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. The printing system includes a carriage that moves a printhead with a plurality of columnar marking elements based on input provided by an encoder and a printer controller for reformatting the image data and controlling the marking elements. A light receiving unit receives reflected light from the irradiated object. The application member may further comprise at least one wall on the base portion. Specifically, the present invention provides for a speaker system that is configured to digitally process an audio signal in a manner such that studio-quality sound that can be reproduced.