ELECTRICAL BEHAVIOR OF IMPLANTED CARBON IMPURITIES IN FLUORINE CO-IMPIANTED GAAS

The effect of fluorine co-implantation in carbon-implanted GaAs has be en investigated by secondary-ion-mass spectrometry (SIMS), Hall, C-V a nd deep level transient spectroscopy (DLTS) techniques. The variation of carbon activation with different co-implanted doses of fluorine has been analyzed on tile basis of thr concentration and mobility versus depth profiles of the samples, obtained via the differential Hall tech nique. The acceptor activation is found to increase With the co-implan ted F dose only in the surface region, whereas in the deeper part of t he carbon-implanted layer the co-implantation process is less effectiv e, if not counterproductive. The presence of a midgap hole trap level. with an emission energy E(T)=0.48 eV, has been observed by means of t he DLTS technique. The trap concentration is found to be higher in the samples with the lower C activation level (corresponding to lower co- implanted F dose): furthermore, by comparing C-V measurements (at 77 K and room temperature) and SIMS profiles, the trap concentration profi le is found to be almost coincident with the unactivated C concentrati on: In other words, the difference between the implanted C and the act ivated acceptor concentration corresponds to the hole trap concentrati on. This result enables a better understanding of the anomalous behavi or observed when implanted carbon is used to compensate donor impuriti es, with almost 100% efficiency, while as an acceptor iis activation i s much lower. All these effects cannot be ascribed to any chemical bon d of the co-implanted F since from SIMS analysis it results that it co mpletely outdiffuses after the rapid thermal anneal process. (C) 1996 American Institute of Physics.