Abstract-Fermi-level pinning phenomena due to DX centers in AlGaAs/GaAs HEMT's are analyzed using two-dimensional numerical simulation based on a drift-diffusion model. A DX center model is introduced assuming Fermi-Dirac statistics for ionized donor density with the aluminum mole fraction dependence of the deep-donor energy level. The calculated results reveal that the decrease in transconductance of AlGaAs/GaAs HEMT's in a high gate-bias region is caused by the existence of DX centers. This is because the Fermi level is pinned at deep donor levels in the n-AIGaAs layer. Furthermore, the superiority of AlGaAs/InGaAs pseudomorphic HEMT's is discussed in terms of the Fermi-level pinning.

The chemical reaction of residues formed on a quartz surface in an electron cyclotron resonance plasma during the etching of Al and resist film by Cl2 and BCl3 plasma was characterized in situ by infrared reflection absorption (IRA) spectroscopy and quadrupole mass spectrometry (QMS). The plasma was generated in a chamber with a structure similar to a conventional production machine. Incident ions and molecules impacting onto a quartz surface at the chamber wall were analyzed by QMS. Then the residue formed on a quartz film on a sample mounted on the chamber wall was analyzed by IRA spectroscopy. The residue was identified as B2O3 which is formed by incident boron chloride ions that diffuse down through the B2O3 residue to the quartz surface and, there, thermally react with OH in the quartz. The residue film produced on the quartz surface could be identified by etching a 1-μm-thick Al film ten times at the etching rate of 12 nm/s. This combination of IRA and QMS is a promising technique for refining on-line etching by residue control.

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Electron tomography has rapidly developed in the last decade with the progress of modern computationally controlled electron microscopy and the development of algorithms for the Radon transformation and image processing with interpolation [1]. On the other hand, electron holography has been one of the standard techniques for observing phase maps of electron waves since the commercialization of the field emission electron gun. The technological combination of tomography and holography has also led to elucidation of the distributions of the mean inner potential of materials [2]. In the case of the magnetic field, the component B y parallel to the rotation axis (see Fig. 1) can be calculated from the phase shift Δ y by using the conventional tomography algorithm [3], but the other two components (B x , B z) perpendicular to the rotation-axis cannot be calculated, because the two components are mixed together with a rotation angle θ. In the case of a magnetic field in free space, however, the phase shift Δ θ projected to the optical axis is described simply [4] as Eq. 2, for which B x and B z can be separated.

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