Examining the effect of Tl content on the optical, electrical, and structural properties of TlGaAs films

Tl containing III-V semiconductor alloy materials are of interest for use in new infrared detector structures and other applications requiring low bandgap material. Additions of relatively small amounts of Tl can significantly reduce the bandgap without large changes in lattice constant. However, the properties of the Tl containing III-Vs have not been extensively studied because it is difficult to produce material with high Tl content. In this work we examine the properties of Tl_xGa_1-xAs films grown at very low (<220°C) temperatures by solid-source molecular beam epitaxy (MBE). The optical, electrical, and structural properties of TlGaAs films have been characterized by a variety of techniques, including spectroscopic ellipsometry, high resolution x-ray diffraction, Rutherford back-scattering spectrometry, atomic force microscopy, Hall effect measurement, and transmission electron microscopy. We will discuss the properties of these TlGaAs films as a function of both MBE growth conditions and resulting film Tl composition, with a particular emphasis on the change in film optical and electrical properties with changing Tl content.