Electrical behavior of implanted carbon impurities in fluorine co-implanted GaAs

• Published in: Journal of applied physics 1996-10, Vol.80 (7), p.3834-3839
• Main Authors: Peroni, Marco, D’Eustacchio, Patrizio, Di Virginio, Nazzareno, Graffitti, Roberto, Gasparotto, Andrea
• Format: Article
• Language: English
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.363337

The effect of fluorine co-implantation in carbon-implanted GaAs has been investigated by secondary-ion-mass spectrometry (SIMS), Hall, C–V and deep level transient spectroscopy (DLTS) techniques. The variation of carbon activation with different co-implanted doses of fluorine has been analyzed on the basis of the concentration and mobility versus depth profiles of the samples, obtained via the differential Hall technique. The acceptor activation is found to increase with the co-implanted F dose only in the surface region, whereas in the deeper part of the carbon-implanted layer the co-implantation process is less effective, if not counterproductive. The presence of a midgap hole trap level, with an emission energy ET=0.48 eV, has been observed by means of the 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 profile is found to be almost coincident with the unactivated C concentration: In other words, the difference between the implanted C and the activated acceptor concentration corresponds to the hole trap concentration. This result enables a better understanding of the anomalous behavior observed when implanted carbon is used to compensate donor impurities, with almost 100% efficiency, while as an acceptor its activation is much lower. All these effects cannot be ascribed to any chemical bond of the co-implanted F since from SIMS analysis it results that it completely outdiffuses after the rapid thermal anneal process.