R. C. Bowman

Optical and structural characterization of heavily boron-implanted CdTe

Abstract CdTe single crystals were subjected to multiple-energy boron ion implants with total doses up to 1.5×10 16 B + ions/cm 2 . Various diagnostic techniques were used to assess the structural and electronic properties of these crystals in their as-implanted condition and after anneals under vacuum. The degradation of crystallinity following the boron implants was clearly evident. Annealing temperatures up to 500°C were not effective to remove the damage from these heavy dose implants. The chosen boron implant conditions and annealing procedures have not produced substitutional boron donor centers. Excellent correlations were obtained for model calculations of boron projected range and implant damage profiles with the corresponding experimental parameters.

Studies of interdiffusion in Ge m Si n strained layer superlattices

We present the results on the characterization and interdiffusion behavior of GemSin strained layer superlattices (SLS’s) composed of alternating monolayers of pure Ge and pure Si. Such GemSin SLS’s were grown on top of thick relaxed GeySi1-y buffer layers so as to symmetrize the strain distribution and to maintain the pseudomorphic growth of the superlattices. Samples with different superlattice periodicities (i.e. d = dGe + dSi and different layer thickness ratios (i.e. dGe:dSi were prepared for comparison. Raman scattering spectroscopy and x-ray diffraction were used to characterize these samples. Initial results on thermal stability of these GemSin SLS’s are also reported

Structural characterization of SimGen strained layer superlattices

SimGen strained layer superlattice (SLS) structures were grown by molecular beam epitaxy on GexSi1−x buffer layers on 〈100〉 Si substrates to determine the effects of buffer layer composition, SLS thickness ratio, and superlattice periodicity, on the overall quality of these structures. X‐ray diffraction methods were used to determine how closely actual periodicities and compositions met targeted values, and to evaluate the quality of these samples. In most instances the as‐grown structures matched the targeted values to within 10%, though in some instances deviations of 20–25% in either the period or composition were observed. The quality of the SLS structures was greatly dependent on the composition of the buffer layer on which it was grown. SimGen SLS structures grown on Si‐ and Ge‐rich buffer layers were of much higher quality than SimGem SLSs grown on Ge0.50Si0.50 layers, but the x‐ray rocking curves of the SimGen samples indicated that they were far from perfect and contained moderate levels of defec...

Study of ultra-thin Ge/Si strained layer superlattice

Abstract Ultra-thin Ge/Si strained layer superlattices (SLSs) with periodicities of a few monolayers (MLs) have been successfully grown and characterized by Raman scattering spectroscopy. Structures with alternating Ge and Si layers were grown on Si substrates of different orientations. A thick 200 nm Ge 0.4 Si 0.6 buffer layer was grown prior to the growth of the superlattice to make the strain distribution of the superlattice symmetrical and thus to maintain the pseudomorphic growth of the superlattices. Folded acoustic phonon peaks observed from these Ge/Si SLS samples can be used to determine the superlattice periodicity. The observed optical phonon frequencies were found to depend strongly superlattice periodicity. A quantitative interpretation of this phenomena was presented. Subsequent annealing of these samples reveals that the transition from pure Ge and /or Si layers to Ge x Si 1− x alloy becomes more pronounced as the annealing time and temperature increase.

Raman study of Ge /Si strained layer superlattices grown on different substrate orientations

We present the growth and characterization of Ge/Si strained layer superlattices grown on different substrate orientations. Prior to the growth of the superlattices, a relaxed thick GexSi1-x buffer layer is grown on Si substrate to symmetrize the strain distribution and thus maintain pseudomorphic growth of the superlattices. The effective Ge fraction x is used to define the degree of interface mixing of these superlattices. It is found that for samples grown on the same orientaion, the degree of interface mixing is higher for samples with smaller period lengths. The samples grown on (110) and (111) substrates also have a higher degree of interface mixing than those grown on (100) substrates. The thermal stability of these Ge/Si strained layer superlattice samples is also studied.

Optical And Structural Characterization Of Boron Implanted GaAs

The effects of boron ion implants on the properties of undoped semi-insulating (100) GaAs single crystals have been studied. Raman scattering, Rutherford backscattering spectrometry (RBS) with ion channeling, double-crystal x-ray diffraction (DCD), photoreflectance spectroscopy, and electron paramagnetic resonance measurements have been used to provide a more complete description of the implant damage. Multiple energy implants with total doses up to 1.5x1016 ions/cm 2 generated uniformly damaged regions from the surface to various depths that exceed a micron. The boron implants caused substantial changes in the intensities and linewidths of the Raman spectra which were correlated with the damage indicated by the channeling measurements. Partial removal of the implant damage was observed upon annealing. While both furnace anneals at 850°C and 925°C rapid thermal anneals via quartz lamps can remove much of the lattice strain as seen by changes in the Raman and DCD results, the RBS and photoreflectance measurements indicated that considerable disorder remained.

Raman And RBS Studies Of Ion Implanted Semiconductors

Raman spectroscopy and Rutherford backscattering spectrometry (RBS) have been used to assess boron and silicon implants on the properties of single crystal silicon, GaAs, and CdTe. The behavior of these different semiconductors under identical implant conditions has been compared. Changes in the Raman optic phonon spectra reflect the extent of lattice damage caused by the ion implants as well as ability of various annealing procedures to remove this damage. The Raman results are generally confirmed by PBS ion-channeling measurements. Furthermore, these techniques are shown to provide complementary information on the distribution and nature of implant damage.