GB2322002A - Semiconductor light emitting device - Google Patents
Semiconductor light emitting device Download PDFInfo
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- GB2322002A GB2322002A GB9702547A GB9702547A GB2322002A GB 2322002 A GB2322002 A GB 2322002A GB 9702547 A GB9702547 A GB 9702547A GB 9702547 A GB9702547 A GB 9702547A GB 2322002 A GB2322002 A GB 2322002A
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/02—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
- H01L33/26—Materials of the light emitting region
- H01L33/30—Materials of the light emitting region containing only elements of group III and group V of the periodic system
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L33/00—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/02—Semiconductor devices with at least one potential-jump barrier or surface barrier specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
- H01L33/26—Materials of the light emitting region
- H01L33/30—Materials of the light emitting region containing only elements of group III and group V of the periodic system
- H01L33/305—Materials of the light emitting region containing only elements of group III and group V of the periodic system characterised by the doping materials
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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
- H01S5/30—Structure or shape of the active region; Materials used for the active region
- H01S5/32—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures
- H01S5/323—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser
- H01S5/32308—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser emitting light at a wavelength less than 900 nm
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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
- H01S2302/00—Amplification / lasing wavelength
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- Semiconductor Lasers (AREA)
Abstract
A laser or LED is formed using a quarternary In x (Al y Ga 1-y ) 1-x As semiconductor compound. Devices having In 0.18 (Al 0.34 Ga 0.66 ) 0.82 As and In 0.24 (Al 0.35 Ga 0.65 ) 0.76 As active layers with low residual oxygen concentrations (< 1x10<SP>17</SP> atoms/cc) grown at a temperature of 630‹C provide emission at 739nm and 741nm. These wavelengths of light are particularly suited to phototherapy treatment of human or animal tissue in conjunction with the use of the m-tetrahydroxyphenolhacteriochlorin (m-THBC) photosensitizer.
Description
OPTICAL DEVICES
The present invention relates to optical devices and, more particularly, to semi-conductor lasers and light emitting diodes. The present invention also relates to the use of such optical devices for the treatment of tissue of or taken from an animal or human body.
Chemical Society Reviews, the Royal Society of Chemistry,
Cambridge, Volume 24 (1995), Photosensitisers of the porphyrin and the phthalocyanine series for photodynamic therapy, Raymond Bonnet, page 19-33, discloses a method of treatment of human tissue called phototherapy or photodynamic therapy in which visible or near visible light is used as a therapeutic agent in clinical medicine. Phototherapy comprises two categories: direct, without an administered photosensitizer (the treatment of neonatal jaundice with blue/white light); and indirect, where the therapeutic effect is achieved via an administered photosensitizer which is the effective light absorber. Phototherapy, generally, relates to the damage of living tissue by a combination of a photosensitizer, visible light and oxygen.
One area of application of photodynamic therapy is tumour phototherapy. The underlying basic idea of tumour phototherapy is: (a) to identify a photosensitizer which shows some
selectivity for photo damage to tumour tissue; (b) to inject or to treat the tumour tissue with the
photosensitizer and wait a predeterminable period of
time (which depends upon the photosensitizer and the
tissue type) for equilibration between biological
compartments to give maximum differentiation between
normal and tumour tissue; and (c) to irradiate the tumour with visible light.
The result of photodynamic therapy after irradiation of the tumour with an appropriate dose of visible light is a necrosed tumour or necrosed tissue.
Since photosensitisers have some selectivity for tissue type and since light is highly directional, it is possible to target tissue to be destroyed with a reasonable degree of precision. Using fibreoptics and a source of coherent light, such as a laser or laser diode, it is possible to irradiate tumours which are surrounded by normal tissue so that the methods of treatment are not restricted to tumours at or near the surface of the patient.
The wavelength of the light used to treat any tissue will be dependent upon the photosensitizer utilised. One such photosensitizer is m-tetrahydroxyphenolbacteriochlorin (m-THPBC), a bacteriochlorin photodynamic therapy photosensitizer. This photosensitizer is operable when illuminated with light having a wavelength of substantially 739 nm.
GaAs quantum well (QW) lasers grown by metal organic vapour phase epitaxy (MOVEP) are well established and commercially available devices having operating wavelengths of from 820 nm to 880 nm. However, this wavelength range is not suitable for use with some photosensitisers and, in particular, m-THPBC.
Metal organic vapour phase epitaxy is well known within the art and described in, for example, 'Recollections and
Reflections of MO-CVD', H.M. Manasevit Journal of Crystal
Growth, Vol 55, Number 1, pages 1-9, (1981)., the entire contents of which are incorporated herein by reference.
The technique is suitable for fabrication of semiconductor devices including lasers and light emitting diodes.
The addition of aluminium to the GaAs quantum well structure is a potentially simple method of achieving a shorter emission wavelength. However, it has been found that merely increasing the aluminium content of an existing GaAs quantum well laser does not produce a satisfactory laser due to the inclusion of extrinsic oxygen. Without wishing to be bound by any particular theory, it is believed that this may be due to the incorporation of oxygen related recombination centres associated with the aluminium precursor, such recombination centres being found to significantly degrade quantum efficiency. Furthermore, AlGaAs quantum well lasers can degrade as a consequence of the formation of dark line defects.
It is an object of the present invention to mitigate the problems associated with the prior art and, in particular, to provide an optical device capable of emitting light at a wavelength of between 670 nm to 750 nm, more particularly having a wavelength of between 720 nm and 750, and preferably, 741 or 739 nm.
Accordingly the present invention provides an optical device comprising a quaternary material system for producing light having disposed on opposite sides thereof p-type and n-type barrier and cladding regions, the ntype region being deposited on an n-type substrate, wherein said quaternary material system has a composition given by Inx(AlyGaly)(l=)As.
An alternative embodiment provides an optical device comprising a quaternary material system for producing light having disposed on opposite sides thereof p-type and n-type barrier and cladding regions, the p-type region being deposited on a p-type substrate, wherein said quaternary material system has a composition given by Inx(AlyGa1-y)(1-x)As.
Advantageously, the optical devices according to the present invention enable the production of coherent or laser light for use in photodynamic therapy, and, in particular, for use with a bacteriochlorin photosensitizer.
A second aspect of the present invention provides an optical device arranged to produce light having a wavelength of between 670 nm and 750 nm inclusive, and preferably a wavelength within the range of 720 nm to 750 nm inclusive.
Preferably the optical device produces light having a wavelength of substantially 739 nm or 741, which are the wavelengths at which the effectiveness of m-THPBC as a photosensitiser is substantially maximum.
A third aspect of the present invention provides an optical device the value of x is between 0.05 and 0.24, and is preferably either 0.18 or 0.24. The Indium is utilised to provide sufficient stiffness to the crystal lattice of the quantum well for appropriate light producing operation. The minimum Indium fraction required to achieve sufficient stiffness is 0.05.
A fourth aspect of the present invention provides an optical device for producing laser light, wherein the value of y lies within 0.2 and 0.45. Preferably the value of y is either 0.34, 0.35 or 0.45.
It will be appreciated that in order to form a quantum well there must exist a potential difference between the In(AlyGa1y)(lx)As and the material on either side thereof.
Accordingly, an embodiment of the present invention provides an optical device optical device wherein the ptype barrier and cladding region comprises first and second p-type layers having compositions AlyGa1rAs, where the first p-type layer has a value of y of 0.34 and is deposited adjacent to the quaternary material system; the second p-type layer has a value of y of 0.59 and is deposited adjacent to the first p-type layer.
Preferably, an embodiment provides an optical device as claimed in claim 10, wherein the thickness of the first p-type layer is 0.25cm. A further embodiment provides an optical device as wherein the thickness of the second ptype layer is 2pm or 1.5 pm.
Typically, the p-type barrier and cladding region is doped with carbon. It is preferred if the concentration of the dopant of the first p-type layer is approximately 1 x 1017 cm-3 Similarly, the concentration of the dopant in the second p-type layer is between 1 and 2 x 1018 cam~3 and preferably at a concentration of 1.6 x 1018 cm3.
A further embodiment of the present invention provides an optical device wherein the n-type barrier and cladding region comprises first and second n-type layers, both having compositions of AlyGalyAs, wherein the first n-type layer has a value of y = 0.34 and is deposited adjacent to the quaternary material system; the second n-type layer has a value of y = 0.59 and is deposited adjacent to the first n-type layer.
The thicknesses of the layers needs to be considered when producing either a light emitting diode or a semiconductor laser. Suitably, an embodiment provides an optical device wherein the thickness of the first n-type layer is 0.25um. A further embodiment provides an optical device wherein the thickness of the second n-type layer is 1.5um or 2um.
The thicknesses of the optical devices are advantageously configured according to their modes of operation.
In a preferred embodiment the n-type barrier and cladding region is doped with silicon, the concentration of the dopant in the first n-type layer being between 1 and 4 x 1017 cm~3 inclusive and is, preferably, 4 x 1017 cm~3.
Similarly, the an embodiment provides an optical device wherein the concentration of the dopant in the second ntype layer is between 1 x 1018 cam~3 and 2 K 1018 cam~3.
Preferably, the concentration of the dopant in the second n-type layer is substantially 1.3 x 1018 cam~3.
It will be appreciated that in order to operate correctly, a current must be supplied to the optical device. Therefore an embodiment of the present invention provides a Zinc or Silicon doped GaAs contact layer, the doping being at a concentration of 5 x 1018 cam~3 to 2 x 1019 cm'3, preferably 5 x 1018 cam~3. The thickness of the GaAs contact layer is dependent upon whether a light emitting diode or semi-conductor laser is being fabricated.
Preferably the thickness of the GaAs contact layer is around 500A in the case of a light emitting diode and 2000A in the case of a semi-conductor laser.
A still further embodiment of the present invention comprises a buffer layer disposed between the substrate and the second n-type layer. In a preferred embodiment of the present invention, the buffer layer is doped with silicon at a concentration of 1 x 1018 cam~3.
A further embodiment of the present invention provides a graded GaAs layer doped with silicon at a concentration of 1 x 1018 cm'3 disposed between the buffer layer and the second n-type layer.
An embodiment of the present invention provides an optical device the p-type barrier and cladding region comprises first and second p-type layers having compositions AlJGalyAs, where the first p-type layer has a value of y of 0.45 and is deposited adjacent to the quaternary material system; the second p-type layer has a value of y of 0.8 and is deposited adjacent to the first p-type layer.
Such a structure advantageously produces a semi-conductor laser. A suitable thickness for the optical device of the first p-type (206;410) layer would be 0.15um.
Similarly, a suitable thickness for the second p-type layer would be 1.5 pm.
A still further embodiment provides an optical device as wherein the p-type barrier and cladding region is doped with carbon. Preferably, an embodiment provides an optical device wherein the concentration of the dopant of the first p-type layer is less than or equal to 1 x 1017 cm'3 and the concentration of the dopant of the second ptype layer is between 1 and 2 x 1018 cm'3 inclusive.
Yet another embodiment of the present invention provides an optical device wherein the n-type barrier and cladding region comprises first and second n-type layers, both having compositions of AlyGa1 s, wherein the first n-type layer has a value of y = 0.45 and is deposited adjacent to the quaternary material system; the second n-type layer has a value of y = 0.8 and is deposited adjacent to the first n-type layer.
Another aspect of the present invention provides a method of manufacturing an optical device comprising a quaternary material system for producing light, the method comprising the steps of depositing, on a substrate, an n-type barrier and cladding region, depositing the quaternary material system having a composition of Inx(Aly,Ga1-y)(1-x)As, (,,,,As, and depositing a p-type confinement region, wherein a high purity alkyl of aluminium is used for depositing the Aluminium Gallium material such that the total oxygen residue is no greater than 1 x 1017 oxygen atoms per cc.
Preferably the materials are deposited using a metal organic vapour phase epitaxy technique. In a preferred embodiment of the present invention the growth temperature for the structures of the optical device is relatively low and is preferably substantially 630 C.
An alternative embodiment provides a method of manufacturing an optical device comprising a quaternary material system for producing light, the method comprising the steps of depositing, on a substrate, a ptype barrier and cladding region, depositing the quaternary material system having a composition of
Inx=(AlyGal-y)(1-x)As, and depositing an n-type confinement region, wherein a high purity alkyl of aluminium is used for depositing the Aluminium Gallium material such that the total oxygen residue is no greater than 1 x 1017 oxygen atoms per cc.
The deposition of the material of the optical device is adapted so as to allow uniform distribution of the Indium throughout the In,(A1,Ga,~,) ,,~,,As layer for a large surface area of the GaAs substrate.
Preferably the method of manufacturing an optical device according to the present invention further comprises the steps of using a pure aluminium alkyl capable of depositing AlAs such that the total oxygen residue is not greater than 1 x 1017 oxygen atoms per cubic centimetre.
A still further aspect of the present invention relates to a method of treatment of tissue or cells of or taken from a human or animal body, said method comprising the steps of treating the tissue with a photosensitizer, and illuminating the treated tissue with an optical device according to the present invention until the treated tissue is damaged or necrosed.
It will be appreciated by those skilled in the art that, for example, tumour tissue or cells may be removed from the animal or human body and then treated with a photosensitizer and subsequently illuminated with light generated by an optical device according to the present invention in order to identify the tissue or cell type or type of tumour. Once the type of tumour has been identified this may then assist a doctor in diagnosis or prescribing a course of treatment. Cells, such as tumour cells, which have been grown in a culture may also be used to test the efficiency of newly developed photosensitisers.
Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: figure 1 shows schematically the structure of a light emitting diode having a quaternary Inx(AlyGaly)(x)As material system according to a first embodiment; figure 2 shows schematically the structure of a semiconductor laser having a quaternary an Inx(AlyGaly)(1-x)As material system according to a second embodiment; figure 3 shows schematically the structure of a light emitting diode having a quaternary Inx(AlyGa1-y)(1-x)As material system according to a first embodiment; figure 4 shows schematically the structure of a semiconductor laser having a quaternary an Inx(AlyGaly)(lx)As material system according to a second embodiment.
Referring to figure 1, there is shown a schematic representation of an optical device, a light emitting diode 100, for producing light having a wavelength of substantially between 720 nm and 750 nm FWHM, and preferably 739 nm or 741 nm, such light being suitable for photodynamic therapy applications.
The precise values of x and y are determined by keeping the fraction of Indium constant and varying the Aluminium fraction by + 2%. Therefore, the fraction of Aluminium given by Al0.34, may vary between Alo3s and Al0.33.
The device 100 is fabricated having a surface layer 102 of zinc doped GaAs which acts as a p-type contact. The concentration of the doping is 5 x 1018 cm~3 to 2 x 1019 cm 3. The thickness of the layer 102 is 500A to 1000A, and in the illustrated case 500A as the device is a light emitting diode. The optical device 100 also comprises an n-type contact 104 fabricated as a silicon doped GaAs substrate. A quaternary material system 106
Inx(AlyGa(1-y)1-x)AS, more particularly In0.18(Al0.34 Ga0.66)0.82As, is substantially centrally disposed within the optical device 100.
In determining the thickness of the quaternary material system or quantum well, a balance must be maintained between the sub-band spacing and optical overlap. The thickness of the quaternary material system layer 106 is within the range of 40A to 150A. Preferably, the thickness of the quaternary material system is between and and 150A, such as 80A.
Deposited on opposite sides of the quaternary material system 106 are p-type and n-type separate confinement heterostructures 108 and 110 respectively, also known as barrier and cladding regions. Each heterostructure comprises two layers. The p-type separate confinement heterostructure 108 has first 112 and second 114 p-type layers. The composition of the first p-type layer 112 is a ternary material system, AlyGa(ly)Ast more particularly Alo34GaO66As, and is doped with Carbon at a concentration of approximately 1 x 1017 cm~3. The thickness of the first p-type layer 112 is 0.25 pm. The second p-type layer 114 has a composition of Al059Ga04lAs and is Carbon doped at a concentration of 1 x 1018 cm-3. The thickness of the second p-type layer 114 is 2 pm.
The n-type separate confinement heterostructure 110 also comprises two layers, that is to say, a first n-type layer 116 and a second n-type layer 118. The first ntype layer 116 has an AlyGal-yAs composition substantially identical to that of the first p-type layer 112.
However, the first n-type layer 116 is silicon doped at a concentration of 4 x 1017 cm~3. The second n-type layer 118 has an AlyGa1rAs structure substantially identical to that of the second p-type layer 114. However, the second n-type layer 118 is silicon doped at a concentration of 1.3 x 1018 cm3.
Preferably, the optical device according to the first embodiment 100 also comprises a further GaAs layer disposed between the second n-type layer 118 and the GaAs substrate 104. This layer 120, known as a buffer layer, has a silicon doped GaAs composition, the doping being at a concentration 1 x 1016 cm~3. The thickness of the buffer layer 120 is 0.5 pm. The function of the buffer layer 120 is to aid nucleation of the AlGaAs layer by forming a perfect crystalline surface.
A still further preferred embodiment of the present invention comprises an Al7Ga1.As silicon doped layer similar to the second n-type layer 118 but for the former having a concentration of 1 x 1018 cm~3. The further layer 122 is utilised to provide a graded aluminium content between the buffer layer 120 and the second n-type layer 118. The graded layer reduces the inherent barrier to current flow across a GaAs/Al0.5gGaO4lAs interface.
The quantum well optical device according to the present invention has a number of advantages over conventional light emitting diodes composed of bulk semi-conductors wherein light generation occurs at the PN junction.
Firstly, the presence of Indium provides an increased degree of stiffening to the crystal lattice thereby reducing the propagation of crystal defects which are known to adversely shorten the operational life of an optical device. Secondly, the inclusion of Indium creates a compressive strain which affects the carrier recombination within the quantum well thereby enhancing light generation. These effects are desirable within optical devices such as light emitting diodes and semiconductor lasers where compressive strain positively influences threshold current and slope efficiency.
Referring to Figure 2, there is shown a second embodiment of an optical device, a semi-conductor laser 200, comprising a quaternary material system 201 having deposited on opposite sides thereof p and n-type separate confinement heterostructures 202 and 204 or barrier and cladding regions. The p-type confinement heterostructure 202 comprises first 206 and second 208 ternary material system layers both having AlGa1As compositions. The first p-type layer 206 has a composition of Alo45GaO55As which is doped with carbon at a concentration of approximately 1 x 1017 cam~3. The thickness of the first ptype layer 206 is 0.15 pm. The second p-type layer 208 has a composition of Alo8GaO2As which is carbon doped at a concentration of between 1 and 2 x 1018 cm-3. The thickness of the second p-type layer 208 is 1.5 pm.
The n-type separate confinement heterostructure 204 comprises first 210 and second 212 AlrGalrAs layers both of which are silicon doped. The doping of the first ntype layer 210 is 3 x 1017 cm-3. The doping of the second 212 n-type layer is 5 x 1017 cm~3. The composition of the first n-type layer 210 is Alo45Ga0.55As. The composition of the second n-type layer 212 is Alo8Ga02As.
A surface layer 214 of Zinc doped GaAs is provided as a p-type contact for the optical device 200 according to the second embodiment. The concentration of the Zinc dopant is between 5 x 1018 cm~3 and 2 x 1019 cm~3. The optical device 200 is formed on an n-type substrate which is, according to the present embodiment, a silicon doped
GaAs substrate 216.
Optionally, the optical device 200 according to the second embodiment may comprise a transitional ternary material system layer 218 disposed between the second ntype 212 and the substrate 216. This layer 218 is known as a buffer layer 218. The composition of the ternary material system of the buffer layer 218 is Alo45Ga055As and is doped with silicon at a concentration of 1 x 1018 cam-3.
The thickness of the buffer layer 218 is 1000A.
The optical device 200 according to the second embodiment has a substantially centrally disposed In(AlyGa1Y)lxAs quaternary material system having a composition of Ino24(Alo35Gao65)o76As The quaternary material system layer 201 has a thickness of between 50A and 150A, preferably 50A.
The first and second embodiments of the present invention were deposited using metal organic vapour phase epitaxial growth techniques at a pressure of 1.2 x 105 Pa (920 torr) using a Cambridge Instruments Quantax reactor fitted with a load lock horizontal reactor.
In order to reduce oxygen contamination a 100% arsine was dried by an eutectic melt of Aluminium Indium Gallium such as is disclosed in J. R. Shealy, G. Kreismanis, D.
K. Wagner and J. M. Woodhall, Applied Physics Letters 42 (1983) page 83, entitled "A New technique for gettering oxygen and moisture from gases used in semiconductor processing", the entire contents of which are incorporated herein, and high purity trimethylaluminium (TMA) was used. The alkyl of aluminium must be capable of depositing AlAs with a total oxygen residue of no greater than 1 x 1017 oxygen/cc. Therefore, the growth temperature can be significantly reduced while maintaining high photoluminescent efficiency. Suitably pure TMA is commercially available from EMF, Winfor,
Church Road, Wentworth, Ely, Cambridgeshire, CB6 3QE, or
EPICHEM, Power Road, Bromborough, Wirral, Mersyside.
The Inx(AlyGa1-y)(1-x)As strained quantum wells were deposited at 620 C to 670 C, preferably at 630 C.
All substrates were vertical gradient freeze silicon doped GaAs substrates misoriented by 3 from crystal plain (100) to (110).
Optionally, a silicon doped GaAs buffer layer can be deposited upon the substrate and arranged to have a thickness of between l000A and 0.5 pm.
The n-type silicon doped separate confinement heterostructure layers 116, 118, 210 and 212 are deposited upon the buffer layer. Preferably, a graded transition layer is disposed between the buffer layer and the second n-type layer. The ternary material system layer has a composition given by AlyGa1yAs. Growth rates were referenced to a value of 1.73 micrometres per hour for GaAs and the AsH3 mole fraction was maintained at 2.7 x 10 for the quantum wells and barriers. To minimise growth time, high Al content indirect barrier compositions should be deposited from two trimethylaluminium sources, one of said sources defining the InX(AlrGa1y)(lx)As quantum well.
The growth should be continuous between barriers and quantum wells. A conditioning layer of AlGaAs is grown at 700"C and introduces aluminium into the reactor for the first time. Such a deposit pins or getters impurities containing oxygen, which may be present on the cooler upstream sections of the reactor. Finally, a GaAs capping or surface layer should be grown on all optical devices to inhibit surface oxidation of the p- or n-type
AlGaAs.
Although the two embodiments of optical devices have been described with reference to separate confinement heterostructures, it will be appreciated by one skilled in the art that graded index separate confinement heterostructure layers can also be grown.
Although the illustrated embodiments illustrated in figures 1 and 2 depict optical device having n-type substrates, the present invention is not limited thereto.
Embodiments can equally well be fabricated in which the doping of the layers should in figures 1 and 2 is reversed thereby producing optical devices having p-type substrates and having deposited thereon p-type cladding and confinement regions, then the InAlGaAs optical element and the n-type confinement and cladding regions.
Such alternative embodiments are illustrated in figures 3 and 4. The description in relation to figures 1 and 2 is equally applicable to figures 3 and 4 mutatis mutandis. It will be noted that the doping of the contact layers and the substrates of the embodiments in figures 3 and 4 are different as compared to figures 1 and 3. This changes is necessary as a consequence of the change in the type of the dopant immediately adjacent to those layers.
The slope efficiency of a semi-conductor laser according to the above embodiments is 0.56 W/A, for uncoated facets. The power output was found to be up to 900mWatts at 2 Amps
The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.
All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.
Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
The invention is not restricted to the details of the foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.
Claims (56)
1. An optical device (100;200) comprising a quaternary
material system (101;201) for producing light having
disposed on opposite sides thereof p-type (108;202)
and n-type (110;204) barrier and cladding regions,
the n-type region being deposited on an n-type
substrate (104;216), wherein said quaternary
material system has a composition given by Inx( AlyGa1-y ) (1-x)AS. As.
2. An optical device (300;400) comprising a quaternary
material system for producing light having disposed
on opposite sides thereof p-type (310;404) and n
type (308;402) barrier and cladding regions, the p
type region being deposited on a p-type substrate (304;416), wherein said quaternary material system
has a composition given by Inx(Al,Gal)(lx)As.
3. An optical device as claimed in either of claims 1
or 2, wherein said device is arranged to produce
light having a wavelength of between 670 nm and 750
nm inclusive.
4. An optical device as claimed in any preceding claim,
wherein the device is arranged to produce light
having a wavelength of between 720 nm and 750 nm.
5. An optical device as claimed in any proceeding
claim, wherein said device is arranged to produce
light having a wavelength of substantially 739 nm or
741 nm.
6. An optical device as claimed in any proceeding
claim, wherein the value of x lies within the range
of 0.05 to 0.24 inclusive.
7. An optical device as claimed in any proceeding claim
wherein x has a value of either 0.18 or 0.24.
8. An optical device as claimed in any proceeding
claim, wherein y lies within the range of 0.2 to
0.45 inclusive.
9. An optical device as claimed in any proceeding claim
wherein y has a value of 0.34, 0.35 or 0.45.
10. An optical device as claimed in any proceeding claim
wherein the p-type barrier and cladding region
comprises first (112;316) and second p-type
(114;318) layers having compositions AlyGalyAs, where
the first p-type layer has a value of y of 0.34 and
is deposited adjacent to the quaternary material
system; the second p-type layer has a value of y of
0.59 and is deposited adjacent to the first p-type
layer.
11. An optical device as claimed in claim 10, wherein
the thickness of the first p-type (112;316) layer is
0.25pm.
12. An optical device as claimed in either of claims 10
or 11, wherein the thickness of the second p-type
layer is 2pm (114) or 1.5 pm (318).
13. An optical device as claimed in any proceeding
claim, where the p-type barrier and cladding region
is doped with carbon.
14. An optical device as claimed in claim 13, wherein
the concentration of the dopant of the first p-type
layer (112;316) is approximately 1 x 1017 cam~3.
15. An optical device as claimed in either of claims 13
or 14, wherein the concentration of the dopant of
the second p-type layer (114;318) is between 1 and 2 x 101e cm-J inclusive.
16. An optical device as claimed in claim 15, wherein
the concentration of the dopant of the second p-type
layer (114;318) is 1.6 x 1018 cm'3.
17. An optical device as claimed in any proceeding
claim, wherein the n-type barrier and cladding
region comprises first (116;312) and second
(118;314) n-type layers, both having compositions of AlYGalyAs, wherein the first n-type layer has a value
of y = 0.34 and is deposited adjacent to the
quaternary material system; the second n-type layer
has a value of y = 0.59 and is deposited adjacent to
the first n-type layer.
18. An optical device as claimed in claim 17, wherein
the thickness of the first n-type layer (116;312) is 0.25pom.
19. An optical device as claimed in either of claims 17
or 18, wherein the thickness of the second n-type
layer (118;314) is 1.5pm or 2pm.
20. An optical device as claimed in any proceeding
claim, wherein the n-type barrier and cladding
region (110;308) is doped with silicon.
21. An optical device as claimed in any of claims 17 to
20, wherein the concentration of the dopant in the
first n-type layer (116;312) is between 1 x 1017 cam~3 and 4 x 1017 cm~3 inclusive.
22. An optical device as claimed in any of claims 17 to
21, wherein the concentration of the dopant of the
first n-type layer (116;312) is 4 x 1017 cm3.
23. An optical device as claimed in any of claims 20 to
22, wherein the concentration of the dopant in the
second n-type layer (118;314) is between 1 x 1018 cam~3 and 2 x 1018 cm~3.
24. An optical device as claimed in claim 23, wherein
the concentration of the dopant in the second n-type
layer (118;314) is substantially 1.3 x 1018 cam~3.
25. An optical device as claimed in any proceeding
claim, wherein the p-type barrier and cladding
region comprises first (206;410) and second p-type
(208;412) layers having compositions AlrGalrAs, where
the first p-type layer has a value of y of 0.45 and
is deposited adjacent to the quaternary material
system; the second p-type layer has a value of y of
0.8 and is deposited adjacent to the first p-type
layer.
26. An optical device as claimed in claim 25, wherein
the thickness of the first p-type (206;410) layer is 0.15pom.
27. An optical device as claimed in either of claims 25
or 26, wherein the thickness of the second p-type
(208;412) layer is 1.5 pm.
28. An optical device as claimed in any proceeding
claim, where the p-type barrier and cladding region
is doped with carbon.
29. An optical device as claimed in claim 28, wherein
the concentration of the dopant of the first p-type
layer (206;410) is approximately 1 K 1017 cam~3.
30. An optical device as claimed in either of claims 28
or 29, wherein the concentration of the dopant of
the second p-type layer (208;412) is between 1 and
2 x 1018 cm~3 inclusive.
31. An optical device as claimed in any proceeding claim
wherein the n-type barrier and cladding region (204)
comprises first (210;406) and second (212;408) n
type layers, both having compositions of AlyGa1yAs, wherein the first n-type layer has a value of y =
0.45 and is deposited adjacent to the quaternary
material system; the second n-type layer has a value
of y = 0.8 and is deposited adjacent to the first n
type layer.
32. An optical device as claimed in claim 31, wherein
the thickness of the first n-type layer (210;406) is
0.15pm.
33. An optical device as claimed in either of claims 31
or 32, wherein the thickness of the second n-type
layer (212;408) is 1.5pm.
34. An optical device as claimed in any proceeding claim
wherein the n-type barrier and cladding region
(204;402) is doped with silicon.
35. An optical device as claimed in claim 34, wherein
the concentration of the dopant in the first n-type
layer (210;406) is substantially 3 x 1017 cm3.
36. An optical device as claimed in any of claims 34 to
35, wherein the concentration of the dopant in the
second n-type layer (212;408) is between 1 x 1018 cam~3 and 2 x 1018 cm~3.
37. An optical device as claimed in any proceeding claim
further comprising a doped GaAs contact layer
(102;214;302;402) deposited on the most distant
layer from the substrate (104;216;304;416).
38. An optical device as claimed in claim 37, wherein
the contact layer (102;202;302;402) has a thickness
of 500A to 2000A.
39. An optical device as claimed in claim 38, wherein
the contact layer (102;202;302;402) is doped with
Zinc or Silicon.
40. An optical device as claimed in claim 39, wherein
the concentration of the dopant is between 5 x 1018
and 2 x 1019 cm'3.
41. An optical device as claimed in any proceeding claim
further comprising a buffer layer (120;320) disposed
on the substrate.
42. An optical device as claimed in claim 41, wherein
the buffer layer (120;320) is doped with either
silicon or carbon at a concentration of 1 x 1018 cm~3.
43. An optical device as claimed in any preceding claim,
further comprises a graded AlGaAs layer (122) to
reduce the series resistance between the GaAs layer
(120) and the second n-layer (118).
44. An optical device as claimed in any preceding claim,
further comprising a graded AlGaAs layer (322) to
reduce the series resistance between the GaAs layer
(120) and the second p-type layer (320).
45. An optical device as claimed in any proceeding
claim, further comprising a graded index GaAs layer
doped with silicon at a concentration of 1 x 1018 cm
3, said graded index layer being deposited between
the quantum well and the first n-type layer to
provide a graded aluminium content or refractive
index therebetween.
46. An optical device as claimed in any of claims 1 to
44, further comprising a graded index GaAs layer
doped with carbon at a concentration of 1 x 1018 cam~3, said graded index layer being deposited between the
quantum well and the first p-type layer to provide
a graded aluminium content or refractive index
therebetween.
47. An optical device substantially as described herein
with reference to and/or as illustrated in the
accompanying drawings.
48. An illumination device comprising a plurality of
optical devices as claimed in any preceding claim.
49. A method of manufacturing an optical device
comprising a quaternary material system for
producing light, the method comprising the steps of
depositing, on a substrate, an n-type barrier and
cladding region, depositing the quaternary material
system having a composition of In(AlyGaly)(l)As, and
depositing a p-type confinement region, wherein a
high purity alkyl of aluminium is used for
depositing the Aluminium Gallium material such that
the total oxygen residue is no greater than 1 x 1017
oxygen atoms per cc.
50. A method of manufacturing an optical device
comprising a quaternary material system for
producing light, the method comprising the steps of
depositing, on a substrate, a p-type barrier and
cladding region, depositing the quaternary material
system having a composition of In=(AlyGa1y)(l=)As, and
depositing an n-type confinement region, wherein a
high purity alkyl of aluminium is used for
depositing the Aluminium Gallium material such that
the total oxygen residue is no greater than 1 x 1017
oxygen atoms per cc.
51. A method for manufacturing an optical device as
claimed in either of claims 49 or 50, wherein the
various regions and layers are deposited using a
metal organic vapour phase epitaxy technique.
52. A method as claimed in any of claims 50 to 51,
wherein the growth temperature for the optical
device is substantially in the range of 620"C to 670"C, preferably 630 C.
53. A method of manufacturing an optical device
substantially as described herein.
54. A method of treatment of tissue or cells derived
from a human or animal source, which comprises the
steps of treating the tissue or cells with a
photosensitizer and illuminating the tissue or cells
with a device according to any of Claims 1 to 48.
55. Use of a device according to any of Claims 1 to 48
in the irradiation of human or animal tissue or
cells, wherein the tissue or cells have been treated
with a photosensitizer prior to irradiation.
56. A method according to Claim 54 or use according to
Claim 55, wherein the photosensitizer is
m-tetrahydroxyphenolbacteriochlorin.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9702547A GB2322002A (en) | 1997-02-07 | 1997-02-07 | Semiconductor light emitting device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9702547A GB2322002A (en) | 1997-02-07 | 1997-02-07 | Semiconductor light emitting device |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB9702547D0 GB9702547D0 (en) | 1997-03-26 |
| GB2322002A true GB2322002A (en) | 1998-08-12 |
Family
ID=10807264
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9702547A Withdrawn GB2322002A (en) | 1997-02-07 | 1997-02-07 | Semiconductor light emitting device |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2322002A (en) |
Citations (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS59107588A (en) * | 1982-12-10 | 1984-06-21 | Fujitsu Ltd | Optical semiconductor device |
| EP0437385A1 (en) * | 1990-01-10 | 1991-07-17 | France Telecom | Semiconductor structure for optoelectronic devices |
| US5073895A (en) * | 1990-04-18 | 1991-12-17 | Mitsubishi Denki Kabushiki Kaisha | Semiconductor laser |
| US5197077A (en) * | 1992-02-28 | 1993-03-23 | Mcdonnell Douglas Corporation | Low divergence laser |
| US5216684A (en) * | 1990-09-07 | 1993-06-01 | Massachusetts Institute Of Technology | Reliable alingaas/algaas strained-layer diode lasers |
| US5222090A (en) * | 1992-03-05 | 1993-06-22 | Mcdonnell Douglas Corporation | 700-850 nanometer semiconductor diode laser |
| JPH08172241A (en) * | 1994-12-16 | 1996-07-02 | Furukawa Electric Co Ltd:The | Semiconductor light emitting element with algainas multiple quantum well |
| US5541949A (en) * | 1995-01-30 | 1996-07-30 | Bell Communications Research, Inc. | Strained algainas quantum-well diode lasers |
-
1997
- 1997-02-07 GB GB9702547A patent/GB2322002A/en not_active Withdrawn
Patent Citations (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS59107588A (en) * | 1982-12-10 | 1984-06-21 | Fujitsu Ltd | Optical semiconductor device |
| EP0437385A1 (en) * | 1990-01-10 | 1991-07-17 | France Telecom | Semiconductor structure for optoelectronic devices |
| US5073895A (en) * | 1990-04-18 | 1991-12-17 | Mitsubishi Denki Kabushiki Kaisha | Semiconductor laser |
| US5216684A (en) * | 1990-09-07 | 1993-06-01 | Massachusetts Institute Of Technology | Reliable alingaas/algaas strained-layer diode lasers |
| US5197077A (en) * | 1992-02-28 | 1993-03-23 | Mcdonnell Douglas Corporation | Low divergence laser |
| US5222090A (en) * | 1992-03-05 | 1993-06-22 | Mcdonnell Douglas Corporation | 700-850 nanometer semiconductor diode laser |
| JPH08172241A (en) * | 1994-12-16 | 1996-07-02 | Furukawa Electric Co Ltd:The | Semiconductor light emitting element with algainas multiple quantum well |
| US5541949A (en) * | 1995-01-30 | 1996-07-30 | Bell Communications Research, Inc. | Strained algainas quantum-well diode lasers |
Non-Patent Citations (2)
| Title |
|---|
| Materials Science and Engineering, B21 (1993) pp 228-231, K Panzlaff et al "InGaAlAs multilayers" * |
| Patent Abstracts of Japan, Section E, Section No 272, Vol 8, No 226, Pg 92, 17/10/84 & JP 59 107 588 A * |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9702547D0 (en) | 1997-03-26 |
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