Semiconductor devices and methods of making the same include forming a first channel region on a first semiconductor region. A second channel region is formed on a second semiconductor region, the second semiconductor region being formed from a semiconductor material that is different from a semiconductor material of the first semiconductor region. A gate dielectric layer is formed over one or more of the first and second channel regions. A nitrogen-containing layer is formed on the gate dielectric layer. A gate is formed on the gate dielectric.