WIDE-GAP CD1-XMGXTE - MOLECULAR-BEAM EPITAXIAL-GROWTH AND CHARACTERIZATION

We have grown the ternary alloy Cd1-xMgxTe as well as Cd1-xMgTe/CdTe q uantum well structures by molecular beam epitaxy - to our knowledge fo r the first time. Cd1-xMgxTe exhibits some very interesting features: The band gap has been determined as a function of Mg concentration, an d a band gap of 3.0 eV was found for zincblende MgTe at room temperatu re. Cd1-xMgxTe thin films with Mg concentrations of up to 0.75 were fa bricated, which corresponds to a band gap of 2.8 eV at low temperature s. Therefore, the whole visible band gap range (at room temperature) c an be covered with Mg concentrations between 0.30 (red) and 0.75 (blue ). Bulk MgTe crystallizes in the wurtzite structure, but zincblende Mg Te could be grown on (100) oriented CdTe substrates up to a layer thic kness of approximately 500 nm. The lattice mismatch between zincblende MgTe and CdTe was found to be as small as 1.0%. The growth of cubic M gTe could be followed by reflection high energy electron diffraction ( RHEED) oscillations. In general, excellent structural quality could be reached, which is demonstrated by the FWHM of 22 arc sec for a Cd1-xM gxTe thin film with 0.44 Mg concentration on a Cd1-xZnxTe nearly latti ce matched substrate. The Poisson number of Cd1-xMgxTe has been determ ined by X-ray diffraction as a function of Mg concentration. Cd1-xMgxT e/CdTe single quantum well structures have been fabricated with a larg e confinement energy of up to 0.8 eV. The photoluminescence spectra sh ow exciton lines with very narrow linewidths. We are able to observe e xcited exciton states, and from the energetic difference between 1s an d 2s heavy hole exciton lines we deduce exciton binding energies. Very bright luminescence could be seen even at room temperature, which is an indication of a large exciton binding energy and an effective radia tive recombination.