Abstract:

Due to their important technological applications, such as low-threshold lasers, nanometer scaled memories or single photon sources and detectors etc, semiconductor Quantum Dots (QDs) have attracted an enormously interest in recent years. Imaging of energy eigenfunction in semicond uctor Quantum Dots (QD) by STM for cleaved InAs/GaAs QDs or uncapped InAs/GaAs QDs offers a unique opportunity to investigate the properties of QDs. In this communication, we report on cross-sectional Scanning Tunneling Microscopy and Spectroscopy and subsequent electronic wave-function imaging at low temperature (T=77 K) on cleaved In(Ga)As/GaAs QDs. The Sample, consisted of four arrays of QDs separated by 40nm highly Beryllium doped GaAs spacers, was grown by Molecular Beam Epitaxy on GaAs(100) substrate. Self assembled In(Ga)As QDs are formed by the deposition of a 2.0 ML (monolayer) of InAs at 500°C. After slicing the array of QDs by cleavage, Cross-Sectional STM experiment reveals numerous dots with different lateral base lengths but quite uniform height. Spatially resolved Scanning Tunneling Spectroscopy (STS) are subsequently measured on a series of selected individual dots with different lateral size. At positive voltage, the dI/dV spectra measured by STS exhibit a set of discrete and well-defined peaks in the unoccupied QDs state. Furthermore, differential conductance dI/dV maps display clearly the real space spatial variation of the electron wavefunctions for the successive ground state and excited states. The images, recorded at specific voltages corresponding to the QD eigenvalue, strikingly match to the well-known atomic wave-function. These experimental results have recently initiated a simulation study performed in the frame of the envelope function approximation and k.p multibands formalism to calculate the energy level and wavefunction in cleaved quantum dots.
 
 
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