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The measurement of the energy band discontinuities in GaAs:(Al,Ga)As heterostructures is described. These values are deduced from the activation energy governing current transport in the direction perpendicular to the heterojunction interface. Using complementary structures (fabricated with an Al mole fraction of ≂0.38), we study both electron and hole transport to independently measure the conduction and valence-band discontinuities respectively. The results obtained are self-consistent and indicate that the total band-gap difference distributes approximately in the ratio 60:40 between the conduction band and valence band. Measurement of the conduction-band discontinuity for an Al mole fraction of ≂0.24 yields a similar ratio. Preliminary measurements of the valence-band discontinuity in structures fabricated using (Al,Ga)As with an indirect band gap (Al mole fraction of ≂0.60) are also described.
Batey et al. (Tue,) studied this question.