Yan-Ten Lu

Epitaxial Growth and the Art of Computer Simulations

The results of kinetic simulations of the aggregates formed during the deposition of atoms on a semiconductor surface are reviewed. Because the kinetic parameters are poorly known and the accuracy of the existing interatomic potentials has not been sufficiently tested, the goal has been to reach a qualitative understanding of the formation of unusual patterns during growth, such as the segregation of aluminum during the growth of aluminum-gallium-arsenide (AlGaAs) coherent tilted superlattices and the formation of thin, long, and parallel islands during the deposition of Si on an Si(100) surface. Kinetic mechanisms for these phenomena are proposed.

Theory of electronic structure in superlattices

Abstract This review begins with a survey of various methods of calculating the subband structures of semiconductor superlattices, showing the complementary nature of the self-consistent potential approach and the bulk-based empirical approach. The nature of the subbands is described in terms of a group theory analysis. Finally, as an example, the subbands of the GaAs/AlAs superlattice are synthesized from the results of computations and of experiments. Physical pictures for key features, such as the fundamental gap and various valley mixings, are explored.

The migration of a Si atom adsorbed on the Si(100)-2 × 1 surface

Abstract We use the Stillinger-Weber potential to examine the migration of a Si atom adsorbed on Si(100)-2 × 1 surface. The adsorption sites and the barriers between them are determined by energy minimization and used to estimate the rates of the site to site hopping. A stochastic kinetic simulation uses these rates to determine how the adsorbed atom migrates on the surface. We find that the mobility is highly anisotropic and that the motion is quasi one-dimensional. The particle diffuses along the dimer row and then it gets trapped on sites located between the dimers. The activation energy for the diffusion constant is a complicated function of the energy barriers separating the surface sites and the pre-exponential factor may have unusual values.

Adsorption and diffusion sites of a Si atom on a reconstructed Si(100)-(2 × 1) surface

Abstract We use Monte Carlo and molecular dynamics simulations to determine the adsorption sites, the barriers preventing site to site migration, and the dynamics of adsorption for a Si atom on a Si(100)-(2 × 1) surface. We find that the barriers to diffusion are highly anisotropic and strongly favor migration along the dimer rows. The site population at early times is controlled by the shape of the potential energy surface and it differs from the equilibrium population which is controlled by the binding energy.

Growth kinetics simulation of the Al-Ga self-organization on GaAs(100) stepped surfaces

Abstract We present results of a stochastic kinetic simulation of Al and Ga segregation during the mobility enhanced epitaxial deposition of an Al & Ga monolayer on the As face of a stepped GaAs(100) surface. The simulation deposits the atoms on the surface and moves them from site to site so that the frequency of each event is proportional to its rate. Since the rate constants needed in the simulation have not been measured we use guesses based on the available information and analogies with similar systems. The simulations generate exactly the growth pattern corresponding to a given set of rates. We have found a set of rate constants which generates Al & Ga growth patterns having all the properties observed experimentally. The predicted aggregation patterns are stable with respect to reasonable changes in the numerical values of the kinetic parameters. By varying the corresponding rates we find how the elementary kinetic steps affect segregation. One of the more interesting results is that to obtain good segregation with smooth Al-Ga borders it is essential that the Al-Al interactions are anisotropic and are stronger than the Ga-Ga interactions.

Growth kinetics simulation of the Al-Ga self-organization on (100) GaAs vicinal surfaces

We present results of a stochastic kinetic simulation of the segregation of Al and Ga during the mobility‐enhanced epitaxial deposition on the As face of a stepped (100) GaAs surface.

Studies of band alignment and two-dimensional electron gas in InGaPN/GaAs heterostructures

Room-temperature photoreflectance (PR) and photoluminescence (PL) spectra are measured for a series of In0.54Ga0.46P1−yNy∕GaAs heterostructures grown on GaAs (100) substrate. Redshifts of the PR and PL peaks indicate that the band gap of In0.54Ga0.46P1−yNy is dramatically reduced as nitrogen is incorporated. The emergence of additional peaks in PR spectra as nitrogen is incorporated indicates that the band alignment switches from type I to type II, due to the lowering of the conduction band, thus forming a two-dimensional electron gas (2DEG) in the interface region between In0.54Ga0.46P1−yNy and GaAs. The band gap energy and transition energies between the confined levels in the 2DEG are determined for samples with various nitrogen concentrations y. The number of confined levels in the 2DEG is found to increase with y; the composition-dependent bowing parameter is determined.

MBE growth of tilted superlattices: advances and novel structures

Abstract The vicinal surface ordering required for the TSL deposition has been studied as a function of temperature and composition for Ga x Al 1−x As, GaSb and AlSb surfaces. The interface sharpness observed during the Al-Ga co-deposition and self-organization on a vicinal surface has been modeled using a stochastic kinetics method. The modeling reproduces well the observations. To avoid critical effects of the tilt parameter variations, a novel structure, the serpentine superlattice, has been proposed. This structure has a “build in” two-dimensional confinement and yields uniform luminescence properties over large wafer areas. Finally, the TSL concept has been demonstrated for a novel system, the GaSb-AlSb system.

Two-mode InGaSb/GaSb strained-layer superlattice infrared photodetector

An interesting two-mode photodetector was constructed using an In/sub 0.19/Ga/sub 0.81/Sb/GaSb strained-layer superlattice (SLS). Such a structure is, at the same time, of type I for heavy hole and type II for light hole. The mini-subbands of this In/sub 0.19/Ga/sub 0.81/Sb/GaSb SLS are calculated using the modified Kronig-Penney model, as a function of well width at 300 K. A ten-period In/sub 0.19/Ga/sub 0.81/Sb/GaSb SLS structure can be applied as a two-mode photodetector with near-zero and reverse bias. This phenomenon can be proved by the spectral response of the structure grown by low-pressure metalorganic chemical vapor deposition (MOCVD). The wavelengths of dominant absorption peaks are 1.92 and 1.77 mu m at near-zero and reverse bias, respectively. The experimental data are in good agreement with the theoretical deductions.<<ETX>>

HIGH CONDUCTION-BAND OFFSET OF ALINASSB/INGAAS MULTIPLE QUANTUM WELLS GROWN BY METALORGANIC VAPOR PHASE EPITAXY

Unstrained Al0.66In0.34As0.85Sb0.15/In0.53Ga0.47As multiple-quantum-well (MQW) structures have been grown by metalorganic vapor phase epitaxy. Low-temperature photoluminescence was performed for these MQW structures. We compared the experimental data with the theoretical calculations. The conduction-band offset ratio of AlInAsSb/InGaAs heterojunction was set as an adjustable parameter in the theoretical model. We estimated the conduction-band offset ratio to be 0.90±0.05 for the Al0.66In0.34As0.85Sb0.15/In0.53Ga0.47As heterojunction.