Plasma Edge Modification in Strongly Compensated Semiconductors

Abstract

We demonstrate that the electron-impurity interaction can modify the reflectivity in the vicinity of plasma minimum giving rise to a small dip oii the plasma edge. Experimental spectra taken for Ηgι-x C ox S e for x < 0.02 at various temperatures confirm this theoretical prediction. The position of the structure can be used to determine the plasma frequency in highly compensated materials at low temperatures.PACS numbers: 71.45. Gm, 78.30.Fs, 72.30.+q The infrared absorption coefficient is most often described in terms of the simple Dude-Zener theory assuming frequency independent damping constants of free-carrier plasma and phonon excitations. Such approximation can be used to interpret the experimental data taken for lightly doped or uncompensated materials. However, in heavily doped and/or highly compensated semiconduction some deviations from such "classical" picture can be expected due to the increasing role of the collective plasma (plasmon) excitations in the process of the free-carrier absorption. Plasmon generation in the process of photon absorption by free-electron gas in semiconduction is possible only if ionized impurities or other imperfections breaking the translational invariance are present in the system. Resonant behaviour of the free-carrier loss function above the plasma frequency leads to the enhancement of the damping parameter in the ac conductivity.A lot of studies have been devoted to the role of collective excitations in the free-carrier absorption. They were primarily related to the question of plasmon excitation in the process of electron-impurity scattering (for the references see,

Electron–phonon coupling and a resonant-like optical observation of a band inversion in topological crystal insulator Pb1−x Sn x Se

“…A step in reflectivity spectra resulting from an influence of plasmon-phonon coupling on the electron-impurity interaction in the free carrier absorption and corresponding to the optical phonon mode frequency can also be expected in this case. This effect was previously demonstrated for LO phonon in a narrow-gap semiconductor with an inverted band structure, HgSe [28]. The optical phonon softening accompanied by an anomaly in the phonon linewidth resulting from electron-phonon interaction observed in Raman spectra for Sb 2 Se 3 bulk crystal were explained by an electronic topological transition occurring under pressure for this compound [29].…”