Nanocrystals of group-IV semiconductor materials (Si, Ge, and SiGe) have been fabricated in SiO2 by ion implantation and subsequent thermal annealing. The microstructure of these nanocrystals has been studied by transmission electron microscopy. Critical influences of the annealing temperatures and implantation doses on the nanocrystal size distributions are demonstrated with the Ge-implanted systems. Significant roughening of the nanocrystals occurs when the annealing temperature is raised above the melting temperature of the implanted semiconductor material.

Planar layers of Au clusters with diameters between 5 and 30 nm were synthesized by implanting 2.75-MeV Au+ ions in fused silica. The metal-glass composite layer was 0.85 μm below the surface and had a width of 0.5 μm. Thermal annealing enhanced the optical absorption of the annealed samples near 2.4 eV. The third-order nonlinear optical response time is ≤35 ps; the magnitude of the effective nonlinear susceptibility is 200 times that of similar clusters embedded in ruby-gold melt glass.

We describe a new method for removing thin, large area sheets of diamond from bulk or homoepitaxial diamond crystals. This method consists of an ion implantation step, followed by a selective etching procedure. High energy (4–5 MeV) implantation of carbon or oxygen ions creates a well-defined layer of damaged diamond that is buried at a controlled depth below the surface. For C implantations, this layer is graphitized by annealing in vacuum, and then etched in either an acid solution, or by heating at 550–600 °C in oxygen. This process successfully lifts off the diamond plate above the graphite layer. For O implantations of a suitable dose (3×1017 cm−2 or greater), the liftoff is achieved by annealing in vacuum or flowing oxygen. In this case, the O required for etching of the graphitic layer is also supplied internally by the implantation. This liftoff method, combined with well-established homoepitaxial growth processes, has considerable potential for the fabrication of large area single crystalline diamond sheets.

Transient absorption spectra of ion-implanted Si nanocrystals (NCs) exhibit two picosecond photoinduced absorption features, attributed to carriers in NC quantized states (high-energy band) and Si/SiO2 interface states (low-energy band). Fast relaxation of the high-energy band indicates that populations of quantized states are short lived and decay on the sub-10-ps time scale due to efficient surface trapping. This shows that the red emission in our samples is not due to carriers in quantized states but rather is a result of deactivation of surface traps.

We present observations of optical second-harmonic generation (SHG) from silicon nanocrystals embedded in SiO2. SHG sensitivity to Si/SiO2 interface states, charge on the nanocrystals, and particle density gradients is demonstrated. SHG is proven to be a powerful noncontact nondestructive diagnosis tool for characterization of Si-nanocrystal-based devices and materials.

The formation of supersaturated substitutional alloys by ion implantation and rapid liquid-phase-epitaxial regrowth induced by pulsed laser annealing has been studied using Rutherford backscattering, ion channeling analysis. Group-III (Ga, In) and group-V (As, Sb, Bi) dopants have been implanted into single-crystal silicon at doses ranging from 1×1015 to 1×1017/cm2. The samples were annealed with a Q-switched ruby laser (energy density ∼1.5 J/cm2, pulse duration ∼15×10−9 sec). Ion channeling analysis shows that laser annealing incorporates these dopants into substitutional lattice sites at concentrations far in excess of the equilibrium solid solubility. Channeling measurements indicate the silicon crystal is essentially defect free after laser annealing. Also values for the maximum dopant concentration (Cmaxs) that can be incorporated into substitutional lattice sites are determined for our annealing conditions. Dopant profiles determined by Rutherford backscattering are compared to model calculations which incorporate both dopant diffusion in liquid silicon and a distribution coefficient from the liquid. It is necessary to assume an interfacial distribution coefficient (k′) far greater than the equilibrium value k0 to fit the experimental data. The relationship of Cmaxs and k′ to the formation of these supersaturated alloys is discussed.

We have studied optical properties of CdS nanocrystals formed by sequential Cd+ and S+ ion implantation into Al2O3 matrices. Two bands related to free excitons in the wurtzite CdS are clearly observed in the absorption spectrum at low temperatures. Efficient photoluminescence (PL) appears near the absorption edge. At high temperatures, the band edge PL band consists of two components. One is the free-exciton emission with a short lifetime (several hundreds of picoseconds), while the other is the bound exciton emission at shallow localized states with a long lifetime (several nanoseconds). The temperature dependence of the band gap energy has been determined for wurtzite CdS nanocrystals. Spectroscopic analysis shows that high-quality compound semiconductor nanocrystals are fabricated by the ion-beam synthesis technique.

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