bluuebunny/crossref_metadata_2025 huggingface dataset:
Light-enhanced molecular-beam epitaxial growth in II–VI and III–V compound semiconductors
Authors: Farrell H. H. , Nahory R. E. , Harbison J. P.
Published: July 2002

In this paper we suggest mechanisms by which light interacts with surface species during growth using molecular-beam epitaxy (MBE) and related techniques. Such mechanisms are discussed, not only for impurity incorporation, but also for the growth of undoped compound semiconductors. This work provides a conceptual framework for understanding these light-induced processes that, in and of themselves, represent a major breakthrough in the MBE fabrication of such materials. It opens up the possibility of making p–n junctions in II–VI materials and the subsequent potential for their use in applications requiring new kinds of electronic, photonic, and photolithographic devices.
Capacitive hysteresis effects in 5.0 nm single and double barrier AlAs/GaAs tunneling structures grown by molecular-beam epitaxy
Authors: Campbell A. C. , Kesan V. P. , Crook G. E. , Maziar C. M. , Neikirk D. P. , Streetman B. G.
Published: July 2002

Single and double 50 Å AlAs barrier structures with n+ electrode regions and 50 Å GaAs ‘‘spacer’’ layers are examined using impedance-phase measurements, deep level transient spectroscopy (DLTS), and pulsed I–V measurements. Resonant tunneling curves with a peak-to-valley ratio of 2:1 at 300 K are obtained from the double barrier devices. Under thermal stress of temperatures >390 K or large terminal voltage conditions, an abrupt transition from a low impedance, resistive state to a high impedance, capacitively reactive state is observed. The high impedance, reactive state is dynamically observed in all the device structures examined. In many cases, the high impedance state is persistent for extensive periods of time. Repeatable switching between the high and low persistent impedance states can be accomplished by the application of large (1–4 V) terminal voltages. However, both persistent states are stable under small applied biases for long durations. Impedance-phase measurements have been performed on both the low impedance and the persistent high impedance state as a function of frequency for bias levels from −2.0 to 2.0 V. The low impedance state shows a much greater frequency dependence of the resistive and reactive components than the persistent high impedance state. Pulsed I–V measurements of Schottky barrier contacted devices reveal two characteristic I–V curves which are followed qualitatively for all the devices examined. The first is a series resistance limited diode with a turn-on voltage above 1.5 V. The second characteristic, followed after the abrupt switching, is that of a diode-like exponential current dependence on the applied voltage. Single and double barrier devices with Ohmic contacts displayed similar switching behavior at large biases. The persistent nature of the low and high impedance states observed are consistent with the formation and destruction of an inversion layer at the AlAs/GaAs interface. Silicon autodoping of the AlAs barrier regions may also give rise to DX-like hot electron trapping, similar to

that observed in low mole fraction Al1−xGaxAs [T. N. Theis, B. D. Parker, P. M. Solomon, and S. L. Wright, Appl. Phys. Lett. 49, 1542 (1986)]. The possibility of a filamentary conduction process is also discussed.
Studies of molecular-beam epitaxy growth of GaAs on porous Si substrates
Authors: Mii Y. J. , Lin T. L. , Kao Y. C. , Wu B. J. , Wang K. L. , Nieh C. W. , Jamieson D. N. , Liu J. K.
Published: July 2002

GaAs has been grown on porous Si directly and on Si buffer layer–porous Si substrates by molecular-beam epitaxy. In the case of GaAs growth on porous Si, transmission electron microscopy (TEM) reveals that the dominant defects in GaAs layers grown on porous Si are microtwins and stacking faults, which originate from the GaAs/porous Si interface. GaAs is found to penetrate into the porous Si layers. By using a thin Si buffer layer (50 nm), GaAs penetration diminishes and the density of microtwins and stacking faults is largely reduced and localized at the GaAs/Si buffer interface. However, there is a high density of threading dislocations remaining. Both Si (100) aligned and four tilted substrates have been examined in this study. TEM results show no observable effect of the tilted substrates on the quality of the GaAs epitaxial layer.
Excimer laser lithography using contrast enhancing material
Authors: Endo M. , Sasago M. , Nakagawa H. , Hirai Y. , Ogawa K. , Ishihara T.
Published: July 2002

A new process of excimer laser lithography is presented in this paper. A water soluble, contrast enhancing material, we have developed for the KrF (248 nm) excimer laser has made this new process possible. This material, named WSP-EX (water soluble photopolymer for excimer laser), is characterized by the use of 5-diazo-Meldrum’s acid and has good contrast enhancing capability in both photobleaching and photoreactive speed at 248 nm. By utilizing this new material, we can obtain large focus-depth lattitude. In this paper, the problem of matching the contrast enhancing material with the resist is also discussed.
High-rate ion etching of GaAs and Si at low ion energy by using an electron beam excited plasma system
Authors: Yu Jin-Zhong , Hara Tamio , Hamagaki Manabu , Yoshinaga Takashi , Aoyagi Yoshinobu , Namba Susumu
Published: July 2002

By using a newly developed electron beam excited plasma (EBEP) system, etching characteristics of GaAs and Si in an ion energy range of 5 to 100 eV were investigated. Anisotropic etching profiles with high aspect ratios were obtained by both Ar ion beam etching (IBE) and Cl2 reactive ion beam etching (RIBE). Etching rates of 1.2 μm/min for GaAs and 0.5 μm/min for Si were demonstrated for the first time by Cl2 RIBE at ultralow ion acceleration voltage of 5 V. Selective ratios of etching rates for Si/SiO2 and GaAs/SiO2 are ∼33 and 80, respectively. Electrical and optical measurements on the etched samples indicated that damage degree introduced by the low-energy ions is negligible. Therefore, the EBEP system cannot only provide high etching rate because of its high ion current but also realize damageless ion etching due to its low ion energy.
On the gate capacitance of metal–oxide semiconductor structures in N-channel inversion layers on ternary chalcopyrite semiconductors
Authors: Ghatak K. P. , Biswas S.
Published: July 2002

An attempt is made to derive model expressions of the gate capacitance of metal–oxide semiconductor structures in n-channel inversion layers on ternary chalcopyrite semiconductors at low temperatures, taking n-channel inversion layers on CdGeAs2 as examples, under both the weak and strong electric field limits, respectively. It is found, on the basis of newly derived two-dimensional electron energy spectra within the frame work of k↘⋅p↘ formalism for both the limits by considering the anisotropies of the band parameters, that the gate capacitances increase with increasing surface electric field in an oscillatory manner and the crystal-field splitting parameter enhances the numerical values of the gate capacitance for both the limits. In addition, the corresponding well-known results for n-channel inversion layers on parabolic energy bands are also obtained from the generalized expressions.
An investigation of the roughening of silicon(100) surfaces in Cl2 reactive ion etching plasmas by i
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i
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u ellipsometry and quadrupole mass spectrometry
Authors: Thomas D. J. , Southworth P. , Flowers M. C. , Greef R.
Published: July 2002

The conditions which cause silicon roughening in Cl2 RIE plasmas are investigated. In situ ellipsometry provides a quantitative interpretation of the extent and nature of the roughening process, while mass spectrometry yields complementary information regarding the composition of the plasma. The degree of roughening is reproducible when base pressures are ≊10−5 Torr but is strongly dependent on the rf power and process pressure. Careful selection of these parameters (50 W, 100 mTorr) retains a smooth silicon surface and gradually smooths those which have been roughened. Water vapor has a very significant effect on the etching reactions. In low concentrations it induces roughening and in high concentrations it prevents any etching of silicon. We suggest that silicon oxide micromasks are not responsible for roughening. Instead we propose that hydroxyl (SiOH) groups are the more likely masking species. Roughening of silicon is efficiently prevented when the wafer is patterned with positive photoresist. It is possible that CClx (x=1–4) species can remove the micromasks to retain a smooth surface.
Fabrication and characterization of Si-coupled superconducting field effect transistors with 0.1 μm gate
Authors: Hatano Mutsuko , Murai Fumio , Nishino Toshikazu , Hasegawa Haruhiro , Kure Tokuo , Kawabe Ushio
Published: July 2002

A 0.1-μm-gate-length superconducting field effect transistor (FET) with a coplanar structure is realized by a self-aligned fabrication process using electron beam lithography. A T-shaped gate structure with an insulated sidewall makes it possible to form the spacing between the superconducting source and drain electrodes to be <0.15 μm without causing an electrical short. The characteristics of this FET measured at 4.2 K indicate that the superconducting current and normal-state resistance can be successfully controlled by the applied gate bias.
Studies of barrier height mechanisms in metal–silicon nitride–silicon Schottky barrier diodes
Authors: Sobolewski M. A. , Helms C. R.
Published: July 2002

In this paper we present a complete experimental study and theoretical treatment of the barrier height of metal–silicon nitride–silicon Schottky barrier diodes. This study avoids the ambiguities of previous investigations of metal–insulator semiconductor Schottky barriers by use of a more complete and more exact model and a wider range of experimental conditions. The barrier height of these diodes was measured as a function of nitride thickness for a variety of contact metals. From this data the effects of interface traps, fixed charge defects and band lineups can be distinguished from each other and the role that each of these mechanisms plays in determining the barrier height can be ascertained. The barrier height vs metal and barrier height vs thickness data show no signs of the effects of interface traps. Instead, the differences in barrier height observed depend solely on the band lineup at the metal–nitride interface, and fixed charge defects.
Type II to type I conversion of pseudomorphic GaAs on InP dependent on growth direction
Authors: Nolte D. D.
Published: July 2002

Predictions of band offsets assign a type-II offset for the GaAs–InP interface without inclusion of strain effects, with the conduction- and valence-band-edge offsets approximately given by 0.4 and 0.3 eV, respectively. It has been demonstrated recently that pseudomorphic GaAs grown on [100]-oriented InP also has a type-II interface, but with the conduction-band offset reduced by the hydrostatic deformation potential of GaAs. Poisson’s ratio in GaAs for [111]-directed uniaxial stress is smaller by 40% than the value for [100]-directed stress. The lattice constant perpendicular to the growth interface is therefore not reduced as much for [111] growth compared with the [100]-growth case, leading to a consequently larger shift of the conduction-band-edge energy. Based on the recently measured value of −9 eV for the conduction-band-edge hydrostatic deformation potential in GaAs, the band offset for pseudomorphic GaAs grown on (111) InP has been calculated to be type I. This material system should therefore show type II to type I conversion dependent on the growth direction of the pseudomorphic layer. The issues involved in the growth and measurement of GaAs grown on (111) InP are discussed briefly.
Investigations of ammonium sulfide surface treatments on GaAs
Authors: Carpenter M. S. , Melloch M. R. , Cowans B. A. , Dardas Z. , Delgass W. N.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) and reflection high-energy electron diffraction (RHEED) results are presented for ammonium sulfide treated (100)GaAs surfaces. XPS shows that the sulfur coverage is independent of the ammonium sulfide concentration, although the relative amount of arsenic decreases as the sulfide concentration increases. RHEED patterns show that higher temperatures are required for the surface to restructure following treatment with higher sulfide concentration. In addition to the order of magnitude changes in the diode saturation current densities following ammonium sulfide treatment, we observe that the characteristics of gold and aluminum Schottky barriers on sulfide-treated GaAs surfaces also vary with the substrate temperature during metal deposition.
Spectroscopic and electrical studies of GaAs metal–oxide semiconductor structures
Authors: Freeouf J. L. , Silberman J. A. , Wright S. L. , Tiwari Sandip , Batey J.
Published: July 2002

Recent studies of plasma-enhanced chemical vapor deposition of SiO2 upon Si epitaxial layers grown in situ upon epitaxial GaAs layers, with the deposited interfacial Si of order 10 Å, strongly suggest that greatly reduced state densities at SiO2/GaAs interfaces have been attained with this approach. We report spectroscopic ellipsometry results for molecular-beam epitaxy (MBE) Si/GaAs samples both before and after SiO2 deposition, as well as before and after annealing. The ellipsometric results indicate that the SiO2/GaAs interface is <9 Å thick. The amount of unreacted silicon ranged from 3±3 to 0.4±0.2 Å equivalent thickness for the best fit cases. Ellipsometric results for samples without the deposited SiO2 suggest of order 0.4-Å unoxidized silicon at the interface. Results of x-ray photoelectron spectroscopy (XPS) studies of the samples (without deposited SiO2) suggest that all silicon is being oxidized prior to SiO2 deposition for at least some of the ‘‘unpinned’’ samples. Raman studies find no Si–Si bonds for some of the unpinned samples. Our data strongly suggest that the reduced interface state density is not dependent upon the presence of unoxidized silicon, at least in the amount required to form the Si/GaAs heterojunction previously assumed in explaining this improved interface. We further report preliminary electrical data for a sample prepared with no silicon deposition; indentical heat treatments on this sample gave similar results, i.e., reduced interface states for n-GaAs metal–oxide semiconductor capacitors.
Electronic and chemical properties of hydrogen exposed GaAs(100) and (110) surfaces studied by photoemission
Authors: Landesman J. P. , Mabon R. , Allan G. , Lannoo M. , Priester C. , Bonnet J. E.
Published: July 2002

Various aspects of the physics of the interaction of GaAs surfaces with H2 discharges are shown in this paper. Ultraviolet photoemission measurements have been done on (110) cleaved surfaces. Comparison of the core-level spectra with electronic structure calculations (molecular orbital model) shows that some of the Ga atoms on the hydrogenated surface have two dangling bonds, instead of one on the clean relaxed surface. This indicates that Ga–As bonds on the (110) surface have been broken by exposure to the hydrogen in our discharge conditions. In parallel, some new surface states in the valence-band region are detected which we have tentatively attributed to the formation of As–H bonds. On p-type (110) cleaved surfaces, the Fermi level is pinned near valence-band maximum (VBM) +0.4 eV after hydrogenation. In a second part of the paper, we describe x-ray photoemission spectroscopy results on the plasma treatments of GaAs(100) wafers in H2/AsH3 (deoxidation, Fermi level position as a function of the surface stoichiometry, etc.).
Reflectivity reduction by oxygen plasma treatment of capped metallization layer
Authors: Maa J.-S. , Meyerhofer D. , O’Neill J. J. , White Larry , Zanzucchi Peter J.
Published: July 2002

Oxygen plasma treatments of thin cap layers of Ti, Ta, W, or W–10% Ti deposited over Al or refractory metal silicide films can significantly reduce the optical reflectivity. The reduction is proportional to the thickness of oxide film grown on the cap layer. The oxidation occurs mostly in the first 5 min of plasma treatment and is a function of temperature. The oxide films have been characterized by Auger spectroscopy, Rutherford backscattering spectrometry, and ellipsometry. The measured reflectivities agree very well with the calculated results. This reduction in reflectivity is useful for photoresist processing as demonstrated by both computer modeling and experimental photoresist linewidth measurement.
The investigation of mixed halogen freon/oxygen tungsten reactive ion etching chemistries with extension to silicon
Authors: Daubenspeck T. H. , White E. J. , Sukanek P. C.
Published: July 2002

Tungsten reactive ion etching formulations obtained from CF2Cl2 in combination with CF4/O2, and from CF3Cl with O2, are known to exhibit distinct etch rate and etch selectivity advantages relative to other chemistries used for tungsten patterning. Within this work, it is found that CF3Cl in place of CF2Cl2 causes a similar result and that it is the balanced presence of atomic F, Cl, and O in the discharge that governs the etch rate of tungsten. Limiting case approximations suggest that the mechanism of tungsten etch enhancement does not depend upon the potential for tungsten removal as a volatile chloride. The participation of tungsten oxide is also studied. Finally, the novel chemistries are extended to silicon etching, resulting in a similarly beneficial etch rate and selectivity advantage.
Properties of HgTe–Hg0.15Cd0.85Te superlattices grown by molecular-beam epitaxy
Authors: Lansari Y. , Han J. W. , Hwang S. , Kim L. S. , Cook J. W. , Schetzina J. F. , Schulman J. N. , Otsuka N.
Published: July 2002

The structural and optical properties of a series of molecular-beam epitaxy (MBE) grown HgTe–Hg0.15Cd0.85Te superlattices (SL) have been studied. Vertical cross-section transmission electron microscopy studies show no evidence of Hg interdiffusion, confirming the high quality of these multilayered structures. Transmittance and reflectance measurements were performed on each sample and analyzed to obtain optical absorption coefficients. The absorption coefficient versus photon energy spectra show consecutive rises and plateaus characteristic of two-dimensional quantum structures. A two-band tight-binding model was used to analyze the absorption data and identify the quantum transitions. The observation of both light-hole and heavy-hole transitions allowed the determination of both the superlattice band gap and the valence-band offset. The offset was found to be 300 meV (±20 meV) for the superlattices studied, which extrapolates to 350 meV (±20 meV) for the HgTe–CdTe binary interface.
Si/GexSi1−x/Si  resonant tunneling diode doped by thermal boron source
Authors: Rhee S. S. , Karunasiri R. P. G. , Chern C. H. , Park J. S. , Wang K. L.
Published: July 2002

A study of resonant tunneling of holes in a Si/GexSi1−x/Si double barrier structure doped by a thermal boron doping source is presented. The source consists of a pyrolytic boron nitride crucible and uses filament heating. Sharp and constant doping levels between 1×1017 and 4×1019 cm−3 are obtained with a maximum K-cell temperature of ∼1560 °C. The double barrier tunneling devices realized by this source shows 2.1/1 peak-to-valley ratio at 4.2 K in current–voltage characteristics. Magnetotunneling measurements confirm that both the light and heavy holes participate in the resonant tunneling.
Growth and characterization of doped GaAs/AlGaAs multiple quantum well structures on Si substrates for infrared detection
Authors: Mii Y. J. , Karunasiri R. P. G. , Wang K. L. , Bai Gang
Published: July 2002

Doped GaAs/AlGaAs multiple quantum well structures were grown on Si substrates by molecular-beam epitaxy. The crystallinity of the epitaxial layers was examined by cross-sectional transmission electron microscopy and an x-ray rocking curve technique. The threading dislocation density of the multiple quantum well region was estimated to be 108 cm−2 by transmission electron microscopy. The x-ray rocking curve measurement revealed a full width at half-maximum of 380 arcsec, with no superlattice peak observed. Electrical and optical characterizations by tunneling current and intersubband infrared absorption showed comparable properties with similar structures grown directly on a GaAs substrate. The effect of crystallinity on the electrical and optical properties of the multiple quantum well structures is discussed.
Commutativity of the GaAs/AlAs (100) band offset
Authors: Yu E. T. , Chow D. H. , McGill T. C.
Published: July 2002

X-ray photoelectron spectroscopy is used to measure the valence-band offset in situ for GaAs/AlAs (100) heterojunctions grown by molecular beam epitaxy. Ga 3d and Al 2p core level to valence-band edge binding energy differences are measured in GaAs (100) and AlAs (100) samples, respectively, and the Al 2p to Ga 3d core level binding energy difference is measured in GaAs–AlAs (100) and AlAs–GaAs (100) heterojunctions. Measurements of the Al 2p to Ga 3d core level energy separations indicate that the band offset for GaAs/AlAs (100) is commutative; the value we obtain is ΔEv=0.46±0.07 eV. Our observation of commutativity is believed to be a consequence of the high quality of our GaAs/AlAs (100) heterojunctions, and of the inherent commutativity of the GaAs/AlAs (100) band offset.
Lateral confinement of microchemical surface reactions: Effects on mass diffusion and kinetics
Authors: Zeiger H. J. , Ehrlich D. J.
Published: July 2002

This paper investigates the effects of lateral confinement on the chemical kinetics of surface reactions that involve diffusive mass transport in the phase above the surface. The phenomena to be expected are illustrated by a theoretical treatment of the reaction types A+D⇄2C or B⇄A+2C, where A is a surface species, and B and C are both gaseous species. The case explored is one in which the back reaction due to the product species C is important. It is assumed that species B is the major constituent of the vapor, and remains so throughout the course of the reaction. The spatial profiles of A and C as a function of time are found by the use of a Green’s function formalism and evaluated numerically for illustrative cases. The results of the calculations provide a possible explanation of the drastic rate enhancement produced in some cases by lateral confinement resulting from the use of focused energy beams. The possibility of dramatic lateral variation of chemical kinetics due to strong concentration gradients of the product species is demonstrated. The results could have application to a broad class of transportlimited surface processing reactions confined by focused beams or by lithographic masking.
Low-temperature formation of metal/molecular-beam epitaxy-GaAs(100) interfaces: Approaching ideal chemical and electronic limits
Authors: Viturro R. E. , Chang S. , Shaw J. L. , Mailhiot C. , Brillson L. J. , Terrasi A. , Hwu Y. , Margaritondo G. , Kirchner P. D. , Woodall J. M.
Published: July 2002

We report soft x-ray photoemission studies of metal/molecular-beam epitaxy (MBE)-GaAs(100) interfaces formed at low temperature. Our results indicate that rectifying barrier heights are proportional to the metal work function in accordance with Schottky’s original description of metal–semiconductor contacts. These results confirm the predictions of a self-consistent model of metal–semiconductor interfaces, and suggest that metal-induced gap states and native defect mechanisms are not major factors in determining the Fermi level energy at ‘‘ideal’’ interfaces. We attribute deviations from the ideal Schottky limit behavior observed for interfaces formed at room temperature to metallization-induced atomic relaxations (rather than electronic relaxations) occurring at metal–semiconductor contacts. We present a useful methodology for analyzing electronic properties at metal–semiconductor interfaces. The pronounced differences in barrier height formation between MBE vs melt-grown GaAs can evidence the role of deep states in controlling Schottky barriers at metal/melt-grown GaAs.
I
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t
u calibration of growth surface temperature for molecular-beam epitaxy of CdTe
Authors: Rajavel D. , Mueller F. , Benson J. D. , Wagner B. K. , Benz R. G. , Summers C. J.
Published: July 2002

A new in situ technique has been developed to measure the growth surface temperature of a substrate, and to calibrate the temperature of substrate holders. The technique has been demonstrated to be accurate to better than 5 °C and was verified for calibrating substrate temperatures between 160–220 °C. Condensation of an incident Te2 flux occurred on CdTe surfaces when the flux of the incident Te2 dimers exceeded the flux desorbing from the surface. The surface temperature at the onset of condensation was calculated by equating the expressions for the incident Te2 flux and the desorbing Te2 flux. Experimentally, the onset of condensation was determined by a change in the reflection high-energy electron diffraction pattern of the substrate.
A two-zone molecular-beam epitaxy furnace for evaporation of II–VI materials
Authors: Cook J. W. , Eason D. B. , Harris K. A.
Published: July 2002

The design and operation of a two-zone furnace and crucible for the evaporation of II–VI semiconducting materials is described. The furnace contains separate heating elements and temperature sensors for each of the zones. The second zone is located at the open end of the furnace. The use of two independently-controlled temperature zones allows for the elimination of clogging problems that often occur with the evaporation of materials such as tellurium. The pyrolytic boron nitride (PBN) crucible contains a cap with a 2 mm inside diameter and 16 mm long orifice, which is designed to yield higher operating temperatures and better flux stability. A special PBN crucible retainer has also been designed to minimize contact of evaporated material with the tantalum structure of the furnace.
Strain in epitaxial GaAs on CaF2/Si(111)
Authors: Schowalter L. J. , Ayers J. E. , Ghandhi S. K. , Hashimoto S. , Gibson W. M. , LeGoues F. K. , Claxton P. A.
Published: July 2002

Epitaxial layers of (111) GaAs of approximately 1 μm thickness were grown on epitaxial CaF2 buffer layers that were either 140 or 380 nm thick on Si(111) substrates. The best nucleation temperature for the GaAs on CaF2/Si(111) we have observed was 620 °C. This resulted in high quality GaAs films, which exhibited channeling minimum yields of 4%. The density of threading dislocations in the GaAs layers was observed by transmission electron microscopy (TEM) to be ∼108 cm−2. Double-crystal x-ray diffraction measurements showed that the strain (ε⊥) was less than 2.2×10−4 in both sets of GaAs samples. However, ion channeling revealed a large tetragonal strain of 3.5×10−3 (ε⊥=1.7×10−3) in the thinner (140 nm) CaF2 buffer layers. By doing ion channeling with high energy (2.5 MeV) protons, it was possible to determine strain more accurately. Using this technique, we were able to set an upper limit for the tetragonal strain of 2.5×10−4 in both the GaAs (which implies ε⊥<8×10−5) and CaF2 (ε⊥<1.5×10−4) layers for the thicker (380 nm) CaF2 buffer layer structure. These results are in good agreement with the strain predicted from previous strain measurements of CaF2 epitaxial layers on Si.
Heteroepitaxy of InP on Si: Reduction of defects by substrate misorientation and thermal annealing
Authors: Crumbaker T. E. , Lee H. Y. , Hafich M. J. , Robinson G. Y. , Al-Jassim M. M. , Jones K. M.
Published: July 2002

The results of a study of the effects of substrate misorientation and ex situ thermal annealing on the morphology, defect density, and low temperature photoluminescence (PL) emission of epitaxial films of InP grown on Si substrates are presented. InP films were grown by gas-source molecular beam epitaxy on both (100) oriented and (100) misoriented 4° towards the [011] Si wafers. InP films on misoriented substrates were mirror-like over the entire 3-in. wafer and exhibited a factor of 2 lower dislocation density than films on oriented substrates, as determined by double crystal x-ray diffraction and transmission electron microscopy (TEM). Thermal annealing resulted in a significant enhancement of the low temperature near band edge PL emission and a decrease in the density of dislocations and stacking faults. The best results obtained were for annealed films on misoriented substrates with an x-ray linewidth of 440 arcsecs, a TEM dislocation density of ∼2×108 cm2, a stacking fault density of ∼2×107 cm−2, and a PL linewidth of 6 meV.
Plasma-deposited amorphous carbon films as planarization layers
Authors: Pang S. W. , Horn M. W.
Published: July 2002

A dry planarization process has been developed that utilizes plasma-enhanced chemical vapor deposition of amorphous carbon films. The characteristics of the films depend on deposition conditions such as source gas composition, rf power, degree of ion bombardment, temperature, pressure, and electrode spacing. Planar films were deposited at low temperatures (< 50 °C) with low ion bombardment energy (< 10 V) and high deposition rates (100–300 nm/min). These conditions are desirable for ultra-large-scale integrated circuits fabrication, in which the thermal budget and damage must be minimized while maintaining a high throughput. A high degree of planarization over long distances was obtained. By using 2.5-μm-thick carbon films, the height of 1.5 μm steps was reduced to less than 0.2 μm for 400-μm-wide trenches, providing better than 85% planarization. The planar films have low viscosity and molecular weight, and their molecular structure is similar to that of the source gas. A post-deposition hardening step was utilized to improve the compatibility of the films with subsequent processing steps. Submicrometer features were patterned in bilayer resists consisting of these planarization layers in combination with either wet- or dry-deposited inorganic imaging layers.
Photoresist etching in a hollow cathode reactor
Authors: Gross M. , Horwitz C. M.
Published: July 2002

The submicron photoresist patterning capabilities of hollow cathode and asymmetric diode (‘‘reactive ion etch’’) reactors are compared here. Confined hollow cathodes etch more than 15 times faster than a diode at a given target voltage, at pressures of 2 Pa and below. Etch directionality has been studied using measurements of undercut in deep submicron patterns. Low-pressure hollow cathode etch anisotropy is similar to that obtained in a diode reactor, at all target voltages. At high target voltages both reactor designs result in less than a few percent of total undercut and sidewall bowing using 0.7-μm period, 3-μm-thick structures. This level of bowing is often seen in submicron etched apertures; we show how such bowing is affected by mask sidewall slope, and by the aspect ratio of etched structures. We review theories of sidewall bowing, concluding that electrostatic deflection and ion reflection from mask edges cause most of the sidewall bowing under our low-pressure conditions.
Characterization of etch rate and anisotropy in the temperature-controlled chemically assisted ion beam etching of GaAs
Authors: Grande W. J. , Johnson John E. , Tang C. L.
Published: July 2002

Independent adjustment of etch rate and sidewall profiles in chemically assisted ion beam etching (CAIBE) of GaAs is demonstrated by controlling the temperature of the sample. GaAs etch rate data as a function of sample temperature, ion beam flux, and reactive gas flow is presented for CAIBE using a 500 eV argon ion beam and molecular chlorine. At a constant etch rate of 0.5 μm/min, etch profiles ranging from vertical to crystallographically faceted are obtained. This demonstrated flexibility, combined with the inherent reproducibility of dry etching, make CAIBE an attractive choice for processing advanced semiconductor devices. To illustrate the range of capabilities available with temperature-controlled CAIBE, etched-facet laser structures, self-aligned mesas and fine tips suitable for field-emitting devices are fabricated.
Extremely high selective, highly anisotropic, and high rate electron cyclotron resonance plasma etching for n+ poly-Si at the electron cyclotron resonance position
Authors: Samukawa Seiji , Sasaki Masami , Suzuki Yasuhiro
Published: July 2002

Extremely high selective, highly anisotropic, and high rate electron cyclotron resonance (ECR) plasma etching for n+ poly-Si is achieved at the ECR position in a newly developed ECR plasma etching system. The selectivity ratio of the n+ poly-Si etching rate to the SiO2 etching rate is more than 100 at 5×10−4 Torr and 260 at 3×10−3 Torr in pure Cl2 gas at a substrate temperature of 30 °C. Furthermore, the selectivity ratio increases infinitely by using a Cl2/O2 gas mixture at 5×10−4 Torr. The n+ poly-Si etching rate is more than 3000 Å/min with no radio frequency (rf) bias under the above selectivity ratio conditions. The etching selectivity is generated by low ion energy at the ECR position. The high etching rate is achieved by high ion current density at the ECR position in the plasma chamber.
Interface strain at the lattice-matched In0.53Ga0.47As/InP(001) heterointerface
Authors: Hybertsen Mark S.
Published: July 2002

A series of self-consistent calculations have been done for lattice-matched In0.53Ga0.47As/InP (001) interfaces to elucidate the atomic structure and electronic band offsets. For chemically abrupt interfaces, the interface bond lengths deviate significantly from those of the bulk. By varying interface composition, the net interface strain is altered. Comparison is made with recent x-ray diffraction experiments and implications for measuring interface abruptness and chemical composition are discussed. Inclusion of the correct equilibrium interface bond length is crucial for calculation of the valence band offset across this interface. However, the offset is independent of variations in interface composition. The calculated valence band offset is in good agreement with experiment.
Photoexcited carrier lifetimes and spatial transport in surface-free GaAs homostructures
Authors: Smith L. M. , Wolford D. J. , Martinsen J. , Venkatasubramanian R. , Ghandhi S. K.
Published: July 2002

We show that both the radiative efficiencies and lifetimes of photoexcited carriers in epitaxial GaAs may be enhanced by 3–4 orders of magnitude by the preparation of n+, doped layers at surface and substrate interfaces. Samples were prepared by organometallic vapor phase epitaxy, with n-region thicknesses of 3–10 μm, and narrow layers Si-doped to n+ concentrations of 5×1018 cm−3. Time-resolved luminescence in such structures, under both surface and bulk (near-band-edge) excitation conditions, reveal near-edge-excitonic or band-to-band-dominated recombination spectra, with carrier lifetimes ranging from 1.5 ns at 1.5 K to nearly 1 μs at room temperature. This is in contrast to the subnanosecond lifetimes typical in conventionally prepared GaAs, but is comparable to the best reported for high-purity liquid phase epitaxy prepared GaAs/AlxGa1−xAs double heterostructures. The spatial distributions of photoexcited carriers in these structures are observed to expand by over an order of magnitude during their 1 μs, room temperature lifetime. The expansion is diffusive, with a measured minority carrier (hole) diffusion constant of 8 cm2/s at 300 K. This corresponds to a room temperature hole mobility of 300 cm2/V s, comparable to previously measured majority carrier (hole) mobilities in p-type GaAs of similar purity. The measured temperature dependence of the photoexcited hole mobilities show that μ∼T−2.1, indicating that the spatial transport of carrier in these structures is limited by scattering with acoustic and optic phonons, just as in high-purity p-type GaAs. These results are clear evidence that the narrow, heavily doped layers effectively ‘‘shield’’ minority carriers from the interfaces, thereby virtually eliminating interface recombination.
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u x-ray photoelectron spectroscopic study of remote plasma enhanced chemical vapor deposition of silicon nitride on sulfide passivated InP
Authors: Lau W. M. , Jin S. , Wu X.-W. , Ingrey S.
Published: July 2002

The changes in chemical composition and Fermi level position of n- and p-InP surfaces induced by reactions with sodium sulfide and ammonium sulfide solutions and with vapor from ammonium sulfide solution have been characterized by x-ray photoelectron spectroscopy (XPS). Further, in situ XPS analysis was used to study interfaces formed on sulfide passivated surfaces by remote plasma enhanced chemical vapor deposition of silicon nitride. We found that both indium and phosphorus sulfide phases were formed as a result of exposing InP to sulfide vapor at room temperature. However, most of the surface native sulfides dissolved in water and the resultant surface was then covered with about one monolayer of indium sulfide. Further, reduction in donor states in the upper band gap was evident by these sulfide treatments. However, heating the sulfide passivated sample caused an increase in surface states. Sulfur doping effect was also observed upon heating InP covered with the air oxidation products of the sulfide vapor. In the study of silicon nitride deposition, we found that the formation of native nitride could be avoided by optimizing the processing parameters. In addition, we also found that the surface native sulfide on InP reacted with the deposited silicon nitride. Capitance–voltage (C–V) data collected at 1 MHz indicate that a low interface state density could be obtained on silicon nitride/sulfide passivated InP. However, measurements of surface band bending of InP as a function of charging potential on a 10 nm silicon nitride on InP by XPS indicate that slow surface states were present which restricted changes in band bending to less than 0.3 eV when the applied voltage on the thin dielectric was −2 V.
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u removal of native oxide from silicon wafers
Authors: Sherman Arthur
Published: July 2002

In many integrated circuit fabrication steps, it is important to be able to ensure that there is no native oxide on a silicon surface before the next layer is deposited. For example, when tungsten is deposited by chemical vapor deposition (CVD) by silicon/hydrogen reduction of WF6, attack of the silicon surface can be extensive (i.e., wormholes) if there is a native oxide layer.1 Similarly, growing epitaxial silicon on a single-crystal substrate at a low temperature also depends critically on the removal of such a native oxide. The standard procedure for attempting to remove any surface oxide involves various wet etches, generally concluding with a dip in dilute HF. However, exposing a clean wafer to the atmosphere for even a short time allows some oxide to regrow, since silicon is an extremely reactive material. Accordingly, it would be desireable to develop an in situ procedure for cleaning of native oxide, and that will be the subject of this brief note.
Thermal stability and Schottky barrier of Sb overlayers on GaAs(110) and InP(110)
Authors: Esser N. , Reckzügel M. , Srama R. , Resch U. , Zahn D. R. T. , Richter W. , Stephens C. , Hünermann M.
Published: July 2002

The adsorption of thin Sb overlayers on GaAs(110) and InP(110) and their behavior during thermal annealing were studied with Raman spectroscopy, soft x-ray photoelectron spectroscopy, Auger electron spectroscopy, and low-energy electron diffraction. When deposited at room temperature, Sb forms a fairly well ordered monolayer with amorphous Sb on top. Upon annealing, the Sb forms crystalline islands which desorb at temperatures above 475 K leaving a well ordered monolayer of Sb behind. On InP(110) this monolayer is stable only up to around 500 K, whereas on GaAs(110) it remains stable to annealing temperatures above 580 K. For this well ordered Sb monolayer, the Schottky barriers are found also to be different for GaAs and InP. On GaAs, the barrier is low on both p- and n-type substrates, whereas on InP we find a low barrier on n-type and a barrier of 0.6 eV on p-type substrates. The differences in Schottky barriers and thermal stability of the ordered Sb monolayer leads to the conclusion that Sb bonds differently to GaAs and InP.
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u low-energy ion scattering analysis of InP surface during molecular-beam epitaxy
Authors: Kubo Minoru , Narusawa Tadashi
Published: July 2002

Low-energy ion scattering (LEIS) is introduced as a new analytical technique for in situ molecular-beam epitaxy (MBE) monitoring. LEIS is highly sensitive to the atomic structure of topmost layers, and offers an ideal in situ monitoring system. We have built a coaxial impact collision LEIS spectrometer, which is combined with a MBE system. Well-collimated He+ ion beams are provided through the ion beam line and scattered by the substrate surface under MBE growth, and detected by a time-of-flight energy analyzer. When the incident direction of the primary beam with respect to the substrate crystal is aligned to a major channeling direction, scattering is limited to the topmost layers, and gives us information on the coverage and epitaxial quality. In order to demonstrate the feasibility of LEIS, we have made in situ analysis of MBE growth on InP surfaces. During the layer-by-layer growth of InAs/AlAs on As-stabilized InP(111)A surface, we have observed characteristic variation of the 〈111〉 aligned scattering intensity.
Observation of negative differential resistance in tunneling spectroscopy of MoS2 with a scanning tunneling microscope
Authors: Youngquist M. G. , Baldeschwieler J. D.
Published: July 2002

A scanning tunneling microscope has been used for imaging and tunneling spectroscopy of 2Hb–MoS2 in ultrahigh vacuum. Atom-resolved images obtained in three distinct imaging modes–measuring z at constant current, barrier height at constant current, and current at constant z–are presented. Current–voltage (I–V) tunneling spectra reveal the occasional presence of negative differential resistance. Possible origins of the effect are discussed. Convolution of the sample energy density of states (DOS) with a contamination-induced peak in the tip DOS is the probable cause. Other mechanisms that may be active include charging of electron traps in the barrier or on the tip, and resonant tunneling in a double-barrier quantum well structure resulting from layer separation in the MoS2 crystal.
A study of the use of ultraviolet–ozone cleaning for reduction of the defect density on molecular beam epitaxy grown GaAs wafers
Authors: Kopf R. F. , Kinsella A. P. , Ebert C. W.
Published: July 2002

A problem with molecular beam epitaxy growth of semiconductors is the presence of defects. Since most of them originate at the substrate/epitaxial interface, special attention must be given to the treatment of the surface before growth. It must be clean on an atomic scale. This study has found that a combination of ultraviolet–ozone treatment and chemical etching produces the lowest defect density in the grown layer.
Performance of the EL-3+ maskmaker
Authors: Hartley John , Groves Timothy , Pfeiffer Hans
Published: July 2002

IBM’s new e-beam maskmaker, designated EL-3+, is installed and operating in the IBM Advanced Mask Facility in Burlington, Vermont. This tool represents a significant extension in the state of the art in the manufacture of masks, particularly in the areas of minimum feature size and overlay. The tool routinely operates with 0.35 μm ground rules at 70 nm (3σ) registration to grid. The tool has demonstrated the ability to work at 0.25 μm ground rules as well. The primary mission of the tool is the production of 1X x-ray masks. Some of the tool parameters include a 50 keV electron beam operating at a current density of 20 A/cm2. The system uses a shaped spot with a maximum size of 2×2 μm2. Exposures are made over areas with dimensions of up to 80 by 80 mm with a 2.1 mm field size. Deflection within a field is done through a combination of magnetic and electric deflection in a variable axis immersion lens (VAIL) configuration. During exposure the pattern data is stored on-line in a 1 G-byte buffer. The pattern buffers are loaded directly from a host IBM 4381. The system automatically corrects for any field distortions to a level of 6.25 nm using a calibrated reference grid.
Nanostructures processing by focused ion beam implantation
Authors: Petroff P. M. , Li Y. J. , Xu Z. , Beinstingl W. , Sasa S. , Ensslin K.
Published: July 2002

We present several novel methods that use a focused ion beam (FIB) processing of quantum well structures for lateral band gap engineering and doping on a nanoscale. Antidots and electron dots have been made by FIB and some of their transport properties are presented. In situ FIB processing of buried stressor structures and localized band bending are also demonstrated as a means of achieving lateral carrier confinement.
Growth rate and composition calibration of III/V materials on GaAs and InP using reflection high-energy electron diffraction oscillations
Authors: Kopf R. F. , Kuo J. M. , Ohring M.
Published: July 2002

The use of reflection high-energy electron diffraction oscillations to obtain lattice-matched In0.53Ga0.47As and In0.52Al0.48As on InP is described. This method has also been extended to the growth of strained InyGa1−yAs and InxAl1−xAs on InP as well as that of quaternary In1−x−yGaxAlyAs compositions, lattice-matched in InP.
Treatment of ZnSe substrates for homoepitaxy
Authors: Ohkawa K. , Karasawa T. , Mitsuyu T.
Published: July 2002

We have developed a novel treatment of ZnSe substrates for homoepitaxy using dry etching with a BCl3 plasma. The dry-etched substrates exhibited mirror-like morphology even after 10-μm etching in thickness to remove polishing damage, and the quality of its surface was remarkably improved. Subsequent thermal etching of ZnSe was found by reflection high-energy electron diffraction observation to be valid in the temperature range from 440 to 650 °C. Highest-quality ZnSe homoepitaxial layer has been obtained by growth on the substrate etched at the BCl3 pressure of 60 mTorr. Crystallinity of the layer was as good as that of the dry-etched substrate. Low-temperature optical analysis indicated the layer to be high purity and to be free from in-plane biaxial strain.
CH4/H2 reactive ion etching for gate recessing of pseudomorphic modulation doped field effect transistors
Authors: Pereira R. , Van Hove M. , De Raedt W. , Jansen Ph. , Borghs G. , Jonckheere R. , Van Rossum M.
Published: July 2002

Pseudomorphic AlGaAs/InGaAs modulation doped field effect transistors have been fabricated by using methane/hydrogen (CH4/H2) reactive ion etching for gate recessing. Source-drain resistance and Hall measurements on as etched and annealed samples are presented. The electrical degradation introduced by the plasma can be recovered after annealing at 400 °C. A threshold voltage (Vth) standard deviation of 14 mV over a 5 cm (2 in.) wafer was obtained.