Patent Publication Number: US-2023161222-A1

Title: Entangled-photon pair emitting device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This U.S. non-provisional patent application claims priority under 35 U.S.C. § 119 of Korean Patent Application No. 10-2021-0161312, filed on Nov. 22, 2021, and 10-2022-0056265, filed on May 6, 2022, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND 
     The present disclosure herein relates to an entangled-photon pair emitting device, and more particularly, to an entangled-photon pair emitting device using a piezoelectric structure. 
     A quantum dot refers to a semiconductor crystal having a size less than about 10 nm. When the quantum dot has a size less than an excitonic Bohr radius, the quantum dot may emit photons having various emission wavelengths by a quantum confinement effect. Particularly, the quantum dot is known to be an only material capable of emitting certainly rather than stochastically an entangled-photon pair used for quantum transmission or quantum imaging. 
     Here, the quantum dot may emit the entangled-photon pair in a method of artificially applying an electric field or a local stress from the outside of the quantum dot unless an ideal condition in which a structure of the quantum dot has a perfectly circular shape. Particularly, in case of applying the local stress, a wavelength of the entangled-photon pair generated according to an intensity of the stress may be significantly varied. That is, when a strong stress is applied to the quantum dot, a wavelength range of the entangled-photon pair emitted from the quantum dot may be widely controlled. Thus, methods for applying a strong stress to the quantum dot to widely control the wavelength range of the entangled-photon pair emitted from the quantum dot are being actively researched. 
     SUMMARY 
     The present disclosure provides an entangled-photon pair emitting device capable of applying a strong stress to a quantum dot to widely control a range of a wavelength of the entangled-photon pair emitted from the quantum dot. 
     An embodiment of the inventive concept provides an entangled-photon pair emitting device including: a piezoelectric structure having a first surface and a second surface, which face each other, wherein the piezoelectric structure includes an opening passing through the piezoelectric structure from the first surface to the second surface; a stress transfer medium configured to fill the opening; a light source emitting part disposed on the stress transfer medium; an upper electrode disposed on the first surface of the piezoelectric structure; and a lower electrode disposed on the second surface of the piezoelectric structure. Here, the light source emitting part includes a semiconductor thin-film and a quantum dot in the semiconductor thin-film. 
     In an embodiment, the opening may have a circular or polygonal shape in terms of a plane, and the opening may have a diameter or a width of about 10 μm to about 200 μm. 
     In an embodiment, the piezoelectric structure may further include a plurality of recesses defined in the first surface of the piezoelectric structure and connected with the opening. 
     In an embodiment, the stress transfer medium may include at least one of a polymer, a dielectric material, or metal or combination thereof. 
     In an embodiment, the polymer may include at least one of polydimethylsiloxane (PDMS), benzocyclobutene (BCB), hydrogen silsesquioxane (HSQ), and polyimide (PI). 
     In an embodiment, the semiconductor thin-film may include at least one of GaAs, InP, InGaAsP, GaN, or InAlAs, the quantum dot may include at least one of InAs, InGaN, or InGaAs, and the semiconductor thin-film may have a thickness of about 100 nm to about 500 nm. 
     In an embodiment, the light source emitting part may include a first pattern and second patterns, and the second patterns may be arranged in a form of a concentric circle with the first pattern at a center of the concentric circle. 
     In an embodiment, the piezoelectric structure may include at least one of lead zirconate titanate (PZT) or PMN-PT, and the piezoelectric structure may have a thickness of about 10 μm to about 500 μm. 
     In an embodiment, a top surface of the semiconductor thin-film may have a level less than that of the first surface of the piezoelectric structure. 
     In an embodiment, the light source emitting part may overlap the opening in a vertical direction. 
     In an embodiment of the inventive concept, an entangled-photon pair emitting device includes: a piezoelectric structure having a first surface and a second surface, which face each other, wherein the piezoelectric structure includes an opening passing through the piezoelectric structure from the first surface to the second surface; a stress transfer medium configured to fill the opening; a light source emitting part disposed on the stress transfer medium; an upper electrode disposed on the first surface of the piezoelectric structure; and a lower electrode disposed on the second surface of the piezoelectric structure. Here, the light source emitting part includes a semiconductor thin-film and a quantum dot in the semiconductor thin-film, the piezoelectric structure contacts the stress transfer medium while being spaced apart from the semiconductor thin-film, and the semiconductor thin-film contacts the stress transfer medium. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The accompanying drawings are included to provide a further understanding of the inventive concept, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the inventive concept and, together with the description, serve to explain principles of the inventive concept. In the drawings: 
         FIG.  1    is a perspective view illustrating an entangled-photon pair emitting device according to an embodiment of the inventive concept; 
         FIG.  2 A  is a top plan view illustrating the entangled-photon pair emitting device of  FIG.  1   ; 
         FIG.  2 B  is a bottom plan view illustrating the entangled-photon pair emitting device of  FIG.  1   ; 
         FIG.  2 C  is a cross-sectional view taken along line A-A′ of  FIG.  2 A ; 
         FIG.  2 D  is an enlarged view of portion B of  FIG.  2 C ; 
         FIGS.  3 A and  4 A  are cross-sectional views illustrating a method for manufacturing an entangled-photon pair emitting device according to an embodiment of the inventive concept; 
         FIGS.  3 B and  4 B  are cross-sectional views taken along line I-I′ of  FIGS.  3 A and  4 A , respectively; 
         FIG.  5    is a graph showing results of a wavelength variation experiment according to a comparative example; and 
         FIG.  6    is a graph showing results of a strain variation simulation according to an embodiment of the inventive concept and the comparative example. 
     
    
    
     DETAILED DESCRIPTION 
     Advantages and features of the present invention, and implementation methods thereof will be clarified through following embodiments described with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. Further, the present invention is only defined by scopes of claims. Like reference numerals refer to like elements throughout. 
     In the following description, the technical terms are used only for explaining a specific exemplary embodiment while not limiting the present disclosure. In the specification, the terms of a singular form may include plural forms unless referred to the contrary. The meaning of “include,” “comprise,” “including,” or “comprising,” specifies a property, a region, a fixed number, a step, a process, an element and/or a component but does not exclude other properties, regions, fixed numbers, steps, processes, elements and/or components. 
     Additionally, the embodiment in the detailed description will be described with sectional views as ideal exemplary views of the present invention. Also, in the figures, the dimensions of layers and regions are exaggerated for clarity of illustration. Accordingly, shapes of the exemplary views may be modified according to manufacturing techniques and/or allowable errors. Therefore, the embodiments of the present invention are not limited to the specific shape illustrated in the exemplary views, but may include other shapes that may be created according to manufacturing processes. For example, an etched region having a right angle illustrated in the drawings may have a round shape or a shape having a predetermined curvature. Areas exemplified in the drawings have general properties, and are used to illustrate a specific shape of a semiconductor package region. Thus, this should not be construed as limited to the scope of the present invention. 
     Hereinafter, an entangled-photon pair emitting device according to an embodiment of the inventive concept will be described in detail with reference to the accompanying drawings. 
       FIG.  1    is a perspective view illustrating an entangled-photon pair emitting device according to an embodiment of the inventive concept.  FIG.  2 A  is a top plan view illustrating the entangled-photon pair emitting device of  FIG.  1   .  FIG.  2 B  is a bottom plan view illustrating the entangled-photon pair emitting device of  FIG.  1   .  FIG.  2 C  is a cross-sectional view taken along line A-A′ of  FIG.  2 A .  FIG.  2 D  is an enlarged view of portion B of  FIG.  2 C . 
     Referring to  FIGS.  1  to  2 D , an entangled-photon pair emitting device  1  may include a piezoelectric structure  10 , a stress transfer medium  20 , a light source emitting part  30 , upper electrodes  42 , and a lower electrode  44 . The piezoelectric structure  10  may include a first surface  10   a  and a second surface  1   b , which face each other. 
     In this specification, a first direction D 1  represents a direction parallel to the first surface  10   a  of the piezoelectric structure  10 . A second direction D 2  represents a direction parallel to the first surface  10   a  of the piezoelectric structure  10  and cross the first direction D 1 . A third direction D 3  represents a direction perpendicular to the first surface  10   a  of the piezoelectric structure  10 . 
     The piezoelectric structure  10  may include an opening  12  passing through the piezoelectric structure  10  from the first surface  10   a  to the second surface  10   b  in the third direction D 3 . The opening  12  may have various shapes in terms of a plane. For example, the opening  12  may have a circular or polygonal shape in terms of the plane. The opening  12  may have a constant diameter in terms of the plane or a width R in the first direction D 1 . For example, the opening  12  may have the diameter or the width R in the first direction D 1 , which is about 10 μm to about 200 μm. 
     The piezoelectric structure  10  may include a piezoelectric material. For example, the piezoelectric structure  10  may include lead zirconate titanate (PZT) or PMN-PT. The piezoelectric structure  10  may have a thickness in the third direction D 3 , which is about 10 μm to about 500 μm. 
     The piezoelectric structure  10  may include a plurality of recesses  14  defined in the first surface  10   a  of the piezoelectric structure  10  and connected with the opening  12 . Each of the recesses  14  may have a line shape in terms of the plane. For example, in terms of the plane, the opening  12  may have a rectangular shape, and each of the recesses  14  may extend from each of vertices of the opening in a diagonal direction. The recesses  14  may not completely pass through the piezoelectric structure  10 . 
     The stress transfer medium  20  that fills the opening  12  of the piezoelectric structure  10  may be provided. The stress transfer medium  20  may contact an inner surface of the piezoelectric structure  10 . According to some embodiments, a top surface of the stress transfer medium  20  may have a level less than that of the first surface  10   a  of the piezoelectric structure  10 . According to other embodiments, the top surface of the stress transfer medium  20  may have a level equal to or greater than that of the first surface  10   a  of the piezoelectric structure  10 . Also, a bottom surface of the stress transfer medium  20  may have a level higher than that of the second surface  10   b  of the piezoelectric structure  10 . Also, a bottom surface of the stress transfer medium  20  may have a level higher than that of the second surface  10   b  of the piezoelectric structure  10 . 
     The stress transfer medium  20  may include a material capable of transmitting a strain generated in the piezoelectric structure  10  to the light source emitting part  30  that will be described later in a form of a stress. For example, the stress transfer medium  20  may include a polymer, a dielectric material, or metal. The polymer may include, e.g., polydimethylsiloxane (PDMS), benzocyclobutene (BCB), hydrogen silsesquioxane (HSQ), and polyimide (PI). The dielectric material may include, e.g., polycrystalline silicon (Si). 
     The light source emitting part  30  may be disposed on the stress transfer medium  20 . The light source emitting part  30  may be disposed on the stress transfer medium  20 . The light source emitting part  30  may be spaced apart from an inner wall of the opening  12  of the piezoelectric structure  10 . 
     The light source emitting part  30  may include a first pattern  32  and second patterns  34 . In terms of the plane, the second patterns  34  may be arranged in a form of a concentric circle or an ellipse with the first pattern  32  at a center thereof. In terms of the plane, the first pattern  32  may have a circular or elliptical shape. In terms of the plane, each of the second patterns  34  may have a circular ring or an elliptical ring shape. The first pattern  32  and the second patterns  34  of the light source emitting part  30  may provide a circular optical grating structure. As the light source emitting part  30  has the circular optical grating structure, a light source emitted from the light source emitting part  30  may be prevented from being emitted in the first direction D 1  and the second direction D 2 . Through this, an optical loss may be reduced, and an extraction efficiency of the entangled-photon pair emitted from the light source emitting part  30  may increase. 
     According to some embodiments, a top surface of the light source emitting part  30  may have a level less than that of the first surface  10   a  of the piezoelectric structure  10 . According to other embodiments, the top surface of the light source emitting part  30  may have a level equal to or greater than that of the first surface  10   a  of the piezoelectric structure  10 . 
     Each of the first pattern  32  and the second patterns  34  of the light source emitting part  30  may include a material capable of emitting an entangled-photon. As illustrated in  FIG.  2 D , each of the first pattern  32  and the second patterns  34  may include a semiconductor thin-film  36  and a quantum dot  38  in the semiconductor thin-film  36 . The semiconductor thin-film  36  may include GaAs, InP, InGaAsP, GaN, or InAlAs. The quantum dot  38  may include InAs, InGaN, or InGaAs. 
     According to other embodiments, unlike  FIG.  2 D , each of the first pattern  32  and the second patterns  34  may include tungsten diselenide (WSe2) and/or tungsten disulfide (WS2). The light source emitting part  30  may have a third directional thickness of about 100 nm to about 500 nm. 
     The upper electrodes  42  may be disposed on the first surface  10   a  of the piezoelectric structure  10 . In terms of the plane, the upper electrodes  42  may surround the opening  12  and the stress transfer medium  20 . The upper electrodes  42  may be spaced apart from the opening  12  and the stress transfer medium  20  in the first direction D 1  and the second direction D 2 . In terms of the plane, the upper electrodes  42  may be spaced apart from each other with the recesses  14  therebetween. 
     Each of the upper electrodes  42  may include metal. For example, each of the upper electrodes  42  may include titanium (Ti), chromium (Cr), platinum (Pt), germanium (Ge) and/or gold (Au). 
     The lower electrode  44  may be disposed on the second surface  10   b  of the piezoelectric structure  10 . The lower electrode  44  may not overlap the stress transfer medium  20  and the opening  12  of the piezoelectric structure  10  in a vertical direction. The lower electrode  44  may overlap the upper electrodes  42  in the vertical direction. The lower electrode  44  may include metal. For example, the lower electrodes  44  may include titanium (Ti), chromium (Cr), platinum (Pt), germanium (Ge) and/or gold (Au). 
     An electric field may be applied to the piezoelectric structure  10  by applying a voltage to the upper electrodes  42  and the lower electrode  44 . A displacement may be generated in the piezoelectric structure  10  by the electric field. As the upper electrodes  42  are provided in plurality, a direction of the displacement generated in the piezoelectric structure  10  may be easily adjusted. According to some embodiment, only one upper electrode  42  may be provided. The recesses  14  of the piezoelectric structure  10  may prevent displacements generated in the piezoelectric structure  10  in different directions from overlapping each other. 
     The displacement of the piezoelectric structure  10  may apply a stress to the stress transfer medium  20 , and the applied stress may cause a displacement of the stress transfer medium  20 . The displacement of the stress transfer medium  20  may apply a stress to the light source emitting part  30  to emit the entangled-photon pair from the light source emitting part  30 . As the light source emitting part  30  is disposed in the piezoelectric structure  10 , i.e., in the opening  12 , the stress applied to the light source emitting part  30  may increase. Particularly, the applied stress may increase as a diameter of the opening  12  of the piezoelectric structure  10  or a width R in the first direction D 1  decreases. As the stress applied to the light source emitting part  30  increases, an entangled-photon pair emitting efficiency may increase, and a wavelength control range of the entangled-photon pair may widen. 
       FIGS.  3 A and  4 A  are cross-sectional views illustrating a method for manufacturing an entangled-photon pair emitting device according to an embodiment of the inventive concept.  FIGS.  3 B and  4 B  are cross-sectional views taken along line I-I′ of  FIGS.  3 A and  4 A , respectively. 
     Referring to  FIGS.  3 A and  3 B , a piezoelectric structure  10  may be formed. An opening  12  and recesses  14  may be formed in a piezoelectric material through laser etching. 
     Upper electrodes  42  may be formed on a first surface  10   a  of the piezoelectric structure  10 . A lower electrode  44  may be formed on a second surface  10   b  of the piezoelectric structure  10 . The upper electrodes  42  and the lower electrode  44  may be formed on the first surface  10   a  and the second surface  10   b , respectively, through a photolithography process and a deposition process. A plating process may be performed instead of the deposition process. 
     Referring to  FIGS.  4 A and  4 B , a stress transfer medium  20  may be formed in an opening  12 . When the stress transfer medium  20  is a polymer, the stress transfer medium  20  may be formed by filling the polymer in the opening  12  and then heating and curing the filled polymer. When the stress transfer medium  20  is a dielectric material or metal, the stress transfer medium  20  having a shape corresponding to that of the opening  12  may be manufactured from the outside and then put into the opening  12 . 
     Referring to  FIGS.  2 A,  2 C, and  3 D  again, a light source emitting part  30  may be formed. The light source emitting part  30  including a first pattern  32  and second patterns  34  may be formed by performing a photolithography process and an etching process on a semiconductor thin-film  36  containing a quantum dot  38  therein. The light source emitting part  30  may be manufactured separately from the outside and then transferred and attached onto the stress transfer medium  20 . Alternatively, the light source emitting part  30  may be manufactured directly on the stress transfer medium  20  instead of being manufactured separately from the outside. Thus, an entangled-photon pair emitting device  1  may be manufactured. 
       FIG.  5    is a graph showing results of a wavelength variation experiment according to a comparative example.  FIG.  6    is a graph showing results of a strain variation simulation according to an embodiment of the inventive concept and the comparative example. 
     The comparative example represents an entangled-photon emitting device in which a quantum dot is disposed on a piezoelectric material without an opening, and upper electrodes and a lower electrode are disposed on a top surface and a bottom surface of the piezoelectric material, respectively. 
     Referring to  FIG.  5   , a difference between wavelengths of light sources generated when a voltage in a range from about −200 V to about 200 V to the piezoelectric material of the comparative example is only 0.2 nm or less. 
     Referring to  FIG.  6   , three right-side dots of the simulation (dots corresponding to Square 100 μm, Square 50 μm, Square 20 μm of a horizontal axis) show calculated values of strains generated in the light source emitting part  30  according to the diameter or width of the opening  12  when a voltage of about 200 V is applied in an embodiment of the inventive concept. One left-side dot of the simulation (a dot corresponding to Normal of the horizontal axis) shows a calculated value of a strain generated in the quantum dot when a voltage of about 200 V is applied in the comparative example. The calculated values according to an embodiment of the inventive concept are about 5%, about 10%, and about 25% when the diameter or width of the opening  12  is about 100 μm, about 50 μm, and about 20 μm, respectively. The calculated value of the strain according to the comparative example is about 0.05%. From this, it may be known that the stain value according to an embodiment of the inventive concept is greater than that according to the comparative example. 
     According to the embodiment of the inventive concept, as the light source emitting part including the quantum dot is disposed in the opening of the piezoelectric structure, the intensity of the stress transmitted from the piezoelectric structure to the light source emitting part may increase. Thus, the efficiency of emitting the entangled-photon pair may increase, and the wavelength control range of the entangled-photon pair may widen. 
     Also, the optical loss in the plane direction may be reduced by the circular optical grating structure of the light source emitting part, and the light extraction efficiency may increase. 
     Although the embodiments of the present invention have been described, it is understood that the present invention should not be limited to these embodiments but various changes and modifications can be made by one ordinary skilled in the art within the spirit and scope of the present invention as hereinafter claimed.