We have grown aluminum nitride thin films by ultrahigh vacuum reactive sputter deposition on Si(111) and Si(001) substrates. We show results of film characterization by Raman scattering, ion beam channeling, and transmission electron microscopy, which establish the occurrence of epitaxial growth of wurtzitic aluminum nitride thin films on Si(111) at temperatures above 600 °C. In contrast, microstructural characterization by transmission electron microscopy shows the formation of highly oriented polycrystalline wurtzitic aluminum nitride thin films on Si(001). Real-time substrate curvature measurements reveal the existence of large intrinsic stresses in aluminum nitride thin films grown on both Si(111) and Si(001) substrates.

Growth of GaN thin films on AlN-buffered Si(111) by ultrahigh-vacuum rf glow discharge reactive magnetron sputtering is reported. Epitaxy of GaN is established by x-ray and electron diffraction. Raman scattering from the epitaxial films consistent with that of wurtzitic GaN is observed. The ion energies involved in the growth process are quantified by measuring the plasma potentials of the Ar/N2 glow discharge by an emissive Langmuir probe technique. As a function of increasing input power, a systematic increase in ion energies and a systematic straining of the GaN lattice are observed. Measured GaN phonon energy scales with lattice strain.

Real-time measurements of intrinsic stresses during growth of polycrystalline and epitaxial aluminum nitride (AlN) thin films on Si(111) are reported. Our room-temperature measurements on polycrystalline films corroborate previous post-growth measurements. Our high-temperature measurements provide evidence of large intrinsic stresses during epitaxial growth of AlN on Si(111) and insignificant stress relaxation during growth.

The role of defects in limiting the thermal conductivity of synthetic diamond films has not been fully explored. In order to shed light on phonon-defect interactions in this material, we have studied the thermal conductivity of single crystal diamond irradiated with fast neutrons. For low fluences neutrons produce lattice vacancies and small regions of disordered carbon [1], two important types of defects which occur in diamond films.

This article addresses stress effects in sputter deposited aluminum nitride (AlN) thin films on Si(111). One of the elastic constants of AlN (C33) was measured directly. Real time stress measurements during growth of AlN thin films yield corroborating results for polycrystalline film growth and new results which indicate large intrinsic stresses during epitaxial growth of AlN on Si(111).

The process of reactive sputtering of elemental Al and Zr in an Ar/N2 mixture has been examined by atomic absorption spectroscopy. Results have been presented further supporting the existence of a chemical competition effect during dual source reactive sputtering. The growth of epitaxial AlN film on Si (111) by laser beam interference is monitored in real time, which yielded a measurement of the true growth rate. By correlating the two measurements, a linear proportionality between the true growth rate of AlN and the gas phase Al density has been demonstrated.

Results of room-temperature optical studies on â€â€?10 micron free-standing diamond films are reported. The films were grown on Si(100) substrates by hot filament-assisted chemical vapor deposition (CVD) from a methane/hydrogen mixture. The as-grown, free surface of the film exhibits a surface roughness of scale 0.2-5 microns, depending on the methane/hydrogen ratio of the growth gas mixture, which introduces significant optical scattering losses for frequencies greater than 0.5 eV. Reflection and transmission spectra in the range 0.01-10 eV were collected for films grown in different methane/hydrogen mixtures. Below the threshold for interband adsorption, the film behaves approximately as a thin parallel plate of refractive index 2.4, with the rough free surface leading to increasingly larger loss of specular transmission/reflection with decreasing wavelength (λ). For λ>s, where s is the average scale of the surface roughness, distinct interference maxima are observed, and the data in this region can be analyzed to determine the refractive index and film thickness. Structure associated with absorption from one-, and multi-phonon processes and chemisorbed hydrogen are also observed. Near 5.3 eV the onset of interband adsorption is observed, in good agreement with the value of the indirect bandgap in crystalline type IIa diamond. The films are found to exhibit optical properties similar to that of bulk diamond. However, the surface roughness must be better controlled by the deposition process, if these CVD films are to be used in applications as protective, high refractive index optical coatings.

We have measured the thermal conductivity of two diamond films grown by a chemical vapor deposition process. At room temperature the thermal conductivity is of the order of 10 W cm−1 K−1, i.e., as high as naturally occurring (type Ia) single-crystal diamonds. This value exceeds the thermal conductivity of copper at room temperature by a factor of 2. Since these films consist of microcrystallites of diamonds of dimensions on the order of 2 μm, boundary scattering of phonons is expected to be large. The expected effect of boundary scattering on the lattice thermal conductivity is calculated, and is in qualitative agreement with the observed results above about 30 K. However, important differences between the measured conductivity and that expected for boundary scattering are observed below this temperature. It is proposed that a small amount of disorder present in the lattice (identified through Raman studies) can account for this unusual behavior.

Raman scattering from bound electrons has been observed in Si-doped GaAs–A1xGa1−xAs multiple heterostructures. The donor-related features show broadening due to the dependence of the donor spectrum on the position of the impurity in the well. Transitions from 1s to 2s states and bound excitations associated with intersubband transitions were identified. The latter observation confirms the existence of resonant impurity states in quantum-well structures.

Resonant Raman scattering experiments on GaAs(Si doped)-${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ quantum-well structures show transitions involving the ground state of the donors and narrow resonant donor states derived from higher conduction subbands. These new impurity-related features, which occur at slightly higher energies than the associated conduction intersubband excitations, have been studied as a function of power density, temperature, and well width.

Amorphous Ti2O3 films with thicknesses ≳103 Å have been obtained by cw laser irradiation of Ti50Zr10Be40 exposed to low oxygen pressures. In contrast, thermal oxidation of (nonirradiated) samples reveals scales composed of crystalline oxides. Raman scattering, x-ray, and electron microscopy data on the layers are reported. It is suggested that irradiation leads to an enhanced oxidation rate preventing crystallization. Possible mechanisms of enhancement are discussed.

Resonant Raman spectra of photoexcited semi-insulating GaAs and Fe/GaAs show features characteristic of two-dimensional electron plasmas. The results are ascribed to the presence of a space-charge layer at the surface, originating in a slight mismatch of Fermi-level positions at the vacuum (or metal) interface and in the bulk. Calculations using values of intersubband transition energies from the data give an estimated shift of ∼0.04 eV for the Fermi-level position at T = 85K.

Transitions involving donor states were observed in resonant Raman scattering experiments on Si-doped $\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}\ensuremath{-}{\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ multiple quantum wells. The electronic scattering gradually transforms into photoluminescence as the exciting energy is tuned across the resonance. The largest contribution in the spectra is associated with $1S\ensuremath{\rightarrow}2S$ transitions of donors near the center of the wells. The experimental results show good agreement with recent calculations.