We present the theoretical foundations and implementation methods for forming GaAs compliant substrates that have a 'stretchable' lattice to be used for high quality lattice- mismatched heteroepitaxial growth. The theoretical calculations predict an increase of several orders of magnitude in the critical thickness of a film when it is grown on another thin film that has been wafer-bonded to an angularly misaligned bulk substrate. The calculations show that the increase in critical thickness is sustained even for a 3 percent lattice mismatch between the growth and the stretchable lattice. The dependence of the growth's critical thickness on a variety of parameters are presented including the bonding energy between the compliant and bulk substrates, the lattice mismatch between the growth and compliant substrates, and the thickness of the misaligned film. Thick films of In0.35Ga0.65P were grown on the compliant substrates. Bright-field transmission electron micrographs of the growth's cross-section showed no dislocations, whereas the same films grown on bare GaAs substrates produced stacking faults and threading dislocations. The concept and technology of compliant substrates may have important applications in forming optoelectronic devices of new characteristics and wavelengths.
This paper describes the wafer bonding technology and its applications to optoelectronic devices and circuits. It shows that the wafer bonding technology can create new device structures with unique characteristics and can form integrated optoelectronic circuits containing optical, electronic and micro-mechanical devices.
The new optoelectronic integrated technology--wafer bonding is described. The results of wafer bonding and applications in several new types of optoelectronic devices are presented.
How micro is laser microdissection? This study compared the spatial resolution of laser microdissection achieved by two laser systems: the ArF excimer laser which is strongly absorbed by tissue protein, and the Er:YAG laser which is strongly absorbed by tissue water. Both lasers penetrate tissue only a couple microns and are suitable for laser microdissection, and in this report the lasers ablated the outer dead-cell layer of the skin called the stratum corneum. The study involved dorsal skin sites on 8 rats for the ArF excimer and 10 rats for the Er:YAG. Ag/AgCl-gel electrodes were used to measure the passive DC resistance (R) and the active DC voltage (V) of skin sites which had received increasing numbers of ablative laser pulses (9 mJ/pulse, Er:YAG; 48 mJ/pulse, ArF excimer). About 8 pulses were required before a sudden drop in Ra and a sudden rise in V was observed. The R dropped from 4 +/- 0.2 (18) Mohm down to 1.5 +/- 0.2 (18) Mohm; mean +/- standard deviation (number of skin sites). The V was initially -56 +/- 5 mV, then dropped to -3 +/- 0.4 mV after laser ablation penetrated and destroyed the battery. The Er:YAG laser required 8.3 +/- 1.5 pulses to achieve 50% of the full change in R and V; the ArF excimer laser required 76 +/- 2 pulses. The changes in R and V per depth of tissue ablated were identical for the two lasers, despite their distinct differences in absorbing chromophore and efficiency of ablation.
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