Simulation of TF-μSR histograms in germanium in the presence of cyclic charge state transitions of muonium

Thomas Prokscha

doi:10.1088/1742-6596/551/1/012049

Abstract

It has recently been shown that at T < 270 K a persistent inversion from n- to p-type can be induced by illumination in a 200-nm-thick surface layer of lowly-doped commercial germanium wafers [1]. The presence of photo-generated holes is detected by the appearance of a fast relaxing component in TF-μSR measurements, caused by cyclic muonium charge state transitions Mu−T + h+ ⇋ Mu0T. For a quantitative determination of the photo-induced hole carrier concentration we use a Monte-Carlo simulation to generate muon decay histograms for different hole capture rates (forward reaction), and ionization rates (reverse reaction due to thermal activation) [2]. The hole carrier concentration is determined by comparing simulated and experimental relaxation rates. These results have been used to estimate the photo-induced hole concentration in low-energy μSR experiments [1].

Highlights

In semiconductors the presence of free charge carriers can give rise to charge state transitions of muonium
The change of the charged diamagnetic state to the neutral paramagnetic state Mu0 causes a loss of muon spin phase coherence due to the hyperfine interaction in Mu0, which can be the origin of the appearance of a fast relaxing component in either longitudinal (LF) or transverse field (TF) μSR experiments
The temperature dependence of the carrier capture rate of T −2.4(2) indicates the significance of holes, if one assumes that the carrier capture rate is governed by the carrier mobility: the electron mobility in Ge scales with T −1.7, whereas the hole mobility scales with T −2.3 [7], in agreement with the present data

Summary

Introduction

In semiconductors the presence of free charge carriers can give rise to charge state transitions of muonium. The change of the charged diamagnetic state (either Mu+ or Mu−) to the neutral paramagnetic state Mu0 causes a loss of muon spin phase coherence due to the hyperfine interaction in Mu0, which can be the origin of the appearance of a fast relaxing component in either longitudinal (LF) or transverse field (TF) μSR experiments. In view of a potential application of this effect to device technology it is important to know the photo-generated hole carrier concentration p. This question has motivated the current study, where we will show that p can be determined from the observed fast relaxation rate Λf of the diamagnetic signal by means of a Monte-Carlo technique [2]

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Conclusion