A carbon/tunneling-barrier/carbon diode and method for forming the same are disclosed. The carbon/tunneling-barrier/carbon may be used as a steering element in a memory array. Each memory cell in the memory array may include a reversible resistivity-switching element and a carbon/tunneling-barrier/carbon diode as the steering element. The tunneling-barrier may include a semiconductor or an insulator. Thus, the diode may be a carbon/semiconductor/carbon diode. The semiconductor in the diode may be intrinsic or doped. The semiconductor may be depleted when the diode is under equilibrium conditions. For example, the semiconductor may be lightly doped such that the depletion region extends from one end of the semiconductor region to the other end. The diode may be a carbon/insulator/carbon diode.