Charge coupled cyclotron motion of electrons and holes in InGaAsN epitaxial layers
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Charge coupled cyclotron motion of electrons and holes in InGaAsN epitaxial layers H. E. Porteanu, O. Loginenko, and F. Koch Physik-Department E16, TU München, James-Franck-Str. 1, 85747 Garching, Germany, G. Dumitras, L. Geelhaar, and H. Riechert Infineon Technologies, Corporate Research, CPR 7 D-81730 München, Germany ABSTRACT Time resolved cyclotron resonance measurements are used to investigate more in further detail the effective mass of electrons and holes in InGaAsN epitaxial layers. The In and N content in the alloy are adjusted to yield the latticematching of the epilayers (200 nm thick) to GaAs. A continuous increase of the effective mass of electron and an increase of the resonance associated with holes is observed. Through the evolution of the imaginary part of conductivity as a function of the elapsed time we show that this observation is a coupled cyclotron resonance that may have maxima in the real part of conductivity but should not be necessarily correlated with the “increase” of the effective mass.
INTRODUCTION The influence of substitutional nitrogen in compound semiconductors like GaAs, GaP, or InGaAs is still a subject of fundamental research. Usually the nonlinear dependence of the energy gap on the concentration of the substitutional element is expressed by the bowing parameter. For most elements, the bowing parameter is a small, resulting in a minimal deviation from the linear interpolation. Using the available data of energy gaps for GaAsN or InGaAsN (few percents of N), one obtains a surprisingly high bowing parameter [1]. Even in dilute concentrations of N (0.05 %), there is a significant redshift of the energy gap observed in photoluminescence (PL) and PL excitation (PLE) spectra. However, below the bandgap PL, there are a number of molecular-like transitions, their position being not influenced by the shift of the energy gap [2]. These results suggest that an apparently shallow donor with the energetic distance to the nearest host crystal band of 7 meV should have simultaneously a big delocalization (=100 Å) in order to shift the bandgap and a strong localization in order to show molecular transitions [3]. At higher concentrations, a continuum of states below the bandgap PL, with a longer decay time are observed [4]. Furthermore, it was observed in electroreflectance measurements the appearance of an additional level (band) above the conduction band minimum (CBM) due to the presence of N [5]. The above mentioned facts suggest that an estimation of the effective mass of electrons could be a useful measure of the strength of interaction of the localized states of N with the continuum of states of the conduction band. The first estimations of the effective mass of electrons were done using electroreflectance measurements [6]. However, the attribution of the observed peaks to transition between certain confined levels is questionable. Values of up to 0.5 m0 for the effective mass of electrons, just for the lowest concentration of N are not reliable. However, already this experiment
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