Built-in electric-field effects in wurtzite AlGaN/GaN quantum wells

AlGaN/GaN quantum well (QW) structures are grown on c-plane sapphire substr ates by molecular beam epitaxy. Control at the monolayer scale of the well thickness is achieved and sharp QW interfaces are demonstrated by the low p hotoluminescence linewidth. The QW transition energy as a function of the w ell width evidences a quantum-confined Stark effect due to the presence of a strong built-in electric field. Its origin is discussed in terms of piezo electricity and spontaneous polarization. Its magnitude versus the Al mole fraction is determined. The role of the sample structure geometry on the el ectric field is exemplified by changing the thickness of the AlGaN barriers in multiple-QW structures. Straightforward electrostatic arguments well ac count for the overall trends of the electric-field variations. (C) 1999 Ame rican Institute of Physics. [S0021- 8979(99)07719-1].