Formation of Hydrogen Impurity States in Silicon and Insulators at Low Implantation Energies

Abstract

The formation of hydrogenlike muonium (Mu) has been studied as a function of implantation energy in intrinsic Si, thin films of condensed van der Waals gases (N2, Ne, Ar, Xe), fused and crystalline quartz, and sapphire. By varying the initial energy of positive muons (mu+) between 1 and 30 keV the number of electron-hole pairs generated in the ionization track of the mu+ can be tuned between a few and several thousand. The results show the strong suppression of the formation of those Mu states that depend on the availability of excess electrons. This indicates that the role of H-impurity states in determining electric properties of semiconductors and insulators depends on the way in which atomic H is introduced into the material.

Depth dependence of the ionization energy of shallow hydrogen states in ZnO and CdS

“…4 to determine the asymmetries A D (T ) and A Mu (T ). The decreasing neutral fraction with decreasing implantation energy below 26.5 keV is a characteristic normally observed in insulators and semiconductors 55 . This is attributed to the fact, that a substantial fraction of Mu is formed by those thermalized µ + which may capture one of the excess electrons generated in its own ionization track (so-called delayed Mu formation).…”

“…Typically, this delayed Mu formation saturates if the stopping depth -i.e. the track length -of the µ + is of the order of hundred nanometer 55 . This length scale fits to earlier observations where the analysis of µSR experiments with applied electric fields on bulk insulators suggested a similar length scale for delayed Mu formation 56 .…”

Interaction of low-energy muons with defect profiles in proton-irradiated Si and 4H -SiC

“…The energy scans in Fig. 3(a) illustrate this point more clearly: The decrease of F D with increasing muon energy reflects the onset of a delayed Mu 0 BC formation with the increasing availability of excess electrons [32]. in a larger Mu + fraction in the target material and hence an increased value of F D .…”

“…With the limited time resolution and statistics of the setup, only Mu precession frequencies <60 MHz can be resolved, which is sufficient for a direct observation of the Mu 0 BC transitions at an applied field of 0.15 T. The transition frequencies between the triplet states of Mu 0 T at this field, however, are too high to be resolved with the experimental time resolution of about 10 ns FWHM, and a low field of 0.5 mT is used to observe the Mu 0 T precession frequency. (Note that at this low field, the Mu 0 BC transitions frequencies are too heavily damped to be observed [32]). Fig.…”

“…In addition to the observed temperature and doping dependence, the formation of Mu 0 BC is also affected by the implantation energy of the muon itself: When the μ + is implanted into the material, electron-hole pairs (around 10 3 for the energies used in a LEM experiment [30]) are generated and while some of them quickly recombine, there is a non-negligible probability that some of them may combine with the stopped μ + to form Mu 0 BC . For Si and various insulators it was previously shown that Mu 0 BC is formed via this so-called delayed formation process and that a sufficiently large amount of excess electrons generated in the ionization track is required [31,32]. (In contrast, Mu 0 T is formed during slowing down in charge-exchange cycles and a subsequent thermalization of the muonium due to elastic collisions).…”