Dielectric Response of ZnTe–Ti/Al Schottky Junctions with CdTe Quantum Dots Studied by Impedance Spectroscopy

Eunika Zielony,Grzegorz Karczewski,Ewa Płaczek-Popko

doi:10.3390/cryst10030170

Abstract

The electrical properties of ZnTe–Ti/Al Schottky junctions were investigated by the impedance spectroscopy (IS) method. Current-voltage (I-V) and capacitance-voltage (C-V) measurements were also performed. The studied samples were the CdTe quantum dot structures embedded in ZnTe matrix and a reference ZnTe sample without quantum dots. C-V characteristics confirmed the presence of quantum dots (QDs) in the structures. Electric modulus and impedance data were analyzed. IS studies proved that long-range conductivity governs the relaxation processes in the junctions. For both samples, the data were fitted with a simple RC circuit composed of a depletion layer capacitance in parallel with bulk resistance and a series resistance of contacts. The activation energy of the relaxation process observed for the reference sample obtained from the Arrhenius plot of the resistance, imaginary impedance, and electric modulus equals 0.4 eV at zero bias. For the quantum dot sample, the value of activation energy determined with the help of the same methods equals 0.2 eV. In conclusion, it was assumed that the relaxation processes for the reference sample are attributed to the trap present in ZnTe host material, whereas those observed for the QD structure are assigned to the deep level associated with defects located close to the QDs created during their growth.

Highlights

Self-organized quantum dots (QDs) have been investigated widely for several years for comprehension of fundamental physics of zero-dimensional structures and for their attractive application in quantum dot dot (QD) semiconducting devices, such as lasers, detectors of radiation, or solar cells.The most important parameter determining the thermal emission of carriers from the dots is the energy level position of discrete QD states relative to the band edges of the barrier material [1]
Sample electric exhibits smooth typical for bulk factor semiconductor-metal relaxation process, a semicircle is obtained for all the aforementioned functions when their real in and characteristic step (“plateau”), which is normally seen within the negative voltage bias range the imaginary parts are plotted in the complex plane
The studies presented in this paper were dedicated to a sample with CdTe self-assembled quantum dots embedded in Zinc telluride (ZnTe) (p-type) matrix and a reference structure, without the QDs

Summary

Introduction

Self-organized quantum dots (QDs) have been investigated widely for several years for comprehension of fundamental physics of zero-dimensional structures and for their attractive application in QD semiconducting devices, such as lasers, detectors of radiation, or solar cells.The most important parameter determining the thermal emission of carriers from the dots is the energy level position of discrete QD states relative to the band edges of the barrier material [1]. Quantum dot layers embedded in a semiconducting structure behave like giant traps, and the techniques used to study deep traps in standard semiconductor devices became applicable for QD structures. Deep level transient spectroscopy (DLTS) is a widely used technique to study the parameters of deep traps present in the energy gap of semiconductor junctions [2]. Besides the DLTS method, impedance spectroscopy (IS) has become the most common technique to probe electronic properties of QD systems [3]. It is an alternating current (AC) electric technique used to observe the current response of a system to which an AC voltage is applied as a function of the frequency.

Methods

Results

Conclusion