Abstract:
Provided are electronic devices having quantum dots and methods of manufacturing the same. An electronic device includes a first nanorod, a quantum dot disposed on an upper surface of the first nanorod, and a second nanorod that covers a lateral surface of the first nanorod and the quantum dot. The first nanorod and the second nanorod are of opposite types.

Description:
RELATED APPLICATIONS 
     This application claims priority from Korean Patent Application No. 10-2014-0043681, filed on Apr. 11, 2014 in the Korean Intellectual Property Office, the disclosure of which is incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Field 
     Apparatuses and methods consistent with exemplary embodiments related to electronic devices, and more particularly, to electronic devices having quantum dots and methods of manufacturing the same. 
     2. Description of the Related Art 
     A device containing quantum dots may be used in various devices, such as light-emitting diodes (LEDs), laser diodes (LDs), detectors, power devices, and single electron transistors. 
     In such a device, the confinement state of the quantum dots may directly affect the characteristics of the device. In the case of a light-emitting device, the better the confinement of the quantum dots, the higher the efficiency of the light-emitting device. 
     As an example of a device that uses quantum dots, there is a device formed by a process of, after forming Si or InN nanorods on an Si substrate, growing a GaN layer by using the nanorods as a buffer layer. However, this process is relatively complicated and many crystal defects may still occur in the GaN layer that is finally formed. 
     SUMMARY 
     Exemplary embodiments provide electronic devices containing a quantum dot that have high efficiency and may be manufactured simply and methods of manufacturing the same. 
     According to an aspect of an exemplary embodiment, there is provided an electronic device including: a first nanorod; a quantum dot disposed on an upper surface of the first nanorod; and a second nanorod that covers a lateral surface of the first nanorod and the quantum dot, wherein the first and second nanorods are of opposite types. 
     The first nanorod may be formed directly on a substrate. 
     The electronic device may further include an insulating film and a resin film disposed on the insulating material, and the insulating film and the resin film are disposed around a lateral surface of the first nanorod. 
     An upper surface of a second nanorod may be located above the quantum dot, and a resin film may be located around the second nanorod. 
     The second nanorods may be disposed on the insulating film between the first nanorod and the resin film. 
     The resin film may include a hole, and the first nanorod may be disposed in the hole without contacting the resin film. 
     The second nanorod may be disposed in the hole and may be located between the edge of the hole and the first nanorod. 
     A lateral surface and an upper surface of the second nanorod may be covered by a conductive oxide film, and the first nanorod and the conductive oxide film may be separated from each other. 
     An upper surface of the conductive oxide film may be flat, and electrodes may be formed on the upper surface of the conductive oxide film. 
     According to an aspect of another exemplary embodiment, there is provided a method of manufacturing an electronic device, the method including: forming an insulating film on a substrate; forming a first hole through which the substrate is exposed in the insulating film; forming a first nanorod in the first hole; forming a quantum dot on an upper surface of the first nanorod; forming a resin film including a second hole on the insulating film, wherein the second hole exposes a portion of the insulating film around the first nanorod; forming a second nanorod covering the first nanorod and the quantum dot on the portion of the insulating film exposed by the second hole; forming a conductive oxide film on the resin film to cover the second nanorod; and forming an electrode on the conductive oxide film, wherein the first and the second nanorod different. 
     The forming the first nanorod in the first hole may include: growing a base film on a portion of the substrate that is exposed through the first hole and growing the first nanorod on the base film, wherein the base film includes a material that is the same as that of the first nanorod. 
     The first nanorod may be formed using a metal organic chemical vapor deposition (MOCVD) method or a molecular beam epitaxial (MBE) method. 
     The first nanorod and the quantum dot may be simultaneously formed by using a vapor liquid solid (VLS) epitaxial method. 
     The forming the first hole through which the substrate is exposed in the insulating film may include: forming a catalyst layer on the substrate; dividing the catalyst layer into a plurality of droplets; forming the insulating film around the droplets on the substrate, the insulating film having a thickness smaller than that of the droplets; and removing the droplets. 
     The forming the quantum dot may include: forming a Ga quantum dot on the upper surface of the first nanorod by using a droplet method; and doping the Ga quantum dot with As. 
     The second nanorod may be formed using a MOCVD method or a MBE method. 
     The first nanorod, the quantum dot, and the second nanorod may be formed in-situ. 
     The conductive oxide film may be formed by using a lateral overgrowth method. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects will become apparent and more readily appreciated from the following description of exemplary embodiments, taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a cross-sectional view of an electronic device containing quantum dots, according to an exemplary embodiment; 
         FIGS. 2 through 12  are perspective views and cross-sectional views illustrating a method of manufacturing an electronic device containing quantum dots, according to an exemplary embodiment; 
         FIG. 13  is scanning electron microscope (SEM) images showing, as an example of first nanorods, GaN nanorods formed on a silicon substrate in an electronic device according to an exemplary embodiment; and 
         FIG. 14  is SEM images showing GaAs nanorods (nanowires) grown on a GaN substrate. 
     
    
    
     DETAILED DESCRIPTION 
     An electronic device containing high quality quantum dots that are stably confined and a method of manufacturing the electronic device will be described herein with reference to the accompanying drawings. In the drawings, the thicknesses of layers and regions are exaggerated for the sake of clarity. 
     First, an electronic device containing quantum dots will be described.  FIG. 1  is a cross-sectional view of an electronic device containing quantum dots, according to an exemplary embodiment. 
     Referring to  FIG. 1 , an insulating film  34  is formed on a substrate  30 . A plurality of holes H 1  through which the substrate  30  is exposed are formed in the insulating film  34 . The holes H 1  may be separated from each other by predetermined distances. Regions where first nanorods (or nanowires)  40  are grown are defined by the holes H 1 . Accordingly, a diameter of the holes H 1  may be determined by taking the desired diameter of the first nanorods  40  into consideration. The first nanorods  40  may be referred to as lower nanorods. The substrate  30  may be a p-type substrate. The substrate  30  may be a silicon substrate, but is not limited thereto. The silicon substrate may be, for example, a (111) silicon substrate. The insulating film  34  may be an insulating oxide or nitride. The insulating film  34  may be, for example, silicon oxide. The silicon oxide may be, for example, SiO 2 . The portions of the substrate  30  exposed by the holes H 1  are covered by the first nanorods  40 . The holes H 1  are filed with portions of the first nanorods  40 . The first nanorods  40  that fill the holes H 1  extend upwards, that is, in a direction away from the substrate  30 . Quantum dots  42  are formed on upper surfaces of the first nanorods  40 , respectively. A crystal surface of a lateral surface and a crystal surface of an upper surface of the first nanorod  40  may be different types of crystal surfaces. The crystal surface of the upper surface of the first nanorod  40  may be a crystal surface that is appropriate for forming the quantum dots  42 . Accordingly, the quantum dots  42  may be selectively formed on the upper surfaces of the first nanorods  40 , respectively. The quantum dots  42  may be a material having a relatively wide band gap and a relatively low refractive index. The first nanorods  40  have a band gap in a range from about 1.4 eV to about 6.0 eV. The first nanorods  40  have a refractive index in a range from about 2.1 to about 3.8. The first nanorods  40  may be, for example, GaN nanorods or BN nanorods that are doped with an n-type dopant, but are not limited thereto. The first nanorods  40  may be formed from GaP, AlP, GaAs, AlAs, AlN, or AlGaN. The quantum dots  42  may be semiconductor quantum dots, for example, compound semiconductor quantum dots. The semiconductor quantum dots may be, for example, GaAs quantum dots. 
     The extended portions of the first nanorods  40  and the quantum dots  42  are covered by second nanorods  50  (or nanowires). The second nanorods  50  may directly contact lateral surfaces of the first nanorods  40  and may directly contact the quantum dots  42 . The second nanorods  50  are formed on the insulating film  34 . That is, the second nanorods  50  contact the insulating film  34  around the holes H 1 . A diameter of the second nanorods  50  is wider than the diameter of the first nanorods  40 . The second nanorods  50  extend above the quantum dots  42  such that upper surfaces of the second nanorods  50  are located above the quantum dots  42 . The second nanorods  50  may be nanorods of a type opposite to a type of the first nanorods  40 , i.e., may have properties opposite to those of the first nanorods  40 . For example, when the first nanorods  40  are P-type nanorods, the second nanorods  50  may be N-type nanorods doped with an N-type conductive dopant. Alternatively, the first nanorods  40  may be N-type nanorods, and the second nanorods  50  may be P-type nanorods. The second nanorods  50  may be nanorods having a relatively wide band gap and a relatively low refractive index or the second nanorods  50  may have a band gap range and a refractive index range that are the same as those of the first nanorods  40 . The second nanorods  50  may be, for example, GaN or BN nanorods. The number of second nanorods  50  may be equal to the number of first nanorods  40 . The second nanorods  50  may be referred to as upper nanorods. The first nanorods  40  are directly grown on the substrate  30  and may have relatively fewer crystal defects than in the related art. The quantum dots  42  are formed on the first nanorods  40 , and the second nanorods  50  directly cover the entire extended portions of the first nanorods  40  and all the quantum dots  42 , and thus, the first nanorods  40 , the quantum dots  42 , and the second nanorods  50  may constitute an electronic device, for example, a light-emitting diode, directly grown on the substrate  30 . Since the second nanorods  50  directly cover the entire extended portions of the first nanorods  40  and all the quantum dots  42 , the confinement of the quantum dots  42  by the first and second nanorods  40  and  50  is superior to devices in the related art. Accordingly, when the electronic device is a light-emitting diode, the efficiency, for example, the light emission efficiency, of the electronic device is superior to devices in the related art. 
     The second nanorods  50  are separated from each other. Parts of the insulating film  34  that are between the second nanorods  50  may be covered by a resin film  44 . That is, the resin film  44  is formed between the second nanorods  50 . The resin film  44  may be formed of, for example, an epoxy resin or a material having a patterning characteristic that is similar to that of an epoxy resin. The resin film  44  may be formed of SU-8, BCB, PDMS, or SiO 2 , but is not limited thereto. 
     The second nanorods  50  and the resin film  44  are covered by a conductive oxide film  60 . The entire surface of the second nanorods  50  may be covered by the conductive oxide film  60 . An upper surface of the conductive oxide film  60  may be a flat surface. The upper surface of the conductive oxide film  60  is located above the upper surfaces of the second nanorods  50 . The conductive oxide film  60  may be formed of, for example, ZnO or indium tin oxide (ITO), but is not limited thereto. The thicknesses of the insulating film  34 , the resin film  44 , and the conductive oxide film  60  may vary depending on the height of the first and second nanorods  40  and  50 . 
     Electrodes  70  may be formed on the conductive oxide film  60 . The electrodes  70  may be formed of Al, but are not limited thereto, that is, the electrodes  70  may be formed of any material that is used for forming electrodes for optical devices or semiconductor devices. 
     Next, a method of manufacturing an electronic device will be described with reference to  FIGS. 2 through 12 . The electronic device formed according to the method may be the electronic device described with reference to  FIG. 1 . In the descriptions below, like reference numerals are used to indicate elements that are substantially the same elements described with reference to  FIG. 1 , and repeated descriptions thereof will be omitted.  FIGS. 2 through 12  are perspective views and cross-sectional views illustrating a method of manufacturing an electronic device having quantum dots, according to an exemplary embodiment. 
     Referring to  FIG. 2 , a catalyst layer  32  is formed on a substrate  30 . The catalyst layer  32  may be, for example, a gold layer, but is not limited thereto. After the catalyst layer  32  is formed, the resultant product is annealed at a predetermined temperature. As a result, as depicted in  FIG. 3 , a plurality of Au droplets  32   a  are formed on the substrate  30 . The size of the Au droplets  32   a  may be determined by taking into consideration the desired diameter of the first nanorods  40  of  FIG. 1 . That is, there is a relationship between the size of the Au droplets  32   a  and the diameter of the first nanorods  40 . The Au droplets  32   a  may be separated from each other. The annealing temperature may be a temperature at which the Au droplets  32   a  may be formed, for example, approximately 650° C. The annealing temperature may vary slightly based on the material that is used as the catalyst layer  32 , the thickness of the catalyst layer  32 , and the annealing atmosphere. 
     Referring to  FIG. 4 , an insulating film  34  is formed on the substrate  30  on which the Au droplets  32   a  are formed. The insulating film  34  may be, for example, an oxide film and may be formed by supplying oxygen gas. The process of forming the insulating film  34  may be performed at, for example, 800° C. for approximately 10 minutes. The insulating film  34  may be formed to have a thickness that may cover a surface of the substrate  30  between the Au droplets  32   a . The thickness of the insulating film  34  may be smaller than the thickness or height of the Au droplets  32   a . After the insulating film  34  is formed, the Au droplets  32   a  are removed by etching the Au droplets  32   a . As a result, as depicted in  FIG. 5 , a plurality holes H 1  are formed in the insulating film  34 . 
     Referring to  FIG. 5 , the substrate  30  is exposed through the holes H 1 . 
     As depicted in  FIG. 6 , a surface of the substrate  30  that is exposed through the holes H 1  is covered by base films  36 . The base films  36  may be formed by an epitaxial method. The substrate  30  around the holes H 1  are covered by the insulating film  34 . Accordingly, the base films  36  may be selectively formed on a surface of the substrate  30  that is exposed through the holes H 1 . Each of the base films  36  may be a single layer or multiple layers that include a nano material. When the base film  36  includes a single layer, the base film  36  may be formed of, for example, GaN or BN. When the base film  36  includes multiple layers, the base film  36  may be a stacked film in which an AlGaN film and a GaN film are sequentially stacked. 
       FIG. 7  is a cross-sectional view taken along line  7 - 7 ′ of  FIG. 6 . Referring to  FIG. 7 , the base films  36  may have a smaller thickness than that of the insulating film  34 . 
     Referring to  FIG. 8 , the first nanorods  40  are formed on the base films  36 , respectively. The base films  36  may be formed from the same constituent element as the first nanorods  40 . Accordingly, the base films  36  and the first nanorods  40  may not be distinguished. However, in the drawing, the base films  36  and the first nanorods  40  are distinguished for the sake of convenience. The first nanorods  40  may be formed by using a growing method, for example, a metal organic chemical vapor deposition (MOCVD) method or a molecular beam epitaxy (MBE) method. Also, the first nanorods  40  may be formed by using a vapor liquid solid (VLS) epitaxial method. When the first nanorods  40  are formed by using a VLS epitaxial method, the first nanorods  40  may be formed together with quantum dots  42  on upper surfaces of the first nanorods  40  according to a well-known growing mechanism. The first nanorods  40  respectively fill the holes H 1  and may extend to a desired length in a direction away from the substrate  30 .  FIG. 13  is scanning electron microscope (SEM) images of actually grown first nanorods  40 . Referring to  FIG. 13 , the first nanorods  40  are formed on the substrate  30 . 
     Next, referring to  FIG. 9 , the quantum dots  42  are formed on the upper surfaces of the first nanorods  40 , respectively. When the first nanorods  40  are formed by using an MOCVD method or an MBE method, the quantum dots  42  may be formed by using a droplet method. For example, when the quantum dots  42  are GaAs quantum dots, after forming Ga on upper surfaces of the first nanorods  40 , the GaAs quantum dots may be formed on the upper surfaces of the first nanorods  40  by supplying As gas onto the upper surfaces of the first nanorods  40 . In this process, as the crystal surface of a lateral surface of the first nanorod  40  is different from that of the upper surface of the first nanorods  40 , GaAs is not grown on the lateral surfaces of the first nanorod  40 . Accordingly, the quantum dots  42  may be selectively formed on the upper surfaces of the first nanorods  40 . Also, when the first nanorods  40  are formed using a VLS epitaxial method described above, the quantum dots  42  may be respectively formed on the upper surfaces of the first nanorods  40  according to a growing mechanism.  FIG. 14  is SEM images showing GaAs nanorods (nanowires) actually grown on a GaN substrate. 
     Referring to  FIG. 10 , after forming the quantum dots  42 , a resin film  44  is formed on the insulating film  34  between the first nanorods  40 . Regions on the insulating film  34 , where second nanorods  50  will be formed, are defined by the resin film  44 . The resin film  44  includes a plurality of holes H 2 . The first nanorods  40  are located inside the holes H 2 , respectively. Edges of the holes H 2  are separate from, i.e., not in contact with the first nanorods  40 . 
     Referring to  FIG. 11 , the second nanorods  50  are formed on the insulating film  34  in the holes H 2 . The second nanorods  50  may be formed using an MOCVD method or an MBE method. The second nanorods  50  may be formed so to cover the entire exposed lateral surfaces of the first nanorods  40  and all the quantum dots  42 . The second nanorods  50  may extend upwards above the quantum dots  42 . 
     Referring to  FIG. 12 , a conductive oxide film  60  is formed on the resin film  44  to cover the second nanorods  50 . The conductive oxide film  60  may be grown under a lateral overgrowth condition. Accordingly, the conductive oxide film  60  may be formed so to cover the lateral and the upper surfaces of the second nanorods  50 , and thus a planarized upper surface may be obtained. After forming the conductive oxide film  60 , electrodes  70  are formed on the conductive oxide film  60 . 
     In the method described above, the first nanorods  40  are directly grown on the substrate  30 , and the quantum dots  42  and the second nanorods  50  are sequentially formed on the first nanorods  40 . Accordingly, the first nanorods  40 , the quantum dots  42 , and the second nanorods  50  may be formed in-situ, and thus, the manufacturing process may be simplified. Also, since the quantum dots  42  are grown on the upper surfaces of the first nanorods  40 , a high quantum confinement is realized, and thus, a device having improved efficiency (for example, light-emitting efficiency) may be obtained. Also, the first and second nanorods  40  and  50  are materials having a relatively wide band gap, and thus, an electronic device according to an exemplary embodiment may be applied to high pressure resistance devices or power devices. 
     The electronic device described above includes an upper conductive nitride nanorod and a lower conductive nitride nanorod and quantum dots included between the upper and lower conductive nitride nanorods, and thus a device having a high quantum confinement may be realized. Accordingly, when the electronic device is a light-emitting device, an optical device having a high light-emitting efficiency may be realized. 
     The upper and lower conductive nitride may have a relatively wide band gap, and may be formed of a nitride (for example, GaN or BrN) having a relatively small refractive index, and thus, the electronic device may be applied to various devices, for example, QWIR detectors, high voltage or power devices, single electron tunneling transistors, or single photon detectors. 
     Further, by adding SPR etc. to a site controlled quantum device that may affect the band gap and tunnel junction of the electronic device, the efficiency of the electronic device may be further increased. 
     Further still, in the context of manufacturing the electronic device, materials having different lattice constants, for example, GaN and GaAs, may be directly grown on a substrate and grown into nanorod type, and thus, a stack structure (for example, GaN/GaAs/GaN) that is one dimensionally grown without strain may be realized. Accordingly, the manufacturing process may be simplified and operational characteristics may be further improved. 
     While exemplary embodiments have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the inventive concept.