Defects Formed During 1 MeV Si Ion-Irradiation of GeSi/Si Strained Layer Heterostructures at Elevated Temperature

The strain relief observed in GeSi/Si strained-layer heterostructures irradiated with MeV ions at elevated temperature (253°C) is shown to be consistent with the accumulation of excess vacancies in the alloy layer. Partial recovery of the asgrown strai

Ion-Implantation-Induced Extended Defect Formation in (0001) and (1120) 4H-SiC

We study the effect of substrate orientation namely (11 2̄ 0) and (0001) oriented crystals on defect formation in 4H-SiC. The microstructure of the various samples, as-implanted with P and annealed, were studied by Rutherford backscattering spectrometr

Transmission Electron Microscopy Characterization of Secondary Defects Created by MeV Si, Ge, and Sn Implantation in Silicon

Extended defects created in Si by ion implantation to doses below the amorphization threshold have been studied after annealing at 800 °C for 15 min. The implant species were the group IV elements Si, Ge, and Sn, and structural defects created by simila

Inhibited carrier transfer in ensembles of isolated quantum dots

We report significant differences in the temperature-dependent and time-resolved photoluminescence (PL) from low and high surface density InxGa1-xAs/GaAs quantum dots (QD's). QD's in high densities are found to exhibit an Arrhenius dependence of the PL intensity, while low-density (isolated) QD's display more complex temperature-dependent behavior. The PL temperature dependence of high density QD samples is attributed to carrier thermal emission and recapture into neighboring QD's. Conversely, in low density QD samples, thermal transfer of carriers between neighboring QD's plays no significant role in the PL temperature dependence. The efficiency of carrier transfer into isolated dots is found to be limited by the rate of carrier transport in the InxGa1-xAs wetting layer. These interpretations are consistent with time-resolved PL measurements of carrier transfer times in low and high density QD's

Medium-range order in amorphous silicon investigated by constrained structural relaxation of two-body and four-body electron diffraction data

The structures of four types of amorphous silicon are examined by an experimentally constrained structural relaxation method (ECSR). Experimental selected area electron diffraction data and fluctuation electron microscopy normalized diffraction variance data were used as constraints to guide a Monte Carlo relaxation procedure towards best fit models. A Tersoff potential was also used to further restrict the space of possible solutions. The materials examined were self-ion-implanted silicon and pressure-amorphized silicon, both in their as-prepared and thermally annealed states. In the fitted models for these materials regions containing two types of medium-range order were identified. One type involves formation of paracrystallites with cubic and hexagonal structures, where both short-range crystalline and medium-range order are present. The other type of medium-range order appears in the form of extended crystalline planes without associated short-range crystalline order. These two types can coexist. It is observed that the best fit models for both as-prepared samples contain approximately 10-15% paracrystalline ordered regions, reducing to about 5-10% in the annealed materials. None of the models are true continuous random networks. We conclude that, with long computational times and with a suitable potential function, the ECSR procedure provides a powerful, although at present semi-quantitative, tool for determining the structural form of medium-range order in thin amorphous materials

Strain effect in a GaAs-In0.25Ga0.75As-Al0.5Ga0.5As asymmetric quantum wire

We report a theoretical investigation of the strain effects on the electronic energy band in a GaAs-In0.25Ga0.75As-Al0.5Ga0.5As asymmetric quantum wire formed in a V-grooved substrate. Our model is based on the sp3s* tight-binding model. It includes different spatial distributions of the lattice-mismatch-induced strain. We solve numerically the tight-binding Hamiltonian through the local Green's function from which the electronic local density of states (LDOS) is obtained. The detailed energy band structure (discrete localized states and energy bands of extended states) and the spatial distribution of the eigenfunctions (wave function amplitude of nondegenerate states or sum of the wave function amplitudes of degenerate states) are directly reflected in the LDOS. Spatial mapping of the LDOS's shows a reduction of the lowest excitation energies in different regions of the system when the local lattice structure of the In0.25Ga0.75As layer relaxes from completely strained to completely relaxed. By comparing the calculated results with photoluminescence measurement data, we conclude that the strain in the In0.25Ga0.75As layer relaxes linearly from the heterointerface with the Al0.5Ga0.5As buffer layer to the heterointerface with the top GaAs layer

Dislocation-induced changes in quantum dots: step alignment and radiative emission

A new type of quantum dot (QD) alignment for an InGaAs/GaAs QD multilayered structure has been observed. In addition to two distinct types of InGaAs dot alignment in vicinal GaAs (001), an abrupt transition in QD sizes and concentrations was seen. This was accompanied by bright QD emission, even after formation of a dislocation array, and different behaviors with thermal intermixing

Optical properties of arsenic ions implanted GaAs/AlGaAs V-grooved quantum wires

Asymmetric double GaAs/AlGaAs V-grooved quantum wires, grown by low pressure metalorganic chemical vapor deposition, are studied using photoluminescence (PL) spectroscopy. The structure was selectively treated by ion implantation at different arsenic (As) doses after growth. The ion implantation strongly reduces the efficiency of the emissions from the implanted well regions or even quenches the PL emissions from certain well regions due to irradiation damage. Wire emission is clearly resolved in the samples after treatment by low dose implantation. The temperature dependence of the wire emission intensity shows an enhancement at a temperature of around 45 K. The wire emission peak with a shoulder at its high energy side at low temperatures develops into double peaks in a temperature region between 20 and 140 K, and the high energy transition component dominates the PL spectra at temperatures above 140 K. The deduced energy separation between two peaks is about 10 meV. With further increasing temperatures the wire emission related to the light hole state can be observed at temperatures above 150 K. Deduced splitting between the heavy and light states is about 35 meV in our structures

Role of Implantation-Induced Defects on the Response Time of Semiconductor Saturable Absorbers

To shorten the response times of GaAs-based saturable absorber structures, arsenic ion implantation with thermal annealing was employed. Results showed that both the concentration and type of residual defects determines the ultimate shortening of the carrier lifetime. To eliminate amorphization, poor recrystallization and polycrystalline layers after annealing, high implantation doses should be avoided since the response time is increased under these conditions