T. G. Finstad

Lattice‐matched Sc1−xErxAs/GaAs heterostructures: A demonstration of new systems for fabricating lattice‐matched metallic compounds to semiconductors

Successful growth of lattice‐matched Sc1−xErxAs layers buried in GaAs with a room‐temperature resistivity of ∼50 μΩ cm demonstrates the feasibility of fabricating heterostructures of lattice‐matched rare‐earth monopnictides and monochalcogenides in semiconductors. Reflection high‐energy electron diffraction oscillations during ScAs, ErAs, and Sc1−xErxAs growth indicate monolayer‐by‐monolayer growth.

Characterization of Ge nanocrystals embedded in SiO2 by Raman spectroscopy

Ge nanocrystals formed in a SiO2 matrix by ion implantation were studied by Raman spectroscopy. It is shown that Raman analysis based on the phonon confinement model yields a successful explanation of the peculiar characteristics resulting from the nanocrystals. A broadening and a shift in the Raman peak are expected to result from the reduced size of the crystals. Asymmetry in the peak is attributed to the variations in the size of the nanocrystals. These effects were observed experimentally for the Ge nanocrystals prepared by ion implantation and explained theoretically by incorporating the effect of size and size distribution into the theoretical description of the Raman shift. A comparison with the transmission electron microscopy images indicated that this analysis could be used to estimate the structural properties of nanocrystals embedded in a host matrix. The evolution of nanocrystal formation with annealing temperature, i.e. the size growth, was monitored by Raman spectrometry for several samples and the corresponding nanocrystal sizes were estimated using the phonon confinement model.

Low temperature interdiffusion in Au/In thin film couples

Abstract Interdiffusion in Au/In thin film couples was studied by in situ backscattering spectrometry. The substrate temperature was varied in the range from -170 to +50 °C. It was found that a uniform layer of AuIn 2 grows at the same rate as that at which gold condenses onto an indium film for substrate temperatures down to -50 °C. This is the fastest formation of intermetallic phases that has been reported. By lowering the substrate temperature the formation of an AuIn 2 layer during evaporation is suppressed. In this case the temperature of the thin film couple has to be raised considerably (to about 20 °C) to obtain interdiffusion within a reasonable time, and the final state of the thin film couple is different from that obtained when the phase formation is completed during evaporation. A possible explanation for this behaviour is discussed. The formation and growth of AuIn 2 after evaporation may be characterized by an activation energy of 0.23 eV.

Design and construction of a four-point bending based set-up for measurement of piezoresistance in semiconductors

We describe an experimental set-up for measurement of piezoresistivity coefficients of crystalline semiconductors, especially p-type silicon. We have aimed at good control of doping and temperature as well as the magnitude and the direction of applied stress and electric field. This is realized by applying the stress by the well known four point bending technique to a Si beam cut from a wafer. The set-up allows for high precision mechanical loading and alignment. The mechanical loading is done by a piezoelectric actuator. This allows us to cycle the load within a closed environment. A fiber optical interferometer has been developed to measure the center deflection of the Si beams. We derive analytical expressions relating center deflection to mechanical stress. From the analytical expressions we estimate the measurement uncertainty due to imperfections in alignment and machining. We also evaluate other factors. We have good accuracy and excellent repeatability and we find that thermal effects sets the lim...

Interdiffusion and phase formation in Au/Sn thin film couples with special emphasis on substrate temperature during condensation

The interdiffusion of gold and tin thin films was studied, with special emphasis on the influence of the substrate temperature during evaporation. A special target chamber makes it possible to evaporate several films in succession and to analyse them by Rutherford backscattering at any stage in the interdiffusion process without exposing the specimens to the atmosphere. The samples can be kept at any temperature between -170 and +150°C during the evaporation, the heat treatment and the analysis. The interdiffusion of Au/Sn films is complex, with several competing processes going on at the same time. If the tin is evaporated at low temperatures, the initial stage of the interdiffusion will be dominated by grain boundary diffusion of gold into the tin film followed by diffusion into the tin grains, resulting in the formation of the AuSn4 phase. The growth of the AuSn4 phase was found to be linear with time. Concurrently the AuSn phase grows in a planar manner from the original interface. The thickness of this phase grows as t12 and is believed to be limited mainly by the grain boundary diffusion of gold through the AuSn phase. This diffusion has an activation energy Ea = 0.59±0.06eV. When the substrate temperature during evaporation of the tin film is decreased, we observe an increase in the growth rate of the AuSn phase. This is believed to be caused by the decrease in grain size.

The 1.54-μm photoluminescence from an (Er, Ge) co-doped SiO2 film deposited on Si by rf magnetron sputtering

In this work, we report on quite strong 1.54‐μm photoluminescence (PL) from an (Er, Ge) co-doped SiO2 film deposited by rf magnetron sputtering. The PL intensity reaches a maximum value after the film is annealed at 700°C for 30min in N2. High-resolution transmission electron microscopy observation, together with energy dispersive x-ray spectroscopy analysis, indicates that amorphous Ge-rich nanoclusters precipitate in the film after 700°C annealing. X-ray diffraction shows the presence of Ge nanocrystals after 900°C annealing, and increasing Ge nanocrystal size with increasing annealing temperature up to 1100°C. The results suggest that the amorphous Ge-rich nanoclusters are more effective than Ge nanocrystals in exciting the Er3+ PL.

A diffusion marker in Au/Sn thin films

Abstract Argon was implanted into Au/Sn thin films to study the relative rates of diffusion of the two metals using Rutherford backscattering spectroscopy for analysis. The experiments indicate that the argon functions as a true Kirkendall marker. Under this assumption, it was found that gold diffuses through a layer of AuSn about three times faster than tin does.

Thermoelectric properties of Cu doped ZnSb containing Zn3P2 particles

We prepared ZnSb containing Zn3P2 particles of size ranging from a few tens to several hundred nanometers by melting powders of Zn, Sb, and P. Materials with Zn3P2 content up to 3.75% were made and subsequently ball-milled and hot pressed. A reduction in the thermal conductivity of 15% was achieved. By adding 0.2% Cu the carrier concentration increased an order of magnitude, to 2.0 × 1019 cm−3, while the mobility remained unaffected. The resulting increase in electrical conductivity together with the reduced thermal conductivity, led to a significant increase in the dimensionless figure of merit, in excess of 0.9 around 550 K.

Etch rates of (100), (111) and (110) single-crystal silicon in TMAH measured in situ by laser reflectance interferometry

Abstract Laser reflectance interferometry has been used to measure in situ etch rates of (100), (110) and (111) single-crystal silicon planes in 5–35 wt.% tetramethyl ammonium hydroxide (TMAH) solutions. The laser reflectance method was seen to give very accurate etch rates for samples that developed a surface roughness lower than 100 nm during the experiments. The etch rate of (100) and (111) was found to decrease with increasing etchant concentration, while the highest and lowest etch rates of (110) were observed for the 25 and 15 wt.% solutions, respectively. Activation energies were calculated as 0.54–0.59 eV for the 20–35 wt.% solutions, about 0.54 eV for the 25–35 wt.% solutions and 0.50–0.54 eV for the 25–35 wt.% solutions for the (100), (111) and (110) crystal orientation, respectively.

Characterization of evaporated gold-indium films on semiconductors

Abstract Evaporated Au-In films with total thicknesses in the range 200–6000 A have been studied by backscattering of 1.5 MeV He + ions, SEM, X-ray diffraction and with the electron microprobe. Both Si and GaAs were used as substrates, and the atomic percentage of Au in the films was less than 30. A fast diffusion within the films was observed which resulted in the formation of the AuIn 2 phase at room temperature. The compositional structure and the annealing behaviour of the films have been studied in the temperature range 25°–600°C. A model for the annealing behaviour of the films is presented. The Au-In films have been used for ohmic contacts to GaAs and a correlation between the resistance of such contacts and the alloying behaviour is attempted.