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Arrays of strained nanoscale InP islands in an In0.49Ga0.51P host on a GaAs(100) substrate and InAs islands in a In0.53Ga0.47As host on an InP(100) substrate are obtained by metalorganic vapor-phase epitaxy (MOVPE). Their structural and photoluminescence properties are investigated. It is shown that the nanoscale islands that are formed measure 80 nm (InP/InGaP) and 25–60 nm (InAs/InGaAs). The photoluminescence spectra of the nanoscale islands display bands in the wavelength ranges 0.66–0.72 and 1.66–1.91 µm at 77 K with maxima whose position does not vary as the effective thickness of InP and InAs increases. The radiation efficiency of the nanoscale InP islands is two orders of magnitude greater than the luminescence intensity of the InAs islands.

Spin splitting of optically active and inactive excitons in nanosized n-InP/InGaP islands has been revealed. Optically inactive states become manifest in polarized-luminescence spectra as a result of excitons being bound to neutral donors (or of the formation of the trion, a negatively charged exciton) in InP islands. The exchange-splitting energies of the optically active and inactive states have been determined.

Strained layer GaAs.95P.05 photo cathodes are presented, which emit electron beams spinpolarized to a degree of P = 75% typically. Quantum yields around QE = 0.4% are observed routinely. The figure of merit P2 × QE = 2.3 × 10−3 is comparable to that of the best strained layer cathodes reported in literature. The optimum wavelength of irradiating light around 830 nm is in convenient reach of Ti:sapphire lasers or diode lasers respectively. The cathodes are produced using MOCVD-techniques. A GaAs.55P.45-GaAs.85P.15 superlattice structure prevents the migration of dislocations from the substrate and bottom layers to the strained overlayer. The surface is protected by an arsenic layer so that no chemical cleaning is necessary before installation into vacuum. The source of polarized electrons attached to the Mainz race track microtron MAMI works with such cathodes now. More than 1000 hours beamtime have been performed successfully.

Results are presented of investigations of the growth of self-organizing nanosize InP and InAsP clusters in an In0.5Ga0.5P matrix. The structure was characterized by low-temperature photoluminescence and transmission electron microscopy. The photoluminescence measurements revealed highly efficient radiative recombination from the quantum dots and indicated that the structures were of good optical quality. The average density and size of the InP clusters, determined from the results of the transmission electron microscope measurements, are 3×109 cm−2 and 80 nm, respectively.

Low-temperature near-field scanning optical microscopy was used to study the dependence of the emission spectra of single self-organized InAs on GaAs, InAs on AlAs and InP on GaInP quantum dots (QDs) on contact pressure exerted by a near-field optical fiber tip (nanoindentation). A large energy shift (up to 150 meV), broadening (up to 10 meV), and intensity increase (up to one order of magnitude) of single QD emission lines have been observed at tip compressions up to 70 nm. Ground state energy shift rates from 0.5 to 3.5 meV/nm have been measured for different aperture types (rounded and flat, metal coated and uncoated) and sizes (50--300 nm) in agreement with numerical calculations using Picus--Bir orbital-strain Hamiltonian. A reduction of the hydrostatic pressure coefficient due to a nonuniform In distribution in self-organized QDs has been observed. Anomalously strong lateral inhomogeneity of the local stress field has been observed.

When a lattice-mismatched layer is grown on a substrate, the misfit between the layers at the interface is accommodated in the epitaxial layer and lifts the orbital degeneracy of the levels at the valence band maximum. Hence, the polarization of optically oriented electrons may be enhanced compared to unstrained cubic material. We report the first results of high spin polarization in electron photoemission from Semiconductor heterostructures with strained GaAs/sub 1-x/P/sub x/ (x=0.05;0.1 and 0.3) overlayers on GaAs/sub 1-y/P/sub y/ buffer (y=0.32;0.35 and 0.65 respectively). The polarization of photoelectrons emitted from negative electron affinity surface of the samples was measured at residual pressure 3E-11 Torr with LEED detector. Statistical error were 1% at quantum yield smaller than 1E-3 and 0.5% at quantum yield bigger than 1E-2. The light beam energy width was 15nm. Both the quantum yield and polarization were measured in the light energy range 1.3-2.7 eV. Negative electron affinity was achieved by activation of atomically clean surfaces with cesium and oxygen. All samples were grown in the horizontal MOCVD reactor. The properties of the layers were checked by photoluminescence and X-ray diffraction measurements. At room temperature we measured the polarization up to P=84% (x=0.05, overlayer thickness d=140 nm), P=83% (x=0.3, d=140 nm), P=72% (x=0.1, d=70 nm). It shows that high residual strain exists in the layers even when their thickness is about ten times more than the critical one. We have shown that by varying the phosphorus fraction in the overlayer the highest polarization value can be tuned to AlGaAs laser diode wavelength.

Experimental and theoretical investigations of high-energy shifts of single InAs, InGaAs, InAlAs and InP quantum dot (QD) emission lines induced by contact pressure exerted by a near-field optical fiber tip are reported. “Pressure” coefficients of 0.65–3.5 meV/nm have been measured for ground state emission lines in agreement with numerical calculations. We show that the observed increase of the tip-induced energy shift with increasing aperture diameter is caused by a decrease of the uniaxial strain component. We also report the effect of emission instability of single QD emission intensity under tip-induced pressure.

We present low-temperature near-field scanning optical microscopy (NSOM) measurements of self-organized InP quantum dots (QD) embedded in a GaInP layer. We observed an anomalously strong increase in the emission energy (∼270 meV) of a single QD by changing the tip-to-surface distance over ∼100 nm in the near-field region. The effect indicates the formation of a near-field nanocavity having extremely high photon-exciton mixing and can be interpreted as the observation of the coupled photon-exciton pair

The effects of negative polarization charge at the n-InGaN∕p-GaN interface on the performance of hydride vapor phase-epitaxy deposited single heterostructure n-InGaN∕p-GaN LEDs with p-side down are investigated. The strong peak emission wavelength blueshift and concomitant superlinear increase in light output as the injection current increases below 25A∕cm2 are characteristic of radiative tunneling. We show that the combination of two-dimensional hole gas formation on the n-InGaN side of the heterointerface and enhancement of the electron barrier to transport across this interface results in only ∼10% efficiency droop up to 500A∕cm2 without implementation of an AlGaN electron-blocking layer or a second heterointerface.

An investigation was made of the possibility of using reduced-pressure MOC hydride epitaxy to fabricate highly strained (compressive stress) InxGa1−xAs/In0.53Ga0.47As quantum wells on indium phosphide (100) substrates. The photoluminescence properties of these heterostructures were investigated. It was shown that these heterostructures are potentially useful for laser diodes emitting in the 1.5–2 μm range, which is important for environmental monitoring.

The photoluminescence spectra of samples of the solid solution In(0.5)Ga(0.5)P before and after implantation of high-energy nitrogen ions to doses of 1011−5×1012 cm−2 shows that the photoluminescence of the implanted (and annealed) samples may be the result of the formation of essentially one-dimensional semiconductor structures along the individual ion tracks.

We have studied high-energy shifts of single quantum dot (QD) emission lines induced by contact pressure exerted by a near-field optical fiber tip. “Pressure” coefficients of 0.65-3 meV/nm have been measured for self-organized InAs/GaAs, InAs/AlAs and InP/GaInP QDs in agreement with numerical calculations of the local strain field. We found an increase of the tipinduced pressure with increasing aperture diameter from 50-300 nm. A correlation between the shift rate and QD stiffness was obtained. We also observed an order of magnitude increase of single QD emission intensity with increased pressure.