He ion channeling experiments have been performed on molecular beam grown Si/SiGe superlattices to determine the strain fields. Angular yield scans provide directly the tetragonal strains in the layers. In Si/Si0.5Ge0.5 superlattices grown on (100) Si only the SiGe layers are strained. Almost equal but opposite strains in the Si and SiGe layers have been found in a Si/Si0.5Ge0.5 superlattice deposited on a 230 nm thick SiO.71Ge0.29 buffer layer. Strain symmetrization yields the minimum elastic energy and thus to the most stable structure.

We have calculated stress distribution and critical thickness for the growth of strained epilayers having various values of mismatch between the epilayer and the substrate. The present analysis has been carried out assuming that the nucleation of a misift dislocation is controlled by the activation energy. Further, a misfit dislocation is nucleated when the areal strain energy density of the coherent film exceeds the activation energy associated with the misfit dislocation configuration. The latter term has been deternmined using the discrete dislocation method in conjunction with a surface dislocation analysis. The surface dislocation configuration is obtained by minimizing the total energy associated with the two-phase medium. It is verified that the free surface boundary conditions and the continuity of stresses acrosss the interface are satisfied by the surface dislocation array. These energy calculations are expected to be more accurate than those performed by previous workers.

Thin films of germanium have been prepared using an ultrahigh vacuum ionized-cluster beam (ICB) system. The dopant concentration of the films was varied by alloying the germanium source material with aluminum, a p-type dopant. X-ray diffraction analysis of the films has shown that an epitaxial (100) germanium film can be deposited on a (100) silicon substrate with a substrate temperature as low as 300°C. The results confirm that ICM deposition can be used to prepare epitaxial germanium films, but ionization of the clusters does not appear to affect the film growth.

The mechanisms which control low energy (10–100 eV) beam deposition of silicon onto a relaxed (111) silicon substrate have been studied using a molecular dynamics technique. A many-body empirical potential was used to describe the covalent Si-Si bonding. 10 eV silicon beams with near-perpendicular incidence were simulated to study capture mechanisms and the local lattice excitation resulting from impact. Grazing angles of incidence (3°–30°) were studied for beam energies of 20–100 eV. For incidence angles less than an energy- and orientation-dependent critical value, the phenomenon of ‘surface channeling’ is predicted, in which the incoming particle is steered parallel to, and roughly 2 Å above, the surface of the substrate through inelastic substrate interactions. The phenomena seen in low-energy beam deposition offer new avenues of control over growth of modulated semiconductor structures.

Heteroepitaxial growth of alkaline earth fluoride films on Si substrates and Si, Ge, and GaAs films on the fluoride/Si structures, is reviewed. Growth of single crystalline fluoride films on Si is first discussed. Then the usefulness of novel heteroepitaxial technologies, the predeposition method and the electron beam irradiation method, is demonstrated in the growth of Si and Ge films on CaF2/Si structures. Finally fundamental growth characteristics of GaAs films on CaF2/Si structures and annealing effects on the crystallinity of the GaAs films are described.

The results of recent developments on device fabrication in a heteroepitaxial Si/CaF2/Si structure have been presented and discussed. A high quality heteroepitaxial Si/CaF2/Si structure has been obtained by successive molecular beam epitaxy of CaF2 and Si. The epitaxial Si film on CaF2/Si structure has an ion channeling minimum yield of 7 %. It was found, however, that Ca and F segregated at the surface of epitaxial Si films. A possibility of reducing the segregation effect by the use of solid phase epitaxy of Si has been proposed.

Si-gate CMOS devices have been successfully fabricated in a Si/CaF2/Si structure with alt improved CMOS proress. The maximum effective mobiliiies are about 570 cm2/V.sec and 240 cm2/V.sec for n-channel and p-channel transistors, respectively. Propagation delays below 360 ps have been obtained for CMOS inverter chains with Leff = 2 μm. These results indicate that the Si/CaF2/Si structure has potential for the fabrication of high-speed silicon-on-insulator devices.

Epitaxial, lattice-matched GaAs/Ca0.45Sr0.55/F2 heterostructures were grown on Ge(100) substrates by molecular beam epitaxy. The films were analyzed by Rutherford backscattering and secondary ion mass spectroscopy to determine crystallinity and Ge outdiffusion. The Xmin (channeling over random yield) of a 1.5 μm-thick GaAs film grown on the fluoride is 0.075, indicating reasonably good epitaxy. After rapid thermal annealing, the crystallinity of higher-Xmin films improves, and Ge diffuses only 200 A into the fluoride, indicating that a thin fluoride layer is an effective barrier to Ge outdiffusion.

We present evidence on the types of structural changes caused by the rapid thermal annealing of two types of heteroepitaxial layers: CaF2/CoSi2/Si(111) and Si(100) on A12O3 (1102). We find that grains in a film can be merged into a single crystal and that the microtwin density can be dramatically lowered. We also find a number of changes in the structure of the heteroepitaxial interfaces.

CaF2 is an insulator with a number of attractive properties for epitaxial growth on Si1 Epitaxial CaF2 layers have been grown on Si(111) by Molecular Beam Epitaxy and are found to have smooth surfaces and a high degree of crystalline perfection.1 For applications such as a gate insulator in metal-insulator-semiconductor field-effect transistors or in silicon-on-insulator technology, the electrical properties of these layers are also critical.

Epitaxial CdTe has been grown onto Si(lll) wafers by MBE with the aid of a composition graded (Ca,Ba)F2 buffer layer to surmount the large misfit of 19%. Untwinned CdTe layers with smooth surfaces, narrow X-ray lines and strong photoluminescence with a narrow near band edge peak were obtained. The results indicate a comparable structural quality to well known CdTe layers on sapphire, InSb or GaAs used as buffers to grow (Hg, Cd)Te for IR-device applications. In addition, the CdTe layers are near strain free despite a large thermal expansion mismatch. This is most probably due to dislocations which are able to move along the fluoride/Si interface even after growth and down to near room temperature.

Results are reported for a single temperature Si-BP-Si process which utilizes 0.2 and 0.4 μm of high resistivity BP covered by a single 1–5 μm silicon epitaxial layer on which PMOS devices were fabricated. Transistor and capacitor measurements were used to characterize the quality of the silicon films. Impurity concentrations on 1.0 and 2.0 μm silicon layers were as high as 3×1017cm−3 due to auto doping from the BP layer. MOS transistors manufactured on these layers did not work properly. Device characteristics improved on thicker silicon layers. The impurity concentration was as low as 1015 cm−3 on the 5.0 μm silicon layers. Surface state densities were found to be as low as 5×1011 eV−1cm−2 with subthreshold currents as low as 10−11 amperes. On all wafers the subthreshold slope varied from 90 to 100 mV/decith little variation due to silicon thickness. Linear and saturation mobilities were process limited with values on the 5.0 μm layers as high as 250 and 160 cm2/V-s respectively. Characteristics of devices fabricated on 5 μm silicon layers were comparable to those of devices fabricated on bulk silicon processed at the same time indicating high quality silicon growth.

Formation of a Si-on-insulator structure by a solid phase process was investigated. Examination by µ-RHEED method revealed that oriented crystal growth propagated from the seeding area by a solid phase epitaxy (SPE) in the low temperature range around 550 °C. In addition . a new local doping method was developed. This realized a relatively large lateral-SPE area on insulating regions (14 µm from the seeding area). Crystal quality and electrical properties of SPE layers were precisely examined utilizing µ-Raman spectroscopy and MOSFET fabrication. A small stress field and high electron mobility comparable to that of bulk Si were obtained.

Single-crystal Si1−x Gex(O<×≲1) layers are grown by seeded growth on partially SiO2-masked Si-substrates, using a one-step liquid phase epitaxy (LPE) process. The seed regions are stripe- and hole-shaped windows in the oxide, having linear dimensions between 1.5 and 100 μm. The windows extend in different orientation on (111) and (100) orientated substrates. Lateral overgrowth over the oxide-masked areas is achieved up to 70 μm in <110>-directions. X-ray diffraction and Raman scattering show that the epitaxial islands are homogeneous and of excellent crystal quality. In the regions of lateral overgrowth the dislocation density is reduced considerably as shown by defect-etching and cross section transmission electron microscopy.

Defects generated in β-SiC grown on a (001) silicon substrate by chemical vapor deposition (CVD) are charaterized and their mechanism of formation discussed. It is argued that nucleation plays a primary role in this heteroepitaxial system where the lattice mismatch is so large.

Single crystal ZnSxSel−x films have been grown for the first time on (111) Si substrates by low-pressure MOCVD. The epitaxial films clearly show a passivating effect on silicon solar cells, and act as antireflective coatings. Attempts at incorporating Al as an n-type dopant were unsuccessful as the films remain semi-insulating.

Epitaxial Si/CoSi2/Si structures can be grown under ultra-high vacuum conditions. The metallic CoSi2 films can be extremely thin typically between 1 nm and 20 nm. The electrical properties of these heterostructures are presented, mainly the transport of electrons in the metallic films parallel to the interfaces and the transfer of electrons through the metal ilm. The influence of pinholes in the CoSi2 layers will be discussed.

We have performed electrical transport measurements on ultrathin films of epitaxial CoSi2 on Si(111) with film thickness ranging down to ∼10A. The resistivities exhibit temperature dependences characteristic of a metal and a thickness dependence which rises steeply with decreasing thickness suggestive of a quantum size effect. At the lowest temperatures (≲ 10K) the resistivities of the thinner films increase logarithmically with inverse temperature characteristic of transport in the weak localization regime as has been confirmed by magnetoresistance measurements. Hall effect measurements establish that carrier densities (holes) in the ultrathin films are essentially identical to those in bulk CoSi2, i.e. 26 × 1022 cm−3.

We report results of an extensive study examining the usefulness of low frequency capacitance measurements for the characterization of interface states at intimate Schottky contacts. Our measurements on epitaxial as well as on nonepitaxial silicides reveal that the imaginary component of the low frequency ac-admittance is usually inductive. This inductance is caused by minority carriers that are injected by the Schottky contact and modulate the conductivity of the series resistance of the bulk silicon. The frequently reported excess capacitances (instead of inductances) that were ascribed to interface states are only reproducible when we use imperfect back-contacts to the bulk Si that add a contact resistance to the equivalent dc-circuit of the Schottky diode. Excess low frequency capacitances at intimate Schottky contacts are therefore not related to interface states but rather to the contact resistance of the back-contact.

The properties of the interface states of MBE grown CoSi2/n-Si(111) intimate contacts has been investigated using forward bias capacitance measurement. The barrier height øbn for this structure is 0.66±0.01 V. It has been found that there is an interface state band located in 0.44–0.50 eV bfow the conduction band edge of Si. The density of states D it is about 4×1012 cm−2 eV−1, lower than those made by other methods. This intrface state band is in equilibrium with Si and the charge exchange occurs mainly with the electrons in the conduction band of Si. The electron capture cross section oa is about 3×10−15 cm2 . In addition, some discrete interface states were found at 0.53 eV, 0.51 eV and 0.47 eV below the conduction band edge of Si, respectively for several samples. The density of states D it ranges (1.5–3.5)×1010 cm−2 . They are probably caused by localized point defects formed during CoSi2 growth.

Ultrathin epitaxial CoSi2 films on Si(111) have been grown in ultrahigh vacuum by room temperature deposition of Co on Si(111) followed by a high temperature anneal at ~600°C. Characterization of the thin films with transmission electron microscopy has revealed pseudomorphic growth up to thicknesses ~30Å. Pinholes present in the pseudomorphic thin films are thought to prevent the trapping of dislocations within the film. A clear transition to films containing a regular network of misfit dislocations occurs at ~40Å. Evidence for the growth of CoSi2 via intermediate metal-rich silicide phases is observed.