Nanostructurale nature of the porous GaAs layer formed on p-GaAs substrate by electrochemical anodization

A porous GaAs layer has been formed by electrochemical anodization in HF based solution on extremely doped p-type GaAs substrate. Porous nature of the elaborated sample has been evidenced by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Nanostructurale nature of the porous layer has been demonstrated by X-ray diffraction analysis (XRD) and confirmed by photoluminescence spectroscopy (PL).     

Recombination emission from InAs quantum dots grown on vicinal GaAs surfaces

Photoluminescence (PL) spectra of InAs/GaAs heteroepitaxial structures with quantum dots (QDs) have been studied. The structures were grown by submonolayer migration-enhanced epitaxy on vicinal substrates with the amount of deposited InAs close to the critical value of 1.8 monolayer (ML). The origin and evolution of the structure of PL spectra were studied in relation to the direction and angle of misorientation, temperature, and power density and spectrum of the exciting radiation. A blue shift and narrowing of the PL band with increasing misorientation angle was established experimentally. The fact that QDs become smaller and more uniform in size is explained in terms of a lateral confinement of QDs on terraces with account taken of the step bunching effect. The temperature dependences of the positions and full widths at half-maximum (FWHM) of PL bands are fundamentally different for isolated and associated QDs. The exciton ground states contribute to all low-temperature spectral components. The excited exciton state contributes to the recombination emission from QDs, as evidenced by the temperature dependence of the integrated intensity of the PL bands. A quantitative estimate is given of the electronic structure of different families of InAs QDs grown on GaAs substrates misoriented by 7° in the [001] direction.     

Dependence of electrical properties on interfacial layer of Ta2O5 films

The change in the thickness and chemical states of the interfacial layer and the related electrical properties in Ta₂O₅ films with different annealing temperatures were investigated. The high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy analyses revealed that the 700 °C-annealed Ta₂O₅ film remained to be amorphous and had the thinnest interfacial layer which was caused by Ta-silicate decomposition to Ta₂O₅ and SiO₂. In addition, the electrical properties were improved after annealing treatments. Our results suggest that an annealing treatment at 700 °C results in the highest capacitance and the lowest leakage current in Ta₂O₅ films due to the thinnest interfacial layer and non-crystallization.     

Effects of external fields on the excitonic emission from single InAs/GaAs quantum dots

A low-temperature micro-photoluminescence (μ-PL) investigation of InAs/GaAs quantum dots (QDs) exposed to a lateral external electric field is reported. It is demonstrated that the QDs PL signal could be increased several times by altering the external and/or the internal electric field. The internal field in the vicinity of the dots could be altered by means of an additional infra-red laser. We propose a model, which is based on an essentially faster lateral transport of the charge carriers achieved in an external electric field. Consequently, also the capture probability into the dots and subsequently the dot luminescence is also enhanced. The results obtained suggest that the lateral electric fields play a major role for the dot luminescence intensity measured in our experiment.     

InAs/GaAs quantum dots grown on different GaAs substrates with graded InxGa1-xAs strain-reducing layer

Self-assembled InAs quantum dots with graded composition strain-reducing layer (SRL) grown on exact substrates were studied. It is shown that a graded InxGa1-xAs SRL leads to growth quality improvement, emission efficiency enhancement, and wavelength blueshift. Samples grown on 2° misoriented substrates with different In contents in graded InxGa1-xAs SRL were also investigated, and emission efficiency enhancement and wavelength blueshift were found when graded SRL was introduced and when the change rate of In content in graded InxGa1-xAs SRL was enlarged.     

Preliminary comparison of ballistic electron emission spectroscopy measurements on InAs quantum dots in a GaAs/AlGaAs heterostructure grown by MBE and MOVPE

Self-assembled InAs quantum dots (SAQDs) in GaAs/GaAlAs structures grown by molecular beam epitaxy (MBE) and metal-organic vapour phase epitaxy (MOVPE) of similar size was examined by ballistic electron emission spectroscopy. Ballistic current-voltage characteristics through the QD in the voltage range from 0.55 to 0.9 V (range where the presence of resonance states of QD is expected) with its derivative (the derivation of the spectroscopic characteristics represents quantum levels in the QD) are given. Differences in the intensities and sharpnesses of the QD levels for MBE and MOVPE grown QDs are observed.     

Theoretical study of InAs/GaAs quantum dots grown on [11k] substrates in the presence of a magnetic field

Eight-band k.p theory including strain and piezoelectric effects are employed to calculate the strain distribution and electron and hole energy levels of InAs/GaAs quantum dots grown on [11k] substrates in the presence of an external magnetic field. Height of the dot determines how the increasing of k influences isotropic part of the strain tensor while biaxial part of the strain tensor is always reduced with increasing k. Because of the reduced symmetry of high index surfaces, influence of piezoelectric effect on the electronic structure becomes more dominant with increasing k. Electron energy levels are influenced by the isotropic part of the strain compared to the hole energy levels, where strong heavy hole–light-hole mixing is observed. For the dots grown on the [11k] surfaces magnetic field has smaller influence on the electron and hole energy levels as compared to the referent case.     

Continuous stimulated emission at T=293 K from separate-confinement heterostructure diode lasers with one layer of InAs quantum dots grown on vicinal GaAs(bd001) surfaces misoriented in the [010] direction in the active region

The electroluminescence and stimulated emission of lasers with one layer of InAs quantum dots (QD’s) grown in a single molecular-beam epitaxial process on vicinal GaAs(001) surfaces misoriented in the direction [010] by 2, 4 and 6° are investigated. It is discovered that an increase in the misorientation angle leads to a blue shift and a decrease in the full width at half maximum (FWHM) of the electroluminescence spectrum. This effect is attributed to a decrease in the size of the quantum dots and improvement in their size uniformity. A strong dependence of the threshold current density on the width of the spontaneous luminescence spectrum is discovered. The room-temperature threshold current density of the lasers with one layer of quantum dots and the spontaneous luminescence spectrum having the smallest FWHM (54 meV) equals 210 A/cm². Fiz. Tekh. Poluprovodn. 32, 1482–1486 (December 1998)