Vertically stacked and laterally ordered InP and In(Ga)As quantum dots for quantum gate applications

Abstract

We report on the epitaxial growth of vertically stacked InP and In(Ga)As quantum dot (QD) layers to realize a triple dot quantum gate structure consisting of an asymmetric control double dot and a single target dot suitable for a CNOT gate structure. Structural analysis as well as studies on the optical properties are presented. For studies on control dot structures we analyze the growth of InP islands in a GaInP barrier on (100) GaAs substrates. By stacking InP QD layers with intentional asymmetric design in QD size of each layer and adjustment of the barrier width between the double dots, coupling and control of the coupling via barrier layer width-design can be demonstrated. For defined gate action single dot spectra of aligned dots are indispensable. Therefore QD density reduction is studied. We study two possibilities to affect the QD density and control the dot site by manipulating the surface potential of InP island nucleation. (i) Growth of InP islands on top of a low density In(Ga)As QD seed layer (ii) Growth of InP islands on patterned (100) GaAs substrates. We present microsphere photolithography in combination with wet chemical etching as a fast and low-cost method to produce regular hole arrays in a GaAs surface, which are suitable for controlled nucleation of self-assembled InP islands.1 Introduction During the last decades the growth of semiconductor quantum dots (QDs) by metal-organic vaporphase epitaxy (MOVPE) has highly improved and linewidths as well as luminescence efficiencies are reported, e.g., for the InAs/GaAs system [1] reaching the quality of samples grown by molecular beam epitaxy [2,3]. This allows for the fabrication of atom-like structures due to a three-dimensional charge carrier confinement even on a mass production scale. The epitaxial growth process enables a relatively easy implementation of QDs in electronic systems and therefore makes semiconductor QDs to promising building blocks for single-photon and single-electron devices suitable for applications in quantum information processing (QIP) [4,5]. Today, research is focusing on the functionalization of QDs, including the implementation in resonator and electronic structures. For the realization of quantum gate structures also the coupling of QDs forming a quantum dot molecule

Optical investigations on single vertically coupled InP/GaInP quantum dot pairs

“…More details can be found in Ref. 12 and in the article by Koroknay et al 13 in this issue. To investigate single QDMs, mesas of 200 nm diameter were fabricated using electron‐beam lithography and dry etching wheras the sample containing single QDs discussed in Section 3.4 was equipped with a chromium shadow mask.…”

Photoluminescence Characterization of Vertically Coupled Low Density InGaAs Quantum Dots for the application to Quantum Information Processing Devices

“…Especially, the zero-dimensional structures such as quantum dots (QDs) have been of great interest for quantum information processing devices, e.g. single photon sources [1,2] and quantum gates [3]. Among many other possible materials, In(Ga)As QDs are favorable for the realization of quantum information processing devices due to matured growth technology.…”