PHASE-TRANSFORMATIONS AND THE NATURE OF THE SEMICONDUCTOR-TO-METAL TRANSITION IN BULK A-GASB AND A-(GE-2)(1-X)(GASB)(X) SEMICONDUCTORS UNDER HIGH-PRESSURE

The pressure-induced transitions in bulk amorphous GaSb and Ge-GaSb so lid solutions, prepared by a solid state amorphization of the high-pre ssure phases after decompression, were studied under pressure up to 9 GPa. According to x-ray diffraction, volume, and resistivity measureme nts the amorphous semiconductors reversibly transform to crystalline h igh-pressure metallic phases (GaSb II or solid solutions with GaSb II- like structure). For Ge-GaSb alloys the transition occurs abruptly in the range 4.5-6.5 CPa for various concentrations of the components. Th e a-GaSb samples gradually transform in a wide pressure range between 3.5 and 8.5 GPa. It is shown that such behavior is due to heterogeneit y of microscopic structural characteristics of the network and to part ial crystallization of zinc-blende GaSb. A semiconductor-to-metal tran sition in a-GaSb is observed at 3.5-4 GPa, and is driven by the percol ation mechanism. Bulk moduli of amorphous compounds exhibit substantia l softening above P similar to 1-2 GPa, which is accompanied by intens ification of the irreversible resistivity relaxation with pressure. At room pressure the amorphous tetrahedral network of a-GaSb (B approxim ate to 35 GPa) is more compressible than the crystalline lattice of Ga Sb (B approximate to 55 GPa). Thermodynamics of the structural transfo rmation in a-(Ge-2)(0.27)(GaSb)(0.73) was studied by differential ther mal analysis, and discussed in the framework of the nonequilibrium pha se diagram of an amorphous solid.