W. Katz

Ge diffusion at Ge/GaAs heterojunctions

Interdiffusions at Ge/GaAs heterojunctions formed by the epitaxial deposition of Ge films on GaAs have been studied for temperatures ranging from 650–800 °C. The diffusion coefficients of Ge in GaAs have been found to be 1.6×10−5 exp(−2.06/kT) for Cr: and Si:doped GaAs. After the diffusion heat treatment, Ge was found to be p type and ohmic.

Low‐temperature sintered AuGe/GaAs ohmic contact

Ohmic contacts with low specific‐contact resistivity and with contact morphology superior to conventionally alloyed contacts have been made to n‐type GaAs by sintering AuGe films on GaAs at 315 and 330 °C for several hours. The specific contact resistivities were found to decrease with sintering time and values as low as 3×10−6 Ω cm2 were obtained for contacts on GaAs (doped with silicon to a concentration of 1018 cm−3) after sintering at 330 °C for 1 h. Secondary Ion Mass Spectrometry profiling of the sintered films has been used to show that the ohmic contact formation is due to an enhanced diffusion of Ge into GaAs.

Role of short‐circuiting pathways in reduced ZnO varistors

Electrical measurements and secondary ion mass spectrometry (SIMS) observations have been made to elucidate the mechanisms involved in the degradation of ZnO varistors at elevated temperatures in reducing atmospheres. The electrical measurements indicate that the degradation sensitivity depends to some extent on varistor composition but can be highly variable for different varistors of the same formulation and even within a given varistor sample. The SIMS data indicate that oxygen ions are highly mobile when varistors are heated above 290 °C, and it is proposed that flaws, such as microcracks in the varistors, act as conduits for oxygen at elevated temperatures. A circuit model in which a reduced varistor is characterized by short‐circuiting regions around such flaws predicts an electric field versus current density that is similar to that observed in experiments.

Reduction in the effective barrier height in PtSi-p-Si Schottky diodes by using low energy ion implantation☆

Abstract A reduction in the effective barrier height in a PtSi-p-Si Schottky diode was achieved using low energy ion implantation to introduce a shallow p + layer on a p-Si substrate. After the Schottky diode had been implanted with 3 keV 11 B + ions to a dose of 4 × 10 12 ions cm -2 , the barrier height was observed to decrease from 0.26 to 0.16 eV. The reduction in barrier height correlated well with the boron concentration found at or near the PtSiSi interface.

The effects of PtxSi growth on the redistribution of p-type dopants in silicon

Abstract The redistribution of p-type dopants (boron and indium) during Pt x Si growth was studied as a function of annealing time using secondary ion mass spectrometry. It was found that both boron and indium atoms redistribute into the silicide during a thermal anneal. Initially, the dopant becomes trapped at the Pt x SiSi interface and concomitantly getters to defect sites located at the moving PtPt x Si interface. Even after silicide formation is complete, the dopant continues to out-diffuse to the surface via an enhanced mechanism due to defects and/or grain boundaries. Finally, no evidence for a “snowplow” effect was observed for either boron or indium at the implant dose of 2 × 10 13 ions cm −2 .

Contact resistivity and dopant activation in pulsed-laser-annealed AuGe/GaAs contacts

Abstract The electrical activation of dopants in the heavily doped GaAs layers of pulsed-laser-annealed AuGe/GaAs contacts were deduced and shown to be higher than that in bulk GaAs. The electrical activation is shown to decrease towards the GaAs surface and is used to explain the previously observed minimum in contact resistivity profiles in terms of arsenic loss during the laser annealing. These results will be shown to be consistent with observations of concentration-dependent activation in bulk GaAs.

Quantitative analysis in chemically dissimilar matrices by secondary ion mass spectrometry

Abstract The ability of secondary ion mass spectrometry (SIMS) to achieve detection limits of a ppm or less for many of the elements throughout the periodic table makes SIMS one of the most sensitive characterization techniques available to the materials analyst. However, due to the wide variability of secondary ion yields, the ability to perform quantitative analysis has long been hampered by the requirement of a standard for the matrix being examined. We report here for the first time the ability to determine the boron concentration in a series of thermally grown PtSi layers on Si without the use of a separate standard for each matrix. This technique should be generally applicable to any material containing two dissimilar, coupled matrices. This study describes in detail the method used for quantification and its applications.

Surface and Subsurface Morphology of Laser Bean Annealed Auge/Gaaa Ohmic Contacts

A study of the pulsed laser annealing of AuGe films on GaAs using a Nd:YAG laser has revealed differences between the surface and subsurface morfhologies. At laser energy densities lower than 1.1 J/cm 2 , the surface retained the smooth, “golden” appearance of deposited AuGe films, while evidence of damage was observed below the surface. At higher energy densities, surface damage was observed. SIMS profiles of Ga and As in the AuGe layer and a laser heating model have been used to explain the presence or absence of damage in terms of the outdiffusion of As and Ga through the laser created melt which leads to the presence or absence of Ga and As at the surface and below the surface.

Reduction in the Effective Barrier Height in Ptsi-P-Si Schottky Diodes by Using Low Energy Ion Implantation

A reduction in the effective barrier height in a PtSi-p-Si Schottky diode was achieved using low energy ion implantation to introduce a shallow p + layer on a p-Si substrate. After the Schottky diode had been implanted with 3 keV 11 B + ions to a dose of 4 × 10 12 ions cm −2 , the barrier height was observed to decrease from 0.26 to 0.16eV. The reduction in barrier height correlated well with the boronconcentration found at or near the PtSi-Si interface.