Growth and photoluminescence study of ZnSe quantum dots

Abstract

Special Issue Paper 173Quantum dots (QDs) have received much attention because of their potential applications in optical and opto-electronics devices. 1,2 Various ways of producing QDs have been demonstrated. 3-5 Self-organized QDs attracted the most attention because of their nondestructive and non-growth-interrupted nature. InAs quantum dots on GaAs 6 and Ge quantum dots on Si 7 are well-known examples. These quantum dots were found to grow under the Stranski-Krastanov mode: a layer was first grown in two-dimension, and threedimensional islands were formed after some critical thickness was reached. These dots were formed to relax strain energy without creating dislocations between the dots and the underlying layer, and are epitaxially and coherently grown. The fact that the QDs are defect free is an important reason why QDs usually have very good optical properties.Recently, we showed that high quality QDs could be grown in a metal-organic chemical vapor deposition system by controlling the flow duration of the precursors. 8 The basic idea of the approach is to embed QDs directly in another material with wider bandgap but without introducing a two-dimensional layer. To do so, a rough surface was first prepared as a starting layer. QDs were then grown on this rough surface. Dot size was controlled by growth duration. By using this We report detailed photoluminescence (PL) studies of ZnSe quantum dots grown by controlling the flow duration of the precursors in a metal-organic chemical vapor deposition system. The growth time of the quantum dots determines the amount of blue shift observed in the PL measurements. Blue shift as large as 320 meV was observed, and the emission was found to persist up to room temperature. It is found that changing the flow rate and the total number of quantum dot layers also affect the peak PL energy. The temperature dependence of the peak PL energy follows the Varshni relation. From analyzing the temperaturedependent integrated intensity of the photoluminescence spectra, it is found that the activation energy for the quenching of photoluminescence increases with decreasing quantum dot size, and is identified as the binding energy of the exciton in ZnSe quantum dot.Key words: ZnSe, quantum dots, exciton, photoluminescence method, we were able to grow ZnSe QDs with good properties. In this paper, we report detailed photoluminescence (PL) studies of ZnSe quantum dots grown with different growth parameters. The growth time of the QDs determines the amount of blue shift of the PL from these QDs. Blue shifts ranging from 320 meV to 190 meV were observed for growth duration time between 1 s to 5 s and the emission persists up to room temperature. However, for growth time larger than 5 s, only very weak defect-related emission could be detected. The temperature dependence of the peak emission energy was found to decrease with increasing temperature. Effect of the flow rate of the precursor on the blue shift was studied. We found that, with the same growth duration, the smaller the DESe flow...

Successful growth of two different quantum dots on one substrate

“…It appears that when the growth time is long, the small quantum dots merge together to form a big cluster, and the density of the smaller dots actually decreases. In the previous study we found that PL intensity decreases and sometimes disappears completely with increasing ZnSe growth time [4][5][6]. This is consistent with the SEM results which show that as the growth time increases, the density of small QDs that are responsible for the high e cient light emission decreases with growth time.…”

“…1(c), when the growth duration time is 10 s, large clusters show up and are the dominant feature of the surface. These high-resolution SEM pictures provide the evidence we claimed previously that it is not a S-K growth, or a layer plus island growth, instead, the growth is a Volmer-Weber mode, or direct island growth [4][5][6][7]. An important feature to be noted from these pictures is that when the growth time is short, the QD size is also small.…”

“…Quantum dots (QDs) systems have brought much attention because of their potential applications in the optical and opto-electronic devices [1][2][3][4][5][6][7][8][9][10]. Various ways of producing QDs have been demonstrated.…”

“…that the high-quality QDs could be grown in a metal organic chemical deposition (MOCVD) system by controlling the ow duration of the precursors [4][5][6]. The basic idea is to embed QDs into another material with wider gap but without introducing a wetting layer.…”

Optical properties of type-I PbSe/CdSe core/shell quantum dot

“…Core is made up of a semiconducting material (PbSe) which is coated with the lattice matched shell material (CdSe) in order to improve its optical properties. These core/shell materials show novel optical properties better than the bare quantum dots [13][14][15]. PbSe related colloidal core/shell heterostructures have been investigated for optoelectronic applications [16].…”