Top-Down Etched Site-Controlled InGaN/GaN Quantum Dots.

by Lei Zhang

Institution: University of Michigan
Department: Physics
Degree: PhD
Year: 2015
Keywords: site-controlled InGaN/GaN quantum dot; single-photon emission; strain relaxation; top-down etch; voltage controlled photoluminescence; electrically driven; Physics; Science
Record ID: 2058016
Full text PDF: http://hdl.handle.net/2027.42/111576


Quantum technologies such as quantum communication and computation may one day revolutionize the landscape of communication and computing industry, which so far has been largely based on the classical manipulation of the flow of many photons and electrons. Many important quantum technologies have been demonstrated on single atoms which have discrete energy levels and can interact strongly with light, both functionalities are key to quantum technologies. However, single atoms are difficult to integrate with other photonic and electronic components, which are equally crucial to most of the applications. Semiconductor quantum dots are considered as the key building block to scalable quantum technologies due to their atom-like functionality and solid-state integrability. To date, many proof-of-principle integrated quantum devices have been demonstrated based on single quantum dots. However, most of the devices were not suitable for large-scale practical applications mainly due to the adoption of self-assembled III-As quantum dots, which form at random sites and operate only at liquid-helium temperatures. These drawbacks may be resolved by using III-N quantum dots with controlled forming site and optical properties, and high operating temperatures. This thesis studies site-controlled InGaN/GaN quantum dots fabricated by top-down etching a planar single quantum well. Compared to other existing site-controlled III-N quantum dots, ours have the following advantages: 1) the fabrication approach allows flexible control of the emission energy, oscillator strength and polarization of each quantum dot; 2) their emission is free from wetting layer contamination leading to purer single-photon emission; 3) they can be efficiently driven by electrical current. We demonstrate in this thesis that these quantum dots have all the essential properties required for most quantum technologies. They are efficient light emitters due to the strain relaxation that enhances the radiative recombination and limits the nonradiative surface recombination. They have discrete energy levels due to the strong exciton-exciton interaction by the small lateral size, manifested by both optically and electrically driven single-photon sources using our quantum dots. Finally, the net charges in each quantum dot can be controlled electrically via Coulomb blockade, which enables the understanding of exciton charging and fine structures crucial to many quantum technologies.