Misoriented Si Research Articles

Monolithically integrated HgCdTe focal plane arrays

The cost and performance of hybrid HgCdTe infrared (IR) focal plane arrays are constrained by the necessity of fabricating the detector arrays on a CdZnTe substrate. These substrates are expensive, fragile, available only in small rectangular formats, and are not a good thermal expansion match to the silicon readout integrated circuit. We discuss in this paper an IR sensor technology based on monolithically integrated IR focal plane arrays that could replace the conventional hybrid focal plane array technology. We have investigated the critical issues related to the growth of HgCdTe on Si read-out integrated circuits and the fabrication of monolithic focal plane arrays: (1) the design of Si read-out integrated circuits and focal plane array layouts; (2) the low-temperature cleaning of Si(001) wafers; (3) the growth of CdTe and HgCdTe layers on read-out integrated circuits; (4) diode creation, delineation, electrical, and interconnection; and (4) demonstration of high yield photovoltaic operation without limitation from earlier preprocessing such as substrate cleaning, molecular beam epitaxy (MBE) growth, and device fabrication. Crystallographic, optical, and electrical properties of the grown layers will be presented. Electrical properties for diodes fabricated on misoriented Si and readout integrated circuit (ROIC) substrates will be discussed. The fabrication of arrays with demonstrated I-V properties show that monolithic integration of HgCdTe-based IR focal plane arrays on Si read-out integrated circuits is feasible and could be implemented in the third generation of IR systems.

Growth of wurtzite‐GaN on silicon (100) substrate by molecular beam epitaxy

We report on the growth of wurtzite-GaN layers by molecular beam epitaxy using ammonia on Si(100) substrates. We show that using 4° misoriented Si(100) substrates, GaN layers are obtained with a dominant orientation. The nucleation conditions of the AlN buffer layer as well as the entire growth process are described and compared with the process developed for the growth on Si(111) substrates, already well optimised in our laboratory [1]. The crystalline quality and polarity are assessed by transmission electron microscopy, X-ray diffraction and chemical etching. The most noticeable features of the layers grown are the high crystal quality of the AlN/Si interface, the Ga-polarity of the final GaN layer and especially the presence of the wurtzite phase only. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Fabrication and electron-beam-induced polymerization of C 60 nanoribbon

We have presented a method of fabricating an array of C 60 nanoribbons on a Si(111) surface and have investigated the electron-beam-induced polymerization of C 60 nanoribbons using scanning tunneling microscopy (STM) and spectroscopy (STS). By selective growth of C 60 multilayers on the terrace of a misoriented Si(111)√3×√3R30°-Ag surface, a uniformly oriented array of C 60 nanoribbons having the dimensions of 40 nm×4–5 nm (width×thickness) has been fabricated. The length of these nanoribbons exceeds several micrometers. The cluster-shaped C 60 oligomer has been created on the nanoribbons after electron beam irradiation. In the case of the oligomer, we have observed a higher electron density near the Fermi level than in the case of the nonpolymerized C 60 molecules.

Characterization of the surfaces of hydrogen-passivated silicon by STM

Hydrogen-passivated silicon (amorphous, microcrystalline or crystalline silicon) is characterized by a low density of surface states. Thus, standard tunnelling theory, which relies on tunnelling at the Fermi energy, may not be applicable to this class of materials and it may be difficult to optimize scanning tunnelling microscopy. We performed simultaneous measurements of topography (by constant-current imaging) and of the distribution of the local apparent barrier height, ΦA, as a function of the tunnelling voltage on hydrogen-passivated, misoriented Si(111) samples that were prepared by etching with NH4F solution. Tunnelling conditions were identified, which allow the characterization of inhomogeneities related to both local roughness and chemical composition.

The influence of growth temperature on the period of RHEED oscillations during MBE of Si and Ge on Si(111) surface

The thickness of a film growing during one oscillation period at MBE of silicon and germanium on a slightly misoriented Si(111) surface was measured as a function of temperature. The temperature elevation was found to result in either an increase or decrease in the oscillation period. That was accounted for by the occurrence of various barriers for incorporation of adatoms at the upper terrace into differently directed steps. The activation energies of nucleation of two-dimensional islands were determined. In the case of a decrease in the oscillation period the activation energy was 1.45±0.1 eV and 1.1±0.1 eV for epitaxy of silicon and germanium, respectively. In the case of a increase in the oscillation period the activation energy was 0.91±0.1 eV and 0.49±0.1 eV for epitaxy of silicon and germanium, respectively.

TEM investigation of the dependence of structural defects on prelayer formation in GaAs-on-Si thin films

We present a transmission electron microscopy (TEM) study of the dependence of structure defects on the kind (Ga or As) and the growth temperature of the prelayer in GaAs-on-Si films grown by molecular beam epitaxy (MBE) on vicinal (100) Si substrates. Generally the prelayer formation conditions do not change the appearance and the density of threading dislocations that remain the main structural defect. However the structural characteristics for each cut-off angle appear to depend eventually on the [011] direction of GaAs epilayer relatively to the [011] misoriented Si substrate direction. Planar defects can be avoided only for midrange angles (e.g. 4.5°) using As prelayer at 400°C.

Thermodesorption mass spectrometry study of the adsorption of Sb on misoriented Si(111)

Adsorption of Sb on a misoriented Si(111) surface is investigated by thermodesorption mass spectrometry (TD-MS). The spectra confirm the existence, in the submonolayer range, of new adsorption sites induced by the presence of steps, previously shown by Auger spectroscopy thermodesorption (TD-AES) and tentatively attributed, through simulations, to molecular adsorption at the steps rather than dissociative on the terraces. The present TD-MS measurements completely confirm this interpretation, and also give new information on the nature of the species leaving the surface (essentially Sb 2) and on their emission laws (orientational desorption).

PbS Thin Film Formation on Terrace-Step Surface by Pulsed Laser Deposition

PbS layer growth by laser ablation on slightly misoriented Si and NaCl substrates has been investigated. An analysis of the substrate atom core level XPS spectra dependence on layer growth indicated a “flat” layer growth on terrace-step surface. The influence of substrate surface morphology on layer growth and on layer component electron spectra was observed. An additional structure of Pb core levels in the photoelectron spectra was observed in PbS layers grown on misoriented substrate. The additional components of Pb core levels have a shift equal to 1.0 eV. The formation of clusters with excess of Pb is considered to be responsible for the new lines.

Generation and suppression process of crystalline defects in GaP layers grown on misoriented Si(1 0 0) substrates

We have investigated the generation process of crystalline defects in GaP layers grown on Si substrates (GaP/Si) by molecular beam epitaxy (MBE) and migration enhanced epitaxy (MEE). Transmission electron microscopy observations revealed that few threading defects such as stacking faults and threading dislocations are detected in GaP/Si by MEE. In addition, a regular network of misfit dislocations was generated during the lattice relaxation process. On the other hand, stacking faults were generated in high density at the hetero-interface and threading dislocations as well as interfacial misfit dislocations were observed in GaP/Si by MBE. The generation of stacking faults would be related to the coalescence or expansion of isolated GaP islands and the presence of stacking faults would affect the generation of threading dislocations.

Structured Roughness of Si Surface Obtained by Molecular Beam Epitaxy on Highly Misoriented Si(111) Substrate

We present the results of an X-ray analysis of the surface morphology of a sample obtained by Si MBE onto a higly misoriented Si(111) substrate. X-ray reflectivity and diffuse scattering provide a description of the surface. The amplitude of the surface profile is about 6.6 nm, with a sawtooth shape. Satellites in the diffuse scattering indicate a 215±5 nm periodicity int he miscut direction. The analysis of satellite intensities shows an asymmetry of the surface shape. The results are in agreement with AFM images of the surface.

Step-driven molecular adsorption of Sb on Si(111)

Adsorption of Sb on a misoriented Si(111) surface is investigated by thermodesorption Auger spectroscopy. The spectra reveal that, in the submonolayer range, new adsorption states appear for the vicinal surface which do not exist for the nominal one. Quenched molecular-dynamics simulations, in which Si and Sb are modeled by many-body tight-binding potentials, allow us to interpret these new states as due to a molecular adsorption at the steps instead of a dissociative one on the terraces.

Anomalous strong repulsive step-step interaction on slightly misoriented Si(113)

We have used scanning tunneling microscopy to study Si(113) 0.2° misoriented towards [11-bar0]. Rapid quenching of this surface from 1500–1575 K to room temperature results in a uniformly stepped single-domain surface, whereas slower cooling gives rise to clustering of steps. The thermally induced step wandering and the terrace width distribution of the uniformly stepped surface are analyzed in order to determine the strength of the energetic and entropic step-step interactions. Beside the short-range attractive step-step interaction found by Song and Mochrie [Phys. Rev. Lett. 73, 995 (1994)] on Si(113) misoriented 1°–5° towards [001], we found an anomalously strong long-range repulsive step-step interaction on Si(113) 0.2° misoriented towards [11-bar0]. The coexistence of a long-range repulsive and a short-range attractive step-step interaction may explain the transition from a uniformly stepped surface at high freeze in temperature to a faceted surface at lower freeze in temperatures.

Silicon homoepitaxy on high index surfaces and the effect of antimony on this growth

We report on the structure of Si films grown by molecular beam epitaxy on highly misoriented Si(111) surfaces and on the influence of Sb on this growth. Although the equilibrium morphology of these surfaces is a mixture of single and triple height steps, one observes for temperatures lower than the 1 × 1 to 7 × 7 transition one, by LEED, AFM and HRTEM, that the MBE growth gives rise to an important roughness. On the contrary, at higher temperature or when Si and Sb are coevaporated, we stabilize a regular array of steps. We show that these steps are triatomic in the former case and monoatomic in the latter. Such a behaviour illustrates the major role played by the 7 × 7 reconstruction on the growth morphology of Si films.

Heteroepitaxial CdTe(111) grown by MBE on nominally flat and misoriented Si(001) substrates: characterization by electron microscopy and optical methods

Transmission electron microscopy (TEM), and low temperature reflectance and photoluminescence (PL) have been used to characterize heteroepitaxial CdTe(111) layers grown by molecular beam epitaxy directly onto nominally flat and misoriented Si(001) substrates. TEM observations confirmed that 1° offcut toward [110] in the Si(001) substrate suppressed formation of double domains, while increasing the azimuthal angle of the offcut relative to [110] suppressed twin formation. Under optimized growth conditions, residual twinning defects disappeared within about 2 μm from the substrate. Atomic-scale details of interfaces in this system were successfully recorded. Clear splitting of exciton states at the direct gap in optical reflectance and PL spectra demonstrated the existence of residual biaxial tensile strain of about 7 × 10−4 in the CdTe layers, due to thermal expansion mismatch. A strain-shifted neutral acceptor-bound exciton peak dominated the 1.7 K photoluminescence spectrum, together with donor-to-acceptor and band-to-acceptor transitions involving a 49 meV shallow acceptor level. The sharpness of bound exciton peaks (about 0.6 meV full width at half maximum) supported the high layer quality.

HRLEED and STM Study of Misoriented Si (100) with and without a Te Overlayer

AbstractThe growth of high quality Te on misoriented Si(100) is important as an intermediate phase for epitaxial growth of CdTe. The misorientation angle plays a key role in the growth quality of CdTe/Si(100); this incited our curiosity to investigate the effect of the misorientation angle on the topography of the surface structure of Si(100). Our main goal is to show the relation between the misorientation angle, the terrace width and the step height distributions. HRLEED ( High Resolution Low Energy Electron Diffraction ) provides information in reciprocal space while STM gives real space topographic images of the surface structure. STM and HRLEED measurements were performed on Si(100) with misorientation angle υ= 0.5°, 1.5° and 8° towards the ]110] direction and υ= 4° towards the ]130] direction. Except for the 8° misorientation in which case a regular step array with diatomic step height was observed, for the other misorientations the terrace width was variable. The average terrace width decreased with increasing misorientation angle. A mixture of diatomic and monatomic step heights was observed on the 0.5° and 1.5° misoriented Si(100) samples. It proves that one can not assume purely monatomic step height for low misorientation angles. Our results do not agree with the belief that at low miscut angle A and B terraces are equal and that as the misorientation angle increases the B terrace tends to be wider than the A terrace. In fact, pairing of terraces was not observed at all. Te was deposited at a substrate temperature of 200 C. We observed a significant reduction in the terrace widths for all miscut angles.

Molecular beam epitaxy of gallium arsenide on 0.3°-misoriented epitaxial Si substrates

APD (antiphase domain) free GaAs is grown by molecular beam epitaxy on an epitaxial (100)Si substrate with an offset angle of 0.3° without conventional high-temperature pretreatment. Reflection high energy electron diffraction (RHEED) demonstrates the presence of a double-domain reconstruction structure on the 0.3° misoriented Si substrate after pretreatment at 400–600°C. However, the GaAs epitaxial layers grown on these substrates by the two-step method were APD free. KOH etching and double crystal X-ray diffraction (DCXD) show the crystalline quality of GaAs grown on the epitaxial Si substrate is comparable to that of GaAs grown on conventional Si substrates heat-treated at 900°C. The evaluation by atomic force microscopy (AFM) shows the surface flatness of GaAs layer grown on the 0.3°-misoriented epi-substrate is much more superior to that grown on the epi-substrate with 2° offset.

Microstructure of heteroepitaxial CdTe grown on misoriented Si(001) substrates

Transmission electron microscopy has been used to characterize the microstructure of heteroepitaxial CdTe (111) layers grown by molecular beam epitaxy directly on nominal and misoriented Si(001) substrates. High-resolution electron micrographs showing atomic-scale details of the CdTe (111)/Si(001) interface have been recorded. Layer quality depended on the substrate tilt parameters, including the offcut orientation angle θ, and the azimuthal angle φ relative to [110]. Small φ values (4° and 10°) gave high densities of stacking fault twins throughout the epilayer whereas larger misorientation angles led to a rapid falloff away from the substrate. Under optimized growth conditions, the occurrence of twins effectively dropped to zero within a distance of less than 2.5 μm from the substrate surface.

Dependence of Time Dependent Dielectric Breakdown Characteristics on Mechanism for Silicon Epitaxial Growth on Misoriented Czochralski Silicon Crystal

The reliability of oxide films formed on the surface in a misoriented Si(100) epitaxial wafer was studied by time dependent dielectric breakdown (TDDB). The accidental failure of TDDB decreases with an increase in misorientation and a drastic change is found at misorientation of 0.08° or less. A model, consisting of island growth and lateral growth in the epitaxial growth, has been proposed to explain the observation. In this model, the dominant growth mechanism changes from the island growth to the lateral growth at critical misorientation 0.11°. The appearance of the island growth may give rise to a TDDB weak point and cause the accidental failure.

Shape transition in the epitaxial growth of gold silicide in Au thin films on Si(111).

Growth of epitaxial gold silicide islands has been observed when an Au film deposited on a bromine-passivated vicinal (4\ifmmode^\circ\else\textdegree\fi{} misoriented) Si(111) substrate was annealed around the Au-Si eutectic temperature. The islands grow in the shape of equilateral triangles, reflecting the symmetry of the (111) substrate, up to a critical size beyond which the symmetry of the structure is broken, resulting in a shape transition from triangle to trapezoid. The island edges are aligned along the three equivalent {11\ifmmode\bar\else\textasciimacron\fi{}0} directions of the Si(111) surface. The elongated islands, instead of growing along three equivalent {11\ifmmode\bar\else\textasciimacron\fi{}0} directions, grow only along one preferential direction. This has been attributed to the vicinality of the substrate surface as the steps on this substrate are expected to run along the observed preferential growth direction. We have observed, under various conditions, elongated islands with an aspect ratio as large as 15:1.

Suppression of twin formation in CdTe(111)B epilayers grown by molecular beam epitaxy on misoriented Si(001)

CdTe(lll)B layers have been grown on misoriented Si(001). Twin formation inside CdTe(lll)B layer is very sensitive to the substrate tilt direction. When Si(001) is tilted toward [110] or [100], a fully twinned layer is obtained. When Si(001) is tilted toward a direction significantly away from [110], a twin-free layer is obtained. Microtwins inside the CdTe(111)B layers are overwhelmingly dominated by the lamellar twins. CdTe(111)B layers always start with heavily lamellar twinning. For twin-free layers, the lamellar twins are gradually suppressed and give way to twin-free CdTe(111)B layer. The major driving forces for suppressing the lamellar twinning are the preferential orientation of CdTe[11-2] along Si[1-10] and lattice relaxation. Such preferential orientation is found to exist for the CdTe(111)B layers grown on Si(001) tilted toward a direction between [110] and [100].