is lightly etched with a NaOH:H202 aqueous solution.
.
~S~1388 The channeled substrate is then cleaned and loaded into a liquid phase epitaxy (LPE) boat. The boat (not shown) passes beneath successive reservoirs of various compositions with temperature conditions ensuring the progressive deposition of the layers 12, 14, 16 and 18. The LPE technique applied to the growth of heterostructure systems is well known in the semiconductor laser art.
During growth of the first confining layer 12, the shoulders 26 are partially melt-etched so distorting the initially dovetail section channels obtained during etching of the substrate.
` 10 To achieve the layer structure of Figure 3, the epitaxial growth conditions under which the successive layer are grown are those which, in a planar structure, would result in a first confining layer of 2 to 3ym, an active layer of about 0.1 to 0.2ym, a second confining layer of 2 to 3ym and a capping layer of about 0.5ym.
After growth of the four layer constricted double i~ heterostructure, a 5ym wide zinc diffused region 36 is introduced into the capping layer and standard oxide-stripe technology is used for depositing 20~m wide Cr:Pt:Au stripe contacts 32 and 34 in vertical alignment with the central channel 24.
As previously mentioned, the layers I2, 14, 16 and 18 follow the liquid phase epitaxial growth dependence on the surface curvature which produces enhanced growth in concaYe parts of the surface. However, the channel 24, unlike channels 20 and 22, is sufficiently small that there is negligible excursion from planarity of the active and first confining layer portions overlying the channel ,!, 24. The first confining layer 12 does, however, have a region of abruptly increasing thickness owing to its growth within the channel 24.
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The active layer 14 is relati~ely uniform in thickness but may be slightly reduced in thickness at locations 27 over the shoulders 26 of mesa 28.
In operation, an electrical current in the range 50 to 300 mA is directed between the two contacts across the pn junction formed within the heterostructure. As pre~iously indicated, there are a number of interactive effects.
Firstly, some lateral mode confinement is produced by the localized decrease in active layer thickness at the boundaries of the mesa 28. Also the effective refractive index of the active layer 14 tends to reduce the amount of light resonating in the active layer zones overlaying the mesa 28 except at the channel 24 where the substrate is separated from the active region by about 3~m.
The increased effective refractive index of the active layer at this zone has the effect, with a drive current greater than 100 mA, of reducing the higher order modes in the laser output.
Referring to Figure 4, there is shown the far field monitored light output of a three channel laser, the graph illustrating the output light intensity as a function of monitoring angle. It can be seen that using drive currents of 145 mA and 180 mA, there are a number of side bands which do not appear when the laser is operated at a higher current of 220 mA.
It ;s believed that as the current rises, the normal gain guiding effects of current passage through the device and the light limiting effects of the constricted active layer at the edge of the mesa 28 are increasingly influenced by the index guiding influence of the thickened first confining region within the channel 24.
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The operating advantage illustrated by the Figure 4 graph stems apparently from the creation of the sma11, abrupt, centrally located increase in thickness of the first confining layer 12. In the publications discussed in the introduction to this specification, Scifres et al, Burnham et al, and Botez all recognize the advantages of a centrally located increase in thickness of the first confining layer but in these disclosures the confining layer profile is believed not to be of optimal shape. In Burnham et al, it reduces in thickness towards the channel centre and in Botez it increases in thickness towards the ridge or mesa centre. In the present invention and, as shown in Scifres et al, the localized thicker region of the first confining layer is of substantially uniform thickness. However, the channel envisioned in Scifres is relatively large. Moreover, it appears to be practical1y impossib1e, using a substrate with only one channel instead of three, simultaneously to epitaxially grow an active layer which is essentially planar over a central channel, and which extends very close to the substrate outside the confines of the channel. These structural differences account for the fact that using the three channel structure, the far field profile tends to become cleaner at higher power whereas with the other channeled structures, the reverse seems to be the case.
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Figure 2 marked PRIOR ART shows in section a known double channeled substrate double heterostructure laser,, Figure 3 shows in section a triple channeled substrate double heterostructure laser according to the in~entioni and Figure 4 is a graph comparing the far field light output of the Figure 3 laser at high and lo~ operating powers.
; Referring to Figures 1 and 2, these drawings show respectively single and double channeled substrate lasers which have been discussed in the introduction to this specification.
Referring in detail to Figure 3, there is shown a , double heterostructure laser having a substrate ~0, a, first confining layer 12, an active layer 14, a second confining layer 16, and a ', ca,pping layer 18. The compositions of these four layers are as follows:
, First confining l.ayer - tellurium doped n-type ., 20 GaO 63Alo ~7As i; Active layer . - germanium doped p-type GaO 95Alo o5As Second confining layer- germanium doped p-type GaO.63AlO.37As ,-' Capping layer - tellurium doped n-type ., - 4 -.
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133~38 The substrate has three channels 20? 22 and 24.
The central channel 24 is 2.5~m wide and 2~m deep. The flanking channels 22 and 24 are 5~m wide, 5~m deep and have a centre-to-centre separation of 36~m~ The channel form of the substrate 1`0 is followed in the overlaying layers 12, I4, 16 and 18 but the upper layers have slope changes which are less abrupt than those of the lower layers and of the substrate top surface. Also, the active laYer 14 is slightly reduced in thickness where it overlays the shoulder 26 of a central mesa 28. The active layer 14 has dips 30 corresponding to channels 20 and 22 but is essentially planar over the central channel 24, epitaxial growth being such that the influence here of the shallow ; central channel 24 is negligible. The crystal has top and bottom metal chromium - gold contacts 32 and 34 which are centrally aligned with the channel 24.
To fabricate the laser, starting with an n-type GaAs wafer, a series of the channels 24 are first etched into the substrate surface. Etching is performed using SiO2 window masks and an etchant solution consisting of H2S04, H202, and H20 in a volume ratio of 1:8:8 at 20C. The SiO2 film is subsequently removed with buffered HF at the intended sites of channels 20 and 22 throughout the wafer and a layer of SiO2 is deposited over the formed channels 24 to passivate their surfaces. Under similar conditions, channels 20 and 22 are then etched, the channels of each laser being on 36~m centers.
The two flanking channels 20, 22 are etched for twice as along as the central channel 24 to give a cross sectional area of approximately 5~m x 5~m. The remaining SiO2 film is then removed with buffered HF
and the whole surface is lightly etched with a NaOH:H202 aqueous solution.
.
~S~1388 The channeled substrate is then cleaned and loaded into a liquid phase epitaxy (LPE) boat. The boat (not shown) passes beneath successive reservoirs of various compositions with temperature conditions ensuring the progressive deposition of the layers 12, 14, 16 and 18. The LPE technique applied to the growth of heterostructure systems is well known in the semiconductor laser art.
During growth of the first confining layer 12, the shoulders 26 are partially melt-etched so distorting the initially dovetail section channels obtained during etching of the substrate.
` 10 To achieve the layer structure of Figure 3, the epitaxial growth conditions under which the successive layer are grown are those which, in a planar structure, would result in a first confining layer of 2 to 3ym, an active layer of about 0.1 to 0.2ym, a second confining layer of 2 to 3ym and a capping layer of about 0.5ym.
After growth of the four layer constricted double i~ heterostructure, a 5ym wide zinc diffused region 36 is introduced into the capping layer and standard oxide-stripe technology is used for depositing 20~m wide Cr:Pt:Au stripe contacts 32 and 34 in vertical alignment with the central channel 24.
As previously mentioned, the layers I2, 14, 16 and 18 follow the liquid phase epitaxial growth dependence on the surface curvature which produces enhanced growth in concaYe parts of the surface. However, the channel 24, unlike channels 20 and 22, is sufficiently small that there is negligible excursion from planarity of the active and first confining layer portions overlying the channel ,!, 24. The first confining layer 12 does, however, have a region of abruptly increasing thickness owing to its growth within the channel 24.
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The active layer 14 is relati~ely uniform in thickness but may be slightly reduced in thickness at locations 27 over the shoulders 26 of mesa 28.
In operation, an electrical current in the range 50 to 300 mA is directed between the two contacts across the pn junction formed within the heterostructure. As pre~iously indicated, there are a number of interactive effects.
Firstly, some lateral mode confinement is produced by the localized decrease in active layer thickness at the boundaries of the mesa 28. Also the effective refractive index of the active layer 14 tends to reduce the amount of light resonating in the active layer zones overlaying the mesa 28 except at the channel 24 where the substrate is separated from the active region by about 3~m.
The increased effective refractive index of the active layer at this zone has the effect, with a drive current greater than 100 mA, of reducing the higher order modes in the laser output.
Referring to Figure 4, there is shown the far field monitored light output of a three channel laser, the graph illustrating the output light intensity as a function of monitoring angle. It can be seen that using drive currents of 145 mA and 180 mA, there are a number of side bands which do not appear when the laser is operated at a higher current of 220 mA.
It ;s believed that as the current rises, the normal gain guiding effects of current passage through the device and the light limiting effects of the constricted active layer at the edge of the mesa 28 are increasingly influenced by the index guiding influence of the thickened first confining region within the channel 24.
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The operating advantage illustrated by the Figure 4 graph stems apparently from the creation of the sma11, abrupt, centrally located increase in thickness of the first confining layer 12. In the publications discussed in the introduction to this specification, Scifres et al, Burnham et al, and Botez all recognize the advantages of a centrally located increase in thickness of the first confining layer but in these disclosures the confining layer profile is believed not to be of optimal shape. In Burnham et al, it reduces in thickness towards the channel centre and in Botez it increases in thickness towards the ridge or mesa centre. In the present invention and, as shown in Scifres et al, the localized thicker region of the first confining layer is of substantially uniform thickness. However, the channel envisioned in Scifres is relatively large. Moreover, it appears to be practical1y impossib1e, using a substrate with only one channel instead of three, simultaneously to epitaxially grow an active layer which is essentially planar over a central channel, and which extends very close to the substrate outside the confines of the channel. These structural differences account for the fact that using the three channel structure, the far field profile tends to become cleaner at higher power whereas with the other channeled structures, the reverse seems to be the case.
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Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A double heterostructure semiconductor laser comprising a semiconductor substrate having three parallel channels formed in a top surface thereof, a central channel being shallower than two flanking channels, a double heterostructure grown on the substrate, electrical contact means on top and bottom surfaces of the laser for directing current across a heterojunction within the heterostructure along a path generally centered on the central channel, the laser having opposed mirror facets defining ends of a resonant cavity.
2. A laser as claimed in claim 1, in which the depth of the central channel is approximately half the depth of the flanking channels.
3. A laser as claimed in claim 1, in which the heterostructure comprises a first confining layer adjacent the substrate, an active layer, and a second confining layer, the active layer and the second confining layer over the central channel being essentially planar.
4. A laser as claimed in claim 3, in which the substrate is n-type GaAs, the first confining layer is n-type GaAlAs, the active layer is lightly doped p-type GaAlAs and the second confining layer is p-type GaAlAs.
5. A laser as claimed in claim 3, in which a means of the substrate material exists between the flanking channels, and the active layer at positions overlying respective boundaries of the mesa is locally reduced in thickness.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000401935A CA1150388A (en) | 1982-04-29 | 1982-04-29 | High power diode lasers |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000401935A CA1150388A (en) | 1982-04-29 | 1982-04-29 | High power diode lasers |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1150388A true CA1150388A (en) | 1983-07-19 |
Family
ID=4122681
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000401935A Expired CA1150388A (en) | 1982-04-29 | 1982-04-29 | High power diode lasers |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1150388A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0199588A2 (en) * | 1985-04-23 | 1986-10-29 | Sharp Kabushiki Kaisha | A semiconductor laser device |
| DE3626701A1 (en) * | 1985-08-09 | 1987-02-19 | Sharp Kk | SEMICONDUCTOR LASER ARRANGEMENT |
-
1982
- 1982-04-29 CA CA000401935A patent/CA1150388A/en not_active Expired
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0199588A2 (en) * | 1985-04-23 | 1986-10-29 | Sharp Kabushiki Kaisha | A semiconductor laser device |
| EP0199588A3 (en) * | 1985-04-23 | 1988-01-13 | Sharp Kabushiki Kaisha | A semiconductor laser device |
| US4819245A (en) * | 1985-04-23 | 1989-04-04 | Sharp Kabushiki Kaisha | Semiconductor laser device having substriped channels for forming an active layer which is thin in an inside portion |
| DE3626701A1 (en) * | 1985-08-09 | 1987-02-19 | Sharp Kk | SEMICONDUCTOR LASER ARRANGEMENT |
| US4751709A (en) * | 1985-08-09 | 1988-06-14 | Sharp Kabushiki Kaisha | Semiconductor laser array device |
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