To render to a 2D texture array, create a render textureA special type of Texture that is created and updated at runtime. To use them, first create a new Render Texture and designate one of your Cameras to render into it. Then you can use the Render Texture in a Material just like a regular Texture. More info
See in Glossary and set the Dimension property to 2D Array.
If you use the Graphics.SetRenderTarget API, set the depthSlice parameter to the slice you want to render to.
If the platform supports geometry shaders, use a geometry shaderA program that runs on the GPU. More info
See in Glossary to render to individual slices, or set depthSlice to -1 to render to all the slices.