We investigate the kinetic role of a surfactant in the epitaxial Si/Ge crystal growth using ab initio molecular dynamics approach. We examine the previously suggested dimer-exchange mechanisms and find that kinetics plays a crucial role in determining the exchange process. We further find that the diffusion of adatoms on an island in the presence of a surfactant is quite different from the dimer-exchange process on a flat surface.

Growth of ZnSe-based compounds on the GaAs surface terminated by ultra-thin Ge epitaxial layer was carried out by molecular beam epitaxy and the influence of Ge layer on the growth of ZnSe was investigated. When the thickness of Ge layer was 1 atomic layer (AL), 2-dimensional growth occurred in the initial stage of ZnSe layer growth and anti-phase boundary (APB) free ZnSe layer was obtained. For Ge layer thickness of 10 AL, ZnSe grew 3-dimensionally and APBs were generated in the ZnSe layer. The crystalline quality of ZnMgSSe layer was also strongly influenced by the thickness of Ge layer. These phenomena were identified to be due to the transition of Ge surface structure from single domain to double domain with increasing Ge layer thickness.

We have used cross-sectional scanning tunneling microscopy to study the atomic-scale interface structure of InAs/Ga, _In.xSb superlattices grown by molecular-beam epitaxy. Detailed, quantitative analysis of interface profiles obtained from constant-current images of both (110) and (1ī0) cross-sectional planes of the superlattice indicates that interfaces in the (1ī0) plane exhibit a higher degree of interface roughness than those in the (110) plane, and that the Ga1-xln xAs interfaces are rougher than the InAs-on-Gal1-xInxSb interfaces. The roughness data are consistent with anisotropy in interface structure arising from anisotropic island formation during growth, and in addition with a growth-sequence-dependent interface asymmetry resulting from differences in interfacial bond structure between the superlattice layers. Roughness data are compared with measurements of anisotropy in low-temperature Hall mobilities of the samples.

Diffuse x-ray reflection from a SiGe/Si multilayer grown pseudomorphically on slightly miscut Si(OOl) substrates has been studied theoretically and experimentally. In the framework of the Distorted-Wave Born Approximation (DWBA), we demonstrated that the distribution of the diffusely scattered intensity gives conclusive information on both the amount and the in-plane and inter-plane correlation properties of the interface roughness. The best model for the description of the interface-morphology was found to be a combination of a two-level model and a staircase model.

We have investigated ZnSSe and ZnMgSSe epitaxial layers lattice-matched to GaAs (001) substrates grown by molecular beam epitaxy using atomic force microscopy and transmission electron microscopy. Under II-rich conditions with c(2x2) surface reconstruction, surface morphology exhibited corrugation aligned in the [1ī0] direction and composition modulation was observed in the same [1ī0] direction. Under VI-rich condition with (2x1) surface reconstruction, the surface morphology becomes rounded grain-like and composition modulation was not observed. The formation of composition modulation is associated with the surface corrugated structures.

Currently, there are no direct-bandgap alloy semiconductors that can be grown lattice-matched to GaP substrates. A strained layer of GaInP can be grown on GaP, however, with difficulties. First, GaInP is an indirect-bandgap material for In concentrations up to ∼30%. Second, the band alignment between GaInP and GaP is type-II for In concentrations up to ∼60%. The Mathews-Blakeslee critical thickness of GaInP layer on GaP is prohibitively small in the useful In concentration range. GaInP is known to grow in an ordered phase in certain growth conditions. By changing the growth conditions, a heterojunction of ordered GaInP and disordered GaInP can be grown. The conduction band offset going from a disordered GaInP phase to an ordered GaInP phase has been reported to be about 150 meV. Using a layer of ordered GaInP, a QW with type-I band alignment may be grown on GaP for a wider range of composition.

We have grown a series of approximately 60 Å thick GaP/GaInP/GaP strained quantum wells of various compositions using OMVPE. Strong photoluminescence, which exhibited an unusual temperature dependence, has been observed on many samples. A study of the QW’s using X-ray diffraction, TEM, and variable temperature PL reveals behaviors consistent with direct bandgap GaInP quantum wells containing ordered and disordered domains.

We proposed use of a new CdF2/CaF2 heterointerface for the formation of large conduction band discontinuities to apply quantum effect devices fabricated on Si substrates. Resonant tunneling diodes using this heterointerface on Si were fabricated and negative differential resistance whose P/V current ratio of 24 at highest was observed at room temperature.

Silicon CCDs have limited sensitivity to particles and photons with short penetration depth, due to the surface depletion caused by the inherent positive charge in the native oxide. Because of surface depletion, internally-generated electrons are trapped near the irradiated surface and therefore cannot be transported to the detection circuitry. This deleterious surface potential can be eliminated by low-temperature molecular beam epitaxial (MBE) growth of a delta-doped layer on the Si surface. This effect has been demonstrated through achievement of 100% internal quantum efficiency for UV photons detected with delta-doped CCDs.

In this paper, we will discuss the modification of the band bending near the CCD surface by low-temperature MBE and report the application of delta-doped CCDs to low-energy electron detection. We show that modification of the surface can greatly improve sensitivity to low-energy electrons. Measurements comparing the response of delta-doped CCDs with untreated CCDs were made in the 50 eV-1.5 keV energy range. For electrons with energies below 300 eV, the signal from untreated CCDs was below the detection limit for our apparatus, and data are presented only for the response of delta-doped CCDs at these energies. The effects of multiple electron hole pair (EHP) production and backscattering on the observed signals are discussed.

We have studied the effect of surface orientation on the optical and morphological characteristics of coherently-strained InP islands grown on GaInP/GaAs. The differences between islands grown on the (100) orientation and the (311)A orientation are studied. Islands grown on the (311)A orientation are more dense than the islands grown on the (100) orientation. For the (100) orientation, the island height distribution is bimodal peaked at 20 Å and 220 Å. For the (311)A orientation, the island height distribution is also bimodal peaked at 15 Å and 60 Å. Photoluminescence measurements for the (311)A orientation show a peak at 1.9 eV attributed to small islands. This peak is shifted to higher energies in comparison to the corresponding peak for the (100) orientation which is at 1.77 eV. This peak shift is due to the fact that the small islands on the (311)A orientation are smaller than the corresponding islands on the (100) orientation.

In-situ organization of InSb quantum dots on Al0.5Ga0.5Sb is reported. Samples were grown on just (100), 5°off (100) towards [0-1-1],(311)A, and (311)B surfaces of GaAs by molecular beam epitaxy. The growth mechanism and characteristics of quantum dots were analyzed using reflection high-energy electron diffraction, atomic force microscopy, and photoluminescence. Observed photoluminescence peak shift towards lower energy side with InSb thickness was interpreted by the development of quantum dots. Substrate orientation effect was examined and found to be useful to increase the dot density. As a result, as high as ~3xl 09 cm-2 dot density was achieved on the (311 )B substrate whereas the typical value on the (100) was ~2xl 08 cm-2 .

Self-organized Ge-dots on (001)-oriented Si-substrates have been studied using two-dimensionally resolved high resolution x-ray diffraction and reflectivity. The degree of the vertical correlation of the dot positions ("stacking") has been derived as well as a lateral ordering of the dots in a (disordered) square array with main axes parallel to ]100] and ]010].

We present results of the manipulation of antimony clusters on Si(001) by means of a scanning tunneling microscope. By adjusting tip-sample separation and pulse voltage, an antimony cluster can be removed from the sample surface without damaging it. The success rate of the removed-cluster redeposition from the tip back onto the surface is 30%. In the remainder of the attempts a square shaped structure is created that had a hillock in the center. The hillock exhibits a metallic-like I-V curve. Such a structure cannot be created without an Sb cluster previously removed from the surface and located on the tip.

GaAs micro crystals in line were grown on a sulfur-terminated GaAs surface by low energy focused ion beam. Ga ions, picked out from a liquid Ga ion source, were accelerated up to 10 KV to obtain a focused ion beam. The ions were given a positive bias to reduce their kinetic energy by retarding lens.The Ga ions landed on the surface softly and formed a series of Ga droplets. By subsequent As molecule supply to the Ga droplet, GaAs micro crystals in line were grown. This method was found to be useful to make fine structures directly on the semiconductor materials.

The growth and energetics of Ga chains on a Si(112) facet surface have been investigated. Low energy electron diffraction (LEED) and Reflectance Difference Anisotropy (RDA) experiments have been performed in UHV to examine the kinetics of the Ga atom chain formation process along the Si steps. This is a self-limiting process for substrate temperatures in the 400°C to 500°C range, since the binding energy of the metal atoms at the step edges is greater than that on the (11l)-type terraces. At saturation coverage, the Ga chains exhibit sixfold periodicity along the step edges, but below saturation, these chains exhibit fivefold periodicity. A model has been suggested from these results in which the periodicities of the chains are determined by the metal atom vacancies, which balance the tensile stress created by the larger metal atoms. We have used RDA to study the time evolution of the surface kinetics and changes in the surface reconstruction of Ga deposited on these facet (112) Si surfaces, as a function of substrate temperature and Ga deposition rate. The RDA measurement is shown to be sensitive to the formation of both the 5×1 as well as 6 × 1 reconstructions and to island formation at low substrate temperatures. The diffusion-controlled Ga line formation process at low temperatures has also been characterized as well as the evaporation controlled regime, which is evident at substrate temperatures over 400°C.

The morphologies of nanoscale epitaxial islands of TISi2 are studied. The islands are prepared by deposition of ultrathin Ti (3-20Å) on both smooth and roughened.Si(001) substrates. The island formation is initiated by annealing to 800-1000°C. The roughened substrates are prepared by etching with atomic H produced in a plasma. The morphologies of the substrate before and after island formation are examined by atomic force microscopy (AFM). In particular, the influence of surface-roughness on both the formation of islands and the size distribution of islands is investigated. On a rough substrate islands with a lateral dimension of ~350Å and a vertical dimension of ~25Å were observed with size uniformity of ~20%. Also it was observed that the roughness of the surface reduced the island size and affected the island distribution. The results are discussed in terms of surface energy and the strain field around the islands.

Defect formation in thick InxGa1-xAs layers, 0.06 ≤ x ≤ 0.17, grown by liquid phase electroepitaxy (LPEE) on partially masked GaAs substrates has been studied. The InxGa1-xAs ingots were 6 mm in thickness and, in some cases, more than 53 mm long in one direction. Prior to the LPEE growth, a thin SiO2 layer was deposited on the (100) oriented GaAs substrate by plasma enhanced chemical vapor deposition (PECVD), and patterned by photolithography with oxide free seeding windows of different geometry. The growth of a ternary crystal from a slightly supercooled melt originated in the form of islands within the window areas and extended laterally over the SiO2 layer to result, as the growth proceeded by LPEE, in a continuous layer with no apparent boundaries between merging islands. The two main structural defects have been identified in these compositionally uniform ternary crystals: microtwins and microcracks. They were found to result from the crystal/substrate misfit stress, when insufficiently suppressed by the SiO2 layer, and/or from improper seeding window geometry. The microcrack and microtwin formation in large diameter InxGa1-xAs crystals has been suppressed by the right choice of the seeding window geometry as well as by minimizing damage to the SiO2 layer caused by the H2 atmosphere and high growth temperature.

The paper reviews the work in mostly Si and SiGe epitaxy and some III-V work on patterned substrates. Results of metalorganic chemical vapor deposition (MOCVD), low pressure chemical vapor deposition (LPCVD), gas source molecular beam epitaxy (GSMBE), and solid source molecular beam epitaxy (MBE) were discussed in the context of facet formation and mass accumulation. A model was shown to explain the facet formation and its evolution in the process of growth. Further work on surface diffusion and nucleation processes as functions of temperature and other growth parameters will provide needed information for accurate modeling of the facet growth process.

A study of selective area epitaxy (SAE) of GalnP lattice matched to GaAs is presented. The selectively regrown GaInP is used as the emitter of a novel heterojunction bipolar transistor (HBT) device structure. Successful SAE of GalnP on both dark field (mostly covered) and light field (mostly open) SiO2 masks is compared. To characterize the critical regrown heterojunction, diodes and HBTs were fabricated and measured. It is found that a pre-growth pause of either TEGa or PH3 results in forward bias characteristics with low leakage and an ideality factor of ~1.25, indicating low interfacial defect density. Non-self aligned regrown emitter HBTs grown with a dark field mask scheme have been fabricated. Devices with an emitter area of 3x12 μm exhibit small signal current gain up to 80 with an fT and fMAX of 22 GHz and 18 GHz, respectively. To further improve the performance of these devices, a structure with a self-aligned refractory metal base contact and light field regrowth is proposed.

We propose and demonstrate a new mask material of AlGaAs native oxide for selective area metalorganic vapor phase epitaxy (MOVPE) which has several advantages over conventional SiNx or SiO2 masks. GaAs selective area growth occurs on masked substrate of AlGaAs native oxide whose Al composition is 0.4, and the wire structures with trapezoidal cross section are formed along ]100] direction on (001) GaAs substrates with line & space mask pattern. Furthermore, after annealing the selectively grown GaAs wire samples, GaAs layers can be regrown with atomically smooth surface, in which GaAs wires are perfectly buried. The results show that this novel selective area MOVPE technique using AlGaAs native oxide masks are promising for quantum nano-structure device fabrication.

Selective epitaxial growth (SEG) of silicon-germanium (SiGe) films on patterned-oxide silicon substrates, using a tubular hot-wall low pressure chemical vapor deposition (LPCVD) system, is demonstrated in this study. This conventional system is proposed as a low cost alternative for SiGe epitaxial growth. Three process improvements needed to achieve quality growth are discussed. First, the hydrogen bake process is modified to eliminate Ge-outgassing. Secondly, a Si SEG buffer layer is deposited prior to SiGe SEG. Finally, a small flow of dichlorosilane is introduced during the temperature ramp-down period prior to SiGe SEG. The growth results are discussed in terms of growth selectivity, thickness uniformity, growth rate, defect density, SiGe film composition, and electrical properties.