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Fabrication of high quality CdSe quantum dots is described in this paper. The source material was CdSe compound and the amount of the source supply was fixed to 2.2 monolayers throughout the study. The orientation of GaAs substrates, the source supply rate and the growth interruption time were changed as growth parameters. Photoluminescence (PL) was measured at 14 K. The high PL intensity and the narrow line width were used as measures of high quality. Optimum growth conditions were established.

Single quantum dots (QD) luminescence from MBE-grown CdSe/ZnSe QD was observed by micro-cathodoluminescence measurement. The scanning area of the exciting electron beam was decreased from 100 × 100 μm2 to 0.2 × 0.2 μm2. A broad emission was observed till an area of 2 × 2 μm2, and sharp emission lines were clear at a scanning area of 1 × 1 μm2 or less. The spatial resolution of this measurement was determined to be 0.45 μm from the number of sharp lines and the QD density. The luminescence intensity mapping was performed at arbitrarily selected wavelengths, and QD existence was clearly shown at different positions at each wavelength. Thus, the luminescence observation of the CdSe single QD and its mapping were successfully performed by micro-cathodoluminescence measurement for the first time. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

InN/Si heterojunctions consisting of InN with an oxygen concentration of ∼3% and a bandgap of 1.8 ∼ 2.0 eV were formed by MBE. The band alignment of the heterojunctions turned out be type II with a band discontinuity of 1.49 ∼ 1.60 eV. A SiNx intermediate layer with a thickness of 2.1 nm was observed by angle-resolved X-ray photoemission spectroscopy. The heterojunction showed good rectifying characteristics with a reverse current of 1 × 10−7 A/cm2. Separation of the InN/Si interface and the p–n interface by insertion of n-Si layer with a thickness of 200 nm resulted in a reduction of the reverse current in the heterojunction.

We studied the growth conditions for controlling CdSeTe epilayer composition. Te atoms are readily incorporated into CdSeTe epilayers. However, we could not control the Te composition by the beam intensity ratio of Te to Cd. Therefore, Te atoms are not preferentially chemisorbed on Cd atoms. Both the difference in the desorption rate of the physisorbed atoms and the difference in the formation energies of CdSe and CdTe affect the composition. The epilayers composition could be well controlled in the entire range by the beam intensity ratio of J Se /(J Se + J Te ) when the epilayers were grown on the Cd-stabilized surface. A simple growth model is presented and the sticking probabilities of Se and Te were determined from the growth rate to be 0.1 and 1, respectively.

CdSeTe layers were grown on GaAs(1 0 0) substrates by molecular beam epitaxy. The beam-intensity ratios of Se to Te atoms were changed to control the composition of the CdSeTe mixed crystals. The Te atoms were more readily incorporated into the epilayers than the Se atoms under the competition for incorporation of Se and Te atoms. The J VI / J II beam-intensity ratio dependence of the Se composition was studied. The Se composition increased with decrease in J VI / J II ratio. At a J VI / J II ratio of 0.05 the beam-intensity ratio of Se to Se+Te coincided with the Se composition. This result indicates that the Se and Te atoms are incorporated without competition on the Cd stabilized surface. We considered the behavior of physisorbed atoms and the heat of formation of the compounds and discussed the situation of the growing surface of the CdSeTe epilayers, comparing it with the reported results of ZnSeTe epilayers.

Impurity incorporation from a SiO 2 mask in epitaxially laterally overgrown (ELO) GaN was depicted using a newly developed cryogenic scanning photoluminescence (PL) microscope. Both plan-view and cross-sectional PL images with a spatial resolution of 0.3 μm were obtained for emissions ascribed to free excitons (E XA ) and excitons bound to donors (D 0 X) at 15 K. In the cross-sectional μ-PL images, a bright emission of D 0 X was observed in the area adjacent to the SiO 2 mask within a distance of approximately 8 μm from the mask, indicating an enhanced incorporation of donors such as Si atoms during the lateral growth. In the area beyond 8 μm from the mask, the D 0 X emission was suppressed, showing a decrease in the donor incorporation after coalescence of ELO GaN on the SiO 2 mask.

We successfully fabricated wurtzite quantum-well structures with Zn 0.4 Cd 0.6 Se barrier layers and a four monolayer CdSe well layer on cubic ZnSe/GaAs(111)B substrates by molecular beam epitaxy. Although the cubic CdSe well layer grew on the cubic ZnSe/GaAs(111)B substrate, the wurtzite CdSe well layer grew on the wurtzite-Zn 0.4 Cd 0.6 Se/cubic-ZnSe/GaAs(111)B structure. The CdSe well layer was compressed in the (0001) plane and dilated to the [0001] direction judging from the X-ray diffraction measurement. Weak orange photoluminescence was observed in this quantum-well structure.

Self-assembled CdSe single- and multi-quantum-dots layer structures were grown by molecular beam epitaxy with ZnSe barrier layer and were evaluated by photoluminescence measurements. The peak wavelengths of the emission spectra were around 480 nm for 1.7–2.3 monolayer (ML) supply and around 530 nm for 2.6–4.0 ML supply in the single-quantum-dots layer samples. The optimum supplied amount of CdSe for the quantum-dots formation was determined to be around 2.6 ML. The integrated emission intensities increased on increasing the ZnSe barrier-layer thickness in the multi-quantum-dots layer samples with the same total barrier-layer thicknesses. The integrated emission intensities of the multi-quantum-dots layer structures with constant barrier-layer thickness proportionally increased on increasing the total barrier-layer thickness and were saturated above the total thickness of about 2200 A, which corresponds to the thickness dependence of the number of photo-generated carriers that are provided to the quantum dots.

Self-assembling CdTe quantum dots were grown on ZnSe epilayers by alternate supplying and molecular beam epitaxial methods. RHEED observation implies that the growth mode of CdTe on ZnSe was the Volmer–Weber one owing to the large lattice mismatch between CdTe and ZnSe. Temperature dependence of photoluminescence spectra suggested that the emissions originated from quantum dots. The emission wavelength increased with increasing the supplied amount of source materials and with decreasing the growth temperature. The influence of these growth parameters on the dot formation is discussed.

Green light emitting diodes were fabricated by molecular beam epitaxy using CdSe quantum dots (QDs) as emission layers. The diode structure was “Au electrode/p-ZnTe/pseudo-graded bandgap structure of ZnSeTe/p-ZnSe:N/undoped ZnSe/emission layer/undoped ZnSe/n-ZnSe:Cl/n-GaAs(0 0 1) substrate/In electrode”. The emission layers consisted of the CdSe QDs layers and the ZnSe intermediate layers, and were fabricated changing such structures. Green injection electroluminescence (EL) was clearly observed at room temperature at a current of 20 mA. The emission intensities were studied on the different emission layer structures. The penetration depth of carriers into the emission layer is estimated to be in the range between 60 and 120 nm in the present samples.

We grew Zn 0.8 Cd 0.2 Se/ZnSe strained quantum-well structures on GaAs(1 1 1)A substrates 10°-misoriented toward [1 0 0] direction by molecular beam epitaxy. The growth rates and the Cd composition in the ZnCdSe epilayers on (1 1 1)A substrates were small compared to those on (1 0 0) substrates at the same growth conditions. Therefore, in order to compare (1 1 1) and (1 0 0) samples with the same structures, these were grown separately. The piezoelectric properties were characterized by photoluminescence measurements at 11 K. The emission energies of the (1 1 1) quantum wells shifted toward lower energy compared to those of the (1 0 0) quantum wells with the same well width, owing to the piezoelectric effect. We calculated the internal electric field of these samples to be 0.9 × 10 7 V/m. The difference from the theoretical value (1.9 × 10 7 V/m) was discussed. The emission intensities decreased with increasing well width. We observed the screening of the piezoelectric field by the photogenerated carriers.

GaAs1-xBix alloys were grown on GaAs by molecular beam epitaxy (MBE). The lattice constants perpendicular and parallel to the surface of epilayers were estimated by high-resolution X-ray diffraction (XRD) analysis. The GaBi molar fraction was estimated by the Rutherford backscattering spectroscopy (RBS). GaAs1-xBix epilayers with GaBi molar fractions less than 5% were almost coherently grown on GaAs substrate with compressive strain. The lattice mismatch between GaAs1-xBix (x=5%) and GaAs was estimated to be approximately 0.5%.

Quantitative surface analysis includes the determination of the elemental composition and the structure of the sample under investigation. Although LEED, XPS, and SPM etc. have been used to investigate the surface structure of the materials, ambiguity remains in determining quantitatively the topmost atomic species and its alignment on an atomic scale. Therefore, we adopted coaxial impact collision ion scattering spectroscopy (CAICISS) to identify the terminating structure of compound materials such as SrTiO 3 (001), InP(001) etc. As a result of the measurements, we could determine the topmost atomic plane of those materials. CAICISS is considered to be a powerful tool for those topmost surface analysis of the materials.

ZnSe films were grown on GaAs(1 1 1)B substrates by molecular beam epitaxy. The observation of reflection high-energy electron diffraction confirmed that the epilayers on both just and 10 o -misoriented (1 1 1)B substrates consist of twins. The photoluminescence of the undoped epilayers showed defect-related Y-line emissions and deep emissions owing to the twins. Nitrogen was doped to the epilayers using an RF plasma cell. The photoluminescence spectra of the doped epilayers suggested that the nitrogen doping to ZnSe is enhanced using the GaAs(1 1 1)B substrates instead of the GaAs(1 0 0) substrates. We discussed the reason based on the bond number of the growing surface.

The properties of ZnSe(111) films grown on misoriented GaAs(111)A substrates by molecular beam epitaxy, which includes the improvement in the crystalline quality and nitrogen-doping characteristics of ZnSe(111)A epilayers, were reported. Mirror-like surface morphologies, twin-free crystals, and, in the PL spectra, a remarkable decrease in the deep-level emission and an increase in the exciton emissions were obtained in ZnSe(111) epilayers on misoriented substrates. The net acceptor concentration decreased with increasing the amount of nitrogen gas supplied to the plasma cell. This character was opposite to the results of N-doped ZnSe(100) epilayers prepared in our laboratory. The doping character in ZnSe(111)A epilayers was discussed based on the N-Zn bond number on the (111)A surfaces.

We have tried nitrogen doping to ZnSe using a capacitively coupled RF plasma cell. The plasma was very stable throughout the doping experiment. The net acceptor concentration ( N a − N d ) showed a dip with increasing the nitrogen supply to the cell. The highest N a − N d obtained was as high as 6 × 10 17 cm −3 . This value seems to be limited by the pumping ability of our system. In the photoluminescence spectra, deep DA pair emissions were dominantly observed in almost all the samples. In the plasma emission spectra, the emissions of N 2 radicals were clearly observed, but those of excited N atoms were not observed. The relation between N a − N d and the plasma emissions is discussed.

The mass density was evaluated by Rutherford backscattering spectroscopy for silicon nitride (SiNx) films with considerably low carbon concentration deposited from hexamethyldisilazane by the radical beam deposition method. The mass density of the film deposited at a low substrate temperature (room temperature ~ 400°C) was comparable to those of conventional SiNx films deposited from SiH4. This indicates a compatibilty of the film in this work with conventional films. For the films deposited at a substrate temperature above 400°C, H and excess N were eliminated from the film, and the mass density was evaluated to be 3.2 g/cm3, which is comparable to that of Si3N4 formed by the sintering method.

GaNyAs1-x-yBix alloy was grown by molecular beam epitaxy. The lattice matching between the GaNyAs1-x-yBix epilayer and the GaAs substrate was achieved by adjusting the N composition used in this experiment. Photoluminescence (PL) at the wavelength of 1.3 µm was observed at room temperature for the GaNyAs1-x-yBix epilayer lattice matched to the GaAs substrate. The temperature coefficient of the PL peak energy for this GaNyAs1-x-yBix epilayer in the temperature range of 150–300 K was 0.14 meV/K which was much smaller than the temperature dependence of the band gap of GaInAsP alloy.

Silicon nitride (SiNx) film has been deposited at a substrate temperature in the range of 200–800°C by a new radical-beam deposition technique. In the new technique, hexamethyldisilazane is decomposed not in plasma directly, but in a reaction with atomic nitrogen, in order to reduce carbon concentration into the film. The carbon concentration of the film is estimated to be of the order of 1019 cm-3 at most, based on secondary ion mass spectroscopy. The resistivity and the dielectric constant of the film are evaluated to be ~1013 Ωcm at 3 MV/cm and 5.7 at 300 kHz, respectively, which makes the film quality comparable to that of SiNx films deposited by plasma chemical vapor deposition.

ZnSe epilayers were grown on GaAs(100) substrates at 250°C by molecular beam epitaxy (MBE) to establish optimum growth conditions. Molecular beam intensities and beam intensity ratios of the VI element to the II element ( J VI / J II ) were taken as growth parameters. The beam intensity dependence of the growth rates at a J VI / J II around unity was investigated. At the low growth rates region, the rates increase nearly linearly with the beam intensity, which is the normal MBE growth mode. In contrast, at the high growth rates region, the rates increase super-linearly with the beam intensity. This anomalous increase can be explained rather well by taking account of the contribution of Zn atoms on the Zn-exposed surface to the ZnSe growth. The crystallinity can be improved by decreasing the growth rate at a J VI / J II around unity. However, the optimum J VI / J II is revealed to be around 1.6 at a conventional growth rate of around 0.5 μm/h, judging from the photoluminescence spectra, surface morphologies and reflection high-energy electron diffraction (RHEED) patterns.

The hetero- and homoepitaxial deposition of GaAs films by the ionized cluster beam technique in connection with subsequent neutral beam deposition forming a double layer structure have been studied. It is found that ICB-deposited films have superior quality in comparison with conventional ion beam deposited films and comparable quality like MBE or MOCVD-deposited films. By the fabrication of device structures, it has been proved that the start of film growth from an interface formed by an ICB-deposited As layer is advantageous. Additionally, surface cleaning by low-energy ionized cluster beams has been studied. For the first time, defect-free surface cleaning by low-energy cluster ion beams has been realized.

A 6H-SiC bulk crystal was grown by a sublimation method. We have studied the surface morphology of the grown layer and considered the growth mechanism by observing the surface morphology. In this paper, the growth mechanism and defect formation are discussed.

We have carried out the annealing of InN epilayers grown by molecular beam epitaxy and capped with in situ deposited SiNx in vacuum at 450–650°C. With the increase in annealing temperature, the crystallinity and carrier mobility of the InN layer clearly improved, and the residual carrier concentration of the layer decreased. Annealing without the SiNx capping layer increased the number of defects and carrier concentration, probably due to the formation of N vacancies and O incorporation.

The absolute concentration of oxygen in polycrystalline InN was measured using a combination of Rutherford backscattering and x-ray photoemission spectroscopy. Polycrystalline InN was grown on quartz and glassy carbon at 500 °C by molecular-beam epitaxy using In metal and activated nitrogen species generated in rf plasma. The optical bandgap of polycrystalline InN increased from 1.55 to 2.27 eV with increasing oxygen concentration from 1% to 6%. Polycrystalline InN with an optical bandgap of 1.9 eV, which has often been reported, contains oxygen of a molar fraction of 3%.

Al 2 O 3 thin films have been deposited by reduced-pressure photo-CVD for the first time using a D 2 lamp as excitation source and aluminum-tri-isopropoxide as source material. The measured absorption band of the source material vapor overlaps the emission lines of the D 2 lamp in the vacuum ultraviolet region. At deposition temperatures below 270°C, the deposition rate was enhanced and the film qualities such as tan δ and the refractive index were improved. Above 270°C, in contrast, the effect of the D 2 lamp irradiation is not so clear. These results are discussed compared with the previous photo-CVD results obtained using low-pressure Hg lamps as light source.

The surface structure of a Si (100) substrate exposed to an As ionized cluster beam (ICB) was investigated by means of coaxial impact collision ion scattering spectroscopy (CAICISS). As a result of the measurements, first, it was proven that the Si surface is not damaged by As ICB exposure, although implanted As atoms of several percent were detected in the surface region. Second, both As and Si atoms from double domains of 2×1 and 1×2, and the predominant domain seems to be 2×1. Furthermore, 1×2 domain of As contributes to a lateral contraction of the surface.

It has been found that the exposure of a Si (100) surface to an As ionized cluster beam (ICB) is effective in the preparation of the surface prior to epitaxial growth of GaAs under conventional high vacuum conditions of 2×10−5 Pa. This process is achieved at a temperature as low as 600 °C. A clear 1×2 or 2×2 reflection high energy electron diffraction pattern observed after the procedure indicates good ordering of the sample surface. The cleaning process is attributed to chemical and physical sputtering by As ICB in the first stage and to the subsequent As termination of Si dangling bonds. It has been found that the optimum preparation conditions are an accelerating voltage of the As ionized cluster beam of 1.3 kV and a substrate temperature of 600 °C. GaAs films deposited on As ICB treated Si (100) substrates show good crystal quality with single domain structure.

We have investigated light irradiation effects on donor and acceptor impurity doping in photoassisted MBE growth of ZnSe. Li and N were chosen as acceptor impurities, and Ga and Cl as donor impurities. A He-Cd laser with a wavelength of 441.6 nm (250 mW/cm 2 ) was used as an irradiation source. Bound exciton emissions of neutral acceptor (I S 1 ) or neutral donor (I 2 ) were observed in photoluminescence spectra. The binding energies of I S 1 and I 2 of the irradiated epilayers are the same as those of the nonirradiated epilayers. The intensities of bound exciton emissions of Li, N and Cl were decreased by the irradiation, and that of Ga was increased. It was revealed that the changes in the intensities were not attributable to the surface-stoichiometry change by the irradiation. The increase and decrease in the intensities are discussedon the basis of photodesorption of impurity atoms during photoassisted MBE growth of ZnSe.

Crystal growth of on Si(100), (111) substrate was carried out by atmospheric pressure chemical vapor deposition using hexamethyldisilane and gas mixtures. Temperature dependence of growth rate and crystallinity of films were examined. The growth process was characterized by a mass spectrometric study of the decomposition of HMDS and mixtures. Using HMDS as a source material, low temperature epitaxy was realized at a substrate temperature of 1100°C. With and without a carbonized buffer layer, single‐crystal was grown on Si(111) substrate at the growth rates as high as 700 A/min. With Si(100) as a substrate, single crystals were grown only with a buffer layer.

Effects of electron-beam and light irradiation on the desorption and adsorption processes of Zn and Se adatoms on ZnSe(100) surfaces were studied using the intensity variation of the specular spot of RHEED. The desorption rate constants of physisorbed and chemisorbed atoms were obtained and discussed.

We have found for the first time that the total photodesorption of adatoms from physical- and chemical-adsorption state reduces when a DC electric field is applied normal to the surface. Considering this result and other irradiation effects on MBE growth, a model of the behavior of surface adatoms is proposed. In this model the important role of both photogenerated electrons and holes is emphasized. Moreover, we have succeeded in improving the surface morphologies of light-irradiated epilayers using misoriented (100)GaAs substrates toward the [0 1 1] direction. This improvement is explained taking into account the atomic steps on this surface.

The crystallinity of 3C-SiC on Si by CVD is significantly influenced by B2H6, trimethylaluminum (TMA) and triethylgallium (TEG) addition at relatively low temperatures. These acceptor doping agents lower the epitaxial temperature and doped 3C-SiC is epitaxially grown at 1100–1150 ° C without buffer layer formation. Below 1150 ° C, TMA addition affects the growth rate and decreases the activation energy for the deposition of 3C-SiC from 34.7 kcal/mol for undoped growth to 8.7 kcal/mol for Al-doped growth.

ZnSe epilayers have been grown by photo-assisted MBE on GaAs substrates at various substrates temperatures and under various molecular beam intensity ratios of group VI to group III element. A He-Cd laser with 441.6 mm wavelength was used as a light source. From the temperature dependence of the photo-desorption rate constants, the activation energies of photo-desorption of Zn and Se adatoms from the physical adsorption state (EPZn, EPSs) and from the chemical adsorption state (EC) are obtained, that is, EPZn=7.8 kcal/mol, EPSe=6.7 kcal/mol and EC=16.1 kcal/mol. Thus, the photo-desorption observed is photo-enhanced “thermal” desorption. ZnSe epilayers have been successfully grown at a temperature as low as 150°C. A sharp and strong free-excition emission is observed in photoluminescence spectra at 11 K in the low-temperature grown samples, which shows that the crystallinity is almost comparable with that of the unirradiated epilayer grown at 340°C (the optimum growth temperature without irradiation).

The effects of light irradiation of a He-Cd laser (441.6 nm) on MBE growth of ZnS x Se 1− x ( x =0−0.13) were studied. The growth rates of the epilayers were reduced and the photo-desorption rate constanSts of Zn, Se and S were obtained. In the photoluminescence spectra at 11 K, the intensities of the free exciton emission increased, and thus the crystallinity of the epilayers was found to be improved. The behavior of surface adatoms on the growing surface under laser irradiation is discussed.

An optimum composition x of MBE-ZnSxSe1−x/GaAs has been studied by surface morphology, X-ray diffraction and fluorescence microscopic study to obtain epilayers with the best quality. The epilayers with a lattice-matching composition at the growth temperature (xgt=0.083) had extremely smooth surfaces and the minimum FWHM of X-ray rocking curves in spite of thermal strain. Also, the orange emission due to Ga diffusion from the substrate was not observed at the epilayer-substrate interface in these epilayers. The epilayers with the best quality were grown with the composition of xgt.

In this study, MBE growth of GaN/sub y/As/sub 1-y/ at a low T/sub sub/ was studied based on X-ray diffraction (XRD) and secondary ion mass spectroscopy (SIMS). Recently, GaN/sub y/As/sub 1-y/Bi/sub x/ has been successfully created on the basis of both this study and MBE growth of GaAs/sub 1-x/Bi/sub x/. GaN/sub y/As/sub 1-y/ was grown on a GaAs(100) substrate using solid sources of Ga, As and Bi. Activated nitrogen generated from N/sub 2/ gas in rf plasma was used as a nitrogen source. The GaAs substrate was pre-treated by thermal flush at T/sub sub/ of 600/spl deg/C, followed by GaAs growth at T/sub sub/ of 500/spl deg/C. GaN/sub y/As/sub 1-y/ layers with a thickness approximately 500 nm were grown on the GaAs layer at T/sub sub/ ranging 260/spl deg/C and 400/spl deg/C. CaN/sub y/As/sub 1-y/ epilayers grown at F/sub sub/ ranging 260/spl deg/C and 400/spl deg/C showed XRD patterns with clear thickness fringes, which indicates that good crystal quality was achieved even though the epilayer was grown at T/sub sub/ of 260/spl deg/C. To clarify lattice deformation of GaN/sub y/As/sub 1-y/epilayers, we carried out XRD measurements regarding (400) and (511) diffractions.

The terminating structure of 6H–SiC(0001) substrates fabricated by the Acheson method was directly identified by means of coaxial impact collision ion scattering spectroscopy (CAICISS). The CAICISS spectra showed that the topmost surfaces of the samples were Si-terminated planes for both the front and rear faces. It was also shown that the (0001)Si face was composed of Si-terminated flat terraces and steps, the height of which corresponded to one-half the unit cell length along the 6H–SiC c axis.

Summary form only given. CdSe/sub x/Te/sub 1-x//ZnSe quantum-dots structures have a large conduction and valence band offset at an appropriate composition and are expected to be highly-efficient light-emitting material in the green region. However, to our knowledge, there have been very few reports on CdSeTe epilayers. Composition control of II-VI/sub x/VI/sub 1-x/ mixed crystals is difficult because the vapor pressures of VIth elements are high. In this report, the growth conditions were studied for controlling CdSeTe-epilayer composition.

Low‐temperature growth of 3C‐SiC by atmospheric‐pressure chemical vapor deposition was carried out using hexamethyldisilane (Si2(CH3)6) as a source material. Single‐crystal undoped SiC was grown on Si(111) without employing a carbonized buffer layer and on Si(100) with a buffer layer. In the case of adding Al(CH3)3 to the source gas, the Al‐doped initial layer works as a buffer layer which controls the initial nucleation. The Al doping lowers the expitaxial temperature of this gas system down to 1000 °C.

GaAs1–xPx (0.2 x < 0.7) was grown by metalorganic molecular beam epitaxy with a GaP buffer layer on Si for visible light-emitting devices. Insertion of the GaP buffer layer resulted in bright photoluminescence of the GaAsP epilayer. Pre-treatment of the Si substrate to avoid SiC formation was also critical to obtain good crystallinity of GaAsP. Dislocation formation, microstructure and photoluminescence in GaAsP grown layer are described. A GaAsP pn junction fabricated on GaP emitted visible light (˜1.86 eV). An initial GaAsP pn diode fabricated on Si emitted infrared light.