Amorphous carbon films grown with fluorohydrocarbons can be grown to have dielectric constant values around 2.0. The behavior of these films when subjected to thermal excursion is studied. We have investigated material deposited in an ECR plasma, and find that the F:H ratio of the gas mixture is a good guide to material properties. Films deposited at 5°C were placed in a vacuum chamber at 400°C as long as 60 minutes. The film thickness, dielectric constant, and infrared absorption spectrum change with the F:H ratio of the incoming gas and thermal cycling. It was found that the dielectric constant and loss tangent decrease upon heating and that there is an apparent increase in C=C groups. As expected, as the F:H ratio increases, the dielectric constant and thermal stability decrease. Good thermal stability is shown for F:H ratios of 1.5, which result in films with a dielectric constant of ∼2.4 after heating.

We report a surface-normal optically controlled optoelectronic modulator made from a reversed biased p-i (multiple quantum well)-n GaAs/AlGaAs structure with ultrathin barriers (5 Å) whose recovery time is based on diffusive conduction. Modulation of reflectivity from 0.3 to 0.6 and back again in about 50 ps was demonstrated using a 750 fJ control pulse at 855 nm. We also demonstrated modulated changes in power greater than the control pulse power—a type of signal gain—by a factor of 1.8-to-1. Strong changes in reflectivity combined with low required control power make this device potentially useful for high-speed switching arrays in such applications as time division demultiplexing.

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Two high speed diffusion mechanisms in semiconductor heterostructures, diffusive conduction, and giant ambipolar diffusion, are compared and shown to be nearly equivalent descriptions of the same physical process. Fundamental limits of this process are discussed.

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