Quantum dots, and electronic devices and electronic equipments including same

1. A quantum dot, comprising

a core comprising a first semiconductor nanocrystal comprising a Group II-VI compound; and

a shell disposed on an outer surface of the core and comprising a second semiconductor nanocrystal;

wherein the quantum dot does not comprise cadmium, lead, mercury, or a combination thereof, and

an effective mass of the second semiconductor nanocrystal is about 0.5 times to about 2.0 times an effective mass of the first semiconductor nanocrystal.

2. The quantum dot of claim 1 , wherein the effective mass of the second semiconductor nanocrystal is about 0.5 to about 1.5 times the effective mass of the first semiconductor nanocrystal.

3. The quantum dot of claim 1 , wherein a bandgap energy of the second semiconductor nanocrystal is greater than a bandgap energy of the first semiconductor nanocrystal.

4. The quantum dot of claim 1 , wherein the second semiconductor nanocrystal has an electron effective mass of less than 0.39 m e .

5. The quantum dot of claim 1 , wherein a difference between the electron effective mass of the second semiconductor nanocrystal and the first semiconductor nanocrystal is less than or equal to about 0.2 m e .

6. The quantum dot of claim 1 , wherein the second semiconductor nanocrystal comprises a Group III element and a mole ratio of the Group III element to the Group II element is greater than about 0:1 and less than or equal to about 10:1.

7. The quantum dot of claim 1 , wherein the second semiconductor nanocrystal comprises a Group III element and a mole ratio of the Group III element to the Group II element of the core is greater than about 0:1 and less than or equal to about 10:1.

8. The quantum dot of claim 1 , wherein the second semiconductor nanocrystal comprises a Group III element and a mole ratio of the Group III element to the Group VI element is greater than about 0:1 and less than or equal to about 10:1.

9. The quantum dot of claim 1 , wherein the second semiconductor nanocrystal comprises a Group III element and a mole ratio of the Group III element to the Group VI element of the core is greater than about 0:1 and less than or equal to about 10:1.

10. The quantum dot of claim 1 , wherein the second semiconductor nanocrystal comprises a compound represented by M 1 X 1 ,

wherein

M 1 is In, Ga, or a combination thereof, and

X 1 is S, Se, Te, or a combination thereof.

11. The quantum dot of claim 1 , wherein the second semiconductor nanocrystal comprises a compound represented by Chemical Formula 1

(M 2 2-x M 3 x )(X 2 3-y X 3 y )  Chemical Formula 1

wherein, in Chemical Formula 1,

M 2 and M 3 are each independently In, Ga, or a combination thereof,

X 2 and X 3 are each independently S, Se, Te, or a combination thereof,

x is 0 to 2, and

y is 0 to 3.

12. The quantum dot of claim 1 , wherein the quantum dot comprises a shell comprising a third semiconductor nanocrystal and the third semiconductor nanocrystal comprises a Group II-VI compound, a Group III-V compound, or a combination thereof.

13. The quantum dot of claim 1 , wherein

the quantum dot comprises a shell comprising a Group II-VI compound between the core and the shell comprising the second semiconductor nanocrystal.

14. The quantum dot of claim 1 , wherein

the quantum dot comprises two or more shells comprising a Group II-VI compound between the core and the shell comprising the second semiconductor nanocrystal, and

the shells comprising the Group II-VI compound are different in type, amount, or a combination thereof of the Group VI element.

15. The quantum dot of claim 14 , wherein a shell comprising the Group II-VI compound closest to the core comprises Se.

16. The quantum dot of claim 14 , wherein a shell comprising the Group II-VI compound farthest from the core comprises S.

17. The quantum dot of claim 1 , wherein

outside the shell comprising the second semiconductor nanocrystal,

the quantum dot comprises a shell comprising a third semiconductor nanocrystal comprising a Group II-VI compound.

18. The quantum dot of claim 1 , wherein a mole ratio of tellurium to selenium in the first semiconductor nanocrystal is greater than about 0:1 and less than or equal to about 5:1.

19. The quantum dot of claim 1 , wherein a mole ratio of tellurium to selenium in the quantum dot is greater than about 0:1 and less than or equal to about 5:1.

20. The quantum dot of claim 1 , wherein a mole ratio of tellurium to zinc in the quantum dot is greater than about 0:1 and less than or equal to about 5:1.

21. The quantum dot of claim 1 , wherein a maximum emission peak of the quantum dot has a full width at half maximum of less than or equal to about 40 nanometers.

22. The quantum dot of claim 1 , wherein the quantum dot has a quantum efficiency of greater than or equal to about 40%.

23. A quantum dot, comprising

a semiconductor compound having an electron effective mass of less than or equal to about 0.34 m e is present in a mole ratio of greater than or equal to about 0.3:1 and less than or equal to about 1.0:1 relative to a total number of moles in the quantum dot,

wherein the quantum dot does not comprise cadmium, lead, mercury, or a combination thereof.

24. The quantum dot of claim 23 , wherein the semiconductor compound having the electron effective mass of less than or equal to about 0.34 m e comprises a Group II-VI compound, a Group III-V compound, a Group III-VI compound, or a combination thereof.

25. The quantum dot of claim 23 , wherein the semiconductor compound having the electron effective mass of less than or equal to about 0.34 m e comprises a compound M 4 X 4 , wherein M 4 is Zn, Ga, or a combination thereof, and X 4 is S, Se, Te, or a combination thereof.

26. The quantum dot of claim 23 , wherein the semiconductor compound having the electron effective mass of less than or equal to about 0.34 m e comprises zinc selenide, zinc telluride, gallium sulfide, or a combination thereof.

27. The quantum dot of claim 23 , wherein the semiconductor compound having the electron effective mass of less than or equal to about 0.34 m e is not a binary element compound of zinc sulfide.

28. The quantum dot of claim 23 , wherein

the quantum dot comprises

a core comprising a semiconductor nanocrystal; and

n shells disposed outside the core,

wherein n is an integer greater than or equal to 1, and

wherein at least one of the n shells comprises the semiconductor compound having the electron effective mass of less than or equal to about 0.34 m e .

29. The quantum dot of claim 28 , wherein the core comprising the semiconductor nanocrystal comprises a semiconductor compound having an electron effective mass of less than or equal to about 0.34 m e .

30. The quantum dot of claim 28 , wherein the core comprising the semiconductor nanocrystal comprises a zinc chalcogenide compound.

31. The quantum dot of claim 28 , wherein

n is an integer greater than or equal to 2, and

a number m of the n shells comprise a semiconductor compound having an electron effective mass of less than or equal to about 0.34 m e , wherein m is an integer greater than or equal to n/2.

32. The quantum dot of claim 28 , wherein the quantum dot further comprises a shell comprising a binary element compound of zinc sulfide.

33. A quantum dot polymer composite, comprising

a polymer matrix; and

quantum dots dispersed in the polymer matrix;

wherein the quantum dot comprises the quantum dot of claim 1 .

34. An electronic device comprising

a first electrode;

a second electrode facing the first electrode; and

an active layer between the first electrode and second electrode,

wherein the active layer comprises the quantum dot of claim 1 .

35. An electronic device comprising

a light source; and

a light emitting element,

wherein the light emitting element comprises the quantum dot of claim 1 , and

wherein the light source is configured to provide incident light to the light emitting element.

36. An electronic apparatus comprising the quantum dot of claim 1 .