MOVPE Growth and Characterization of AlInN FET Structures on Si(111)
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MOVPE Growth and Characterization of AlInN FET Structures on Si(111) Christoph Hums1, Aniko Gadanecz1, Armin Dadgar1, Jürgen Bläsing1, Hartmut Witte1, Thomas Hempel1, Annette Dietz1, Pierre Lorenz2, Stefan Krischok2, Jürgen Alois Schaefer2, Jürgen Christen1, and Alois Krost1 1 Institute of Experimental Physics, Otto-von-Guericke-University Magdeburg, Universitätsplatz 2, Magdeburg, 39106, Germany 2 Institute of Micro- and Nanotechnologies and Institute of Physics, Technical University Ilmenau, Weimarerstr. 32, Ilmenau, 98684, Germany ABSTRACT In this work metalorganic chemical vapor phase epitaxy (MOVPE) growth and characterization of AlInN in the whole compositional range and the impact on the development of field effects transistors (FET) structures will be presented. Due to the large difference in the lattice parameters of the binaries AlN and InN the growth of AlInN with high indium concentrations is ambitious, and first the growth conditions for the alloy will be discussed. An experimental phase diagram and corresponding theoretical calculations will be displayed. The critical layer thickness of AlInN on GaN has been experimentally determined. Relaxation of the AlInN-layer has a strong influence on the sample morphology. At indium concentration exceeding 30% an polarization induced hole gas is expected at the AlInN/GaN interface from theoretical calculations, but no p-channel conductivity could be confirmed. The absence of the two dimensional hole gas will be discussed. INTRODUCTION Because of their wide band gaps, wurtzite-structure AlN (6.2eV) [1], and GaN (3.44eV) [2] are widely used for the fabrication of optoelectronic and electronic devices. Alloying with InN (0.68eV [3]) is used to tune the band gaps and lattice constants, but is limited for InGaN and AlInN due to the immiscibility of the binaries in a wide concentration range. In contrast to InGaN which is widely explored because of its importance for light emitters, basic properties of AlInN (band gap, miscibility, optical properties) are still unknown. Only Al1-xInxN nearly lattice matched (LM) to GaN (x ~ 17.5 % [4]) has been investigated in detail, since it is an excellent material for DBRs and VCSELs [5] because of its high refractive index contrast to GaN. In addition LM-AlInN has been successfully applied for strain free AlInN/GaN FET structures [6] with the advantage of higher sheet carrier concentrations compared to conventional AlGaN/GaN FETs (FIG.1b) originating in a high spontaneous polarization of the alloy. MOVPE growth of AlInN is quite challenging because of the different growth conditions of the binaries AlN and InN: Growth of AlN requires a high temperature because of the low Al-adatoms mobility and a low V-III-ratio whereas InN requires low temperature and a high V-III-ratio due high indium desorption. In this work the miscibility of the alloy is determined for the whole compositional range. Additionally the critical layer thickness dcritical for pseudomorphic growth of AlInN on GaN is presented. Caused by the wurtzite st
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