MIXED As-Sb ALLOYS

Authors:  H.-Richard Blank, Sheila Mathis, Herbert Kroemer and Jim Speck

[Questions regarding this research may be addressed to]:  blank@xanadu.ece.ucsb.edu

We are currently investigating mixed-anion compounds such as Ga(As,Sb) and Al(As,Sb) for their potential use for device applications. As-Sb mixed-anion alloys can be grown lattice-matched to all technological important substrates and have potential applications in a variety of devices, such as InP-based lasers, InAs-based mid-infrared lasers, InAs/Al(As,Sb) HEMTs, and resonant tunnel diodes. Al(As,Sb) offers — in addition to its high bandgaps — the opportunity to apply lateral oxidation techniques.

In contrast to mixed-cation compounds, the composition of molecular beam epitaxial (MBE) grown Ga(As,Sb) and Al(As,Sb), is not simply determined by the As:Sb flux ratio, it also depends very sensitively on the substrate temperature, growth rate, total group-V flux, and is also influenced by a miscibility gap [1]

So far, we have established well controlled MBE growth of (Al,Ga)(As,Sb) and have characterized structural and electrical properties of Al(As,Sb) bulk layers and InAs/Al(As,Sb) heterostructures over wide range of compositions. Both structural and electrical properties were found to be very sensitive on the growth temperature and additional electrically active defects were formed if Al(As,Sb) was grown at 450^oC or lower. The current across InAs/Al(As,Sb) was greatly reduced with increasing As [1].

Our studies of low-temperature-growth (LTG) Al(As,Sb) showed that we have achieved high single-crystal quality of Al(As,Sb) at substrate temperatures as low as 275^oC. However — as verified by transmission electron microscopy (TEM) and electrical measurements — we find no evidence for the formation of precipitates upon annealing LTG-Al(As,Sb) [2].

We have also characterized InAs/Al(As,Sb) heterojunctions by determining both conduction and valence band offsets using ballistic electron emission microscopy (BEEM). With increasing the arsenic content in the Al(As,Sb) barrier we find a decrease in the conduction band offset and we gain this decrease plus the increase in bandgap in the valence band offset at the heterojunction. Therefore, the current across the InAs/Al(As,Sb) heterojunction is substantially reduced with increasing As in the Al(As,Sb) barrier. We have confirmed the transition from a staggered lineup for InAs/AlSb to a straddled lineup for InAs/AlAs_0.16Sb_0.84 [3].

[1] "Al(As,Sb) heterobarriers on InAs: growth, structural properties and electrical transport"

     H.-R. Blank, E. Hall, S. Mathis, S. Bhargava, H. Kroemer, V. Narayanamurti (submitted to

     Journal of Crystal Growth)

[2] "Growth and characterization of low-temperature-grown Al(As,Sb)"

     H.-R. Blank, S. Mathis, H. Kroemer, J. Speck (submitted to Appl. Phys. Lett.)

[3] "Conduction and valence band offsets at the InAs/AlAs_xSb_1-x heterojunction"

     S. Bhargava, H.-R. Blank, V. Narayanamurti, H. Kroemer (submitted to Appl. Phys. Lett.)

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