Passivation of Implantation-Induced Defects

We believe that the luminescence at 1.0 eV is due to a structural damage induced by ion implantation rather than to a chemical doping effect, since the spectrum does not depend on the chemical species of the ion. These centers may be similar to the vacancies induced by 3-MeV electron-beam irradiation, as reported by Troxell and Watkins (1979), who find donorlike and acceptorlike levels —0.1 eV from the band edges. 

The temperature dependence of luminescence from the sample irradiated at 1 x 1013 cm-2 with 28Si+ indicates, above —110 K, an activation energy of 90 meV for the competing nonradiative recombination process— this competing process may be the thermal dissociation of geminate pairs or bound excitons at donorlike or acceptorlike centers. The 0.09-eV value of activation energy is consistent with the results of Troxell and Watkins (1979). 

Samples of ion-implanted c-Si that have not been annealed in atomic hydrogen exhibit a weak, broad emission peaking at —0.7 eV. Vacuum annealing at 300°C for 30 minutes causes the —0.7eV peak to grow by a factor of five and a contribution at 1.0 eV to appear. Annealing in atomic hydrogen at 300°C for 30 minutes greatly enhances the 1.0-eV peak and quenches the 0.7-eV emission. 

Ion implantation generates many dangling bonds that form centers for nonradiative recombination. These centers decrease the carrier lifetime and compete effectively with radiative transitions. However, after hydrogenation, since hydrogen ties dangling bonds, the luminescence process becomes more efficient. Furthermore, since the 1.0-eV emission is obtained even before hydrogen is introduced, the new radiative center may be formed due to residual hydrogen in the c-Si that combines with the implantation-induced defects. 

Johnson, N.M., Biegelsen, D.K. and Moyer, M.D. (1982). Appl. Phys. Lett. 40, 882. Kaplan, D., Sol, N., Velasco, G., and Thomas, P.A. (1978). Appl. Phys. Lett. 33, 440. Magee, C.W. (Evans East, Plainsboro, NJ) and Wu, C.P. (David Sarnoff Research Center, Princeton, NJ) (1983). Unpublished results. 

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A wide variety of process-induced defects in Si are passivated by reaction with atomic hydrogen. Examples of process steps in which electrically active defects may be introduced include reactive ion etching (RIE), sputter etching, laser annealing, ion implantation, thermal quenching and any form of irradiation with photons or particles wih energies above the threshold value for atomic displacement. In this section we will discuss the interaction of atomic hydrogen with the various defects introduced by these procedures. 

The passivation of two deep-level electron traps induced in n-type Ge by a Q-switched ruby laser anneal was found [141]. As with the corresponding case in Si, plasma exposures of 10 minutes at 100 C were sufficient to neutralize the electrical activity of such centers. In Ge most radiation damage or quenched-in centers that have been found are vacancy-related, and again the propensity of hydrogen to neutralize this type of defect is seen by the effectiveness of hydrogen plasma exposures in passivating Co-60 Y-induced hole traps [142], quenched-in acceptors [143], and ion-implanted oxygen-related deep levels [144]. 

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