Comment on ‘‘Mechanism responsible for the semi-insulating properties of low-temperature-growth GaAs’’ [Appl. Phys. Lett. 65, 3002 (1994)]

o In a recent letter in this journal, Liuet al. drew a conclusion on the mechanism responsible for the semi-insula properties of GaAs epilayers grown by molecular beam taxy ~MBE! at low-substrate temperatures and subseque annealed. They concluded that their experiments suppo the ‘‘arsenic antisite defect’’ model 2 and not the ‘‘buried Schottky barrier’’ model. 3 We question some of their inte pretations of the experimental data that led to this con sion. When GaAs is grown at low substrate temperatures MBE with otherwise normal growth conditions, excess As incorporated. These low-temperature-grown ~LTG! GaAs epilayers are of high crystal quality 4 in spite of containing as much as 2% excess arsenic in the form of point defe 5