Abstract: Semi-insulating (SI) GaAs single crystals with low dislocation density are grown by the vertical gradient freezing (VGF) method.The as-grown VGF-SI-GaAs exhibits low resistivity,low mobility,weak electrical compensation,and poor uniformity.SI-GaAs wafers sliced from the single crystal ingots are annealed at three different temperatures in a sealed quartz tube with controlled arsenic pressure.The results indicate that resistivity and carrier mobility of the VGF-SI-GaAs are enhanced significantly after annealing at 1160℃ for 12h.Using the Hall effect,thermally stimulated current spectroscopy (TSC),and infrared absorption spectroscopy,the electrical property,deep level defects,and concentration of EL2 and C in the as-grown and the annealed VGF-SI-GaAs samples are analyzed,respectively.A conventional LEC SI-GaAs sample is also measured for comparison.The as-grown VGF-SI-GaAs has lower EL2 content than LEC-SI-GaAs.However,the EL2 content in VGF-SI-GaAs increases after the thermal annealing,while defects with shallower levels are suppressed effectively,resulting in better electrical compensation and improved properties.

Key words: VGF, SI-GaAs, electrical compensation, defect