Electro-optical characterization of Ti/Au–ZnTe Schottky diodes with CdTe quantum dots

Abstract

In this study the electric and optical spectroscopy techniques have been applied to investigate ZnTe (p-type)–Ti/Au Schottky diodes containing a layer of CdTe self-assembled quantum dots (SAQDs). The reference sample was the ZnTe–Ti/Au diode without dots. Both samples were grown by molecular beam epitaxy technique. Raman measurements confirmed the presence of the CdTe layer while the photoluminescence proved that CdTe quantum dots were formed in the investigated structure. The PL spectra reveal the CdTe QD electron-hole recombination energy equal to 2.1eV at 10K. Based on the temperature PL measurements the activation energy of PL quenching has been determined to be equal to 22meV. Further confirmation for the QD formation has been obtained from the C–V characteristics which exhibited a step related to the charge accumulation at the QD states. DLTS spectra for the sample with QDs yield three hole-related signals with apparent activation energies equal to EH1=0.16eV, EH2=0.2eV and EH3=0.4eV. For the reference ZnTe–Ti/Au diode solely single signal was observed of signature close to the level H3 in the QD sample. Detailed characterization of the traps as well as the PL studies lead to the conclusion that the level H2 is related to the defects located close to the QDs created during the growth while the other traps are associated with defects present in the ZnTe bulk material.