Structural properties of pressure-induced structural phase transition of Si-doped GaAs by angular-dispersive X-ray diffraction

摘要

Pressure-induced phase transitions in n-type silicon-doped gallium arsenide (GaAs:Si) at ambient temperature were investigated by using angular-dispersive X-ray diffraction (ADXRD) under high pressure up to around 18.6 (1) GPa, with a 4:1 (in volume ratio) metha-nol-ethanol mixture as the pressure-transmitting medium. In situ ADXRD measurements revealed that n-type GaAs:Si starts to transform from zinc-blende structure to an orthorhombic structure [GaAs-Ⅱ phase], space group Pmm2, at 16.4 (1) GPa. In contrast to previous studies of pure GaAs under pressure, our results show no evidence of structural transition to Fmmm or Cmcm phase. The fitting of volume compression data to the third-order Birch-Murnaghan equation of state yielded that the zero-pressure isothermal bulk moduli and the first-pressure derivatives were 75 (3) GPa and 6.4 (9) for the B3 phase, respectively. After decompressing to the ambient pressure, the GaAs:Si appears to revert to the B3 phase completely. By fitting to the empirical relations, the Knoop microhardness numbers are between H_(PK) = 6.21 and H_A - 5.85, respectively, which are substantially smaller than the values of 7-7.5 for pure GaAs reported previously. A discontinuous drop in the pressure-dependent lattice parameter, N-N distances, and V/V_0 was observed at a pressure of 11.5 (1) GPa, which was tentatively attributed to the pressure-induced dislocation activities in the crystal grown by vertical gradient freeze method.