Metamorphic Te-doped Al0.4In0.6Sb/Ga0.4In0.6Sb HEMT structures for low power and high frequency applications

We report on the molecular beam epitaxial growth of metamorphic AlInSb/GaInSb high-electron-mobility-transistor structures for low power, high frequency applications on 4-inch GaAs substrates. The structures consist of a Ga_0.4In_0.6Sb channel embedded in Al_0.4In_0.6Sb barrier layers which are grown on top of an insulating metamorphic buffer, which is based on the linear exchange of Ga versus In and a subsequent exchange of As versus Sb. Growth parameters were systematically investigated by means of HRXRD, AFM and TEM measurements. The beam-equivalent-pressure ratio As/Sb (~3.5) in conjunction with the substrate temperature were found to be the key parameters to get good crystalline quality, demonstrated by the presence of crosshatching, a root mean square roughness of 2.0 nm and good electrical performance. Buffer isolation is determined to be about 1MΩ/□ for optimised growth conditions. Van-der-Pauw Hall measurements at room temperature reveal electron densities of 2.2 × 10¹² cm^-2 in the channel at mobility values of 22.000 cm²/Vs for single-sided Te δ-doped samples and 5.4 × 10¹² cm^-2 and 17.000 cm²/Vs for double-sided Te δ-doped structures, respectively. These high sheet carrier densities combined with maintained high electron mobilities, attributed to our new sophisticated buffer design, are essential for the fabrication of high frequency, high power MMICs.