Height-selective etching for regrowth of self-aligned contacts using MBE
Advanced III-V transistors require unprecedented low-resistance contacts in order to simultaneously scale bandwidth, f max and f t with the physical active region [M.J.W. Rodwell, M. Le, B. Brar, in: Proceedings of the IEEE, 96, 2008, p. 748]. Low-resistance contacts have been previously demonstrated using molecular beam epitaxy (MBE), which provides active doping above 4 x 10 19 cm -3 and permits in-situ metal deposition for the lowest resistances [U. Singisetti, M.A. Wistey, J.D. Zimmerman, B.J. Thibeault, M.J.W. Rodwell, A.C. Gossard, S.R. Bank, Appl. Phys. Lett., submitted]. But MBE is a blanket deposition technique, and applying MBE regrowth to deep-submicron lateral device dimensions is difficult even with advanced lithography techniques. We present a simple method for selectively etching undesired regrowth from the gate or mesa of a III-V MOSFET or laser, resulting in self-aligned source/drain contacts regardless of the device dimensions. This turns MBE into an effectively selective area growth technique.
Characteristics of AlGaAs/GaAs heterostructures grown by migration-enhanced epitaxy at high temperatures
Migration-enhanced epitaxy at relatively high temperatures has been reported to deteriorate the crystal quality and photoluminescence characteristics of AlGaAs/GaAs heterostructures, and we investigated this phenomenon by comparing the AlGaAs/GaAs heterostructures grown by migration-enhanced epitaxy with those grown by conventional molecular beam epitaxy. The single-quantum-well structures grown by migration-enhanced epitaxy at 580 and 660 degrees C exhibited defect-induced photoluminescence. Consideration of the surface equilibrium suggests that this degradation is caused by the evaporation of As from the growing surface, and we found that this can be prevented by applying a supplementary As beam during the deposition of Ga or Al or both. This supplementary beam is much less intense than that needed to sustain the growth by molecular beam epitaxy (only 5% at 580 degrees C). The photoluminescence degradation reported by others, however, is too extensive to be reproduced in our experiment even considering the shortage of As on the growing surface. Their result may be caused by an additional contamination not directly related to the migration-enhanced epitaxy process.
A model for predicting heat transfer through gypsum‐board/wood‐stud walls exposed to fire
To facilitate the development of cost-effective and flexible design options there is a need to develop models to predict the fire resistance of wood-frame building assemblies. Such assemblies often derive much of their fire resistance from a protective membrane composed of gypsum board. A simple two-dimensional computer model is presented to predict heat transfer through gypsum-board/wood-stud walls exposed to fire. Input data for the thermophysical properties of gypsum board were measured exploying standard bench-scale tests. Input data for wood were selected from the literature. Small-and full-scale fire resistance tests were conducted on gypsum-board/wood-stud wall assemblies to provide data for the validation of the model. The model is shown to predict heat transfer through these walls rather well.