RICERCA ITALIANA     

Spatially controlled nucleation of quantum dots for single photon emitters

Università degli Studi di Roma "Tor Vergata"

Abstract

Single quantum dots (QD) are attractive from scientific and application viewpoints because their density of states is peculiar and make them very similar to artificial atoms. It is possible to control and manipulate a number of charged carriers by confining them in a spatial region of a few tens of nanometers. Controlling the carrier storage inside the dot is the starting point to built single photon emitters. The present project deals with the growth of III-V semiconductor QDs, namely InAs dots, on GaAs patterned substrates in order to realize the selective nucleation of a single dot inside a 50-100 nm -sized hole suitable for single emitter optical devices. To this end the nanoemitter must be an efficient source of light, implying that both size and position random fluctuations must be avoided. Efficient localization strategies will be developed based on substrate pre-patterning and guided by accurate theoretical predictions of surface kinetics on realistic time and length scales. The experimental technique proposed to achieve selective nucleation of QDs makes use of a SiO2 mask deposited over the substrate in which nanoholes are drilled by electron beam lithography and where InAs dots will be subsequently nucleated. To understand the nucleation mechanisms of QDs we plan to describe the kinetic processes taking place on the WL of GaAs in correspondence of the 2D->3D transition by using atomistic simulations and realistic kinetic models, relying on the surface >>>

Principal Investigator

Adalberto BALZAROTTI Università degli Studi di ROMA "Tor Vergata"

Research Objectives

Among the most promising applications of quantum dots for novel optoelectronic devices, there are LED emitters in microcavity. The practical development of such a device implies the capability of nucleating a single quantum dot in a selected area, of typically 100 nm,in a controlled and reproducible way. This target, although pursued by several research groups using various strategies combining epitaxial growth techniques with substrate patterning, has not been fully achieved yet.
The main goal of the present project is to growth InAs QDs on GaAs patterned substrates in order to realize the selective nucleation of a single dot suitable for optical applications. To be used as a single photon emitter, the nanoemitter must be an efficient source of light. Special configurations of dots must be considered that increase the photon generation rate. The spatial distribution of QDs inside a microcavity should be such that the coupling between the QD electronic states and the cavity modes of the electromagnetic field maximize the spontaneous emission rate (SER) of the artificial atom, modelled as a two-level quantum system.
The strategy followed to achieve selective nucleation of QDs makes use of a SiO2 mask deposited over the GaAs substrate in which nanoholes are drilled by electron beam lithography and chemical etching and where InAs dots will be subsequently nucleated. This configuration takes advantage of the different diffusion of element III on SiO2 and GaAs to >>>

Timescale

24 months

National and international background

Quantum dots (QDs) are semiconductor nanostructures whose electronic states are fully quantized and thus they share a close analogy with atoms. For instance, in the case of QDs made of direct gap semiconductors, such as gallium arsenide (GaAs) and indium arsenide (InAs), the interaction between the single QD and radiation gives rise to discrete emission lines, fine structure etc., typical of atomic spectroscopy, as well as to the generation of non-classical e.m. states, strong coupling effects and whatever, typical of quantum optics.
In the last years, single QDs, particularly InAs/GaAs dots, have been strongly successful in several applications such as the generation of single photon states[1] and their use in quantum cryptography [2], the control of spontaneous emission in microcavities [3] , the proof of the interference between two photons emitted by single QDs [4] and the strong coupling between a single exciton and a microcavity mode [5]. Moreover, coherent charge and spin control can been used to exploit quantum gates and even a quantum computer, as proposed in several theoretical papers [6,7] and proved experimentally [8,9]. It follows that the possibility of growing laterally confined In(Ga)As quantum dots on GaAs substrates in spatial regions as small as a few tens of nanometers is extremely relevant from both fundamental and application viewpoints. However, several not yet fully understood factors affect the growth of QDs, such as the anisotropic >>>