Invited Paper EM2-ThA8
Novel Nitrides and Bismides: Growth and Optical Properties

Thursday, October 31, 2013, 4:20 pm, Room 101 B

Recent research on the growth by MBE and optical properties of two classes of novel highly mismatched semiconductor will be presented, namely, dilute nitride antimonides and dilute bismide antimonides. These have potential applications ranging from thermophotovoltaics within the 2-4 micron range to night vision in the 8-14 micron IR transmission window. The incorporation of N in GaSb, GaInSb and InSb as a function of temperature and growth rate is investigated using x-ray diffraction, secondary ion mass spectrometry and kinetic modelling. For GaNSb, the optical properties are studied by absorption spectroscopy. In addition to providing evidence of the well-known band anticrossing interaction between the N localized states and the host GaSb conduction band, a strong influence of both lifetime broadening and N pair states is apparent. Meanwhile, incorporation of Bi is a little-explored approach to band gap and lattice constant tuning for GaSb and related materials, in spite of intensive recent studies of GaAsBi and sporadic study of InSbBi over the last thirty or so years. Alloying with Bi offers the potential to reduce the band gap more effectively than with indium (and may even be used in conjunction with N alloying), enabling greater valence band offsets for enhanced hole confinement and also increased spin orbit splitting. Here, MBE growth is reported of GaSbBi with Bi occupying in excess of 3% of the group V sublattice, as estimated from the increase in lattice constant determined by x-ray diffraction. This contrasts markedly with previous reports of GaSbBi MBE growth where lattice contraction was observed upon Bi incorporation and the maximum Bi content, from Rutherford backscattering, was only 0.7%. Our MBE growth study explores the Bi incorporation dependence upon the Bi flux, substrate temperature and growth rate and is compared to our Ga(In)NSb results. The influence of the Bi alloying on the band gap is also reported from Fourier transform infrared optical absorption measurements. The results are compared with predictions of both the lattice parameters and band gaps from our density functional theory calculations employing hybrid functionals. This research is performed principally in collaboration with the University of Warwick, UK, and University College London and is supported by EPSRC grant EP/G004447/2.