Maskless selective area growth of InP on Sub-μm V-groove patterned Si(001)

Low pressure metalorganic chemical vapor deposition of InP onexactly oriented Si(OOl) substrates with a periodic V-groove pattern of periodicity ≤1.2 μm using a two temperature growth sequence (400 and 640°C) is reported. Planar InP layers with extremely low defect density of 7 × 10⁴ cm⁻² are obtained. For InP on V-grooves of width g ≤1.0μm, a planar surface is formed after less than 1 μm of growth. Formation or suppression of antiphase domains (APDs) is a function of the widths of the (OOl)-oriented ridges. For s ≤1 μm, epilayers are single domain and the direction is oriented parallel to the grooves. At 400°C, nucleation starts homogeneously on {111}-sidewallsand (001)-facets. While heating up to 640°C, InP migrates into the grooves, depleting almost completely the (001)-facets. During growth of the main layer, first the V-grooves are filled up. Subsequently (001)-ridges are overgrown laterally or voids are formed on top of them. This mechanism is responsible for both planarization and APD-suppression. The surface migration length of InP on Si(001) at 640°C is estimated to be ≈0.5 μm.     

Microstructures of InAs1−xSbx (x = 0.07–0.14) alloys and strained-layer superlattices

Growth of InAs_1−xSb_x alloys by metalorganic chemical vapor deposition at 475°C results in CuPt ordering even at Sb concentrations as low as x = 0.07-0.14. The two {111}_B variants are present, but each exists separately in 1-2 μm regions. However, the ordering is incomplete: it occurs in platelet domains lying on habit planes tilted 30° from (001) within a disordered matrix and is not continuous at the atomic scale within the domains. This ordering apparently explains the reduction in infrared emission energies relative to the bandgaps of bulk alloys. Similar ordering is found in an InAs_0.91Sb_0.09/In_0.g7Ga_0.13As strained-layer superlattice with lower-than-expected emission energy. High-resolution images indicate that the superlattice layers flat and regularly spaced. Infrared LEDs have been made from such superlattices.     

Diffuse diffracted features and ordered domain structures in GalnP layers grown by organometallic vapor phase epitaxy

Transmission electron diffraction (TED) and transmission electron microscope (TEM) studies have been made of organometallic vapor phase epitaxial Ga_xIn_1−xP layers (x ≈ 0.5) grown at temperatures in the range 570–690°C to investigate ordering and ordered domain structures. TED and TEM examination shows that the size and morphology of ordered domains depend on the growth temperature. The ordered domains change from a fine rod-like shape to a plate-like shape as the growth temperature increases. The domains are of width 0.6∼2 nm and of length 1∼10 nm. Characteristic diffuse features observed in TED patterns are found to depend on the growth temperature. Extensive computer simulations show a direct correlation between the ordered domain structures and such diffuse features. A possible model is suggested to describe the temperature dependence of the ordered domain structure.     

Dislocation arrangements in gaas/ga1−xlnxas multilayers grown on (001), (111) and (112) substrates

GaAs/Ga_1−xIn_xAs strained layer superlattices with well-widths of 7 nm, barrier widths of 14 nm and periods of 10 to 30 have been examined by transmission electron microscopy in plan view and in cross-section for (001), (111) and (112) substrates. Individual layers are below the critical thickness while the overall SLS's are above the critical thickness for dislocation generation. (001) substrates give rise to square grids of 60° dislocations lying parallel to 〈110〉 directions with inclined 1/2 〈101〉 Burgers vectors, resulting from dislocation motion on 8 slip systems. (111) substrates give triangular networks of 60° dislocations lying parallel to 〈110〉 directions resulting from motion on 6 slip systems. (112) substrates have two sets of primary dislocations lying along (132) directions, along with secondary 60° dislocations lying along [110]. Long Lomer-Cottrell dislocations with Burgers vectors lying parallel to the substrate/SLS interface are occasionally observed for (001) substrates, while short segments are observed for (112) substrates; these are formed by reaction between conjugate dislocations. These dislocations arrangements are discussed in terms of the resolved shear stresses resulting from epitaxy for the various substrates orientations. Dislocation densities are much less than those required for complete strain relief. This is analyzed in terms of the reduction in the stress acting on dislocations from partial strain relief, along with a friction stress due to a combination of the Peierls stress and solution hardening from the In substitution. A friction stress ∼10^-3μ is required to explain the observed dislocation densities (μ, is the shear modulus).     

Comparison of MBE Growth of InSb on Si (001) and GaAs (001)

We describe the epitaxial growth of InSb films on both Si (001) and GaAs (100) substrates using molecular-beam epitaxy and discuss the structural and electrical properties of the resulting films. The complete 2 μm InSb films on GaAs (001) were grown at temperatures between 340°C and 420°C and with an Sb/In flux ratio of approximately 5 and a growth rate of 0.2 nm/s. The films were characterized in terms of background electron concentration, mobility, and x-ray rocking curve width. Our best results were for a growth temperature of 350°C, resulting in room-temperature mobility of 41,000 cm²/V s.  For the growth of InSb on Si, vicinal Si(001) substrates offcut by 4° toward (110) were used. We investigated growth temperatures between 340°C and 430°C for growth on Si(001). In contrast to growth on GaAs, the best results were achieved at the high end of the range of T _S =  C, resulting in a mobility of 26,100 cm²/V s for a 2 μm film. We also studied the growth and properties of InSb:Mn films on GaAs with Mn content below 1%. Our results showed the presence of ferromagnetic ordering in the samples, opening a new direction in the diluted magnetic semiconductors.     

Molecular beam epitaxy—Grown ZnSe nanowires

Molecular beam epitaxy (MBE) via the vapor-liquid-solid (VLS) reaction was used to grow ZnSe nanowires (NWs) on (111), (100), and (110) oriented GaAs substrates. Through detailed transmission electron microscopy (TEM) studies, it was found that 〈111〉 orientation is the growth direction for NWs with size ≥30 nm, while NWs with size around 10 nm prefer to grow along the 〈110〉 direction, with a small portion along the 〈112〉 direction. These observations have led to the realization of vertical ZnSe NWs with size around 10 nm grown on a GaAs (110) substrate. An ordered ZnSe NW array fabricated on a GaAs (111) substrate with a novel prepatterning method associated with plasma etching shows a high degree of ordering and a good size uniformity of the as-grown NWs. The diameter of the NWs in the array is around 80 nm and most of them are found to orient vertically, but some tilt to one of the six possible directions of the 〈111〉 family.     

Low Fatigue in Epitaxial Pb(Zr<Subscript>0.2</Subscript>Ti<Subscript>0.8</Subscript>)O<Subscript>3</Subscript> on Si Substrates with LaNiO<Subscript>3</Subscript> Electrodes by RF Sputtering

Epitaxial PZT (001) thin films with a LaNiO₃ bottom electrode were deposited by radio-frequency (RF) sputtering onto Si(001) single-crystal substrates with SrTiO₃/TiN buffer layers. Pb(Zr_0.2Ti_0.8)O₃ (PZT) samples were shown to consist of a single perovskite phase and to have an (001) orientation. The orientation relationship was determined to be PZT(001)[110]∥LaNiO₃(001)[110]∥SrTiO₃ (001)[110]∥TiN(001)[110]∥Si(001)[110]. Atomic force microscope (AFM) measurements showed the PZT films to have smooth surfaces with a roughness of 1.15 nm. The microstructure of the multilayer was studied using transmission electron microscopy (TEM). Electrical measurements were conducted using both Pt and LaNiO₃ as top electrodes. The measured remanent polarization P _r and coercive field E _c of the PZT thin film with Pt top electrodes were 23 μC/cm² and 75 kV/cm, and were 25 μC/cm² and 60 kV/cm for the PZT film with LaNiO₃ top electrodes. No obvious fatigue after 10¹⁰ switching cycles indicated good electrical endurance of the PZT films using LaNiO₃ electrodes, compared with the PZT film with Pt top electrodes showing a significant polarization loss after 10⁸ cycles. These PZT films with LaNiO₃ electrodes could be potential recording media for probe-based high-density data storage.     

Domain epitaxial growth of TiN/Si(001), TiN/GaAs(001), and Si/TiN/Si(001) heterostructures by laser physical vapor deposition: Theory and experiment

We have successfully deposited epitaxial titanium nitride films on (001) silicon and (001) gallium arsenide substrates and multilayer Si/TiN/Si(001) epitaxial heterostructures using pulsed laser (KrF: λ = 248 nm, τ = 25 ns) physical vapor deposition. The deposition of TiN was carried out at a substrate temperature of 600°C on Si(001) and 400°C on GaAs(00l). The interfaces were sharp without any indication of interfacial reaction. The epitaxial relationships were found to be <001> TiN ‖<001> Si on the silicon substrate, <001> Si ‖<001> TiN |<001> Si on the heterostructure, and [1-10] TiN‖[110] GaAs and [001] TiN ‖[110] GaAs on the GaAs substrate. The growth in these large-mismatch systems is modeled and the various energy terms contributing to the growth of these films are determined. The domain matching epitaxy provides a mechanism of epitaxial growth in systems with large lattice mismatch.The epitaxial growth is characterized by domain epitaxial orientation relationships with m lattice constants of epilayer matching with n of the substrate and with a small residual domain mismatch present in the epilayer. This residual mismatch is responsible for a coherent strain energy. The magnitude of compression of Ti-N bond in the first atomic layer, contributing to the chemical free energy of the interface during the initial stages of growth, is found to be a very important factor in determining the orientation relationship. This result was used to explain the differences in the orientaion relationships between TiN/Si and TiN/GaAs systems. The various energy terms associated with the domain epitaxial growth are evaluated to illustrate that the domain epitaxial growth is energetically favorable compared to the lattice mismatched epitaxial growth. The results of this analysis illustrate that the observed variations in the epitaxial growth are consistent with the minimum energy configurations associated with the domain epitaxial growth.     

(001)InP晶片[110]及[1 0]取向的最新判别法

本文提出了一种判别(001)晶片[110]和[ ]方向的简便方法。将去掉机械划痕的 InP 衬底放入浓 HCl,发现腐蚀出的条形沟方向是和片子的[110]方向一致。并对腐蚀沟的形成做了初步分析。     

Reciprocal space mapping of ordered domains in InxGa1−xP

We applied high resolution x-ray diffraction techniques to determine the three dimensional domain shape in nominally lattice-matched, CuPt_B ordered, In_xGa_1−xP epitaxial layers deposited on GaAs by metal organic vapor phase epitaxy. A technique of reciprocal space mapping is described which provides three-dimensional information on the shape and size of the ordered domains. The domain shape is obtained by reciprocal space mapping along orthogonal crystallographic directions. Applying this technique shows that, at large miscut angles, the domains are oriented close to the growth direction, and are elongated by differing extents along the [110] and [ ].     

Photoluminescence studies of heteroepitaxial gaas on si

We present a systematic study of the photoluminescence of undoped GaAs layers deposited by MOCVD on Si substrates. The study includes an examination of substrate and layer thickness effects in thin GaAs layers, and a detailed investigation of the stress effects on the intrinsic band-edge transitions in thicker samples. For sample thickness,t ≤ 0.5(μm), we observe strong midgap emission bands associated with defects close to the interface. These bands depend strongly on the nature of the Si substrate. The crystal quality improves with sample thickness, and fort ≥ 0.5 μm the emission is dominated by lines in the band edge region which are relatively independent of substrate preparation. Photoluminescence excitation spectra reveal that the highest energy line is due to an intrinsic exciton transition, and that a splitting of this line observed fort ≥ 2 μm reflects the presence of two different regions of strain in the material. The magnitude of the strain is estimated from the shift of the exciton lines relative to unstrained GaAs, and is found to be consistent with an upper limit provided by the thermal expansion mismatch between GaAs and Si.     

Nanowires in the CdHgTe Material System

HgTe nanowires have been grown by molecular beam epitaxy (MBE). They are nucleated at Au particles on Si or GaAs substrates and subsequently self-organize and grow laterally on the surface into 20–50 nm wide, 0.5–1 μm long twisted, but single-crystal, wires. Further growth gives longer, wider, and straighter polycrystalline wires. When unimpeded by Au particles on the surface, the wires become straight and consist of segments of cubic 〈111〉 HgTe and hexagonal 〈001〉 Te parallel to the wire. Te nanowires and Au␣nanowires have also occasionally been formed. All attempts to grow CdHgTe on Si substrates with or without Au particles have resulted in polycrystalline layers. The phase diagrams and diffusion coefficients imply that CdHgTe or HgTe nanowires will not grow by the vapor–liquid–solid technique at the low MBE growth temperatures. SiO₂ functions as a mask for selective growth of HgTe, but not for CdHgTe.     

Structural properties of GaAsN grown on (001) GaAs by metalorganic molecular beam epitaxy

Detailed transmission electron microscopy (TEM) and transmission electron diffraction (TED) examination has been made of metalorganic molecular beam epitaxial GaAsN layers grown on (001) GaAs substrates. TEM results show that lateral composition modulation occurs in the GaAs_1−xN_x layer (x 6.75%). It is shown that increasing N composition and Se (dopant) concentration leads to poor crystallinity. It is also shown that the addition of Se increases N composition. Atomic force microscopy (AFM) results show that the surfaces of the samples experience a morphological change from faceting to islanding, as the N composition and Se concentration increase. Based on the TEM and AFM results, a simple model is given to explain the formation of the lateral composition modulation.     

New developments in the heteroepitaxial growth of Be-chalcogenides based semiconducting alloys

We have studied the heteroepitaxial growth of Zn(Mg)BeSe alloys on both GaAs and Si substrates. X-ray measurements show that ZnMgBeSe quaternary alloys can be grown with a high structural quality on GaAs(001). Linewidths as low as to 20 arcsec have been obtained from double x-ray diffraction and the etch pit density is in the range of 10⁻³ cm⁻². The growth of ZnBeSe ternary alloys on vicinal Si(001) substrates has been investigated. Optical properties of Zn_0.55Be_0.45Se which is lattice-matched to silicon have been studied by photoluminescence and reflectivity and a fundamental bandgap E₀ of 3.85 eV has been measured. Therefore, this material is a potential candidate for ultraviolet B detection. However, it is important to note that these measurements are not conclusive about the direct nature of alloys bandgaps.     

Electrical properties of Pb1−xCdxS epitaxial films

We have measured the resistivity ρ and Hall coefficient R_H at 300, 77, and 4.2 K of p-type Pb_1−XCd_XS epitaxial films as a function of substrate temperature T_s, film thickness d, and composition x. The films were vapor deposited on cleaved (111) BaF₂ (111) SrF₂ , and (001) NaCl and polished (001) BaF₂ substrates. The Hall mobility μ_H at 77 K of p-type PbS films increased approximately linearly from 1 × 10⁴ to 2 × 10⁴ cm² V⁻¹ sec⁻¹ as T_s was varied from 400 to 500°C, respectively. Both μ_H and R_H increased with d due to the presence of a strong p-type surface layer on the exposed surface. The x of the films was controlled by the x of the source material and T_s. The mole fraction of CdS could be varied between 0.002 < x < 0.06 by varying T between 513 and 410°C, respectively, and using source material with x = 0.06. The electrical properties of samples grown on freshly cleaved (111) BaF₂ and (111) SrF₂ were essentially identical even though the lattice constant of SrF₂ is a better match to Pb_1−XCd_XS than BaF₂. The R_H and μ_H at 77 K were independent of thickness for low substrate temperatures and were observed to increase with increasing thickness for high substrate temperatures. The μ_H increased with decreasing temperature and became temperature independent below about 30 K, which is similar to the behavior observed in other lead salt compounds. However, the magnitude of μ_H was considerable lower throughout the 300 to 4.2 K temperature range than for PbS films. The R_H showed little temperature variation, which is typical lead salt behavior. Supported by Naval Surface Weapons Center Independent Research Funds.     

Metalorganic chemical vapor deposition growth and characterization of InGaP/GaAs superlattices

Lattice-matched In_0.49Ga_0.51P/GaAs superlattices were grown on (001) GaAs substrates using metalorganic chemical vapor deposition. The interface properties were characterized by photoluminescence, transmission electron microscopy, and x-ray diffraction. By varying the growth temperature, the precursor flow rates, and the growth interruption at the interfaces, we found that, while arsenic and phosphorus carry over have some effect on the formation of a low-bandgap InGaAsP quaternary layer at the interfaces, the In surface segregation seems to play an important role in the formation of the interface quaternary layer. Evidence of this indium segregation comes from x-ray and photoluminescence studies of samples grown at different temperatures. These studies show that the formation of an interfacial layer is more prominent when the growth temperature is higher. Growing a thin (∼1 monolayer thick) GaP intentional interfacial layer on top of the InGaP before the growth of the GaAs layer at the P→As transition effectively suppresses the formation of the low-bandgap unintentional interface layer. On the other hand, the growth of a thin GaAsP (or GaP) layer before the growth of the InGaP layer, at the As→P transition increases the formation of a low-bandgap interfacial layer. This nonequivalent effect of a GaP layer at the two interfaces on the PL properties is discussed.     

A new technology for manufacturing the dielectric isolation of elements of microelectronic devices by oxidizing grooves in single-crystal silicon

The formation of the dielectric isolation of elements of microelectronic devices by oxidizing grooves in single-crystal silicon is considered. The new technological process makes it possible to shorten the manufacturing cycle and to improve the reliability and parameters of devices. It is shown that this result is attained by substantially shortening the time of oxidation of silicon, suppressing the “bird’s beak” irregularity, and reducing the capacitance of the metal-insulator-semiconductor structure through the etching of grooves with certain geometric parameters in silicon nitride. These parameters are the groove width 0.5–1.5 μm, the ratio of the width to the spacing between the grooves 0.56: 0.44, and the groove depth, which is larger than the width. The results of two-dimensional physical simulation support the advantages of the new technology over the standard process. The simulation was accomplished with the use of the SSUPREM4 program of the Silvaco bundled software.     

Optical spectra of wide band gap BexZn1−x Se alloys

We report optical measurements (photoluminescence, Raman scattering, and infrared reflectance) of direct band gap and of optical phonon energies of Be_xZn_1−x Se alloys grown by MBE on (001) GaAs substrates for a wide range of Be concentrations. The high band gap of BeSe (5.15 eV) suggests the possibility of using isoternary alloys for ultraviolet optoelectronic applications. Be_xZn_1−x Se has the unique advantage that it can be lattice matched to Si at about x=0.5. We observed a strong linear shift of the Be_xZn_1−x Se direct band gap to higher energies with increasing Be content (to 3.63 eV for x=0.34). Furthermore, optical phonon parameters for the entire range of BeSe content have been obtained. Finally, polarized infrared and Raman spectra revealed local atomic ordering (anti-clustering) effects in the group-II sublattice. Fiz. Tekh. Poluprovodn. 33, 1120–1122 (September 1999) This article was published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Growth of Thick Epitaxial CdTe Films by Close Space Sublimation

This paper reports on a detailed study of the development of the close space sublimation method, which has been widely used in the preparation of polycrystalline CdTe/CdS solar cells, as an epitaxial method for the growth of thick CdTe single crystal films over 200 μm on GaAs and Ge substrates for high-energy radiation detectors. The resulting microscopic growth phenomena in the process are also discussed in this paper. High-quality single crystalline CdTe thick films were prepared with x-ray rocking curves full width at half maximum (FWHM) values, which were ∼100 arcsec on Ge substrates and 300 arcsec on GaAs substrates. The quality of thick films on Ge(100) showed a substantial improvement with nucleation in a Te-rich growth environment. No Te inclusions in the CdTe films grown on GaAs(211)B and Ge(100) were observed with IR transmission imaging. Photoluminescence of CdTe/Ge shows a large reduction in the 1.44 eV defect energy bands compared with films grown on GaAs substrates. The film resistivity is on the order of 10¹⁰ Ω cm, and the film displayed some sensitivity to alpha particles.     

Comparative study of spectral and morphological properties of blends of P3HT with PCBM and ICBA

We report a comparative study on spectral and morphological properties of two blend systems for polymer solar cells: the donor material poly(3-hexylthiophene) (P3HT) in combination with the acceptor material of either [6,6]-phenyl-C₆₁ butyric acid methyl ester (PCBM) or indene-C₆₀ bisadduct (ICBA) that was reported to enhance efficiencies of polymer solar cells. Optical microscopy and grazing incidence X-ray scattering reveal the stronger tendency of PCBM to from larger and more ordered domains/grains than ICBA either in pure or blend films. Compared to PCBM, the presence of ICBA also substantially perturbs the organization and longer-range ordering of P3HT in increasing the ICBA ratio in blends. With larger and more ordered phase-separated domains, the P3HT/PCBM blend films exhibit significant optical scattering at higher PCBM ratios. Yet, such optical scattering is not significant for P3HT/ICBA blends (even with high ICBA ratios). Overall, results here suggest the reported higher efficiencies of P3HT/ICBA solar cells (vs. P3HT/PCBM cells) cannot be attributed to larger and/or more ordered phase-separated donor–acceptor domains and other characteristics play more important roles in this case.