Conduction-band structure dependence of persistent photoconductivity in Si-doped AlxGa1−xAs studied by Hall measurements under hydrostatic pressure

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Abstract
Low‐temperature Hall measurements under hydrostatic pressure in Si‐doped Alx Ga1−x As with x=0.165 and 0.32 confirm the earlier observation of Chand and co‐workers that persistent photoconductivity has a strong band structure dependence. The band structure can be changed by changing either x or pressure. Each kilobar of pressure on Alx Ga1−x As has the same effect on the band structure as increasing x by 1%. The density of photoexcited carriers goes through a maximum value at about 15 kbar applied pressure for the Al0.165 Ga0.835 As sample and at 1 bar for the Al0.32 Ga0.68 As sample. It drops dramatically on further increasing the pressure. After photoexcitation, the electron mobility was found to increase in all cases. Shubnikov–de Haas measurements on these samples at 4.2 K indicated that for x ≤ 0.4 all of the free electrons after photoexcitation were in the Γ valley. The Hall curves were linear against magnetic fields up to 20 T which also indicated that after photoexcitation one type of carriers alone contributed to the conduction process with no involvement of holes or electrons in the L or X valleys.