A comparison of dopant type and aluminium mole fraction on persistent photoconductivity in HEMT structures grown by MOVPE

The authors report the results of an investigation of persistent photoconductivity (PPC) in Al x Ga 1-x As/GaAs HEMT structures grown by MOVPE, and the effects of different dopants and Al x Ga 1-x As compositions. Temperature- and time-dependent Hall measurements for combinations of selenium-/silicon-doped, x=0.32/x=0.45 Al x Ga 1-x As/GaAs layers are presented, allowing comparison of the factors influencing PPC. From their results they conclude that the amount of PPC exhibited by MOVPE grown HEMT structures is significantly reduced by using Se as the dopant, as opposed to Si. The PPC of the Se-doped samples also shows a virtual independence to Al x Ga 1-x As composition. The relative stability of these Se-doped Al x Ga 1-x As/GaAs structures at cryogenic temperatures should correspond to a significant reduction in the amount of drain-current collapse seen in HEMTS at low temperatures.