Infrared photodetector device

Abstract

A photodetector device (100) is provided. The photodetector device (100) comprises: a quantum well nanostructure (120) extending perpendicularly to a first direction (x); a quantum dot nanostructure (130) extending perpendicularly to the first direction (x), the quantum dot nanostructure (130) being stacked on the quantum well nanostructure (120) along the first direction (x). The quantum well nanostructure (120) and the quantum dot nanostructure (130) are made of the same material. The quantum well nanostructure (120) and the quantum dot nanostructure (130) define a conduction band of the photodetector device (100) comprising: a minimum energy state (S(0)) of the conduction band; a set of first energy states (S(l)) of the conduction band, the first energy states (S(l)) of the conduction band being at a higher energy than the minimum energy state (S(0)) of the conduction band, and a set of second energy states (S(h)) of the conduction band, the second energy states (S(h)) of the conduction band being at a higher energy than the first energy states (S(l)) of the conduction band. The minimum energy state (S(0)) of the conduction band and the first energy states (S(l)) of the conduction band are generated by the quantum dot nanostructure (130). The second energy states (S(h)) of the conduction band are generated by the quantum well nanostructure (120) and comprise one or more resonant energy states (SR) located in the continuous portion of the conduction band.

Description

[0001] INFRARED PHOTODETECTOR DEVICE

[0002] DESCRIPTION

[0003] Background of the present invention

[0004] Field of the present invention

[0005] The present invention relates to the field of infrared photodetectors, and in particular to an infrared photodetector device based on nanostructures.

[0006] Background of related art

[0007] An infrared photodetector device, also known as an infrared photodetector, is a device capable of detecting electromagnetic waves in the infrared band, that is, electromagnetic waves whose wavelength is between 700 nm and 1 mm.

[0008] Many of the traditional infrared photodetectors are not particularly efficient in detecting infrared (i.e., infrared light) at room temperature, especially if the radiation to be detected is in the far infrared (or long infrared, in English “Long Wave InfraRed”, “LWIR”) spectral region, i.e., with wavelengths in the range 8 pm - 15 pm, and require the use of specific external cooling systems to improve the signal -to-noise ratio. This is necessary to suppress the thermal excitation of the electric charge carriers (hereinafter also referred to as “charge carriers”), which becomes more significant at longer detection wavelengths, due to transition energies close to thermal energy.

[0009] In order to mitigate this problem, several studies have been conducted aimed at the realization of infrared photodetector devices made with “Quantum Well” (“QW”) semiconductor material nanostructures or with “Quantum Dot” (“QD”) semiconductor material nanostructures.

[0010] The term nanostructure (or nanoaggregate or cluster) indicates a system consisting of a number of atoms or molecules (for example, ranging from a few units to a few thousand) and whose dimensions are of the order of nanometers.

[0011] As known to those skilled in the art, a quantum well nanostructure is a nanostructure characterized by a potential well with discrete energy states, obtained by forcing charge carriers, e.g., electrons - initially free to move in three dimensions - to occupy a planar region, so that such charge carriers are free to move only in two dimensions. In other words, a quantum well nanostructure exerts a ID confinement on the charge carriers, in the sense that it reduces the freedom of movement of the charge carriers by one dimension (from three dimensions to two dimensions).

[0012] The advantages of infrared photodetector devices made with quantum well semiconductor nanostructures include: a rather large charge carrier capture cross-section, which allows for a high probability of charge carrier capture, and a large “Density Of States”, “DOS”, which implies a large amount of electrons ready to absorb radiation.

[0013] A quantum dot nanostructure is a nanostructure characterized by a potential well with discrete energy states, obtained by forcing charge carriers, e.g., electrons - initially free to move in three dimensions - to occupy a substantially point-like region, so that such charge carriers are no longer free to move. In other words, a quantum dot nanostructure exerts a 3D confinement on the charge carriers, in the sense that it reduces the freedom of movement of the charge carriers by three dimensions (from three dimensions to zero dimensions).

[0014] The advantages of infrared photodetector devices made of quantum dot semiconductor material nanostructures include: a narrow density of states (such as an impulsive-like density of states, or “delta”-type density of states), which implies a reduced probability of charge carriers interacting with phonons (a phenomenon known as the “phonon bottleneck”), and which therefore reduces the probability of thermal escape of charge carriers from the “ground state” of the quantum dot (i.e., from the minimum and indefinitely stable energy state of the quantum dot), even at high temperatures, and the ability to absorb normal radiation, incident perpendicularly to the surface of the photodetector exposed to the radiation.

[0015] Summary of the present invention

[0016] The Applicant found that infrared photodetector devices made with quantum well nanostructures are not efficient, as they suffer from drawbacks.

[0017] In particular, since a quantum well nanostructure is characterized by a large density of states, there will be a high probability of scattering by phonons, causing a reduction in detection efficiency at higher temperatures, due to thermal escape of electrons.

[0018] Furthermore, according to the quantum selection rules for intra-band transitions in the dipole approximation, a quantum well nanostructure is not able to absorb normal radiation, incident perpendicularly to the photodetector surface exposed to the radiation, and therefore the detection of radiation is possible only by using very complex optical couplings.

[0019] The Applicant found that infrared photodetector devices made with quantum dot nanostructures are also not efficient, as they suffer from further drawbacks.

[0020] In particular, since a quantum dot structure is characterized by a narrow DOS, the probability of charge carriers interacting with phonons is reduced. Consequently, the thermalization process of free charge carriers to the ground state of the quantum dot is hindered due to the unlikely interaction of electrons with phonons along the longitudinal optical direction. Furthermore, since the spatial extension of a quantum dot structure is very small, the capture cross-section of charge carriers is also very small.

[0021] The combination of having a narrow DOS with having a small spatial extent makes it very difficult to supply the ground state of a quantum dot nanostructure with electrons.

[0022] In view of the above, the Applicant has devised an improved infrared photodetector device which is not affected (or at least is affected to a limited extent) by the above-mentioned drawbacks.

[0023] One or more aspects of the present invention are set forth in the independent claims, with advantageous features of the invention itself being set forth in the dependent claims, the wording of which is herein incorporated verbatim by reference (with any advantageous feature which is set forth with reference to a specific aspect thereof applying mutatis mutandis to any other aspect thereof).

[0024] In particular, one aspect of the present invention relates to a photodetector device.

[0025] The photodetector device comprises a quantum well nanostructure extending perpendicular to a first direction.

[0026] The photodetector device comprises a quantum dot nanostructure extending perpendicular to the first direction.

[0027] Said quantum dot nanostructure is stacked on the quantum well nanostructure along the first direction.

[0028] Said quantum well nanostructure and said quantum dot nanostructure are made of a same material.

[0029] Said quantum well nanostructure and said quantum dot nanostructure define a conduction band of the photodetector device comprising: a minimum energy state of the conduction band; a set of first conduction band energy states, said first conduction band energy states being higher in energy than said minimum conduction band energy state, and a set of second conduction band energy states, said second conduction band energy states being higher in energy than said first conduction band energy states. Said minimum energy state of the conduction band and said first energy states of the conduction band are generated by the quantum dot nanostructure.

[0030] Said second energy states of the conduction band are generated by the quantum well nanostructure and comprise one or more resonant energy states located in the continuous portion of the conduction band.

[0031] According to an embodiment of the present invention, said quantum dot nanostructure extends, perpendicularly to the first direction, to an extent such as to cover, along the first direction, a sub-portion of the quantum well nanostructure.

[0032] According to an embodiment of the present invention, said quantum dot nanostructure extends, perpendicularly to the first direction, to an extent such as to define portions of the quantum well nanostructure that are not covered, along the first direction, by the quantum dot nanostructure.

[0033] According to an embodiment of the present invention, said photodetector device comprises a first confinement zone for electrons in the conduction band corresponding to the quantum dot nanostructure and to said sub-portion of the quantum well nanostructure covered by the quantum dot nanostructure.

[0034] According to an embodiment of the present invention, said photodetector device comprises a second confinement zone, for electrons in the conduction band, corresponding to said portions of the quantum well nanostructure not covered by the quantum dot nanostructure.

[0035] According to an embodiment of the present invention, said sub-portion of the quantum well nanostructure covered by the quantum dot nanostructure is equal to a selected percentage in the range 10% - 70% of the total extent of the quantum well nanostructure perpendicular to the first direction.

[0036] According to an embodiment of the present invention, the quantum well nanostructure has a thickness, along the first direction, comprised between 0.2 and 5 nm.

[0037] According to an embodiment of the present invention, the quantum well nanostructure and the quantum dot nanostructure comprise a semiconductor material selected from GaAs, Si, Ge, AlGalnAs, AlGalnSb, AlGalnP, AlGalnN, CdSe, CdTe, CdS, ZnSe, ZnS.

[0038] According to an embodiment of the present invention, the quantum dot nanostructure has a thickness, along the first direction, between 1 nm and 15 nm.

[0039] According to an embodiment of the present invention, the semiconductor material of the quantum well nanostructure, and preferably the semiconductor material of the quantum dot nanostructure, is n-type doped. According to an embodiment of the present invention, said photodetector device is a photodetector for detecting electromagnetic waves in the infrared band.

[0040] A further aspect of the present invention relates to a method of manufacturing a photodetector device, particularly a photodetector device according to the previous aspect and comprising:

[0041] - a quantum well nanostructure extending perpendicular to a first direction;

[0042] - a quantum dot nanostructure extending perpendicular to the first direction, said quantum dot nanostructure being stacked on the quantum well nanostructure along the first direction, wherein:

[0043] - said quantum well nanostructure and said quantum dot nanostructure are made of the same material;

[0044] - said quantum well nanostructure and said quantum dot nanostructure defining a conduction band of the photodetector device comprising: a minimum energy state of the conduction band; a set of first energy states of the conduction band, said first energy states of the conduction band being at a higher energy than said minimum energy state of the conduction band, and a set of second energy states of the conduction band, said second energy states of the conduction band being at a higher energy than said first energy states of the conduction band,

[0045] - said minimum energy state of the conduction band and said first energy states of the conduction band being generated by the quantum dot nanostructure, and

[0046] - said second energy states of the conduction band being generated by the quantum well nanostructure and including one or more resonant energy states located in the continuous portion of the conduction band.

[0047] The method comprises:

[0048] - epitaxially depositing a layer of semiconductor material on top of a buffer layer to form the quantum well nanostructure;

[0049] - depositing a set of semiconductor material drops on top of the quantum well nanostructure using the drop epitaxial deposition technique;

[0050] - causing the deposited droplets to crystallize to form the quantum dot nanostructure. Brief description of the drawings

[0051] These and other features and advantages of the present invention will appear more clearly by reading the following detailed description of exemplary and nonlimiting embodiments thereof. For its better intelligibility, the following description should be read with reference to the attached drawings, in which:

[0052] Figure 1 is a sectional view of an infrared photodetector device according to an embodiment of the present invention;

[0053] Figure 2 illustrates an energy profile of the conduction band of the device of Figure 1 according to an embodiment of the present invention;

[0054] Figure 3 is a flowchart of steps in the operation of the detection mechanism of the device of Figure 1, according to an embodiment of the present invention;

[0055] Figures 4A-4G illustrate phases of a manufacturing process of the device of Figure 1, according to an embodiment of the present invention.

[0056] Detailed description of exemplary and non-limiting embodiments of the present invention

[0057] Referring to the drawings, Figure 1 is a sectional view illustrating in very schematic terms an infrared photodetector device 100 (hereinafter also simply referred to as “device 100”) according to an embodiment of the present invention.

[0058] The infrared photodetector device 100 according to an embodiment of the present invention is obtained by combining a quantum well semiconductor material nanostructure with a quantum dot semiconductor material nanostructure. According to an embodiment of the present invention, the quantum well semiconductor material nanostructure and the quantum dot semiconductor material nanostructure are made of the same material.

[0059] The description of the device 100 will be carried out by referring to the three orthogonal directions x, y, z as illustrated in Figure 1.

[0060] According to an embodiment of the present invention, the device 100 includes a first contact layer 105.

[0061] According to an embodiment of the present invention, the first contact layer 105 has a thickness, along the x direction, comprised between 0.5 and 2 pm, for example equal to 1 pm. It should be emphasized that the concepts of the present invention can however also be applied in the case of thicknesses of different extent.

[0062] According to an embodiment of the present invention, the first contact layer 105 is made of a semiconductor material, such as gallium arsenide (GaAs) doped with silicon (Si). Non-exhaustive examples of other possible materials for the first contact layer 105 include group IV semiconductors (e.g., silicon and / or germanium) doped with donors (n-type), or group III-V compound semiconductors (e.g., AlGalnAs, AlGalnSb, AlGalnP, or AlGalnN) doped with donors (n-type), or group II-VI compound semiconductors (e.g., CdSe, CdTe, CdS, ZnSe, or ZnS) doped with donors (n-type).

[0063] According to an embodiment of the present invention, the device 100 further comprises a first buffer layer 110 that covers the first contact layer 105 from above (along the x direction).

[0064] According to an embodiment of the present invention, the first buffer layer 110 has a thickness, along the x direction, of between 100 nm and 1 pm, for example equal to 350 nm. It is emphasized that the concepts of the present invention can however also be applied in the case of thicknesses of different extent.

[0065] According to an embodiment of the present invention, the first buffer layer 110 is made of a semiconductor material, such as aluminum gallium arsenide (AlGaAs), e.g., Alo.3Gao.7As. Non-exhaustive examples of other possible materials for the first buffer layer 110 include group IV semiconductors (e.g., silicon and / or germanium) or compound semiconductors of groups III-V (e.g., AlGalnAs, AlGalnSb, AlGalnP, or AlGalnN) or compound semiconductors of groups II-VI (e.g., CdSe, CdTe, CdS, ZnSe, or ZnS).

[0066] According to an embodiment of the present invention, the device 100 comprises a quantum well nanostructure 120 comprising a quantum well layer that covers from above (along the x direction) the first buffer layer 110. According to an embodiment of the present invention, the lateral dimensions of the quantum well layer along the y and z directions may vary depending on the specific application for which the device 100 is intended. For example, the dimensions of the quantum well layer along the y and z directions may vary from a few tens of pm to a few cm. For example, in case the device 100 is a single detector, the quantum well layer may have a dimension along the y direction of 40 pm and a dimension along the z direction of 40 pm. In case the device 100 is a focal plane array chip (“Focal Plane Array”) for imaging applications, the quantum well layer can have a dimension along the y direction of a few cm and a dimension along the z direction of a few cm.

[0067] It is emphasized that the concepts of the present invention can however also be applied in case the quantum well layer has different dimensions along the y and z directions.

[0068] According to an embodiment of the present invention, the quantum well nanostructure 120 has a thickness, along the x direction, of between 0.2 and 5 nm, for example equal to 2 nm. It is emphasized that the concepts of the present invention can however also be applied in the case of thicknesses of different extent.

[0069] According to an embodiment of the present invention, the quantum well nanostructure 120 is made of semiconductor material, such as n-type doped gallium arsenide (e.g., doped with silicon). Non-exhaustive examples of other possible materials for the quantum well nanostructure 120 include group IV semiconductors (e.g., silicon and / or germanium) doped with donors (n-type) or group III-V compound semiconductors (e.g., AlGalnAs, AlGalnSb, AlGalnP, or AlGalnN) doped with donors (n-type) or group II- VI compound semiconductors (e.g., CdSe, CdTe, CdS, ZnSe, or ZnS) doped with donors (n-type).

[0070] According to an embodiment of the present invention, the device 100 comprises a quantum dot nanostructure 130 comprising an array of quantum dot units 135 located above (along the x direction) the quantum well nanostructure 120.

[0071] According to an embodiment of the present invention, the quantum dot nanostructure 130 extends (along the y and z directions) to cover only a sub-portion of the quantum well nanostructure 120. In other words, the quantum well nanostructure 120 has “uncovered” portions, identified in Figure 1 by the reference 138, which result not covered by the quantum dot nanostructure 130.

[0072] According to an embodiment of the present invention, the extension, along the y and z directions, of the quantum dot nanostructure 130 is such that the quantum dot nanostructure 130 covers a sub-portion of the quantum well nanostructure 120 ranging from 10% to 70% of the total extension of the quantum well nanostructure 120 (depending on the specific application for which the device 100 is intended). It is emphasized that the concepts of the present invention can however also be applied in the case of percentages of different extent.

[0073] According to an embodiment of the present invention, the quantum dot nanostructure 130 has a thickness, along the x direction, of between 1 nm and 15 nm. It is emphasized that the concepts of the present invention can however also be applied in the case of thicknesses of different extent.

[0074] According to an embodiment of the present invention, each quantum dot unit 135 is made of semiconductor material (doped or undoped), such as gallium arsenide. Non-exhaustive examples of other possible materials for the quantum dot units 135 include group IV semiconductors (e.g., silicon and / or germanium) or group III-V compound semiconductors (e.g., AlGalnAs, AlGalnSb, AlGalnP, or AlGalnN) or group II- VI compound semiconductors (e.g., CdSe, CdTe, CdS, ZnSe, or ZnS). According to an embodiment of the present invention, the device 100 comprises a cover layer 140 that covers (along the x direction) the quantum dot nanostructure 130 and the uncovered portions 138 of the quantum well nanostructure 120

[0075] According to an embodiment of the present invention, the cover layer 140 has a thickness, along the x direction, of between 5 nm and 100 nm. It is emphasized that the concepts of the present invention can however also be applied in the case of thicknesses of different extent.

[0076] According to an embodiment of the present invention, the cover layer 140 is made of semiconductor material, such as aluminum gallium arsenide (AlGaAs), e.g., Alo.3Gao.7As. Non-exhaustive examples of other possible materials for the cover layer 140 include group IV semiconductors (e.g., silicon and / or germanium) or compound semiconductors of groups III-V (e.g., AlGalnAs, AlGalnSb, AlGalnP, or AlGalnN) or compound semiconductors of groups II- VI (e.g., CdSe, CdTe, CdS, ZnSe, or ZnS).

[0077] According to an embodiment of the present invention, the device 100 further comprises a second buffer layer 150 that covers from above (along the x direction) the cover layer 140.

[0078] According to an embodiment of the present invention, the second buffer layer 150 has a thickness, along the x direction, of between 100 nm and 1pm, for example 350 nm. It is emphasized that the concepts of the present invention can however also be applied in the case of thicknesses of different extent.

[0079] According to an embodiment of the present invention, the second buffer layer 150 is made of semiconductor material, such as aluminum gallium arsenide (AlGaAs), e.g., Alo.3Gao.7As. Non-exhaustive examples of other possible materials for the second buffer layer 150 include group IV semiconductors (e.g., silicon and / or germanium) or compound semiconductors of groups III-V (e.g., AlGalnAs, AlGalnSb, AlGalnP, or AlGalnN) or compound semiconductors of groups II-VI (e.g., CdSe, CdTe, CdS, ZnSe, or ZnS).

[0080] According to an embodiment of the present invention, the device 100 includes a second contact layer 160.

[0081] According to an embodiment of the present invention, the second contact layer 160 has a thickness, along the x direction, of between 100 nm and 1 pm, for example 500 nm. It is emphasized that the concepts of the present invention can however also be applied in the case of thicknesses of different extent.

[0082] According to one embodiment of the present invention, the second contact layer 160 is made of a semiconductor material, such as gallium arsenide (GaAs) doped with silicon (Si). Non-exhaustive examples of other possible materials for the second contact layer 160 include group IV semiconductors (e.g., silicon and / or germanium) doped with donors (n-type), or group III-V compound semiconductors (e.g., AlGalnAs, AlGalnSb, AlGalnP, or AlGalnN) doped with donors (n-type), or group II- VI compound semiconductors (e.g., CdSe, CdTe, CdS, ZnSe, or ZnS) doped with donors (n-type).

[0083] Due to the peculiar structure of the device 100 according to the embodiments of the invention described in relation to Figure 1, the device 100 presents the following two confinement zones for the electrons: a first confinement zone, identified in Figure 1 with reference 180, corresponding to the quantum dot nanostructure 130 and to the portion of the quantum well nanostructure 120 located below the quantum dot nanostructure 130, and a second confinement zone, identified in Figure 1 with reference 190, corresponding to the uncovered portions 138 of the quantum well nanostructure 120.

[0084] According to an embodiment of the present invention, the first confinement zone 180 has a larger dimension than the second confinement zone 190, since the thickness (along the x direction ) of the first confinement zone 180 is given by the sum of the thickness of the quantum dot nanostructure 130 and the thickness of the quantum well nanostructure 120, while the thickness (along the x direction) of the second confinement zone 190 is equal to the thickness of the quantum well nanostructure 120 only.

[0085] Accordingly, the conduction band of the device 100 according to embodiments of the present invention is such that the ground state and the lower energy states (i.e., of lower energy) have characteristics similar to those of the energy states of a quantum dot, while the higher energy states (i.e., of higher energy) have characteristics similar to those of the energy states of a quantum well.

[0086] This behavior is illustrated in Figure 2, which schematically shows an energy profile of the conduction band of the device 100 of Figure 1 according to an embodiment of the present invention.

[0087] According to an embodiment of the present invention, thanks to the presence of the first confinement zone 180, the ground state - identified with reference SO - and the energy states corresponding to lower energies - identified overall with reference S(l) - are mainly generated by the quantum dot nanostructure 130, and therefore have characteristics similar to those of the energy states of a quantum dot.

[0088] According to an embodiment of the present invention, thanks to the presence of the second confinement zone 190, the energy states corresponding to higher energies - identified overall with reference S(h) - are mainly generated by the quantum well nanostructure 120, and therefore have characteristics similar to those of the energy states of a quantum well. Furthermore, thanks to the peculiar structure of the device 100 according to embodiments of the present invention, the energy states S(h) comprise one or more resonant energy states - only one visible in Figure 2 and identified with reference SR - located in the continuous portion of the conduction band.

[0089] Due to the fact that in the device 100 according to the embodiments of the present invention the quantum well nanostructure 120 and the quantum dot nanostructure 130 are made of the same material, the assembly comprising the quantum well nanostructure 120 and the quantum dot nanostructure 130 is a single, unique structure (i.e., formed from the same material) which locally behaves as a quantum well or as a quantum dot. Due to the presence of such a single structure made of the same material:

[0090] - the presence of multiple interfaces between the quantum well nanostructure 120 and the quantum dot nanostructure 130 that could cause carrier scattering is advantageously avoided, and

[0091] - the confining potential with respect to the conduction band barrier is the same along the entire structure of the device 100.

[0092] Referring to the flowchart illustrated in Figure 3, the operation of the detection mechanism of the device 100 according to an embodiment of the present invention comprises three main steps 310, 320, 330.

[0093] According to an embodiment of the present invention, the first step 310 provides that free electrons in the conduction band are captured and reach the ground state SO by thermalization. Thanks to the presence of the quantum well nanostructure 120, characterized by a high probability of electron capture and a large density of states, the ground state SO is therefore kept supplied with electrons in a very efficient manner.

[0094] According to an embodiment of the present invention, the second step 320 provides that the electrons located in the ground state SO are excited to higher energy states by the absorption of infrared radiation (the infrared radiation to be detected). Thanks to the presence of the quantum dot nanostructure 130, the process of absorption of the infrared radiation is favored due to the strong localization of the energy states and the possibility of absorbing radiation in the normal direction, incident perpendicularly to the surface of the photodetector exposed to the radiation.

[0095] According to an embodiment of the present invention, the third step 330 provides that excited electrons that have reached higher energy states are extracted and collected. Thanks to the presence of the quantum well nanostructure 130, the existence of one or more resonant energy states SR located in the continuous portion of the conduction band allows for an easier extraction and collection of electrons that have reached such resonant energy states SR, since it is not necessary to overcome potential barriers to extract and collect such electrons.

[0096] A peculiarity of the device 100 according to the embodiments of the invention described herein is that it exploits the positive aspects of quantum wells and quantum dots, without having to incur their negative aspects.

[0097] Referring now to Figures 4A - 4G, a possible fabrication process of the device 100 according to an embodiment of the present invention will now be schematically described.

[0098] According to an embodiment of the present invention, the first step of the fabrication process illustrated in Figure 4A provides that the first contact layer 105 is grown by deposition starting from an undoped GaAs wafer in a molecular beam epitaxial growth chamber (“Molecular Beam Epitaxy”).

[0099] According to an embodiment of the present invention, the first buffer layer 110 is then deposited on top of the first contact layer 105 (Figure 4B).

[0100] According to an embodiment of the present invention, the quantum well nanostructure 120 is formed by deposition over the first buffer layer 110 (Figure 4C).

[0101] According to an embodiment of the present invention, the quantum dot nanostructure 130 is fabricated on top of the quantum well nanostructure 120 (Figure 4D) using a droplet epitaxial deposition (“droplet epitaxy”), such as the modified droplet epitaxial deposition described in the article “Modified droplet epitaxy GaAs / AlGaAs quantum dots grown on a variable thickness wetting layer" by S. Sanguinetti, K. Watanabe, T. Tateno, M. Gurioli, P. Werner, M. Wakaki, N. Koguchi, Journal of Crystal Growth 253 (2003) 71-76, which allows to obtain a unique structure comprising the quantum well nanostructure 120 and the underlying quantum dot nanostructure 130. The substrate temperature is raised to about 150°C and 3 ML of Ga are deposited at a rate of 0.1 ML / s and at a background pressure of less than 2 x 10'9torr. Maintaining the same temperature, a chamber valve is opened to supply As to crystallize the deposited Ga droplets with an equivalent beam pressure of 5 x 10'5torr.

[0102] According to an embodiment of the present invention, the cover layer 140 is then deposited on top of the quantum dot nanostructure 130 (Figure 4E) by means of a migration-enhanced epitaxial deposition (“migration enhanced epitaxy”) at 400°C followed by annealing for 5 minutes, to increase the crystalline quality. According to an embodiment of the present invention, the second buffer layer 150 is deposited on top of the cover layer 140 (Figure 4F), and the second contact layer 160 is deposited on top of the second buffer layer (Figure 4G).

[0103] According to an embodiment of the present invention not shown in the figures, the product is then subjected to photolithography and wet-etching processes in order to create protruding areas (“mesas”) and finally the electrical contacts of the device 100 are formed by evaporation.

[0104] Of course, in order to meet local and specific requirements, a person skilled in the art may apply various logical and / or physical modifications and alterations to the invention described above. More specifically, while the present invention has been described with a certain degree of particularity with reference to its preferred embodiments, it should be understood that various omissions, substitutions and modifications in form and details, as well as other embodiments, are possible. In particular, various embodiments of the invention may also be practiced without the specific details set forth in the foregoing description to provide a more thorough understanding thereof; conversely, well-known functions may have been omitted or simplified so as not to burden the description with unnecessary detail.

Claims

CLAIMS1. A photodetector device (100) comprising:- a quantum well nanostructure (120) extending perpendicular to a first direction (x);- a quantum dot nanostructure (130) extending perpendicular to the first (x) direction, said quantum dot nanostructure (130) being stacked on the quantum well nanostructure (120) along the first (x) direction, where:- said quantum well nanostructure (120) and said quantum dot nanostructure (130) are made of the same material;- said quantum well nanostructure (120) and said quantum dot nanostructure (130) define a conduction band of the photodetector device (100) comprising: a minimum energy state (S(0)) of the conduction band; a set of first energy states (S(l)) of the conduction band, said first energy states (S(l)) of the conduction band being at a higher energy than said minimum energy state (S(0)) of the conduction band, and a set of second energy states (S(h)) of the conduction band, said second energy states (S(h)) of the conduction band being at a higher energy than said first energy states (S(l)) of the conduction band,- said minimum energy state (S(0)) of the conduction band and said first energy states (S(l)) of the conduction band are generated by the quantum dot nanostructure (130), and- said second energy states (S(h)) of the conduction band are generated by the quantum well nanostructure (120) and include one or more resonant energy states (SR) located in the continuous portion of the conduction band.

2. The photodetector device (100) of claim 1, wherein said quantum dot nanostructure (130) extends, perpendicularly to the first direction (x) for an extension such as to:- cover, along the first direction (x), a sub-portion of the quantum wellnanostructure (120),- define portions (138) of the quantum well nanostructure (120) which are not covered, along the first direction (x), by the quantum dot nanostructure (130).

3. The photodetector device (100) of claim 2, wherein said photodetector device (100) comprises: a first confinement zone (180) for electrons in the conduction band corresponding to the quantum dot nanostructure (130) and to said sub-portion of the quantum well nanostructure (120) covered by the quantum dot nanostructure (130), and a second confinement zone (190) for electrons in the conduction band corresponding to said portions (138) of the quantum well nanostructure (120) not covered by the quantum dot nanostructure (130).

4. The photodetector device (100) of claim 2 or claim 3, wherein said subportion of the quantum well nanostructure (120) covered by the quantum dot nanostructure (130) is equal to a selected percentage in the range of 10% - 70% of the total extension of the quantum well nanostructure (120) perpendicular to the first direction (x).

5. The photodetector device (100) of any of the previous claims, wherein the quantum well nanostructure (120) has a thickness, along the first direction (x), between 0.2 and 5 nm.

6. The photodetector device (100) of any of the preceding claims, wherein the quantum well nanostructure (120) and the quantum dot nanostructure (130) comprise a semiconductor material selected from GaAs, Si, Ge, AlGalnAs, AlGalnSb, AlGalnP, AlGalnN, CdSe, CdTe, CdS, ZnSe, ZnS.

7. The photodetector device (100) of any of the preceding claims, wherein thequantum dot nanostructure (130) has a thickness, along the first direction (x), between 1 nm and 15 nm.

8. The photodetector device (100) of any of the preceding claims, wherein the semiconductor material of the quantum well nanostructure (120), and preferably the semiconductor material of the quantum dot nanostructure (130), is n-type doped.

9. The photodetector device (100) of any of the preceding claims, wherein said photodetector device (100) is a photodetector for detecting electromagnetic waves in the infrared band.

10. A method for manufacturing a photodetector device (100) comprising:- a quantum well nanostructure (120) extending perpendicular to a first direction (x);- a quantum dot nanostructure (130) extending perpendicular to the first (x) direction, said quantum dot nanostructure (130) being stacked on the quantum well nanostructure (120) along the first (x) direction, wherein:- said quantum well nanostructure (120) and said quantum dot nanostructure (130) are made of the same material;- said quantum well nanostructure (120) and said quantum dot nanostructure (130) defining a conduction band of the photodetector device (100) comprising: a minimum energy state (S(0)) of the conduction band; a set of first energy states (S(l)) of the conduction band, said first energy states (S(l)) of the conduction band being at a higher energy than said minimum energy state (S(0)) of the conduction band, and a set of second energy states (S(h)) of the conduction band, said second energy states (S(h)) of the conduction band being at a higher energy than said first energy states (S(l)) of the conduction band,- said minimum energy state (S(0)) of the conduction band and said first energy states (S(l)) of the conduction band being generated by the quantum dot nanostructure(130), and- said second energy states (S(h)) of the conduction band being generated by the quantum well nanostructure (120) and including one or more resonant energy states (SR) located in the continuous portion of the conduction band, the method comprising:- depositing a layer of semiconductor material epitaxially onto a buffer layer (110) to form the quantum well nanostructure (120);- depositing using an epitaxial drop deposition technique a set of droplets of semiconductor material on the quantum well nanostructure; - crystallizing the deposited drops to form the quantum dot nanostructure (130).

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