The generation–recombination noise in doped-channel quantum-well AlGaAs/GaAs/InGaAs micro-Hall devices is characterized using deep level noise spectroscopy. The source of this low-frequency noise contribution is identified as a single deep level with activation energy of 476 meV. This level is associated with DX centers located in the Al0.30Ga0.70As near the heterointerfaces. A detailed analysis of the experimental data further indicates a trap ionization energy of about 250 meV, an electron capture cross section of about σ0≃1×10−11 cm2, and a total integrated defect concentration of about Nts≃1.4×1010 cm−2.

Strikingly strong many-body enhancement of the oscillator strength for interband transitions is observed in the photoluminescence (PL) of heavily doped pseudomorphic AlxGa1-xAs/InyGa1-yAs/GaAs heterostructures under condition of the n = 2 subband filling. The many-body excitations reveal a remarkable stability with respect to thermal and excitation density decay. Such behaviour is addressed the intersub-band coupling in high-density one-component plasma of InGaAs quantum well in the presence of defects localising the heavy holes.

Quantum well micro-Hall devices based on uniformly Si-doped Al0.3Ga0.7As/GaAs and Si-δ-doped Al0.3Ga0.7As/GaAs/In0.3Ga0.7As heterostructures are investigated as function of electric field and compared in terms of sensitivity and noise properties. The data show that at high electric fields, doped-channel quantum well devices are advantageous over high-mobility structures and that the use of pseudomorphic InGaAs results in better performance than does GaAs. A maximal signal-to-noise sensitivity (SNS) of 138dBT−1 is achieved in a 10μm×10μm device at 300K, at frequency of 100kHz and bandwidth of 1Hz. This performance corresponds to a lowest detection limit of 127nTHz−1/2, with no degradation for electric fields up to 2.4kVcm−1; these values represent the best reported at such high electric fields. Furthermore, our results suggest that a signal-to-noise sensitivity of 160dBT−1 and a lowest detection limit of 10nT is achievable in doped-channel structures.

Fundamentally different behavior of the Fermi-edge singularity (FES) in photoluminescence of heavily doped pseudomorphic modulation-doped ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{A}\mathrm{s}/\mathrm{I}\mathrm{n}}_{y}{\mathrm{Ga}}_{1\ensuremath{-}y}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ heterostructures is observed. The noteworthy features are: (i) the FES enhancement from ${E}_{F}$ of $n=1$ electronic subband is observed under condition of the $n=2$ subband population, (ii) the heavy-hole localization energy is directly observed in the FES development, (iii) the magnitude of the FES increases with increasing temperature at low temperatures, and (iv) the FES is a nonmonotonic function of the excitation density. A qualitative analysis is performed in terms of heavy-hole localization by potential fluctuations in the ${\mathrm{In}}_{y}{\mathrm{Ga}}_{1\ensuremath{-}y}\mathrm{As}$ quantum well.

Pseudomorphic modulation-doped AlxGa1-xAs/InyGa1-yAs/GaAs heterostructures with high electron density show a fundamental change of the photoluminescence spectrum under excitation density and/or temperature elevation. The coexistence, of Fermi-edge singularity with excitonic states causes fundamental changes in the high energy tail of the photoluminescence peak. At low temperature the origination of the Fermi-edge singularity feature being absent initially is detected for the first time under the excitation density increase. Strong screening of the n = 2 exciton state by photo-excited carriers is observed. The photoluminescence behavior near the Fermi edge is explained in terms of a strong effect of the carrier density on the appearance of the Fermi-edge singularity; the details of this effect have not yet been fully theoretically explored.

Photoluminescence spectroscopy is used to investigate the size distribution of InAs quantum dots embedded in GaAs quantum wells as function of substrate temperature and InAs coverage. For intermediate InAs coverage, quantum dots of more than one distinct size class coexist with each other. We show that the quantum dot size distribution is bimodal for relatively high growth temperatures (T(G)congruent to 505 degrees C) and becomes multimodal for relatively low growth temperatures (T(G)congruent to 420 degrees C) with growth interruptions. We explain this behavior in terms of two distinct thresholds for dot formation: (i) the minimum InAs coverage which can lead to islanding and (ii) the coverage consistent with the optimal dot size for the given growth conditions. Further, thermally activated electron transfer from dots in the smaller size class to those in the larger size class is investigated using the temperature dependence of the photoluminescence.

The dependence of disorder on InyGa1-yAs thickness in pseudomorphic strained-layer Al-x Ga1-xAs/InyGa1-yAs/GaAs heterostructures is studied by means of photoluminescence (PL) and Raman scattering. PL and Raman data indicate that, for both y = 0.10 and 0.15, the InyGa1-yAs layers (with thickness not greater than 20 nm) are purely pseudomorphically strained. For InyGa1-yAs wells narrower than about 15 nm, the broad PL emission, small correlation length derived from Raman measurements of the longitudinal optical (LO) phonons, the asymmetry of the LO phonon peak and the presence of a disorder-activated longitudinal acoustic (DALA) phonon signal in the Raman scattering data are all indicative of disordered InGaAs. For well widths of 20 nm, however, the narrow PL emission, the details of the LO phonon data and the absence of an observable DALA signal are all indicative of much less disorder than in the thinner quantum wells.

We present new results concerning the valence-band structure of pseudomorphic modulation-doped Al0.2Ga0.8As/In0.1Ga0.9As/GaAs heterostructures explored by means of a novel sensitive magnetooptical method based on optical detection of quantum oscillations via photoluminescence in a magnetic field. The quantum oscillations with the Fermi sea reveal two distinct periods in 1/B for samples with a quantum well width less than 15 nm. This behavior is attributed to the presence of two sorts of localized hole states: 0 those which are scattered near the top of valence band and are practically "free" in potential relief, ii) those which are strongly localized in separated by 10 meV from valence band discrete state. This localization is assumed to be caused by random alloy fluctuations, probably in indium content.

Planar ordering of dense self-organized arrays of InP/In0.48Ga0.52P quantum dots is investigated using grazing incidence small-angle X-ray scattering (GISAXS), atomic force microscopy (AFM), and transmission electron microscopy (TEM). Using the two-dimensional Fourier transform of the AFM data together with the GISAXS data, we show that the degree of ordering increases with increasing InP deposition time and, therefore, with increasing quantum dot density. This increase in ordering is seen both in that the dot period is less variable and in the appearance of longer ranged ordering of the dots on the surface. Intense photoluminescence due to radiative recombination of heavy holes and electrons in the quantum dots is observed at an energy between the band gaps of InP and In0.48Ga0.52P.

A photoluminescence (PL) study of pseudomorphic modulation-doped AlxGa1-xAs/InyGa1-yAs/GaAs heterostructures with high-electron density reveals a fundamental change in the PL spectrum under increased excitation density. The high-energy tail of the PL is transformed due to the mutual repulsion of the Fermi-edge singularity (FES) and the excitonic states. The details of this repulsion depend on the excitation density and temperature. At low temperature, the dependence of the existence of the FES feature on excitation density has been demonstrated for the first time. The appearance of the FES is accompanied by the formation of an abrupt high-energy edge and occurs at intensities far below those required for the appearance of the hybridized n=2 exciton. Strong screening of the n=2 exciton state by photoexcited carriers is observed. The PL behavior under excitation density and temperature variation near the Fermi edge is explained in terms of a strong effect of the carrier density on the appearance of the FES; the details of this effect have not yet been fully theoretically explored.

The structural and optical properties of dense self-organized arrays of InP/In0.48Ga0.52P quantum dots are studied. Dense and well ordered arrays of islands with a base area between 400 and 600 nm(2) gradually build up. In order to quantitatively study the planar ordering of the quantum dots, we investigate the two-dimensional Fourier transform of the atomic force microscopy data, and grazing incidence small-angle x-ray scattering spectra. We find that with increasing InP deposition time the degree of ordering is increased. Intense photoluminescence is observed at an energy between the band-gaps of InP and In0.48Ga0.52P. This line is attributed to radiative recombination of heavy-holes and electrons in the quantum dots.

Peculiarities of photoluminescence (PL) spectra have been observed in the modulation-doped pseudomorphic strained-layer AlxGa1-xAs/InyGa1-yAs/GaAs heterostructures (x = 0.2, y = 0.1). In particular, the character of PL spectra dramatically depends on the quantum well width, changing from excitoniclike in wider wells to (two-dimensional) electron-heavy-hole band transitions in narrower quantum wells. Low-energy structure in the photoluminescence is weakly observed in the InyGa1-yAs quantum well and interpreted in terms of a two-dimensional electron gas hole bound to acceptor transitions.