Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Electromagnetic or particle radiation
Reexamination Certificate
2002-07-15
2004-03-30
Munson, Gene M. (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Electromagnetic or particle radiation
C257S189000, C257S448000, C257S457000, C257S615000
Reexamination Certificate
active
06713832
ABSTRACT:
TECHNICAL FIELD
The present invention concerns a photodetection device as well as a procedure for the manufacture of this device.
As will be seen better as follows, the device that is the objective of the present invention offers a wide range of selection for the wave length, extreme speed and great sensitivity.
It is applicable to any field liable to take advantage of at least one of these qualities such as, for example, the microscopic detection of molecules and, more specifically, very high speed optical telecommunications, greater than or equal to 100 Gbits per second.
PRIOR STATE OF THE ART
MSM (Metal-Semiconductor-Metal) type photodetectors are generally quite simple to manufacture, they are easily fitted into field effect transistors and allow relatively high speed to be obtained but to the detriment of performance. Hereinafter, some MSM photodetectors are considered that are known as well as their drawbacks.
In a known photodetector based on InGaAs, whose distance between the electrodes is 1 &mgr;m, the transit time of the holes is around 10 ps, which corresponds to a cut-off frequency of less than 20 GHz. Therefore the distance between the electrodes must be reduced in order to cut down the transit time for the holes. When the distance between the electrodes drops below 0.1 &mgr;m, the transport can no longer be considered as stationary. The transit time then becomes much lower than 1 ps.
The masking of the active zone by the electrodes is one of the main drawbacks of the known MSM structures and limits their quantum yield. Furthermore, because of the limited absorption of the materials used in these structures (the length of absorption is greater than 1 &mgr;m), the thickness of the absorption zone must be limited so as to prevent the creation of charge carriers far away from the electrodes. The quantum efficiency of the known photodetectors, since they have a range between the electrodes of less than 0.1 &mgr;m, is therefore extremely bad.
On the contrary, the known MSM structures, whose external quantum yield is good, have a low speed.
But nowadays a super-fast photodetector (whose response time is less than 1 ps) is a crucial element for very high speed optical telecommunications (100 Gbits/s and above). The performance levels sought include great sensitivity and broadband, at wavelengths between 1.3 &mgr;m and 1.55 &mgr;m. Whatever type of photodetector it may be (P(I)N diode or Metal-Semiconductor-Metal structure), the target of high speed forces the distance between the electrodes to be short (less than 100 nm) and that the light to be detected must be absorbed in a minimum volume.
Hence, the bulk InGaAs semiconductor has a characteristic absorption length of around 3 &mgr;m at a wavelength of 1.55 &mgr;m.
In the PIN diodes and in the MSM structures, the reduction of the transit time for the charge carriers is directly linked to a drop in the external quantum yield.
The design of the known photodetectors therefore is necessarily the subject of a compromise between yield and speed.
OVERVIEW OF THE INVENTION
The device that is the subject of the invention aims to radically question this compromise and uses a vertical microresonator, which allows, for example, a quantum yield of over 70% to be attained in a low capacity structure, whose range between the electrodes may be less than 50 nm and may lead to a bandwidth of over 1 THz.
The principle for a device in accordance with the invention consists of concentrating the light that we may wish to detect in a resonant manner, in a low volume MSM type structure, by using the fast drop in evanescent modes excited in the Metal/Semiconductor interface.
The surface plasmon modes allow this aim to be achieved.
Unlike the known structures, the plasmons do not spread horizontally (that is to say in parallel to the substratum of the structure), but rather they remain confined along the vertical surface of the electrodes in the structure.
In a precise manner, the aim of the present invention is a photodetection device intended to detect an incident light with a predefined wavelength, propagating in a propagation medium, with this device being characterised by the fact that it includes an electrically insulating layer that does not absorb this light and, on this layer, at least one element, including a semiconductor material, and at least two biasing electrodes, intended to be carried respectively to potentials that are different from one another, with the electrodes surrounding the element, with the set formed by the element and the electrodes being adapted to absorb the incident light (in other words, the element and/or the electrodes are suitable for absorbing this light), with the element and the electrodes having a shape that is substantially parallelepipedal and extending following the same direction, with the dimmensions of the electrodes and the element, counted transversally to this direction, being chosen according to the predefined wavelength, in such a way as to increase the light intensity in the set formed by the element and the electrodes with respect to the incident light, by making at least one of two modes resonate, that is to say a first mode which is a surface plasmon mode and which made to resonate between the interfaces that this set includes with the insulating layer and the propagation medium, with the resonance of this first mode taking place at the interface between the element and at least one of the electrodes, with this first mode being excited by the component of the magnetic field associated with the incident light, a component that is parallel to the electrodes, and a second mode which is a transverse electrical mode of an optical waveguide which is perpendicular to the insulating layer and includes the two electrodes, with this second mode being excited by the component of the electric field associated with the incident light, a component which is parallel to the electrodes.
Preferentially, when the surface plasmon mode is made to resonate, the width of each element, counted perpendicularly to the direction of the electrodes, is less than &lgr; and greater than 0.02×&lgr;, where &lgr; is the wavelength of the incident light and the thickness of each element is less than &lgr;/(2n), where n is the average refractive index for each element.
According to a first particular form for building the device that is the subject of the invention, the electrodes are made of the same electrically conductive material and are the same height, counted perpendicularly to the insulating layer.
According to a second particular form for building it, the electrodes have at least one of the following two properties (a) they are made of different electrically conductive materials and (b) they have different heights, counted perpendicularly to the insulating layer, in such a way that the resonance takes place essentially on the side of the electrode which collects the slow charge carriers at the time of the biasing of the electrodes.
The element that the device carries may include a semiconductor heterostructure.
According to a particular mode for its construction, the device that is the subject of the invention includes several elements and electrodes that alternate on the insulating layer, with each electrode being made of a single metal or of two different metals.
In this case, in a first particular mode for its implementation, the electrodes are intended to be carried to potentials which grow from one end electrode to the other end electrode in the set of electrodes.
The device that is the subject of the invention may then also include a resistive material, for stabilising potentials, which is in contact with the electrodes and runs from one end electrode to the other end electrode in the set of electrodes. The latter allows the set of elements to be polarised under a high voltage.
In a second particular mode for its implementation, the electrodes are intended to be carried to potentials whose absolute values are equal and whose signs alternate.
According to a preferred mode for the implementation of the devi
Collin Stéphane
Pardo Fabrice
Pelouard Jean-Luc
Teissier Roland
Centre National de la Recherche Scientifique
Munson Gene M.
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