Semiconductor devices

1. A semiconductor device, comprising:

an active region extending in a first direction on a substrate;

a gate structure intersecting the active region and extending in a second direction on the substrate; and

a source/drain region on the active region and at least one side of the gate structure,

wherein the source/drain region includes:

a plurality of first epitaxial layers spaced apart from each other in the first direction, the plurality of first epitaxial layers including first impurities of a first conductivity type; and

a second epitaxial layer filling a space between the plurality of first epitaxial layers, the second epitaxial layer including second impurities of the first conductivity type.

2. The semiconductor device as claimed in claim 1 , wherein:

each of the plurality of first epitaxial layers includes the first impurities in a first concentration, and

the second epitaxial layer includes the second impurities in a second concentration that is higher than the first concentration.

3. The semiconductor device as claimed in claim 1 , wherein:

the first impurities include arsenic (As), and

the second impurities include phosphorus (P).

4. The semiconductor device as claimed in claim 1 , wherein:

the plurality of first epitaxial layers are SiAs layers, and

the second epitaxial layer is an SiP layer.

5. The semiconductor device as claimed in claim 1 , wherein:

the active region includes doping regions in contact with the plurality of first epitaxial layers, the doping regions including the first impurities, and

the doping regions are spaced apart from each other in the first direction.

6. The semiconductor device as claimed in claim 5 , wherein:

each of the plurality of first epitaxial layers include the first impurities in a first concentration, and

each of the doping regions include the first impurities in a third concentration that is lower than the first concentration.

7. The semiconductor device as claimed in claim 1 , wherein:

the active region includes a recess region recessed from an upper surface thereof on the at least one side of the gate structure, and

the source/drain region is in the recess region.

8. The semiconductor device as claimed in claim 7 , wherein:

the plurality of first epitaxial layers are on each of two side walls of the recess region, and

the second epitaxial layer fills remaining parts of the recess region.

9. The semiconductor device as claimed in claim 1 , wherein:

the plurality of first epitaxial layers further include the second impurities, and

the second epitaxial layer further includes the first impurities.

10. The semiconductor device as claimed in claim 9 , wherein a concentration of the first impurities in the plurality of first epitaxial layers, in the second epitaxial layer and in the active region has a maximum value in the plurality of first epitaxial layers.

11. The semiconductor device as claimed in claim 1 , further comprising plurality of channel layers on the active region, the plurality of channel layers being spaced apart from each other in a third direction perpendicular to the first direction and the second direction,

wherein the gate structure surrounds the plurality of channel layers.

12. The semiconductor device as claimed in claim 11 , wherein the plurality of first epitaxial layers:

are on side surfaces of the plurality of channel layers, and

are spaced apart from one another in the third direction.

13. The semiconductor device as claimed in claim 12 , wherein the plurality of first epitaxial layers include:

first regions on the side surfaces of the plurality of channel layers, respectively, that are spaced apart from one another in the third direction, and

a second region spaced apart from the first regions and on the active region at a lower end of the source/drain region.

14. The semiconductor device as claimed in claim 11 , wherein the plurality of first epitaxial layers continuously extend along sides of the plurality of channel layers on the active region.

15. A semiconductor device, comprising:

an active region extending in a first direction on a substrate;

a plurality of channel layers on the active region, the plurality of channel layers being spaced apart from each other in a third direction perpendicular to the first direction;

a gate structure on the substrate intersecting the active region and the plurality of channel layers and extending in a second direction, the gate structure surrounding the plurality of channel layers; and

a source/drain region on the active region and at least one side of the gate structure, the source/drain region being in contact with the plurality of channel layers,

wherein the source/drain region includes:

a plurality of first epitaxial layers on side surfaces of the plurality of channel layers in the first direction, each of the plurality of first epitaxial layers including first impurities of a first conductivity type; and

a second epitaxial layer filling a space between the plurality of first epitaxial layers and including second impurities of the first conductivity type.

16. The semiconductor device as claimed in claim 15 , wherein the plurality of first epitaxial layers are spaced apart from one another in the third direction.

17. The semiconductor device as claimed in claim 16 , wherein the second epitaxial layer extends between the plurality of first epitaxial layers that spaced apart from one another in the third direction.

18. The semiconductor device as claimed in claim 15 , further comprising internal spacer layers on both sides of the gate structure on a lower surface of each of the plurality of channel layers,

wherein the plurality of first epitaxial layers protrude in the first direction towards the second epitaxial layer relative to a side surface formed by the internal spacer layers and the channel layers.

19. A semiconductor device, comprising:

an active structure extending in a first direction on a substrate and having channel regions;

gate structures intersecting the channel regions and extending in a second direction; and

source/drain regions on both sides of the gate structures,

wherein each of the source/drain regions includes:

a first semiconductor layer including first impurities in a first concentration; and

a plurality of second semiconductor layers separated from each other to be in contact with the channel regions, respectively, between the first semiconductor layer and the channel regions, and including second impurities in a second concentration that is lower than the first concentration.

20. The semiconductor device as claimed in claim 19 , wherein the first impurities and the second impurities have a same conductivity type.