Thermal Cleaning Research Articles

Origin of non-uniformity in MBE grown nanometer-sized InGaAs ridge quantum wires and its removal by atomic hydrogen-assisted cleaning

The origin of non-uniformity of MBE-grown InGaAs ridge quantum wires (QWRs) in sub 10-nm wire width range was investigated in detail by SEM, in situ XPS, TEM and PL measurements. InAlAs/InGaAs/InAlAs wires were selectively grown on InGaAs ridge structures prepared also by MBE on 〈 1 ̄ 10〉 stripe patterned (001) InP substrates. The main source of non-uniformity was thermal cleaning of InP in As 4 done prior to InGaAs ridge formation which produced ridges having irregular sized InGaAs islands due to an initial As–P exchange reaction. Low temperature atomic hydrogen cleaning removed this problem, and led to successful formation of sub 10-nm QWRs.

Improvement in photovoltaic conversion efficiency of InGaP solar cells grown on Si substrate by thermal cleaning using Si 2H 6

A new type of thermal cleaning for Si surfaces, using Si 2H 6, has been developed for growing GaAs buffer layers with an A-step surface on an Si substrate by metaloraganic vapor-phase epitaxy (MOVPE). This process made it possible, for the first time, to grow an A-step surface InGaP solar cell structure on an Si substrate with good surface morphology. An improvement in photovoltaic conversion efficiency has been achieved by this newly developed process.

Hydrogen effects on ZnSe/GaAs interface: A photoreflectance study

ZnSe/GaAs heteroepitaxial structures were prepared by metalorganic chemical vapor deposition with the use of thermal cleaning treatments at varying hydrogen flow rates in preparing the substrate. The photoreflectance spectra for the samples prepared revealed Franz–Keldysh oscillation (FKO) signals with the superimposition of free exciton transition features. The FKO signals changed depending on the hydrogen flow rate while the exciton transition features remained unchanged. Fitting through Aspnes’ and Franz–Keldysh’s model showed that the built-in electric field at the interface increased as the hydrogen flow rate decreased. These results imply that the hydrogen flow rate in the course of thermal etching plays a crucial role in the change of the energy-band profile at the interface.

Effect of grain size and domain state on thermal demagnetization tails

Thermal demagnetization of viscous remanence (VRM) and partial thermoremanence (pTRM) of 20‐ and 135‐µm natural magnetites reveals a broad spectrum f(TUB) of unblocking temperatures TUB, both > and < TB, the blocking temperature. In contrast, 0.04‐µm single‐domain (SD) grains demagnetize sharply at TUB ≈ TB. High‐ and low‐TUB tails of f(TUB) were wider for 135‐µm multidomain (MD) grains than for 20‐µm PSD grains. 10‐mT alternating‐field demagnetization rendered the VRM of the 20‐µm magnetite more SD‐like in subsequent thermal cleaning, selectively erasing both low‐ and high‐TUB tails of f(TUB). Primary and secondary remanences are then cleanly separated, and non‐linear Thellier paleointensity determination becomes linear. Our results agree well with (TB, TUB) data for 105‐year thermoviscous overprints in the Milton Monzonite over the range of log(time) common to the two studies. Because (TUB)av ≈ TB for PSD and MD as well as SD grains, the Pullaiah et al. paleothermometry method will work if (TUB)av values are used instead of (TUB)max values.

Nitridation of GaP (100) Surfaces by rf Nitrogen Radicals and by Electron Cyclotron Resonance Nitrogen Plasma

The nitridation process of a GaP (100) surface using rf nitrogen radicals and electron cyclotron resonance (ECR) N2 plasma at 400–500°C has been investigated by reflection high-energy electron diffraction (RHEED), in situ X-ray photoemission spectroscopy (XPS), atomic force microscopy (AFM) and cathodoluminescence (CL) methods. The P-stabilized (2×4) surface prepared by ultra high-vacuum (UHV) thermal cleaning was used as an initial surface. At the initial stage of nitridation, both the P–N and Ga–N components were formed on the GaP surface. The subsequent radical process led to the dominant formation of strained small granular grains of cubic GaN with diameters of 5–10 nm. Further nitridation produced much larger hemispherical GaN grains. The surface exposed to ECR N2 plasma for 60 min exhibited an anisotropic surface morphology with rectangular structures which aligned to the [011] direction. Clear CL peaks originating from the cubic GaN structure were observed on these nitrided surfaces.

Permian and Mesozoic extensional faulting within the Caledonides of central south Norway

Palaeomagnetic data from fault rocks along major faults in the Laerdal-Gjende Fault System cutting the Caledonian structure in the Jotunheimen area of central south Norway reveals a multi-component remanence pattern. Sample and site-mean directions from the fault rocks obtained by thermal cleaning demonstrate a simple pattern of normal polarity low blocking components and reverse polarity high-blocking directions. The magnetic signature of the Laerdal-Gjende Fault System fault rocks is identical to that observed on breccias on late faults along the west coast of Norway. Based on available palaeomagnetic reference data, we assign ages of mid-late Permian and late Jurassic-early Cretaceous for important phases of faulting and breccia formation along the Laerdal–Gjende Fault System in central south Norway. Structural windows, partly exposing basement along the axis of the Caledonides in southern Norway were exhumed by footwall uplift on major faults in the Laerdal–Gjende Fault System. The consanguinity of fault rock data from the Laerdal–Gjende Fault System and fault rocks in western Norway, and comparison with displacement on the offshore continuation of the Laerdal–Gjende Fault System along the Hardangerfjorden Shear Zone, indicate that the main tectonic events responsible for the development of the North Sea basin also significantly affected the geology of central south Norway.

Chemical Vapor Cleaning of 6H‐SiC Surfaces

The techniques (temperature range of study) of in situ thermal desorption (500‐1100°C) and chemical vapor cleaning (CVC) via exposure to and/or (750‐1100°C) have been investigated for preparing surfaces suitable for epitaxial growth of SiC and III‐nitride films, and are compared with regard to surface purity, stoichiometry, and structural order. Oxide removal below the detection limits of Auger electron spectroscopy was achieved for all orientations via annealing in at 850‐900°C or ≈200° lower than necessary by thermal desorption. No non‐SiC carbon was detected on the surface by X‐ray photoelectron spectroscopy. An approximately one‐tenth of a monolayer of oxygen coverage and significant quantities of non‐SiC carbon were detected for all 6H‐SiC surfaces prepared by thermal desorption. In contrast to the predominantly non‐SiC carbon‐rich surfaces prepared by thermal desorption, the stoichiometry of the SiC surfaces prepared by CVC could be manipulated from Si‐rich to C‐rich without non‐SiC carbon formation by either extending the exposures or by following with exposure. The latter surfaces also had lower concentrations of both oxygen and non‐SiC carbon and increased surface order. © 1999 The Electrochemical Society. All rights reserved.

Lowering of Silicon Surface Cleaning Temperature by Irradiating Low Energy Electron Beams

Thermal cleaning of Si surfaces for homo- and heteroepitaxial growth on Si substrates was performed at temperatures below 700°C by irradiating low energy and low intensity electron beams. In order to evaluate the cleaned Si surfaces, thin single-crystalline GaAs films were grown at 450°C using an organometal gas decomposition technique immediately after cleaning. No surface contamination, such as oxide and carbide, remained in the interface between the GaAs films and the Si substrates.

Magnetostratigraphy of the Canadian Continental Drilling Program Cretaceous-Tertiary (K-T) Boundary Project core holes, western Canada

The Canadian Continental Drilling Program (CCDP) Cretaceous-Tertiary Boundary Project cored three holes, to 160, 188, and 170 m in southern Alberta, Saskatchewan, and Manitoba, respectively, to intersect the Cretaceous-Tertiary boundary. One hundred and seventy to 200 samples from 50 to 60 levels were taken from each of these unoriented cores for magnetostratigraphy. Samples were subjected to both alternating field (AF) and thermal cleaning. AF demagnetization in steps of 5 mT up to 30 mT showed that samples from all three cores carried only a low-coercivity viscous overprint, which was largely removed at 10 mT. Thus, three samples from each depth were routinely demagnetized at 10 mT or 100°C. The magnetic inclination of the sample giving the smallest measuring error was chosen to indicate the polarity at that depth. With the aid of palynologic control, magnetochrons 29n to 30r inclusively, in the Ravenscrag, Frenchman, Battle, Whitemud, and Eastend formations, were identified in the Elkwater core hole, western Cypress Hills, Alberta (49°36'N, 110°18'W). The Cretaceous-Tertiary boundary is missing at the Frenchman-Ravenscrag contact. The Wood Mountain core hole (49°05'N, 106°16'W) spans the interval from magnetozone 28n to 30r in the Ravenscrag, Frenchman, Battle, Whitemud, Eastend, and Bearpaw formations. The Cretaceous-Tertiary boundary is present in 29r. The Turtle Mountain core (49°01'N, 100°33'W) has a number of significant disconformities; only magnetozones 28n, 28r, 29n, 30n, and 32n or 33n are present in the Turtle Mountain, Boissevain, and Pierre formations. At the Cretaceous-Tertiary contact near the base of the Turtle Mountain Formation, there is a hiatus of 0.6 × 106 to 0.8 × 106 years. At the Campanian-Maastrichtian contact, between the Odanah and Coulter members of the Pierre Formation, there is a time gap of at least 3 × 106 years but probably about 6 × 106 years.

Effects of Initial Thermal Cleaning Treatment of a Sapphire Substrate Surface on the GaN Epilayer

We investigated the effects of the in situ thermal cleaning treatment of a (0001) sapphire substrate surface in hydrogen ambient on the structural, optical, and electrical properties of epitaxial GaN films grown by metalorganic chemical vapor deposition (MOCVD). Hall effect, X-ray diffraction (XRD), and photoluminescence measurements of GaN films grown at 1040°C clearly indicate that the film quality is strongly affected by the thermal cleaning treatment of the substrate surface. GaN films under the optimized thermal cleaning treatment at 1070°C for 10 min showed minimum full-widths at half maximum (FWHMs) of 273 arcsec and 728 arcsec for (002) and (102) XRD peaks, respectively. In addition, the FWHM of the band-edge emission peak was as narrow as 28.3 meV, and the intensity ratio between the band edge emission and the yellow band emission was as high as 100 at room temperature. It was also found that the roughness of sapphire surface was reduced after the thermal treatment.

Epitaxial growth of nitride semiconductor films by laser ablation

GaN epitaxial films on (0001) sapphire substrates were fabricated by laser ablation, An ArF excimer laser (193 nm, 25 ns) with an energy of 140 ml/pulse was used for ablating cold-pressed GaN targets made from high-purity GaN powders. Just before the deposition, thermal cleaning of the substrate surface at 1073 K was essential. The substrate temperature was varied between 873 and 1073 K, Above 973 K, the epitaxial layers were obtained, When a buffer layer of GaN was deposited at lower temperatures before the epitaxial growth, the crystalline quality and surface morphology were greatly improved.

Charge Trapping Sites in Spherulitic Polypropylene

Charged areas of spherulitic polypropylene (PP) samples were visualized by a simple technique of attaching oppositely charged fine dye particles. A combination of this visualization technique and thermally stimulated current (TSC) spectroscopy was applied to identify the regions where shallow and deep charge traps exist densely in positively corona-charged spherulitic PP. The shallow and deep traps in the PP sample are directly related to its two TSC bands, BL and BH, appearing at temperatures around 60°C and above 100°C, respectively. From visualized charge patterns of the PP samples with and without thermal cleaning of the BL band, it was found that the shallow traps mainly exist in the boundaries and the peripheral regions of spherulites while the deep traps are located in the central parts. Furthermore, the relative numbers of the shallow and the deep traps in the PP spherulites were estimated and found to depend on spherulite size: the ratio of shallow to deep traps decreased from 60/40 for 130–190 µm spherulites to 43/57 for 320–400 µm spherulites.

Thermal cleaning of air-exposed p-type InGaAs films and CBE regrowth of carbon-doped InGaAs layers for optical device applications

We have studied thermal cleaning of air-exposed Zn-doped InGaAs films and regrowth of carbon-doped InGaAs layers in terms of carrier concentration profiles and residual oxides. As the cleaning temperature prior to CBE regrowth is increased, the residual oxides at the regrowth interface exponentially decrease, and the carrier concentration at the interface approaches the intentional doping level. Elevating the temperature to 575°C provides a “clean” interface, i.e., the carrier profiles are flat. SIMS reveals that the carbon atoms doped to 10 20 cm −3 in the CBE film do not diffuse to the adjacent Zn-doped MOCVD film at all. The thermal cleaning and regrowth procedure was applied to an air-exposed MOCVD film with laser structure for the purpose of nonalloy ohmic contact layer. 1.3 μm-wavelength buried-heterostructure laser diodes with cleaved facets have a large light output of more than 20 mW per facet.

The palaeomagnetism of (Mesoproterozoic) Eriksfjord Group red beds, South Greenland: multiphase remagnetization during the Gardar and Grenville episodes

The Eriksfjord Group comprises ∼3000 m of lavas and sediments rapidly deposited in a rift which developed within an Andean-type batholith in juxtaposition to the southern margin of the Laurentian Shield in South Greenland at ca. 1300 Ma. The lavas have been shown to preserve a detailed record of the geomagnetic field at the time of eruption, incorporating normal, reversed and transitional directions. This study has examined the magnetic properties of the intervening red sediments. They are found to possess a diagenetic remanence imparted by mediating fluids at later times. The impact of diagenesis is stratigraphically controlled: the base of the rift infill has magnetizations partially resident in magnetite which are either unstable to thermal cleaning or record a single polarity ‘B’ magnetization (D/I=284/67°, 31 samples, α95=5.5°, palaeopole at 244.1°E, 47.5°N, dp/dm=7.5/9.1°). This corresponds in polarity, and closely in direction, to remanence observed in mid-Gardar gabbro giant dykes and dyke swarms emplaced along the axis of the rift system at ca. 1160 Ma; the causative diagenetic magnetite appears to have grown from hydrothermal systems motivated by this magmatism in a sealed reservoir setting within the lower part of the rift infill. The Ilímaussaq alkaline igneous complex was emplaced into the southern extension of the rift at ca. 1130 Ma and possesses a dual polarity magnetization (D/I=327/81°, α95=6.4°, 10 sites). Eriksfjord lavas within the thermal aureole are overprinted to varying degrees by comparable magnetizations with steep inclinations. The mean pole position (283°E, 71°N, dp/dm=12/12°) lies near the apex of an apparent polar wander loop incorporating the Gardar Track (ca. 1300–1140 Ma) and the Keweenawan Track (ca. 1115–1050 Ma). Magnetizations in the Eriksfjord sedimentary succession have not been significantly reset by emplacement of the Ilímaussaq complex, but higher levels of the rift infill are dominated by an ‘A’ magnetization (D/I=305/34°, α95=4.3°, 57 samples, palaeopole at 202.1°E, 32.4°N, dp/dm=2.8/4.9°) resident in haematite. The pole position does not correspond with any part of the Gardar Track, but does correlate with the return Keweenawan Track at ca. 1090 Ma, close to the time of Grenville orogenesis along the bordering southeastern margin of the Laurentian Shield. This remanence is attributed to diagenesis during extensional tectonism linked to the collapse of the Grenville Orogen formerly sited 100–200 km to the south.

Magnetostratigraphy of the Canadian Continental Drilling Program Cretaceous-Tertiary (K-T) Boundary Project core holes, western Canada

The Canadian Continental Drilling Program (CCDP) Cretaceous-Tertiary Boundary Project cored three holes, to 160, 188, and 170 m in southern Alberta, Saskatchewan, and Manitoba, respectively, to intersect the Cretaceous-Tertiary boundary. One hundred and seventy to 200 samples from 50 to 60 levels were taken from each of these unoriented cores for magnetostratigraphy. Samples were subjected to both alternating field (AF) and thermal cleaning. AF demagnetization in steps of 5 mT up to 30 mT showed that samples from all three cores carried only a low-coercivity viscous overprint, which was largely removed at 10 mT. Thus, three samples from each depth were routinely demagnetized at 10 mT or 100°C. The magnetic inclination of the sample giving the smallest measuring error was chosen to indicate the polarity at that depth. With the aid of palynologic control, magnetochrons 29n to 30r inclusively, in the Ravenscrag, Frenchman, Battle, Whitemud, and Eastend formations, were identified in the Elkwater core hole, western Cypress Hills, Alberta (49°36'N, 110°18'W). The Cretaceous-Tertiary boundary is missing at the Frenchman-Ravenscrag contact. The Wood Mountain core hole (49°05'N, 106°16'W) spans the interval from magnetozone 28n to 30r in the Ravenscrag, Frenchman, Battle, Whitemud, Eastend, and Bearpaw formations. The Cretaceous-Tertiary boundary is present in 29r. The Turtle Mountain core (49°01'N, 100°33'W) has a number of significant disconformities; only magnetozones 28n, 28r, 29n, 30n, and 32n or 33n are present in the Turtle Mountain, Boissevain, and Pierre formations. At the Cretaceous-Tertiary contact near the base of the Turtle Mountain Formation, there is a hiatus of 0.6 × 106 to 0.8 × 106 years. At the Campanian-Maastrichtian contact, between the Odanah and Coulter members of the Pierre Formation, there is a time gap of at least 3 × 106 years but probably about 6 × 106 years.

Real-Time Spectroscopic Ellipsometry Study of the Thermal Cleaning Process for Silicon Epitaxial Growth by UHV-CVD

ABSTRACTReal-time spectroscopic ellipsometry (RTSE) method was applied to study thermal cleaning process of silicon surfaces for epitaxial growth by ultra-high vacuum chemical vapor deposition (UHV-CVD). For the first time, in-situ observation of oxide decomposition process under Si2H6 ambience was carried out. The substrates with thin oxide formed by wet chemical treatment were heated up by infrared heater under UHV or under Si2H6 ambience in an UHV-CVD chamber and the oxide decomposition processes were observed by RTSE. Ellipsometric parameters Psi and Delta increase with the progress of oxide decomposition process and become constant with the completion of the decomposition. It was found that the oxide decomposition process consists of two phases and rate-determing processes are different in each phase. It was also found that Si2H6 lowers the activation energies of oxide decomposition process in each phase.

Modelling of thermally stimulated depolarization current peaks obtained by global and thermal cleaning experiments

Thermally stimulated depolarization current thermograms were obtained from modelling experiments on polar systems, assuming that the polarization can be described by a weighted summation of elementary Debye-like processes. The analysed situations were studied both by global and by cleaned experiments and the features of the obtained spectra were discussed and compared with the characteristics of the systems and the experimental conditions. The polarization distribution through the time relaxation axis during a cleaned experiment for a case characterized by a distribution of activation energies was calculated for all experimental steps. It was shown that the activation energy obtained by the Bucci method must be lower than the mean energy of the isolated processes.

Non-first-order thermoluminescent peaks in topaz

In thermoluminescence, knowledge of the kinetic order of the glow peaks is often essential for the interpretation of the results. Here we report results on the kinetic behaviour and activation energy determination of the peak that occurs at 222°C with high intensity in many samples of Brazilian colourless topaz from different origins, when heated at 1°C/s. The methods employed to study this peak were: the initial rise and the curve fitting, both combined with thermal cleaning procedures, and the Tm × Tstop . The average activation energy obtained by the initial rise method was 1.32 eV. The curve fitting and Tm × Tstop methods indicate a non first order kinetics. Other peaks were detected at 122°C and 195°C, after annealing the sample and irradiating it with gamma rays of 60Co. It was observed that the peak at 195°C shifts to lower temperatures with increasing doses.

Surface cleaning with hydrogen plasma for low-defect-density ZnSe homoepitaxial growth

This article investigates in depth the conditions for cleaning of the (100) ZnSe substrate surface for ZnSe homoepitaxial growth. Wet etching with a K2Cr2O7-based etchant as a pre-growth treatment is found to result in a Se-rich ZnSe surface that retains its original flatness. Reflection high energy electron diffraction patterns show that plasma irradiation during thermal cleaning is indispensable for removing the oxide layer on ZnSe substrate and keeping the flatness. In hydrogen plasma cleaning, the etch pit density (EPD) of the homoepitaxial film increases at rf power higher than 265 W, indicating the optimum cleaning temperature is between 260 and 280 °C. As for the dependence of the EPD on the cleaning time, a minimum EPD of 2.7×104/cm2 can be obtained for a plasma cleaning time of 20 min. A correlation between the interfacial residual oxygen concentration and the defect density in an epitaxially grown ZnSe film is also found.

ZnSe/ZnS Distributed Bragg Reflectors in the Blue Region Grown on (311)B GaAs Substrates

High-reflectivity distributed Bragg reflectors (DBRs) in the blue region consisting of II–VI semiconductors were grown on (311)B GaAs substrates for the first time using metalorganic vapor phase epitaxy. ZnSe/ZnS alternative layers were used as the DBR. To realize atomically flat surfaces, the conditions of the thermal cleaning and the growth of ZnSe and ZnS on (311)B GaAs surfaces were investigated using atomic force microscopy and X-ray diffraction. The supply of sufficient organic As flow during the thermal cleaning led to extremely-flat (311)B GaAs surfaces, and it was attributed to the suppression of As desorption from (311)B surfaces. Through the examination of the growth conditions for ZnSe and ZnS layers on (311)B GaAs substrates, a DBR with a high reflectivity was fabricated. The maximum reflectivity of the ZnSe/ZnS DBR grown on the (311)B GaAs substrate, measured at room temperature, was 94.5% with only 10 periods at a wavelength of 468 nm, which is in good agreement with the calculated reflectivity of 94.8%.