GB2228824A - Radiation detectors - Google Patents
Radiation detectors Download PDFInfo
- Publication number
- GB2228824A GB2228824A GB8904649A GB8904649A GB2228824A GB 2228824 A GB2228824 A GB 2228824A GB 8904649 A GB8904649 A GB 8904649A GB 8904649 A GB8904649 A GB 8904649A GB 2228824 A GB2228824 A GB 2228824A
- Authority
- GB
- United Kingdom
- Prior art keywords
- radiation
- radiation detector
- detector
- layers
- quantum well
- 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.)
- Withdrawn
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- 230000005855 radiation Effects 0.000 title claims abstract description 54
- 229910001218 Gallium arsenide Inorganic materials 0.000 claims abstract description 21
- 229910000980 Aluminium gallium arsenide Inorganic materials 0.000 claims abstract description 9
- 239000004065 semiconductor Substances 0.000 claims abstract description 7
- 239000000463 material Substances 0.000 claims abstract description 5
- 230000007704 transition Effects 0.000 claims description 3
- 230000006335 response to radiation Effects 0.000 claims description 2
- 238000010276 construction Methods 0.000 claims 1
- 230000004888 barrier function Effects 0.000 description 9
- 239000000203 mixture Substances 0.000 description 6
- 229910052782 aluminium Inorganic materials 0.000 description 5
- 239000000758 substrate Substances 0.000 description 5
- 238000010521 absorption reaction Methods 0.000 description 4
- 238000001514 detection method Methods 0.000 description 3
- 230000005281 excited state Effects 0.000 description 2
- 229910000661 Mercury cadmium telluride Inorganic materials 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 239000004411 aluminium Substances 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 230000008878 coupling Effects 0.000 description 1
- 238000010168 coupling process Methods 0.000 description 1
- 238000005859 coupling reaction Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 230000005684 electric field Effects 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 238000005036 potential barrier Methods 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
- H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
- H01L27/144—Devices controlled by radiation
Landscapes
- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Electromagnetism (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Computer Hardware Design (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Light Receiving Elements (AREA)
Abstract
An infrared detector (1) for detecting radiation of different wavelengths (e.g. 3 mu m and 10 mu m) comprises a number of detector sections (2, 3) connected in series, the sections being made operable separately by application of a control voltage to the selected section. The current flow through the series circuit is monitored, and the current level will be dominated by the photocarriers generated by the 3 mu m radiation or the 10 mu m radiation impinging on the detector, in dependence upon which of the sections is selected for operation. The detector may comprise a stack of alternating layers (5, 6; 8, 9) of semiconductor materials of different band gaps (e.g. AlGaAs and GaAs) forming a multiple quantum well structure. Alternatively, the detector may comprise a number of superlattice structures in series. In each case, the layer structure of each section determines the wavelength to which the section responds. <IMAGE>
Description
Radiation Detectors
This invention relates to radiation detectors, and particularly to detectors for infrared wavelengths.
The detection of an object in a static scene or in a moving scene by detecting thermal radiation from the object at lOpm wavelength is well-known. A number of detection devices have been proposed, including devices which involve the use of narrow bandgap
II-VI semiconductors, such as CdHgTe alloys. Such devices suffer from a number of problems. Firstly, it is difficult to grow crystals which are of satisfactory quality and which can sustain the various processing steps which are needed to fabricate useful devices.
Furthermore, wafer integration of these delicate devices with the semiconductor devices required for signal processing is difficult.
It has therefore been proposed to produce a long-wavelength infrared photo detector device based on the principle of inter-subband absorption in multiple quantum wells in III-V semiconductor devices.
Such devices have the advantages over the Group Il-Vi devices that (i) the materials system used, such as GaAs/AlGaAs, is more mature and the required signal processing devices are available, and (ii) the precise conditions for the absorption can be tailored by, for example, varying the width of the quantum wells and the aluminium composition in the barriers. Such devices operate only at a single radiation wavelength.
It is an object of the present invention to provide an
improved radiation detector which is capable of detecting radiation of a plurality of different wavelengths.
According to the invention there is provided a radiation detector comprising first and second radiation-responsive devices electrically connected together in series and operative to pass current therethrough in response to radiation impinging thereon, said first and second devices being responsive to first and second radiation wavelengths, respectively, which are different from each other, one or the other of said devices being selectable for operation, as required, by the application of a control voltage to that device.
Preferably, the first and second devices are formed as a single structure, which structure is preferably monolithic.
Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawing, in which
Figure 1 shows a schematic cross section of a two-frequency multiple quantum well radiation detector in accordance with the invention, and
Figure 2 shows a schematic cross section of a two-frequency superlattice radiation detector in accordance with the invention.
Referring to Figure 1, a first two-frequency radiation detector 1 comprises first and second multiple quantum well (MQW) structures 2 and 3, separated by a relatively thick n+ doped GaAs layer 4 of, say, at least 100nm thickness.
The MQW structure 2 comprises four GaAs layers 5 of 6nm thickness interleaved with five AlGaAs layers 6 of IOnm or greater thickness and of 23.5% Al composition. The thickness of each layer is such that the wells are not significantly intercoupled. This constitutes a detector for infrared radiation of 10pom wavelength.
The structure 2 is formed on a semi-insulating GaAs substrate 14, with an intervening n+ doped GaAs contact layer 7 of thickness greater than 100nm.
The MQW structure 3 comprises four GaAs layers 8 of 3.2nm thickness, interleaved with five AlGaAs layers 9 of lOnm or greater thickness and of 80% Al composition. This constitutes a detector for infrared radiation of 3pm wavelength.
A layer 10 of nf GaAs of thickness greater than 100nm is deposited over the upper AlGaAs layer, and an ohmic contact 11 is formed thereon. Ohmic contacts 12 and 13 are also provided on the
GaAs layers 7 and 4, respectively.
Each of the quantum wells is arranged so that the lowest confined state is bound and, due to doping, is occupied. The first excited state is arranged to have an extra energy of 0.12eV equivalent to the energy of 10pm radiation. This excited state is arranged to be close to the conduction band energy of the confining barrier. In other realisations, this energy may be just below or just above the barrier height. The barrier height is determined by the fractional
Al composition and is approximately given by 0.65 x 1.24 x X eV, where 1.24 is the factor by which the total bandgap of subscripts increases with X, and 0.65 being the proportion of this increase associated with the conduction band.The use of a simple parabolic bandstructure for
GaAs shows that a well width of 6.0nm and 23.5% Al composition in the barriers provides for the excited level to be coincident with the top of the barrier. The same calculation shows that a 3.2nm wide well with 80% Al composition in the barriers gives a structure in which the excited level is now 0.41eV above the lowest level, i.e. is equivalent to the energy of 3ym radiation, and still has its excited energy close to the top of the potential barrier.
In operation of the detector, a bias voltage is applied to the contacts 12 and 13 or to the contacts 13 and 11 and the total current through the structure is monitored. Depending upon whether the bias is applied across the structure 3 or the structure 2, the monitored current will be dominated by the photocarriers generated by the 3pm or the 10pm radiation impinging thereon.
Although four GaAs layers 5 and five AlGaAs layers 6 are provided in the above-described embodiment, any desired number of GaAs layers, from one upwards, may be used, provided that each GaAs layer is bounded by two AlGaAs layers.
Referring to Figure 2, a second two-frequency radiation detector comprises two superlattice structures 15 and 16, separated by an n+ doped GaAs collector layer 17, the structures being supported by a semi-insulating substrate 30.
The structure 15 comprises four or more periods of alternate n doped GaAs layers 18 of 70t thickness and undoped AlxGa1#As barrier layers 19 of 20t thickness. In the latter layers x = 0.3. The barrier layers 19 are sufficiently thin so that the adjacent GaAs layers 12 are strongly coupled. A layer 20 of AlxGal xAs of thickness greater than 1000 and in which x = 0.3, prevents transport between the lowest miniband and the collector layer. This structure constitutes a detector for 10pom wavelength radiation, calculated assuming a parabolic band structure. An n+AlxGa1#xAs contact layer 21 (where x#0.05) is interposed between the structure 15 and the substrate 30.
The structure 16 comprises a layer 22 of AlAs of thickness greater than 10nm followed by at least four periods of alternate n+ doped GaAs layers 23 of 30R thickness and undoped AlAs layers 24 of 200 thickness. The layer 22 ensures a low dark current by impeding conduction via the first miniband. This structure constitutes a detector for 3#m wavelength radiation. The highest energy miniband is arranged to have an energy near the bulk AlAs conduction band. A contact layer 25 of n+AlxGa1#xAs (where x#0.22) is deposited on the uppermost layer of the structure 16, followed by a contact layer 26 of n+GaAs.
In the structures 15 and 16 the maximum number of superlattice periods should not exceed the diffusion length in the upper miniband.
Ohmic contacts 27, 28 and 29 are formed on the layers 21, 17 and 26, respectively.
In operation of the detector, a bias voltage is applied to the contacts 27 and 28 or to the contacts 28 and 29, and the total current through the detector is monitored. Depending upon whether the bias is applied across the structure 15 or across the structure 16, the monitored current will be dominated by the photocarriers generated by the 10ym radiation or the 3#m radiation impinging thereon.
The latter embodiment using superlattices has some possible advantages over the multiple quantum well configuration. The superlattice configuration is more tolerant to variation in growth parameters than the MQW configuration, so the correct operating wavelength is more readily achieved. Furthermore, the superlattice configuration possibly has lower noise and more tailorable bandwidth than the MQW configuration.
It will be appreciated that each of the above-described embodiments provides an easily fabricated and easily operated two-frequency infrared detection. In order to change the frequency detected it is merely necessary to switch over the d.c. bias voltage from one MQW or superlattice structure to the other.
Although the detectors in the above-described embodiments are constructed to detect 3pm and 10pm wavelength radiation, it would be possible to construct detectors to detect radiation of other wavelengths.
Further MQW or superlattice structures could be added, to make the detector switchable between three or more frequencies.
Although a detector is conveniently fabricated as a single unit as described above, it would be possible to provide two or more separate sections, such as the structures 2 and 3 or the structures 15 and 16, either side-by-side on a substrate or even on separate substrates. The sections must, of course, be electrically connected in series.
Other semiconductor materials could be used for the layers 5, 6 and 8, 9 in the above embodiments, provided that the alternate layers have different bandgaps such that a sufficiently large conduction band discontinuity exists to support intersubband or interminiband transitions, as the case may be.
In order that the structures can function efficiently as detectors, the radiation must be coupled into the structures in such a way that there is a component of the electric field vector perpendicular to the planes of the layers, so that intersubband and interminiband absorption of the radiation can take place. The method of coupling the radiation into the structures, and the number of layers used, should be optimised to ensure efficient absorption, so as to obtain high responsivity of the device.
Claims (15)
1. A radiation detector comprising first and second radiation-responsive devices electrically connected together in series and operative to pass current therethrough in response to radiation impinging thereon, said first and second devices being responsive to first and second radiation wavelengths, respectively, which are different from each other, one or the other of said devices being selectable for operation, as required, by the application of a control voltage to that device.
2. A radiation detector as claimed in Claim 1, wherein said first and second radiation-responsive devices together constitute a single structure.
3. A radiation detector as claimed in Claim 1 or Claim 2, wherein said first and second radiation-responsive devices are of monolithic construction.
4. A radiation detector as claimed in any preceding claim, wherein said first radiation-responsive device comprises a multiple quantum well structure.
5. A radiation detector as claimed in any preceding claim, wherein said second radiation-responsive device comprises a multiple quantum well structure.
6. A radiation detector as claimed in Claim 4 or Claim 5, wherein the or each multiple quantum well structure comprises alternating layers of semiconductor materials having mutually different band gaps whereby a sufficiently large conduction band discontinuity exists to support intersubband transitions.
7. A radiation detector as claimed in Claim 6, wherein the or each multiple quantum well structure comprises layers of AlGaAs interleaved with layers of GaAs.
8. A radiation detector as claimed in Claim 7, comprising two of said multiple quantum well structures separated by a layer of n+ doped
AlGaAs.
9. A radiation detector as claimed in any one of Claims 1-3, wherein said first radiation-responsive device comprises a first superlattice structure.
10. A radiation detector as claimed in any one of Claims 1, 2, 3 or 9 wherein said second radiation-responsive device comprises a second superlattice structure.
11. A radiation detector as claimed in Claim 9 or Claim 10, wherein the or each superlattice structure comprises alternating layers of semiconductor materials having mutually different band gaps whereby a sufficiently large conduction band discontinuity exists to support interminiband transitions.
12. A radiation detector as claimed in Claim 11, wherein said first superlattice structure comprises at least four periods of alternate layers of n doped GaAs and undoped AlxGa1#xAs.
13. A radiation detector as claimed in Claim 12, wherein x = 0.3.
14. A radiation detector as claimed in Claim 11, wherein said second superlattice structure comprises at least four periods of alternate layers of n doped GaAs and undoped AlAs.
15. A radiation detector substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawing.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8904649A GB2228824A (en) | 1989-03-01 | 1989-03-01 | Radiation detectors |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8904649A GB2228824A (en) | 1989-03-01 | 1989-03-01 | Radiation detectors |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB8904649D0 GB8904649D0 (en) | 1989-09-13 |
| GB2228824A true GB2228824A (en) | 1990-09-05 |
Family
ID=10652524
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8904649A Withdrawn GB2228824A (en) | 1989-03-01 | 1989-03-01 | Radiation detectors |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2228824A (en) |
Cited By (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5329136A (en) * | 1993-04-30 | 1994-07-12 | At&T Bell Laboratories | Voltage-tunable photodetector |
| US5479032A (en) * | 1994-07-21 | 1995-12-26 | Trustees Of Princeton University | Multiwavelength infrared focal plane array detector |
| US5539206A (en) * | 1995-04-20 | 1996-07-23 | Loral Vought Systems Corporation | Enhanced quantum well infrared photodetector |
| US5552603A (en) * | 1994-09-15 | 1996-09-03 | Martin Marietta Corporation | Bias and readout for multicolor quantum well detectors |
| FR2766919A1 (en) * | 1997-07-30 | 1999-02-05 | Schlumberger Services Petrol | Hydrostatic pressure and-or temperature transducer useful for oil well pressure sensor |
| US6054718A (en) * | 1998-03-31 | 2000-04-25 | Lockheed Martin Corporation | Quantum well infrared photocathode having negative electron affinity surface |
| DE102005001280A1 (en) * | 2004-09-30 | 2006-04-13 | Osram Opto Semiconductors Gmbh | radiation detector |
| US7525083B2 (en) | 2004-09-30 | 2009-04-28 | Osram Opto Semiconductors Gmbh | Radiation detector with an epitaxially grown semiconductor body |
| WO2009094966A2 (en) | 2008-01-31 | 2009-08-06 | Osram Opto Semiconductors Gmbh | Radiation receptor, and method for the production thereof |
Citations (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1220333A (en) * | 1967-08-09 | 1971-01-27 | Parnall & Sons Ltd | Improvements for electrical circuits |
| GB1290637A (en) * | 1970-06-29 | 1972-09-27 | ||
| GB1414169A (en) * | 1971-10-05 | 1975-11-19 | Eastman Kodak Co | Photoelectric transducer |
| GB1519466A (en) * | 1974-09-17 | 1978-07-26 | Northern Telecom Ltd | Photodiode detector |
| GB2030359A (en) * | 1978-07-21 | 1980-04-02 | Sumitomo Electric Industries | Integrated multi-photodiodes |
| US4238760A (en) * | 1978-10-06 | 1980-12-09 | Recognition Equipment Incorporated | Multi-spectrum photodiode devices |
| GB2082763A (en) * | 1980-07-31 | 1982-03-10 | Zeiss Jena Veb Carl | Infrared-sensitive Multiple Photon Detector |
| GB2136202A (en) * | 1983-03-02 | 1984-09-12 | Int Standard Electric Corp | Photodiode |
| US4513305A (en) * | 1982-12-06 | 1985-04-23 | Gte Laboratories Incorporated | Multi-wavelength demultiplexer for fiber optical communication |
| EP0146375A2 (en) * | 1983-12-19 | 1985-06-26 | Kabushiki Kaisha Toshiba | Visible/infrared imaging device with stacked cell structure |
| GB2164792A (en) * | 1984-07-24 | 1986-03-26 | Sharp Kk | A semiconductor device |
| US4656109A (en) * | 1984-09-19 | 1987-04-07 | Fuji Electric Co., Ltd. | Layered solid state color photosensitive device |
-
1989
- 1989-03-01 GB GB8904649A patent/GB2228824A/en not_active Withdrawn
Patent Citations (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1220333A (en) * | 1967-08-09 | 1971-01-27 | Parnall & Sons Ltd | Improvements for electrical circuits |
| GB1290637A (en) * | 1970-06-29 | 1972-09-27 | ||
| GB1414169A (en) * | 1971-10-05 | 1975-11-19 | Eastman Kodak Co | Photoelectric transducer |
| GB1519466A (en) * | 1974-09-17 | 1978-07-26 | Northern Telecom Ltd | Photodiode detector |
| GB2030359A (en) * | 1978-07-21 | 1980-04-02 | Sumitomo Electric Industries | Integrated multi-photodiodes |
| US4238760A (en) * | 1978-10-06 | 1980-12-09 | Recognition Equipment Incorporated | Multi-spectrum photodiode devices |
| GB2082763A (en) * | 1980-07-31 | 1982-03-10 | Zeiss Jena Veb Carl | Infrared-sensitive Multiple Photon Detector |
| US4513305A (en) * | 1982-12-06 | 1985-04-23 | Gte Laboratories Incorporated | Multi-wavelength demultiplexer for fiber optical communication |
| GB2136202A (en) * | 1983-03-02 | 1984-09-12 | Int Standard Electric Corp | Photodiode |
| EP0146375A2 (en) * | 1983-12-19 | 1985-06-26 | Kabushiki Kaisha Toshiba | Visible/infrared imaging device with stacked cell structure |
| GB2164792A (en) * | 1984-07-24 | 1986-03-26 | Sharp Kk | A semiconductor device |
| US4656109A (en) * | 1984-09-19 | 1987-04-07 | Fuji Electric Co., Ltd. | Layered solid state color photosensitive device |
Cited By (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5329136A (en) * | 1993-04-30 | 1994-07-12 | At&T Bell Laboratories | Voltage-tunable photodetector |
| US5479032A (en) * | 1994-07-21 | 1995-12-26 | Trustees Of Princeton University | Multiwavelength infrared focal plane array detector |
| US5552603A (en) * | 1994-09-15 | 1996-09-03 | Martin Marietta Corporation | Bias and readout for multicolor quantum well detectors |
| US5539206A (en) * | 1995-04-20 | 1996-07-23 | Loral Vought Systems Corporation | Enhanced quantum well infrared photodetector |
| FR2766919A1 (en) * | 1997-07-30 | 1999-02-05 | Schlumberger Services Petrol | Hydrostatic pressure and-or temperature transducer useful for oil well pressure sensor |
| US6054718A (en) * | 1998-03-31 | 2000-04-25 | Lockheed Martin Corporation | Quantum well infrared photocathode having negative electron affinity surface |
| DE102005001280A1 (en) * | 2004-09-30 | 2006-04-13 | Osram Opto Semiconductors Gmbh | radiation detector |
| US7525083B2 (en) | 2004-09-30 | 2009-04-28 | Osram Opto Semiconductors Gmbh | Radiation detector with an epitaxially grown semiconductor body |
| DE102005001280B4 (en) | 2004-09-30 | 2022-03-03 | OSRAM Opto Semiconductors Gesellschaft mit beschränkter Haftung | radiation detector |
| WO2009094966A2 (en) | 2008-01-31 | 2009-08-06 | Osram Opto Semiconductors Gmbh | Radiation receptor, and method for the production thereof |
| WO2009094966A3 (en) * | 2008-01-31 | 2009-10-08 | Osram Opto Semiconductors Gmbh | Radiation receptor, and method for the production of a radiation receptor |
| US8659107B2 (en) | 2008-01-31 | 2014-02-25 | Osram Opto Semiconductors Gmbh | Radiation receiver and method of producing a radiation receiver |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8904649D0 (en) | 1989-09-13 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |