Structural and electrical properties of lattice-matched (Ca,Sr)F (2)/GaAs structures grown by molecular-beam epitaxy.

Single-crystalline, lattice-matched (Ca,Sr)F(2) films have been grown by molecular-beam epitaxy on GaAs (100) and (111) As substrates. The ratio of the Rutherford backscattering yields from the fluoride films in the aligned normal direction to a random direction, or chi(min), is 0.03 for a (100) sample and 0.05 for a (111) sample, indicating excellent epitaxy. In fact, the chi(min) of 0.03 for the (100) sample is the best of all reported as-grown fluoride films on the (100) surface of a semiconductor. It is nearly the same as chi(min) from a bulk single-crystalline fluoride. For the (111) sample channeling measurements show that the film has the same orientation as the substrates, i.e., type A. Plan-view transmission electron microscopy confirms these results. Electrical measurements show that the film has a resistivity of 3 x 10(14) Omega-cm and breakdown fields of 7 x 10(5) to 3 x 10(6) V/cm. At room temperature I-V and C-V curves show various amounts of hysteresis that is completely eliminated at low temperature, indicating the presence of positive ions.