Kinematical Analysis of the Evolution of Reflection High Energy Electron Diffraction Patterns of Quantum Dot Heterostruc
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0924-Z08-09
Kinematical Analysis of the Evolution of Reflection High Energy Electron Diffraction Patterns of Quantum Dot Heterostructures: Correlation with Strain and Anisotropy Andrea Feltrin, and Alexandre Freundlich Center for Advanced Materials, University of Houston, 724 Science & Research Building 1, Houston, Texas, 77204-5004
ABSTRACT The strain distributions and of reflection high energy electron diffraction (RHEED) patterns of uncapped pyramidal shape InAs Stranski-Krastanov quantum dots fabricated on GaAs(001) substrate are investigated theoretically. The three dimensional strain anisotropy is computed with an atomistic elasticity approach, using inter-atomic Keating potentials and the strain energy is minimized using the conjugate gradient numerical method. RHEED images are predicted in the framework of the kinematical theory, by taking into account the refraction of the electron beam at the quantum dot/vacuum interface. Clear correlation between RHEED image features and quantum dot structural properties is established. The study stresses the potential of RHEED for future experimental real-time (during growth) detections and deciphering of strain anisotropies in quantum dots. INTRODUCTION Semiconductor nanostructures have demonstrated a profound impact on research and applications in solid state physics. This success has been possible because of joint efforts, developments and breakthroughs in many different physical disciplines as the fabrication of semiconductor nanostructures, their processing, characterization and theoretical understanding. Over the past decade, research on semiconductor nanostructures has largely focused on quantum dots. Their potential to exploit subtle quantum effects has driven several studies in different areas such as photon anti-bunching processes for single photon on demand emitters, creation of entangled quantum states for quantum computation and cryptography and solid state cavity quantum electrodynamics. As a result, the requirements to reproduce reliably critical parameters of the quantum dot structure such as size, shape or composition have increased, because these properties determine their electronic and optical properties. Thus, much effort has been devoted in order to improve the control of the density, the size and the positions of the quantum dots. The ability to control and design these parameters is fundamental to many present applications, too. In the case of lasers, the quantum dot density and especially the size distribution of the quantum dots critically affects the performance of the device in terms of emission wavelength and threshold current. As part of this effort and in order to improve the control and reproducibility over the quantum dot structure, new diagnostic tools have been developed. The combination of experimental TEM measurements with theoretical simulations has proven very valuable in the study of the structural properties of quantum nanostructures as quantum wells, allowing the mapping of strain distributions and chemical profiles [1]. In the
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