II-VI semiconductors are important for many device applications, particularly for light emitting devices. Recently, Be chalcogenides have been of great interest due to enhanced material hardness. This is promising for improving II-VI semiconductor-based device performance. To take advantage of these materials requires a thorough knowledge of their properties. Here, we investigate the optical properties of bulk ZnBeSe (undoped, n-type and p-type) with various Be compositions. This provides a better understanding of their properties especially as functions of the Be composition.; II-VI semiconductor-based low-dimensional structures have become the focus of intensive research due to their interesting physics and novel device applications. Specifically, CdZnSe/ZnSe self-assembled quantum dot (QD) structures are potential candidates for light emitting devices in the green/blue spectral range. Structural studies (e.g. transmission electron microscopy) showed that there is always a distribution in the Cd composition and the size of these QDs. Here we use a novel approach combining optical studies and model calculations to obtain the Cd composition and the size of optically active QDs. We further show that the introduction of Be into these structures (CdZnSe/ZnBeSe) enhances both the Cd composition and the quantum confinement of QDs. Additionally, another material of interest is the Zn-Se-Te system, whose optical properties have been dominated by isoelectronic bound excitons. Here, we, for the first time, explicitly prove the existence of ZnTe/ZnSe QDs in this material system, which have a type-II band alignment. Interestingly, along with these type-II QDs, there is also a existence of isoelectronic centers. This coexistence of type-II QDs and isoelectronic centers allows one to probe the transition between these two, which is crucial for the understanding of scaling laws in this small size range. Another emerging II-VI material of great interest is the ZnO, which has a high bandgap energy (∼3.36eV at room temperature) and a high exciton binding energy (∼60meB). These properties make ZnO a very promising candidate for the ultra-violet light emitting devices. The ZnO nanorods are expected to further improve device performance. However, due to very small exciton Bohr radius (∼2.3nm), all the previously-grown ZnO nanorods (with radius larger than 10nm) do not show any quantum confinement effects. Here, with a colloidal-synthesized ZnO nanorod system, we, have observed the quantum confinement effect. This quantum confinement enhances exciton binding energies, which could further improve device performance. We also study the origin of the so-called green PL usually observed for ZnO using the PL shift as a result of the quantum confinement effect.
展开▼
