Patent Publication Number: US-2010117058-A1

Title: Multi-structure nanowire and method of manufacturing the same

Description:
TECHNICAL FIELD 
     The present invention relates to a semiconductor nanowire structure and a method of manufacturing the same, and more particularly, to a multi-structure of nanorods of a compound semiconductor and silicon nanowires and a method of manufacturing the multi-structure nanowire. 
     The present invention was supported by the Information Technology (IT) Research &amp; Development (R &amp; D) program of the Ministry of Information and Communication (MIC) [project No. 2005-S-605-02, project title: IT-BT-NT Convergent Core Technology for advanced Optoelectronic Devices and Smart Bio/Chemical Sensors]. 
     BACKGROUND ART 
     Nano-structures such as nanowires or nanorods have been intensively studied in the last decade due to their new electrical, catalytic, and optical characteristics. Nanowires have a diameter of a few tens of nanometers and have no limit in length, and nanorods have the same diameters as the nanowires and generally have a length of three to five times of the diameter thereof. Basic characteristics of nanowires and nanorods can be varied by simply changing the dimensions thereof while chemical compositions thereof are maintained constant. Such nano-structures have intermediate characteristics between a molecule and a bulk shape. For example, a nano-structure based on a semi-conductor material shows a three-dimensional quantum confinement phenomenon in both electrons and holes, and this phenomenon results in the increase in an effective band gap of a material together with a reduction in size of the nano-structure. Accordingly, as the size of the nano-structure is reduced, optical absorption and emission of the nano-structure is biased towards blue light. As another example, when a nanowire has a multi-layer structure, the nanowire can be further effectively used as an optical device or an electron device. A nanowire having a structure in which doping concentration is controlled in an axis direction or a nanowire formed of different materials is known as a multi-structure nanowire. 
     However, despite the high functional potential of the nano-structures, only a few applied products have been developed. One of the reasons for this is due to the difficulty of producing nano-structures. It is even more difficult to produce a multi-structure nanowire. If it is possible to produce a multi-structure nanowire, a functional device such as an ultra small optical device or a tunneling electronic device can be developed. 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     To address the above and/or other problems, the present invention provides a multi-structure nanowire that can be used as an optical device or an electron device and a method of manufacturing the multi-structure nanowire. 
     Technical Solution 
     According to an aspect of the present invention, there is provided a multi-structure nanowire in which silicon nanowires are junctioned at both ends of a compound semi-conductor nanorod. 
     The compound semiconductor may be one selected from the group consisting of AlN, AlP, AlAs, GaN, GaP, GaAs, InP, InAs, InSb, AlInGaP, AlGaAs, InGaN, CdS, CdSe, CdTe, ZnO, ZnS, ZnSe, ZnTe, TiO 2 , HgTe, and CdHgTe. 
     The compound semiconductor nanorod may have a length of 2 to 100 nm and may have a diameter of 10 to 100 nm. 
     According to an aspect of the present invention, there is provided a method of manufacturing a multi-structure nanowire, comprising: providing a compound semi-conductor nanorod; forming metal catalyst tips on both ends of the compound semi-conductor nanorod; and growing silicon nanowires on both ends of the compound semiconductor nanorod where the metal catalyst tips are formed. 
     The compound semiconductor may be one selected from the group consisting of AlN, AlP, AlAs, GaN, GaP, GaAs, InP, InAs, InSb, AlInGaP, AlGaAs, InGaN, CdS, CdSe, CdTe, ZnO, ZnS, ZnSe, ZnTe, TiO 2 , HgTe, and CdHgTe. 
     The compound semiconductor nanorod may have a length of 2 to 100 nm and may have a diameter of 10 to 100 nm. 
     The metal catalyst tips may comprise a material selected from the group consisting of Au, Ag, and Ni. 
     The growing silicon nanowires on the both ends of the compound semiconductor nanorod where the metal catalyst tips are formed may comprise: dispersing the compound semiconductor nanorods on a substrate; placing the substrate on which the compound semiconductor nanorod is dispersed in a chamber; and heat treating the chamber in a silicon source atmosphere to decompose the silicon source to silicon atoms or silicon molecules, whereby growing silicon nanowire on the both ends of the compound semiconductor nanorod. 
     The silicon source may comprise a mixture powder of Si and C or a silane gas SiH 4 . 
     Advantageous Effects 
     According to the present invention, metal catalyst tips are formed on both ends of a compound semiconductor nanorod, and silicon nanowires are grown from both ends of the compound semiconductor nanorod. Thus, a multi-structure nanowire comprising a compound semiconductor and silicon can be formed. A multi-structure nanowire formed in this way can be used in an optical device or an electron device. 
    
    
     
       DESCRIPTION OF DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a schematic perspective view of a multi-structure nanowire according to an embodiment of the present invention; and 
         FIGS. 2A through 2D  are schematic drawings for explaining a method of manufacturing a multi-structure nanowire, according to an embodiment of the present invention. 
     
    
    
     BEST MODE 
     Referring to  FIG. 1 , the multi-structure nanowire  100  according to the current embodiment of the present invention has a structure in which silicon nanowires  130  are junctioned at both ends of a nanorod  110  formed of a compound semiconductor. The diameter of the multi-structure nanowire  100  may be 10 to 100 nm. The length of the nanorod  110  may be 2 to 100 nm, and the length of the silicon nanowires  130  can be controlled according to usage. 
     Mode for Invention 
     The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The 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. In the following descriptions, it is understood that when a layer is referred to as being ‘on’ another layer or substrate, it can be directly on the other constituent element, or intervening a third constituent element may also be present. Also, in the drawings, the thicknesses of layers and regions are exaggerated for clarity, and like reference numerals in the drawings denote like elements. Terminologies used in the descriptions are to explain the present invention, and do not confine the limit of meanings and the range of the present invention. 
       FIG. 1  is a schematic perspective view of a multi-structure nanowire  100  according to an embodiment of the present invention. Referring to  FIG. 1 , the multi-structure nanowire  100  according to the current embodiment of the present invention has a structure in which silicon nanowires  130  are junctioned at both ends of a nanorod  110  formed of a compound semiconductor. The diameter of the multi-structure nanowire  100  may be 10 to 100 nm. The length of the nanorod  110  may be 2 to 100 nm, and the length of the silicon nanowires  130  can be controlled according to usage. 
     The compound semiconductor used to form the nanorod  110  can be a Group III-V compound such as AlN, AlP, AlAs, GaN, GaP, GaAs, InP, InAs, InSb, AlInGaP, AlGaAs, or InGaN, or a Group II-VI compound such as CdS, CdSe, CdTe, ZnO, ZnS, ZnSe, ZnTe, TiO 2 , HgTe, or CdHgTe. However, the compound semiconductor that can be used to from the nanorod  110  of the multi-structure nanowire  100  is not limited to the above materials. 
     As described above, since the multi-structure nanowire  100  has a structure in which the silicon nanowires  130  are formed at both ends of the nanorod  110 , the applicability of the multi-structure nanowire  100  can be increased. For example, it may be difficult to combine a compound semiconductor nano-structure with a silicon-based device due to physical property differences between the compound semiconductor and silicon. However, since the silicon nanowires  130  are formed at both ends of the nanorod  110 , it is easier to combine the nanorod  110  and a silicon-based device. The reference number  120  is a metal catalyst tips used for junctioning silicon nanowires  130  at the ends of the nanorod  110  and the metal catalyst tips  120  can be removed. 
       FIGS. 2A through 2D  are schematic drawings for explaining a method of manufacturing a multi-structure nanowire, according to an embodiment of the present invention. In the present embodiment, a cadmium selenide is used to form a compound semiconductor nanorod. Referring to  FIG. 2A , a cadmium selenide nanorod  110  is formed. The cadmium selenide nanorod  110  can be formed using a well-known wet method. In order to form the cadmium selenide nanorod  110 , a mixture of dimethyl cadmium and tributylphosphine in which selenium powder is dissolved is mixed with a mixed solution  200  of trioctylphosphineoxide (TOPO) and tetradecylphosphonic acid. In this regard, the dimethyl cadmium and the tributylphosphine in which the selenium powder is dissolved are mixed in a ratio of 1.5:1. The mixed solution  200  of TOPO and tetradecylphosphonic acid may be maintained at a temperature of approximately 300° C. The diameter of the cadmium selenide nanorod  110  formed in this way is 10 to 100 nm. The length of the cadmium selenide nanorod  110  can be controlled by controlling the temperature and reaction time, and may be in a range of 2 to 100 nm. In particular, in order to be used as a nano-optical device, the length of the cadmium selenide nanorod  110  may be approximately 3 nm. In the present embodiment, cadmium selenide is used to form a nanorod; however, a material for forming the nanorod is not limited to cadmium selenide, and can be, for example, CdSe, CdTe, ZnO, TiO 2 , GaO, SiC, ZnS, or CdS. 
     Referring to  FIG. 2B , metal catalyst tips  120  are formed on both ends of the cadmium selenide nanorod  110 . The metal catalyst tips  120  can be formed of Au. In order to form the metalcatalyst tips  120  formed of Au, the cadmium selenide nanorod  110  and Aucl 3  are immersed in a mixed solution  300  of toluene, dodecyldimethylammonium, and dodecylamine, and the mixture is stirred. In this manner, nanorods  112  having hemisphere-shaped Au catalyst tips on both ends thereof can be formed. Meanwhile, the metal catalyst tips  120  can be formed of Ag, Ni, Pt, Pd, Cu, Co, Ir, Ro, or Ru, besides Au. 
     Referring to  FIG. 2C , the mixed solution  300  in which the nanorods  112  having the metal catalyst tips  120  is immersed, is dispersed on a substrate  400  formed of a material such as silicon using a method such as spin coating. Afterwards, the mixed solution  300  is evaporated, leaving the nanorods  112  remaining on the substrate  400 . 
     Referring to  FIG. 2D , the substrate  400  on which the nanorods  112  are dispersed is moved to a chamber in which silicon nanowires can be formed, and silicon nanowires  130  are grown on both ends of the nanorods  112 . A silicon raw material for forming the silicon nanowires  130  can be a Si+C powder or a silane gas SiH 4 . In thermal decomposition of silicon atoms or molecules from a silicon raw material, a decomposition temperature of approximately 800° C. or greater is required when Si+C powder is used, and a decomposition temperature of approximately 300° C. or greater is required when silane gas is used. Silicon atoms or silicon molecules decomposed from a silicon raw material form a eutectic mixture on both ends of the nanorods  112 , and if the silicon molecules are super-saturated, the silicon nanowires  130  grow. 
     In this way, as depicted in  FIG. 1 , a multi-structure nanowire  100  in which the cadmium selenide nanorod  110  is positioned in the center and the silicon nanowires  130  are formed on both ends of the cadmium selenide nanorod  110  is formed. 
     Meanwhile, after the silicon nanowires  130  are grown, the metal catalyst tips  120  remaining on both ends of the silicon nanowires  130  can be removed using a wet method. 
     According to the present invention, metal catalyst tips are formed on both ends of a compound semiconductor nanorod, and silicon nanowires are grown from both ends of the compound semiconductor nanorod. Thus, a multi-structure nanowire comprising a compound semiconductor and silicon can be formed. A multi-structure nanowire formed in this way can be used in an optical device or an electron device. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.