T. P. Humphreys

Effectiveness of strained‐layer superlattices in reducing defects in GaAs epilayers grown on silicon substrates

In GaAs‐GaAsP strained‐layer superlattices grown lattice matched to GaAs are effective buffer layers in reducing dislocations in epitaxial GaAs films grown on Si substrates. The strained‐layer superlattice structure permits high values of strain to be employed without the strained‐layer superlattice generating dislocations of its own. We find that the strained‐layer superlattice buffer is extremely effective in blocking threading dislocations of low density and is less effective when the dislocation is high. It appears that for a given strained‐layer superlattice there is a finite capacity for blocking dislocations. Transmission electron microscopy has been used to investigate the role of the superlattice buffer layer.

Chemical vapor deposition of diamond films from water vapor rf-plasma discharges

Polycrystalline diamond films have been deposited from water vapor rf‐plasma discharges at 1.0 Torr containing various alcohol vapors. No other gases such as H2, F2, or Cl2 were admitted to the growth chamber. Scanning electron microscopy and Raman spectroscopy have been used to characterize the diamond films. In addition, a water‐ethanol mixture has been used for homoepitaxial deposition with a full‐width‐half‐maximum narrower than the bulk substrate (2.60 and 2.75 cm−1, respectively). This technique represents a remarkable new approach to the growth of diamond which does not depend on delivery of hydrogen, fluorine, hydrocarbon, or halocarbon gases that have been typically used by other workers. The nucleation density and topography of the polycrystalline diamond films deposited from the water alcohol mixtures are quite sensitive to the choice of alcohol. Water vapor discharges, by producing H atoms and OH radicals, become the functional equivalent to molecular H2 discharges producing H atoms characteri...

Low‐defect‐density germanium on silicon obtained by a novel growth phenomenon

Heteroepitaxial Ge on Si has been grown using molecular beam epitaxy at a Si substrate temperature of 900 °C. Electron microscopy results reveal a highly faceted interface, indicating localized Ge melting and subsequent local alloying with Si. Furthermore, this phenomenon is associated with extensive threading dislocation confinement near the Ge/Si interface. Etch pit density measurements obtained on Ge heteroepitaxial films that have undergone interfacial melting are as low as 105 cm−2.

High‐quality eutectic‐metal‐bonded AlGaAs‐GaAs thin films on Si substrates

Device quality GaAs‐AlGaAs thin films have been obtained on Si substrates, using a novel approach called eutectic‐metal‐bonding (EMB). This involves the lattice‐matched growth of GaAs‐AlGaAs thin films on Ge substrates, followed by bonding onto a Si wafer. The Ge substrates are selectively removed by a CF4/O2 plasma etch, leaving high‐quality GaAs‐AlGaAs thin films on Si substrates. We have obtained a minority‐carrier lifetime of 103 ns in a EMB GaAs‐AlGaAs double heterostructure on Si, which is nearly forty times higher than the state‐of‐the‐art lifetime for heteroepitaxial GaAs on Si, and represents the largest reported minority‐carrier lifetime for a freestanding GaAs thin film. In addition, a negligible residual elastic strain in the EMB GaAs‐AlGaAs films has been determined from Raman spectroscopy measurements.

Metalorganic chemical vapor deposition and characterization of the In‐As‐Sb‐Bi material system for infrared detection

We report the first results pertaining to the growth by metalorganic chemical vapor deposition of InSb1−xBix (0.01<x<0.14) and InAs1−x−ySbyBix with 0.5<y<0.7 and 0.01<x<0.04 epitaxial films on both semi‐insulating GaAs(100) and InSb(100) substrates. Electrical measurements for the undoped InSb0.99Bi0.01 epitaxial layers show a room‐temperature mobility of 20 215 cm2/V s with a carrier concentration of ND−NA ∼1016 cm−3. A degradation in the surface morphology of the InSb1−xBix and InAsSbBi epitaxial films correspond to an increase in the InBi mole fraction was observed. We attribute this deterioration in surface morphology to the formation of polycrystalline phases of Bi and the growth of metallic bismuth‐antimony crystallites.

Properties of interfaces of diamond

Abstract Results related to two different interface aspects involving diamond are described: (1) the initial states of CVD diamond film growth, and (2) the negative electron affinity and formation of metal-diamond interfaces. The surface and interface properties are probed with STM, Raman scattering/photoluminescence and angle-resolved UV photoemission spectroscopy (ARUPS). STM measurements of diamond nuclei on Si after various plasma growth processes show both flat and hillocked structures characteristics of 2-dimensional and 3-dimensional growth modes, respectively. STS measurements show distinct I – V characteristics of the nuclei and the substrate. The presence of optical defects and the diamond quality are studied with micro-Raman/photoluminescence measurements. The results indicate an increased density of impurity-related defects during the initial stages of growth. The interface properties of Ti on natural crystal (1 1 1) and (1 0 0) surfaces are studied with ARUPS using 21.2 eV HeI emission. Prior to deposition the diamond (1 1 1) is chemically cleaned, and a sharp (0.5 eV FWHM) peak is observed at the position of the conduction band minimum, indicating a negative electron affinity surface. After a subsequent argon plasma clean this peak disappears, while the spectrum shows a shift of 0.5 eV towards higher energies. Upon sub-monolayer titanium deposition on (1 1 1) diamond, the negative electron affinity peak reappears. Further titanium depositions causes this titanium-induced negative electron affinity peak to be attenuated, indicating that the emission originates from the interface. A similar experiment, done on the diamond (1 0 0) surface, however, does not result in a negative electron affinity. By determining the relative positions of the diamond valence band edge and the titanium Fermi level, the Schottky barrier height of titanium on diamond is measured. A model, based on the Schottky barrier height of titanium on diamond, and the work function of titanium, is proposed for the observed titanium-induced negative electron affinity.

Observation of antiphase domain boundaries in GaAs on silicon by transmission electron microscopy

Boundaries between different antiphase domains have been unambiguously identified in heteroepitaxial GaAs on silicon substrates by transmission electron microscopy. A simple and reliable method is described for assessing the presence or absence of these domain boundaries in GaAs. The domain size was found to be as small as ∼0.1 μm in GaAs that had been grown on nominal Si(001) in which a buried, implanted oxide had been previously formed. These boundaries are expected to degrade electrical performance and device reliability modify electronic transport and degrade device performance.

High temperature rectifying contacts using heteroepitaxial Ni films on semiconducting diamond

The first results pertaining to the fabrication of high-temperature rectifying contacts using heteroepitaxial Ni films deposited on natural p-type semiconducting diamond substrates are reported. The contact diodes were deposited at 500°C by the thermal evaporation of Ni from a W filament in ultra-high vacuum. The epitaxial nature of the deposited Ni layers has been established from an inspection of in situ low-energy electron diffraction (LEED) patterns. The Ni films exhibit excellent adhesion properties with the underlying diamond substrate. As evidenced by current-voltage (I-V) measurements stable rectifying characteristics for the Ni/diamond contacts were observed in the 25-400°C temperature range.

Growth of GaAs on High Temperature Hydrogen Pretreated (100) Si Substrates by Molecular Beam Epitaxy

High-quality GaAs epitaxial layers have been grown by molecular beam epitaxy on nominally (100) oriented silicon substrates that were previously annealed in a hydrogen ambient at 1250°C. The growth procedure involves an in situ thermal annealing step after the initial deposition of a thin GaAs buffer layer. Rutherford backscattering and channeling of 2.1 MeV He+ ions, interference optical microscopy, transmission electron microscopy, and X-ray diffraction techniques have been used to characterize these layers. Comparative studies indicate that the epitaxial layers grown on hydrogen-ambient annealed substrates have a superior surface morphology and a lower interface disorder than those on the chemically cleaned nominal silicon (100) substrates. Furthermore, a significant reduction in the density of microtwins is observed in layers grown on the preannealed substrates. This improvement in crystalline quality may be attributed to a lower degree of disorder at the silicon surface that was achieved by high temperature hydrogen-ambient annealing. However, dislocation densities were comparable and the presence of antiphase domain boundaries were observed in both cases.

Epitaxial Cu contacts on semiconducting diamond

Abstract In this study Cu films of 30 nm and 200 nm thickness have been grown on natural type IIb semiconducting diamond C(001) substrates by electron-beam evaporation at 500 °C in UHV. As evidenced by Rutherford backscattering/channeling techniques and in situ low-energy electron diffraction, the as-deposited layers were shown to be epitaxial, with χCu = 49%. In addition, the technique of atomic force microscopy has demonstrated island morphology, indicative of three-dimensional growth. Moreover, the Cu films displayed excellent adhesion properties with the underlying diamond substrate. Corresponding current-voltage (I–V) measurements conducted at room temperature have shown rectifying characteristics. In addition, a Schottky barrier height of ΦB ≈ 1.1eV has been determined from ultraviolet photoemission spectroscopy.