Janusz Andrzejewski

The energy-fine structure of GaInNAs∕GaAs multiple quantum wells grown at different temperatures and postgrown annealed

We report photoreflectance investigations of the energy-fine structure of GaInNAs∕GaAs multiple quantum wells (MQWs) grown at different temperatures and postgrown treated by rapid thermal annealing (RTA). A “splitting” of the ground and excited QW transitious due to the presence of different nitrogen nearest-neighbor environments, i.e., N‐Ga4−mInm(0⩽m⩽4) short-range-order clusters, has been observed. The RTA induces a nitrogen redistribution between the five possible N‐Ga4−mInm configurations and thus leads to a blueshift of QW transitions. The magnitude of the blueshift and its dependence on the growth temperature and annealing temperature are investigated in this paper.

Wetting layer states of InAs∕GaAs self-assembled quantum dot structures: Effect of intermixing and capping layer

The authors present a modulated reflectivity study of the wetting layer WL states in molecular beam epitaxy grown InAs/GaAs quantum dot QD structures designed to emit light in the 1.3‐1.5 m range. A high sensitivity of the technique has allowed the observation of all optical transitions in the QD system, including low oscillator strength transitions related to QD ground and excited states, and the ones connected with the WL quantum well QW. The support of WL content profiles, determined by transmission electron microscopy, has made it possible to analyze in detail the real WL QW confinement potential which was then used for calculating the optical transition energies. We could conclude that in spite of a very effective WL QW intermixing, mainly due to the Ga‐In exchange process causing the reduction of the maximum indium content in the WL layer to about 35% from nominally deposited InAs, the transition energies remain almost unaffected. The latter effect could be explained in effective mass envelope function calculations taking into account the intermixing of the QW interfaces described within the diffusion model. We have followed the WL-related transitions of two closely spaced QD layers grown at different temperatures, as a function of the In content in the capping layer. We have shown that changing the capping layer from pure GaAs to In0.236Ga0.764As has no significant influence on the composition profile of the WL itself and the WL QW transitions can be usually interpreted properly when based on the cap-induced modification of the confinement potential within a squarelike QW shape approximation. However, some of the observed features could be explained only after taking into consideration the effects of intermixing and InGaAs cap layer decomposition.

Eight-band k⋅p calculations of the composition contrast effect on the linear polarization properties of columnar quantum dots

We present eight-band k⋅p calculations of the electronic and polarization properties of columnar InzGa1−zAs quantum dots (CQD) with high aspect ratio embedded in an InxGa1−xAs/GaAs quantum well. Our model accounts for the linear strain effects, linear piezoelectricity, and spin-orbit interaction. We calculate the relative intensities of transverse-magnetic (TM) and transverse-electric (TE) linear polarized light emitted from the edge of the semiconductor wafer as a function of the two main factors affecting the heavy hole—light hole valence band mixing and hence, the polarization dependent selection rules for the optical transitions, namely, (i) the composition contrast z/x between the dot material and the surrounding well and (ii) the dot aspect ratio. The numerical results show that the former is the main driving parameter for tuning the polarization properties. This is explained by analyzing the biaxial strain in the CQD, based on which it is possible to predict the TM to TE intensity ratio. The conclu...

Controlling the aspect ratio of quantum dots: From columnar dots to quantum rods

We demonstrate the feasibility and flexibility of artificial shape engineering of epitaxial semiconductor nanostructures. Novel nanostructures including InGaAs quantum rods (QRs), nanocandles, and quantum dots (QDs)-in-rods were realized on a GaAs substrate. They were formed by depositing a short-period GaAs/InAs superlattice (SL) on a seed QD layer by molecular beam epitaxy growth. The InAs layer thickness in the SL plays an important role in obtaining the QRs. The growth of the QRs is very sensitive to growth interruption and growth temperature. By properly choosing both growth parameters, QRs with length of 41 nm corresponding to an extremely large aspect ratio of 4.1 were obtained. The evolution from a 0-D to 1-D confinement type is evidenced in the optical properties. The origin of the optical transitions from the QRs was understood by calculations of the electronic states within a fully 3-D approach in the eight-band k

Optical and electronic properties of GaAs-based structures with columnar quantum dots

cdot

Electron-irradiation enhanced photoluminescence from GaInNAs∕GaAs quantum wells subject to thermal annealing

p approximation. The QRs are embedded in a GaAs matrix and are therefore free from surface traps. This feature enables high material quality and consequently their application in real devices. At room temperature, laser diodes based on QR active regions lasing around 1120 (or 1130) nm are demonstrated.

Polarization Properties of Columnar Quantum Dots: Effects of Aspect Ratio and Compositional Contrast

The electronic properties of a structure with columnar quantum dots obtained by close stacking of InAs submonolayers have been investigated by contactless electroreflectance (CER) and photoluminescence. These dots have an almost ideally rectangular cross section and uniform composition, which is promising for polarization independent gain. After energy level calculations in the effective mass approximation using composition profiles obtained from cross-sectional transmission electron microscopy the part of the CER spectrum related to the two-dimensional surrounding layer has been explained and single heavy-hole-like and light-hole-like transitions related to the columnar dots identified, due to a single electron state confined in a shallow in-plane potential.

Photoreflectance investigations of quantum well intermixing processes in compressively strained InGaAsP∕InGaAsP quantum well laser structures emitting at 1.55μm

Electron irradiation of a 1.3‐μm‐GaInNAs∕GaAs multi-quantum-well heterostructure, grown by molecular beam epitaxy and subsequently rapid-thermal annealed, is found to induce much stronger photoluminescence than what is observed for an identical as-grown sample upon annealing. Annealing of the irradiated sample also causes a small additional spectral blueshift and reduces alloy potential energy fluctuations at the conduction band minimum. These irradiation-related phenomena are accompanied by small but discernable changes in x-ray diffraction features upon annealing, which indicate compositional and∕or structural changes in the quantum wells.

Height-driven linear polarization of the surface emission from quantum dashes

We report a systematic theoretical and experimental investigation of the polarization properties of columnar quantum dots (CQDs) with extremely large aspect ratio and high compositional contrast. A strong variation of the polarization of the dominant interband transitions as a function of the CQD composition and aspect ratio is predicted by the theory and observed experimentally. In optimized InAs CQDs grown on GaAs, dominant emission and lasing is obtained in the transverse-magnetic polarization, which shows the potential of this approach for polarization-independent amplifiers on GaAs.

On optimizing Jacobi-Davidson method for calculating eigenvalues in low dimensional structures using eight band k·p model

We have investigated the effects of interdiffusion and its technological parameters on the subband structure in compressively strained InGaAsP quantum wells (QWs) using photoreflectance and photoluminescence techniques. p-i-n laser structures with three QWs were grown by gas source molecular beam epitaxy and capped with dielectric films deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition and annealed using a rapid thermal annealing process. A numerical real-time wave-packet propagation method including static electric field, strain in the wells and barriers, and error function interface diffusion modeling is used to calculate the transition energies for the diffused QWs. It has been shown that the shift of the energy levels due to the interdiffusion related changes of the well confinement potential profile is a consequence of two competing processes: a change of the well width and an effective increase of the band gap energy resulting in a net blueshift of all optical trans...