Active solid-state devices (e.g. – transistors – solid-state diode – Heterojunction device – Light responsive structure
Reexamination Certificate
1998-12-29
2001-01-30
Mintel, William (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Heterojunction device
Light responsive structure
C257S185000, C257S440000, C257S441000, C257S442000, C438S093000, C438S094000, C438S095000
Reexamination Certificate
active
06180967
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a dual-band infrared detector with space-time coherence and to its method of manufacture.
In a dual-band detection device with space and time coherence, infrared photons coming from two different wavelength bands are detected at the same point in a focal plane of the detector and at the same time, dual-band infrared detectors finding many applications, notably in the production of infrared cameras and in the study of the atmosphere, observations of the Earth and other applications in the space field.
PRIOR ART
A wide variety of infrared detectors are known, whose specific design makes it possible to favor certain detection characteristics. Dual-band infrared detectors can thus be judged according to various criteria such as their performance, their production costs, their compactness, and also their manufacturing technology. Obviously, all these criteria depend more or less on each other and it is difficult to optimise them all simultaneously. A first example of a known dual-band infrared detector is given by Reine et al. “Independently Accessed Back-to-Back HgCdTe photodiodes: A New Dual-Band Infrared Detector”, Rensselaer Polytechnic Institute, Troy, N.Y., 12180, 1993, U.S. Workshop on the physics and chemistry of Mercury Cadmium Teluride and other IR materials—Seattle (Wash.). This detector has a stacking of a number of layers of semiconductor material which forms two detection diodes biased in opposition with respect to each other and coupled by n-type doped layers or regions, i.e. doped with impurities of the donor type. Like the majority of infrared detectors, the layers of semiconductor material are thin layers of CdHgTe compound, that is to say of Cadmium-Mercury-Telurium compound, or CMT, deposited epitaxially on a substrate. The detector is produced according to the technology known as “MESA”. “MESA” technology means a production of a semiconductor device where the delimitation of the active layers is effected by an etching which leaves a number of “reliefs”. This etching can be either mechanical, for example mechanical abrasion, or chemical in the case of the dual-band detector of Reine et al. The etching defines detection points or pixels which have a height of around a tenth of a micrometer.
Producing detectors according to “MESA” technology presents a number of difficulties. Producing integrated semiconductor devices and particularly producing infrared detectors requires a certain number of so-called photolithographic steps which consist in depositing masking patterns on the structure in order to protect certain parts thereof and define the components to be produced, or so-called resin coating steps which also serve to protect certain parts of the structure. The masking patterns cannot be correctly produced simultaneously at different heights or altitudes on the device, i.e. both at the top and bottom of a MESA detection pixel for example. Likewise, during the resin coating steps, it is difficult to obtain a homogeneous and constant thickness. Imprecisions in the production of the patterns by photomasking and resin layers during steps of manufacture of the detector do not allow good definition so small patterns.
Moreover, in the detector of Reine et al., various stacked layers, which form the detector open out on the side of the pixel. Passivation of the pixel is therefore all the more difficult since it must be produced on a sloping side, which can cause electrical leakages at the junction. Finally it may be noted that, in Reine et al., the common contact layer of the pixels is produced from a p-type material. Such a material exhibits mobility of the carriers (holes) lower than that of n-type materials (electrons) and consequently a higher resistivity.
U.S. Pat. No. 5,113,076 gives a second example of a dual-band infrared detector. The device described in this document has two oppositely poled diodes connected in series, and intended respectively for measuring infrared photons with long and short wavelengths. It is formed by a stacking of a layer of n-doped CdHgTe compound, a layer of p-doped CdHgTe and then an n-doped CdHgTe layer. However, the photocurrent of the diode with long wavelengths cannot be read at the same time as the diode with the shorter wavelengths. The device is therefore not time-coherent.
Yet another example is given by U.S. Pat. No. 4,956,686. The detector according to this document has buried structures which allow a so-called “planar” technology in distinction to “MESA” technology; planar technology consists of locally producing active layers on the surface of a substrate by effecting diffusions, implantations or epitaxial deposits through masks. Detection elements sensitive on the one hand to short wavelength and on the other hand to long wavelengths are however produced alongside each other in the focal plane. The detection is therefore in this case not spatially coherent. In addition, the detection elements described in this document are of the MIS (Metal Insulating Semiconductor) type, which proves to have a lower performance from the production point of view than elements of the photovoltaic type.
In the same way as U.S. Pat. No. 4,956,868, EP 0 475 525 can be cited, which concerns an infrared detector sensitive to several different wavelengths, but where the detection elements corresponding to these wavelengths are also disposed alongside each other.
One object of the present invention is to provide a dual-band infrared detector which is both space and time coherent and which does not exhibit the previously mentioned drawbacks.
Another object of the invention is to provide a method of producing the detector which is both simple to implement and avoids the drawbacks mentioned above.
DISCLOSURE OF THE INVENTION
To this end, the invention more precisely relates to a dual-band planar infrared detector with space-time coherence with at least one detection element having, a direction y, a stacking of semiconductor layers forming first and second photodiodes electrically connected in series and oppositely poled, characterized in that it has a planar structure where each layer has a part showing on a surface of the detection element, the surface being substantially perpendicular to the direction y.
According to one method of implementing the invention, the stack has a first layer made from a material of a first conduction type, at least one second layer made from a material of a second conduction type, a third layer made from a material of the second conduction type, separated from the first layer by the second layer, and the fourth layer made from a material of the first conduction type, separated from the second layer by the third layer, the first and third layers forming respectively, with the second and fourth layers, the first and second photodiodes.
According to one aspect of the invention, the materials used from the different layers of the detector are CMT materials.
CMT material means an alloy incorporating the elements Cadmium (Cd), Mercury (Hg) and Telurium (Te). Advantageously, it is possible to adjust the energy or the Prohibited band of these materials by acting on the chemical composition of the alloy, and therefore to select the wavelengths to which the detection elements are sensitive.
As each detection layer has a part flush showing on a plane surface, it is easier to produce electrical connections for connecting the detector to an electronic measuring circuit for example.
According to a particular advantageous embodiment of the invention, the layers of material of the first condition type are n-doped, i.e. with impurities or defects of the donor type supplying negative-charge electrical carriers. The layers of the second conduction type are on the other hand p-doped, i.e. with impurities or defects of the acceptor type capable of supplying positive-charge electrical carriers.
It is of course possible, according to another embodiment, to choose the layers of material of the first conduction type to be p-doped and the layers of material of the second conduction type to be n-d
Duvaut Philippe
Ferret Pierre
Zanatta Jean-Paul
Commissariat A l'Energie Atomique
Mintel William
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
LandOfFree
Bicolor infrared detector with spatial/temporal coherence does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Bicolor infrared detector with spatial/temporal coherence, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Bicolor infrared detector with spatial/temporal coherence will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2486139