CA1177943A - Photodetector sensitive to close-range infrareds - Google Patents
Photodetector sensitive to close-range infraredsInfo
- Publication number
- CA1177943A CA1177943A CA000397447A CA397447A CA1177943A CA 1177943 A CA1177943 A CA 1177943A CA 000397447 A CA000397447 A CA 000397447A CA 397447 A CA397447 A CA 397447A CA 1177943 A CA1177943 A CA 1177943A
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- photodetector
- value
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- substrate
- type
- Prior art date
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- 239000000758 substrate Substances 0.000 claims abstract description 15
- 230000035945 sensitivity Effects 0.000 claims abstract description 4
- 229910052782 aluminium Inorganic materials 0.000 claims description 5
- 229910052738 indium Inorganic materials 0.000 claims description 5
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 claims description 4
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 4
- 229910052796 boron Inorganic materials 0.000 claims description 4
- 239000013078 crystal Substances 0.000 claims description 4
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 claims description 4
- BDOSMKKIYDKNTQ-UHFFFAOYSA-N cadmium atom Chemical compound [Cd] BDOSMKKIYDKNTQ-UHFFFAOYSA-N 0.000 claims description 3
- 229910052793 cadmium Inorganic materials 0.000 claims description 2
- 239000000969 carrier Substances 0.000 claims description 2
- 238000002513 implantation Methods 0.000 claims description 2
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 claims description 2
- 229910052753 mercury Inorganic materials 0.000 claims description 2
- 230000003595 spectral effect Effects 0.000 claims description 2
- 238000009792 diffusion process Methods 0.000 claims 2
- 230000005855 radiation Effects 0.000 description 12
- 238000005513 bias potential Methods 0.000 description 4
- 230000015556 catabolic process Effects 0.000 description 4
- 238000000034 method Methods 0.000 description 4
- 239000002674 ointment Substances 0.000 description 3
- 230000003287 optical effect Effects 0.000 description 3
- 229910000645 Hg alloy Inorganic materials 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 239000004411 aluminium Substances 0.000 description 2
- 239000013307 optical fiber Substances 0.000 description 2
- 229910000925 Cd alloy Inorganic materials 0.000 description 1
- 229910001215 Te alloy Inorganic materials 0.000 description 1
- 238000003486 chemical etching Methods 0.000 description 1
- 229910052681 coesite Inorganic materials 0.000 description 1
- 229910052906 cristobalite Inorganic materials 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000005684 electric field Effects 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 230000000873 masking effect Effects 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000009740 moulding (composite fabrication) Methods 0.000 description 1
- 230000006798 recombination Effects 0.000 description 1
- 238000005215 recombination Methods 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 235000012239 silicon dioxide Nutrition 0.000 description 1
- 229910052682 stishovite Inorganic materials 0.000 description 1
- PORWMNRCUJJQNO-UHFFFAOYSA-N tellurium atom Chemical compound [Te] PORWMNRCUJJQNO-UHFFFAOYSA-N 0.000 description 1
- 229910052905 tridymite Inorganic materials 0.000 description 1
- 230000003245 working effect Effects 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices 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; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/08—Semiconductor devices 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; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
- H01L31/10—Semiconductor devices 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; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors characterised by potential barriers, e.g. phototransistors
- H01L31/101—Devices sensitive to infrared, visible or ultraviolet radiation
- H01L31/102—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier
- H01L31/103—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier the potential barrier being of the PN homojunction type
- H01L31/1032—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier the potential barrier being of the PN homojunction type the devices comprising active layers formed only by AIIBVI compounds, e.g. HgCdTe IR photodiodes
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices 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; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/0248—Semiconductor devices 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; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
- H01L31/0256—Semiconductor devices 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; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by the material
- H01L31/0264—Inorganic materials
- H01L31/0296—Inorganic materials including, apart from doping material or other impurities, only AIIBVI compounds, e.g. CdS, ZnS, HgCdTe
- H01L31/02966—Inorganic materials including, apart from doping material or other impurities, only AIIBVI compounds, e.g. CdS, ZnS, HgCdTe including ternary compounds, e.g. HgCdTe
Landscapes
- Physics & Mathematics (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- Electromagnetism (AREA)
- General Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Computer Hardware Design (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Power Engineering (AREA)
- Chemical & Material Sciences (AREA)
- Inorganic Chemistry (AREA)
- Light Receiving Elements (AREA)
- Photometry And Measurement Of Optical Pulse Characteristics (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
In a photodetector having its maximum sensitivity between 0.8 and 2 µm, comprising a P type substrate of Hg1-x Cdx Te, x being selected within a range extending from 0.4 to 0.9, and a doped N-type zone formed on the substrate, the resulting function being of the P-N type, characterized in that x is selected as a function of the desired current gain.
In a photodetector having its maximum sensitivity between 0.8 and 2 µm, comprising a P type substrate of Hg1-x Cdx Te, x being selected within a range extending from 0.4 to 0.9, and a doped N-type zone formed on the substrate, the resulting function being of the P-N type, characterized in that x is selected as a function of the desired current gain.
Description
il~717~43 The present invention relates to a photodetector whose maximum sensitivity is between 0.8 and 2 ~m, comprising a P type substrate of Hg1 x Cd Te, and an N type zone for-ming a P-N junction with the substrate.
In photodetectors, it may be desirable that the response ti~e be as short as possible, particularly when such detectors are used for detecting the light signals transmitted by optical fibres, the digital rate in this type of link being extremely high.
It is known that the attenuation in optical fibre transmi~3ion is minimum for two values of the wave-length of the transmitted signal, namely 1.3 jum and 1.6 ~um.
Applicants'French Patent Application No. 80 16788, published under No. 2 488 o48 on February 5, 1982, already relates to photodetectors which, by the use of a P type substrate of Hg1 Cd Te, have a very short response time and are sensitive to the above wave-lengths, the molar fraction x being selected within a range of from 0.4 to 0.9, as a function of the wave-length to be received.
However, such photodectors do not necessarily fur-nish, on the one hand, a considerable output current and, on the other hand, a very high signal-*o-noise ratio. In other words, as the light intensity passing in the optical fibres is weak, the current gain of the dectectors, i.e. the ratio, at a given wave-length, between the light intensity received and the electric current created, may not be sufficient.
A process which partially overcomes this drawback is known, whereby the photodector is inversely biased, under a high voltage, in order to place its working in the break-down region.
.,,~.~
~1'7'79~3 In fact, this high bias is possible since the~unction useæ a very weakly doped ~ubstrate and therefore ha~ a weak capacitance, so that the time constant, or the response time, o~ the detector i8 weak especially at high inverse potentials.
However, one drawback of this prooes~ is that the wor-king point, due to thls high lnverse bias, is near the un-controlled breakdown voltage, ln other words near the break-down voltage of the ~unction.
This inverse bia~ potential, of the ordor of a few tens or hundred~ of volts, is furnished by a more or les~ complex or expensive BUpp~y neces~itating a ~ource of energy.
It is an object of the present invention to overcome these drawbacks and to propose a photodetector having a high gain, and consequently being able to operate under a weak inverse bias potential.
To thi~ end, the present invention relates to a photo-detector having its maximum sensitivity bet~een 0.8 and 2 ym, comprising a P type sub~trate of Hg1 x CdX ~e, x being selec-t~d within a rangc extending from 0~4 to 0.9, and a doped N-type zone formed on the ~ubstrate, the resulting Junctionbeing of the P-N type, wheroin x is selected a~ a funotion of the desired current gain.
It is known that ~uch photodetectors present the pheno-menon of the ~pectral respon~e, and ~ore particularly the cut-oif wavo-l~ngth, being dopendant on s.
~ hus, as the value o~ x i8 already imposed a priori by the choice of the desired wave-length, it would appear lnof-~cctual to soek to discover whether anothor phenomenon, al80 depending on the value o~ x, could not be the origin of a greater electric output curront.
1~7'~943 Applicants nevertheless sought to di~cover whether the current gain, in other words the figure of merit of the junc-tion, likewise advantageously depended on ~. Applicants not only demon~trated thi~ phenomenon, namely that the figure of merit, of which the value involves that of the output current, effectively depends on the molar fraction x, but they also obæerved that the value of x, propibious to a greater current, was very close to the value optimali~ing the detection of a oertain wave-length.
More particularly, Applicants have shown that the figure o~ merit, and therefore the output current, reached its maxi-mum for a value of x close to but different from ths one which corresponds~to the optimal dete¢tion, with a short response time, of a radiation o* wave-length of t.3 pm.
The invention will be more readily understood on reading the iollowing description with reference to the accompanying drawings, in which s - Fig~. 1 to 7 illu~trate the dif~erent pha~es of the procsss for manufaoturing the photodetector according to the invention;
- Fig. 8 shows the ~pectral re~ponse ourves of the detec-tor of the invention, for several value~ of the inverse bias;
- Fig, 9 showsJ on the one hand, the curve of the cut-off wave-le~gth and, on the other hand, the vPlue of the figure o~ merit, function~ of the molar fraction of the substrate of the detector according to the invention, and - Fig. 10 show~ the curve of the current gain of the de-tector according to the invention as a function of the inverse bias voltage, for the chosen value of ~.
~0 Referring now to the drawings, the detector shown therein _ ~ _ 11~7'~9~3 is well adapted for a wave-length close to 1.3 ~m. It compri-ses a substrate constituted by an alloy of mercury, cadmium and tellurium, Hg1 x CdX Te in which the molar fraction x is between 0.4 and 0.9 as indicated in French Application No 80 16788, published under No. 2 488 040.
To mam1facture the detector of the invention, one starts with P type substrate 1 (cf. Fig. 1), formed by a crystal of Hg1 CdX Te of very high purity, therefore having a very low concentration of P carriers, of the order of 1015/cm3. Such a crystal may be obtained, for example, by the method described in an article by R. Triboulet, entitled "Cd Te and Cd Te:Hg alloys crystal growth using stoichio-metric and off-stoichiometric zone passing techniques", which appeared in the Revue de Physique Appliquée of February 1977.
On the substrate 1 is deposited a layer 2 ~f Cd Te, for example by cathode sputerring. A masking layer 3, preferably o ZnS, SiO or SiO2, is then deposited on layer 2 (Fig. 2). At least one opening 10 is then made in the layers 2 and 3, so as to lay bare part of the surface la of the substrate 1 (Fig. 3). A planar P-N junction i9 then made by a firYt diffu~ion in the substrate 1 of an element such as cadmium or mercury or of an impurity such as aluminium, indium or boron (arrow 5, Fig. 4).
A zone 6 of N type is thus obtained, with a doping of about 10 atomsJcm3, wnich forms a junction 7 with the substrate P.
However, with a view to reducing the curvature of this junction 7 at its ends, and therefore to reducing the valus of the electric field, and consequently the risk of breakdown in these regions, one of the same elements may previously be 11~;J';J943 di~fused, unde~ th~ ~ame oonditions, in a¢cordance with the so-cal:Led keeper ring technique (Fig. 5), in order finally to obt~n 8 zone 8 o~ ~ type with a larger curv~ture.
Another procese which may be used to form the N 20ne is the ionic implantation of atoms having, after appropriate ~nnealing, an electrical N type activity~ such as atoms of indium In, aluminium Al or boron B.
~ layer 4 of the ~ame nature as layer 3 i~ then deposited over the whole suriace, then an openlng 9 i9 made in layer 4 (Fig. 6) by chemical etching and this opening i8 filled with a conducting metal such a~ Al or In in order to make a con-tact 10 ~Fig. 7).
The above-de~cribed detector ~ u~ed ~or detecting radia-tion in the near infrared.
The choice of the value of the molar fraction ~ depends on the following con~iderations.
To define the structure o~ the electronic bands, the conduction band, ~orbidden band and valence band model ma~ be used.
The arrival o~ a photon of the radiation received create~, ii its energy i9 ~ufficient, a hole-electron palr which parti-cipateo ln a current proportional to the lnoident ~lu~.
It wlll be readlly understood that, when the wave-length of the radiation exceeds a oertain threshold, the energy o~
the photons, proportional to ~ no longer su~ficient to create hole-electron pair~0 This i~ why, for a given value o~ ~, i.e. for a glven value ~E o~ the width o~ the forbidden band, there is a cut off wave-length ~c~ ~uch that, when the radiation has a wave-length ;~ > ~ c~ no current is oreated in the ~unotion, llt7 ~9,~3 this explaining the appearance of the curve~ of Fi~. 8, which represent the response ~ of the detector, i.e. the ratio bet-ween the current created and the light inten~ity received, as a fl~ction of the wave-length ~ of the radiation received, ~or three values of the blas potential V of the ~nction, and a predetermined value of x. It i8 noted that, in the e~ample of Fig. 8, the current gain is already Gonsiderable for a weak inverse bias.
The curve 100 of Fig. 9 represents the cut-o~ wave-tO length Ao as a function o~ ~, in lum.
~ hus, in order optimally to receive a radiation o~ wave-len~th 1.3 ~m, the cut-oii wave-lsngth must be greater than 1.~ pm, but preferably falrly near ae indicated by the spec-tral response curves (Fig. 8)~
Thus, to detect a radiation o~ a wave-length o~ 1.3 pm, which corresponds to a mlnimum attenuation in the optical fi-bree, the optimum value o~ ~ would be near 0.7, considering the curve 100 of Fig. 9. However, the above-mentioned draw-back, namely the weak output current of the detector, would no~ nece~sarily be overcome.
. Another band, a so-called epin-orblt band, exi~ts ln the etructure o~ the electronic bands o~ the ~emlconduotor envi~aged.
It has been found that the energy di~erenee ~B' between the ~pin-orbit band and the valence band was capable, depen-ding o~ its value, to play a role concerning the generation~-recombi~ations of hole~electrons created by the photonsO More partioularl~, for ~ wide range o~ values of ~ ' i8 15 to 10 times greater than ~R and, in thi~ ca~e, the spin-orbit band ha~ only a slight influence on the generations-recombi-il~7'79~3 nations o~ the hole-electrone. However, for certain values of ~, between about 0.6 and 0.8; the value o~ ~' is ~airly close to that of ~, both having for order o~ magnitude 0.9 eV. It is readlly appreciated that the properties o~
creation and of recombination o~ the hole-electron pairs will then be substa~tially di~ferent from those oorresponding to the model which does not take into account the epln-orbit band.
The phenomenon is as ~ollow~. When the spin-orbit band has little or non influenoe on the photoelectrio phenomenon, a current of electron~ and a current o~ holes, which are substantially equal, i.e. ionisation coe~ficients and ~ of ~ubstantially equal values, are created by the radiation received.
However, when ~ iæ in a range extending ~rom about 0.6 to 0.8, the influencer1o~ the spin-orbit band i8 real and very dif~erent ionisation coefficients a and ~ are obtained. In ~act, the ratio l~ proportional to the term P = (1 _ ~ ) 2 , called ~igure oi merit, illustrated by ~B
curve 101 of Fig. 9, which repre~ents the value of the figure oi merit F as a ~u~ction o~ the oompo~ition o~ the sub~trate, i.e. of ~. It i~ observed that thi~ ~alue pa~ses throu~h a ma~imum ~or a value o~ ~ subatantlally equal to 0.67 and that it ie greater than 10 when ~ is included between 0.55 and 0.85.
The value~ o~ ~ and ~ are then ~ery different, the ourrent gain as a ~unction o~ the bias potential i8 better controlled and the signal-to-noise ratio ia higher.
It i~ therefore necessary to choo~e, on the one hand, a value of ~ such that the worth ~actor and consequently the output current are high, and, on the other hand, a value of 11'7'7943 optimali~Qing the reception of a radiation o~ wave-length 1.3 pm, optimal value ~or optical fibre transmis~lon.
The two most satisfactory value~o~ ~, one for the cur-rent, the other for the wave-length, are different.
The present invention therefore relates to a detector capable both o~ detecting a radiation of wave-length o~ 1.3 ~m and o~ furnishing a high output current, i.e. havlng a high ourrent gain, without having to apply a considerable inverse bia6 potential. Thi~ charaoteri~tic i~ also to be found on the curve o~ Fig. 10, representing the gain G defined herein~
above, function of the inverse bias potential V, for the chosen value o~ ~. It is ob~erved that thi~ gain begins to increase for a voltage of about -4 or -5 volts, to reach a value of 30, which is more than ~ati~actory, for a value o~
V of the order of -10 volt~, con~idered as weak.
For x = 0.67, which therefore corresponds to a maximum gain, the cut-o~f wave-length ~ c i~ equal to t.43 ~m, whlch length is per~ectly suitable for receiving a radiation of wave-length of 1.3 ~.
The characteri~tice o~ the photo-detectors are advanta-geou~ly a~ ~ollow~s - Active area s 1 x 10 4 cm2 - Inverse bias potential V : 10 volts - Current gain ~ 2 30 - Saturation current : < 1nA
- Dark current (V = -10V) : ~ 10~A
- Total capacitance (V = -10V) s ~ lpF
- Junction capacitance (V = -10V~ s < 0.2 pP
- Resi~tance-area product (V=Ov) : 6 ~ 104 Q ~cm2 - Response in current ( ~ = 1.3 ~m) : > 0.5 A/w - Operational temperature : 300E.
In photodetectors, it may be desirable that the response ti~e be as short as possible, particularly when such detectors are used for detecting the light signals transmitted by optical fibres, the digital rate in this type of link being extremely high.
It is known that the attenuation in optical fibre transmi~3ion is minimum for two values of the wave-length of the transmitted signal, namely 1.3 jum and 1.6 ~um.
Applicants'French Patent Application No. 80 16788, published under No. 2 488 o48 on February 5, 1982, already relates to photodetectors which, by the use of a P type substrate of Hg1 Cd Te, have a very short response time and are sensitive to the above wave-lengths, the molar fraction x being selected within a range of from 0.4 to 0.9, as a function of the wave-length to be received.
However, such photodectors do not necessarily fur-nish, on the one hand, a considerable output current and, on the other hand, a very high signal-*o-noise ratio. In other words, as the light intensity passing in the optical fibres is weak, the current gain of the dectectors, i.e. the ratio, at a given wave-length, between the light intensity received and the electric current created, may not be sufficient.
A process which partially overcomes this drawback is known, whereby the photodector is inversely biased, under a high voltage, in order to place its working in the break-down region.
.,,~.~
~1'7'79~3 In fact, this high bias is possible since the~unction useæ a very weakly doped ~ubstrate and therefore ha~ a weak capacitance, so that the time constant, or the response time, o~ the detector i8 weak especially at high inverse potentials.
However, one drawback of this prooes~ is that the wor-king point, due to thls high lnverse bias, is near the un-controlled breakdown voltage, ln other words near the break-down voltage of the ~unction.
This inverse bia~ potential, of the ordor of a few tens or hundred~ of volts, is furnished by a more or les~ complex or expensive BUpp~y neces~itating a ~ource of energy.
It is an object of the present invention to overcome these drawbacks and to propose a photodetector having a high gain, and consequently being able to operate under a weak inverse bias potential.
To thi~ end, the present invention relates to a photo-detector having its maximum sensitivity bet~een 0.8 and 2 ym, comprising a P type sub~trate of Hg1 x CdX ~e, x being selec-t~d within a rangc extending from 0~4 to 0.9, and a doped N-type zone formed on the ~ubstrate, the resulting Junctionbeing of the P-N type, wheroin x is selected a~ a funotion of the desired current gain.
It is known that ~uch photodetectors present the pheno-menon of the ~pectral respon~e, and ~ore particularly the cut-oif wavo-l~ngth, being dopendant on s.
~ hus, as the value o~ x i8 already imposed a priori by the choice of the desired wave-length, it would appear lnof-~cctual to soek to discover whether anothor phenomenon, al80 depending on the value o~ x, could not be the origin of a greater electric output curront.
1~7'~943 Applicants nevertheless sought to di~cover whether the current gain, in other words the figure of merit of the junc-tion, likewise advantageously depended on ~. Applicants not only demon~trated thi~ phenomenon, namely that the figure of merit, of which the value involves that of the output current, effectively depends on the molar fraction x, but they also obæerved that the value of x, propibious to a greater current, was very close to the value optimali~ing the detection of a oertain wave-length.
More particularly, Applicants have shown that the figure o~ merit, and therefore the output current, reached its maxi-mum for a value of x close to but different from ths one which corresponds~to the optimal dete¢tion, with a short response time, of a radiation o* wave-length of t.3 pm.
The invention will be more readily understood on reading the iollowing description with reference to the accompanying drawings, in which s - Fig~. 1 to 7 illu~trate the dif~erent pha~es of the procsss for manufaoturing the photodetector according to the invention;
- Fig. 8 shows the ~pectral re~ponse ourves of the detec-tor of the invention, for several value~ of the inverse bias;
- Fig, 9 showsJ on the one hand, the curve of the cut-off wave-le~gth and, on the other hand, the vPlue of the figure o~ merit, function~ of the molar fraction of the substrate of the detector according to the invention, and - Fig. 10 show~ the curve of the current gain of the de-tector according to the invention as a function of the inverse bias voltage, for the chosen value of ~.
~0 Referring now to the drawings, the detector shown therein _ ~ _ 11~7'~9~3 is well adapted for a wave-length close to 1.3 ~m. It compri-ses a substrate constituted by an alloy of mercury, cadmium and tellurium, Hg1 x CdX Te in which the molar fraction x is between 0.4 and 0.9 as indicated in French Application No 80 16788, published under No. 2 488 040.
To mam1facture the detector of the invention, one starts with P type substrate 1 (cf. Fig. 1), formed by a crystal of Hg1 CdX Te of very high purity, therefore having a very low concentration of P carriers, of the order of 1015/cm3. Such a crystal may be obtained, for example, by the method described in an article by R. Triboulet, entitled "Cd Te and Cd Te:Hg alloys crystal growth using stoichio-metric and off-stoichiometric zone passing techniques", which appeared in the Revue de Physique Appliquée of February 1977.
On the substrate 1 is deposited a layer 2 ~f Cd Te, for example by cathode sputerring. A masking layer 3, preferably o ZnS, SiO or SiO2, is then deposited on layer 2 (Fig. 2). At least one opening 10 is then made in the layers 2 and 3, so as to lay bare part of the surface la of the substrate 1 (Fig. 3). A planar P-N junction i9 then made by a firYt diffu~ion in the substrate 1 of an element such as cadmium or mercury or of an impurity such as aluminium, indium or boron (arrow 5, Fig. 4).
A zone 6 of N type is thus obtained, with a doping of about 10 atomsJcm3, wnich forms a junction 7 with the substrate P.
However, with a view to reducing the curvature of this junction 7 at its ends, and therefore to reducing the valus of the electric field, and consequently the risk of breakdown in these regions, one of the same elements may previously be 11~;J';J943 di~fused, unde~ th~ ~ame oonditions, in a¢cordance with the so-cal:Led keeper ring technique (Fig. 5), in order finally to obt~n 8 zone 8 o~ ~ type with a larger curv~ture.
Another procese which may be used to form the N 20ne is the ionic implantation of atoms having, after appropriate ~nnealing, an electrical N type activity~ such as atoms of indium In, aluminium Al or boron B.
~ layer 4 of the ~ame nature as layer 3 i~ then deposited over the whole suriace, then an openlng 9 i9 made in layer 4 (Fig. 6) by chemical etching and this opening i8 filled with a conducting metal such a~ Al or In in order to make a con-tact 10 ~Fig. 7).
The above-de~cribed detector ~ u~ed ~or detecting radia-tion in the near infrared.
The choice of the value of the molar fraction ~ depends on the following con~iderations.
To define the structure o~ the electronic bands, the conduction band, ~orbidden band and valence band model ma~ be used.
The arrival o~ a photon of the radiation received create~, ii its energy i9 ~ufficient, a hole-electron palr which parti-cipateo ln a current proportional to the lnoident ~lu~.
It wlll be readlly understood that, when the wave-length of the radiation exceeds a oertain threshold, the energy o~
the photons, proportional to ~ no longer su~ficient to create hole-electron pair~0 This i~ why, for a given value o~ ~, i.e. for a glven value ~E o~ the width o~ the forbidden band, there is a cut off wave-length ~c~ ~uch that, when the radiation has a wave-length ;~ > ~ c~ no current is oreated in the ~unotion, llt7 ~9,~3 this explaining the appearance of the curve~ of Fi~. 8, which represent the response ~ of the detector, i.e. the ratio bet-ween the current created and the light inten~ity received, as a fl~ction of the wave-length ~ of the radiation received, ~or three values of the blas potential V of the ~nction, and a predetermined value of x. It i8 noted that, in the e~ample of Fig. 8, the current gain is already Gonsiderable for a weak inverse bias.
The curve 100 of Fig. 9 represents the cut-o~ wave-tO length Ao as a function o~ ~, in lum.
~ hus, in order optimally to receive a radiation o~ wave-len~th 1.3 ~m, the cut-oii wave-lsngth must be greater than 1.~ pm, but preferably falrly near ae indicated by the spec-tral response curves (Fig. 8)~
Thus, to detect a radiation o~ a wave-length o~ 1.3 pm, which corresponds to a mlnimum attenuation in the optical fi-bree, the optimum value o~ ~ would be near 0.7, considering the curve 100 of Fig. 9. However, the above-mentioned draw-back, namely the weak output current of the detector, would no~ nece~sarily be overcome.
. Another band, a so-called epin-orblt band, exi~ts ln the etructure o~ the electronic bands o~ the ~emlconduotor envi~aged.
It has been found that the energy di~erenee ~B' between the ~pin-orbit band and the valence band was capable, depen-ding o~ its value, to play a role concerning the generation~-recombi~ations of hole~electrons created by the photonsO More partioularl~, for ~ wide range o~ values of ~ ' i8 15 to 10 times greater than ~R and, in thi~ ca~e, the spin-orbit band ha~ only a slight influence on the generations-recombi-il~7'79~3 nations o~ the hole-electrone. However, for certain values of ~, between about 0.6 and 0.8; the value o~ ~' is ~airly close to that of ~, both having for order o~ magnitude 0.9 eV. It is readlly appreciated that the properties o~
creation and of recombination o~ the hole-electron pairs will then be substa~tially di~ferent from those oorresponding to the model which does not take into account the epln-orbit band.
The phenomenon is as ~ollow~. When the spin-orbit band has little or non influenoe on the photoelectrio phenomenon, a current of electron~ and a current o~ holes, which are substantially equal, i.e. ionisation coe~ficients and ~ of ~ubstantially equal values, are created by the radiation received.
However, when ~ iæ in a range extending ~rom about 0.6 to 0.8, the influencer1o~ the spin-orbit band i8 real and very dif~erent ionisation coefficients a and ~ are obtained. In ~act, the ratio l~ proportional to the term P = (1 _ ~ ) 2 , called ~igure oi merit, illustrated by ~B
curve 101 of Fig. 9, which repre~ents the value of the figure oi merit F as a ~u~ction o~ the oompo~ition o~ the sub~trate, i.e. of ~. It i~ observed that thi~ ~alue pa~ses throu~h a ma~imum ~or a value o~ ~ subatantlally equal to 0.67 and that it ie greater than 10 when ~ is included between 0.55 and 0.85.
The value~ o~ ~ and ~ are then ~ery different, the ourrent gain as a ~unction o~ the bias potential i8 better controlled and the signal-to-noise ratio ia higher.
It i~ therefore necessary to choo~e, on the one hand, a value of ~ such that the worth ~actor and consequently the output current are high, and, on the other hand, a value of 11'7'7943 optimali~Qing the reception of a radiation o~ wave-length 1.3 pm, optimal value ~or optical fibre transmis~lon.
The two most satisfactory value~o~ ~, one for the cur-rent, the other for the wave-length, are different.
The present invention therefore relates to a detector capable both o~ detecting a radiation of wave-length o~ 1.3 ~m and o~ furnishing a high output current, i.e. havlng a high ourrent gain, without having to apply a considerable inverse bia6 potential. Thi~ charaoteri~tic i~ also to be found on the curve o~ Fig. 10, representing the gain G defined herein~
above, function of the inverse bias potential V, for the chosen value o~ ~. It is ob~erved that thi~ gain begins to increase for a voltage of about -4 or -5 volts, to reach a value of 30, which is more than ~ati~actory, for a value o~
V of the order of -10 volt~, con~idered as weak.
For x = 0.67, which therefore corresponds to a maximum gain, the cut-o~f wave-length ~ c i~ equal to t.43 ~m, whlch length is per~ectly suitable for receiving a radiation of wave-length of 1.3 ~.
The characteri~tice o~ the photo-detectors are advanta-geou~ly a~ ~ollow~s - Active area s 1 x 10 4 cm2 - Inverse bias potential V : 10 volts - Current gain ~ 2 30 - Saturation current : < 1nA
- Dark current (V = -10V) : ~ 10~A
- Total capacitance (V = -10V) s ~ lpF
- Junction capacitance (V = -10V~ s < 0.2 pP
- Resi~tance-area product (V=Ov) : 6 ~ 104 Q ~cm2 - Response in current ( ~ = 1.3 ~m) : > 0.5 A/w - Operational temperature : 300E.
Claims (7)
1. A photodetector having its maximum sensitivity between 0.8 and 2 µm, comprising a P-type substrate formed by a crystal of Hgl-xCdxTe of very high purity, having a concentration of P carriers less than about 1015/cm3, a doped N-type zone on the substrate forming a PN junction, and a contact on said N-type zone for the application of a weak bias voltage between said contact and said substrate, x being selected within a range extending between 0.4 to 0.9 and as a function of a desired current gain.
2. The photodetector of claim 1, wherein x is substantially equal to 0.67.
3. The photodetector of claim 1, wherein said bias voltage is substantially equal to -10V.
4. The photodetector of claim 1, wherein x is also selected as a function of a desired spectral response.
5. The photodetector of claim 1, wherein said N-type zone is formed by at least one thermal diffusion of cadmium, mercury, aluminum, indium or boron.
6. The photodetector of claim 1, wherein said N-type zone is formed by two thermal diffusions.
7. The photodetector of claim 1, wherein said N-type zone is formed by ionic implantation of indium, aluminum of boron.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR8104712A FR2501915A1 (en) | 1981-03-10 | 1981-03-10 | SENSITIVE PHOTODETECTOR IN NEAR INFRA-RED |
| FR8104712 | 1981-03-10 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1177943A true CA1177943A (en) | 1984-11-13 |
Family
ID=9256029
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000397447A Expired CA1177943A (en) | 1981-03-10 | 1982-03-02 | Photodetector sensitive to close-range infrareds |
Country Status (5)
| Country | Link |
|---|---|
| EP (1) | EP0060743B1 (en) |
| JP (1) | JPS57161515A (en) |
| CA (1) | CA1177943A (en) |
| DE (1) | DE3264361D1 (en) |
| FR (1) | FR2501915A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5144396A (en) * | 1987-02-17 | 1992-09-01 | British Telecommunications Public Limited Company | Capping layer fabrication |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2592740B1 (en) * | 1986-01-08 | 1988-03-18 | Commissariat Energie Atomique | HETEROJUNCTION HGCDTE PHOTOVOLTAIC DETECTOR AND MANUFACTURING METHOD THEREOF |
| FR2598558B1 (en) * | 1986-05-07 | 1988-11-10 | Telecommunications Sa | HGCDTE AVALANCHE PHOTODIODE SENSITIVE TO WAVELENGTH RADIATION GREATER THAN 2 MM |
| DE3743288A1 (en) | 1986-12-30 | 2015-06-18 | Société Anonyme de Télécommunications | Bispectral electromagnetic radiation receiving device |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3638026A (en) * | 1970-06-29 | 1972-01-25 | Honeywell Inc | Or photovoltaic device |
| FR2336804A1 (en) * | 1975-12-23 | 1977-07-22 | Telecommunications Sa | IMPROVEMENTS MADE TO SEMICONDUCTOR DEVICES, ESPECIALLY TO PHOTOVOLTAIC DETECTORS INCLUDING A SUBSTRATE BASED ON A CDXHG1-XTE ALLOY, AND PROCESS FOR MANUFACTURING SUCH A PERFECTED DEVICE |
| FR2488048A1 (en) * | 1980-07-30 | 1982-02-05 | Telecommunications Sa | SENSITIVE PHOTOVOLTAIC DETECTOR IN NEAR INFRARED |
-
1981
- 1981-03-10 FR FR8104712A patent/FR2501915A1/en active Granted
-
1982
- 1982-02-22 DE DE8282400309T patent/DE3264361D1/en not_active Expired
- 1982-02-22 EP EP19820400309 patent/EP0060743B1/en not_active Expired
- 1982-03-02 CA CA000397447A patent/CA1177943A/en not_active Expired
- 1982-03-10 JP JP3670682A patent/JPS57161515A/en active Pending
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5144396A (en) * | 1987-02-17 | 1992-09-01 | British Telecommunications Public Limited Company | Capping layer fabrication |
Also Published As
| Publication number | Publication date |
|---|---|
| EP0060743B1 (en) | 1985-06-26 |
| FR2501915A1 (en) | 1982-09-17 |
| FR2501915B1 (en) | 1984-08-10 |
| EP0060743A1 (en) | 1982-09-22 |
| JPS57161515A (en) | 1982-10-05 |
| DE3264361D1 (en) | 1985-08-01 |
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