KR20070032389A - An optically-configurable nanotube or nanowire semiconductor device - Google Patents

Abstract

The present invention comprises at least two electrodes; And at least one nanotube or nanowire, in particular carbon nanotube or nanowire. The device includes at least one semiconducting nanotube or nanowire having at least one region covered at least in part by at least one layer of molecules or nanocrystals of at least one photosensitive material. And the at least two electrodes are electrically connected by at least one nanotube, that is, the semiconducting nanotube or nanowire, or at least one other nanotube or nanowire.

Description

Optically configurable nanotube or nanowire semiconductor devices {AN OPTICALLY-CONFIGURABLE NANOTUBE OR NANOWIRE SEMICONDUCTOR DEVICE}

The present invention relates to nanotube or nanowire semiconductor devices such as optically configurable transistors or diodes and to their use in optically reconfigurable electronic circuits.

Applied Physics Letters, Vol. 79, No. 14, 2258 (2001), entitled "Molecular desorption from single-walled carbon nanotubes," reports that strong illumination in ultraviolet or visible light leaves oxygen molecules present on the electrode. It is disclosed that the electrical properties of the nanotube transistor can be changed. This phenomenon is fast, but when it comes to reversibility, typically tens of minutes are required to recover the initial current. This phenomenon, which requires a large amount of power, is not wavelength specific and is difficult to reverse.

Applied Physics Letters, K. Balasubramanian et al. 84, No. 13 (2004), entitled "Photoelectronic transport imaging of individual semiconducting carbon nanotubes", describes photons having wavelengths located at 514.5 nanometers (nm) and / or 647 nm. Disclosed is the possibility of generating photo-current in non-functionallized carbon nanotube transistors. The current is generated very weakly to less than 1 nanoamps (nA) and can only be detected when the transistor is in the off state.

Nano Letters, Vol. 3, No. 8, pp. 1067-1071 (2003), entitled "Photoconductivity of single carbon nanotubes," shows that nanotube transistors can be used to detect infrared photons. The current in a nanotube transistor is one of the allowed transitions between the half-hop singularities (eg, forbidden bands) of the semiconducting nanotubes that serve as the channel of the transistor. It can be altered by photons with a wavelength of light corresponding to one energy, in general, this wavelength is raised to the infrared of the first two accessible transitions, which is the atomic structure of the nanotubes (diameter and chirality). Is finally defined by)).

The changes observed in the electrical properties of transistors by nanotubes due to the presence of light are very small. Although they can be used to detect infrared emission, transistors must be purely "optically controlled". Only the off state of the transistor changes in a very small amount. As a result, the method used to directly generate electron-hole pairs through the ban on nonfunctionalized nanotubes has a very small quantum efficienby of 10 ⁻⁷ orders.

Nano Letters by A. Star et al., Published in June 2004, entitled “Nanotube optoelectronic memory devices,” used carbon nanotubes with photosensitive polymers to provide memory functionality. To functionalize the device. For this purpose, a group of nanotubes is covered by a thick polymer film that is drop deposited onto the chip. It thus relates to very large molecules of polymer deposited in an uncontrolled form with very thick layers. When the device is illuminated, the Id (Vgs) electrical property is shifted, indicating that electrons are transferred to the polymer. When illumination is interrupted, the device retains its characteristics for a very long time (minutes), providing a "memory" effect. This technique is limited to "memory" type features and is not suitable for dense integration.

By Rotkin and Zmarov, International Journal of Nanoscience, Vol. 1, Nos. 3 and 4 (2002), pp. A paper entitled "Nanotube light-controlled electronic switch" published in 347-355 describes the use of shape-changing molcule to displace charges around carbon nanotubes. Suggest. When photons are absorbed, the molecule is modified. According to this theoretical study, when a molecule moves a charge at its tip away from a nanotube, the charge is mechanically directed to or off the tube. This serves to change the characteristics of the device. In any case, this technique requires that shape-modifying molecules be used.

Other features and advantages of the present invention will become more apparent by reading the following detailed description with reference to the drawings below.

1A shows an example of a carbon nanotube field effect transistor (CNTFET), and FIGS. 1B and 1C constitute various examples of devices that can be used in the context of the present invention.

2 a to c show the different positions of the photosensitive layer and the effects resulting therefrom.

3 shows a series of experiments with and without excitation by laser light.

4A and 4B show drain current Id characteristics according to the gate source voltage Vgs of a transistor in the dark and the illumination of a red laser having a wavelength of 647.1 nm, respectively. 4b shows the same curve using a semilogarithmic coordinate.

5A to 5 show gate source voltages Vgs [Vs] in order to show various effects that can be obtained in p-type carbon nanotube transistors in the operating range of voltages Vgs in the range of -1 V to +1 V. The empirical curve of drain current (Id) [nA] at nA according to V] is used.

6 a to c show various optically reconfigurable circuits applied to one or more devices according to the present invention.

It is an object of the present invention to provide a semiconductor device comprising at least one nanotube, in particular carbon nanotube, or at least one nanowire. The device is optically configurable and reversible with advantageous quantum efficiency without any noticeable memory effect. In other words, the device returns to its initial state when illumination is interrupted. Advantageously, the device is optically configurable by light at a selected wavelength depending on the function of the selected photosensitive material.

The invention also provides a semiconductor device comprising at least two electrodes and at least one nanotube or nanowire, in particular carbon nanotube or nanowire. The device comprises at least one semiconducting nanotube or nanowire having at least one region covered at least in part by at least one layer of molecules or nanocrystals of at least one photosensitive material; The at least two electrodes are electrically connected by at least one nanotube, that is, the semiconducting nanotube or nanowire, or at least one other nanotube or nanowire.

Advantageously the molecule is amphiphilic.

The materials are, in particular, phthalocyanine in which a metal center atom consisting of metal center atoms (particularly copper atoms) is present, porphyrine, azopororphyrine or derivatives thereof, or indeed dyes. (dye) or chromophores, in particular amphilipic chromophore. Or the materials may be actual composite molecules consisting of at least two parts, a chromophoric center and a graftable part that can be selectively covalently grafted onto the device. have. Variously, the material may be nanocrystals of semiconductor materials.

The material may be in the form of a thin film having layers of 0 to 20, in particular 1 to 10, consisting of molecules of the material. Thinner films are preferred because they are suitable for obtaining fast optoelectronic effects.

Advantageously, the thin film can be replaced by selectively covalent grafts of molecular monolayers at selected portions of the device (nanotubes, electrodes, and / or surfaces that support the tubes).

The region on which the material is deposited or grafted may be the outer and / or inner surface of the nanotube or nanowire, the electrode of a semiconductor device, the actual surface of the gate insulating film of the transistor, or of the substrate on which the nanotube or nanowire is located. It may be the actual surface.

The device may have one or more regions each covered in at least one layer composed of different photosensitive materials.

The present invention also provides a control method of the semiconductor device described above. The control method is characterized in that the illumination of at least one said region is applied by light of a wavelength located in the light-absorbing region of said material.

Depending on the structure (chirality), single-walled carbon nanotubes can be metallic or semiconducting. They are connected to the electrodes to form an electronic component. Thus, in the period from 1996 to 2004, these nanotubes were used to manufacture diodes, single-electron transistors (SETs), and carbon nanotube field-effect transistors (CNTFETs). Used as a basic ingredient. Such CNTFETs can be used in the manufacture of memory components, individual logic gates, detectors of gases or biological molecules, or detectors of actual emitters and infrared photons. have.

The CNTFET type field effect transistor is constituted by, for example, semiconducting single-walled carbon nanotubes 1 connected by two electrodes, that is, a source S and a drain D, and an insulating film 2 (gate Oxide) is controlled by a third electrode, ie gate G, which is separated from the tube. The current flowing along the channel constituted by the carbon nanotubes 1 between the source S and the drain D is regulated by the gate voltage. The above configuration is not only possible configuration. In particular, the gate electrode may be located above or below the nanotubes.

Since 1998, particularly over the past two years, implementation of these components has continued to improve to reach levels similar to silicon transistors.

One of the main features of these electronic components by carbon nanotubes is that they are very sensitive to the environment. The presence of molecules absorbed in various parts (tubes, electrodes, surfaces) of this component changes the electron transfer properties very significantly.

The environment of a CNTFET can change the electrical properties of the CNTFET in a variety of ways.

a) Molecules adsorbed or chemically bound to the nanotubes can transfer charges (donating or accepting electrons) to the nanotubes. This change results in a change in the doping level of the nanotubes.

b) At the periphery of the nanotubes, molecules adsorbed or chemically bound to the electrodes can alter the carrier injection into the channel. To enter the nanotubes, the charge in the electrodes must overcome the potential barrier caused by the Schottky contact. The height of this barrier is sensitive to the presence of certain molecules, especially polar molecules.

c) Adsorption of molecules on the periphery or the surface of the nanotubes can also alter the electrical properties of the component without any charge transfer between the molecules and the nanotubes. In particular, charged or high polarity molecules around the tube alter the electrostatic potential in the tube and thus function like the voltage applied to the gate. This is referred to as "chemical gating" or chemically-induced gate potential.

The present invention attempts to use light in particular for triggering, stopping, increasing, decreasing and / or reversible effects of this type.

Various classes of molecules have photochemical or photophysical properties. Very generally speaking, when a molecule absorbs a photon, the molecule is switched to an excited state. This approach of energy can have various consequences. Molecules are divided into fragments; Luminesce; Experiencing non-radiative transitions; Ionized; Change shape; React with other molecules to form new components or transfer charges; You can move that excitation to another molecule. Some of these mechanisms, particularly the last four, can be used to control the transfer properties of nanotube transistors.

a) photoexcitation doped (Photo - induced doping )

Certain molecules in solution can either donate or accept electrons when they absorb photons. In the example below, molecules are adsorbed to a tube that transfers charge when in an excited state (a in FIG. 2). This changes the doping level of the transistor channel.

It is also possible to take advantage of the excellent optical properties of semiconducting nanocrystals, typically CdSe. When photons are absorbed by semiconducting nanocrystals, electron-hole pairs (excitons) form. Then charges traveling towards the molecules present on the surface of the nanocrystals can be observed. Accordingly, hole movement is observed when the surface of the nanocrystals is functionalized by molecules of reducing properties such as thiols or poly-aromatics. Semi-conducting nanocrystals, possibly grafted to or deposited directly on the nanotubes by advanced functionalization of the surface, may enable photoexcitation doping. Another advantageous property of nanocrystals is how the absorption spectrum depends on the size or type of chalcogenide (CdTe, CdSe, CdS) used. Therefore, by using nanocrystals having different diameters or compositions, it is possible to select the wavelength of radiation causing the light-doping effect.

b) change of charge injection photoexcitation

It is known that the absorption of photons can alter the chemical structure of a particular molecule. This may be the result of changing the electrical dipole moment, especially when the distribution of the center of the positive or negative charge differs from one state to another. Once these molecules are grafted to the electrodes of CNTFER (Fig. 2b), the injection of carriers into the nanotubes will be sensitive to the state of the molecules, and thus light.

c) photoexcitation gate potential

It is also possible to use such molecules grafted on the surface of the nanotubes or gate oxides (FIG. 2C). Adsorption of photons then alters the electrostatic enviroment, thus creating an effect similar to that of chemical gating.

Eg electrical, which can be altered by light Characteristic  Carbon nanotube transistor

In this example, the nanotube transistor is covered with a phthalocyanine Langmuir-Blodgett film known as CuS18. The chromophore molecules used are chromophore hearts with four C18 aliphatic chains (ie four C18 aliphatic chains with 18 carbons each) in positive amounts. It is an amphiphilic phthalocyanine with (heart). CuS18 is described by Serge Palacin in 1986 by S. Palacin, A. Ruaudel-Teixier, A. Barraud, J. Phys. Chem., 90, 6237-6242 (1986). The name CuS18 was advantageous in a system for naming a series of compounds of similar structure. Full name is tetraoctadiyl tetrapyridino [3,4-b: 3 ', 4'-g: 3' ', 4' '-1,3' '', 4 '' '-q] popyrazinium (tetraoctadecyltetrapyridino [3,4-b: 3 ', 4'g: 3' ', 4''1: 3' '', 4 '' '-q] porphyrazinium).

A typical size of this molecule is a 1.7 nm diameter chromophore core with a 2.0 nm chain that binds to its edge or mobile. Langmuir blowjet deposition techniques allow precise control of the amount of molecules deposited by stacking monolayers from monolayer to monolayer. The effect described below reproduces a single layer, two layers, and a thermal layer of molecules on the transistor. In practice, for example, it is possible to overlap in a single layer or more of approximately twenty layers.

The present invention is not limited to using a layer deposited by Langmuir jetjet deposition techniques. There are other deposition methods known to those skilled in the art, such as chemical vapor deposition (CVD). It is possible to functionalize nanotubes before assembling them in the device.

In the illumination of a given wavelength corresponding to the maximum absorption of the molecule's spectral, in this case 647.1 mm wavelength laser illumination, by means of wavelength selectivity depending on the molecule used, the molecules in contact with the tube transfer electrons into the tube Is charged. The presence of positively charged molecules in the above reduces the density of positive charges (holes) in the tube. Because holes at the negative gate voltage cause the current to flow through the transistor, the reduction in their number greatly reduces the current through the transistor when the transistor is illuminated.

To show the dynamics of this phenomenon, FIG. 3 is a group of curves over time and shows the cycle of sweeping through voltage Vgs. This results in a string of Id (Vgs) properties. A sudden drop in current is observed when light is on. Of particular note is the rapid reversibility of this phenomenon.

Other studies, particularly the aforementioned ones, represent photoexcitation phenomena that are difficult to reverse: charge-away of molecules from the electrode to the transistor and charge storage in the photosensitive polymer. The fact that the curves in FIG. 3 recover to their original properties as soon as the laser is turned off indicates that another mechanism is involved. The power of the laser was experimentally increased until it reached the light-absorption phenomenon. Before reaching the light-excitation threshold, there is a wide range of powers that enable advantageous phenomena by the fast dynamics observed by itself.

FIG. 4A shows the Id (Vgs) characteristics of the transistor in the dark and when there is illumination of a red laser with a wavelength of 647.1 nm. The Id (Vgs) characteristic is obtained by averaging records of Id (Vgs) corresponding to the curve of FIG. It is very clear that this property is greatly changed by photons, especially in the on state. This is a significant difference from the prior art.

In order to also know the off state, the same curve is shown in FIG. 4B using a semilogarithmic scale. It can be clearly seen that the off state also changes significantly at grid voltages greater than the threshold voltage.

As a result, it is important to observe that this phenomenon is firm. The laser can be cycled by very many times without degrading the layer of molecules.

The present invention works with nanotubes and relatively small molecules (relatively small molecules as compared to polymer molecules), by working in very small amounts up to a single layer of molecules, thereby achieving a fast and potentially localized electrical effect. It is possible to maximize the interaction between them. This not only reconfigurable but also makes it possible to use transistors in integrated circuits.

Such transistors can be used in the fabrication of optically reconfigurable circuits. It acts like a switch controlled by light. If the voltage Vgs is set to a negative value (e.g., -10 V as in the special case shown in Figure 4), the transistor is prevented from flowing current in the presence of light. As can be clearly seen from the logarithimic scale, Id << 10 ⁻¹¹ A. When the component is located at its input in a sub-circuit, this subcircuit is activated by the absence of light and deactivated by the presence of light.

In the context of the present invention, an actual group of two semiconducting nanotubes or nanowires (FIG. 1), connected between two electrodes (source S and drain D in the transistor of FIG. 1B), at least one of which is semiconducting Nanotubes and / or nanotubes, the actual group of nanowires that are at least one semiconducting that connects the two electrodes by themselves to provide a path to the electrodes (source and drain in the transistor of FIG. It is also possible to apply nanotubes.

The various examples of FIGS. 1B and 1C have the advantage that the charge has high mobility, up to 79000 cm ² / V / s, in the carbon nanotubes. This is in contrast to the values in organic materials from 10 ⁻³ cm ² / V / s to 10 ⁻¹ cm ² / V / s.

Other molecules may be used, such as:

Phthalocyanines whose central valence is a metal other than copper and / or other phthalocyanines in which an aliphatic chain can be replaced by another chain.

Porphyrine, azoporphyrine or derivatives thereof.

Fluorophores or chromophores comprising semiconducting nanocrystals, for example CdTe, CdSE or CdS. Nanocrystals can be used as such or can be altered while enclosing in the covering of other materials, eg, shells or molecules such as ZnSE. For example, it is possible to prevent the photon absorbed by ZnSe from being re-radiated.

Several deposition techniques can be implemented for the deposition of the molecules.

The first consists in depositing a layer of one or more molecules in a controlled number on an existing transistor, as in the previous example. In particular, it is possible to use the following amphoteric molecules.

Phthalocyanines having a central metal atom with an aliphatic chain of length C18 or other length that provides an ampliphilic nature inside,

Porphyrins, azoporphyrins, amphilic derivatives thereof, or

-Amphiphilic chromophores or dyes.

A second technique of selectively applying covalent bonds consists in depositing a layer of molecules, typically one in a controlled number, by chemisorption or physiosorption to the existing transistor.

The third technique consists in assembling nanotubes and molecules in solution, optionally by applying covalent bonds. The nanotubes then cover a small number of molecules, typically a single layer. Such nanotubes can be used inductively to produce transistors (or diodes).

These three techniques are suitable for fabricating high density circuits corresponding to multiple wavelengths. In the first two cases, circuits are formed before the molecules and nanotubes are combined. Because of the successful masking of certain parts of the circuit, it is possible to deposit other molecules on top of other transistors (or other circuit parts). Optionally, a dip pen type technique may be used to functionalize another transistor with different molecules. Such techniques (for example CA Science 1999, 283, 661 by Piner et al., Or CA Science 1999, 286, 523 by Hong et al., Or indeed techniques well documented in the CAScience 2000, 288, 1808 literature by Hong et al.), Pen ", which consists of using the molecule as an" ink "along with the tip of an atomic force microscope (AFM). The tip of the AFM moves up to the supply of molecules and then to the device to be modified. Under certain conditions, molecules migrate from the tip of the AFM to the adjacent surface.

Optionally, selective chemical functionalization in the transistor can be performed by electro-grafting. By bringing the circuit into contact with a reactant, for example by immersing it and electrically biasing one (or more) transistors, the transistor can be specially functionalized without affecting the unbiased transistor.

With regard to the deposition of the electrode, it should be observed that all the chromophore molecules which are finished by the thiol group (SH) can be grafted onto the electrode composed of gold by forming a bond of gold and sulfur. With regard to the gate, a method of functionalizing silicon oxide by molecules of chloro-silane or ethoxy-silane type can be used, which is suitable for manufacturing carbon nanotube transistors. . In particular, literature was produced in the following publications.

-K.C. Choi, J.P. Bourgoin, S. Auvray, D. Esteve, G.S. Duesberg, S. Roth, Burghara, Surface Science 462, 195 (2000); And

-E. Valentin, S. Auvray, A. Filoramo, A. Ribayrol, M. Goffman, L. Cape, J.P. Bourgoin, J.N. Patillon, Mat.Rers. Soc. Symp. Proc. 772, M4.7.1 (2003).

5A to 5 show, for example, various effects that can be obtained in a p-type carbon nanotube transistor in an operating range set between gate / source voltage Vgs in the range of −1 V to +1 V. FIG. Similar effects can be obtained in n-type transistors.

A of FIG. 5: stopped (non-illuminated) transistor

5 b: the effect of light allows the transistor to survive in the off state in the operating range. This corresponds to the use of electron donor molecules, as in the example above.

C: the effect of light is to ensure that the transistor is always on in the operating range. This corresponds to electron accepting molecules.

D in FIG. 5: The effect of light is to cause the p-type transistor to transform into an n-type transistor. This corresponds to electron donor molecules illuminated such that the hole current is Vgs <0 and the electron current appears at Vgs> 0, as shown in FIG.

E of FIG. 5: The effect of light is to allow transconductance to be improved. This corresponds to reducing the height of the Schottky barrier by increasing hole injection.

5: The effect of light is to reduce the transconductance. This corresponds to limiting hole injection to increase the height of the Schottky barrier.

In summary, the effects shown in Figures a through d correspond to "doping," while the effects shown in Figures 5 e and f correspond to changing the injection by changing the electrons.

The wavelength of the light controlling the transistor is selected in accordance with the light absorption by the molecules used. Therefore, this wavelength can be selected in a wide range including near visible and ultraviolet rays depending on the material used. The possibility of adjusting the control wavelength by parameters outside the nanotubes is an important factor in using this control in the fabrication of circuits. It makes it possible to observe circuits comprising a plurality of transistors functionalized by different molecules and reacting to different wavelengths.

The present invention also provides a reconfigurable electronic circuit comprising at least one semiconductor device as described above. The semiconductor device is coupled to at least one optical device suitable for modifying electronic parameters and / or functions of at least one of the semiconductor devices.

Functionally speaking, the electronic circuit can be thought of as a "black box" that converts a group of electrical input signals E1-En into a group of output signals S1-Sn (FIG. 6). The function performed by this circuit is a function f which gives the output signals in accordance with the input signals. The overall circuit may include a subcircuit that operates on a limited range of input signals and provides an immediate limited set of output signals.

The circuit is optically reconfigurable if the overall function f varies with illumination (with or without illumination, intensity I and wavelength λ). For this purpose, various configurations can be considered.

The circuit of a of FIG. 6 is a simple circuit. Design as a group of subcircuits is unnecessary. f is a function of illumination: f (I, λ);

The circuit of b of FIG. 6 consists of subcircuits that each respond differently to light: f _scn (I _n , λ _n ). Optionally, certain subcircuits need not be sensitive to light. In this case, the subcircuits must be functionalized by other types of molecules.

The circuit of FIG. 6c consists of subcircuits which do not respond to light but whose activation is controlled by a control transistor T ₁ to T _n which is itself photosensitive. In this case, only the control transistors can be chemically functionalized to make the control transistors photosensitive at one or more selected wavelengths.

The present invention provides a semiconductor device comprising at least one nanotube, in particular carbon nanotube, or at least one nanowire. The device is optically configurable and reversible with advantageous quantum efficiency without any noticeable memory effect. In other words, the device returns to its initial state when illumination is interrupted. The device is optically configurable by light at a selected wavelength depending on the function of the selected photosensitive material.

Claims (21)

At least two electrodes; And at least one nanotube or nanowire, in particular carbon nanotube or nanowire, The device, At least one semiconducting nanotube or nanowire having at least one region at least partially covered by at least one layer of molecules or nanocrystals of at least one photosensitive material, And the at least two electrodes are electrically connected by at least one nanotube, ie the semiconducting nanotube or nanowire, or at least one other nanotube or nanowire. The method of claim 1, Wherein said molecule is an amphilipic. The method according to claim 1 or 2, And the material is phthalocyanine in which the metal center atom is present. The method of claim 3, And said central atom is a copper atom. The method according to claim 3 or 4, The phthalocyanine device, characterized in that the presence of an amphilipic chain (chain). The method according to claim 1 or 2, The material is porphyrine (porphyrine), azoporphyrine (azoporphyrine) or a device, characterized in that derivatives thereof. The method according to claim 1 or 2, And said material is a dye or a chromophore. The method according to any of the preceding claims, And the material is in the form of a thin film. The method according to any one of claims 1 to 7, Wherein the material is in the form of a molecular monolayer that is selectively grafted in a covalent manner. The method according to any of the preceding claims, At least one of said layers is ordered. The method of claim 1, And the material is semiconducting nanocrystals. The method according to any of the preceding claims, And the region is an outer surface and / or an inner surface of the semiconducting nanotube or semiconducting nanowire. The method according to any of the preceding claims, And the region is an electrode of the semiconductor device. The method according to any of the preceding claims, A semiconducting nanotube or semiconducting nanowire with the electrodes. The method according to any of the preceding claims, A device comprising a transistor. The method of claim 15, And said region is a surface of a gate insulating film of a transistor. The method of claim 15, And the region is the surface of the semiconducting nanotube or the substrate on which the semiconducting nanowires are located. The method of claim 13, And said semiconductor device is a diode. The method according to any of the preceding claims, And said device comprises at least two said regions, each of said regions being covered with said at least one layer of different photosensitive material. And at least one semiconductor device according to the preceding claims in combination with an illumination device suitable for changing electronic parameters and / or functions of the semiconductor device. 20. A method of controlling a semiconductor device according to any one of claims 1 to 19 or an electronic circuit according to claim 20, Illuminating at least one of said regions by light at a wavelength located in said light-absorbing region of said material.