GB2379086A - Defect reduction for interdiffused mercury cadmium telluride based infrared detector materials - Google Patents

Defect reduction for interdiffused mercury cadmium telluride based infrared detector materials Download PDF

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GB2379086A
GB2379086A GB0216208A GB0216208A GB2379086A GB 2379086 A GB2379086 A GB 2379086A GB 0216208 A GB0216208 A GB 0216208A GB 0216208 A GB0216208 A GB 0216208A GB 2379086 A GB2379086 A GB 2379086A
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telluride
layers
mercury
cadmium
selenide
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Pradip Mitra
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Lockheed Martin Corp
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Lockheed Martin Corp
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    • 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
    • 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
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • H01L31/1828—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof the active layers comprising only AIIBVI compounds, e.g. CdS, ZnS, CdTe
    • H01L31/1832—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof the active layers comprising only AIIBVI compounds, e.g. CdS, ZnS, CdTe comprising ternary compounds, e.g. Hg Cd Te

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Abstract

This invention reduces the dislocation defect density in variable badgap HgCdTe based infrared absorbing materials formed by Metal Organic Chemical Vapour Deposition Interdiffusion Multilayer Process (MOCVD_IPM), which conventionally includes annealing alternatively deposited thin layers of HgTe and CdTe. The present invention comprises firstly depositing a buffer layer 22 upon a CdTe based substrate 20 and incorporating Se into sequentially deposited CdTe layers 32, 34, 36, 38 in order to lattice match them with the HgTe layers 24, 26, 28, 30. The homogenous detector materials 42 thus formed is HgCdSeTe. Alloy compositions formed after the anneal process may be varied, thus varying the wavelengths absorbed, by changing the relative thickness of the CdTeSe layers deposited. A similar process can be carried out using HgTe and lattice matched CdZnTe layers. The materials may be formed into detectors with more than one layer of annealed alloy in order to be able to detect long, medium and short wavelength infrared radiation.

Description

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DEFECT REDUCTION FOR INTERDIFFUSED MERCURY CADMIUM TELLURIDE BASED INFRARED DETECTOR MATERIALS The present invention pertains in general to infrared radiation absorbing material Hg Cd x Te and more specifically to such material structures which are fabricated by use of the interdiffused multilayer growth process.
One process for the production of the infrared absorbing semiconductor material, Hg1-x Cd. Te, is termed MOCVD-IMP (Metalorganic Chemical Vapor Deposition-InterdiSused Multilayer Process). With this manufacturing process, alternating layers of CdTe and HgTe are grown with a total period thickness in the range of20-120 run (nanometers). After these layers have been grown by use of the MOCVD process, the group of layers are annealed which causes them to interdiffuse and form a homogeneous HgCdTe alloy. The mole fraction of the cadmium in the alloy is termed the"x"value, and this determines the wavelength of response for the infrared detector. This process is disclosed in U. S. P. N. 4,566, 918 entitled "Utilizing Interdiffusion Of Sequentially Deposited Links Of HGTE And CDTE". This patent issued on January 28,1986.
With the conventional approach for manufacturing an interdiffused multilayer HgCdTe material, there is a maximum 0.33 percent mismatch in the lattice constants between the CdTe and the HgTe. This results in the production of strain at the interface. Although the individual layer thicknesses for the CdTe and the HgTe are thinner than the critical thickness for the onset of dislocation formation, there is still left a residual strain to accommodate for the weak, elastic constants of the HgTe and the underlying interdiffused HgCdTe. This mismatch in the lattice constants contributes to dislocation formation, which can be as high as 1-5 x 106 crue.
A significant problem encountered in the design and use of semiconductor infrared detectors is that of dislocation defects in the HgCdTe alloy. These dislocations compromise the transport properties of the semiconductor, which in turn also reduce the performance of the HgCdTe infrared detectors. Furthermore, infrared detector devices requiring heterostructures with two or more dissimilar Hg,, Cd x Te alloy compositions have additional misfit dislocations at the interfaces due to the different lattice constants.
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These dislocations also reduce the performance ofHgCdTe detector structures with heterosctructures and heterojunctions. Therefore, there is a need for a method of manufacture, and a resulting infrared sensitive material structure, which has a reduced defect density.
Accordingly, in a first aspect, the invention provides a method for fabricating a variable bandgap infrared absorbing semiconductor material structure, comprising the steps of : forming a cadmium telluride selenide buffer layer on a substrate having a lattice roughly matched to mercury cadium telluride, forming on said buffer layer, by epitaxial growth, alternating layers of mercury telluride, each having a given lattice constant and cadmium telluride selenide wherein said buffer layer and said cadmium telluride selenide layers have a selenide mole fraction to produce therein a lattice constant substantially similar to the lattice constant of said mercury telluride layers, and annealing said structure to interdiffuse said mercury telluride and said cadmium telluride selenide layers to produce a homogenous mercury cadmium telluride selenide alloy.
In a second aspect, the invention provides A variable bandgap infrared absorbing semiconductor material structure, comprising: a substrate having a lattice roughly matched to mercury cadium telluride, a buffer layer epitaxially grown on said substrate, said buffer layer comprising cadmium telluride selenide, and a homogenous alloy structure of mercury cadmium telluride selenide formed by epitaxial growth on said buffer layer of alternating layers of mercury telluride and cadmium telluride selenide, said cadmium telluride selenide layers and said buffer layer having a selenium mole fraction to produce therein a lattice constant substantially similar to the lattice constant of said mercury telluride layers, and wherein said mercury telluride and cadmium telluride selenide layers are annealed to form said homogenous alloy structure.
According to a third aspect, the invention provides a method for fabricating a variable bandgap infrared absorbing semiconductor structure comprising: providing a substrate having a lattice substantially matched to mercury cadium telluride;
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and forming thereon a homogenous alloy of the formula (HgTe) l-x (CdTel-zSez) x wherein z represents the mole fraction of selenium and x represents the mole fraction of the cadmium telluride selenide.
In a fourth aspect, the invention provides a method of fabricating a variable bandgap infrared absorbing semiconductor material structure responsive to infrared radiation, comprising: a) forming a thin layer of CdTel-zSez on a substrate having a lattice substantially matched to mercury cadium telluride, wherein z represents the mole fraction of selenium such that the lattice constant of the cadmium selenium telluride is substantially similar to the lattice constant of the mercury telluride; b) forming a layer of HgTe on the previously deposited layer of CdTel-zSez ; c) repeating steps a) and b) a predetermined number of times to create alternating layers of CdTel-zSez and HgTe; d) annealing the resulting layers to form a homogenous alloy structure.
In a fifth aspect, the invention provides a method of fabricating a variable bandgap infrared absorbing semiconductor material structure responsive to infrared radiation, comprising: a) forming a thin layer ofCdTe). zSez on a buffer layer having a lattice substantially matched to mercury cadium telluride, wherein z represents the mole fraction of selenium such that the lattice constant of the cadmium selenium telluride is substantially similar to the lattice constant of the mercury telluride ; b) forming a layer of HgTe on the previously deposited layer of CdTel-zSez ; c) repeating steps a) and b) a predetermined number of times to create alternating layers of CdTel. zSez and HgTe; d) annealing the resulting layers to form a homogenous alloy structure.
In a sixth aspect, the invention provides a method of fabricating a variable bandgap infrared absorbing semiconductor material structure responsive to infrared radiation, comprising: a) forming a thin layer of HgTe on a substrate having a lattice substantially matched to mercury cadium telluride; b) forming a layer ofCdTei. zSez, wherein z represents the mole fraction of selenium on the
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previously deposited layer of CdTel zSez such that the lattice constant of the cadmium selenium telluride is substantially similar to the lattice constant of the mercury telluride ; c) repeating steps a) and b) a predetermined number of times to create alternating layers of CdTe ;. zSez and HgTe; d) annealing the resulting layers to form a homogenous alloy structure.
In a seventh aspect, the invention provides a method of fabricating a variable bandgap infrared absorbing semiconductor material structure responsive to infrared radiation, comprising: a) forming a thin layer of HgTe on a buffer layer having a lattice roughly matched to mercury cadium telluride ; b) forming a layer ofCdTezSez, wherein z represents the mole fraction of selenium on the previously deposited layer of CdTel-zSez such that the lattice constant of the cadmium selenium telluride is substantially similar to the lattice constant of the mercury telluride ; c) repeating steps a) and b) a predetermined number of times to create alternating layers of CdTeJ-zSez and HgTe; d) annealing the resulting layers to form a homogenous alloy structure.
In an eighth aspect, the invention provides a method of forming two or more lattice matched quaternary alloys of infrared absorbing materials comprising; a) forming a first region by (i) forming a thin first layer having a predetermined thickness of a composition of the formula CdTeI-zSez wherein z is the mole fraction of selenium such that the lattice constant of the cadmium selenium telluride is substantially similar to the lattice constant of the mercury telluride ; (ii) forming a second layer having a predetermined thickness of a composition of the formula HgTe ; (iii) forming one or more additional alternating layers of said first layer and said second layer ; b) forming a second region of quaternary alloy by (i) forming a third thin layer having a predetermined thickness of a composition of the formula CdTel-zSez wherein z is the mole fraction of selenium such that the lattice constant
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of the cadmium selenium telluride is substantially similar to the lattice constant of the mercury telluride ; (ii) forming a fourth layer having a predetermined thickness of a composition of the formula HgTe having a predetermined thickness ; (iii) forming one or more additional alternating layers of said third and said fourth layers; and c) annealing the resulting layers to form homogenous alloys of (HgTe) j~x (CdTel-zSez) x.
In a ninth aspect, the invention provides a method of forming two or more lattice matched quaternary, alloys of infrared absorbing materials comprising; a) forming a first region by (i) forming a thin first layer having a predetermined thickness of a composition of the formula HgTe ; (ii) forming a second layer having a predetermined thickness of a composition of the formula CdTel zSez wherein z is the mole fraction of selenium such that the lattice constant of the cadmium selenium telluride is substantially similar to the lattice constant of the mercury telluride ; (iii) forming one or more additional alternating layers of said first layer and said second layer; b) forming a second region of quaternary alloy by (i) forming a third thin layer having a predetermined thickness of a composition of the formula HgTe; (ii) forming a fourth layer having a predetermined thickness of a composition of the formula CdTel-zSez wherein z is the mole fraction of selenium having a predetermined thickness and such that the lattice constant of the cadmium selenium telluride is substantially similar to the lattice constant of the mercury telluride ; (iii) forming one or more additional alternating layers of said third layer and said fourth layers; and c) annealing the resulting layers to form homogenous alloys of (HgTe) . x (CdTel-zSez) x.
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In a tenth aspect, the invention provides a variable bandgap infrared absorbing semiconductor structure comprising: a substrate having a lattice substantially matched to mercury cadium telluride; and a homogenous alloy of the formula Hgl-xCd (Tel-zSez) x by depositing alternating layers of mercury telluride and cadmiun selenium telluride, wherein z represents the mole fraction of selenium and x represents the mole fraction of the telluride and selenium, and wherein the lattice constant of the cadmium selenium telluride is substantially similar to the lattice constant of the mercury telluride.
In an eleventh aspect, the invention provides a variable bandgap infrared absorbing semiconductor structure comprising: a substrate having a lattice roughly matched to mercury cadium telluride; a buffer layer; and a homogenous alloy of the formula Hg1-xCd (Tel-zSez) x by depositing alternating layers of mercury telluride and cadmiun selenium telluride, wherein z represents the mole fraction of selenium and x represents the mole fraction of the telluride and selenium, and wherein the lattice constant of the cadmium selenium telluride is substantially similar to the lattice constant of the mercury telluride.
A selected embodiment of the present invention is a method for fabricating HgCdTe based material structure which has a reduced defeat density. The method includes the step of forming a cadmium zinc telluride (Cd1~yZnyTe) buffer layer on a cadmium telluride based substrate. The substrate may include zinc or selenium.
Next, on the buffer layer, alternating layers of mercury telluride and cadmium zinc telluride are epitaxially grown. The mercury telluride has a given lattice constant.
The buffer layer and the cadmium zinc telluride layers have a mole fraction of zinc which produces within these layers a lattice constant which is substantially similar or identical to the lattice constant of the mercury telluride layers. Finally, the structure is annealed to interdiffuse the mercury telluride and the cadmium zinc telluride layers to produce a homogenous mercury cadmium telluride alloy on a cadmium telluride substrate with a lattice matched CdZnTe buffer layer.
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A still further embodiment of the present invention is an infrared radiation material structure having reduced dislocation defects, This structure includes a cadmium telluride based supporting substrate which may include zinc or selenium with a mole fraction of 4% i : 1 %. it further includes a buffer layer which is expitaxially gronw on the substrate wherein the buffer layer comprises cadmium zinc telluride. A homogneous alloy structure of mercury cadmium zinc telluride is formed by vapor phase expitaxy on the buffer layer of alternating layers of mercury telluride and cadmium zinc telluride. The Cd10yZnyTe layers and the buffer layer have a zinc mole fraction y to produce therein a lattice constant which is substantially similar to the lattice constant of the mercury telluride layers. The multiple pairs of mercury telluride and cadmium zinc
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telluride layers are annealed to form th. ; homogenous alloy structure.
The composition of the alloy is controlled by varying the relative thicknesses of mercury telluride (HgTe) and CdZnTe.
In still further embodiments of the present invention, multiple alloy structures can be formed for detecting single or multiple wavelength bands of infrared radiation but all wit the same lattice constants. This is achieved by epitaxial growth of alternating thin layers of HgTe and lattice matched CdZnTe. Only the relative thicknesses of the two lattice matched pairs are varied to adjust the alloy compositions. The number of pairs are selected depending on the overall thickness of the homogenous alloy. Further, CdTeSe can be substituted for the CdZnTe. Instead of cadmium zinc telluride layers, cadmium telluride selenide layers can be used with a composition that is substantially lattice matched to mercury telluride.
Embodiments of the present invention will now be described, by way of example, with reference to the accompanying schematic drawings, in which :- Figure 1 is a section view illustrating the formation of a lattice matching buffer layer on a substrate for the production of an infrared radiation sensitive material structure in accordance with the present invention, Figure 2 is a section view of the growth scheme for producing a semiconductor infrared material structure by use of the interdiffused multiplayer process with multiple pairs of HgTe and CdZnTe as implemented in conjunction with the present invention, Figure 3 is a section view illustrating the structure formed in Figure 2 after it has been annealed to form a homogenous alloy of mercury cadmium zinc telluride, Figure 4A is a section view of a material structure formed with three regions, each with different IMP periods (thickness of a HgTe and CdZnTe pair) for different alloy compositions, such as for short wave, medium wave and long wave infrared
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radiation, Figure 4B is a section view illustrating the semiconductor structure shown in Figure 4A after annealing which produces corresponding homogeneous mercury cadmium zinc telluride alloy regions corresponding respectively to the three different compositions, Figure 5 is a chart illustrating the lattice constants of CdTe-HgTe-ZnTe system as a function of the energy gap for those materials, and Figure 6 is a chart illustrating the structure of conventional three stacked layers of mercury cadmium telluride with different alloy compositions having corresponding lattice constants for each layer and three layers of mercury cadmium zinc telluride, in accordance with the present invention, which has the same lattice constant for each layer with nominally similar bandgaps as the HgCdTe.
The conventional process for manufacturing Hg dz Cd Te alloys by the use of an interdiffusion multilayer process (IMP) is shown in USPN 4, 566,918, which patent is incorporated herein by reference.
The process of the present invention is illustrated beginning with Figure 1. A substrate 20 comprising cadmium telluride forms a supporting substrate and starting material. This substrate may comprise only cadmium telluride or it may include either zinc or selenium. A preferred substrate of this type is manufactured and sold by Johnson Matthey Electronics, a corporation in Spokane, Washington. The preferred substrate 20 is roughly (3-5% zinc content) lattice matched to mercury cadmium telluride. The substrate 20 has a thickness which is approximately 0.8-1 millimeter.
A buffer layer 22 is formed on the surface of the substrate 20 by epitaxial growth. The layer 22 comprises Cd1. yZn,. Te which is grown in a conventional manner.
The layer 22 has a thickness in the range of 2-10 microns and a Zn mole fraction of 0.056 to achieve a lattice constant substantially similar to HgTe.
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After the buffer layer 22 has been grown, alternating layers of HgTe and CdZnTe are grown epitaxially, as shown in Figure 2. Zinc can be added to the MOCVD-IMP manufacturing operation by use of precursors such as dimethylzinctriethylamine or diethyl zinc. Standard precursors can be used for cadmium and tellurium, for example as described in J. B. Mullin and S. J. C. Irvine,"Metalorganic vapor phase epitaxy of mercury cadmium telluride", Progress in Crystal Growth and Characterization vol. 29, pp 217-252 (1994). This structure includes HgTe layers 24, 26,28 and 30. Each of these layers has a preferable thickness of 10-80 nanometers, depending on the desired alloy composition.
The buffer layer 22 is needed because commercially available CdZnTe substrates are known to have significant variations in Zn content due to the high segregation coefficient of Zn in bulk CdZnTe. The buffer layer 22 establishes a uniform crystalline lattice matched structure for forming the multiple pairs of interdiffused layers.
Further referring to Figure 2, there are grown alternating CdZnTe layers 32,34, 36 and 38. Each of these layers has a preferable thickness of 10-30 nanometers. The
preferred composition for each of these layers is Cdn ZnoTe. This mole fraction of Zn produces a lattice constant that is substantially similar to that of mercury telluride. As used herein the term"substantially similar"means a difference of less than 0.1 percent. As noted. previously, a maximum lattice mismatch of 0.33 percent between HgTe and CdTe in conventional MOCVD-IMP produces defects which compromise the electrical transport properties of the HgCdTe alloy and increases the reverse bias dark currents in p-n junction photodiodes, especially at lower temperatures. Both the HgTe layers, such as 24, and the cadmium zinc telluride layers (Cd0.944 Zn0.056Te), such as 32, have a lattice constant of 0.6460 run. Tobin et aI, "The
Relationship Between Lattice Matching and Crosshatch in Liquid Phase Epitaxy "I.-, HgCdTe on CdZnTe Substrates". Journal of Electronic Materials, Vol. 24, No. 9, 1995, p 1189-1199.
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Further referring to Figure 2, the combination of layers 24-3 8 comprises a region 40 Hg1-r (CdO. 944ZnO. 056\Te which is sensitive to infrared radiation. The infrared response wavelength is a function of the x value in a manner similar to Hg1- . CdTe.
Referring to Figure 3, the region 40 has been subject to an anneal treatment process in which the structure is heated for 10-20 minutes at a temperature of approximately 360 degrees centigrade. As a result of this heat treatment, the region 40 becomes a homogeneous quaternary alloy 42 of mercury cadmium zinc telluride.
A still further embodiment of the present invention is illustrated in Figures 4A and 4B. The structure shown in Figures 4A and 4B has a substrate 50 and an epitaxial buffer layer 52, which correspond respectively to the substrate 20 and the buffer layer 22 shown in Figures 1-3. The structure in Figures 4A and 4B has three regions which are formed in sequence. These are regions 54,56 and 58. Region 54 is designed to absorb short wave infrared radiation which is typically in the wavelength range of 1.7- 3.0 microns. Region 56 is designed to absorb infrared radiation which is typically in the medium wave band which is 3.0-5. 0 microns. Region 58 is designed to absorb long wave infrared radiation which is typically in the range of 8. 0-12.0 microns.
For the structure shown in Figure 4A there are alternating layers of HgTe and CdZnTe formed above the buffer layer 52. The CdZnTe layers have the same composition as noted above for the layers such as 24 and 26 in Figure 2. This is
CdZnoTe.
As shown in Figure 4A, there are HgTe layers 60,62, 64 and 66. These are interleaved with CdZnTe layers 68,70, 72 and 74. In region 56, there are HgTe layers 80,82, 84 and 86. These are interleaved with CdZnTe layers 88,90, 92 and 94.
Region 58 comprises HgTe layers 100,102, 104 and 106 interleaved with CdZnTe layers 108,110, 112 and 114.
In the region 54, as shown in Figure 4A, each of the HgTe layers has a preferred thickness of 30 nrn. Each of the CdZnTe layers has a preferred thickness of
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20 nm. In the region 56, the HgTe layers each have a thickness of approximately 46 nm and the CdZnTe layers have a thickness of 20 run. In the region 58, each of the HgTe layers has a thickness of approximately 70 run while each of the CdZnTe layers has a thickness of approximately 20 nm. The change from one region to another in the relative amount of HgTe with respect to the CdZnTe changes the band gap and produces the change in the alloy composition of the HgCdZnTe. However, it does not change the lattice constant, so there is less stress at the interfaces and therefore a reduction in the number of dislocation defects, in comparison to the prior art which does not have the alternating CdZnTe layers for lattice matching, such as shown in the 4,566, 918 patent.
In Figure 4A, although only four pairs of HgTe and CdZnTe are shown for each of the three alloy compositions, the number of pairs can be substantially greater to achieve the overall desired thickness. The actual thickness of the individual pairs are for illustration only and may be varied. The total thickness of a HgTe Cdo944Zno. o56Te pair should be less than or equal to 150 nanometers.
The structure shown in Figure 4B is produced as a result of an anneal operation for the structure shown in 4A The anneal comprises heating at approximately 360 degrees centigrade for a period of 10-20 minutes. The mercury, cadmium and zinc in each region interdiSses and leaves no memory of the IMP periods. The region 54, as shown in Figure 4A, becomes an alloy 120 of mercury cadmium zinc telluride. Similar alloys 122 and 124 are formed respectively from the regions 56 and 58. Each of the alloys 120,122 and 124 retains its particular infrared absorption, for specific bands, as described for the structure shown in Figure 4A The structures shown in Figures 1-4A and 4B can be doped in the same manner as conventional HgCdTe detectors, such as described in P. Mitra, Y. L. Tyan, T. R.
Schimert and F. C. Case,"Donor doping in metalorganic chemical vapor deposition of HgCdTe using ethyl iodide", ppl. Phys. Lett. 65 195-197 (1994), P. Mitra, T. R.
Schimert, F. C. Case, S. L. Barnes, M. B. Reine, R. Starr, M. H. Weiler, and M.
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Kestigian,"MetaJorganic chemical vapor deposition ofHgCdTe p/n junctions using arsenic and iodine doping", J. Electronic Materials 24,1077-1085 (1995), and P.
Mitra, Y. L. Tyan, F. C. Case, R. Starr and M. B. Reine,"Improved arsenic doping in MOCVD of HgCdTe and in situ growth of high performance long wavelength infrared photodiodes", J. Electronic Materials 25, 1328-1335 (1996), which are incorporated herein. The fabrication, biasing and signal detection are likewise the same as for conventional HgCdTe infrared detectors. Structures with multiple alloy compositions
using conventional MOCVD-IMP grown HgCdTe alloys are described in P. Mitra, S.
I IV L. Barnes, F. C. Case, M. B. Reine, P. O'Dette, R Starr, A Hairston, K Kuhler, M R Weiler and B. L. Musicant,"MOCVD of bandgap-engineered HgCdTe p-n-N-P dual-band infrared detector arrays", J. Electronic Materials 26,482-487 (1997). The dual-band infrared detector devices described in this article can be fabricated with reduced defects using the present invention.
Referring to Figure 5, there is shown a chart illustrating the lattice constant of the CdTe-HgTe-ZnTe system with respect to the energy gap for those materials. Note that the lattice constant for HgTe is approximately 6.4600 angstroms (0.64600 run).
Note that Cd1~yZn,. Te having y =. 056 has substantially the same lattice constant as HgTe.
Figure 6 illustrates a chart for the structure described in reference to Figures 4A and 4B and a chart for a prior art for a three layer HgCdTe structure. The line 132 represents the material which corresponds at various segments to the alloys shown in Figure 4B. A segment of the line 132A corresponds to alloy 124, line segment 132B corresponds to alloy 122, and line segment 132C corresponds to alloy 120. The'y' value adjacent each segment represents the ratio of mercury to the combination of cadmium and zinc as indicated in the formula shown just below the line 132. The variation in the quantity"y"represents a change in the alloy composition and therefore the bandgap of the semiconductor. The nominal cutoff wavelengths for the long wave, medium wave and short wave infrared bands is illustrated in Figure 6. These are
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respectively 10 microns, 5 microns and 2.5 microns. A chart line 140 for a conventional structure is shown in Figure 6 with line 140 having line segments 140A, 140B and 140C. Line segment 140A represents x =. 22 for long wave radiation. Line segment 140B represents x =. 30 for medium wave radiation and line segment 140C represents x =. 40 for short wave infrared radiation. Note that for each of the different infrared wavelengths there is a different lattice constant. These lattice constants are respectively the approximate values 6. 4647, 6. 4664 and 6.4685 angstroms. The structure represented by line 140 represents the prior art wherein a change in the cutoff wavelength for a material also changes the lattice constant for that material. A structure, such as shown in Figures 4A and 4B for the present invention, corresponds to the line 132 and shows that such a structure can be built with a constant lattice constant, but with variation in the"y"value to receive infrared radiation in different bands.
A further advantage of the present invention is that by incorporating zinc into the HgCdTe, the resulting quaternary alloy will have an increased hardness and reduced dislocation density due to the shorter ZnTe bond length and the higher energy required for the formation of dislocations. A Sher, A-B. Chen, W. E. Spicer and C-K Shih, "Effects influencing the structural integrity of semiconductors and their alloys", J Vacuum Science and Technology Vol. A3, pp 105-111 (1985).
A lattice matched structure in accordance with the present invention can be
made by substituting CdTe1-zSez in place of CdyZnyTe. This substitution uses the -, Z : rlTe. T s substi composition CdIe1-zSez (cadmium telluride selenide) with an approximate value ofz= 0.0516. An equation supporting this value is shown in D. J. Williams,"Densities and lattice parameters of CdTe, CdZnTe and CdTeSe"in Properties of Narraw Gap Cadmium based Compounds, P Capper ed., EMIS Datareviews Series 10,1994, pp 339-402. This composition of CdTeSe has a lattice constant that is substantially similar to the lattice constant ofHgTe.
In summary, the present invention comprises a method of fabrication for an
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IMP infrared material structure which has a substantially similar lattice constant throughout the structure and therefore has a reduction in the number of dislocation defects.
Although several embodiments of the invention have been illustrated in the accompanying drawings and described in the foregoing Detailed Description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the invention.

Claims (20)

  1. CLAIMS I. A method for fabricating a variable bandgap infrared absorbing semiconductor material structure, comprising the steps of : forming a cadmium telluride selenide buffer layer on a substrate having a lattice roughly matched to mercury cadium telluride, forming on said buffer layer, by epitaxial growth, alternating layers of mercury telluride, each having a given lattice constant and cadmium telluride selenide wherein said buffer layer and said cadmium telluride selenide layers have a selenide mole fraction to produce therein a lattice constant substantially similar to the lattice constant of said mercury telluride layers, and annealing said structure to interdiffuse said mercury telluride and said cadmium telluride selenide layers to produce a homogenous mercury cadmium telluride selenide alloy.
  2. 2. A method for fabricating a variable bandgap infrared absorbing semiconductor material structure as claimed in claim I wherein said substrate is a cadmium telluride based substrate.
  3. 3. A method for fabricating a variable bandgap infrared absorbing semiconductor material structure as claimed in claim 2 wherein said substrate includes selenium.
  4. 4. A variable bandgap infrared absorbing semiconductor material structure, comprising : a substrate having a lattice roughly matched to mercury cadium telluride, a buffer layer epitaxially grown on said substrate, said buffer layer comprising cadmium telluride selenide, and a homogenous alloy structure of mercury cadmium telluride selenide formed by epitaxial
    growth on said buffer layer of alternating layers of mercury telluride and cadmium telluride n selenide, said cadmium telluride selenide layers and said buffer layer having a selenium mole fraction to produce therein a lattice constant substantially similar to the lattice constant of said mercury telluride layers, and wherein said mercury telluride and cadmium telluride selenide layers are annealed to form said homogenous alloy structure.
    <Desc/Clms Page number 17>
  5. 5. A variable bandgap infrared absorbing semiconductor material structure as claimed in claim 4 responsive to at least two different bands of infrared radiation, comprising: a substrate having a lattice roughly matched to mercury cadium telluride, a buffer layer epitaxially grown on said substrate, said buffer layer comprising cadmium telluride selenide, and a first homogenous alloy structure of mercury cadmium telluride selenide formed on said buffer layer by epitaxial growth of alternating layers of mercury telluride and cadmium telluride selenide, said first structure cadmium telluride selenide layers and said buffer layer having a selenium mole fraction to produce therein a lattice constant substantially similar to the lattice constant of said mercury telluride layers, and wherein said first structure mercury telluride and cadmium telluride selenide layers are annealed to form said first structure homogenous alloy, said first structure further having a cadmium mole fraction for producing therein a bandgap responsive to infrared radiation within a first band, and a second homogenous alloy structure of mercury cadmium telluride selenide formed on said first alloy structure by epitaxial growth of alternating layers of mercury telluride and cadmium telluride selenide, said second structure cadmium selenium telluride layer having a selenium mole fraction to produce therein a lattice constant substantially similar to the lattice constant of said mercury telluride layers, and wherein said second structure mercury telluride and cadmium telluride selenide layers are annealed to form said second structure homogenous alloy, said second structure further having a cadmium mole fraction producing therein a bandgap responsive to infrared radiation within a second band.
  6. 6. A variable bandgap infrared absorbing semiconductor material structure as claimed in claim 4, responsive to short wave, medium wave and long wave bands of infrared radiation, comprising: a substrate having a lattice roughly matched to mercury cadium telluride, a buffer layer epitaxially grown on said substrate, said buffer layer comprising cadmium telluride selenide, a first homogenous alloy structure of mercury cadmium telluride selenide formed on said buffer layer by epitaxial growth of alternating layers of mercury telluride and cadmium telluride selenide, said first structure cadmium telluride selenide layers and said buffer layer having a selenium mole fraction to produce therein a lattice constant substantially similar to the lattice
    <Desc/Clms Page number 18>
    constant of said mercury telluride layers, and wherein said first structure mercury telluride and cadmium telluride selenide layers are annealed to form said first structure homogenous alloy, said first structure further having a cadmium mole fraction for producing therein a bandgap responsive to short wave infrared radiation, a second homogenous alloy structure of mercury cadmium telluride selenide formed on said first alloy structure by epitaxial growth of alternating layers of mercury telluride and cadmium telluride selenide, said second structure cadmium telluride selenide layer having a selenium mole fraction to produce therein a lattice constant substantially similar to the lattice constant of said mercury telluride layers, and wherein said second structure mercury telluride and cadmium telluride selenide layers are annealed to form said second structure homogenous alloy, said second structure further having a cadmium mole fraction for producing therein a bandgap responsive to medium wave infrared radiation, and a third homogenous alloy structure of mercury cadmium telluride selenide formed on said second alloy structure by epitaxial growth of alternating layers of mercury telluride and cadmium telluride selenide, said third structure cadmium telluride selenide layer having a selenium mole fraction to produce therein a lattice constant substantially similar to the lattice constant of said mercury telluride layers, and wherein said third structure mercury telluride and cadmium telluride selenide layers are annealed to form said third structure homogenous alloy, said third structure further having a cadmium mole fraction for producing therein a bandgap responsive to long wave infrared radiation.
  7. 7. A variable bandgap infrared absorbing semiconductor material structure as claimed in any of claims 4 to 6 wherein said substrate is a cadmium telluride based substrate.
  8. 8. A variable bandgap infrared absorbing semiconductor material structure as claimed in claim 7 wherein said cadmium telluride based substrate includes selenium.
  9. 9. A method for fabricating a variable bandgap infrared absorbing semiconductor structure comprising: providing a substrate having a lattice substantially matched to mercury cadium telluride; and forming thereon a homogenous alloy of the formula (HgTe)). x (CdTe ; Se ; ;) x wherein z
    <Desc/Clms Page number 19>
    represents the mole fraction of selenium and x represents the mole fraction of the cadmium telluride selenide.
  10. 10. A method as claimed in claim 9 further comprising forming one or more additional layers of a homogenous alloy of the formula (HgTe) J-x (CdTei-zSez) x wherein z represents the mole fraction of selenium and x represents the mole fraction of the cadmium telluride selenide; wherein the value ofx for each layer of alloy is different from the other layers.
  11. 11. A method of fabricating a variable bandgap infrared absorbing semiconductor material structure responsive to infrared radiation, comprising: a) forming a thin layer of CdTel-zSez on a substrate having a lattice substantially matched to mercury cadium telluride, wherein z represents the mole fraction of selenium such that the lattice constant of the cadmium selenium telluride is substantially similar to the lattice constant of the mercury telluride; b) forming a layer of HgTe on the previously deposited layer of CdTe. zSez ; c) repeating steps a) and b) a predetermined number of times to create alternating layers of CdTel-zSez and HgTe; d) annealing the resulting layers to form a homogenous alloy structure.
  12. 12. A method of fabricating a variable bandgap infrared absorbing semiconductor material structure responsive to infrared radiation, comprising: a) forming a thin layer of CdTej. zSez on a buffer layer having a lattice substantially matched to mercury cadium telluride, wherein z represents the mole fraction of selenium such that the lattice constant of the cadmium selenium telluride is substantially similar to the lattice constant of the mercury telluride; b) forming a layer of HgTe on the previously deposited layer of CdTe ;. zSez ; c) repeating steps a) and b) a predetermined number of times to create alternating layers of CdTe. zSez and HgTe; d) annealing the resulting layers to form a homogenous alloy structure.
  13. 13. A method of fabricating a variable bandgap infrared absorbing semiconductor material structure responsive to infrared radiation, comprising: a) forming a thin layer of HgTe on a substrate having a lattice substantially matched to
    <Desc/Clms Page number 20>
    mercury cadium telluride ; b) forming a layer ofCdTel-zSez, wherein z represents the mole fraction of selenium on the previously deposited layer of CdTes zSez such that the lattice constant of the cadmium selenium telluride is substantially similar to the lattice constant of the mercury telluride ; c) repeating steps a) and b) a predetermined number of times to create alternating layers of CdTel-zSez and HgTe; d) annealing the resulting layers to form a homogenous alloy structure.
  14. 14. A method of fabricating a variable bandgap infrared absorbing semiconductor material structure responsive to infrared radiation, comprising: a) forming a thin layer of HgTe on a buffer layer having a lattice roughly matched to mercury cadium telluride ; b) forming a layer of CdTel-zSez, wherein z represents the mole fraction of selenium on the previously deposited layer of CdTel zSez such that the lattice constant of the cadmium selenium telluride is substantially similar to the lattice constant of the mercury telluride ; c) repeating steps a) and b) a predetermined number of times to create alternating layers of CdTel-zSez and HgTe; d) annealing the resulting layers to form a homogenous alloy structure.
  15. 15. A method of forming two or more lattice matched quaternary alloys of infrared absorbing materials comprising; a) forming a first region by (i) forming a thin first layer having a predetermined thickness of a composition of the formula CdTe ;. zSez wherein z is the mole fraction of selenium such that the lattice constant of the cadmium selenium telluride is substantially similar to the lattice constant of the mercury telluride; (ii) forming a second layer having a predetermined thickness of a composition of the formula HgTe ; (iii) forming one or more additional alternating layers of said first layer and said second layer ; b) forming a second region of quaternary alloy by
    <Desc/Clms Page number 21>
    (i) forming a third thin layer having a predetermined thickness of a composition of the formula CdTel-zSez wherein z is the mole fraction of selenium such that the lattice constant of the cadmium selenium telluride is substantially similar to the lattice constant of the mercury telluride ; (ii) forming a fourth layer having a predetermined thickness of a composition of the formula HgTe having a predetermined thickness; (iii) forming one or more additional alternating layers of said third and said fourth layers; and c) annealing the resulting layers to form homogenous alloys of (HgTe) l. x (CdTel-zSezh.
  16. 16. A method as claimed in claim 15 further comprising forming a buffer layer before forming said first region.
  17. 17. A method of forming two or more lattice matched quaternary, alloys of infrared absorbing materials comprising; a) forming a first region by (i) forming a thin first layer having a predetermined thickness of a composition of the formula HgTe; (ii) forming a second layer having a predetermined thickness of a composition of the formula CdTeJ. zSez wherein z is the mole fraction of selenium such that the lattice constant of the cadmium selenium telluride is substantially similar to the lattice constant of the mercury telluride ; (iii) forming one or more additional alternating layers of said first layer and said second layer; b) forming a second region of quaternary alloy by (i) forming a third thin layer having a predetermined thickness of a composition of the formula HgTe; (ii) forming a fourth layer having a predetermined thickness of a composition of the formula CdTeSez wherein z is the mole fraction of selenium having a predetermined thickness and such that the lattice constant of the cadmium selenium telluride is substantially similar to the lattice constant of the mercury telluride ; (iii) forming one or more additional alternating layers of said third layer and said
    <Desc/Clms Page number 22>
    fourth layers; and c) annealing the resulting layers to form homogenous alloys of (HgTe) l-x (CdTeI-zSezh.
  18. 18. A method as claimed in claim 17 further comprising the addition of one or more regions which each when annealed is responsive to a wavelength different from the other regions.
  19. 19. A variable bandgap infrared absorbing semiconductor structure comprising: a substrate having a lattice substantially matched to mercury cadium telluride; and
    a homogenous alloy of the formula Hg1-xCd (Tel-zSez) x by depositing alternating layers of t. by depositing alternating layers of mercury telluride and cadmiun selenium telluride, wherein z represents the mole fraction of selenium and x represents the mole fraction of the telluride and selenium, and wherein the lattice constant of the cadmium selenium telluride is substantially similar to the lattice constant of the mercury telluride.
  20. 20. A variable bandgap infrared absorbing semiconductor structure according to either claim 18 or claim 19 wherein z is about 0.0516.
    20. A structure as claimed in claim 19 further comprising one or more additional layers of a homogenous alloy of the formula Hg1-xCd (Tel-zSez) x wherein z represents the mole fraction of selenium and x represents the mole fraction of the telluride and selenium, and wherein the value ofz in each layer is different.
    21. A variable bandgap infrared absorbing semiconductor structure comprising:
    a substrate having a lattice roughly matched to mercury cadium telluride ; ZD a buffer layer ; and a homogenous alloy of the formula Hgl-xCd (Tel-zSez) x by depositing alternating layers of mercury telluride and cadmiun selenium telluride, wherein z represents the mole fraction of selenium and x represents the mole fraction of the telluride and selenium, and wherein the lattice constant of the cadmium selenium telluride is substantially similar to the lattice constant of the mercury telluride.
    22. A structure as claimed in claim 21 further comprising one or more additional layers of a homogenous alloy of the formula Hgl-xCd (Tel-zSez) x wherein z represents the mole fraction of selenium and x represents the mole fraction of the telluride and selenium, and wherein the value of z in each layer is different.
    <Desc/Clms Page number 23>
    23. A variable bandgap infrared absorbing structure as claimed in claims 9,10, 19, 20, 21 or 22 wherein z is 0.0516.
    <Desc/Clms Page number 24>
    Amendments to the claims have been filed as follows CLAIMS 1. A method for fabricating a variable bandgap infrared absorbing semiconductor material structure, comprising the steps of: forming a cadmium telluride selenide buffer layer on a cadmium telluride based substrate; forming on said buffer layer, by epitaxial growth, alternating layers of mercury telluride, each having a given lattice constant, and cadmium telluride selenide wherein said buffer layer and said cadmium telluride selenide layers have a selenium mole fraction to produce therein a lattice constant substantially similar to the lattice constant of said mercury telluride layers, and annealing said structure to interdiffuse said mercury telluride and said cadmium telluride selenide layers to produce a homogenous mercury cadmium telluride selenide alloy.
    2. A method for fabricating a variable bandgap infrared absorbing semiconductor material structure as claimed in claim 1, wherein said substrate includes selenium.
    3. A variable bandgap infrared absorbing semiconductor material structure, comprising: a cadmium telluride based substrate, a buffer layer epitaxially grown on said substrate, said buffer layer comprising cadmium telluride selenide, and a homogenous alloy structure of mercury cadmium telluride selenide formed by epitaxial growth on said buffer layer of alternating layers of mercury telluride and cadmium telluride selenide, said cadmium telluride selenide layers and said buffer layer having a selenium mole fraction to produce therein a lattice constant substantially similar to the lattice constant of said mercury telluride layers, and
    <Desc/Clms Page number 25>
    wherein said mercury telluride and cadmium telluride selenide layers are annealed to form said homogenous alloy structure.
    4. A variable bandgap infrared absorbing semiconductor material structure according to claim 3, responsive to at least two different bands of infrared radiation, comprising: a cadmium telluride based substrate, a buffer layer epitaxially grown on said substrate, said buffer layer comprising cadmium telluride selenide, and a first homogenous alloy structure of mercury cadmium telluride selenide formed on said buffer layer by epitaxial growth of alternating layers of mercury telluride and cadmium telluride selenide, said first structure cadmium telluride selenide layers and said buffer layer having a selenium mole fraction to produce therein a lattice constant substantially similar to the lattice constant of said mercury telluride layers, and wherein said first structure mercury telluride and cadmium telluride selenide layers are annealed to form said first structure homogenous alloy, said first alloy structure further having a selenium mole fraction for producing therein a bandgap responsive to infrared radiation within a first band, and a second homogenous alloy structure of mercury cadmium telluride selenide formed on said first alloy structure by epitaxial growth of alternating layers of mercury telluride and cadmium telluride selenide, said second structure cadmium telluride selenide layer having a selenium mole fraction to produce therein a lattice constant substantially similar to the lattice constant of said mercury telluride layers, and wherein said second structure mercury telluride and cadmium telluride selenide layers are annealed to form said second structure homogenous alloy, said second alloy structure further having a ratio of cadmium to mercury producing therein a bandgap responsive to infrared radiation within a second band.
    5. A variable bandgap infrared absorbing semiconductor material structure according to claim 3, responsive to short wave, medium wave and long wave
    <Desc/Clms Page number 26>
    bands of infrared radiation, comprising: a cadmium telluride based substrate, a buffer layer epitaxially grown on said substrate, said buffer layer comprising cadmium telluride selenide, a first homogenous alloy structure of mercury cadmium telluride selenide formed on said buffer layer by epitaxial growth of alternating layers of mercury telluride and cadmium telluride selenide, said first structure cadmium telluride selenide layers and said buffer layer having a selenium mole fraction to produce therein a lattice constant substantially similar to the lattice constant of said mercury telluride layers, and wherein said first structure mercury telluride and cadmium telluride selenide layers are annealed to form said first structure homogenous alloy, said first structure further having a cadmium mole fraction for producing therein a bandgap responsive to short wave infrared radiation, a second homogenous alloy structure of mercury cadmium telluride selenide formed on said first alloy structure by epitaxial growth of alternating layers of mercury telluride and cadmium telluride selenide, said second structure cadmium telluride selenide layer having a selenium mole fraction to produce therein a lattice constant substantially similar to the lattice constant of said mercury telluride layers, and wherein said second structure mercury telluride and cadmium telluride selenide layers are annealed to form said second structure homogenous alloy, said second structure further having a cadmium mole fraction for producing therein a bandgap responsive to medium wave infrared radiation, and a third homogenous alloy structure of mercury cadmium telluride selenide formed on said second alloy structure by epitaxial growth of alternating layers of mercury telluride and cadmium telluride selenide, said third structure cadmium telluride selenide layer having a selenium mole fraction to produce therein a lattice constant substantially similar to the lattice constant of said mercury telluride layers, and wherein said third structure mercury telluride and cadmium telluride selenide layers are annealed to form said third structure homogenous alloy, said third
    <Desc/Clms Page number 27>
    structure further having a cadmium mole fraction for producing therein a bandgap responsive to long wave infrared radiation.
    , -" 6. A variable bandgap infrared absorbing semiconductor material structure according to any one of claims 3 to 5, wherein said substrate includes selenium.
    7. A method for fabricating a variable bandgap infrared absorbing semiconductor structure comprising: providing a cadmium telluride based substrate; providing a buffer layer on the substrate; and forming on the substrate, a homogenous alloy of the formula (HgTekx (CdTe1-zSez) x by depositing alternating layers of mercury telluride and cadmium telluride selenide on said substrate and annealing said layers, wherein z represents the mole fraction of selenium, and x represents the mole fraction of the cadmium telluride selenide.
    8. A method according to claim 7, wherein said buffer layer comprises cadmium telluride selenide and has a lattice constant substantially similar to that of the homogenous alloy.
    9. A method according to either claim 7 or claim 8, further comprising forming one or more additional layers of a homogenous alloy of the formula (HgTe) i-x (CdTei. zSez) x wherein z represents the mole fraction of selenium and x represents the mole fraction of the cadmium telluride selenide, and wherein the value of x for each layer of the alloy is different from that for the other layers.
    10. A method of fabricating a variable bandgap infrared absorbing semiconductor material structure, comprising:
    <Desc/Clms Page number 28>
    a) providing a cadmium telluride based substrate; b) providing a buffer layer on the substrate;
    .-* c) forming a thin layer of CdTe1-zSez on the substrate, wherein z represents the mole fraction of selenium such that the lattice constant of the cadmium telluride selenide is substantially similar to the lattice constant of a layer of mercury telluride to be formed thereon; d) forming the layer of HgTe on the previously deposited layer of CdTe1-zSez ; e) repeating steps c) and d) to create a predetermined number of alternating layers of CdTe1-zSez and HgTe; and f) annealing the resulting layers to form a homogenous alloy structure.
    11. A method according to claim 10, further comprising forming one or more additional layers of a homogenous alloy of the formula (HgTe) 1-x (CdTe1-zSez) x wherein z represents the mole fraction of selenium, and x represents the mole fraction of the cadmium telluride selenide, and wherein the value of x for each layer of the alloy is different from that for the other layers.
    12. A method of fabricating a variable bandgap infrared absorbing semiconductor material structure responsive to infrared radiation, comprising: a) forming a buffer layer of CdTe1-zSez on a cadmium telluride based substrate, wherein z represents the mole fraction of selenium such that the lattice constant of the cadmium telluride selenide is substantially similar to the lattice constant of a layer of mercury telluride to be formed thereon; b) forming a thin layer of HgTe on the previously deposited buffer layer ; c) forming a thin layer of CdTe1-zSez ; d) repeating steps b) and c) a predetermined number of times to create to create alternating layers of CdTe1-zSez and HgTe; and e) annealing the resulting layers to form a homogenous alloy structure.
    <Desc/Clms Page number 29>
    13. A method of forming two or more lattice matched quaternary alloys of infrared absorbing semiconductor material comprising; a) providing a cadmium telluride based substrate; b) providing a buffer layer on the substrate; c) forming a first region of quaternary alloy by (i) forming a first thin layer of a composition of the formula CdTe1-zSez from cadmium telluride selenide on the substrate and wherein z is the mole fraction of selenium having a first predetermined thickness and such that the lattice constant of the cadmium telluride selenide is substantially similar to the lattice constant of a second layer of mercury telluride to be formed thereon; (ii) forming a second layer of the composition of the formula HgTe having a second predetermined thickness; (iii) forming one or more additional alternating layers of said first layer and said second layer ; d) forming a second quaternary region by (i) forming a third layer of a composition of the formula CdTei-zSez wherein z is the mole fraction of selenium having a first predetermined thickness and such that the lattice constant of the cadmium telluride selenide is substantially similar to the lattice constant of the fourth layer of mercury telluride to be formed thereon; (ii) forming a fourth layer of a composition of the formula HgTe having a predetermined thickness; (iii) forming one or more additional alternating layers of said third and said fourth layers; and e) annealing the resulting layers to form homogenous alloys of (HgTe) (CdTe1-zSez) x.
    <Desc/Clms Page number 30>
    14. A method of forming two or more lattice matched quaternary alloys of infrared absorbing semiconductor comprising; a) providing a cadmium telluride based substrate; b) providing a buffer layer on the substrate; c) forming a first region of quaternary alloy by: (i) forming a first thin layer of a composition of the formula HgTe having a first predetermined thickness on the substrate; (ii) forming a second layer of the composition of the formula CdTei-zSez wherein z is the mole fraction of selenium having a second predetermined thickness, and such that the lattice constant of the cadmium telluride selenide is substantially similar to the lattice constant of the mercury telluride ; (iii) forming one or more additional alternating layers of said first layer and said second layer ; d) forming a second quaternary region by: (i) forming a third layer of a composition of the formula HgTe having a predetermined thickness; (ii) forming a fourth layer of a composition of the formula CdTe1-zSez wherein z is the mole fraction of selenium having a predetermined thickness and such that the lattice constant of the cadmium telluride selenide is substantially similar to the lattice constant of the mercury telluride ; (iii) forming one or more additional alternating layers of said third and said fourth layers; and e) annealing the resulting layers to form homogenous alloys of (HgTe) i-x (CdTei. zSe.
    15. A method according to either claim 13 or claim 14, wherein the thickness of the layers is selected so that when the composition is annealed the first section and second section will respond to different wavelengths.
    <Desc/Clms Page number 31>
    16. A method according to any one of claims 13,14 or claim 15, wherein the value of z is the same in all layers.
    .
    17. A method according to any one of claims 13 to 16, wherein the variance in lattice constant is less than 0.1 percent between the quaternary alloy and cadmium telluride selenide and mercury telluride.
    18. A variable bandgap infrared absorbing semiconductor structure comprising: a cadmium telluride based substrate; a buffer layer formed on the substrate; and a homogenous alloy of the formula (HgTe),-, (CdTel-zSez) x formed by depositing alternating layers of mercury telluride and cadmium telluride selenide on said substrate and annealing said layers, where z represents the mole fraction of selenium and x represents the mole fraction of the (CdTe1-zSez), and wherein the lattice constant of the cadmium telluride selenide is substantially similar to the lattice constant of mercury telluride.
    19. A variable bandgap infrared absorbing semiconductor structure according to claim 18, further comprising one or more additional layers of a homogenous alloy of the formula (HgTe) 1-x (CdTe1-zSez) x wherein z represents the mole fraction of selenium and x represents the mole fraction of the cadmium telluride selenide, and wherein the value of z for each layer of the alloy is different from that for the other layers.
GB0216208A 1997-06-26 1998-06-23 Defect reduction for interdiffused mercury cadmium telluride based infrared detector materials Expired - Lifetime GB2379086B (en)

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Citations (3)

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US5633514A (en) * 1993-09-07 1997-05-27 Sony Corporation Semiconductor light emitting device with lattice-matching and lattice-mismatching
US5838053A (en) * 1996-09-19 1998-11-17 Raytheon Ti Systems, Inc. Method of forming a cadmium telluride/silicon structure

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Publication number Priority date Publication date Assignee Title
US4954182A (en) * 1980-11-13 1990-09-04 Energy Conversion Devices, Inc. Multiple cell photoresponsive amorphous photo voltaic devices including graded band gaps
US5633514A (en) * 1993-09-07 1997-05-27 Sony Corporation Semiconductor light emitting device with lattice-matching and lattice-mismatching
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