Characterization of Ion Implantation Damage in Capless Annealed GaAs
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CHARACTERIZATION OF ION IMPLANTATION DAMAGE IN CAPLESS ANNEALED GaAs H. KANBER,* M. FENG,* and J. M. WHELAN** *Torrance Research Center, Hughes Aircraft Company, Torrance, CA 90509; **Materials Science Dept., University of Southern California, Los Angeles, CA 90089 ABSTRACT Arsenic and argon implantation damage is characterized by Rutherford backscattering in GaAs undoped VPE buffer layers grown on Cr-O doped semi-insulating substrates and capless annealed in a H2 -As 4 atmosphere provided by AsH3. The damage detected in the RBS channeled spectra varies as a function of the ion mass, the implant depth and the annealing temperature of the stress-free controlled atmosphere technique. This damage is discussed in terms of the stoichiometric disturbances introduced by the implantation process. The as-implanted and annealed damage characteristics of the Ar and As implants are correlated to the electrical activation characteristics of Si and Se implants in GaAs, respectively. INTRODUCTION Ion implantation causes collision damage in compound semiconductor crystal lattices which can become sufficiently extensive to reach the amorphous level depending upon the fluence and energy of the incident ions. For most applications in GaAs discrete devices and integrated circuits, ion implantation followed by an annealing step is necessary to permit the reordering of the near surface damage and to electrically activate the implanted channel layer. Ion beam backscattering and ion channeling can be used to study induced damage in ion implanted samples. The study of disorder by the ion channeling technique [1] is based on the principle that channeled ions detect displacements from regular lattice sites. Thus, ion channeling is sensitive to interstitial host and impurity atoms or changes in the host periodicity, e.g., stacking faults, but is insensitive to isolated vacancies. One of the capabilities of ion beam backscattering is that the depth scale can be established by the analysis of the energy of the backscattered ions. The channeling spectrum from the implanted sample can be converted to relative damage with respect to the random yield versus depth distribution of the damage. This paper compares the damage detected by Rutherford backscattering spectrometry (RBS) of channeled He+ ions resulting from ion implantation and annealing of semi-insulating (SI) GaAs. The upper temperature used, 850°C, is in the range required for substantial electrical activation of donor implants. The samples were impl nted with Ar+ and As+ ions with projected ranges (Rp) of 850 and 1350 ý to illustrate the effects of damage 14 2 caused by different ion masses and energies. The dose of 5x10 cm- was used to avoid full amorphization at any depth. Results are interpreted in terms of the stoichiometric disturbances resulting from ion implantation of compound semiconductors as proposed by Christel and Gibbons [2] and used by Magee et al [3]. According to their model, implantation creates a region at a depth exceeding Rp, where the recoiled Ga and As atoms produce
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