Semiconductor devices and methods of forming the same

A semiconductor device comprising:

• a substrate;
• first and second source/drain regions in the substrate;
• and
• a buried gate structure in the substrate, the buried gate structure comprising:
• a first work function control portion;
• and
• a second work function control portion on the first work function control portion, wherein the second work function control portion:
• is closer, than the first work function control portion, to the first and second source/drain regions;
• and
• comprises a metal alloy comprising a greater, relative to the first work function control portion, concentration of implanted and/or diffused metal atoms.

A semiconductor device comprising:

• a substrate;
• a source/drain region in the substrate;
• a bit line on the source/drain region;
• and
• a buried gate structure in the substrate, the buried gate structure comprising:
• a liner comprising first and second portions, wherein the second portion:
• is closer, than the first portion, to the source/drain region;
• and
• comprises a first concentration of implanted and/or diffused metal atoms that is greater than a second concentration of the metal atoms in the first portion;
• and
• a gate electrode that is adjacent a sidewall of the second portion of the liner and that comprises a lower resistivity than polysilicon.