A method of forming a semiconductor device includes etching a high aspect ratio, substantially perpendicular trench in a semiconductor region doped with a first dopant having first conductivity type and performing a first cycle for depositing silicon doped with a second dopant on an inner surface of the high aspect ratio, substantially perpendicular trench, the first cycle comprising alternately depositing silicon at a first constant pressure and etching the deposited silicon at an etching pressure that ramps up from a first value to a second value, the second dopant having a second conductivity type that is opposite from the first conductivity type.