InAs Self Research Articles

Quantum Confined Stark effect and temperature dependencies of photoluminescence of InAs quantum dots coupled with AlGaAs/GaAs two dimensional electron gas -=SUP=-*-=/SUP=-

AbstractIn this work, Experimental study of the influence of internal electric field and the temperature on the photoluminescence of InAs self assembled quantum dots inserted in AlGaAs/GaAs modulation doped hetero-structure have been investigated. The internal electric field is controlled by an appropriate design of the hetero-structure. We have observed a red shift of the photoluminescence position peaks result from the quantum confined Stark effect due to the local electric field existing in the structure. Estimation values of the internal electric field have been obtained through carrier’s densities values in interface of AlGaAs/GaAs hetero-junction. An anomalous dependence of the full width at half maximum with temperature has been found, which attributed to the carrier’s dynamics between InAs quantum dots layer and the two-dimensional electron gas.

Size dependent carrier thermal escape and transfer in bimodally distributed self assembled InAs/GaAs quantum dots

We have investigated the temperature dependent recombination dynamics in two bimodally distributed InAs self assembled quantum dots samples. A rate equations model has been implemented to investigate the thermally activated carrier escape mechanism which changes from exciton-like to uncorrelated electron and hole pairs as the quantum dot size varies. For the smaller dots, we find a hot exciton thermal escape process. We evaluated the thermal transfer process between quantum dots by the quantum dot density and carrier escape properties of both samples.

Applicability of Steady State Model to Carrier Thermodynamics in InAs Quantum Dot

The carrier thermodynamics of InAs self assembled quantum dot (QD) are investigated. The investigated parameters include the dependence of quantum dot photoluminescence on temperature and the photoluminescence (PL) dependence on the excitation power density. Results are discussed on the basis of steady state model. The model predicts that the photoluminescence integrated intensity has linear dependence on the excitation power density in low temperature range, and super linear in the high temperature range. Our data matches the prediction of the steady state model. In our sample the super linearity starts to take place at T = 150 K and the super linear behavior of the photoluminescence on excitation power density proves that the carrier dynamics in our quantum dot sample are dominated by uncorrelated electron hole pair in the high temperature region.

Optical properties and energy transfer in InGaAsN quantum well – InAs quantum dots tunnel injection structures for 1.3 μm emission

AbstractTunnel injection structure consisting of InAs self assembled quantum dots emitting light at the second telecom window at 1.3 μm and an InGaAsN injector quantum well is investigated by means of optical spectroscopy and the results compared to the injector‐free reference sample. The photoreflectance measurements, supported by calculations, reveal a complex structure of optical transitions in the system of coupled injector, wetting layer and strain reducing layer. The determined energy structure shows that the tunnelling is possible only through the excited states of quantum dots. Photoluminescence excitation proves the carrier transfer (tunnelling) from the injector to the dots at room temperature. The comparison of photoluminescence spectra confirms the tunnelling efficiency, especially at low temperatures. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Quantitative scanning capacitance microscopy on single subsurface InAs quantum dots

Quantitative scanning capacitance microscopy on InAs quantum dots requires low modulation frequencies and complete darkness. Using a modified feedback method on our atomic force microscope, which allows to switch off the laser temporarily while the feedback loop keeps running, images of buried InAs self assembled quantum dots were acquired. The dots are clearly visible as bright areas in a contrast-rich capacitance landscape, which we attribute to thickness variations of the InAs wetting layer. Even at room temperature, spectroscopic data recorded at on-dot and off-dot positions exhibit a completely different behavior and show evidence of quantized states inside the dots.

Room temperature capacitance imaging of single sub-surface InAs quantum dots

Scanning capacitance microscopy (SCM) is known to be a valuable tool for carrier mapping and profiling on nanoscale semiconductor samples. Certain applications, however, such as quantitative capacitance microscopy on InAs quantum dots, e.g. require low modulation frequencies and complete darkness, which are requirements completely incompatible with the current commercial SCM systems relying on a laser feedback system. For this reason, an intercepted feedback method was developed, which allows to switch off the laser temporarily while the feedback loop keeps running. As an application, images of sub surface InAs self assembled quantum dots were recorded. The InAs dots are clearly visible as bright areas in a contrast-rich capacitance landscape, which we attribute to local thickness variations of the InAs wetting layer in our sample.

Size Quantization and Zero Dimensional Effects in Self Assembled Semiconductor Quantum Dots

In this paper we discuss size quantization effects in InAs self assembled quantum dots deposited by molecular beam epitaxy (MBE) on (100) GaAs. The quantum dot size measurements are performed by transmission electron microscopy while the energy levels from the same samples are measured by capacitance, photoluminescence, photovoltage and electroluminescence techniques. Size quantization effects are observed, however variations in the quantum dot shapes, composition fluctuations and non uniform size distribution, which are deposition dependent prevent complete and accurate quantification of these effects. Through infrared absorption measurements together with capacitance measurements, the zero dimensional character of the quantum dots and “the atomic like” shell structure of the electronic levels in the quantum dots are established.

Limits and Properties of Size Quantization Effects in InAs Self Assembled Quantum Dots

AbstractIn this paper we report on the limits and properties of size quantization effects in InAs self assembled quantum dots (QDs). Size, density and character of the InAs islands are investigated by transmission electron microscopy. The electronic and optical properties of the islands in the coherent and dislocated growth regime are studied using capacitance, photoluminescence, photovoltage and photocurrent spectroscopy. In the data measured with the different techniques, the change in dot size and density as well as the transition from coherent to dislocated island growth is clearly observable. An increasing QD size causes a red shift in the energetic position of the QD features while the density of the islands is reflected in the intensity of the QD signal. The decrease in intensity at high InAs coverage is attributed to dislocated island formation.