An apparatus and method, the apparatus comprising: at least one charged substrate (3); a channel of two dimensional material (5); and at least one floating electrode (7A-C) wherein the floating electrode comprises a first area (10A-C) adjacent the at least one charged substrate, a second area (11A-C) adjacent the channel of two dimensional material and a conductive interconnection (9A-C) between the first area and the second area wherein the first area is larger than the second area and wherein the at least one floating electrode is arranged to control the level of doping within the channel of two dimensional material.