CA1189177A - Planar narrow-stripe laser with improved contact resistance - Google Patents
Planar narrow-stripe laser with improved contact resistanceInfo
- Publication number
- CA1189177A CA1189177A CA000417600A CA417600A CA1189177A CA 1189177 A CA1189177 A CA 1189177A CA 000417600 A CA000417600 A CA 000417600A CA 417600 A CA417600 A CA 417600A CA 1189177 A CA1189177 A CA 1189177A
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- Canada
- Prior art keywords
- layer
- laser
- diffusion
- window
- double heterostructure
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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
- H01S5/20—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
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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
- H01S5/20—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
- H01S5/2054—Methods of obtaining the confinement
- H01S5/2059—Methods of obtaining the confinement by means of particular conductivity zones, e.g. obtained by particle bombardment or diffusion
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- Physics & Mathematics (AREA)
- Geometry (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Optics & Photonics (AREA)
- Semiconductor Lasers (AREA)
Abstract
A PLANAR NARROW-STRIPE LASER WITH IMPROVED CONTACT RESISTANCE
Abstract of the Disclosure Double heterostructure lasers which use a narrow stripe contact exhibit linear characteristics with a low lasing threshold current making them suitable for fiber optic communication systems. Unfortunately as the stripe is reduced in width, the contact resistance increases thereby affecting the frequency response of the device and increasing its operating temperature. To overcome these problems while retaining high linearity and low threshold current, a two part diffusion is proposed, one shallow large area diffusion to reduce contact resistance, and a deep narrow diffusion extending close to the active layer to confine the lasing region.
-i-
Abstract of the Disclosure Double heterostructure lasers which use a narrow stripe contact exhibit linear characteristics with a low lasing threshold current making them suitable for fiber optic communication systems. Unfortunately as the stripe is reduced in width, the contact resistance increases thereby affecting the frequency response of the device and increasing its operating temperature. To overcome these problems while retaining high linearity and low threshold current, a two part diffusion is proposed, one shallow large area diffusion to reduce contact resistance, and a deep narrow diffusion extending close to the active layer to confine the lasing region.
-i-
Description
This inven-tion relates to semiconductor lasers of the double heterostructure type~
Typically double heterostructure lasers are made from III-\/
type materials. Examples of such materials are the ternary GaAlAs/GaAs and the quaternary GaInAsP/InP systems. ~y appropriately tailoring the III-V material composition, desired band gap differences between adjacent layers of the double heterostructure can be obtained and crystalline integrity oF -the device is secured.
Typically a double he-terostructure laser has a substrate3 a first confining layer epi-taxially grown on the substrate, an active layer epitaxially grown on the first conFining layer, a second confining layer epitaxially grown on the active layer and a capping layer epitaxially grown on the second confining layer. Opposed facets of the device are rendered very smooth by cleaving in order to deFine the ends of a resonant cavity within the active layer. The lateral limits of the resonant cavity can be defined by a number of techniques but one of the most popular is the provision of a narrow stripe contact on the -top surface of the laser~
A broad area contact is deposited on the bottom, substrate side of the device.
Typically the substrate and first confining layer are n-type materials and the second confining and capping layers are p-type materials. The active layer can be n~ or p-type but is of lower band gap and higher refractive index than the confining layers. In operation, current flows through the double heterostructure from the top stripe contact to the bottom contact~ Carriers are injected into the active layer at the forward biased pn Junction within the double heterostructure and end up in an excited energy state. A recombination process occurs during which pho-tons are emitted within an act-ive region determined by the diffusion length oF the injected carriersD Within the resonant cavity between the two mirror facets stirnulated emission occurs; in other words, the device lases. By appropriately confining current and gain within the laser, it can be made to emit very intense light f`rom a very narrow reyion in the active layer khe light ideally being o~ low order mode since this has advantages in reducing Fiber optic transmission losses.
In addition to the stripe contact it is known to introduce a highly conducting region into the heterostruc-ture by providing a narrow p-type diffusion from the top surface of the device -to a point ~just short oF the active layer~
One of the problems with having a narrow contact stripe and a p-type diffusion underneath it is that contact resistance at the metal-semiconductor interface is high. This is especially so when very narrow stripe of the order of 2-3 ~m s contemplated. The high contact resistance has two disadvantages. Firstly the frequency response of the laser is poor~ and secondly the d@vice operates at higher temperature, In order to overcome these two disadvantages there is proposed according to the present invention a semiconductor laser comprising an n-type substrate, a double heterostructure epitaxially grown on the substrate, the heterostructure having an n-type first confining layer, an active layer, and a p-type second confining layer, the laser further having an n-type blocking layer and a capping layer epitaxially groiln thereon, a top metal contact layer contacting the capping layer, and a bottom metal contact layer contacting the substrate, a first narrow p-type diffusion extending through the capping layer and the blocking layer, the narrow diFfusion having a diffusion front within the second confining layer and a second relatively wide dif-fusion extending throug~
the capping layer, the wide diffusion having a diFfusion front within the blocking layer.
The relatively wide diffusion results in a low resistance con-tact with the top metal contact layer~ The narrow diffusion serves to funnel current into a narrow stripe region, this being required for efFective low order emission of the laser. The junction between -the second confining layer and the blocking layer laterally outside the stripe is reverse biased in operation and so tends to block current spread away from the stripe region.
The laser can be fabricated using any suitable III-V system, for example, the GaAlAs or the GaInAsP systems.
According to another aspect of the invention there is provided a method for fabricating a laser comprising epitaxially growing on a III~V substrate a first confining layer, an active layer9 a second con~ining layer, a blocking layer and a capping layer, depositing a masking layer over the top surface of the wafer, opening a narrow stripe window in the masking layer, performing a diffusion through the window to provide a diffuse region extending from the surface of the capping area into the second confining area, removing part of the mask to expose a relatively large surface part of the capping layer, and perForming a second diffusion to provide a diffuse region extending through the capping layer into the blocking layer, the area of the narrow diffusion being substantially within the area of the wide diffusiorl.
Although not providing such an optimal combination oF narrow resonant cavity and low contact resistance, some improvement over known devices can be 3chieved using a single difFusion~ When diffusing through ~ ~3~
a narrow stripe window there will be some penetration by the diffusing species la-terally under the mask. According to another aspect of the invention, there is proposed d method o-f fabrica-ting a laser by epi-taxially growing a wafer as hereinbefore defined~ depositing a mask on an exposed surface of the wafer, opening a narrow stripe window in the mask, diffusing material through the window so that the cliFfusion front extends to within 0.5 ~m of the active layer and also extends laterally under edges of the mask defining the narrow stripe window, removing the mask so as to expose the lateral extensions of the diffusion, depositing a top metal contact layer over the remaining mask and exposed diffuse region, and depositing a bottom metal contact layer on the substrate.
Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:-Figure 1 is a sectional view of one form of laser according to the invention; and Figure 2 is a sectional view of another form of laser according to the inventionO
The laser illustrated in Figure 1 has in vertically ascending order the following layers:
an n-type InP substrate 10 about 75 microns thick;
an n-type InP tin doped first confining layer 12 of a thickness of 3 to 5 microns;
an n- or p-type Ga1_xInxAsl~yPy tin or zinc doped active layer 14 of a thickness 0.1 to 0~3 rnicrons;
a p-type InP zinc doped second confining layer 16 of thickness 0.2 to 0.5 microns;
7~
an n-type InP tin doped blocking layer 18 of a thickness 1 to 1.3 microns; and an n-type GaO 47InO 53As capping layer 20 of a thickness 0.5 microns.
Extending into the top of the chip is a narrow p-type zinc diffusion 22 which extends from the top surface into the p-type second confining layer with a diffusion Front 24 separated From the active layer 14 by less than 0.5 microns. The width of the diffusion window W1, is typically 2 to 3~m. Also extending from the top surfacé is a second p-type zinc diffusion 26 which has a diffusion window width W2, typically in the range ~ to 10~m. lhis diffusion extends through the capping layer 20 and has a diffusion front 28 within the blocking layer. A bottom metal contact layer 30 extends over the lower surface of the entire substrate and a top metal contact layer 32 extends substantially over the whole of the diffuse region of the capping layer 20, the top metal contact layer 32 being separated from the capping layer 20 outside the diffuse region by an SiO2 layer 34.
In operation a voltaye of about 1.4 volts is applied across the device with a p~larity so as to reverse bias the pn junction between the second confining layer 16 and the blocking layer 18~
As previously indicated, at the active layer 14, electrons are injected from the n-side to the p-side at one of the active layer junctions with the confining layers and these electrons end up in excited energy states in the conduction band. A recombination process occurs on the p-side within an active region width determined by the diffusion length of the injected carriers. When the device is pumped by current directed across the active layer 14, electrons are excited to a higher 7~
energy level ~o achieve population inversion and so emit photons oF the same wavelength, direction and phase as the stirnulating photons. The stimulated emission process occurs very quickly. Although not shown in the Figures, mirrors are needed to define the lasing region or resonant cavity to obtain the stirnulated emission characteristic of laser behaviour. Such mirrors are produced by natural cleavage of the wa-fer.
The function of the narrow diffuse region 22 is -to funnel current through d narrow region of the active layer 14 in order to obtain intense, localized laser output. By maintaining the diffusion front 24 within 0~5 microns of the active layer 14, the laser output can be limited to low order modes~
The wide diffusion 26 has a low contact resistance with the top metal contact 32, the low contact resistance having the advantages of a high frequency response and lower operating temperature.
The use of a wide diffuse region 26 means that current carriers are distributed throughout a relatively wide area when they enter the chip. The relatively deep diffusion 22 funnels some oF the current carriers towards the laser resonant cavity, but that is not sufficient of itself. In order to achieve rigid funnelling of current carriers and so prevent lasing at other parts of the active layer 14 which would generate higher order modes, the n-type blocking layer 18 forms with the p-type second confining layer 16 a reverse biased pn junction~ so preventing current carriers from passing down to the active layer except at the central region defined by the narrow diffusion 22.
The device shown in Figure 1 is fabricated as follows.
Firstly the double heterostructure 12, 1~, 16, the blocking layer 18 and the capping layer 20 are epitaxially grown on an InP substrate 10 using, for example1 the liquid phase epitaxy or -the organo me-tallic pyrolysis techniques which are well known in the art. A 1000-1500 A -thick layer 34 of SiO2 is then chemically vapour deposite(l onto -the top surface of the wafer and is photodefin~d and etchecl to provide a stripe window ~0 of width ~1 2 to 3~mD A first diffusion oF zinc is performed through the window to produce the narrow p-type diffusion 22 extending into the second confining layer 16. The diffusion time depends on the thickness of layers 16, 18 and 20 but is typically in the range of 10 to 35 minutes depending on the diffusion conditions~ The doping level obtained at the surface is typically about 4 x 1018cm 3, The remaining part of the SiO2 layer 34 i~ further deFined and etched with buffered hydrofluoric acid to produce a relatively wide window 42 of width 7 to 10 ~m centered substantially on the original narrow window 40~ A second zinc diffusion is then perFormed for an interval of about 10 minutes depending on the capping layer thickness in order to achieve a diffused region 26 extending through the capping layer 20 into the blocking layer 18. The sectional views of Figures 1 and 2 are not to scale~ In fact in practice, the side diffusion s is approximately equal to the diffusion dep-th d.
Finally top and bottom metal contacts 32, 30 are vapour deposited onto the top and bottom surfaces of the wafer and it is then cleaved into individual devices. The top contact is a Cr/Au layer but could be of alternative composit-ion, For example, Ti/Pt/Au. The bot-tom contact is an Au/~e layer but could be oF~ for example Au/Ge/Ni. The cleaving process leaves facets which are planar, mirror smooth and parallel to one another in order to define opposed surfaces oF the laser resonant cavities.
Although not providing such an optimal combination of narrow resonant cavity and low contact resistance, some improvement over known devices can be achieved using a single diffusion. As shown in Figure 2 3~
when diffusing -through a narrow stripe winclow 40 there will be some penetra-tion 44 by the diFfusing species laterally under the mask 34.
In another aspect of the invention, a wafer is epitaxially grown as previously described. The mask 34 is then deposited on -the exposed surface of the wafer and a narrow s-tripe window 40 is etched in the rnask.
P-type dopant is then diFfused through the window so that the difFusion front 24 extends to within 0.5~rn of the active layer 14 and also as shown at 44 extends laterally under edges oF the mask 34 defining the narrow stripe window 40, Part of the mask is then etched away to expose the lateral extensions 44 of the diffusion 22 and a top metal contact layer 32 is vapour deposited over the remaining par-t of mask 34 and over the exposed diffuse region 22. A bottom metal contact layer 30 is then deposited on the substrate 12 and the wafer is cleaved into individual chipsl at the same time producing mirror facets for the laser resonant cavities.
Typically double heterostructure lasers are made from III-\/
type materials. Examples of such materials are the ternary GaAlAs/GaAs and the quaternary GaInAsP/InP systems. ~y appropriately tailoring the III-V material composition, desired band gap differences between adjacent layers of the double heterostructure can be obtained and crystalline integrity oF -the device is secured.
Typically a double he-terostructure laser has a substrate3 a first confining layer epi-taxially grown on the substrate, an active layer epitaxially grown on the first conFining layer, a second confining layer epitaxially grown on the active layer and a capping layer epitaxially grown on the second confining layer. Opposed facets of the device are rendered very smooth by cleaving in order to deFine the ends of a resonant cavity within the active layer. The lateral limits of the resonant cavity can be defined by a number of techniques but one of the most popular is the provision of a narrow stripe contact on the -top surface of the laser~
A broad area contact is deposited on the bottom, substrate side of the device.
Typically the substrate and first confining layer are n-type materials and the second confining and capping layers are p-type materials. The active layer can be n~ or p-type but is of lower band gap and higher refractive index than the confining layers. In operation, current flows through the double heterostructure from the top stripe contact to the bottom contact~ Carriers are injected into the active layer at the forward biased pn Junction within the double heterostructure and end up in an excited energy state. A recombination process occurs during which pho-tons are emitted within an act-ive region determined by the diffusion length oF the injected carriersD Within the resonant cavity between the two mirror facets stirnulated emission occurs; in other words, the device lases. By appropriately confining current and gain within the laser, it can be made to emit very intense light f`rom a very narrow reyion in the active layer khe light ideally being o~ low order mode since this has advantages in reducing Fiber optic transmission losses.
In addition to the stripe contact it is known to introduce a highly conducting region into the heterostruc-ture by providing a narrow p-type diffusion from the top surface of the device -to a point ~just short oF the active layer~
One of the problems with having a narrow contact stripe and a p-type diffusion underneath it is that contact resistance at the metal-semiconductor interface is high. This is especially so when very narrow stripe of the order of 2-3 ~m s contemplated. The high contact resistance has two disadvantages. Firstly the frequency response of the laser is poor~ and secondly the d@vice operates at higher temperature, In order to overcome these two disadvantages there is proposed according to the present invention a semiconductor laser comprising an n-type substrate, a double heterostructure epitaxially grown on the substrate, the heterostructure having an n-type first confining layer, an active layer, and a p-type second confining layer, the laser further having an n-type blocking layer and a capping layer epitaxially groiln thereon, a top metal contact layer contacting the capping layer, and a bottom metal contact layer contacting the substrate, a first narrow p-type diffusion extending through the capping layer and the blocking layer, the narrow diFfusion having a diffusion front within the second confining layer and a second relatively wide dif-fusion extending throug~
the capping layer, the wide diffusion having a diFfusion front within the blocking layer.
The relatively wide diffusion results in a low resistance con-tact with the top metal contact layer~ The narrow diffusion serves to funnel current into a narrow stripe region, this being required for efFective low order emission of the laser. The junction between -the second confining layer and the blocking layer laterally outside the stripe is reverse biased in operation and so tends to block current spread away from the stripe region.
The laser can be fabricated using any suitable III-V system, for example, the GaAlAs or the GaInAsP systems.
According to another aspect of the invention there is provided a method for fabricating a laser comprising epitaxially growing on a III~V substrate a first confining layer, an active layer9 a second con~ining layer, a blocking layer and a capping layer, depositing a masking layer over the top surface of the wafer, opening a narrow stripe window in the masking layer, performing a diffusion through the window to provide a diffuse region extending from the surface of the capping area into the second confining area, removing part of the mask to expose a relatively large surface part of the capping layer, and perForming a second diffusion to provide a diffuse region extending through the capping layer into the blocking layer, the area of the narrow diffusion being substantially within the area of the wide diffusiorl.
Although not providing such an optimal combination oF narrow resonant cavity and low contact resistance, some improvement over known devices can be 3chieved using a single difFusion~ When diffusing through ~ ~3~
a narrow stripe window there will be some penetration by the diffusing species la-terally under the mask. According to another aspect of the invention, there is proposed d method o-f fabrica-ting a laser by epi-taxially growing a wafer as hereinbefore defined~ depositing a mask on an exposed surface of the wafer, opening a narrow stripe window in the mask, diffusing material through the window so that the cliFfusion front extends to within 0.5 ~m of the active layer and also extends laterally under edges of the mask defining the narrow stripe window, removing the mask so as to expose the lateral extensions of the diffusion, depositing a top metal contact layer over the remaining mask and exposed diffuse region, and depositing a bottom metal contact layer on the substrate.
Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:-Figure 1 is a sectional view of one form of laser according to the invention; and Figure 2 is a sectional view of another form of laser according to the inventionO
The laser illustrated in Figure 1 has in vertically ascending order the following layers:
an n-type InP substrate 10 about 75 microns thick;
an n-type InP tin doped first confining layer 12 of a thickness of 3 to 5 microns;
an n- or p-type Ga1_xInxAsl~yPy tin or zinc doped active layer 14 of a thickness 0.1 to 0~3 rnicrons;
a p-type InP zinc doped second confining layer 16 of thickness 0.2 to 0.5 microns;
7~
an n-type InP tin doped blocking layer 18 of a thickness 1 to 1.3 microns; and an n-type GaO 47InO 53As capping layer 20 of a thickness 0.5 microns.
Extending into the top of the chip is a narrow p-type zinc diffusion 22 which extends from the top surface into the p-type second confining layer with a diffusion Front 24 separated From the active layer 14 by less than 0.5 microns. The width of the diffusion window W1, is typically 2 to 3~m. Also extending from the top surfacé is a second p-type zinc diffusion 26 which has a diffusion window width W2, typically in the range ~ to 10~m. lhis diffusion extends through the capping layer 20 and has a diffusion front 28 within the blocking layer. A bottom metal contact layer 30 extends over the lower surface of the entire substrate and a top metal contact layer 32 extends substantially over the whole of the diffuse region of the capping layer 20, the top metal contact layer 32 being separated from the capping layer 20 outside the diffuse region by an SiO2 layer 34.
In operation a voltaye of about 1.4 volts is applied across the device with a p~larity so as to reverse bias the pn junction between the second confining layer 16 and the blocking layer 18~
As previously indicated, at the active layer 14, electrons are injected from the n-side to the p-side at one of the active layer junctions with the confining layers and these electrons end up in excited energy states in the conduction band. A recombination process occurs on the p-side within an active region width determined by the diffusion length of the injected carriers. When the device is pumped by current directed across the active layer 14, electrons are excited to a higher 7~
energy level ~o achieve population inversion and so emit photons oF the same wavelength, direction and phase as the stirnulating photons. The stimulated emission process occurs very quickly. Although not shown in the Figures, mirrors are needed to define the lasing region or resonant cavity to obtain the stirnulated emission characteristic of laser behaviour. Such mirrors are produced by natural cleavage of the wa-fer.
The function of the narrow diffuse region 22 is -to funnel current through d narrow region of the active layer 14 in order to obtain intense, localized laser output. By maintaining the diffusion front 24 within 0~5 microns of the active layer 14, the laser output can be limited to low order modes~
The wide diffusion 26 has a low contact resistance with the top metal contact 32, the low contact resistance having the advantages of a high frequency response and lower operating temperature.
The use of a wide diffuse region 26 means that current carriers are distributed throughout a relatively wide area when they enter the chip. The relatively deep diffusion 22 funnels some oF the current carriers towards the laser resonant cavity, but that is not sufficient of itself. In order to achieve rigid funnelling of current carriers and so prevent lasing at other parts of the active layer 14 which would generate higher order modes, the n-type blocking layer 18 forms with the p-type second confining layer 16 a reverse biased pn junction~ so preventing current carriers from passing down to the active layer except at the central region defined by the narrow diffusion 22.
The device shown in Figure 1 is fabricated as follows.
Firstly the double heterostructure 12, 1~, 16, the blocking layer 18 and the capping layer 20 are epitaxially grown on an InP substrate 10 using, for example1 the liquid phase epitaxy or -the organo me-tallic pyrolysis techniques which are well known in the art. A 1000-1500 A -thick layer 34 of SiO2 is then chemically vapour deposite(l onto -the top surface of the wafer and is photodefin~d and etchecl to provide a stripe window ~0 of width ~1 2 to 3~mD A first diffusion oF zinc is performed through the window to produce the narrow p-type diffusion 22 extending into the second confining layer 16. The diffusion time depends on the thickness of layers 16, 18 and 20 but is typically in the range of 10 to 35 minutes depending on the diffusion conditions~ The doping level obtained at the surface is typically about 4 x 1018cm 3, The remaining part of the SiO2 layer 34 i~ further deFined and etched with buffered hydrofluoric acid to produce a relatively wide window 42 of width 7 to 10 ~m centered substantially on the original narrow window 40~ A second zinc diffusion is then perFormed for an interval of about 10 minutes depending on the capping layer thickness in order to achieve a diffused region 26 extending through the capping layer 20 into the blocking layer 18. The sectional views of Figures 1 and 2 are not to scale~ In fact in practice, the side diffusion s is approximately equal to the diffusion dep-th d.
Finally top and bottom metal contacts 32, 30 are vapour deposited onto the top and bottom surfaces of the wafer and it is then cleaved into individual devices. The top contact is a Cr/Au layer but could be of alternative composit-ion, For example, Ti/Pt/Au. The bot-tom contact is an Au/~e layer but could be oF~ for example Au/Ge/Ni. The cleaving process leaves facets which are planar, mirror smooth and parallel to one another in order to define opposed surfaces oF the laser resonant cavities.
Although not providing such an optimal combination of narrow resonant cavity and low contact resistance, some improvement over known devices can be achieved using a single diffusion. As shown in Figure 2 3~
when diffusing -through a narrow stripe winclow 40 there will be some penetra-tion 44 by the diFfusing species laterally under the mask 34.
In another aspect of the invention, a wafer is epitaxially grown as previously described. The mask 34 is then deposited on -the exposed surface of the wafer and a narrow s-tripe window 40 is etched in the rnask.
P-type dopant is then diFfused through the window so that the difFusion front 24 extends to within 0.5~rn of the active layer 14 and also as shown at 44 extends laterally under edges oF the mask 34 defining the narrow stripe window 40, Part of the mask is then etched away to expose the lateral extensions 44 of the diffusion 22 and a top metal contact layer 32 is vapour deposited over the remaining par-t of mask 34 and over the exposed diffuse region 22. A bottom metal contact layer 30 is then deposited on the substrate 12 and the wafer is cleaved into individual chipsl at the same time producing mirror facets for the laser resonant cavities.
Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A double heterostructure laser comprising a substrate, a first confining layer, an active layer, a second confining layer, a blocking layer and a capping layer, the laser having opposed mirror facets defining ends of a laser resonant cavity, a narrow stripe diffusion extending from a top surface of a laser through the capping and blocking layers and into the second confining layer, the stripe diffusion functioning in use, to laterally define a lasing region, a wide area, shallow diffusion extending from the top of the laser through the capping layer into the blocking layer, a top metal contact extending over the upper surface of the laser and a bottom metal contact extending over the bottom surface of the laser, the shallow diffusion functioning to lower contact resistance between the top contact and the capping layer.
2. A double heterostructure laser as claimed in claim 1 in which the substrate is n-type III-V material, the first confining layer is n-type III-V material, the active layer is n-type or p-type III-V
material, the second confining layer is p-type III-V material the blocking layer is n-type III-V material and the diffusions are p-type.
material, the second confining layer is p-type III-V material the blocking layer is n-type III-V material and the diffusions are p-type.
3. A laser as claimed in claim 1 in which the confining layers are made of materials which have a higher bandgap than the active layer.
4. A laser as claimed in claim 1 in which the material of the active layer has a higher refractive index than the material of the confining layers.
5. A double heterostructure laser as claimed in claim 2 in which the p-type diffusions are zinc or cadmium diffusions.
6. A double heterostructure laser as claimed in claim 1 in which the narrow diffusion has a diffusion window width of about 2 to 3 microns.
7. A double heterostructure laser as claimed in claim 1 in which the wide area diffusion has a diffusion window width of about 7 to 10 microns.
8. A method of preparing a double heterostructure laser comprising expitaxially growing a double heterostructure on a III-V
substrate and a blocking layer and a capping layer on said double heterostructure, depositing a mask on the top of the capping layer, defining a first window having a width in the range 1 to 4µm in the mask, diffusing material through said window to a depth at which the diffusion front extends to within 0.5µm of the active layer, removing part of the mask to define a second window in the mask substantially wider than the first window, diffusing material through said second window to a depth at which the diffusion front is within the blocking layer, and depositing a metal contact on both the top and bottom surfaces of the structure.
substrate and a blocking layer and a capping layer on said double heterostructure, depositing a mask on the top of the capping layer, defining a first window having a width in the range 1 to 4µm in the mask, diffusing material through said window to a depth at which the diffusion front extends to within 0.5µm of the active layer, removing part of the mask to define a second window in the mask substantially wider than the first window, diffusing material through said second window to a depth at which the diffusion front is within the blocking layer, and depositing a metal contact on both the top and bottom surfaces of the structure.
9. A double heterostructure laser comprising a substrate, a first confining layer, an active layer, a second confining layer, a blocking layer and a capping layer, the laser having opposed mirror facets defining ends of a laser resonant cavity, a narrow stripe diffusion extending from a top surface of a laser through the capping and blocking layers and into the second confining layer, the stripe diffusion functioning in use to laterally define a lasing region, a top metal contact extending over the upper surface of the laser so as electrically to contact the capping layer including all of diffusion exposed thereat, and a bottom metal contact layer extending over the bottom surface of the laser.
10. A method of preparing a double heterostructure laser comprising epitaxially growing a double heterostructure on a III-V
substrate and a blocking layer and a capping layer on said double heterostructure, depositing a mask on the top of the capping layer, defining a narrow stripe window having a width in the range 1 to 4µm in a mask, diffusing material through said window to a depth at which the diffusion front extends to within 0.5µm of the active layer and parts of the diffusion extend laterally under the edges of the mask defining the window, removing a further part of the mask to define a second window substantially wider than the first window so as to expose all of the diffuse region within the capping layer, and depositing metal contacts on both the top and bottom surfaces of the structure.
substrate and a blocking layer and a capping layer on said double heterostructure, depositing a mask on the top of the capping layer, defining a narrow stripe window having a width in the range 1 to 4µm in a mask, diffusing material through said window to a depth at which the diffusion front extends to within 0.5µm of the active layer and parts of the diffusion extend laterally under the edges of the mask defining the window, removing a further part of the mask to define a second window substantially wider than the first window so as to expose all of the diffuse region within the capping layer, and depositing metal contacts on both the top and bottom surfaces of the structure.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000417600A CA1189177A (en) | 1982-12-13 | 1982-12-13 | Planar narrow-stripe laser with improved contact resistance |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000417600A CA1189177A (en) | 1982-12-13 | 1982-12-13 | Planar narrow-stripe laser with improved contact resistance |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1189177A true CA1189177A (en) | 1985-06-18 |
Family
ID=4124140
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000417600A Expired CA1189177A (en) | 1982-12-13 | 1982-12-13 | Planar narrow-stripe laser with improved contact resistance |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1189177A (en) |
-
1982
- 1982-12-13 CA CA000417600A patent/CA1189177A/en not_active Expired
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