Thallium incorporation during TlInAs growth by low-temperature MBE

Molecular-beam epitaxial growth of TlxIn1−xAs has been performed on InAs substrates at substrate temperatures between 150 and 250 °C. Optical microscopy revealed that Tl droplets decrease in size and in density with decreasing growth temperature, and vanish at lower temperatures than 175 °C. Secondary ion mass spectrometry (SIMS) revealed that Tl concentration shows almost flat depth profiles in the samples grown at 150-175 °C, but shows concave profiles in the samples grown at 200-225 °C. Electron probe micro analysis (EPMA) as well as SIMS showed that the Tl mole fraction x in the samples grown at 150-175 °C increases up to 2.7% almost in proportion with Tl flux. X-ray diffraction and cross-sectional transmission electron microscopy studies showed that monocrystalline growth is prevented if the beam equivalent pressure ratio of Tl/In is beyond 4%.