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Notes: We have studied the near-surface stoichiometry profiles of GaAs wafers subjected to rapid thermal annealing in a forming gas environment using the Rutherford backscattering (RBS) technique with a 33-MeV 16O beam. Our measured profiles quantify the extent of arsenic loss at uncapped wafer surfaces for high-temperature anneals. We have observed that a two-temperature step anneal results in a stoichiometry profile which is nearly RBS indistinguishable from that of an unannealed wafer.

Notes: Thin TiN layers have been successfully produced by reactive evaporation combined with rapid thermal annealing. Their stoichiometry as a function of depth has been measured by elastic recoil detection combined with time-of-flight. It is shown that this technique is the most appropriate for stoichiometry determination of TiN layers.

Notes: This article demonstrates that the exposure of a TiN barrier to an ex situ oxygen plasma results in a more stable TiN/AlSiCu interface up to temperatures of 600 °C as shown by the time-of-flight elastic recoil detection measurements. A quaternary phase diagram of the Al–Ti–O–N system was calculated in the range of temperatures between 450 and 550 °C and suggests that the stabilization of the TiN/AlSiCu interface is possible since oxidized TiN reacts with Al to form AlN, TiAl3 and Al2O3 at the interface. A Ti/TiN/(oxygen plasma exposure)/AlSiCu/TiN contact metallization in 1.2-μm-diam and 1.4-μm-deep straight wall contacts to 0.2-μm-deep N+ and P+ diffusions, to gate polysilicon as well as to capacitor polysilicon shows stable electrical results even after a [(450 °C, 60 min)+(500 °C, 60 min)+(550 °C, 60 min)] combined thermal stress. © 1996 American Institute of Physics.

Notes: The stability of TiN barriers deposited between Si or SiO2 substrates and AlSiCu metallic alloy contacts was investigated as a function of the sintering temperature and of the application of an oxidation step to the barrier. It was found that Al penetrates the barrier during the sintering at 450 °C for 1 h, which also results in the diffusion of Ti inside the Al alloy. This mutual interdiffusion increases with temperature but when oxygen is present at the barrier surface, the intensity of diffusion processes decreases considerably. It is also established that the barrier remains more stable on SiO2 than on the Si substrate. It is suggested that the better reaction resistance of oxidized TiN compared with oxygen-free nitride may be due to the blocking of fast-diffusion paths of Al diffusion by oxygen and subsequently the formation of Al2O3, AlN, and TiAl3 phases during sintering. © 1996 American Institute of Physics.

Notes: Soft NiFe-Permalloy fibers and ultrasoft NiCo-based amorphous fibers, having a circular cross section with 30–40 μm in diameter, have been cast by melt extraction. The fibers have been driven by a sinusoidal current with 20 mApp constant amplitude and frequencies from 0.1 to 100 MHz. Both longitudinal and transverse giant magnetoimpedance effects have been observed in these fibers. The longitudinal GMI effect at 30 MHz was 60% in ultrasoft (NiCo)70FeSiBMn fibers for a saturating field of about 7 kA/m. The same effect was found at 10 MHz frequency for Permalloy fibers for a larger saturating field (20 kA/m). The transverse GMI effect was smaller (≈35% for NiCo and ≈20% for NiFe), and showed a maximum at low frequency (3 MHz). The magnetic field responses of the fibers are quadratic. An inverse effect of 10%–30% was observed for both types of fibers in longitudinal as well as in transverse field responses at high current frequency and low field strength. All of the observed effects could prove to be very useful for a new generation of high-sensitivity magnetic field sensors. © 1996 American Institute of Physics.

Notes: TiN layers prepared by reactive evaporation and rapid thermal annealing were tested as diffusion barrier between Al and Si. First, Rutherford backscattering spectroscopy (RBS) analysis of Al/Ti(N)/Ti/Si and Al/Ti(N)/Si multilayer structures showed that Si does not diffuse out up to a sintering temperature of 550 °C. However, as the temperature increases beyond 450 °C, Al starts to react with TiN. This reaction leaves less than half the TiN original thickness after a 30 min anneal at 550 °C. The RBS results indicate that TiN, crystallized at a temperature around 850 °C, forms a good barrier between Al and Si. Electrical measurements on various microelectronic devices were performed to verify this. Annealing of Ti(N) at 900 °C leads to a breakdown of p-MOS (metal–oxide–semiconductor) devices while n-MOS devices still work properly. Annealing at 800 °C gives good results on both MOS types except that the contact resistance of a p-type resistor is higher than desired. The electrical circuit failure is mainly due to dopant loss from the active area of the device into the titanium silicide which forms during the rapid thermal annealing at 800 or 900 °C of the deposited Ti(N) layers. © 1996 American Institute of Physics.

Notes: Thin TiN layers have been successfully produced on Si and SiO2 by reactive evaporation combined with rapid thermal annealing. Results of composition, resistivity, and stress measurements on these layers are reported. The TiN layers have a resistivity around 40 μΩ cm and a high stress of between 1 and 6 GPa. The composition ratio of nitrogen to titanium, measured by elastic recoil detection (ERD), combined with time-of-flight, was found to vary between 0.8 and 1.0 depending on the deposition conditions. In addition to the stoichiometry determination, ERD also clearly shows the presence of a TiSi2 layer between the TiN and the Si substrate. It is also shown that good TiN layers can be produced by reactive evaporation for nitrogen partial pressures between 1.0 and 2.0×10−5 mbar and for titanium evaporation rates between 0.3 and 0.5 nm/s.

Notes: The emission spectra from sulfurized p-InP annealed at temperatures below 300 °C are compared with those from untreated samples annealed under the same conditions. The unsulfurized samples show a VP related emission band at 1.14 eV whose intensity increases linearly with annealing temperature. The sulfurized samples exhibit an emission band at 0.94 eV attributed to a SP deep level. Both bands disappear when a layer of 20 A(ring) is chemically removed. This shows that both VP and SP formation is limited to a few atomic surface layers.

Notes: An analysis and discussion of the device physics for the quantum-confined Stark effect based on barrier height and band alignment considerations is presented. It identifies two important design principles for band structure engineering of the multi-quantum well stack: (1) Due to the counterbalance relationship between field-induced redshift and field-induced polarization of the quantum well eigenstates, design strategies must look to attain an optimal balance or compromise between a minimum drive field and maximum absorption coefficient change. This can be achieved with an appropriate choice of the valence band discontinuity. (2) In III–V semiconductors, the strong asymmetry in the field response of the conduction and valence band eigenstates is due directly to the asymmetry of the conduction and valence band effective masses. As a result, optimum device performance is obtained by using a heterostructure with a disproportionately large conduction band offset to compensate the effective mass asymmetry and balance the field-induced wave function leakage in the conduction band to that in the valence band. The relative wave function leakage between conduction and valence bands is compared by examining tunneling currents through the quantum well barriers as a function of the electric field and barrier height. For conduction and valence band effective masses of, respectively, 0.055 and 0.5 times the free electron mass, the optimal band alignment requires a conduction band discontinuity 3–9 times greater than the valence band discontinuity. Applying these design principles for high speed, low drive voltage optical modulators shows that the overall performance of these devices may be improved by using a combination of balanced band alignments and low valence band barriers. The low valence band barriers reduce the drive field required to operate the devices, which has direct effects upon the drive voltage, device capacitance, attenuation coefficient, and optical coupling and propagation losses. The analysis and discussion is supported by experimental modulation depth and drive field data obtained from strained-layer multiple quantum well InAsP/InP and strain-compensated InAsP/InGaP optical modulators fabricated with layers grown on InP(001) by metalorganic vapor phase epitaxy. © 1998 American Institute of Physics.