Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Utility Patent
1998-06-01
2001-01-02
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S370010
Utility Patent
active
06169284
ABSTRACT:
TECHNICAL FIELD
This invention concerns a system that enables the detection of infrared light (IR, with wavelength &lgr;>800 nm) having high sensitivity and high rejection of light of shorter wavelength.
BACKGROUND ART
The system presented is based in particular on the measurement of the capacitance in structures made of amorphous silicon, constituted by a p
+
-i-n
+
junction, having two electrodes connecting with the outside and susceptible of being built with already-known technologies for thin film deposition. The layers indicated with p
+
and n
+
are made of materials strongly doped with boron and phosphorous atoms respectively, while the i layer indicates the layer lying between the two.
The temperatures during the entire fabrication process are such as to enable the structure's deposit on various substrates, such as glass, plastic, metal. The technologies used enable it to be fabricated over on a large area and also admit a high-resolution two-dimensional matrix conformation.
One fundamental element of the invention concerns the special characteristics required over the intermediate layer (i), indicated by 1 on the drawings, which is the site of numerous electronic defects of a particular type, owing to which electron transitions can be excited that give rise to the detection of infrared radiation (IR).
The subject invention can be used:
to detect phenomena accompanied by the emission of heat, for example in temperature control, or in the making of thermal maps, or in the taking of night images;
for instrumentation used in remote temperature control, or in the fields of chemistry, physics or biology;
for infrared spectroscopy.
The physical phenomena that take place in the detection of infrared radiation by the amorphous silicon structure are intrinsically faster than those taking place in the detection of visible radiation, so that the system in question lends itself as well to performing the function of detection of infrared radiation conducted by optical fibers in optical telecommunications systems. In this particular case the low cost of its construction and the ability of being deposited directly on the optical system make it highly competitive with currently existing detectors.
The invention may be used in the construction of:
fire-detection systems (its rejection of visible light means it can be used even in full daylight);
systems for thermally mapping machinery, and therefore control and alarm systems;
high-resolution IR image matrix detection systems;
signal detection systems on IR optical carriers.
The invention's focal point lies in the ability to absorb infrared radiation by transition between the extended band and semiconductor defects in a particular portion of the structure adopted in the invention. To this purpose, the type of defects that are induced by a suitable deposition technique in the semiconductor of the intermediate layer, i, is fundamental. These defects in fact must have the characteristic of being traps for the majority carriers, while not acting as centers of recombination. In this way, the IR radiation can be absorbed by a transition induced between the extended band and the defect. The number of defects per unit volume is however extremely low in comparison with the number of atoms of material, so that even in a material that has been purposely made with defects the absorption rate remains relatively low when compared with the absorption due to the transition between the two extended bands. In this case what is crucial is the nature of the trap-type defects, in order that photogenerated charge can be accumulated, and the absorption effect be multiplied.
Under these conditions the absorption of IR light dramatically changes the structure capacitance and it is this that makes possible the outside detection. It is in the detection method that provide a second major benefit of the present invention. This benefit occurs because presence of IR radiation can be detected by the measurement of the capacitance at the terminals where the incident radiation is constant or slowly varying, or else by the measurement of the photocapacitance charging and discharging current where there are rapid changes in radiation intensity.
In this invention radiation detection is made possible by the following measures:
the frontal electrode is a metal grid that offers open areas to the incident light, through which the light can pass, or else it is a conducting electrode and transparent to IR radiation;
the doped frontal layer is thin enough not to appreciably absorb the IR radiation;
the presence of trap-type defects enables the absorption of an IR photon by the excitation of an electron. In the preferred embodiment of the present invention, the structure is so formed that this transition is principally formed by the excitation of electrons going from the valence band towards the traps. It is a fact that crystal defects are defined as alterations of the bond configuration that is periodically repeated in the crystal. In semiconductors—and in the rest of this description—in particular the term “defect” is used to define those alterations to which corresponds a local electron state whose energy lies within the forbidden gap, and is therefore able to change its own state of charge by trapping an electron or a hole, depending on the type of defect. Differing alterations of the configurations give rise to differing types of defects, characterized by different energies and different capture sections. The presence of trap-type defects, with low probabilities of transition toward the farther extended band strongly reduces recombination, giving rise to a high accumulation of charge. The structure shows a substantial difference in capacitance with or without the accumulated charge owing to the absorbtion of radiation. To this purpose the material of the intermediate layer i, of the p-i-n structure is made up of material having the following properties: a) it must contain holes prevalently, and b) it must be made with trap-type defects. This material may be made up either of a weakly doped amorphous silicon of type p, or of an amorphous silicon containing dopant of both types, in extremely low concentrations and for this reason called microcompensated.
At present there are on the market a number of infrared radiation detectors that are fundamentally based on two phenomena:
a) bolometers and pyroelectrics having microstructures that, when illuminated by radiation, change temperature. In bolometers the change in temperatures corresponds to a change in electrical resistance, which can be measured. In the pyroelectric detectors the change in temperature corresponds to a change in the electrical dipole moment of the crystal structure, and this gives rise to a measurable charge outside the crystal, through capacitative coupling;
b) the absorption of photons by the generation of electron-hole pairs, detected through photocurrent at the junctions or through changes in resistivity of photoresistances.
Whether in the bolometers or in the pyroelectric detectors, the absorption does not need the generation of carriers and therefore the absorption bands are very much extended but the heat capacity of the component can dramatically reduce the detection speed.
In the second case the junction detectors display a higher response speed since the photogenerated charges are swept by the electric field and rapidly gathered up by the outside electrodes. The photoresistances display a high optical gain, defined as the ratio between current under lighted conditions and current under dark conditions, but they are on the other hand extremely slow, since the photogenerated charges, once the radiation has ceased, cannot be removed by the presence of an electric field but disappear only owing by the effect of recombination.
In ordinary photodetectors the transition between valence band and conduction band demands a photon energy higher than or equal to the semiconductor's forbidden energy gap. For the construction of IR radiation photodetectors special low-gap sem
Caputo Domenico
Palma Fabrizio
Hannaher Constantine
Harrison & Egbert
Israel Andrew
Universita Degli Sudi di Roma “La Sapienza”
LandOfFree
System of infrared radiation detection based on sensors of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with System of infrared radiation detection based on sensors of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and System of infrared radiation detection based on sensors of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2497432