Encouraging results have been reported for discrete heterojunction internal photoemission (HIP) infrared (IR) detectors composed of heavily boron doped Si1−3Gex layers on Si. We desired to build on those results and fabricate 640×480 IR focal plane arrays on 100 mm Si substrates, suitable for commercial microelectronic processing. In this paper we discuss the growth issues for growing these structures by molecular beam epitaxy. Since the wafers had already undergone processing and some had PtSi contacts, the growth temperature was constrained to be no greater than 600 °C. Precise temperature control was obtained by calibrating an optical pyrometer with a thermocouple embedded in the substrate heater assembly, which was calibrated using the eutectic emperatures of Au/Si and Al/Si. The final step of the cleaning process was a 1% HF dip/ spin dry, which resulted in a H-terminated surface. The H was removed at 550 °C in vacuum prior to rowth. The growth of the B-doped SiGe layer was done at 350 °C to minimize segregation and diffusion of the Ge and B. Doping levels of 2×1020/cm3 were obtained with near 100% activation. Using Si0.35, doped with 2×1020 B/cm3, a cut-off wavelength of 11.1 μm and an emission coefficient of 19.8 %/eV were obtained for discrete detectors. Preliminary results from the detector arrays show full functionality in the spectral range of 6.1 to 12.8 μm.

We have fabricated heterojunction p+ Si1−x−yGexCy/ p+ Si diodes. The SiGeC layers were grown epitaxially on Si (100) substrates by the rapid thermal chemical vapor deposition (RTCVD) technique using methysilane gas as a carbon precursor. The germanium concentration is 20% in these SiGeC alloys and the carbon concentrations are in the range of 0% to 1%. By studying the current-voltage characteristics of these diodes as a function of temperature the valence band discontinuities between SiGeC and Si layers were obtained as a function of carbon concentrations. We have found that the valence band discontinuity of the SiGe/Si heterostructure decreases by II meV when 1% of carbon is incorporated. Photoluminescence (PL) results show that 1% carbon increases the bandgap of strained p+SiGe alloys by 25 meV. This would imply that the conduction band discontinuity of SiGe/Si will decrease by 14 meV when 1% carbon is incorporated.

Heterojunction p++ GeSi / Si internal photoemission (HIP) detectors deposited by ultra high vacuum chemical vapor deposition (UHV/CVD) were investigated as alternatives to silicide Schottky-barrier type detectors for infrared focal plane arrays. HIP structures were grown using SiH4, GeH4, and B2H6 source gases on (100) p- Si substrates patterned with thermal oxide windows. Selective epitaxy was maintained over a range of boron concentrations (6×1019 – 6.5×1020 cm-3) and Ge fractions (0.38–0.50), and a maximum selective thickness of ~300Å was determined for silicon growth at 550°C. These structures were fabricated into IR detectors using techniques compatible with standard Si focal plane array processing technology. Photoresponse data were analyzed according to the modified Fowler equation, indicating cut-off wavelengths of 5–12 (μm) and Cl values of 8–21 (%/eV) depending on sample parameters. I(V) characteristics were also measured at various temperatures, yielding electrical barrier heights consistent with optical measurements.

Transmission electron microscopy and grazing incidence X-ray diffraction are used for the structural characterization of ultra-thin PtSi layers on (100) silicon prepared by a two-step rapid thermal annealing process. The roughness of the layers is investigated with atomic force microscopy. Two deposition techniques for the initial Pt layer are compared.

The feasibility of population inversion is studied for the Si/SiGe system. Because of the absence of polar optical phonon scattering, the lifetime difference of the upper and lower lasing levels, to which the population inversion and laser gain are proportional, are an order of magnitude larger than in the III-Vs; nor does this show the large decrease to negative values (loss of population inversion) when the intersuband energy difference exceeds the optical phonon energy. We have investigated the effect of phonon confinement of the Ge-Ge and Si-Ge vibrations on the intersubband scattering rates and find a furthur enhancement of the the intersubband lifetimes as compared to those due to unconfined phonons.

Recent work using ballistic electron emission microscopy (BEEM) and ultra-high vacuum transmission electron microscopy (UHV-TEM) to study structure-property correlations of PtSi/Si(001) contacts is described. The spatial uniformity of the Schottky barrier height (SBH) for diodes grown at room temperature and 350°C was compared with the interface microstructure using TEM. Narrow SBH distributions with standard deviations of 7–12 meV were obtained independent of the deposition system and temperature. Analysis of the distributions compared well with standard current-voltage and capacitance-voltage measurements on the same diode. These low temperature depositions produced fine grained PtSi films (10–20 nm) with an interface roughness dependent on the cleaning process. Probable orientation effects on the SBH distribution were apparently screened out because of the low doping of the substrates that were used. As the deposition temperature is increased the PtSi tends towards polycrystalline epitaxy with island growth beginning at 700°C. Grains are rectangular and develop a large shape anisotropy of great interest for future investigations.

The properties of thin (350 Å) Ti layers deposited on Si0.89Ge0.11 layers epitaxially grown on Si(001) were studied as a function of isochronal (30 min.) thermal treatments in the temperature range Ta=550–800°C. Both as-deposited and annealed at Ta up to 750°C Schottky diodes revealed near-ideal I–V and C–V characteristics with the same flat-band barrier height eV. The results indicate that at these Ta the Fermi level is pinned with respect to the conduction band.

Annealing at 800°C resulted in an improvement of the Schottky diodes quality and a drop in and the series resistance Rs of the contacts. The values of the ideality factor n and ( measured were 1.03±0.02 and 0.56±0.007 eV, correspondingly. The electrical parameters of these metal/semiconductor contacts were correlated with the dynamics of interfacial reactions due to the applied heat-treatments.

This study has addressed the effect of starting surface topography on the nucleation and growth of epitaxial siicide layers. CoSi2 layers were grown via the template technique on one-dimensionally patterned Si (100) substrates. These substrates contained mesa stripes, running parallel to Si[011], and exhibited either smoothly varying sinusoidal profiles, or a number of well defined Si Ihkl) facets. Conventional plan view and high resolution cross section transmission electron microscopy were used to analyze the films grown on these substrates. The orientation and morphology of the CoSi2 grains depend on the angle (θ), between the CoSi2 / Si interface normal and Si (100). High quality (100) oriented CoSi2 grew on the tops and bottoms of mesa structures, where θ < 5°, and formed atomically sharp interfaces with the substrate. In contrast, CoSi2 (110) and CoSi2 (221 ) grains nucleated along the sidewalls of the mesa structures. The CoSi2 (110) grains formed rough interfaces with the substrate and were terminated by regions of step bunching at the grain boundary / substrate triple points. CoSi2 (110) grains were most highly concentrated in regions where θ varied from 5° to 12°. Similarly, the CoSi2 (221 ) grains formed faceted (111) b-type silicide / substrate interfaces, and were most highly concentrated in regions where θ > 10°. These data suggest that double height steps, step bunches and facets on the substrate are related to the nucleation of misoriented silicide grains.

High dose Co implantation into Si has been performed with a metal vapor vacuum arc (MEVVA) ion source at an extraction voltage of 70 kV to doses from 8×1016 to 6×1017 ions cm−2 at substrate temperatures (Ts) in the range of 210°C to 700°C. Annealing was performed in nitrogen at various temperatures for various time intervals by either furnace annealing (FA) or rapid thermal annealing (RTA). The electrical properties of the CoSi2 layers formed were studied using resistivity and Hall effect measurements from 10 to 300K. We found that for all the samples prepared by MEVVA implantation, as long as a continuous CoSi2 layer was formed after annealing, a strong temperature dependence of the Hall coefficient was observed with a large peak at around 90 to 110K. The magnitude of the peak also varies depending on the substrate parameters and processing conditions. However, the temperature dependence of the resistivity for these CoSi2 layers follows the atthiessen's rule. We also found that it does not require high substrate temperature nor very high temperature annealing in order to form a CoSi2 layers with low resistivity by MEVVA implantation. Such low resistivity CoSi2 layers can be formed with a substrate temperature as low as 210°C after either RTA at high temperature for a few seconds or FA at a relatively low temperature of 750°C for one hour. The dependence of the electrical properties on Ts is also presented and discussed.

A new epitaxial CoSi2 phase has been synthesized on Si(111) by molecular beam epitaxy (MBE) at room temperature (RT). Structural investigations revealed, that films grown onto an ultrathin CoSi2 template crystallize with the CsC1 structure with 50% vacancies on the cation lattice. The same is true for codeposited films nucleating from the amorphous phase at very low annealing temperatures (100–200 °C). Upon annealing a gradual transition to the stable bulk phase with the CaF2 structure takes place. For films grown onto a template, some grains of (CsCl)Co0.5Si remain stable up to at least 550 °C, while the films grown without a template are fully transformed.

The results are discussed of the characterization by means of TEM, RBS and XRD of ErSi2-x layers prepared by ion beam synthesis on (111) silicon. It will be shown that high quality (buried) layers can be prepared by channelled implantation of the erbium, whereas unchannelled implantation leads to discontinuous polycrystalline surface layers. The epitaxial growth and vacancy ordering in the silicide are discussed.

Epitaxial CoSi2(100) layers in the thickness range of 20 to 50 nm have been formed by reactive deposition epitaxy (i.e. Co deposition onto a hot Si substrate) without the use of either a template or an intermediate Ti layer. It is explained how growth parameters such as the deposition rate and substrate temperature are crucial in determining the epitaxial nature of the silicide. According to this model, good CoSi2/Si(100) alignment is only achieved when very low deposition rates are used (0.1 Å/s or less), combined with relatively high substrate temperatures during deposition (∼ 600°C or higher). Using these conditions, highly strained, continuous CoSi2 layers with a channeling minimum yield of χmin = 9% could be formed. Using higher rates and/or lower deposition temperatures, an increasing fraction of misoriented CoSi2 grains is presumed from backscattering/channeling and x-ray experiments, the nature of which is under investigation with plan view and cross sectional transmission electron microscopy.

Thin films of (100) oriented CoSi2 have been electron beam evaporated onto Si(100)substrates from a mixed Co-Si target. A sharp c(2×2) low energy electron diffraction (LEED)pattern resulted after annealing the films to 800°C. Extended x-ray absorption fine structure (EXAFS) of the film indicated the phase to be CoSi2. Quantitative x-ray photoelectron spectroscopy (XPS) analysis revealed the surface of the film to be slightly Si rich, indicating the Si terminated CoSi2 variant. Analysis of transmission electron microscope (TEM) diffraction patterns also provided evidence of the (100) orientation of the film.

We have developed successfully the combined ion beam and molecular beam epitaxy (CIBMBE) system with a newly designed Knudsen cell for Si effusion. The CIBMBE system was applied to the epitaxial growth of Sil., Cx alloy thin films on Si using low-energy ( 100 – 300 eV ) C+ ion beam. Preliminary results on the characterization of the deposited films suggest high potential and reliability of the new Knudsen cell for Si effusion, as well as high ability of the CIBMBE method to produce thermally non-equilibrium materials. In addition, they indicate that the value of x decreases with increasing IC, which suggests that the selective sputtering for deposited C atoms by incident C+ ion beams takes place during CIBMBE processing. Precipitates of β-SiC were also found to be formed in the deposited films, whose amount was observed to increase with increasing IC.

A study of the room-temperature growth of ultrathin Ti films (up to 7 ML) on clean and atomically flat Si(111)- (7×7) surfaces using Auger electron spectroscopy (AES) and low energy electron diffraction (LEED) is presented. The variations in the Auger signal due to Si L2.3VV with binding energy of 92 eV are used to model the growth morphology of this system. These measurements indicate the growth of an initial disordered and continuous Ti film of up to 1.6 ML in thickness, where the LEED pattern completely disappears and the Si Auger signal is strongly attenuated. As more Ti is deposited, this is followed by the disintegration of the continuous film and the formation of an intermixed Ti/Si film. This is evidenced by a change in the slope of the Auger signal time (AST) plot, and the reappearance of the LEED pattern. The modification in the overlayer composition for films thicker than 1.6 ML is confirmed by a change in the Si L2.3VV Auger peak that resembles the peak shape due to TiSi2.

Reactions between 1.5 monolayer(ML) Fe deposited on Si(001)-2 × 1 and -dihydride surfaces were studied in situ by reflection high-energy electron diffraction and time-of-flight ion scattering spectrometry with the use of 25 keV H ions. The reactions between Fe and Si which were successively deposited on Si(001)-dihydride surface were also studied. After the room temperature deposition Fe reacted with Si(001)-2 × 1 substrate resulting in the formation of polycrystalline Fe5Si3. By annealing to 560∼650°C composite heteroepitaxial layer of both type A and type B β -FeSi2 was formed. On the dihydride surface polycrystalline Fe was observed after 1.5ML Fe deposition at room temperature, and reaction between Fe and Si(001)-dihydride surface is not likely at room temperature. We observed 3D rough surface when we deposited only Fe layer on the dihydride surface and annealed above 700°C. The hydrogen termination of Si(001) surface prevents the deposited Fe from diffusing into the substrate below 500°C, however the annealing above 710°C leads to the diffusion. We obtained 2D ordered surface, which showed 3 × 3 RHEED pattern as referenced to the primitive unreconstructed Si(O01) surface net, when we deposited 2.5ML Fe and 5.8ML Si successively onto Si(001)-dihydride surface and annealed to 470°C.

CrSi2 layers grown by solid phase epitaxy on a nominal (111) Si surface exhibit in the same proportion two different orientation relationships, named A and B. When CrSi2 is deposited on a 8° vicinal (111) Si surface, B-type orientation is favoured with respect to the A type. This result can be explained by the fact that both the step width introduced by the miscut and the planar coincidence between {1100}Crsi2 and {111}Si are nearly equal to 23Å. Edge type misfit dislocations are observed at the interface with the same spacing. Their Burgers vector component along [111] is almost compensated by the atomic steps along the <110> directions. The role of the steps is discussed in term of elastic energy. Steps introduce misfit dislocations which make possible coherent growth of the B type orientation.

Chemistry, crystal structure, interfacial microstructure and electrical characteristics of novel Cu-Ge alloyed ohmic contacts to n-type GaAs with a very low specific contact resistivity ((4–6)×10−7 Ω·cm2 for n∼1×1017 cm−3) were investigated by various methods. The Cu-Ge alloys with a wide range of Ge concentration, from 15 to 40 at %, were prepared by depositing sequentially Cu and Ge layers (or vise versa) onto GaAs substrates at room temperature followed by annealing at 400°C. It is shown that Cu reacts only with Ge to form the ξ and ε1-Cu3Ge phases. The latter has an orthorhombic structure with average lattice parameters: a = 5.301 Å, bo = 4.204 Å, co = 4.555 Å, arising from the parent hexagonal ξ-phase by Cu-Ge ordering along ao. The interface with GaAs is atomically sharp and free from secondary phases. The ε1-Cu3Ge ordered phase which is chemically inert with respect to GaAs, is believed to be responsible for high thermal stability (up to 450°C), interface sharpness, high contact layer uniformity and low specific resistivity of 6 μΩ cm. Formation of the Cu-Ge phases creates a highly doped n+-GaAs surface layer which leads to the low contact resistivity.

A novel method for patterning of silicide layers based on local oxidation is presented. We investigated unifom and local oxidation of epitaxial CoSi2 layers on Si(100). During thermal oxidation of CoSi2 a SiO2 surface layer forms and the silicide layer moves deeper into the substrate. Single crystalline CoSi2 layers on Si(100) remain single crystalline even if they are shifted into the substrate several hundred nm. Local oxidation of such a silicide layer allows lateral patterning of the silicide. The oxidized regions of the silicide layer are pushed inwards and separate from the surface layer at a critical oxidation time. This allows the formation of buried patterned silicides or metallized mesa structures. The technique seems to be also applicable for polycrystalline silicides.

A method, technological arrangement, and some special features of the process for TiSi2 thin film formation is described in details. Rapid formation of low-resistivity single-phase TiSi2 layers is realized directly during deposition of Ti onto Si from DC plasma of metal vapour with simultaneous powerful self-ion bombardment at Wi > 2.5–3.1 W/cm2. Accelerated reactive diffusion is activated by thermal (dT/dτ ≥ 10°C/sec) and radiation (Eadd ≤ 2500 eV/atom) effects of powerful Ti+-ion bombardment. Thin TiSi2 layers with resistivity ρ = 13–20 μΩcm are formed on different Si substrates under optimum energetic conditions after 50 sec of the deposition. The film structure formation passes through three kinetic stages.