Shazia Yasin

Fabrication of <5 nm width lines in poly(methylmethacrylate) resist using a water:isopropyl alcohol developer and ultrasonically-assisted development

We report on the fabrication of 3–4 nm wide continuous lines in a positive tone electron beam resist poly(methylmethacrylate) on a solid substrate. This narrow linewidth was made possible through the use of a nonsolvent-based developer system, water:isopropyl alcohol, together with ultrasonically-assisted development, which reduced the effective development time thus limiting the swelling of the unexposed resist. This combination of solvent system and development technique results in a smaller radius of gyration in the developing polymer molecules and in a wider exposure dose latitude compared to conventional processing and so allows ultrasmall features to be reproduced.

InGaN quantum dots grown by metalorganic vapor phase epitaxy employing a post-growth nitrogen anneal

We describe the growth of InGaN quantum dots (QDs) by metalorganic vapor phase epitaxy. A thin InGaN epilayer is grown on a GaN buffer layer and then annealed at the growth temperature in molecular nitrogen inducing quantum dot formation. Microphotoluminescence studies of these QDs reveal sharp peaks with typical linewidths of ∼700 μeV at 4.2 K, the linewidth being limited by the spectral resolution. Time-resolved photoluminescence suggests that the excitons in these structures have lifetimes in excess of 2 ns at 4.2 K.

Comparison of MIBK/IPA and water/IPA as PMMA developers for electron beam nanolithography

Abstract In electron beam lithography, resist behavior, such as sensitivity, contrast, exposure dose latitude, roughness and resolution, are influenced by the nature of the resist, the developer type and composition, and the development technique. In earlier work, ultrasonically assisted development was used to improve resolution and line edge roughness. Here we investigate the influence on resist behavior of an unconventional developer consisting of IPA and water. We observe improvements in sensitivity (∼40%), in contrast (∼20%), in exposure dose latitude (∼40%) and in roughness (nearly an order of magnitude) compared to the use of a conventional 1:3 MIBK/IPA developer. These improvements assisted in the fabrication of gratings of minimum size 16 nm equal line spacing in PMMA resist with 3:7 water/IPA developer.

Biexciton and exciton dynamics in single InGaN quantum dots

Time-resolved and time-integrated microphotoluminescence spectrometry of exciton and biexciton transitions in a single self-assembled InGaN quantum dot gives sharp peaks, with the biexciton 41 meV higher in energy. Theoretical modelling in the Hartree approximation (using a self-consistent finite difference method) predicts a splitting of up to 51 meV. Time-resolved microphotoluminescence measurements yield a radiative recombination lifetime of 1.0 ± 0.1 ns for the exciton and 1.4 ± 0.1 ns for the biexciton. The data can be fitted to a coupled DE rate equation model, confirming that the exciton state is refilled as biexcitons undergo radiative decay.

Characterisation of the ultrasonic development process in UVIII resist

The effect of ultrasonically assisted development on the characteristics of electron beam exposed UVIII resist is investigated. Process latitude, ultimate resolution and line edge roughness are seen to be improved compared to conventional dip development. The mechanisms for this improvement are discussed.

Photoluminescence studies of exciton recombination and dephasing in single InGaN quantum dots

This paper reports on time-integrated and time-resolved microphotoluminescence (/spl mu/-PL) measurements of single InGaN quantum dots (QDs). The linewidths of the /spl mu/-PL peaks originating from single metal-organic vapor phase epitaxy-grown III/V InGaN QDs are measured, implying dephasing times of at least 5 ps. Temporal fluctuations of the QD emission energy are observed, and these are explained in terms of randomly generated local electric fields inducing a Stark shift in the optical emission of the InGaN QDs. Time-resolved measurements demonstrate that decay dynamics from single InGaN QDs are exponential in nature. Measurements of the effect of temperature upon the recombination times in individual InGaN QDs have been performed from 4 to 60 K.

Time-resolved dynamics in single InGaN quantum dots (Invited Paper)

We present measurements of microphotoluminescence decay dynamics for single InGaN quantum dots. The recombination is shown to be characterized by a single exponential decay, in contrast to the non-exponential recombination dynamics seen in the two-dimensional wetting layer. The lifetimes of single dots in the temperature range 4 K to 60 K decrease with increasing temperature. Microphotoluminescence measurements of exciton complexes in single MOVPE-grown InGaN quantum dots are also reported. We find the exciton-biexciton and exciton-charged exciton splitting energies to be 25 meV and 10 meV to the higher-energy side of the exciton ground state, respectively. Assignments of the ground state exciton, biexciton and charged exciton are supported by theoretical calculations. These measurements have been extended to investigate the time-resolved dynamics of biexciton transitions in the quantum dots. The measurements yield a radiative recombination lifetime of 1.0 ns for the exciton and 1.4 ns for the biexciton. The data can be fitted to a coupled differential equation rate equation model, confirming that the exciton state is refilled as biexcitons undergo radiative decay.

Theoretical And Experimental Investigation Of Biexcitons And Charged Excitons In InGaN Single Quantum Dots

Micro‐photoluminescence measurements on single InGaN quantum dots at 4K exhibit a rich structure of lines to the high‐energy side of the free exciton (X0), as a function of excitation density. Lines possibly attributable to biexcitons (2X0) and charged excitons (X+ and X−) have been measured. We model the dots as truncated cone shapes, using a self‐consistent finite difference method in the Hartree approximation to compute the ground‐state wavefunctions of the four exciton complexes. We calculate the exciton recombination energy (X0) and the magnitude of the blue‐shifts of the biexciton and charged excitons as a function of dot size and composition. The transition energy depends strongly on both dot composition and dot height, while the magnitude of the blue shift is determined primarily by the piezoelectric field‐induced separation of electrons and holes. We use these two separate effects to place constraints on allowed models for the QDs. The experimentally measured energies are in agreement with these ...