Integration of epitaxical and colloidal semiconductor nanostructures into hybrid structures can potentially open unprecedented functionalities and applications. We present here some results of a study of the structural and optical nature of adsorbed InAs nanocrystal quantum dots (NCQDs) on GaAs(001) substrates containing buried nanostructures, providing the first evidence of excitation transfer from NCQDs to the substrate. Results are also presented for the overgrowth of GaAs on the InAs NCQDs, addressing the all important issue of approach to removal of the chemical contamination left behind by the solvent during adsorption of the NCQDS. It is shown that high structural and optical quality buried integrated structures are feasible, thus opening a new field of investigation.

Short-period superlattices consisting of nanocrystalline Si wells and amorphous SiO2 barriers were analyzed using various structural (transmission electron microscopy, atomic force microscopy, and x-ray diffraction) and optical (Raman scattering and spectroscopic ellipsometry) characterization techniques. We observe parallel layers containing polycrystalline Si wells, primarily with <111> orientation, and an interesting surface morphology due to sputtering damage. Raman spectra show a redshift and broadening due to finite-size effects. The ellipsometry data can be described using the effective medium approximation (since the superlattice period is much shorter than the wavelength of the optical excitation) or a superlattice approach based on the Fresnel equations with a polycrystalline Si dielectric function.

With the continuing push for reduction in the device dimensions into the deep sub-u,m dimensions, the critical need for physical and electrical characterization on this sub-μ,m scale is evident. The National Technology Roadmap has identified need for two-dimensional (2D) dopant/carrier profiling with a spatial resolution of 10 nm. Though current techniques used for dopant profiling such as secondary ion mass spectroscopy (SIMS) and spreading resistance profiling (SRP) have a high sensitivity, these offer good resolution only in the depth direction. The spatial resolution in the lateral direction in these techniques is limited to several tens or hundreds of microns. To acheieve the required lateral spatial resolution different scanning probe based techniques have been explored. One of the most promising of these class of techniques is scanning capacitance microscopy (SCM). In SCM a conductive atomic force microscope (AFM) probe tip is scanned across the surface and simultaneously an a.c. bias is applied between the tip and the sample.

Scanning capacitance microscopy (SCM) is currently one of the most promising tools for twodimensional carrier profiling. This technique, based upon atomic force microscope (AFM) operated in the contact mode, uses a conductive probe which is scanned over the semiconductor surface. The conductive probe, oxide on the surface of the semiconductor, and the semiconductor substrate form a metal-oxide-semiconductor (MOS) structure. An a.c. bias is applied to the tip and the capacitance of the MOS structure is monitored. The a.c. bias changes the depletion of carriers in the semiconductor and thus the total capacitance of the structure. The maximum capacitance of the MOS structure is obtained when the semiconductor is in accumulation and the total capacitance of the structure is the capacitance of the semiconductor surface oxide. The minimum capacitance is obtained when the semiconductor region under the tip is in inversion. Since SCM the output signal is proportional to the differential capacitance, to get a high signal we need to maximize the difference between the maximum and minimum in the total MOS capacitance.

We measured the ellipsometric response from 0.7–5.4 eV of c-axis oriented AlN on Si (111) grown by molecular beam epitaxy. We determine the film thicknesses and find that for our AlN the refractive index is about 5–10% lower than in bulk AlN single crystals. Most likely, this discrepancy is due to a low film density (compared to bulk AlN), based on measurements using Rutherford backscattering. The films were also characterized using atomic force microscopy and x-ray diffraction to study the growth morphology. We find that AlN can be grown on Si (111) without buffer layers resulting in truely two-dimensional growth, low surface roughness, and relatively narrow x-ray peak widths.