Excitonic spectrum of the ZnO/ZnMgO quantum wells

Excitonic spectrum of the wurtzite ZnO/Zn_{1 ? x} Mg _x O quantum wells with a width on the order of or larger than the Bohr radius of the exciton has been studied; the quantum wells have been grown by the method of molecular beam epitaxy (with plasma-assisted activation of oxygen) on substrates of sapphire (0001). Low-temperature (25 K) spectra of photoluminescence excitation (PLE) have been experimentally measured, making it possible to resolve the peaks of exciton absorption in the quantum well. The spectrum of excitons in the quantum well is theoretically determined as a result of numerical solution of the Schrödinger equation by the variational method. The value of elastic stresses in the structure (used in calculations) has been determined from theoretical simulation of measured spectra of optical reflection. A comparison of experimental data with the results of calculations makes it possible to relate the observed features in the PLE spectra to excitons, including the lower level of dimensional quantization for electrons and two first levels of holes for the A and B valence bands of the wurtzite crystal. The values of the electron and hole masses in ZnO are refined, and the value of the built-in electric field introduced by spontaneous and piezoelectric polarizations is estimated.     

Emitters based on semiconductor Bragg microcavities

This paper presents a brief review of the progress in the development of two types of semiconductor emitters based on semiconductor Bragg microcavities. The first type of these emitters is a vertical-cavity laser based on Al _x Ga_1−x As. The laser demonstrates stable single-mode lasing at a wavelength of 795 nm, which opens prospects for its use in miniature atomic frequency standards on the basis of Rb⁸⁷. The second type is a single-photon emitter based on semiconductor quantum dots. The design of such an emitter was developed on the basis of a semiconductor Bragg microcavity providing a high level of external quantum efficiency of the emitter (up to 80%) and high performance due to the Purcell effect.