Clusters and the Nature of Superconductivity in Ltmbe-GaAs

Abstract

The structure and properties of GaAs layers grown by molecular-beam epitaxy at low temperature (150-250 °C) have been studied. The samples were found to contain up to 1.5 at.% extra As, which formed nano-scale clusters under annealing. The dependences of the excessive As concentration and As-cluster size and density on the growth and annealing conditions were established. LT-GaAs layers were found to have high electrical resistivity, however, our investigations of microwave absorption in a weak magnetic field revealed a characteristic signal usually attributed to the superconducting phase. It has been proved that this microwave absorption is unlikely to be due to either the arsenic clusters in LT-GaAs films or indium in the substrate, as it was assumed previously. We suggest a new hypothesis that the superconducting phase in LT-GaAs is Ga nanoclusters formed on the growth surface.

Excess As in low‐temperature grown InAs

“…3, the perpendicular lattice mismatch increases with decreasing growth temperature as the excess As concentration does. Note, however, that the lattice mismatches of the LT grown InAs samples are smaller by almost one order of magnitude than those of LT grown GaAs samples [2][3][4][5][6][7]. For LT grown GaAs, Liu et al [4] deduced the relation of ∆a⊥/a = 1.24×10…”

“…Among those studies, Docter et al [1] have demonstrated that as low as 0.1 % of excess As in LT grown GaAs can be detected by means of secondary ion mass spectroscopy (SIMS). The effect of the excess As to the lattice spacing in LT grown GaAs has been investigated in several studies [2][3][4][5][6][7].…”

Defects in the GaAs and InGaAs layers grown by low-temperature molecular-beam epitaxy

“…The grains have an average size of ~100 nm and are extended along one direction. As the growth temperature increases, the grain size dereases down to 3-5 nm at Т g = 250°С) [6].…”

“…It was shown that a decrease in the growth temperature from conventional values of 500-600°С down to 150-200°С results in the incorporation of excess non-stoichiometric arsenic into the lattice mainly in the form of point defects [1][2][3][4][5][6]. LT-GaAs containing excess arsenic possesses unique physical properties such as high specific resistance (up to 10 8 Ω⋅cm) and a very low lifetime of minority charge carriers (<1 ps).…”

“…In this paper, on the basis of these studies, the problem of defect formation in LT-GaAs and InGaAs is considered. The paper is written using the materials published in [6][7][8][9][10][11][12][13][14][15]. A total review of the current state of the art in the technology of low-temperature molecular beam epitaxy is given in [16].…”