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Material properties of chemical-beam-epitaxy-grown III–V-N materials have been studied extensively in the past few years as a candidate of 1-eV junction in a multi-junction device. In this paper, we present theoretical modeling results to evaluate the criteria of how to achieve high-efficiency multi-junction solar cells using this material. Then, we will review and summarize the recent research progress of this material within this theoretical modeling framework to show how these criteria may be achieved.

The formation mechanism of N-H related defects in GaAsN grown by chemical beam epitaxy is studied by the isotope effects on the local vibration modes (LVMs). When the deuterated tris(dimethylamino)arsenic (TDMAAs) is used as an arsenic source, new signals appear in the spectrum and they are attributed to the N-D related LVM signals. Therefore, the As source molecule contributes to the formation of N-H related defects in GaAsN. When TDMAAs flow rate increases, the concentration of N-H related defects at 2952cm−1 increases. These results suggest that N-CH3 in the molecule is one of the origins of the N-H at 2952cm−1 in the grown films.

We grow BaSi2 films on Ge(111) substrates using various templates. First, we form 30 nm BaGe2 templates by deposition of Ba on hot Ge, followed by molecular beam epitaxy (MBE) at 580 °C to form BaSi2. We succeed to grow a-axis-oriented BaSi2; however BaSi2 is not a continuous film, and hence BaSi2 is easily oxidized after exposed to air. Next, we grow 3 nm BaSi2 template by solid phase epitaxy (SPE) with initial crystal nuclei BaSi2 at 580 °C, followed by MBE at 580 °C. As a result, we achieved highly [100]-oriented BaSi2 continuous films.

The N-H related acceptor defects in p-type GaAsN grown by chemical beam epitaxy are studied by deep level transient spectroscopy (DLTS). Two new signals appear in DLTS spectra at 0.15 and 0.23 eV, when the crystals are grown using deuterated As source (D-TDMAAs). This indicates that the new peaks are originated from N-D related defects. There are two energy levels at 0.11 and 0.19 eV, which are considered to play the role of a double acceptor. The energy difference between 0.15 and 0.11 eV, and that between 0.23 and 0.19 eV are almost same, about 0.04 eV. Although these energy levels become deeper with increasing the growth temperature, the energy differences are almost constant independent of the growth condition. The intensity ratios of the peaks at 0.15 (0.23) eV to that at 0.11 (0.19) eV have a good correlation with the ratio of deuterium amount to that of hydrogen in the grown film. We conclude that the energy shifts occur due to the structural change from N-H to N-D in the same type of defect, and that this acceptor corresponds to N-H related defect.

GaAs nanowires (NWs) growth kinetics by Ga-assisted chemical beam epitaxy on Si(111) substrates is studied as a function of the initial Ga catalyst dimensions and growth parameters such as substrate temperature and V/III flux ratio. The preparation method for substrates is optimized in order to obtain a surface oxide with a thickness around 0.5 nm, allowing the decomposition of Ga metalorganic precursor and the preferential growth of GaAs NWs at the oxide pinholes. The successful self-formation of Ga droplets over the slightly oxidized Si surface has been observed by scanning electron microscopy (SEM), whose initial size is demonstrated to affect both the NW growth rate and the resultant NW aspect ratio. NW morphology is thoroughly analyzed by SEM, showing a self-organized array of vertically aligned match-shaped GaAs NWs with a hexagonal footprint. In addition, the crystalline structure of NWs is monitored in-situ by reflection high-energy diffraction (RHEED), showing pure zincblende phase along the whole NW stem.

To investigate the microstructure of nitrogen-induced localized state (E N ) that perturbs the conduction band of GaAs host material, we adopted the photoreflectance measurements to chemical-beam-epitaxy grown GaAsN thin films. We measured both two split subbands to estimate correct values of E N . It was clearly seen that estimated E N decreased with increasing nitrogen content and temperature. By considering a change of a mean distance between neighboring nitrogen atoms, we concluded that the microscopic structure of E N is not only an isolated nitrogen atom but also nitrogen-related complex, accompanied by low-order pairs of nitrogen atoms and/or nitrogen clusters.

The structural and electrical properties of N-H complexes in GaAsN grown by chemical beam epitaxy are summarized. Using local vibration mode spectroscopy, some of the vibration frequencies are shown to be the same as those in the material grown by liquid encapsulated Czochralski and metal organic chemical vapor deposition, while no vibration modes are common to those in the material grown by molecular beam epitaxy. The dependencies of the vibration frequencies on measurement temperatures and annealing temperatures, and polarization of the vibration directions are studied to understand the structural properties of N-H complexes. The As source flow rate affects ratios of the defect densities, which indicate that those defects have different formation processes. The charge excitations by irradiation light indicate that the charge relaxation processes caused by those defects are in the orders of micro seconds.

Double carrier pulse deep level transient spectroscopy was deployed to identify and characterize the recombination centers in GaAsN grown by CBE. Six electron traps, E1 to E6, with average energy depths of 0.035, 0.125, 0.160, 0.365, 0.505, and 0.710 eV, respectively below the bottom edge of the conduction band minimum were observed. The DLTS peak heights of E2 and E4 were found to decrease with simultaneous injection of majority and minority carriers in the space charge region. This result is explained by the recombination of electrons and holes via E2 and E4 centers. The recombination processes were confirmed to be nonradiative and the possible origins of these two defects were expected to be related to the N-atom.

Impact of substrate temperature, fuxes of As2, P2 and Ga on the layers composition of solid solution GaPxAs1-x(001) during molecular-beam epitaxy (MBE) was experimentally investigated. The experimental data obtained for a wide range of growth conditions were analyzed. The analysis results are represented in the form of the kinetic model describing the formation process for composition of GaPxAs1-x(001) solid solution during MBE. The model can be used for the choice of growth conditions of GaPxAs1-x(001) at a given phosphorus fraction.

Two N-H local vibration modes at 961 and 2952 cm-1 in GaAsN grown by the chemical beam epitaxy have the same preferential N-H bond orientation. The integrated IR absorption intensities showed the two-fold rotational symmetry in (001) plane, which means that the N-H bond directions tend to align along [1-10] in (001) plane. However, the vibration modes at 961 and 2952 cm-1 were indicated to belong to the different types of N-H complexes. Therefore, the different types of N-H complexes have the same preferential N-H bond orientation.

The tridimethylaminoarsenic (TDMAAs) flow rate dependence of minority carrier lifetime (τe) in GaAsN grown by chemical beam epitaxy was investigated by time-resolved-photoluminescence. It was demonstrated that with TDMAAs of more than 1.0 sccm, τe increases up to a nitrogen concentration of 0.6% and then stabilizes. However, it monotonically decreases with a TDMAAs of 0.5 sccm. An obvious reason of these results is the TDMAAs dependence of the density of recombination centers in GaAsN. Four electron traps, E1 to E4, localized at average energy depths of 0.05, 0.11, 0.16, and 0.39 eV, respectively below the bottom edge of the conduction band, were found to monotonically decrease in density with increasing TDMAAs. This result indeed opens interesting future for enhancing the conversion efficiency of GaAsN based solar cells.

A GaAsN solar cell is fabricated by using the chemical beam epitaxy. The properties of the external quantum efficiency and short circuit current density are studied by comparing with the calculated values. The external quantum efficiency of the fabricated GaAsN solar cell was lower in the low wavelength region than the calculated value which does not consider the recombination at the interfaces. That is considered to be the one of the reasons for the low short circuit current density by 15 to 20 percent compared to the calculated value.

The hydrogen that constitutes N-H in GaAsN grown by the chemical beam epitaxy (CBE) equally comes from the nitrogen precursors (monomethylhydrazine) and arsenic precursors (trisdimethylaminoarsenic). The ratio of the contributions from those two precursors to the N-H constitution varied with the growth temperature of GaAsN. Further, the temperature dependence was different in each local vibration mode (LVM) of N-H.

Two nitrogen-related lattice defects were confirmed in GaAsN grown by chemical beam epitaxy (CBE), using deep level transient spectroscopy (DLTS). The first defect is a non-radiative recombination center (E1), with average activation energy of 0.33 eV below the conduction band minimum (CBM) of GaAsN. The lifetime of electrons from the CBM to E1 was calculated to around ∼0.2 ns, using the Shockley-Read-Hall (SRH) model for generation-recombination. These results expected E1 as the main cause of short minority carrier lifetime in GaAsN films. The Second defect is a hole trap (H2), deep acceptor-like state, with average activation energy of 0.15 eV above the valence band maximum (VBM), and originates from the N-H bond. Its density was found to be in good relationship with free hole concentration in p-type films, which were grown under N and H rich growth conditions. This deep acceptor was suggested to be the main cause of high background doping in GaAsN, which prevents the design of a wide depletion region GaAsN based solar cells and drops the minority carrier lifetime.

Within the context of the archetype InAs/GaAs self assembled quantum dot system, we provide an in situ, methodology based on the analysis of reflection high energy electron diffraction (RHEED) patterns and demonstrate its ability for real time and simultaneous determination of the quantum dots facet orientations, average size (height), strain profile, and dot-density during the molecular beam and chemical beam epitaxy growth.

Growth and characterization of tin doped GaAs(100) layers using chemical beam epitaxy are described in this work. The resistivity, type of carriers, as well as their net concentrations and mobilities were obtained by Hall Effect measurements. Layers with electron concentrations between 7.0×1016 and 1.6×1019 cm3 were obtained, while the measured room temperature mobilities were in the range 860–2700 cm2/Vs. Photoluminescence spectra show the presence of a donor related transition, whose intensity increases with the sample doping. Acceptor related transitions, different than the residual carbon doping, were not observed, suggesting that Sn incorporates as a donor with a small compensation ratio.

III–V compound multi-junction solar cells have great potential for space and terrestrial applications because they have high efficiency potential of more than 50% and superior radiation-resistance. We have been studying concentrator multi-junction solar cells under Japanese Innovative Photovoltaic R&D program started since FY2008. This paper presents our new achievements in super high-efficiency multi-junction and concentrator solar cells. We have obtained promising results: 1) 35.8% efficiency InGaP/GaAs/InGaAs 3-junction cells, 2) high quality (In)GaAsN material with higher mobility by chemical beam epitaxy compared to those grown by the other growth methods.

Hetero-epitaxy of GaAs films on Ge were grown by the chemical beam epitaxy (CBE) technique for super-high-efficiency multi-junction solar cells. However, the growth of III-V on Ge remains a key challenge due to anti-phase domains (APDs) and the inter-diffusion at the interface, resulting in the deterioration of the solar cell efficiency. In order to overcome these problems, we introduced the CBE technique, which was carried out under a higher vacuum (∼10−2 Pa) and at relatively lower temperature (360∼460 ¼) as compared with the growth of GaAs on Ge by the typical metalorganic vapor phase epitaxy (MOVPE). The effects of the low growth temperature, the source flow ratio of [V/III] and pre-annealing temperature on crystal qualities and optical properties of GaAs films on Ge were investigated. The results showed that GaAs films on Ge had a good structural quality at growth temperature from 400 to 460 °C with the [V/III] of flow ratio from 50 to 70 by a high resolution x-ray diffraction. The pre-annealing temperature and time were confirmed to play an important role in the modification of Ge substrate surface. The low-temperature (4.5 K) photoluminescence spectra showed the emission peak around 1.51 eV, corresponding to an exciton bound-to-acceptor, in sample grown at 400 °C and the full width at half maximum of this peak was evaluated 10 meV by Gaussian fitting. An emission peak of 1.27 eV caused by Ge diffusion into GaAs film was observed for the sample grown at 460 °C. Such a critical temperature that activates the Ge diffusion seems relatively low in CBE system as compared with that reported in MOVPE system.

GaAsN expilayers were grown on (100), (211)A/B, (311)A/B and (511)A/B GaAs substrates at different temperatures by using a chemical beam epitaxy system. Results of high resolution X-ray diffraction, low- and room-temperature photoluminescence (PL) measurements indicated that dangling bond status (polarity and density) on the growing surface has significant influence on the final N composition and the PL emission behavior in GaAsN epilayers. As compared with the (100) substrate, (n11)B substrates tended to enhance the N incorporation, whereas (n11)A dramatically reduced it. At the growth temperature of 460°C, N composition in (211)B GaAsN is almost 10 times higher than that in (211)A. The extent of enhancement (or reduction) of N incorporation was found to depend on the relative amount of (111)B (or (111)A) component on the growth surface. PL spectra of samples grown at 460oC suggested that optical properties could be improved by most of the adopted (n11) substrates. Especially, efficient N incorporation in GaAsN epilayers can be achieved on (211)B and (311)B substrates while keeping improved crystal quality.

Minority-carrier lifetime (electron) in p-type GaAsN film is improved by chemical beam epitaxy (CBE) and thermal annealing. Growth rate (GR) in CBE is an important factor to improve minority-carrier lifetime in bulk (τ B ). For as-grown samples, τ B is increased from 3.2 × 102 ps (GR = 2 µm/h) to 9.0 × 102 ps (GR = 0.4 ×m/h). The obtained τ B is much longer than the minority-carrier lifetime (∼ 101 ps) predicted by the reported carrier diffusion length and mobility. This improvement is due to the increase of nonradiative recombination lifetime (τ NR ) caused by the decrease of nonradiative recombination centers. By thermal annealing, PL lifetime (τ PL ) is increased. Therefore, CBE and thermal annealing have a high possibility to obtain the minority-carrier lifetime required to solar cells (> 1 ns).

Three infrared active defects in GaAsN grown by chemical beam epitaxy (CBE) are identified as N-H related defects which are determinative of electrical property of (In)GaAsN. One N-H related defect is also observed in GaAsN grown by metalorganic chemical-vapor deposition (MOCVD). However other two N-H related defects are only observed in GaAsN grown by CBE. Therefore there is possibility that these two defects are characteristic defects of CBE. We also clarify number of hydrogen in the N-H related defects which is important factor of the defects' electrical property. One N-H related defect includes two hydrogens and two N-H related defects include one hydrogen, respectively. These results are derived by using deuterated N source.

Here we report on the fabrication of GaAs network of nanowires on silicon (111) substrates using gold metal nanoparticle mediated catalyst. Highly ordered regular arrays of gold nanoparticles are formed by vacuum evaporation of Au through a nanosphere spin coated surfaces. The paper examines and compares the structural properties of GaAs nanowires formed by chemical beam epitaxy and molecular beam epitaxy techniques on these surfaces Scanning electron microscopy and transmission electron microscopy analysis indicate distinct features of the two techniques and the ability of CBE to yield wetting layer free arrays of nanowires

Target of the Japanese Innovative Photovoltaics R&D Program started from fiscal year 2008 is to develop high efficiency solar cells with conversion efficiency of more than 40% and low electricity cost of less than 7 JPY/kWh until 2050. In this program, concentrator III–V compound multi-junction (MJ) tandem solar cells have great potential for high efficiencies of over 50% and low cost of less than 30JPY/W. InGaAsN material is good candidate for 4–6 junction solar cells. In our preliminary stage of our project, 2% and 11.3% efficiencies have been obtained with GaAsN p-n and InGaAsN p-i-n single-junction solar cells. In order to increase efficiency of single and 4-junction solar cells, it is very important to understand and reduce defects and impurities in the grown films. In this paper, characterization of the CBE (Chemical Beam Epitaxy)-grown GaAsN films by Hall effect and DLTS (Deep Level Transient Spectroscopy) measurements is presented.

The addition of multiquantum well structures was found to improve the quantum efficiency of InP based solar cells as the absorption region of the cell extends into the infrared region of the spectral response of the multiquantum structure. However, the open circuit voltages of the solar cells that are under investigation was not up to the expected levels. In order to understand the reason behind this observation, an investigation of electron/hole emission from chemical beam epitaxy grown InAs x P 1−x /InP multiquantum solar cell structures has been carried out. Deep level transient spectroscopy (DLTS) was used to investigate the defects in the samples, their location and their possible role in reduced efficiency. DLTS measurements have revealed that the thermal emission of electrons from the deep level E3 is dependent on the electric field. Emission rate versus field data have been obtained over a wide range of temperature and field values. This data has been successfully fitted with the Poole-Frenkel model in the entire range of the temperature over which the data has been taken.

N induced scattering in GaAs 1−x N x films are quantitatively investigated, and reduction of the scattering is demonstrated. The hole mobility of GaAsN films is separated to individual scattering processes by parameter fitting. The mobility limited by the N induced scattering is fitted by the function of µN = K N T−(0.6±0.2). The amount of N induced scattering center increases linearly with increasing N composition. These results suggest that the origin of induced scattering is point defect contained one N atom. In the case of GaAs (001) 10° off substarte, µN−1 was lower than that grown on a 2µ off substrate. It suggests that the hole mobility can be improved by using high step density substrate.

Here we demonstrate the growth of GaAs and InP nanowires on silicon (111) using gold as the metal seed particle. An ordered array of gold nano dots is integrated on the surface of a silicon substrate using self-assembled polystyrene nanospheres as the Au evaporation template. Growth of the wires is done by chemical beam epitaxy under a vapor phase environment using the Vapor Liquid Solid mechanism. Scanning electron microscopy, photoluminescence and X-ray spectroscopy are used to characterize these nanowires. These nanowires exhibit high crystallinity and good photoluminesce properties stressing their potential for photovoltaic applications.

The reduction of residual acceptors in GaAsN films and the improvement of GaAsN crystal quality evidenced by hole mobility and PL intensity were reported. Si doping using a SiH 4 gas was also studied. Based on these results GaAsN homo-junction solar cells were fabricated by CBE at the first time. The short circuit current, open circuit voltage, fill factor and conversion efficiency of the GaAsN solar cell are 8.99 mA/cm2, 0.48 V, 0.43, and 1.93 %, respectively.

Numerous investigations have studied the performance of lateral transistors based on single nanowires, there are only a few studies of the fabrication and performance of vertical transistors with wrap-gates, so called WIGFETs. Based on our previous study of 800 nm gate length transistors, we have now scaled the technology to sub 100 nm gate length and study the lateral scaling of the nanowires in the transistor structure. It is demonstrated that the scaling provides a mean to adjust the threshold voltage of the transistor.

GaAsN epitaxial thin films were grown on GaAs (001) substrate by chemical beam epitaxy with dimethylhydrazine ((CH3)2 N2H2). In the dependence of growth temperature on the N concentration, there were three distinct regions in which the dependence was different. At the growth temperature of 420degC, the N concentration increased with increasing surface step density that corresponds to misorientation angle of GaAs (001) substrate. When the samples grown on 2 and 10deg off substrates were compared, the root-mean-squares of surface roughness decreased from 1.1 nm to 0.3 nm, despite of the increase of N concentration. In addition, the reduction of the impurity concentrations (hydrogen and carbon) in the sample grown on the 10deg off substrate was also observed. These results showed the surface morphology of the GaAsN thin films is affected by the step density, and the possibility to obtain (In)GaAsN thin film that has high N and low impurity concentration with keeping crystal quality

Crystal quality of GaAsN films can be improved by using chemical beam epitaxy method for low-temperature growth. However, low-temperature growth increases carbon (C) incorporation in the films, which degrades their electrical properties. To reduce the C concentration in the films, C incorporation process was investigated in view of the surface reaction of nitrogen (N) sources on a substrate surface, and monomethylhydrazine (MMHy) and 1,1-dimethylhydrazine (DMHy) were compared. When MMHy was used as an N source, the C concentration in GaAsN drastically increases below 380degC than that in GaAs due to insufficient CHX desorption. In the case of DMHy, N(CH3)2 is desorbed more readily than CHX. Therefore, the C concentration can then be reduced by using DMHy

GaAsN thin films were grown by chemical beam epitaxy using monomethylhydrazine ((CH3)N2H3) as the N sources, and the role of the nitrogen (N) and impurities (hydrogen (H), carbon (C)) on free carrier concentration was investigated. The N, H, and C concentrations increased with decreasing growth temperature. GaAsN thin film grown at 470degC was n-type conduction, and the donor is thought to be the same in GaAs thin film. On the other hand, the films grown at 390~460degC were p-type conduction. In the range of 420~460degC, the hole concentration increased with decreasing growth temperature, and it decreased below 420degC, respectively. In order to clarify the origin of acceptor in p-GaAsN thin films, the dependence of growth temperature on the hole concentration and N, H, and C concentration were investigated, and the relationship between them was discussed

We report a gain-coupled DFB laser grown by chemical beam epitaxy with a quantum well loss grating structure. Device performances with some preliminary system experiment results are included.

Two structures of GaInAsP/InP surface emitting laser structures have been demonstrated grown by chemical beam epitaxy (CBE). The threshold current as low as 2.6mA was obtained under 77K cw operation (the lowest cw threshold at 77K). Near room temperature pulsed operation is also achieved using a composite GaInAsP/InP grown mirror.

By controlling the thickness of the grating depth with chemical beam epitaxy (CBE) growth time, we report in this letter the design and performance of an integrated tunable detector. A carefully designed tunable active filter, which allows only one below threshold Fabry-Perot mode for operation, is integrated with a waveguide detector. The full tuning range of this kind of tunable device can now be utilized for system applications.

GaInNAs films for the ultra high-efficiency (>40%) 4-junction tandem space solar cells ((Al)GaInP/GaAs/ GaInNAs/Ge) have been grown by using chemical beam epitaxy (CBE) in this study. In the growth of GaInNAs films, the selection of nitrogen source and understanding of nitrogen incorporation is important because nitrogen is play an important role in the crystallization and electrical properties of III-V-N compound materials. A proper nitrogen source between monomethylhydrazine (MMHy) and dimethylhydrazine (DMHy) was investigated, and the nitrogen incorporation in samples grown with MMHy was higher. From the dependence of nitrogen concentration on the substrate temperature, three distinct regions were observed, even in the nitrogen concentration usually decreased with increasing the substrate temperature, and a low FWHM value was obtained at an intermediate temperature. In addition, the dependence of the nitrogen incorporation on the ratio of N/(N+As) was investigated, and at a low temperature, the nitrogen concentration increased with increasing the ratio of N/(N+As). From these results, the nitrogen incorporation in GaInNAs films grown with the substrate temperature and the ratio of N/V elements in CBE technique is clarified, and the relationships between the nitrogen incorporation and crystallization of GaInNAs are clear.

An investigation of electron/hole emission from chemical beam epitaxy grown InAs/sub x/P/sub 1-x//InP multiquantum well solar cell structures has been carried out. Detailed analysis of double deep level transient spectroscopy shows that traps E1, E2, E3, and E4 are extended over the whole multiquantum well region including interfaces. The trap E3 exhibits strong field dependence and having large capture cross section, which might act as a strong recombination center. The field dependence of E3, indicates lowering of the emission barrier and an enhancement of the emission rates by the applied electric field.

The self-assembled GaInNAs quantum dot (QD) has proposed as a novel material system for long wavelength lasers on GaAs substrate. In this paper, we have investigated the thermal annealing effect on GaInNAs QDs. The increase of the PL intensity and blue shift of peak wavelength was observed by thermal annealing. For 600/spl deg/C annealing, the PL intensity was increased with the increase of annealing time and maximum intensity was obtained at 2 hours. On the other hand, PL intensity was increased after 30s annealing, then decreased at longer time for 700/spl deg/C annealing. A larger blue shift of peak wavelength compared to GaInNAs quantum well was observed. It is considered that the interdiffusion was enhanced in QD system due to its large strain and interface area between GaAs capping layer.

The self-assembled In(Ga)As quantum dot (QD) laser have been realized for the long wavelength emission and improvement of laser characteristics. However, In(Ga)As QD lasers still have some problems, such as an increase of threshold at high temperature, and low gain. These problems are due to difficulty in control of the size and the density, which are related to the wavelength and the threshold. The GaInNAs system has been developed as the QW for elongating the emission wavelength. The introduction of the nitrogen (N) into In(Ga)As QDs is an attractive choice because of the possibility of independent control of the wavelength and dot density. In this study, we have investigated the growth characteristics of GaInNAs QDs by CBE in detail.

We have investigated heterostructures formed within Vapor-Liquid-Solid grown III-V nanowhiskers. The growth conditions that are typical for chemical beam epitaxy facilitate the creation of atomically abrupt interfaces. In this paper we investigate the properties of heterostructure interfaces including switching of either the column-V material (As, P) or the column-III material (In, Ga).

Polarized far infrared reflectance was measured at oblique incidence for a large number of strained In/sub 1-x/Ga/sub x/As epilayers grown on InP wafers. From these measurements the concentration dependence of the zone-center optical phonon frequencies has been obtained for strained In/sub 1-x/Ga/sub x/As epilayers grown by chemical beam epitaxy on InP[100]. With the method used the reflectance spectra contain sharp Berreman peaks precisely at the optical phonon frequencies. To resolve the contributions of the individual phonon modes, curve fitting of the measured spectra was used. With this analysis it was observed that the modes included GaAs-like longitudinal and transverse optic (LO and TO), a disorder induced (TO-like), and InAs-like LO and TO phonons. The concentration dependence of these phonon frequencies, determined for 0.31

High quality butt joints were fabricated in the InGaAsP system using a Selective Area Chemical Beam Epitaxy (SA-CBE) regrowth step. Coupling losses were as low as 0.1 dB/interface for butt joints between similar transparent layer stacks. Active and passive regions were defined on a single chip using SA-CBE. Semiconductor optical amplifiers (SOAs) and transparent waveguides were fabricated in their appropriate regions. Extended cavity lasers, consisting of SOAs with passive waveguides on both sides, showed stable CW laser operation at a wavelength of 1.56 /spl mu/m. SA-CBE offers maximum design flexibility, since each device can be fabricated in its own optimized layer stack.

InP/InGaAs DHBT technology for 40 Gb/s ICs is first presented. For these circuit applications, a sufficient breakdown voltage (>5 V), a static gain around 50, cutoff frequencies (f/sub T/) and maximum oscillation frequencies (f/sub max/) greater than 100 GHz are needed. High performance InP/InGaAs DHBT grown by chemical beam epitaxy (CBE) are reported with 125 GHz f/sub T/, 128 GHz f/sub max/ and a gain of 50 at a current density of 1/spl times/10/sup 5/ A/cm/sup 2/. Devices geometry optimisation is performed using a geometric model based on a set of analytical equations. This tool allows not only technological optimisation but also function-adapted individual sizing of the devices in the circuits.

The bandgap tuning by dielectric cap quantum well disordering (DCQWD) method has been widely used to realize the integration of optoelectronic or photonic devices without any regrowth step on a single wafer. Since the DCQWD technique has lots of merit in price and fabrication compared with the regrowth technique, there have been a lot of studies about dielectric capping layers to control QWD. In this study, we concerned the effect of dieiectric-semiconductor capping layer combination. Our study was focused to find out the effect of semiconductor capping layer on the DCQWD, and to find out optimum dielectric-semiconductor capping layer combination for a device application. The InGaAs/InGaAsP single quantum well (QW) structure used in this experiment was grown by chemical beam epitaxy (CBE) on a n-type InP substrate. In order to investigate the effect of semiconductor cap layer on DCQWD, three samples with different semiconductor cap layers (InP, InGaAs and InGaAsP(1.25Q)) were prepared.

Monolithic device integration is more and more essential for the realisation of micro and optoelectronic circuits, which can fulfil complex functions with higher performances. The most prevalent approach in the fabrication of photonic integrated circuits (PICs) is the butt-coupling. This can be done in one step by Selective Area Growth (SAG) carried out by Metalorganic Vapour Phase Epitaxy (MOVPE) or by localised selective regrowth by Chemical Beam Epitaxy (CBE). The former technique inconvenient is that the structures of the devices cannot be quite different, especially, if one of them should be doped, the others will be doped as well. The latter method needs one epitaxial step for each integrated structure and requires several etching steps, which can deteriorate the performances of the regrown devices. This study proposes a new procedure to integrate several devices without any etching step.