A report describes an experimental investigation of effects of thermally induced intermixing of In0.6Ga0.4As and GaAs on the dynamics of photoexcited charge carriers in In0.6Ga0.4As/GaAs quantum dots. The quantum dots (nanometer-size islands of In0.6Ga0.4As surrounded by GaAs) were grown by metal-organic chemical-vapor deposition. The dynamics at temperatures from 60 to 300 K were investigated by time-resolved photoluminescence measurements with subpicosecond temporal resolution, on both specimens as grown and specimens in which intermixing had been effected by a post-growth anneal. The measurement data were interpreted as signifying that at lower temperatures, the carrier lifetimes in the dots are determined by radiative recombination, which becomes substantially faster after intermixing, while at temperatures >150 K, thermal emission of carriers predominates. Capture of carriers into the dots was found to be fast and governed by carrier-carrier scattering; at room temperature and high excitation intensity, a carrier capture time of 0.72 ps was observed in the intermixed dots. These findings have implications for the development of quantum-dot lasers.
This work was done by Rosa Leon of Caltech for NASA's Jet Propulsion Laboratory.
NPO-20766
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Capture and Escape of Charge Carriers in Quantum Dots
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Overview
The document presents a technical report on an experimental investigation into the dynamics of photoexcited charge carriers in InGaAs/GaAs quantum dots, focusing on the effects of thermally induced intermixing. Conducted by Rosa Leon at NASA's Jet Propulsion Laboratory, the study explores how intermixing influences carrier lifetimes and dynamics at varying temperatures.
Quantum dots, which are nanometer-sized islands of InGaAs surrounded by GaAs, were grown using metal-organic chemical-vapor deposition. The research utilized time-resolved photoluminescence measurements with subpicosecond temporal resolution to analyze the behavior of charge carriers in both as-grown specimens and those subjected to post-growth annealing to induce intermixing. The temperature range for the investigation spanned from 60 K to 300 K.
Key findings indicate that at lower temperatures, the lifetimes of charge carriers in the quantum dots are primarily determined by radiative recombination processes. Notably, after intermixing, these lifetimes become significantly shorter, suggesting enhanced recombination rates. Conversely, at temperatures above 150 K, thermal emission of carriers becomes the dominant process, overshadowing radiative recombination.
The study also highlights the rapid capture of carriers into the quantum dots, which is governed by carrier-carrier scattering. At room temperature and under high excitation intensity, a remarkably fast carrier capture time of 0.72 picoseconds was observed in the intermixed quantum dots. These findings underscore the potential for manipulating the properties of semiconductor quantum dots through thermal intermixing, which could lead to advancements in quantum-dot laser technology.
The report emphasizes the novelty of the work, noting that the ability to alter photoluminescence lifetimes in quantum dots through a simple thermal process represents a significant improvement over prior methods. The motivation behind the research was to enhance the understanding and control of semiconductor quantum dot properties, which are crucial for various applications in optoelectronics.
Overall, this investigation provides valuable insights into the dynamics of charge carriers in quantum dots and opens avenues for further research and development in the field of quantum-dot lasers and related technologies. The work is documented under NASA's contract and is part of ongoing efforts to advance semiconductor technology.
