Search NASA⌕ Search

Engineering topics

Berkinsky, David B.

Publications and source records attributed to Berkinsky, David B..

8 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Quantum Shell in a Shell: Engineering Colloidal Nanocrystals for a High-Intensity Excitation Regime

Many optoelectronic processes in colloidal semiconductor nanocrystals (NCs) suffer an efficiency decline under high-intensity excitation. This issue is caused by Auger recombination of multiple excitons, which converts the NC energy into excess heat, reducing the efficiency and life span of NC-based devices, including photodetectors, X-ray scintillators, lasers, and high-brightness light-emitting diodes (LEDs). Recently, semiconductor quantum shells (QSs) have emerged as a promising NC geometry for the suppression of Auger decay; however, their optoelectronic performance has been hindered by surface-related carrier losses. Here, we address this issue by introducing quantum shells with a CdS–CdSe–CdS–ZnS core–shell–shell–shell multilayer structure. Further, the ZnS barrier inhibits the surface carrier decay, which increases the photoluminescence (PL) quantum yield (QY) to 90% while retaining a high biexciton emission QY of 79%. The improved QS morphology allows demonstrating one of the longest Auger lifetimes reported for colloidal NCs to date. The reduction of nonradiative losses in QSs also leads to suppressed blinking in single nanoparticles and low-threshold amplified spontaneous emission. We expect that ZnS-encapsulated quantum shells will benefit many applications exploiting high-power optical or electrical excitation regimes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Adversarial autoencoder ensemble for fast and probabilistic reconstructions of few-shot photon correlation functions for solid-state quantum emitters

Second-order photon correlation measurements [g (2) (τ) functions] are widely used to classify single-photon emission purity in quantum emitters or to measure the multiexciton quantum yield of emitters that can simultaneously host multiple excitations – such as quantum dots – by evaluating the value of g (2) (τ = 0). Accumulating enough photons to accurately calculate this value is time consuming and could be accelerated by fitting of few-shot photon correlations. Here, we develop an uncertainty-aware, deep adversarial autoencoder ensemble (AAE) that reconstructs noise-free g (2) (τ) functions from noise-dominated, few-shot inputs. The model is trained with simulated g (2) (τ) functions that are facilely generated by Poisson sampling time bins. The AAE reconstructions are performed orders-of-magnitude faster, with reconstruction errors and estimates of g (2) (τ = 0) that are lower in variance and similar in accuracy compared to Maximum likelihood estimation and Levenberg-Marquardt least-squares fitting approaches, for simulated and experimentally measured few-shot g (2) (τ) functions (~100 two-photon events) of InP/ZnS/ZnSe and CdS/CdSe/CdS quantum dots. The deep-ensemble model comprises eight individual autoencoders, allowing for probabilistic reconstructions of noise-free g (2) (τ) functions, and we show that the predicted variance scales inversely with number of shots, with comparable uncertainties to computationally intensive Markov chain Monte Carlo sampling. Furthermore, this work demonstrates the advantage of machine learning models to perform uncertainty-aware, fast, and accurate reconstructions of simple Poisson-distributed photon correlation functions, allowing for on-the-fly reconstructions and accelerated materials characterization of solid-state quantum emitters.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Quantum Shells Boost the Optical Gain of Lasing Media

Auger decay of multiple excitons represents one of the main obstacles to photonic applications of semiconductor quantum dots (QDs). These non-radiative processes are particularly detrimental to the performance of QD-based electroluminescent and lasing devices. Here, we demonstrate that by using semiconductor quantum shells with an “inverted” QD geometry, it is possible to inhibit Auger recombination, allowing extraordinary improvements to their multi-exciton characteristics. Additionally, we show that quantum shells result in ultralong biexciton lifetimes (>10 ns), and an associated biexciton quantum yield of up to 81%. Furthermore, the energy-dispersive architecture of quantum shells leads to exciton-exciton repulsion, which splits the single-exciton and bi-exciton optical transitions. In this regime, quantum shells produce the longest optical gain lifetime reported for colloidal QDs to date (> 6 ns) over a broad amplification bandwidth. Therefore, the employment of quantum shells in optically- or electrically-pumped gain media can lead to a substantial improvement in device performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗