SEM and EMPA analysis of impurities related to GaAs substrates and MBE grown GaAs layers

Classified abstracts 6628-~636 the brittle to plastic transition takes place around 1500°C. Below this temperature, the helium accumulation at the grain boundaries and the organization of bubbles into strings within grains are responsible for inter- and intragranular microcracking respectively. Above this temperature, because of plasticity, the cracking disappears. But the swelling increases markedly. At 1720°C, for instance, while less than 1% of the implanted helium is retained by the sample, each helium atom is associated with I00 vacancies within tridimensional bubbles responsible for a swelling of 1% per percent of implanted helium. T Stoto et al, Radiat Effects, 105, 1987, 17-30. 32 6628. Microstructural change of AI on H implantation Modifications to the subsurface layer of AI on 25 keV H~ ion implantation to fluences of 4 × 1017 to 2 × 10 TM H + / c m 2 at room temperature were investigated by transmission electron microscopy (TEM) and elastic recoil detection (ERD) with 1.5 MeV He +. N u m e r o u s bubbles ranging in diameter from 50 to 1000 ,~ were observed with a sharp peak at 120 A. irrespective of the ion fluence. Stereomicroscopic observations revealed the depth distribution of the bubbles. At fluences greater than 6 × l017 H + / c m 2, a lateral layer of lower density compared with matrix was observed and named "Swiss cheese structure" since its estimated structure is similar to Emmental cheese containing m a n y holes. This Swiss cheese structure causes the formation of new layers on a free surface, and plays a precursor role for blistering. Hydrogen depth profiling with E R D was performed on every specimen revealing the collapse of the implanted hydrogen profile due to the formation of the Swiss cheese structure. K Kamada et al, Radiat Effects, 103, 1987, 119 133. 32 6629. Phase stability of Cu--Ni-Fe alloys under ion irradiation Ion irradiation of C ~ N i Fe alloys has been carried out in order to investigate the counteraction of cascade mixing and radiation-enhanced diffusion in a periodic two-phase structure. It was found that heavy-ion irradiation (Cu, Ne and N) causes dissolution of the precipitates. Proton irradiation, however, accelerates the process of decomposition and coarsening. The microstructural evolution is determined by displacement rate and temperature. The size of the precipitates influences its stability--a coarser structure dissolves only under higher displacement rates. A model is proposed which interprets these effects as a competition between cascade mixing and the recovery of the two-phase structure by radiationenhanced interdiffusion. F r o m the equalization of both mechanisms, the size of the volume dissolved by a cascade is deduced. This volume decreases with increasing precipitate size due to the low efficiency of mixing for equal sizes of precipitates and cascades. The similarity of results for the heavy ions is explained on the basis of calculated damage spectra. U Sebeuer, Radiat Effects, 105, 1987, 85 106. 32 6630. Radiation damage and annealing in graphite implanted with Hz+ and Mo + Radiation damage due to H~ and Mo + implantation into hot-worked pyrolytic graphite and into single-crystal graphite flakes has been studied using 1-MeV4He + ion channeling. The implant energies used, 35 keV for H~ and 120 keV for Mo +, yielded ranges of about 1600 and 600 ~ , respectively. For H2 implantation, a partially crystalline surface layer remains after a fluence of 2 x 10 t6 H/cm2; this layer is completely disordered at 2 × 1017 H/cm 2. At higher hydrogen fluences a surface layer exfoliates. For Mo implantation the disorder introduced at a fluence of 5 x 10 ~4 M o / c m ~ is sufficient to prevent channeling throughout the range. For both implant species, complete recrystallization of samples disordered up to the surface occurs for annealing only at temperatures above 2800 K. If a surface layer remains crystalline after implantation, recrystallization proceeds both from the bulk and from the surface, and crystallinity is restored at 2300 K. While hydrogen is known to be released at temperatures between 1100 and 1500 K, Mo remains within its original range distribution up to the temperature of complete recrystallization. At a temperature of 2300 K an ordering of the implanted Mo atoms with respect to the c axis is observed, indicating short-range migration within the range distribution. At 2800 K no more Mo could be found in the analyzed surface layer. J Roth et al, J appl Phys, 63, 1988, 2603-2608. 32 6631. Subharmonic responses of ion-implanted arrays reflecting magnetostatic forward volume waves A subharmonic response at twice a fundamental wavelength was observed 510

by refection of magnetostatic forward volume waves on 45 ° oblique incidence ion-implanted arrays. The waves were reflected by two nonperiodic arrays and traveled along a U-shaped path. Each array made o f 25 bars with an average fundamental wavelength of 69 # m was implanted with 3 x 1015 '~B + ions per cm 2 at 150 keV. For such a dose the damaged propagation material was nonferrimagnetic and the subharmonic reflection is attributed to an energy storage consequence of the magnetic field distortion introduced by the crystalline-nonferrimagnetic materialinterface corrugation. It vanished after an annealing at 620°C without great degradation of the fundamental wavelength reflection level. P Hartemann, J appl Phys, 63, 1988, 2742-2746.

33. M O L E C U L A R B E A M E P I T A X Y 33 6632. S E M and E M P A analysis of impurities related to GaAs substrates and M B E grown GaAs layers Distribution of impurities on heat-treated G a A s substrates and layers has been investigated by SEM in conjunction with E M P A analysis. The layers were grown by M B E on both undoped and c h r o m i u m doped semiinsulating substrates. Comparisons of the electron micrographs and the corresponding E M P A spectra suggest that heating causes the impurities, namely Si, Fe and Cr, to diffuse out from the substrate and redistribute themselves on the layer surface resulting in characteristic defect patterns. No effects due to arsenic over-pressure and/or presence of carbon in the growth environment were apparent, as suggested by previous studies. N J Kadhim and D Mukherjee, Vacuum, 38, 1988, 11 12. 33 6633. Magnetoreflectivity study of excitons in molecular-beam epitaxially grown Zn~_ ~Fe,,Se crystals Single-crystal films of (001) Zn~ xFexSe (x = 0.017, 0.027, and 0.043) grown by molecular-beam epitaxy on (001) G a A s have been studied by magnetoreflectivity over the temperature range 4 77 K in magnetic fields up to 8 T in the spectral region near the band gap of 2.8 eV. The excitonic transitions were observed in both Faraday and Voigt geometries, permitting the determination of the Zeeman splitting of the exciton states in both the conduction and valence bands, and showed the Zeeman splitting precisely reflects the magnetization obtained earlier in bulk crystals. Combined with that magnetization data, these splittings yielded the electron/ Fe + exchange energy for both bands. The Fe-concentration dependenceof the data showed the Fe2+-Fe 2+ antiferromagnetic exchange clustering becomes evident for x > 0.02. The temperature dependence of the spectra confirm that this system is a Van Vleck paramagnet and the spinorbit splitting of the lowest Fe 2+ crystal-field states is 2.2 meV. X Liu ct al, J Vac Sci Technol, A6, 1988, 1508 1510. 33 6634. Gallium arsenide on silicon : a review Recent advances in the performance of electronic and optical devices fabricated in G a A s on Si substrates have led to the consideration of this hybrid technology for novel applications. These range from simply replacing G a A s substrates with large area, light weight, high strength Si substrates to highly desirable integration of G a A s and Si devices and circuits on the same chip. Other applications include the use of G a A s as an interlayer for subsequent growth of long wavelength c o m p o u n d semiconductors (III-V and II VI) for focal plane arrays with built-in Si signal processors. H Morko¢ et al, Solid State Technol, 31, 1988, 71 76. 33 6635. Silicon epitaxiai growth for advanced device structures The attainment of narrow (epi/substrate) transition widths with minimal autodoping is crucial to advanced bipolar and BiCMOS device design. The four basic epi processes described herein are Low Temperature/Low Pressure (LT/LP) epi growth, High Temperature/Low Pressure (HT/LP) epi growth, Selective Epitaxial Growth (SEG), and Epi/SO1 technology. These processes yielded high quality CMOS, bipolar, and BiCMOS structures down to 775uC and 7.5 torr using Sill 2C12 in cylindrical epi reactors, John Borland et al, Solid State Technol, 31, 1988, l 11 119. 33 6636. GaAs on Si technology High quality G a A s layers were grown on Si(100) wafers by the heat treatment of the substrates at high temperatures and a subsequent twostep growth sequence at low temperature and then at the conventional