Current instabilities in GaAs/InAs self-aggregated quantum dot structures (original) (raw)
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Current instabilities in GaAs/InAs quantum dot structures
International Conference on Solid State Crystals 2000: Epilayers and Heterostructures in Optoelectronics and Semiconductor Technology, 2001
Unexpected excess current was obtained in GaAs/InAs quantum dot structures at low temperatures and low current levels. This excess current exhibited instabilities with changing the bias, and over the time. It has been concluded that the excess current is a minority injection current connected with the high recombination rate through quantum dots. The instabilities are connected with unstable charge accupation of quantum dots.
Instability of electrical characteristics of GaAs/InAs quantum dot structures
physica status solidi (c), 2005
We report on GaAs samples containing an InAs quantum dot matrix grown from 3 monolayers of InAs. In this case, most of the mechanical stress relaxes by misfit dislocations. Capacitance measurements have been performed on macroscopic devices and, also, from a scanning microscope in which the capacitance is measured between the probe and sample surface. It was found that the electrical characteristics dramatically change during the capacitance measurements. This is explained by a degradation of the quantum dot layer which is attributed to the generation of point defects and/or dislocations. These results draw attention to the fact that, at the microscopic scale measurement, a small current may result in a large local current density which, in turn, degrades the device.
Defect-Related Current Instabilities in InAs/GaAs and AlGaAs/GaAs Structures?
Solid State Phenomena, 2002
Unexpected excess current was obtained in GaAs/InAs quantum dot structures at low temperatures and low current levels. This excess current exhibited instabilities with changing the bias, and over the time. It has been concluded that the excess current is a minority injection current connected with recombination through defects originated from the formation of QDs. The instabilities are connected with unstable occupation of energy levels induced by the above defects, which depend on temperature and on the current level. Excess currents have also been obtained in annealed AlGaAs/GaAs structures. These excess currents exhibited memory effect, which was probably connected with formatin of defects during annealing.
Electrical characterization of InAs/GaAs quantum dot structures
Materials Science and Engineering: C, 2006
The electrical properties of InAs quantum dots (QD) in InAs/GaAs structures have been investigated by space charge spectroscopy techniques, current-voltage and capacitance-voltage measurements. Au/GaAs/InAs(QD)/GaAs Schottky barriers as well as ohmic/GaAs/ InAs(QD)/GaAs/ohmic structures have been prepared in order to analyze the apparent free carrier concentration profiles across the QD plane, the electronic levels around the QD and the electrical properties of the GaAs/InAs(QD)/GaAs heterojunction. Accumulation and/or depletion of free carriers at the QD plane have been observed by Capacitance-Voltage (C-V) measurements depending on the structure parameters and growth procedures. Similarly, quantum dot levels which exhibit distributions in energy have been detected by Deep Level Transient Spectroscopy (DLTS) and Admittance Spectroscopy (AS) measurements only on particular structures. Finally, the rectification properties of the InAs/GaAs heterojunction have been investigated and the influence of the related capacitance on the measured capacitance has been evidenced.
Nonlinear effects of the photocurrent in self-assembled InAs/GaAs quantum dots
Journal of Applied Physics, 2011
We report photocurrent (PC) and its complemented photoluminescence investigations of carrier escape dynamics in multi-layered InAs/GaAs self-assembled quantum dots (QDs) subjected to vertical electric fields. We found a nonlinear dependence of PC on the laser excitation power. This unusual behavior can be tuned by bias voltage. Very well agreement between PC data and theoretical prediction ensures that the accumulation of holes trapped in QDs is responsible for this nonlinearity. It is expected that this laser controlled electronic transport might open many potential applications in optoelectronic devices.
Journal of Applied Physics, 2010
Currently lattice mismatch strain-driven three-dimensional coherent island based quantum dots, dubbed self-assembled quantum dots ͑SAQDs͒, constitute the most developed class of quantum dots with successful applications to lasers and considerable potential for infrared detectors in the 1-12 m regime. This is in no small part a consequence of the extensive studies on the formation and control of the islands and on their capping by appropriate overlayer materials under optimal growth conditions. By contrast, surprisingly few studies have been reported on the presence and nature of the deep levels in SAQD structures, much less direct studies of the impact of deep levels on SAQD based device characteristics. The latter is of particular significance to devices such as detectors that require large numbers of SAQD layers ͓i.e., multiple quantum dot ͑MQD͒ structures͔ and are thus increasingly prone to accumulating strain-induced defect formation with increasing numbers of quantum dot layers. In this paper, we report the results of a study of the density, energy profile, and spatial profile of deep levels in different regions of GaAs͑001͒/InAs/InGaAs/GaAs SAQD structures in which the InGaAs/GaAs capping layers have been grown at different growth conditions. Different types of deep levels are found in different regions and, as expected, their densities are found to increase in the presence of the SAQDs. The study shows that it is the density of deep levels in the GaAs capping layer, forced to be grown at the low temperature of ϳ500°C to suppress In outdiffusion, which has a significant adverse impact on quantum dot device characteristics. Their density can be reduced by growth conditions such as migration enhanced epitaxy that permit high quality overgrowths at temperatures as low as ϳ350°C. Nevertheless, the ultimate performance limitation of thick MQD based devices resides in the ability to realize low density of the deep levels relative to the density of SAQDs.
Capacitance-voltage measurements in InAs-GaAs self-assembled quantum dots
physica status solidi (c), 2005
We report on an investigation of capacitance-voltage spectroscopy of electron-hole dynamics in I-nAs/GaAs self-assembled quantum dots (QDs) under varied reverse bias, and a study of the influence of holes on this process exerted by the Coulomb interactions. The time constant of the electron transport was estimated by making use of the frequency dependence of the capacitance increase due to the InAs dots. The high values found for the tunnelling times suggest that this process is very sensitive to hole accumulation into the dots.
Lateral conductivity in GaAs/InAs quantum dot structures
The European Physical Journal Applied Physics, 2004
Lateral conductivity effects have been investigated in self-organised InAs quantum dot (QD) structures grown in a GaAs matrix with different cap layers. Current-voltage (I-V), capacitance-voltage (C-V), DLTS, capacitance and conductance frequency dependence, fast defect transient (FDT), and electron beam induced conductivity (EBIC) measurements were applied. The conductivity in the QD plane decays within a distance of 10 microns. The capacitance transients are dominated by the local QD-plane transversal conductivity and by the free carrier transport in the cap layer. The nonequilibrium free carrier created by electron beam excitation develop a potential barrier at macroscopic distances from the electrical contacts.