Growth of heavily Zn-doped InGaAs at low temperature by LP-MOCVD

Epitaxial growth of Zn-doped InGaAs on InP substrates has been carried out at 550degreesC by LP-MOCVD. Hole concentration as high as 6 x 10(19)cm(-3) has been achieved at the H-2 flow rate of 20 sccm through DEZn bubbler. The lattice constant of Zn-doped InGaAs was found to be dependent on the flow rate of DEZn, and the tensile strain mismatch increases with increasing H-2 flow rate of DEZn. The negative lattice mismatch of heavily Zn-dopped InGaAs may be due to, the small covalent bonding radius of zinc and the combination of butane from ethyl of DEZn,and TEGa. And the latter accelerates the pyrolysis of TEGa, which is the dominant mechanism in determining the negative mismatch of Zn-doped InGaAs. (C) 2003 Elsevier B.V. All rights reserved.

(Ga, Gd, As) film growth on GaAs substrate by low-energy ion-beam deposit

(Ga, Gd, As) film was fabricated by the mass-analyzed dual ion-beam epitaxy system with the energy of 1000 eV at room temperature. There was no new peak found except GaAs substrate peaks (0 0 2) and (0 0 4) by X-ray diffraction. Rocking curves were measured for symmetric (0 0 4) reflections to further yield the lattice mismatch information by employing double-crystal X-ray diffraction. The element distributions vary so much due to the ion dose difference from AES depth profiles. The sample surface morphology indicates oxidizing layer roughness is also relative to the Gd ion dose, which leads to islandlike feature appearing on the high-dose sample. One sample shows ferromagnetic behavior at room temperature. (C) 2003 Elsevier B.V. All rights reserved.

Low-temperature growth of InN by MOCVD and its characterization

Metalorganic chemical vapor deposition growth of InN on sapphire substrate has been investigated between 400 degrees C and 500 degrees C to seek the growth condition of InN buffer layer, i.e. the first step of realization of the two-step growth method. Ex situ characterization of the epilayers by means of atomic force microscope, scanning electron microscope and X-ray diffraction, coupled with in situ reflectance curves, has revealed different growth circumstances at these temperatures, and conclusion has been reached that the most suitable temperature for buffer growth is around 450 degrees C. In addition, the growth rate of InN at the optimized temperature with regard to different precursor flow rates is studied at length. (c) 2004 Elsevier B.V. All rights reserved.

The influence of V/III ratio in the initial growth stage on the properties of GaN epilayer deposited on low temperature AlN buffer layer

The V/III ratio in the initial growth stage of metalorganic chemical vapor deposition has an important influence on the quality of a GaN epilayer grown on a low-temperature AIN buffer layer and c-plane sapphire substrate. A weaker yellow luminescence, a narrower half-width of the X-ray diffraction peak, and a higher electron mobility result when a lower V/III ratio is taken. The intensity of in situ optical reflectivity measurements indicates that the film surface is rougher at the beginning of GaN growth, and a longer time is needed for the islands to coalesce and for a quasi-two dimensional mode growth to start. A comparison of front- and back-illuminated photoluminescence spectra confirms that many threading dislocations are bent during the initial stage, leading to a better structural quality of the GaN layer. (C) 2007 Elsevier B.V. All rights reserved.

(Ga,Mn,N) compounds growth with mass-analyzed low energy dual ion beam deposition

The (Ga,Mn,N) samples were grown by the implantation of low-energy Mn ions into GaN/Al2O3 substrate at different elevated substrate temperatures with mass-analyzed low-energy dual ion beam deposition system. Auger electron spectroscopy depth profile of samples grown at different substrate temperatures indicates that the Mn ions reach deeper in samples with higher substrate temperatures. Clear X-ray diffraction peak from (Ga,Mn)N is observed in samples grown at the higher substrate temperature. It indicates that under optimized substrate temperature and annealing conditions the solid solution (Ga,Mn)N phase in samples was formed with the same lattice structure as GaN and different lattice constant. (C) 2003 Elsevier Science B.V. All rights reserved.

In0.25Ga0.75As growth on low-temperature thin buffer layers formed on GaAs (001) substrate

High-quality In0.25Ga0.75As films were grown on low-temperature (LT) ultra-thin GaAs buffer layers formed on GaAs (0 0 1) substrate by molecular beam epitaxy. The epilayers were studied by atomic force microscopy (AFM), photo luminescence (PL) and double crystal X-ray diffraction (DCXRD), All the measurements indicated that LT thin buffer layer technique is a simple but powerful growth technique for heteroepitaxy. (C) 2002 Elsevier Science B.V. All rights reserved.

Very low-pressure VLP-CVD growth of high quality gamma-Al2O3 films on silicon by multi-step process

gamma-Al2O3 films were grown on Si (10 0) substrates using the sources of TMA (AI(CH3)(3)) and O-2 by very low-pressure chemical vapor deposition. The effects of temperature control on the crystalline quality, surface morphology, uniformity and dielectricity were investigated. It has been found that the,gamma-Al2O3 film prepared at a temperature of 1000degreesC has a good crystalline quality, but the surface morphology, uniformity and dielectricity were poor due to the etching reaction between 0, and Si substrate in the initial growth stage. However, under a temperature-varied multi-step process the properties Of gamma-Al2O3 film were improved. The films have a mirror-like surface and the dielectricity was superior to that grown under a single-step process. The uniformity of gamma-Al2O3 films for 2-in epi-wafer was <5%, it is better than that disclosed elsewhere. In order to improve the crystalline quality, the gamma-Al2O3 films were annealed for I h in O-2 atmosphere. (C) 2002 Elsevier Science B.V. All rights reserved.

Effect of in situ thermal treatment during growth on crystal quality of GaN epilayer grown on sapphire substrate by MOVPE

GaN epilayers on sapphire substrate grown by metalorganic vapor-phase epitaxy (MOVPE) in a horizontal-type low-pressure two-channel reactor were investigated. Samples were characterized by X-ray diffraction (XRD), Raman scattering, atomic force microscopy (AFM) and photoluminescence (PL) measurements. The influence of the temperature changes between low temperature (LT) deposited GaN buffer and high temperature (WT) grown GaN epilayer on crystal quality of epilayer was extensively studied. The effect of in situ thermal annealing during the growth on improving the GaN layer crystal quality was demonstrated and the possible mechanism involved in such a growth process was discussed. (C) 2001 Elsevier Science B.V. All rights reserved.

Effect of low-temperature SiGe interlayer on the growth of relaxed SiGe

A low-temperature Si0.8Ge0.2 (LT-Si0.8Ge0.2) interlayer was grown at 500 degrees C to improve the relaxed Si0.8Ge0.2 surface and reduce the dislocation density in it, which was confirmed by the change of reflective high-energy electron diffraction (RHEED) pattern from spotty to streaky and etch pits counts. For the same extent of strain; the threading dislocation density was reduced from 8 x 10(7) cm(-2) in the latter to 2 x 10(6) cm(-2) in the former. (C) 2000 Elsevier Science B.V. All rights reserved.

Doping during low-temperature growth of materials for n-p-n Si/SiGe/Si heterojuction bipolar transistor by gas source molecular beam epitaxy

In situ doping for growth of n-p-n Si/SiGe/Si heterojuction bipolar transistor (HBT) structural materials in Si gas source molecular beam epitaxy is investigated. We studied high n-type doping kinetics in Si growth using disilane and phosphine, and p-type doping in SiGe growth using disilane, soild-Ge, and diborane with an emphasis on the effect of Ge on B incorporation. Based on these results, in situ growth of n-p-n Si/SiGe/Si HBT device structure is demonstrated with designed structural and carrier profiles, as verified from characterizations by X-ray diffraction, and spreading resistance profiling analysis. (C) 2000 Elsevier Science B.V. All rights reserved.

Low-temperature growth properties of Si1-xGex by disilane and solid-Ge molecular beam epitaxy

Low temperature (similar to 500 degrees C) growth properties of Si1-xGex by disilane and solid-Ge molecular beam epitaxy have been studied with an emphasis on surface morphology and growth kinetics. It is found that low-temperature growth(<500 degrees C) is in layer-by-layer mode and atomically-smooth surfaces have been obtained in as-grown samples with large Ge composition (>0.5). Ge composition dependence on substrate temperature, Ge cell temperature and disilane flow rate have been investigated. It is found that in low-temperature growth (less than or equal to 500 degrees C) and under large disilane flux, Ge composition increases with the increase of Ge flux and further increase of Ge flux leads to the saturation of Ge composition. Similar compositional dependence has been found at different growth temperatures. The saturated composition increases with the decrease of substrate temperature. The results can be explained if H desorption is assumed to occur from both Si and Ge monohydrides without diffusional exchange and the presence of Ge enhances H desorption on a Si site. (C) 1998 Elsevier Science B.V. All rights reserved.

Ge composition saturation behavior during low-temperature Si1-xGex growth by disilane and solid Ge molecular beam epitaxy

Ge composition dependence on the Ge cell temperature has been studied during the growth of Si1-xGex by disilane and solid Ge molecular beam epitaxy at a substrate temperature of 500 degrees C. It is found that the composition x increases and then saturates when the Ge cell temperature increases, which is different from the composition-dependent behavior in growth at high temperature as well as in growth by molecular beam epitaxy using disilane and germane. The enhanced hydrogen desorption from a Ge site alone cannot account for this abnormal composition-variation behavior. We attribute this behavior to the increase of rate constant of H desorption on a Si site when the Ge cell temperature increases.

Physik der Elektronen in Nanostrukturen und niedrigdimensionalen Systemen - Studie zweier Beispiele

Als Beispiele für die vielfältigen Phänomene der Physik der Elektronen in niedrigdimensionalen Systemen wurden in dieser Arbeit das Cu(110)(2x1)O-Adsorbatsystem und die violette Li0.9Mo6O17-Bronze untersucht. Das Adsorbatsystem bildet selbstorganisierte quasi-eindimensionale Nanostrukturen auf einer Kupferoberfläche. Die Li-Bronze ist ein Material, das aufgrund seiner Kristallstruktur quasi-eindimensionale elektronische Eigenschaften im Volumen aufweist. Auf der Cu(110)(2x1)O-Oberfläche kann durch Variation der Sauerstoffbedeckung die Größe der streifenartigen CuO-Domänen geändert werden und damit der Übergang von zwei Dimensionen auf eine Dimension untersucht werden. Der Einfluss der Dimensionalität wurde anhand eines unbesetzten elektronischen Oberflächenzustandes studiert. Dessen Energieposition (untere Bandkante) verschiebt mit zunehmender Einschränkung (schmalere CuO-Streifen) zu größeren Energien hin. Dies ist ein bekannter quantenmechanischer Effekt und relativ gut verstanden. Zusätzlich wurde die Lebensdauer des Zustandes auf der voll bedeckten Oberfläche (zwei Dimensionen) ermittelt und deren Veränderung mit der Breite der CuO-Streifen untersucht. Es zeigt sich, dass die Lebensdauer auf schmaleren CuO-Streifen drastisch abnimmt. Dieses Ergebnis ist neu. Es kann im Rahmen eines Fabry-Perot-Modells als Streuung in Zustände außerhalb der CuO-Streifen verstanden werden. Außer den gerade beschriebenen Effekten war es möglich die Ladungsdichte des diskutierten Zustandes orts- und energieabhängig auf den CuO-Streifen zu studieren. Die Li0.9Mo6O17-Bronze wurde im Hinblick auf das Verhalten der elektronischen Zustandsdichte an der Fermikante untersucht. Diese Fragestellung ist besonders wegen der Quasieindimensionalität des Materials interessant. Die Messungen von STS-Spektren in der Nähe der Fermienergie zeigen, dass die Elektronen in der Li0.9Mo6O17-Bronze eine sogenannte Luttingerflüssigkeit ausbilden, die anstatt einer Fermiflüssigkeit in eindimensionalen elektronischen Systemen erwartet wird. Bisher wurde Luttingerflüssigkeitsverhalten erst bei wenigen Materialien und Systemen experimentell nachgewiesen, obschon die theoretischen Voraussagen mehr als 30 Jahre zurückliegen. Ein Charakteristikum einer Luttingerflüssigkeit ist die Abnahme der Zustandsdichte an der Fermienergie mit einem Potenzgesetz. Dieses Verhalten wurde in STS-Spektren dieser Arbeit beobachtet und quantitativ im Rahmen eines Luttingerflüssigkeitsmodells beschrieben. Auch die Temperaturabhängigkeit des Phänomens im Bereich von 5K bis 55K ist konsistent mit der Beschreibung durch eine Luttingerflüssigkeit. Generell zeigen die Untersuchungen dieser Arbeit, dass die Dimensionalität, insbesondere deren Einschränkung, einen deutlichen Einfluss auf die elektronischen Eigenschaften von Systemen und Materialien haben kann.

Low-dimensional hydrogen-bonded structures in the 1:1 and 1:2 proton-transfer compounds of 4,5-dichlorophthalic acid with the aliphatic Lewis bases triethylamine, diethylamine, n-butylamine and piperidine

The structures of proton-transfer compounds of 4,5-dichlorophthalic acid (DCPA) with the aliphatic Lewis bases triethylamine, diethylamine, n-butylamine and piperidine, namely triethylaminium 2-carboxy-4,5-dichlorobenzoate C~6~H~16~N^+^ C~8~H~3~Cl~2~O~4~^-^ (I), diethylaminium 2-carboxy-4,5-dichlorobenzoate C~4~H~12~N^+^ C~8~H~3~Cl~2~O~4~^-^ (II), bis(n-butylaminium) 4,5-dichlorophthalate monohydrate 2(C~4~H~12~N^+^) C~8~H~2~Cl~2~O~4~^2-^ . H~2~O (III) and bis(piperidinium) 4,5-dichlorophthalate monohydrate 2(C~5~H~12~N^+^) C~8~H~2~Cl~2~O~4~^2-^ . H~2~O (IV)have been determined at 200 K. All compounds have hydrogen-bonding associations giving in (I) discrete cation-anion units, linear chains in (II) while (III) and (IV) both have two-dimensional structures. In (I) a discrete cation-anion unit is formed through an asymmetric R2/1(4) N+-H...O,O' hydrogen-bonding association whereas in (II), one-dimensional chains are formed through linear N-H...O associations by both aminium H donors. In compounds (III) and (IV) the primary N-H...O linked cation-anion units are extended into a two-dimensional sheet structure via amide N-H...O(carboxyl) and ...O(carbonyl) interactions. In the 1:1 salts [(I) and (II)], the hydrogen 4,5-dichlorophthalate anions are essentially planar with short intramolecular carboxylic acid O-H...O(carboxyl) hydrogen bonds [O...O, 2.4223(14) and 2.388(2)A respectively]. This work provides a further example of the uncommon zero-dimensional hydrogen-bonded DCPA-Lewis base salt and the one-dimensional chain structure type, while even with the hydrate structures of the 1:2 salts with the primary and secondary amines, the low dimensionality generally associated with 1:1 DCPA salts is also found.

Encapsulation of nanoparticles into single-crystal ZnO nanorods and microrods

One-dimensional single crystal incorporating functional nanoparticles of other materials could be an interesting platform for various applications. We studied the encapsulation of nanoparticles into single-crystal ZnO nanorods by exploiting the crystal growth of ZnO in aqueous solution. Two types of nanodiamonds with mean diameters of 10 nm and 40 nm, respectively, and polymer nanobeads with size of 200 nm have been used to study the encapsulation process. It was found that by regrowing these ZnO nanorods with nanoparticles attached to their surfaces, a full encapsulation of nanoparticles into nanorods can be achieved. We demonstrate that our low-temperature aqueous solution growth of ZnO nanorods do not affect or cause degradation of the nanoparticles of either inorganic or organic materials. This new growth method opens the way to a plethora of applications combining the properties of single crystal host and encapsulated nanoparticles. We perform micro-photoluminescence measurement on a single ZnO nanorod containing luminescent nanodiamonds and the spectrum has a different shape from that of naked nanodiamonds, revealing the cavity effect of ZnO nanorod.