Quantum dots having composition gradient shell structure and manufacturing method thereof

Abstract

Provided are quantum dots having a gradual composition gradient shell structure which have an improvedluminous efficiency and optical stability, and a method of manufacturing the quantum dots in a short amount of time at low cost. In the method, the quantum dots can be manufactured in a short amount of time at low cost using a reactivity difference between semiconductor precursors, unlike in uneconomical and inefficient conventional methods where shells areformed after forming cores and performing cleaning and redispersion processes. Also, formation of the cores is followed by formation of shells having a composition gradient. Thus, even if the shells are formed to a large thickness, the lattice mismatch between cores and shells is relieved. Furthermore, on the basis of the funneling concept, electrons and holes generated in the shells are transferred to the cores to emit light, thereby obtaining a high luminous efficiency of 80% or more. The quantum dot structure is not limited to Group II-IV semiconductor quantum dots but can be applied to other semiconductors quantum dots, such as Group III-V semiconductors quantum dots and Group IV-IV semiconductors quantum dots. Also, the manufacturing method can be utilized in the development of semiconductor quantum dots having different physical properties, and in various other fields.

1 - 16 . (canceled) 
     
     
         17 . A quantum dot comprising a core and a shell, wherein:
 the core comprises a first Group II-VI compound;   the shell comprises a second Group II-VI compound;   the second Group II-VI compound has a larger bandgap than the first Group II-VI compound; and   the shell has a gradual composition gradient.   
     
     
         18 . A method of manufacturing quantum dots, comprising:
 mixing a compound comprising a core-forming Group II metal with a compound comprising a shell-forming Group II metal to form a mixture;   heating the mixture comprising the core-forming Group II metal and the shell-forming Group II metal at a temperature between approximately 100° C. and 350° C.;   forming a core by mixing the mixture with a compound comprising a core-forming Group VI element and a compound comprising a shell-forming Group VI element; and   forming a shell having a composition gradient by maintaining the mixture at a temperature between approximately 100° C. and 350° C.   
     
     
         19 . The method according to  claim 18 , wherein at least one of the core-forming Group II metal and the shell-forming Group II metal comprises at least one of zinc, cadmium, and mercury. 
     
     
         20 . The method according to  claim 18 , wherein heating the mixture occurs:
 in at least one of one of a N 2  atmosphere and a Ar atmosphere;   at or below atmospheric pressure;   at a temperature between approximately 100° C. and 350° C.; and   for a duration between approximately 10 minutes and 600 minutes.   
     
     
         21 . The method according to  claim 18 , wherein the compound comprising the core-forming Group II metal is mixed with the compound comprising the shell-forming Group II metal in a 1:1 molar ratio to 1:50 molar ratio. 
     
     
         22 . The method according to  claim 18 , wherein at least one of the core-forming Group VI element and the shell-forming Group VI element comprises at least one of sulfur, selenium, tellurium, and polonium. 
     
     
         23 . The method according to  claim 18 , wherein the compound comprising the core-forming Group VI element is mixed with the compound comprising the shell-forming Group VI element in a 1:1 molar ratio to 1:50 molar ratio. 
     
     
         24 . A quantum dot comprising:
 a core;   an outer shell having a predetermined bandgap energy that is higher than that of the core; and   an inner shell that surrounds the core and that is surrounded by the outer shell, wherein the inner shell has a bandgap energy that gradually decreases in a direction from the outer shell towards the core.   
     
     
         25 . The quantum dot according to  claim 24 , wherein each of the core, the outer shell, and the inner shell is formed by a Group II-VI compound semiconductor comprising a Group II element and a Group VI element. 
     
     
         26 . The quantum dot according to  claim 25 , wherein:
 the Group II element comprises at least one of cadmium, zinc, and mercury; and   the Group VI element comprises at least one of sulfur, selenium, tellurium, and polonium.   
     
     
         27 . The quantum dot according to  claim 26 , wherein the core and the outer shell comprise at least one of:
 a cadmium selenide core and a zinc sulfide outer shell;   a cadmium selenide core and a zinc selenide outer shell;   a cadmium telluride core and a zinc sulfide outer shell;   a cadmium telluride core and zinc selenide outer shell;   a cadmium telluride core and a zinc telluride outer shell;   a cadmium telluride core and a cadmium sulfide outer shell;   a cadmium sulfide core and a zinc sulfide outer shell; and   a zinc selenide core and a zinc sulfide outer shell.   
     
     
         28 . A method of manufacturing quantum dots, comprising:
 reacting compounds to form cores; and   reacting remaining compounds to form shells having a gradual composition gradient,   wherein said reacting compounds and said reacting remaining compounds are sequentially performed due to a difference in reactivity between the compounds.   
     
     
         29 . The method according to  claim 28 , wherein the gradual composition gradient of the shells is achieved due to a reactivity difference between the remaining compounds. 
     
     
         30 . The method according to  claim 28 , wherein the cores and the shells are formed by Group II-VI compound semiconductors comprising a core-forming Group II metal, a core-forming Group VI element, a shell-forming Group Il metal, and a shell-forming Group VI element. 
     
     
         31 . A method of manufacturing quantum dots, comprising:
 forming cores; and   reacting compounds to form shells, wherein the shells are formed having a gradual composition gradient due to a difference in reactivity between the compounds.   
     
     
         32 . The method according to  claim 31 , wherein the cores and the shells are formed by Group II-VI compound semiconductors comprising a core-forming Group II metal, a core-forming Group VI element, a shell-forming Group II metal, and a shell-forming Group VI element.