Showing papers on "Epitaxy published in 1987"

Evidence for the existence of an ordered state in Ga0.5In0.5P grown by metalorganic vapor phase epitaxy and its relation to band‐gap energy

Abstract: The band‐gap energy (Eg) of metalorganic vapor phase epitaxially (MOVPE) grown Ga0.5In0.5P lattice matched to (001) GaAs is presented as a function of a wide range of V/III ratios and growth temperatures. Photoluminescence, Raman scattering spectroscopy, transmission electron microscopy, and impurity diffusion were used to investigate this functional relationship. Two pieces of evidence are shown which demonstrate that MOVPE Ga0.5In0.5P epitaxial layers with ‘‘abnormal’’ Eg∼1.85 eV and ‘‘normal’’ Eg∼1.9 eV correspond to an ordered and a random (Ga,In) distribution on column III sublattices, respectively. In an ordered state, a sequence of (110) planes...GaGaInInGaGaInIn...in the [110] direction is the most probable distribution.

Properties of Fe single‐crystal films grown on (100)GaAs by molecular‐beam epitaxy

Abstract: Single‐crystal (100)Fe films 90–330 A thick have been grown on etch‐annealed (100)GaAs substrates by molecular‐beam‐epitaxy techniques. Ferromagnetic resonance data indicate that the two in‐plane 〈110〉 directions are inequivalent and, together with magnetometry data, show that the average film magnetization decreases as the thickness decreases. The inequivalence is attributed to the nature of the interface bonding at a (100) zinc‐blende surface. The decreased magnetization is attributed to the formation of Fe2As microclusters in the film due to As diffusion which is supported by Auger and electron diffraction studies. In general, the Fe films grown to date on etch‐annealed (100)GaAs substrates are significantly inferior to those grown on (110)GaAs.

Variation of the critical layer thickness with In content in strained InxGa1−xAs‐GaAs quantum wells grown by molecular beam epitaxy

Abstract: The critical width Lc for misfit dislocation generation has been determined for molecular beam epitaxy grown strained InxGa1−xAs (0.1

Defect reduction by thermal annealing of GaAs layers grown by molecular beam epitaxy on Si substrates

Abstract: Post growth thermal annealing has been used to reduce the defect density of GaAs layers grown on Si substrates by molecular beam epitaxy. Transmission electron microscopy indicates a 100× reduction of the true defect density. Twins and stacking faults were eliminated entirely. Most misfit dislocations were confined within the first ∼150 A GaAs layer and formed a regular and narrow network along the Si/GaAs interface. Similar results were obtained from an ion implanted and annealed specimen.

Epitaxial growth and electric characteristics of cubic SiC on silicon

Abstract: Single crystals of cubic SiC were heteroepitaxially grown by chemical vapor deposition (CVD) using a SiH4‐C3H8‐H2 system on silicon substrates. To reduce the large lattice mismatch between cubic SiC and silicon, a buffer layer was made by carbonizing the surface of a Si substrate in the CVD system. An optimum condition for the buffer layer formation was determined by x‐ray rocking curve measurements, reflection electron diffraction, and Auger electron spectroscopy. Electrical properties of the epitaxial cubic SiC layer were measured, and the mobilities on the Si(111) substrate were found to be larger than those on the Si(100) substrate. Diode characteristics of epitaxially grown p‐n junctions were also investigated.

Nonalloyed ohmic contacts to n-GaAs by solid-phase epitaxy of Ge

Abstract: A low resistance nonalloyed ohmic contact to n‐GaAs is formed which utilizes the solid‐phase epitaxy of Ge through PdGe. Discussion focuses on the conditions necessary to attain low specific contact resistivity (∼10−6 Ω cm2 on 1018 cm−3 n‐GaAs) and on the interfacial morphology between the contact metallization and the GaAs substrate. MeV Rutherford backscattering spectrometry and channeling show the predominant reaction to be that of Pd with amorphous Ge to form PdGe followed by the solid‐phase transport and epitaxial growth of Ge on 〈100〉 GaAs. Cross‐sectional transmission electron microscopy and lattice imaging show a very limited initial Pd‐GaAs reaction and a final interface which is planar and structurally abrupt to within atomic dimensions. The presence of excess Ge over that necessary for PdGe formation and the placement of Pd initially in contact with GaAs are required to result in the lowest contact resistivity. The experimental data suggest a replacement mechanism in which an n+‐GaAs surface region is formed when Ge occupies excess Ga vacancies.

Substrate‐orientation dependence of GaN single‐crystal films grown by metalorganic vapor‐phase epitaxy

Abstract: Gallium‐nitride single crystals were grown on (0001)‐ and (0112)‐oriented sapphire substrates by metalorganic vapor‐phase epitaxy. Smooth‐surfaced layers with fine ridgelike facets can be obtained on the (0112) sapphire. They have lower carrier concentrations than the layers on the (0001) sapphire. Deep centers responsible for blue (∼425 nm) and yellow (∼560 nm) emissions from undoped layers are reduced on the (0112) substrates, as compared with the (0001) substrates. On the other hand, the layers on the (0001) sapphire have better crystallinity and higher Zn‐incorporation efficiency than those on the (0112) sapphire. Growth kinetics of GaN layers are discussed by developing a tentative model.

(AlAs)0.5(GaAs)0.5 fractional‐layer superlattices grown on (001) vicinal surfaces by metalorganic chemical vapor deposition

Abstract: (AlAs)0.5(GaAs)0.5 fractional‐layer superlattices with a new periodicity perpendicular to the growth direction was successfully grown by metalorganic chemical vapor deposition on (001) GaAs substrates slightly misoriented toward [110]. The atomic structures were analyzed by x‐ray superlattice satellite diffraction. Superlattice periods were exactly the same as the mean distance of each atomic step on the (001) vicinal surface. The results indicate that lateral growth from nucleation at the step edge is the dominant process compared with the two‐dimensional nucleation on atomically flat terraces.

Nonequilibrium boron doping effects in low‐temperature epitaxial silicon films

Abstract: We report the first preparation of in situ boron‐doped epilayers by a low‐temperature chemical vapor deposition process (T=550 °C). Boron incorporation is approximately linear in source gas concentration, and active levels of boron incorporation exceeding 1×1020 B/cm3 have been achieved in as‐deposited 550 °C epilayers. This value exceeds solid solubility limits for boron in silicon at these temperatures by two orders of magnitude, and highlights the nonequilibrium nature of this process. High resolution transmission electron microscopy lattice imaging of this material shows it to be free of boron precipitates, while both plane view transmission electron microscopy and x‐ray topography fail to reveal extended defects. Utilizing low‐temperature processing throughout, p/n junctions have been fabricated in several of the in situ doped layers, with essentially ideal junction quality factors (n=1.0 –1.05) found for junctions of 1×106 μm2.

Characteristics of Cl‐doped ZnSe layers grown by molecular‐beam epitaxy

Abstract: High‐quality n‐type ZnSe layers have been grown by molecular‐beam epitaxy using chlorine (Cl) as a dopant. The Cl‐doped ZnSe layers showed mirrorlike morphology and good crystallinity, although some degrade in crystallinity is observed at a heavy doping. The carrier concentration of the layer could be widely controlled by a ZnCl2 Knudsen cell temperature. The carrier concentration attained 1×1019 cm−3, where the resistivity was as low as 3×10−3 Ω cm, indicating a remarkable improvement compared to the previous work using group‐III elements as a dopant. Hall mobilities at room temperature were in the range of 200–400 cm2/(V s), depending on the doping level. The Cl‐doped ZnSe layer exhibited strong blue near‐band‐gap photoluminescence (PL) with suppressed deep‐level emission at room temperature. The 4.2‐K PL of the layer was dominated by strong emission of excitons bound to neutral donors originating from substitutional Cl atoms. It was found by a secondary ion‐mass‐spectroscopy analysis that diffusion of ...

Abrupt p‐type doping profile of carbon atomic layer doped GaAs grown by flow‐rate modulation epitaxy

Abstract: Atomic layer doping of p‐type carbon impurity in GaAs was demonstrated using flow‐rate modulation epitaxy An extremely narrow capacitance‐voltage profile with 58 nm full width at half‐maximum is observed in the wafer with a sheet hole density of 95×1011 cm−2 Atomic layer doping of carbon was performed by supplying trimethylgallium or trimethylaluminium instead of triethylgallium It was found that the sheet hole density does not change before and after annealing for 1 h at 800 °C indicating that the carbon is a very stable impurity in GaAs The diffusion coefficient of carbon is estimated to be 2×10−16 cm−2/s at 800 °C This is the lowest value ever reported for p‐type impurities

Ion-beam-induced crystallization and amorphization of silicon

Abstract: Thin amorphous silicon layers can be produced in crystalline silicon substrates by ion-implantation. Subsequent ion-irradiation at elevated temperatures can induce such layers to either crystallize epitaxially or increase in thickness, layer by layer. This paper examines these processes and their dependence on substrate temperature and ion-irradiation parameters. It is shown that both processes, epitaxial crystallization and layer-by-layer amorphization, are controlled by ion-beam induced defect production at, or near, the crystalline/amorphous interface. The competition between defect production (determined by the ion flux and rate of nuclear energy deposition) and dynamic defect annealing (determined by the substrate temperature) is shown to play an important role in determining whether the layer crystallizes or amorphizes. Possible models for the observed behavior are discussed.

Properties of high‐purity AlxGa1−xAs grown by the metalorganic vapor‐phase‐epitaxy technique using methyl precursors

Abstract: The metalorganic vapor‐phase epitaxy (MOVPE) of AlxGa1−xAs most commonly employs the methyl precursors Al(CH3)3 and Ga(CH3)3. These precursors were used in the growth of AlxGa1−xAs over the entire range of alloy composition in a low‐pressure horizontal MOVPE reactor. A complete chemical, electrical, and optical characterization of high‐purity MOVPE AlxGa1−xAs grown over the entire range of growth temperatures (600–800 °C) was carried out in order to determine the relationship of the materials properties to the growth conditions. Carbon, the primary impurity in the layers, dominates the electrical properties of the epitaxial layers. A superlinear dependence of carbon incorporation on AlAs mole fraction is observed, along with a two‐slope dependence on growth temperature. Photoluminescence spectra (2 K) were obtained from materials with AlAs mole fraction over the range 0≤x≤0.80. The photoluminescence intensity of the layers also exhibits a systematic dependence on alloy composition and growth temperature. ...

Initial stages of epitaxial growth of GaAs on (100) silicon

Abstract: Direct observations of early stages of molecular‐beam epitaxial growth of GaAs on oriented and vicinal (100) Si surfaces are presented. Cross‐sectional transmission electron microscopy and plan view scanning electron microscopy images directly reveal three‐dimensional island growth for substrate temperatures above 300 °C. Island size, island spacing, surface morphology, and stacking fault defect spacing all increase with substrate temperature for fixed Ga and As fluxes. Below 300 °C, 7‐nm‐thick films are continuous and uniform. Films deposited on surfaces tilted from (100) coalesce anisotropically with respect to the tilt axis.

Effect of in situ and ex situ annealing on dislocations in GaAs on Si substrates

Abstract: Gallium arsenide layers grown by molecular beam epitaxy on (100) Si substrates were subjected to annealing under As overpressure at 650, 750, and 850 °C for 1/2 h A substantial reduction in the dislocation density near the interface and in the bulk of the epitaxial layers was observed for the 850 °C anneal In situ annealing at 700 °C for 1/2 h after 1/2 h of growth followed by a deposition of InGaAs/GaAs strained‐layer superlattices and bulk layers also resulted in reduced dislocation densities

Growth of high Tc superconducting thin films using molecular beam epitaxy techniques

Abstract: Thin films of the high‐temperature superconductor DyBa2Cu3O7−x have been grown on SrTiO3 substrates using molecular beam epitaxy techniques. Reflection high‐energy electron diffraction patterns observed during deposition indicate incomplete oxidation of copper and growth of oriented metallic copper microcrystals in a matrix of amorphous barium and dysprosium oxides. After post‐growth anneal the films exhibited sharp superconducting transitions with zero resistance observed as high as 89 K and critical current densities of 4.8×105 A/cm2 at 4.2 K and 3.9×104 A/cm2 at 77 K.

Temperature dependence of electrical properties of n‐ and p‐type 3C‐SiC

Abstract: Electrical properties of unintentionally doped n‐type and Al‐doped p‐type 3C‐SiC layers, epitaxially grown on Si by chemical vapor deposition, have been investigated at temperatures between 10 and 1000 K. Activation energies of Al acceptors and residual donors obtained from the temperature dependence of carrier density are 160 and 18 meV, respectively. 40%–60% of Al acceptors in the p‐type epilayers are compensated, and hole mobility is limited by acoustic phonon scattering above 300 K and by ionized impurity scattering below 250 K.

Epitaxial growth of silicon: A molecular-dynamics simulation.

Abstract: We have studied the epitaxial growth of silicon using molecular-dynamics techniques. The model consists of a temperature-controlled Si(111) substrate, with the Si atoms projected towards the substrate as is done in the laboratory. The atoms interact via a potential developed by Stillinger and Weber to simulate the bulk properties of Si. We find that at low substrate temperatures the growth is not well ordered; this is in accordance with experimental observation. It is precisely the opposite of what occurs in spherically symmetric potentials that were used to simulate the growth of metallic films. At higher substrate temperatures the growth is into properly stacked, crystalline Si layers. In contrast to the growth of metals (spherically symmetric potentials), the atomic mobility on the growing surface and the thermal conductivity of the system are much lower for Si; the results of this simulation and those of our previous work are in agreement with experimental observations showing, as expected, that a major determining factor in epitaxial growth of films is the nature of the interaction potential.

Atomic Structure of Ordered InGaP Crystals Grown on (001)GaAs Substrates by Metalorganic Chemical Vapor Deposition

Abstract: InGaP crystals grown on (001)GaAs substrates by metalorganic chemical vapor deposition are structurally evaluated by transmission electron microscopy. High-resolution electron microscopy observation and electron diffraction analysis of both the (110) and the (10) cross-section specimens strongly suggest that ordering of column III atoms on only two sets of the (111) planes with doubling in periodicity of (111) layers, i.e., In/Ga/In/Ga/In/Ga. . ., is occurring in the crystal. The ordering of the crystal is not perfect, and the ordered regions are assumed to be plate-like microdomains.

Use of tertiarybutylarsine for GaAs growth

Abstract: The use of AsH3 in the organometallic vapor phase epitaxial (OMVPE) growth of GaAs and other As containing III/V semiconductors has a number of disadvantages, including toxicity hazard, purity problems associated with storage cylinders, and low pyrolysis rate at the low temperatures often desirable in OMVPE growth. A new organometallic source, tertiarybutylarsine (TBAs), has recently become available. In this letter we report the results of OMVPE growth of GaAs using trimethylgallium (TMGa) and TBAs in a one atmosphere ambient. The major results of the study are (1) the vapor pressure of TBAs is measured to be 96 Torr at 10 °C, (2) the pyrolysis rate of TBAs appears to be greater than that of AsH3 under similar conditions, (3) as a consequence of (2), excellent morphology GaAs layers can be grown at lower values of V/III ratio (approximately unity) using TBAs than using AsH3 (4) no additional carbon incorporation is produced by the use of the organometallic group V source. These factors make TBAs a promis...

Mechanisms of epitaxial growth

Abstract: ‘Epitaxy’ means order in the relative orientation of identical crystals nucleated and grown on a large single-crystal face Every crystal of the deposited material is oriented in such a way that there is coincidence of some vectors of its reciprocal lattice with vectors of the reciprocal lattice of the substrate surface Depending on the length of the coincident vectors, one distinguishes between epitaxy of first order (coincidence of basis vectors), second order, and so on In this paper, selected epitaxial systems (metals on metal, semiconductor and insulator substrates, semiconductors on semiconductors) are used to illustrate the influence of the lattice mismatch, interatomic forces and experimental parameters on the mode of film growth The interaction across the epitaxial interface induces homogeneous strain in ultra-thin films and inhomogeneous strain in thicker deposits The periodic strain is usually described in terms of misfit dislocations or static distortion waves, which are mobile at

Substrate temperature dependence of GaAs, GaInAs, and GaAlAs growth rates in metalorganic molecular beam epitaxy

Abstract: The substrate temperature (Ts) dependence (350–700 °C) of GaAs and Ga1−y InyAs growth rates was investigated in metalorganic molecular beam epitaxy (MOMBE), using triethylgallium (TEG), trimethylindium (TMI), and solid arsenic (As4) sources. For GaAs growth, four distinct Ts dependent regions are observed, including a weak desorption process (500–650 °C) characteristic of MOMBE, preceding atomic Ga desorption (Ts >650 °C). When adding a TMI flux to grow Ga1−yInyAs, this desorption process was much enhanced up to 550 °C, and then decreased above 550 °C when the In desorption phenomenon takes place. Correlatively, the In alloy composition peaks at 550 °C. The same dependence was observed in Ga1−yInyAs growth using solid In and TEG sources. However, in Ga1−xAlxAs growth using solid Al or triethylaluminum (TEA) and TEG sources, the weak desorption observed in GaAs MOMBE was strongly minimized. From these results, possible growth mechanisms are discussed.

Growth and characterization of a delta‐function doping layer in Si

Abstract: We present a procedure whereby a sheet of donor atoms is incorporated in (100) Si during molecular beam epitaxial growth. Analysis by secondary ion mass spectroscopy and transmission electron microscopy shows that the width of such δ‐function doping layers is only a few lattice planes. Tunneling spectroscopy and transport measurements give evidence for quantum confinement of the electronic charge in the layer and thus confirm the narrow width.

Use of tertiarybutylarsine in the metalorganic chemical vapor deposition growth of GaAs

Abstract: Epitaxial films of GaAs have been grown by metalorganic chemical vapor deposition using a new arsenic source, tertiarybutylarsine (TBAs). Films with excellent surface morphology were obtained for low V/III values over a wide temperature range (600–800 °C), and relatively strong free‐exciton emission was observed in the photoluminescence spectra. Hall measurements indicate carrier concentrations as low as 5×1015 cm−3 and mobilities μ300=4000 cm2/V s. These are equivalent or better than results obtained with trimethylarsenic. In contrast to growth with arsine, the layers were found to be n type for all values of V/III ratio investigated (2–20). Higher quality layers can be expected with source repurification of synthesis via a purer chemical process.

A technology for high-performance single-crystal silicon-on-insulator transistors

Abstract: A process for forming transistors and circuits in a thin single-crystal silicon film on a glass substrate is presented. The process involves the electrostatic bonding of a silicon wafer to glass and the subsequent thinning of the wafer using doping-sensitive etchants to retain only the epitaxial layer. NMOS transistors have shown channel mobilities of 640 cm2/V-s, while leakage currents have been measured at less than 10-14A/µm.

Silicon surface cleaning by low dose argon‐ion bombardment for low‐temperature (750 °C) epitaxial silicon deposition. I. Process considerations

Abstract: A low‐energy argon sputter process has been optimized to successfully remove native oxide from a silicon surface at elevated temperatures without introducing permanent damage. The process relies upon confining all sputtering events to the near‐surface region of the silicon and exploits the enhancement of sputter efficiencies observed for silicon and silicon dioxide above 600 °C. The procedure has been implemented as an in situ etch for low‐temperature (below 800 °C), very low‐pressure (1–10 mTorr), epitaxial silicon deposition in a high vacuum ambient. The reactor and conditions employed are presented along with measures of residual substrate damage as a function of processing conditions, and the process limitations are discussed. A companion paper describes the excellent structural quality of the resultant epitaxial films. The ion energies (100 eV) and fluxes (5×1013 cm−2 s−1) employed represent a significant departure from conventional sputter cleaning processes.

Measurement of steady-state minority-carrier transport parameters in heavily doped n-type silicon

Abstract: The relevant hole transport and recombination parameters in heavily doped n-type silicon under steady state are the hole diffusion length and the product of the hole diffusion coefficient times the hole equilibrium concentration. These parameters have measured in phosphorus-doped silicon grown by epitaxy throughout nearly two orders of magnitude of doping level. Both parameters are found to be strong functions of donor concentration. The equilibrium hole concentration can be deduced from the measurements. A rigid shrinkage of the forbidden gap appears as the dominant heavy doping mechanism in phosphorus-doped silicon.

Interface structures in beta-silicon carbide thin films

Abstract: Interface structures in monocrystalline beta‐silicon carbide thin films grown on (001) silicon substrates have been studied by high‐resolution electron microscopy of cross‐sectional specimens. Despite a large lattice mismatch, there is a periodic registry of {111} atom planes across the SiC‐Si interface. Planar defects on SiC {111} planes are grown‐in and arise primarily from lattice and thermal expansion mismatch. Thermal oxidation in wet atmospheres results in preferential attack of the SiC film at sites where planar defects intersect the film surface, whereas oxidation in dry atmospheres does not.