STRUCTURAL AND PHYSICAL-PROPERTIES OF MERCURY-IRON SELENIDE LAYERS AND QUANTUM-WELLS

Epitaxial layers and single quantum wells (SQW's) of Fermi-level pinne d mercury-iron selenide (HgSe:Fe) have been grown by molecular-beam ep itaxy on ZnTe buffer layers and characterized by in situ reflection hi gh-energy electron-diffraction (RHEED) and high-field magnetospectrosc opy investigations. The onset of strain relaxation at the critical thi ckness has been determined by time-dependent intensity-profile analysi s of different reflexes in the RHEED pattern. In spite of the small mi smatch and the very low growth temperature, a growth-mode transition f rom a two-dimensional-to-three-dimensional (2D-to-3D) Stranski-Krastan ov growth mode has been identified, which coincides exactly with the c ritical thickness equilibrium value of about 61 nm predicted by the Ma tthews-Blakeslee theory. Due to this mechanism, the surface roughness transition region is extended and the onset of plastic relaxation is d elayed up to a thickness of about 280 nm, Hall-effect measurements hav e been performed to determine the iron concentration in the HgSe layer s below and above the Fermi-level pinning threshold concentration. Wit h increasing iron concentration both a pronounced increase of the mobi lity and decrease of the Dingle temperature have been found in the lay ers. This agrees well with the present available data from HgSe:Fe bul k crystals and also with the values predicted by the short-range corre lation model. However, the maximum carrier mobility of about 2.7X10(5) cm(-3) measured in a 1.5-mu m-thick HgSe:Fe layer indicates that long -range correlations also have to be considered in the transport mechan ism of mercury-iron selenide. HgSe:Fe SQW's grown in the strained-laye r region below the equilibrium critical thickness have been analyzed b y Shubnikov-de Haas (SdH) measurements and Hall-effect measurements in magnetic fields up to 50 T. The existence of a two-dimensional electr on system (Q2D) in the SQW has been confirmed by the cosine dependence of the SdH oscillation period. The subband splitting in the SQW in de pendence of the quantum-well width has been investigated by Hall-resis tance measurements. One subband has been identified experimentally in a 12-nm HgSe:Fe quantum well, whereas for high magnetic fields at leas t two subbands are measured in the 25-nm structures. The Landau-level splitting has been simulated using the Pidgeon-Brown model. In this wa y the subband splitting and the spin splitting observed experimentally can be explained. The broadening of the localized iron level has been determined from simulation curves.