A method of manufacturing a heterojunction device includes forming a first layer of p-type aluminum gallium nitride; forming a second layer of undoped gallium nitride on the first layer; and forming a third layer of aluminum gallium nitride on the second layer, to provide an electron gas between the second and third layers. A heterojunction between the first and second layers injects positive charge into the second layer to compensate and/or neutralize negative charge within the electron gas.