Conduction Band Structure Dependence of Persistent Photoconductivity in Si Doped Al sub x Ga sub (1-x) As Studied by Hall Measurements Under Hydrostatic Pressure.

Low temperature Hall measurements under hydrostatic pressure in Si-doped Al sub x Ga sub (1-x ) As with x = 0.165 and 0. 32 confirm the earlier observation of Chand and coworkers that persistent photoconductivity (PPC) has a strong band structure dependence. The band structure can be changed by changing either x or pressure. Each kilobar of pressure on Al sub x Ga sub (1-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 Al sub (0.165) Ga sub (0.835) As sample and at 1 bar for the Al sub (0.32) Ga sub (0.68) 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 at 4.2 K indicated that all of the free electrons after photoexcitation were in the GAMMA valley. The Hall curves were linear against magnetic fields up to 20 Tesla 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.