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7288. Construction and operation of an ultrahigh vacuum chemical vapor deposition epitaxial reactor for growth of GexSi1−x
Classified abstracts 7287-7295 33 7287. Growth of boron nitride films by gas molecular-beam epitaxy Boron nitride is a thermally stable and chemically inert material with a wide bandgap. As such, it has potential optoelectronic applications as windows, deep ultraviolet (uv) detectors, or uv light-emitting devices. Since it has a very high surface energy and a lattice parameter which is very similar to diamond, it m a y also prove to be an excellent substrate material for heteroepitaxial thin film growth of this material. This paper reports the preliminary results of the growth of BN thin films using gas source molecular beam epitaxy. The B source evaporated elemental B produced in a new high temperature effusion cell. The nitrogen source consisted o f N ions as well as activated N atoms and molecules obtained from the decomposition of purified N2 by passing it through an electron cyclotron resonance plasma unit designed specifically for molecular-beam epitaxy (MBE) systems. A graded G a N B N layer deposited on a monocrystalline fl-SiC (I00) film was used as the substrate of growth of each BN film. Transmission electron microscopy o f the latter films showed them to be a m o r p h o u s ; however, reflection high-energy electron diffraction ( R H E E D ) patterns obtained during deposition indicated the presence of some microcrystallinity. M J Paisley et al, J Vac Sci Technol, B8, 1990, 323-326. 33 7288. Construction and operation of an ultrahigh vacuum chemical vapor deposition epitaxial reactor for growth of Gex Sil_ x A uhv chemical vapor deposition system suitable for deposition of epitaxial GexSi, -x has been constructed. We report details of its construction and operation and demonstrate deposition of epitaxial silicon and GexSi~ x at temperatures as low as 577°C. Measurements of thickness uniformity both across and between wafers are also presented. D W Greve and M Racanelli, J Vac Sci Technol, B8, 1990, 511 515. 33 7289. Study of isoelectronic In doping in molecular beam epitaxy grown GaAs thyristors Studies have been conducted of isoelectronic In doping in n-GaAs and p-GaAs and p-GaAs grown by molecular beam epitaxy. The concentration of most of the electron and hole traps are suppressed by up to three orders of magnitude by introducing 0.2 1 at% In and increasing growth temperatures from 500 to 550°C. As a result an improvement in minority carrier lifetime and diffusion length is achieved. This is demonstrated by the comparison o f p n p and npn G a A s homojunction transistors grown with and without In doping in base layers. Based on these results, pnpn G a A s h o m o junction thyristors were designed and fabricated with and without In doping in the middle n and p - G a A s layers. More than a factor of 2 reduction in the trigger current was observed as a result of the In doping. H K Kim et al, J Vac Sci Technol, B8, 1990, 374~ 378. 33 7290. Growth of high quality AIGaAs/GaAs heterostructures by gas source molecular-beam epitaxy Unintentional p-type doping of G a A s films grown by gas source molecular-beam epitaxy (GSMBE) was reduced to 2 x 10 ~4cm 3 with a roomtemperature hole mobility of 490 cm 2 V s - ' . Intentional Si doping of G a A s films grown by GSMBE, using an elemental Si source, yielded controlled carrier concentrations from 7 × 10 j4 to 8 x 1018 cm 3 with 77 K mobilities from 62,700 to 2500 cm 2 V s '. Residual carbon incorporation was reduced in AIGaAs by growing at 560°C and using triisobutylaluminum such that 77 K two-dimensional electron gas mobilities as high as 88,600 cm 2 V s - t were obtained. Our study of using trimethylgallium or a graphite filament as a carbon source forp-type doping indicates that doping levels can be controlled in the range of 5 x I0 ~61.5 x 1020 cm -3 with good hole mobility and surface morphology. Preliminary results show an undetectable diffusion of carbon in the AIGaAs/ GaAs heterojunction bipolar transistor (HBT) structures with a base doping level as high as 1.5 × 102° cm 3, using carbon as ap-type dopant, grown at a substrate temperature of 600°C and annealed at 700°C for 30 min. Yu-Min Honng et al, J Vac Sci Technol, B8, 1990, 355-359. 33 7291. Growth of AIN/GaN layered structures by gas source molecularbeam epitaxy A I N / G a N layered structures with layer periods between 1.5 and 40 n m have been grown on (0001) oriented sapphire and a(6H)-SiC substrates.
The growth was performed using a modified gas source molecular-beam epitaxy (MBE) technique. Standard effusion cells were used as sources orAl and Ga, and a small, M B E compatible, electron cyclotron resonance (ECR) plasma source was used to activate nitrogen gas prior to deposition. Chemical analysis of the layers was conducted using Auger spectrometry. X-ray diffractometry, transmission electron microscopy (TEM), and high-resolution electron microscopy (HREM) were employed for the structural and microstructural studies. Coherent interfaces (no relaxation by misfit dislocations) were observed for bilayer periods smaller than 6 nm. By contrast, completely relaxed individual layers of G a N and A1N with respect to each other were present for bilayer periods above 20 nm. Cathodoluminescence showed a shift in the emission peak from 3.42 eV for the sample with individual 10-nm thick G a N wells and A1N barriers to 4.11 eV for the sample having l-nm thick individual layers. Z Sitar et al, J Vac Sci Technol, BS, 1990, 316-322. 33 7292. Molecular beam epitaxial growth of GaAs on silicon and silicon on sapphire incorporating a low temperature buffer G a A s has been grown by molecular-beam epitaxy on both silicon and silicon on sapphire. The incorporation of a low temperature buffer has reduced the film stress from 3.0 to 2.2 kbar for G a A s grown on silicon. However, films stress can be completely removed for growth of G a A s with the incorporation o f the low temperature buffer when grown on silicon on sapphire (SOS). The orientation dependence of G a A s grown on SOS has been investigated by growing on orientations slightly off-axis from the (100) in the [011] direction by 2, 4, and 6". X-ray, mobility and photoluminescence measurements have been made, showing that growth on 6 ° misoriented SOS produces nearly stress free films with materials properties similar to those o f G a A s on silicon, and mobilities six times higher than those of G a A s grown on on-axis (100) SOS. Meta~semiconductor field effect transistors (MESFETs) have been fabricated on G a A s on silicon showing device characteristics comparable with those of G a A s on GaAs. R A Metzger et al, J Vac Sci Technol, B8, 1990, 297 300. 33 7293. Molecular beam epitaxial growth of high-quality GaAs on Si using a high-temperature in situ annealing process In this paper, we report a new process for molecular beam epitaxial (MBE) GaAs-on-Si growth. The process involves high-temperature in situ G a A s annealing above 850°C. The unique points in this new approach are: (1) the thermal cycling layers, or so-called thermal strained superlattices (TSL), are inserted in buffer growth and found to be effective in blocking dislocation propagation; (2) a thin A10.35Ga065As cap layer is deposited after G a A s buffer layer growth to prevent the underneath G a A s epitaxial layer from sublimation during annealing. An 850°C in situ AIGaAs cap annealing (ACA) of the A1GaAs/GaAs buffer layer can eliminate all the twins and stacking faults in the buffer layers and yield high-quality G a A s film. The bulk G a A s overlayer is grown at normal GaAs/Si growth temperature and is never exposed to a high anneal temperature. High-quality GaAs/Si layers with surface dislocation densities 1 x 106 cm 2 and an X-ray linewidth of 130 arc s have been achieved. Y C Kao et al, J Vac Sci Technol, B8, 1990, 250-253. 33 7294. A two-zone molecular-beam epitaxy furnace for evaporation of IIVI materials The design and operation of a two-zone furnace and crucible for the evaporation of II-VI semiconducting materials is described. The furnace contains separate heating elements and temperature sensors for each of the zones. The second zone is located at the open end of the furnace. The use of two independently-controlled temperature zones allows for the elimination of clogging problems that often occur with the evaporation of materials such as tellurium. The pyrolytic boron nitride (PBN) crucible contains a cap with a 2 m m inside diameter and 16 m m long orifice, which is designed to yield higher operating temperatures and better flux stability. A special P B N crucible retainer has also been designed to minimize contact of evaporated material with the tantalum structure of the furnace. J W Cook et al, J Vac Sci Technol, B8, 1990, 196199. 33 7295. Molecular-beam epitaxy growth of ZnSe using a cracked selenium source A double-oven cracking furnace has been used to produce a flux composed of small selenium molecular species for the molecular-beam epitaxy
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The growth was performed using a modified gas source molecular-beam epitaxy (MBE) technique. Standard effusion cells were used as sources orAl and Ga, and a small, M B E compatible, electron cyclotron resonance (ECR) plasma source was used to activate nitrogen gas prior to deposition. Chemical analysis of the layers was conducted using Auger spectrometry. X-ray diffractometry, transmission electron microscopy (TEM), and high-resolution electron microscopy (HREM) were employed for the structural and microstructural studies. Coherent interfaces (no relaxation by misfit dislocations) were observed for bilayer periods smaller than 6 nm. By contrast, completely relaxed individual layers of G a N and A1N with respect to each other were present for bilayer periods above 20 nm. Cathodoluminescence showed a shift in the emission peak from 3.42 eV for the sample with individual 10-nm thick G a N wells and A1N barriers to 4.11 eV for the sample having l-nm thick individual layers. Z Sitar et al, J Vac Sci Technol, BS, 1990, 316-322. 33 7292. Molecular beam epitaxial growth of GaAs on silicon and silicon on sapphire incorporating a low temperature buffer G a A s has been grown by molecular-beam epitaxy on both silicon and silicon on sapphire. The incorporation of a low temperature buffer has reduced the film stress from 3.0 to 2.2 kbar for G a A s grown on silicon. However, films stress can be completely removed for growth of G a A s with the incorporation o f the low temperature buffer when grown on silicon on sapphire (SOS). The orientation dependence of G a A s grown on SOS has been investigated by growing on orientations slightly off-axis from the (100) in the [011] direction by 2, 4, and 6". X-ray, mobility and photoluminescence measurements have been made, showing that growth on 6 ° misoriented SOS produces nearly stress free films with materials properties similar to those o f G a A s on silicon, and mobilities six times higher than those of G a A s grown on on-axis (100) SOS. Meta~semiconductor field effect transistors (MESFETs) have been fabricated on G a A s on silicon showing device characteristics comparable with those of G a A s on GaAs. R A Metzger et al, J Vac Sci Technol, B8, 1990, 297 300. 33 7293. Molecular beam epitaxial growth of high-quality GaAs on Si using a high-temperature in situ annealing process In this paper, we report a new process for molecular beam epitaxial (MBE) GaAs-on-Si growth. The process involves high-temperature in situ G a A s annealing above 850°C. The unique points in this new approach are: (1) the thermal cycling layers, or so-called thermal strained superlattices (TSL), are inserted in buffer growth and found to be effective in blocking dislocation propagation; (2) a thin A10.35Ga065As cap layer is deposited after G a A s buffer layer growth to prevent the underneath G a A s epitaxial layer from sublimation during annealing. An 850°C in situ AIGaAs cap annealing (ACA) of the A1GaAs/GaAs buffer layer can eliminate all the twins and stacking faults in the buffer layers and yield high-quality G a A s film. The bulk G a A s overlayer is grown at normal GaAs/Si growth temperature and is never exposed to a high anneal temperature. High-quality GaAs/Si layers with surface dislocation densities 1 x 106 cm 2 and an X-ray linewidth of 130 arc s have been achieved. Y C Kao et al, J Vac Sci Technol, B8, 1990, 250-253. 33 7294. A two-zone molecular-beam epitaxy furnace for evaporation of IIVI materials The design and operation of a two-zone furnace and crucible for the evaporation of II-VI semiconducting materials is described. The furnace contains separate heating elements and temperature sensors for each of the zones. The second zone is located at the open end of the furnace. The use of two independently-controlled temperature zones allows for the elimination of clogging problems that often occur with the evaporation of materials such as tellurium. The pyrolytic boron nitride (PBN) crucible contains a cap with a 2 m m inside diameter and 16 m m long orifice, which is designed to yield higher operating temperatures and better flux stability. A special P B N crucible retainer has also been designed to minimize contact of evaporated material with the tantalum structure of the furnace. J W Cook et al, J Vac Sci Technol, B8, 1990, 196199. 33 7295. Molecular-beam epitaxy growth of ZnSe using a cracked selenium source A double-oven cracking furnace has been used to produce a flux composed of small selenium molecular species for the molecular-beam epitaxy
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