Optoelectronic properties of ZnO/ZnMgO multiple quantum wells in ZnMgO nanocolumns grown on Si (111)

Superlattice structures formed using the II-VI family of semiconductors have attracted a great deal of attention due to some unique properties (chemical sensors, UV detectors, lasers, white LED). We present a comparison of optical and electrical measurements of 10-period ZnO/ZnMgO multiple quantum wells (MQWs). The structures have been fabricated on (111) Si by molecular beam epitaxy grown at very high temperatures. The optical properties were analyzed by photoluminescence and cathodoluminescence techniques. Cross-sectional SEM-CL mapping shows that the ZnO/ZnMgO multiple quantum wells are located in ZnMgO nanocolumns. Based on these structures, diodes were processed and characterized by current-voltage (I-V), capacitance-voltage and deep level transient spectroscopy techniques (DLTS). I-V measurements confirm that in both diodes, deep traps govern the conduction mechanisms at a forward bias. DLTS studies yield signatures of these traps as well as those related to the presence of QWs. In particular, DLTS results let us estimate the distance of 30 meV from the QW ground state to the barrier conduction band.