Hydrogen ion implantation

At low temperatures, donors and acceptors remain neutral when they trap an electron hole pair, forming a bound exciton. Bound exciton recombination emits a characteristic luminescence peak, the energy of which is so specific that it can be used to identify the impurities present. Thewalt et al. (1985) measured the luminescence spectrum of Si samples doped by implantation with B, P, In, and T1 before and after hydrogenation. Ion implantation places the acceptors in a well-controlled thin layer that can be rapidly permeated by atomic hydrogen. In contrast, to observe acceptor neutralization by luminescence in bulk-doped Si would require long Hj treatment, since photoluminescence probes deeply below the surface due to the long diffusion length of electrons, holes, and free excitons. 

Similar to hydrogen ion implantation, spinel magnesium indium oxide films were irradiated with 1.5 MeV Li+ ions for various fluences and their optical absorption spectra are shown in Figure 9.14a. It is inferred that the absorption spectra have three features the slope from 300 to 350 nm, strong absorption at 365 nm, and broadband around 540 nm. The hump at 2.3 eV (540 nm) is ascribed to surface plasmon resonance of Li nanoparticles and the wide slope is due to the transitions from the lithium sublevels including widely spread defect bands. In comparison with the low fluence irradiated and as-deposited Aims, Mglu204 Alms implanted with LF ions at high fluence have... 

Susceptibility to radiation damage must be considered seriously if reference samples are to be calibrated for use in place of absolute systems. For the measurement of absolute C He, H) cross sections, films of polystyrene (CH) (which is relatively radiation hard) have been used successfiiUy, the RBS determination of carbon providing implied quantitation for the hydrogen present in the film. For a durable laboratory reference sample, however, there is much to recommend a known ion-implanted dose of H deep within Si or SiC, where the loss of hydrogen under room temperature irradiation will be neghgible. 

This is the case for the N(d, p) N reaction, which is exited by a deuteron beam with a 610-keV energy. Figure 6 shows the products of the nuclear reactions taking place upon deuteron irradiation, for the same samples shown in Figure 5. As occurs with hydrogen, nitrogen is also depleted by ion implantation treatment. 

Implantable microelectronic devices for neural prosthesis require stimulation electrodes to have minimal electrochemical damage to tissue or nerve from chronic stimulation. Since most electrochemical reactions at the stimulation electrode surface alter the hydrogen ion concentration, one can expect a stimulus-induced pH shift [17]. When translated into a biological environment, these pH shifts could potentially have detrimental effects on the surrounding neural tissue and implant function. Measuring depth and spatial profiles of pH changes is important for the development of neural prostheses and safe stimulation protocols. 

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. 

The effect of low energy (0.4 eV) H+ ion implantation into Si diffused with Ti, V or Cr has also been examined (Singh et al., 1986). The electrically active concentration of a Cr-related level at Ev + 0.30 eV was reduced after hydrogenation, although substantial loss of this level was also... 

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 conclusion to be drawn from these studies as far as the suitability of different ion-implanted hydrogen standards is concerned is that pre-amorphized silicon is the best target material, though crystalline silicon is an acceptable alternative if room temperature is never exceeded. 

At highest ion fluences the H and O contents achieves a saturated value which vary from 50-70 % of their original value in pristine polymer. Several semiempirical models have been suggested describing hydrogen desoption during ion implantation (see e.g. [122]). 

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