Band Structure, Metallization and Superconducting Transition of Group III-V Semiconductors AlP and AlAs under High Pressure

The results of a full potential linear muffin-tin orbital (FP-LMTO) study on the electronic properties of cubic zinc blende type group III-V semiconductors AlP and AlAs under pressure are presented. The equilibrium lattice constant, bulk modulus, pressure derivative of bulk modulus and the phase transition pressure at which the compounds undergo structural phase transition from ZnS to NaCl and NaCl to CsCl are predicted from the total energy calculations. The ground state properties and band gap values are compared with the experimental results. At normal pressure AlP and AlAs are indirect bandgap semiconductors. When the pressure is increased there is enhanced overlapping between the wave functions of the neighbouring atoms. As a result the widths of the valence and empty conduction bands increase. These changes lead to the narrowing and indirect closing of band gaps in AlP and AlAs (metallization). On further increase of pressure, AlP and AlAs become superconductors, and these materials come under the class of electron-phonon-mediated high pressure superconductors. The superconducting transition temperatures (Tc) of AlP and AlAs are obtained as a function of pressure for CsCl structure. It is also confirmed that the metallization, structural phase transition and onset of superconductivity do not occur simultaneously in these compounds.