Films of III-nitride for semiconductor device growth are planarized using an etch-back method. The link mechanism is arranged to prevent motion of the seat back beyond a predetermined position. The check valve serves to stop the passing of air and water after a period of time. The base is movably connected to the body. Pharmaceutical compositions containing them, as well as their use for the preparation of medicaments intended for the preventative or curative treatment of illnesses which are dependent upon the activation of the interleukin CXCR2 receptor and of the chemokines of the same family, are also subjects of the invention. Base current error compensation circuitry is incorporated into current mirror circuits of the generator to yield a composite current having a desired component, defined exclusively in accordance with the desired bandgap voltage, and a base error component containing the desired bandgap voltage, but modified by a second base current error.