John F. Knudsen

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.

Linearity of Response of Ultrafast Photoconductive Switches: Critical Dependence Upon Ion-implantation and Fabrication Conditions

We have measured the responsivity of photoconductive switches as a function of electrical bias and optical intensity. The switches were fabricated using standard 50 z microstrip transmission line technology on silicon-on-sapphire wafers. Picosecond photoconductive response was produced by self-implanting the silicon to reduce the carrier lifetime. Although all of the switches tested possessed ultrafast response, the linearity of response with electrical bias and optical intensity was dependent on the order of the metallization and ion-implantation processing steps during the fabrication procedure. Switches fabricated using processes reported in the literature to yield switches with linear response (Ohmic contacts) instead yielded switches with nonlinear response (Schottky contacts). Furthermore switches fabricated using processes reported in the literature to yield switches with nonlinear response (Schottky contacts) instead yielded switches with linear response (Ohmic contacts). We discuss the effects of...

Distribution of Boron Atoms in Ion Implanted Compound Semiconductors

The nondestructive neutron depth profiling (NDP) technique was used to measure the boron (10B) distributions in GaAs, CdTe, Hg0.7Cd0.3Te, and Hg0.85Mn0.15Te after multiple energy ion implants. The NDP results are found to be in good agreement with the theoretical ion ranges obtained from Monte Carlo computer simulations. Only minor changes in the boron profiles were seen for the chosen annealing conditions.

X-ray, XTEM and RBS analysis of recrystallized ion beam amorphized CVD Si

Ion beam modification of materials has been used for the formation of high quality single-crystal silicon (c-Si) over oxide, for high speed CMOS device applications. In the lateral solid phase epitaxy (LSPE) technique, thin c-Si layers (typically 300 nm) are formed by ion beam amorphization of a low pressure chemical vapor deposited (LPCVD) polysilicon layer over an oxidized Si wafer in which seed windows have been opened in the oxide. A c-Si layer is formed by LSPE from the single-crystal substrate up and over the thermal oxide adjacent to the oxide window for distances of up to 4 μm beyond the window boundary. We have obtained high quality 〈100〉 single-crystal silicon by conversion of polycrystalline LPCVD-Si, using rapid thermal annealing (RTA) followed by ion implantation amorphization and subsequent thermal recrystallization. Amorphization of LPCVD deposited poly-Si to a depth of 300 nm is achieved by LN2 temperature implants of 5 × 1014 cm−228Si+ at 80 and 230 keV each. The crystallinity upon thermally induced recrystallization is evaluated by X-ray rocking curves, X-ray Read camera, RBS and cross-sectional transmission electron muscopy (XTEM).

Picosecond transient photoreflectance measurements of ion-implanted GaAs

Abstract We have used picosecond transient reflectance techniques to measure the near-surface characteristics of ion-implanted GaAs. These non-destructive laser-based diagnostic techniques allow measurement of the modification of near-surface properties at relatively low implant fluences. Photothermal phenomena dominate these results and yield important information concerning the extent of implant-induced materials modification.

Native silicon oxide agglomeration prior to solid-phase epitaxy using rapid thermal processing

The effect of process parameters on the quality of recrystallized material using rapid thermal processing (RTP) was evaluated. Both X-ray rocking curve and Read camera analysis were used to verify the crystalline quality of the regrown material. It is shown that RTP is a viable method for agglomerating the interfacial oxide at a silicon/polysilicon boundary before epitaxial growth. The material quality was observed to improve with increasing RTP time and temperature cycles. The optimum thermal anneal cycle was 600 degrees C for 18 h and 800 degrees C for 3 h. The improvement in the number of defects over the previously used ion implantation process is about two orders of magnitude.<<ETX>>

X-Ray and Raman Topographic Studies of Gaas Implanted With 28 Si + and Pulsed Laser Annealed

Double-crystal x-ray diffraction and topography, along with Raman spectroscopy and topography are used to study lattice reconstruction and carrier activation for pulsed laser annealed Si implanted GaAs. Although lattice strain is essentially eliminated, along with the production of carrier concentrations to about 3×10 19 cm .3 at the center of laser annealed spots, incomplete removal of implant induced disorder and little dopant activation are observed in surrounding areas. Correlations of Raman and x-ray topographs suggest that concentric regions of partial melting, but without epitaxial regrowth, occur in the periphery of the laser annealed spots.

Nonlinear Optoelectronic Effects In Ultrafast Photoconductive Switches

Ultrafast photoconductive switches have been used to generate electrical waveforms and to sample both electrical and optical waveforms. Widespread use of these switches is anticipated in conjunction with optical interconnects. We present results of an investigation into the electrical bias dependence and optical intensity dependence of the responsivity of photoconductive switches. The switches were fabricated using standard 50 0 microstrip transmission line technology on silicon-on-sapphire wafers. Ultrafast photoconductive response was produced by ion-implanting the silicon to reduce the carrier lifetime. We find that the performance of the switches is critically dependent upon wafer fabrication and ion-implantation conditions. While all of the switches tested possessed picosecond-scale response, the linearity of response with electrical bias and optical intensity was dependent on the order of the metalization and ion-implantation processing steps. In contrast to reports in the literature, fabrication processes which were expected to yield switches with ohmic contacts instead yielded switches with nonlinear response. We discuss the contributions of nonlinear absorption, carrier transport, charge screening and the build-up of space charge as well as other geometrical effects.

Picosecond optical measurements of the properties of heavily carbon-implanted silicon

Abstract We have used picosecond transient photoreflectance techniques to measure the near-surface characteristics of unimplanted silicon and of silicon heavily implanted with carbon. These laser-based diagnostic techniques are non-destructive and allow measurement of the modification of near-surface properties sensitive to both photocarrier and photothermal phenomena. Photothermal phenomena dominate these results and yield important information concerning the extent of implant-induced materials modification.

Influence of Ion-Implantation on Characteristics of Picosecond Photoconductive Switches

Ion-implantation induced amorphization has been used to modify the linearity of response of ultrafast photoconductive switches fabricated on SOS. The extent of amorphization was determined using various materials characterization techniques. TRIM-86 Monte Carlo calculations were used to model the defect densities produced by ion implantation. Linearity of response is critically dependent upon the nature of the semiconductor region under metallic contacts and the character of the response is opposite to that expected from reports in the literature.