GB2212325A - Solid state light source - Google Patents
Solid state light source Download PDFInfo
- Publication number
- GB2212325A GB2212325A GB8726678A GB8726678A GB2212325A GB 2212325 A GB2212325 A GB 2212325A GB 8726678 A GB8726678 A GB 8726678A GB 8726678 A GB8726678 A GB 8726678A GB 2212325 A GB2212325 A GB 2212325A
- Authority
- GB
- United Kingdom
- Prior art keywords
- active region
- light source
- solid state
- quantum wells
- state light
- 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.)
- Granted
Links
Classifications
-
- 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
- H01L33/04—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 with a quantum effect structure or superlattice, e.g. tunnel junction
- H01L33/06—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 with a quantum effect structure or superlattice, e.g. tunnel junction within the light emitting region, e.g. quantum confinement structure or tunnel barrier
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/30—Structure or shape of the active region; Materials used for the active region
- H01S5/34—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/40—Arrangement of two or more semiconductor lasers, not provided for in groups H01S5/02 - H01S5/30
- H01S5/4025—Array arrangements, e.g. constituted by discrete laser diodes or laser bar
- H01S5/4031—Edge-emitting structures
- H01S5/4043—Edge-emitting structures with vertically stacked active layers
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/30—Structure or shape of the active region; Materials used for the active region
- H01S5/34—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers
- H01S5/3428—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers layer orientation perpendicular to the substrate
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/40—Arrangement of two or more semiconductor lasers, not provided for in groups H01S5/02 - H01S5/30
- H01S5/4025—Array arrangements, e.g. constituted by discrete laser diodes or laser bar
- H01S5/4087—Array arrangements, e.g. constituted by discrete laser diodes or laser bar emitting more than one wavelength
Abstract
The light source comprises a monolithic light emitter diode structure having an active region 8 which is located between two materials 9, 11 having wider energy bandgaps than the active region, the active region including multiple quantum wells 12 which have graded well thicknesses through the active region 8, such that the source is capable of emitting light at wavelengths L1, L2 spaced over a range defined by the width and depth of the quantum wells. This enables the light source to be used in optical fibre devices where it replaces a filament lamp and thus gives improved reliability in use. <IMAGE>
Description
SOLID STATE LIGHT SOURCE
This invention relates to a solid state light source. It relates particularly to such a light source which is capable of emitting light over a broad spectral band.
In the construction of optical fibre devices which make use of a spectral filtering technique, it is usual to employ tungsten-halogen incandescent filament lamps in order to provide the broad spectral emission width that is necessary. Unfortunately, the filament lamp is a somewhat fragile article and this makes it unreliable in operation.
The need to include such a lamp is likely to cause eventual breakdown of the complete fibre device particularly when this is used under the severe conditions of operation that are sometimes necessary. The degree of ruggedness and reliability that would be desirable in the lamp part can be found in the light emitter diode construction but these devices have inherently a rather narrow spectral emission width (typically 40 nanometres at a wavelength of 900 nanometres) so that a single conventional LED would be incapable of providing the bandwidth required.
One object of the present invention is to provide a solid state light source fliat will be capable of emitting light over a broad spectral band and which will be reliable in operation.
According to the invention, there is provided a solid state light source comprising a monolithic light emitter diode structure having an active region which is located between two materials having wider energy bandgaps than the active region, the active region including multiple quantum wells which have graded well thicknesses through the active region, such that the source is capable of emitting light at wavelengths spaced over a range defined by the width and depth of the quantum wells.
Preferably, the active region comprises a compound semiconductor material having a direct energy bandgap. The active region may comprise a gallium aluminium arsenide compound.
Alternatively, the active region may comprise a gallium indium arsenide phosphide compound.
By way of example, a particular embodiment of the invention will now be described with reference to the accompanying drawings, in which:
Figure 1 is a graph showing the light wavelengths produced by some commercially available LED devices,
Figure 2 is a diagram showing the energy bands and wavelengths associated with different compound semiconductor materials systems,
Figure 3 is a schematic band diagram of a standard light emitter diode structure,
Figures 4 and 5 are different embodiments of a multiple quantum well construction according to the invention, and,
Figure 6 is a graph showing the light wavelength output of a multiple quantum well device.
Figure 1 shows schematically some typical light outputs from existing light emitter diode devices. The horizontal axis gives the wavelength of emission whilst the vertical axis measures the light intensity output. It will be seen that three existing devices have output curves 1 with very sharply defined centre wavelengths. For obtaining light outputs in a short wavelength (about 0.6 to 0.9 microns) part of the range the semiconductors used could be based on the GaAlAs/GaAs materials system. For obtaining light outputs in a long wavelength (above 1.0 microns) part of the range the
InP/GaInAsP materials system would generally be used.
As already explained, the present invention was devised to provide a broad band of light emission, somewhat as depicted by the output curve 2 on Figure 1.
Figure 2 is a diagram illustrating the useful parts of these semiconductor materials systems with the horizontal axis showing the Wavelength Corresponding to Energy Gap measured in microns.
The vertical axis gives the Lattice Constants (in Angstrom Units) for the materials.
An upper horizontal axis shows the Energy Band (measured in electron volts), whilst at the right hand side lines corresponding to the choice of different device substrate materials have been marked using a substrate of indium phosphide and InGaAsP, wavelengths between 1.0 and 1.6 microns could be expected. Similarly, using a substrate of gallium arsenide and GaAlAs, wavelengths between 0.6 and 0.9 microns should be possible. This illustration thus confirms the figures for wavelength ranges already given.
A first horizontal line portion 3 highlights the properties of
GaA1As/GaAs whilst a second horizontal line portion 4 depicts those for GaInAsP/InP.
Figure 3 is a schematic band diagram of a conventional gallium arsenide/gallium aluminium arsenide light emitter diode construction. The diagram shows on the horizontal axis 6 the distance (by which the thickness of the active region is measured) and on a vertical axis 7 the electron energy, a greater distance from the origin indicating a higher level of energy of the electrons.
Conversely, for holes present in the diagram, a hole nearer the origin will have a higher level of energy than one further from the origin.
In Figure 3, a very thin active region 8 of semiconductor material is sandwiched between cladding layers 9 and 11 of wider bandgap semiconductor material. The layer 9 is of n-gallium aluminium arsenide whilst the layer 11 is of the same chemical composition but of the p-conductivity type. The sandwiched region 8 is also of p-gallium aluminium arsenide.
In operation, electrons are injected from the wide bandgap cladding layer 9 into the p-type active region 8. Similarly, holes are injected from the cladding layer 11 into the active region 8. The recombination of the electrons and holes occurs in the region 8 and this causes the emission of light. For the construction depicted in
Figure 3, the light is emitted at substantially a single wavelength and this would therefore produce a single one of the output curves 1 of
Figure 1. The thickness dimension of the bandgap thus has a single value in the conventional light emitter diode construction.
Figure 4 is a schematic band diagram of a gallium arsenidelgallium aluminium arsenide construction according to the invention. Electrons are injected from the wide bandgap n-GaAlAs cladding layer 9 into the p-type active region 8, where they recombine with holes from a p-type cladding layer 11. The recombination occurs with the emission of light L1 of long wavelength from the side of the gap adjacent the p-type material 11
and of short wavelength light L2 from the side of the gap adjacent
the n-type material 9. The active region 8 includes a number of
quantum wells 12 of varying width. The quantum wells 12 are of
gallium arsenide and they are separated by spacer layers 13 of
gallium aluminium arsenide.These wells 12 act to confine the charge carriers, thus reducing the possibility of all the carriers
drifting to the narrow bandgap side of the active region. It is
necessary to ensure approximately uniform pumping of all the wells
12. One way of arranging such pumping would be by providing
either a positive or a negative built-in field effect by grading the
aluminium concentrations present in the barrier layers.
Figure 5 shows an alternative construction where quantum
wells 12 are located between spacer layers 13 in the active region 8.
The spacer layers 13 are graded in length so that they will provide
the necessary control over the movement of the charge carriers
when the device is in operation.
The construction of the solid state light source begins with
growth of the required semiconductor material which could be by
metal organic chemical vapour deposition (MOCVD) or by molecular
beam epitaxy (MBE).
In MOCVD, gases such as trimethyl gallium, trimethyl indium,
trimethyl aluminium, arsine and phosphine are reacted at
atmospheric or low pressure on a heated substrate of gallium arsenide or indium phosphide. P- or n- type dopant materials are
incorporated by including dimethyl zinc, hydrogen sulphide,
hydrogen selenide or other reagents in the gas stream.
In MBE, elements or compounds containing the required
elements are heated in a high vacuum system and impinge upon a
heated gallium arsenide or indium phosphide substrate to grow the
layers required. Dopants are incorporated by introducing them into
the system in the same way. Gaseous sources may also be used to
provide the reagents.
After the growth of the required semiconductor material, the
diode may then be fabricated using standard semiconductor
processing techniques such as the following:
1. Confinement of current to a particular region by dielectric
isolation, implantation, diffusion or the growth of burying or current
blocking semiconductor regions.
2. Ohmic contact fabrication using diffusion, ion implantation or
metallization using titanium, zinc, gold, indium, germanium,
platinum, chromium, tungsten, cadmium or other suitable metals
deposited by evaporation, sputtering or selective growth.
3. Contact alloying at elevated temperatures.
4. Thinning of wafers by mechanical, chemical or other
techniques.
5. Etching of semiconductors using chemical reagents, ion beam
milling, reactive ion etching or plasma etching.
In order to make the calculations to define well and barrier
thicknesses it is necessary first to calculate energy levels in systems ~of coupled quantum wells. This is usually carried out within the
envelope function approximation in which a simple expression for
the wavefunction in each well or barrier is available. The energy
levels are found by matching boundary conditions. The details of the calculation are similar to those for dielectric multilayer slab
waveguides. Accurate calculations require inclusion of the effect of a non-parabolic bandstructure and the effects of finite well depth
(simple models assume infinite well depth).
Consideration of the above factors allows calculation of energy levels in the two complex sets of quantum wells required for the fabrication of broadband light emitter diode sources.
Figure 6 is a graph of the actual results obtained with an early prototype of the multiple quantum well light emitter diode construction. The horizontal axis gives the wavelength of emission (in microns) whilst the vertical axis measures the light intensity. The curve 14 is that obtained for the prototype construction and curve
16 is that of a typical single wavelength LED for comparison. The
advantage in linewidth of the multiple quantum well construction is clearly visible since there has been an increase in spectral full width
at the half maximum value from 100 to 335 nanometres.
The foregoing descriptions of embodiments of the invention
have been given by way of example only and a number of modifications may be made without departing from the scope of the invention as defined in the appended claims. For instance, it is not essential that the device construction should be based on the gallium arsenide/gallium aluminium arsenide system. This is capable of
giving broadband light emission only over a particular wavelength range. For a different band of emission, alternative materials would be required and a possible choice would be indium phosphide with gallium indium arsenide phosphide.
Claims (6)
1. A solid state light source comprising a monolithic light emitter diode structure having an active region which is located between two materials having wider energy bandgaps than the active region, the active region including multiple quantum wells which have graded well thicknesses through the active region, such that the source is capable of emitting light at wavelengths spaced over a range defined by the width and depth of the quantum wells.
2. A light source as claimed in Claim 1, in which the active region comprises a compound semiconductor material having a direct energy bandgap.
3. A light source as claimed in Claim 1 or 2, in which the active region comprises a gallium aluminium arsenide compound.
4. A light source as claimed in Claim 1 or 2, in which the active region comprises a gallium indium arsenide phosphide compound.
5. A solid state light source substantially as hereinbefore described with reference to any one of Figures 4 to 6 of the accompanying drawings.
6. A method of constructing a solid state light source substantially as hereinbefore described.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8726678A GB2212325B (en) | 1987-11-13 | 1987-11-13 | Solid state light source |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8726678A GB2212325B (en) | 1987-11-13 | 1987-11-13 | Solid state light source |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8726678D0 GB8726678D0 (en) | 1987-12-16 |
| GB2212325A true GB2212325A (en) | 1989-07-19 |
| GB2212325B GB2212325B (en) | 1990-10-03 |
Family
ID=10626945
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8726678A Expired - Fee Related GB2212325B (en) | 1987-11-13 | 1987-11-13 | Solid state light source |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2212325B (en) |
Cited By (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2702602A1 (en) * | 1993-03-12 | 1994-09-16 | Deveaud Pledran Benoit | Semiconductor laser structure with double heterostructure and method of production |
| EP0661782A1 (en) * | 1993-12-28 | 1995-07-05 | Nec Corporation | A semiconductor laser |
| EP0662739A1 (en) * | 1994-01-05 | 1995-07-12 | AT&T Corp. | Article comprising a semiconductor laser that is non-degenerate with regard to polarization |
| US5483547A (en) * | 1994-05-10 | 1996-01-09 | Northern Telecom Limited | Semiconductor laser structure for improved stability of the threshold current with respect to changes in the ambient temperature |
| FR2811150A1 (en) * | 2000-06-20 | 2002-01-04 | Mitel Semiconductor Ab | SEMICONDUCTOR LASERS HAVING VARIABLE QUANTUM WELL THICKNESSES |
| FR2823916A1 (en) * | 2001-04-19 | 2002-10-25 | Natioanl Taiwan University | METHOD FOR INCREASING THE BANDWIDTH OF OPTICAL AMPLIFIERS / SEMICONDUCTOR SUPRALUMINESCENT DIODES USING MULTIPLE QUANTIALLY NON-IDENTICAL WELLS |
| EP1729385A1 (en) * | 2005-06-01 | 2006-12-06 | AGILENT TECHNOLOGIES, INC. (A Delaware Corporation) | Active region of a light emitting device optimized for increased modulation speed operation |
| DE102006025964A1 (en) * | 2006-06-02 | 2007-12-06 | Osram Opto Semiconductors Gmbh | Multiple quantum well structure, radiation-emitting semiconductor body and radiation-emitting component |
| WO2014177367A1 (en) * | 2013-04-29 | 2014-11-06 | Osram Opto Semiconductors Gmbh | Semiconductor layer sequence for an optoelectronic component |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4589115A (en) * | 1983-09-09 | 1986-05-13 | Xerox Corporation | Wavelength tuning of quantum well heterostructure lasers using an external grating |
| US4599728A (en) * | 1983-07-11 | 1986-07-08 | At&T Bell Laboratories | Multi-quantum well laser emitting at 1.5 μm |
-
1987
- 1987-11-13 GB GB8726678A patent/GB2212325B/en not_active Expired - Fee Related
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4599728A (en) * | 1983-07-11 | 1986-07-08 | At&T Bell Laboratories | Multi-quantum well laser emitting at 1.5 μm |
| US4589115A (en) * | 1983-09-09 | 1986-05-13 | Xerox Corporation | Wavelength tuning of quantum well heterostructure lasers using an external grating |
Cited By (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2702602A1 (en) * | 1993-03-12 | 1994-09-16 | Deveaud Pledran Benoit | Semiconductor laser structure with double heterostructure and method of production |
| EP0661782A1 (en) * | 1993-12-28 | 1995-07-05 | Nec Corporation | A semiconductor laser |
| US5636236A (en) * | 1993-12-28 | 1997-06-03 | Nec Corporation | Semiconductor laser |
| EP0662739A1 (en) * | 1994-01-05 | 1995-07-12 | AT&T Corp. | Article comprising a semiconductor laser that is non-degenerate with regard to polarization |
| US5483547A (en) * | 1994-05-10 | 1996-01-09 | Northern Telecom Limited | Semiconductor laser structure for improved stability of the threshold current with respect to changes in the ambient temperature |
| FR2811150A1 (en) * | 2000-06-20 | 2002-01-04 | Mitel Semiconductor Ab | SEMICONDUCTOR LASERS HAVING VARIABLE QUANTUM WELL THICKNESSES |
| GB2363901A (en) * | 2000-06-20 | 2002-01-09 | Mitel Semiconductor Ab | An optical emission device having quantum wells |
| GB2378318A (en) * | 2001-04-19 | 2003-02-05 | Univ Nat Taiwan | Optoelectronic devices |
| FR2823916A1 (en) * | 2001-04-19 | 2002-10-25 | Natioanl Taiwan University | METHOD FOR INCREASING THE BANDWIDTH OF OPTICAL AMPLIFIERS / SEMICONDUCTOR SUPRALUMINESCENT DIODES USING MULTIPLE QUANTIALLY NON-IDENTICAL WELLS |
| GB2378318B (en) * | 2001-04-19 | 2005-06-01 | Univ Nat Taiwan | Semiconductor optoelectronic apparatus having plural quantum wells of different well widths |
| EP1729385A1 (en) * | 2005-06-01 | 2006-12-06 | AGILENT TECHNOLOGIES, INC. (A Delaware Corporation) | Active region of a light emitting device optimized for increased modulation speed operation |
| US7577172B2 (en) | 2005-06-01 | 2009-08-18 | Agilent Technologies, Inc. | Active region of a light emitting device optimized for increased modulation speed operation |
| DE102006025964A1 (en) * | 2006-06-02 | 2007-12-06 | Osram Opto Semiconductors Gmbh | Multiple quantum well structure, radiation-emitting semiconductor body and radiation-emitting component |
| WO2014177367A1 (en) * | 2013-04-29 | 2014-11-06 | Osram Opto Semiconductors Gmbh | Semiconductor layer sequence for an optoelectronic component |
| US9553231B2 (en) | 2013-04-29 | 2017-01-24 | Osram Opto Semiconductors Gmbh | Semiconductor layer sequence and method of operating an optoelectronic semiconductor chip |
| DE102013104351B4 (en) | 2013-04-29 | 2022-01-20 | OSRAM Opto Semiconductors Gesellschaft mit beschränkter Haftung | Semiconductor layer sequence and method for operating an optoelectronic semiconductor chip |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8726678D0 (en) | 1987-12-16 |
| GB2212325B (en) | 1990-10-03 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| 732 | Registration of transactions, instruments or events in the register (sect. 32/1977) | ||
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19961113 |