A study of anion exchange reactions at GaAs surfaces for heterojunction interface control
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A study of anion exchange reactions at GaAs surfaces for heterojunction interface control Maria Losurdo, Danilo Giuva, Pio Capezzuto, Giovanni Bruno Institute of Inorganic Methodologies and of Plasmas, IMIP-CNR and INSTM, via Orabona 4 – 70126 Bari, Italy Terence Brown, Greg Triplett, Gary May Georgia Institute of Technology, Microelectronic Research Center, 791 Atlantic Dr, Atlanta, GA, USA April S. Brown Electronic and Computer Engineering, Duke University, Durham, NC, USA ABSTRACT GaPyAs1-y/GaAs, GaAsySb1-y/GaSb and GaSbyAs1-y/GaAs superlattices (SLs) grown by MBE, by exposure of GaAs to phosphorus and antimonide fluxes, and by exposure of GaSb to an arsenic flux, respectively, have been investigated. The focus is on the abruptness of interfaces and understanding the mechanisms associated with anion incorporation and exchange. In the case of the Sb flux interaction with the GaAs surface, the Sb segregation at the GaAs surface inhibits anion exchange. For the case of As over GaSb reactions, anion exchange results in the formation not only of the ternary alloy GaAsySb1-y, but also of isoelectronic compounds AsSbx that segregate at the GaSb/GaAs interface. In the case of the P flux interfaction with the GaAs surface, fast in-diffusion of P results in graded GaPyAs1-y layer formation. INTRODUCTION In recent years, great attention has been focused on the fabrication of III-V semiconductor heterostructures containing arsenides, phophides, and antimonide compounds for device applications, such as infrared photodetectors, lasers, and HBTs [1]. These material systems offer flexibility in device design due to their wide range of available band alignments and band gaps. An understanding of III-V anion exchange reactions at heterojunction interfaces is of fundamental interest. The performance of these devices is strongly influenced by the composition, microstructure, and thickness of the heterointerfaces. Abrupt and atomically smooth interfaces require control of the anion exchange and of the resultant electronic and optical properties of the interface [2]. In this work, GaPyAs1-y/GaAs, GaAsySb1-y/GaSb and GaSbyAs1-y/GaAs superlattices (SLs) grown by MBE through the exposure of GaAs to a phosphorus and antimonide flux, and GaSb to an arsenic flux have been investigated. These SLs allow the study of the individual heterointerface formation. The SLs pseudodielectric function has been measured, and the analysis gives information on the quality and composition of the interfaces in the SLs, as well layer thickness at Ǻ resolution, and on the optical gap properties. Complementary information on the composition and abruptness of the interfaces obtained by XPS (x-ray photoelectron spectroscopy) and XRD (x-ray diffraction) are discussed. We have studied the formation of the SLs as a function of surface temperature and of Sb, As and P flux exposure time. We found that, depending on the exchanging anion size, different reactions occur. In particular, the small P anion easily exchanges with the As in GaAs, yielding GaPyAs1-y ter
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