INTRINSIC ORIGIN AND COMPOSITION DEPENDENCE OF DEEP-LEVEL DEFECTS AT THE INVERTED GAAS/ALXGA1-XAS INTERFACE GROWN BY MOLECULAR-BEAM EPITAXY

Electronic states in n-type GaAs/AlxGa1-xAs heterojunctions are studied by deep-level transient spectroscopy in the Al mole fraction range from 0.25 to 1.00. A series of four well-defined deep levels is characteristic of the inverted GaAs/AlxGa1-xAs interface (GaAs grown on AlxGa1-xAs) grown by conventional molecular-beam epitaxy under arsenic-stable conditions without growth interruption. It is shown that the series of four levels originates from intrinsic defects which are associated with arsenic vacancies and antisites. In particular, two charge states of the isolated arsenic vacancy VAs can be identified. Except for the sheet very close to the inverted heterointerface the n-type AlxGa1-xAs layers are found to be almost free of intrinsic deep levels in the entire composition range. For the investigated samples, the compositional dependence of the level energies shows that the arsenic vacancy is predominantly surrounded by Al atoms. From the compositional dependence of the level concentrations it follows that the arsenic vacancies at the interface are formed above a composition threshold of 0.25. The distinct distribution of intrinsic defects at the inverted GaAs/AlxGa 1-xAs interface can be explained by a stable defect configuration near the AlxGa1-xAs surface during growth. © 1995 American Institute of Physics.