METALORGANIC VAPOR-PHASE EPITAXY OF WIDE-GAP II-VI SEMICONDUCTORS FOR OPTOELECTRONIC APPLICATIONS - CURRENT STATUS AND FUTURE-TRENDS

The current status and future trends to overcome the major problems of wide-gap II-VI compounds grown by metalorganic vapor phase epitaxy (MOVPE) which are p-type doping and the understanding of interface properties of ZnSSe/ZnSe-based heterostructures will be discussed. Since a low growth temperature is required to reduce defects and impurities and to increase the sticking coefficient of dopant atoms, a matched precursor combination of zinc and selenium compounds or an additional growth assistance (e.g. plasma stimulation) must be employed. The optical and electrical properties of ZnSe doped with nitrogen will be discussed. Emphasis will be put on the fact that most of the MOVPE grown ZnSe:N layers remain highly resistive or that they show only low free hole concentrations. Occurring compensation mechanisms such as parasitic compensating donors associated with nitrogen or compensating nitrogen-hydrogen complexes may be the reason. The ability of MOVPE to handle high vapor pressure elements such as sulphur favours this technology for the growth of sophisticated quantum wells and superlattices to achieve electrical and optical confinement in laser structures and to push the emission wavelength further into the blue. Scanning transmission electron microscope, photoluminescence (PL) and X-ray measurements were used for the analysis of the interface properties. Growth optimization of ZnSSe/ZnSe interfaces results in monolayer fluctuations at the interfaces. High excitation PL experiments show that room temperature stimulated emission is possible with this kind of structures. To realize high bit rate data transmission in the blue spectral range at 2.7 eV the physical properties of optoelectronic modulators based on ZnSSe/ZnSe superlattices were examined.