J. J. Zinck

ISLAND DYNAMICS AND THE LEVEL SET METHOD FOR EPITAXIAL GROWTH

Abstract We adapt the level set method to simulate the growth of thin films described by the motion of island boundaries. This island dynamics model involves a continuum in the lateral directions, but retains atomic scale discreteness in the growth direction. Several choices for the island boundary velocity are discussed, and computations of the island dynamics model using the level set method are presented.

Hydrogen adsorption and phase transitions in fullerite

Hydrogen desorption and adsorption properties of the fullerene materials C60, C70, and fullerite (a mixture of C60 and C70) were measured volumetrically using a Sieverts apparatus. Over several cycles of isotherm measurements at 77 K, the hydrogen storage capacities of one of the fullerite samples increased from an initial value of 0.4 wt % for the first cycle to a capacity of 4.4 wt % for the fourth cycle. Correspondingly, the surface area of this sample increased from 0.9 to 11 m^2/g, and there were changes in its x-ray powder diffraction pattern. In comparison, two other fullerite samples, prepared by a different procedure showed no such behavior. Pure C60 and pure C70 were also cycled and exhibited small and constant capacities of 0.7 and 0.33 wt %, respectively, as a function of number of cycles. The enhanced storage capacity of fullerite material is tentatively attributed to the presence of C60 oxide.

Excimer laser‐assisted metalorganic vapor phase epitaxy of CdTe on GaAs

We have successfully grown CdTe (111) on GaAs (100) at 165 °C using a 248 nm excimer laser to photodissociate dimethylcadmium and diethyltellurium in the gas phase. Good crystalline quality of the layers is confirmed by x‐ray diffractometry. Growth rates up to 2 μm/h have been recorded in real time using time‐resolved reflectivity. Auger analysis reveals that the films are stoichiometric throughout the thickness of the layer, and that carbon and oxygen contaminants are below the level of detectability. We have used laser‐induced fluorescence spectroscopy to examine the photodissociation mechanism of diethyltellurium and have observed a linear dependence of Te atom production on excimer laser power.

Reversible modification of CdTe surface composition by excimer laser irradiation

KrF excimer laser irradiation of CdTe at fluences below the melt threshold (≤75 mJ/cm2) removes surface layers and produces reversible changes in the surface composition that depend upon the laser fluence and number of laser pulses delivered to the surface. At fluences above ∼40 mJ/cm2 a Te‐rich layer is obtained. A stoichiometric composition can be restored by irradiation at reduced laser fluence. The primary desorption products are Cd and Te2, and the velocities of these species are well described by a Maxwellian distribution. The fluence‐dependent changes in CdTe surface composition are consistent with a photothermal mechanism based on the competition between formation and desorption of Te2 and desorption of Cd atoms from the laser‐irradiated surface.

Spin relaxation in [110] and [001] InAs/GaSb superlattices

A 25 times enhancement of the electron spin lifetime is observed in a [110] InAs/GaSb superlattice relative to the corresponding [001] superlattice, an effect that is primarily attributed to suppression of native interface asymmetry.

Room-temperature electric-field controlled spin dynamics in (110)InAs quantum wells

We report the demonstration of room temperature gate control over the electron spin dynamics using the Rashba effect in a (110) InAs∕AlSb two-dimensional electron gas. Our calculations predict that the strong spin–orbit interaction in this system produces pseudomagnetic fields exceeding 1 T when only 140 mV is applied across a single quantum well. Using this large pseudomagnetic field, we demonstrate low-power spin manipulation on a picosecond time scale. Our findings are promising for the prospect of nonmagnetic low-power, high-speed spintronics.

Metalorganic molecular beam epitaxial growth of high-quality Cd1-xZnxTe (0≤x≤0.27) films

High‐quality (001) Cd1−xZnxTe (0≤x≤0.27) films were grown by metalorganic molecular beam epitaxy on (001) GaAs substrates using thermally precracked dimethylcadmium, diethylzinc, and diethyltelluride. Cd1−xZnxTe/GaAs (0≤x≤0.05) films of 6–9 μm thickness exhibited x‐ray rocking curve full widths at half‐maximum of 200–240 arcsec, and 290–350 arcsec was measured for Cd1−xZnxTe/GaAs (0.09≤x≤0.17). The crystalline quality for the range of x values (0≤x≤0.27) reported here surpasses that previously published in the literature. The 5 K photoluminescence spectra of the Cd1−xZnxTe layers were dominated by strong and sharp bound excitonic transitions. In addition, the free excitonic transition was observed in Cd1−xZnxTe layers with 0≤x≤0.06. Secondary ion mass spectrometry measurements showed that the films were free of O and C contamination.

Measurement of photoemission oscillations during molecular beam epitaxial growth of (001) GaAs, AlAs, AlGaAs, InAs, and AlSb

Photoemission oscillations are observed from (001) GaAs, AlAs, AlGaAs, InAs, and AlSb. The periodicity of the oscillations corresponds to that of reflection high‐energy electron diffraction oscillations measured using the same growth conditions. For both methods, the oscillation amplitude is strongly dependent on the substrate temperature, III/V flux ratio, and the nature of the surface on which growth is nucleated for the oscillation measurement.

Experimental demonstration of split side-gated resonant interband tunneling devices

We report a prototype side-gated asymmetric resonant interband tunneling device (RITD) fabricated with an AlSb∕InAs∕GaSb∕AlSb heterostructure for Rashba spin filter applications. This device features independent control gates along the sides of an RITD mesa structure that can be used to provide an electric field orthogonal to the resonant tunneling current. The distribution of lateral wave vectors for electrons approaching the RITD active layers obtains a nonzero average through the application of the orthogonal electric field, a requirement for Rashba spin filter operation. Measured current–voltage curves show a modulation of the tunneling current with a side gate bias, demonstrating lateral electric-field projection into the resonant tunneling mesa structure. The prototype device was fabricated to submicron dimensions utilizing a conformal and scalable processing scheme.

Growth oscillation decay rates for control of III–V molecular beam epitaxy near stoichiometry

We have investigated the decay of reflection high-energy electron diffraction oscillations during growth of InAs (001), as a function of growth parameters, such as the V/III ratio. We have shown that the decay constants are sensitive to changes in growth morphology, as measured by scanning tunneling microscopy. Our experiments show that the values of these decay constants decrease at high V/III ratios, in agreement with previous work. Additionally, we have found that the values of the decay constants diverge as the transition between the (2×4) and (4×2) reconstructions is approached. We propose that the decay constants of the growth oscillations may be used as inputs for control of interface morphology.