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Far-ultraviolet (UV) light sources have attracted much attention for human safe viral inactivation and bacterial disinfection. Due to large optical nonlinearity and transparency to this wavelength region, second harmonic generation (SHG) device made of AlN can be a promising candidate. In this study, a transverse quasi-phase matched AlN channel waveguide with vertical polarity inversion was designed and fabricated. From wavelength spectra and a pump power dependence of an SH intensity, far-UV SHG via a largest nonlinear optical tensor component d 3333 was successfully confirmed under ultrashort pulse laser excitation.

A wavelength conversion device with an input grating coupler that enables easy alignment was fabricated using a vertically polarity inverted GaN layer. The device was excited with a femtosecond laser, and a second harmonic wave with a peak wavelength of 438.4 nm was obtained. A normalized wavelength conversion efficiency of 4.7 × 10−4% W−1 and a spectral bandwidth of the second harmonic wave of 2.9 nm were comparable to the theoretical estimations taking into account serious walk-off and waveguide losses. High efficiency of 33%–34% W−1 can be expected under continuous-wave excitation.

We proposed a nitride semiconductor transverse quasi-phase-matched wavelength conversion device with a polarity inverted structure along the vertical direction formed by surface-activated bonding and etching processes. Inductively coupled plasma etching of a GaN layer with maintaining a root mean square roughness of less than 2 nm in a 100 μm square area was achieved even after deep etching of 1 μm using Cl2/Ar mixture gas and optimizing the antenna and bias powers. This smooth etching enabled surface-activated bonding of the ultrathin GaN layer with designed thickness. The fabrication process of the GaN polarity inverted channel waveguide was established.

Eu-doped GaN (GaN:Eu) are novel candidates for red light-emitting diodes (LEDs). To further improve the luminescent efficiency of the GaN:Eu-based LED, the efficiency-droop under strong excitation conditions should be suppressed. In this paper, we demonstrate droop-free luminescence of GaN:Eu emitted from a sample-edge using a stripe excitation configuration. The Eu emission intensity clearly increases compared to the conventional surface-emission, and the enhancement is more pronounced for stronger excitation conditions. We clarify that the wavelength dependence of the enhancement agrees well with the optical gain spectrum of the GaN:Eu and is attributed to amplified spontaneous emission.

We present a study on the improvement of quality factors (Q-factors) of III-nitride-based two-dimensional photonic crystal (2D-PhC) nanocavities. Although III-nitride-based 2D-PhC cavities have been studied, they typically show relatively low experimental Q-factors due to disorders inevitably introduced during the fabrication processes. In order to realize high-Q-factors, it is necessary to introduce cavities that are tolerant to disorder. We numerically reproduce the experimental disorder in simulations, and discuss the influence of disorder on Q-factors of several types of cavities. We demonstrate the suitability of these cavities for the realization of high-Q-factors, and show which structures have the largest tolerance for disorders.

We proposed a monolithic microcavity wavelength conversion device without a polarity-inverted structure. The device consists of a low birefringence paraelectric material and a dielectric material. A fundamental wave intensity is enhanced significantly in the microcavity with two distributed Bragg reflectors, and a second-harmonic wave is efficiently generated in a very short region close to a coherence length. As a first step of this study, we used GaN as a device material, and succeeded in the blue second harmonic generation with a wavelength of 428 nm.

High-density micro light-emitting diode (μ-LED) arrays are key to next-generation ultrahigh-resolution displays. As a novel candidate, we report monolithic vertically stacked full-color LEDs consisting of Eu-doped GaN and InGaN quantum wells (QWs). Initially growing Eu-doped GaN, which shows a narrow linewidth ultra-stable red emission, allows vertically stacked growth of subsequent InGaN-QW-based blue/green LEDs while maintaining a high crystal quality. Electroluminescence from full-color LEDs has a remarkably wide color gamut, corresponding to 105.5% (147.0%) of the area with 91.2% (96.5%) coverage of the standards of Rec. 2020 (DCI-P3) at its maximum. The maximum luminance of the full-color LEDs reaches ∼3100 cd m−2.

We demonstrate the enhancement of luminescence efficiency in GaN:Eu-based light emitting diodes (LEDs) by surface plasmons utilizing gold nanoparticles (NPs). A gold thin film is deposited on a GaN:Eu layer and subsequently thermal-annealed to form gold NPs. The size of the NPs can be controlled by changing the thickness of the films. The room-temperature photoluminescence (PL) intensity of the GaN:Eu LEDs with the NPs increases by 1.42-times compared with those without the NPs when the film thickness is 15 nm, which is attributed to enhanced light extraction efficiency due to coupling with localized surface plasmons. Time-resolved PL spectra at 10 K of the LEDs with the NPs show a shorter lifetime, supporting the existence of the coupling with local surface plasmons. The injection current-light output intensity profiles of the LEDs with the NPs shows 1.3-times enhancement of the output power due to coupling with local surface plasmons.

A connection between condensed matter physics and basic quantum mechanics is demonstrated as we use the fundamental 3D particle-in-a-box model to explain the optical properties of semiconductor nanocrystals, which are substantially modified due to quantum confinement. We also discuss recent advances in the imaging and measurement capabilities of transmission electron microscopy, which have made it possible to directly image single nanocrystals while simultaneously measuring their characteristic absorption energies. We introduce the basic theory of nanocrystals and derive a simplified expression to approximate the optical bandgap energy of an orthorhombic nanocrystal. CsPbBr3 perovskite nanocrystals are used to demonstrate this model due to their cubic crystal structure, large absorption cross-section, and favourable dielectric properties, which make them ideal for exploring the applications of this simple classroom problem. Various orthorhombic shapes are explored, and the predicted values of the optical bandgap energies using the proposed model are shown to be in good agreement with the experimentally determined values.

Carbon-doped silicon oxide (SiOCH) films were deposited by plasma-enhanced chemical vapor deposition (PECVD) using tetraethoxysilane (TEOS) at low temperatures (27–53 °C). The structural and insulating properties of the films deposited with Ar or N2 plasma were investigated. In the deposition with low plasma density and low substrate temperature, both plasmas produced films with high hydrocarbon (CHn) content. The films prepared using Ar plasma showed a low leakage current of 7×10-10 A/cm2 at 1 MV/cm due to the incorporation of CHn groups, while the films with high CHn content prepared using N2 plasma showed poor insulating properties. The deposition using N2 plasma formed films with a defective structure, resulting in a higher etch rate than that of the films deposited with Ar plasma. The deposition with the low-density plasma of inert Ar gas is suitable for the low-temperature deposition of SiOCH films with high resistivity.

High-quality epitaxial Si films have been grown at low temperatures (500–600 °C) by atmospheric pressure plasma chemical vapor deposition (AP-PCVD) with a high growth rate (0.31 µm/min at 600 °C averaged over the 4-in. wafer). In contrast to the previous reports on other low-temperature CVD Si, the films in the present study are defect-free as observed by transmission electron microscopy and selective etching, and show no oxygen and carbon pileups at the film/substrate interface. To characterize defect-free epitaxial films with high sensitivity, we employed a photoluminescence (PL) method. When the epitaxial layer has better quality than the substrate, PL spectrum at 4.2 K mainly reveals the property of the substrate. On the other hand, room temperature PL measurements clearly show that the PL intensities of the surface-passivated epitaxial Si samples are much higher than that of Czochralski (CZ)-Si, which indicates a longer minority carrier recombination lifetime in the epitaxial Si layer than the bulk lifetime in CZ-Si.

A novel edge-light backlight unit using an optically patterned film (OPF backlight unit) for liquid crystal displays (LCDs) is composed of a light guide plate bonded to the top of fine lenses formed on the OPF, a diffusive sheet, a reflective sheet and a light source. A viewing-angle-dependent luminance distribution of the OPF backlight unit was controllable by changing the shape of a fine lens used for the extraction of light propagating through a light guide plate and the direction control of radiating light, and a luminance distribution in a radiation plane suitable for LCDs was realized by adjusting the interval between lenses. Moreover, the extraction efficiency of the OPF backlight unit was greater than that of a conventional backlight unit. Thus, the OPF backlight unit was shown to be promising for the realization of a brighter, lower power consumption, slimmer and lighter LCD than conventional LCDs.

Interfacial roughness of InxGa1-xAs/InP (x=0.53) multiple quantum wells (MQW) grown by metalorganic vapor phase epitaxy has been investigated by cross-sectional scanning tunneling microscopy (STM). The MQW structure is composed of 125 periods of 11-nm-wide well layers and 44-nm-wide barrier layers on an InP (001) substrate. The observed STM images have revealed that the InGaAs-on-InP interface is extremely sharp compared to the InP-on-InGaAs interface; the roughness and terrace size on the InGaAs-on-InP interface are 1–2 monolayers (ML) and 31 nm, respectively, while they are 3–4 ML and 9 nm on the InP-on-InGaAs interface. The large roughness observed for the InP-on-InGaAs interface is interpreted in terms of the incorporation of residual As atoms on the InGaAs surface.

We have grown InAs quantum structures by droplet hetero-epitaxy on InP nanopyramids and investigated their luminescence property. InP nanopyramids with improved size control were formed successfully by selective-area flow rate modulation epitaxy (FME). The standard deviation of the bottom size of the nanopyramids decreases by means of selective-area FME. Droplet hetero-epitaxy was carried out on InP nanopyramids to grow InAs quantum structures. The shape of the nanopyramids becomes sharper with longer TMIn supply time. In photoluminescence (PL) measurements at 4.2 K, characteristic luminescence is clearly observed. The mapping measurement of the PL intensities reveals that the luminescence originates from the patterned area with the nanopyramids. The PL peak positions shift slightly to a longer wavelength region with increasing supply time. These results suggest that InAs quantum structures are formed on InP nanopyramids.

The generation mechanism of the immiscibility of InGaAsP grown by metalorganic vapor phase epitaxy (MOVPE) is investigated. The growth condition dependence of the immiscibility is examined in detail using particular photoluminescence (PL) characteristics observed in the boundary composition between stable and unstable compositional regions. A lower growth rate or a larger V/III ratio is effective for suppressing phase separation. To explain this growth condition dependence, some factors related to surface energy should be taken into consideration.

Despite the recent progress in red light-emitting diodes (LED) made of gallium nitride doped with europium (GaN:Eu) having sharp emission lines due to the 5D0 → 7F2 transition of Eu3+, unexpected subsidiary Eu emission centers radiate several satellite lines. We investigated these subsidiary emission centers by analyzing the harmonic contents through electronic means, and observed the originally forbidden even harmonics in a specific frequency region of 23-45 MHz. The even-harmonic generation was formulized with a binary response caused by the electronic coupling of emission centers in valence states, i.e. dimerization. The coupling was consistent with the results of the optical analyses of former studies. The binary response was experimentally quantified by using a parameter such as the phase difference between the responses of coupled centers, and a significant phase difference of 63° was observed at 36 MHz. The injection charges were cooperatively captured by the coupled emission centers and were branched into the constituent centers for recombination, resulting in undesired satellite emission lines.

We report on room-temperature 1.54 µm electroluminescence, for the first time, of Er,O-codoped GaAs/GaInP double-heterostructure light emitting diodes grown by organometallic vapor phase epitaxy. The luminescence is due to intra-4f shell transition from the first excited state to the ground state of Er3+ ions. The erbium and oxygen were uniformly doped in the GaAs active layer with a concentration of 8 ×1018 cm-3. Emission lines in the spectrum indicated successful formation of the Er-2O center and a preferential excitation of the center by current injection. The intensity of the main line observed at 1.538 µm increased linearly with current density and exhibited a tendency to saturate at a current density higher than 20 A/cm2.

Noise analysis of the forward current of LEDs was performed to identify the rate-limiting process of a recently developed Eu-doped GaN (GaN:Eu) red LED. Although the noise power spectrum of conventional InGaN blue and AlGaInP amber LEDs followed Poisson distributions, that of the GaN:Eu red LED indicated a 1/f noise. The Poisson distribution that represents electron–hole (e–h) recombination was consistent with the light emitting process of the conventional LED. On the other hand, the 1/f noise revealed that the rate-limiting process of the GaN:Eu LED was trapping of injection charges rather than following e–h recombination to excite Eu. From the detailed analysis of the 1/f noise, several emission centers with different trapping time constants (>3.5 ns) were discovered. These results demonstrated the applicability of the noise analysis to characterization of charge dynamics in the new LEDs.

We have succeeded in growing Eu-doped GaN (GaN:Eu) layers with high crystalline quality by organometallic vapor phase epitaxy, and have demonstrated a low-voltage current-injected red emission from a light-emitting diode (LED) using the GaN:Eu layer with an applied voltage of as low as 3 V. By optimizing growth conditions and device structures, the light output power has increased steadily to up to sub-mW at an injected current of 20 mA. For further improvement of the output power, Eu luminescent centers have been spectroscopically investigated in GaN:Eu. A variety of Eu luminescent sites and a strongly site-dependent energy transfer process were clearly revealed. The energy-transfer efficiency was markedly enhanced by codoping of Mg with Eu. A proposed model for centers with high energy-transfer efficiencies is discussed in relation to the local structure.

The photoluminescence (PL) and electrical properties of Eu-doped ZnO (ZnO:Eu) grown by sputtering-assisted metalorganic chemical vapor deposition (SA-MOCVD) were investigated. Sharp PL lines due to intra-4f transition in Eu3+ ions were observed when ZnO:Eu was annealed at temperatures (T a) higher than 500 °C in O2 ambient. In Hall measurements, the as-grown ZnO:Eu showed a high electron density of 3×1019 cm-3, indicating that the doped Eu ions act as a donor in ZnO. The electron density decreased rapidly at T a≥500 °C and was 2×1017 cm-3 at T a = 600 °C. These results revealed that a complex consisting of a Eu3+ ion and an interstitial oxygen (Eu3+–Oi complex) is formed by high-temperature annealing and acts as a Eu3+ luminescent center in ZnO.

The effects of Mg and Si codoping on Eu luminescence properties have been investigated in Eu-doped GaN (GaN:Eu). The Mg codoping into GaN:Eu produced novel luminescence centers consisting of Eu and Mg, and increased photoluminescence (PL) intensity in Eu,Mg-codoped GaN (GaN:Eu,Mg). However, this increased PL intensity was quenched by thermal annealing in N2 ambient, which is due to activation of Mg acceptors. In GaN:Eu,Mg codoped additionally with Si (GaN:Eu,Mg,Si), on the other hand, the Eu–Mg centers disappeared, while an additional luminescence center appeared. Furthermore, the additional luminescence center showed no quenching under N2 annealing because Si donors compensated for the Mg acceptors in GaN. Thermal quenching of the luminescence center was also approximately half of that in GaN:Eu. These results indicate that the codoping with additional impurities in GaN:Eu is a powerful technique to control Eu luminescence centers for realization of improved device performance in red light-emitting diodes using GaN:Eu.

We report a study on Eu the luminescence properties of Eu-doped GaN (GaN:Eu) grown on a GaN substrate by organometallic vapor phase epitaxy (OMVPE). Thermal quenching of the Eu luminescence was suppressed using the GaN substrate, which is due to the preferential formation of a Eu luminescent site with a local structure with high symmetry. The preferential formation of this luminescent site was supported by the observation of strong near-band-edge emission. The strong near band-edge emission occurred as a result of suppressed formation of the dominant Eu luminescent site in GaN:Eu on a sapphire substrate, which is known to be coupled with a defect and to have a large capture cross section of photogenerated carriers.

The International Conference on Thin Films is the most established conference for all researchers and persons interested in thin films and coatings. It is one of the tri-annual conference series endorsed and co-organized by the Thin Film Division of the International Union for Vacuum Science, Technique and Applications (IUVSTA), a union of national member societies whose role is to stimulate international collaboration in the fields of vacuum science, techniques and applications and related multi-disciplinary topics including solid-vacuum and other interfaces. The 15th International Conference on Thin Films (ICTF-15) is organized by The Vacuum Society of Japan (VSJ) and held at Kyoto TERRSA in Kyoto, Japan on 8–11 November 2011, following the 14th International Conference on Thin Films (ICTF-14), which was held in Ghent, Belgium in 2008. Thin films and coatings are daily becoming increasingly important in the fields of various industries. This International Conference provides a multi-disciplinary forum for recent advances in basic research, development and applications of thin films and coatings. This conference will present a unique opportunity for researchers, engineers and managers to acquire new knowledge of thin films and coatings. We hope that our understanding on thin films and coatings will be deepened through this conference. The conference site, 'Kyoto TERRSA' is located in the historical heart of the old capital Kyoto. Kyoto is an ancient city with a 1200-year history. It was established as Japan's capital under the name 'Heian-kyo' in the year 794. Although many transformations have taken place over the years, Kyoto has always embraced the most advanced standards of the times. It has greatly contributed to the nation's industrial, economic and cultural development. The dauntless spirit of leadership of Kyoto's past as a capital city is still felt here today. Kyoto also preserves the beloved examples of its culture as testimonials of time. This is shown in the ancient temples and shrines, as well as private houses, which are built in styles unique to Kyoto. Furthermore, many festivals, ceremonies and traditional activities reveal the will of this city to convey and develop its 1200-year-old culture. Participants of the conference will also be able to see many world heritage sites in the city. Moreover, November is the best time of year to visit Kyoto. We hope you will enjoy Kyoto very much. We would like to offer our thanks for all the contributions from the members of the International Advisory Committee and Organizing Committee, Symposium Chairs, the Secretary General, the Thin Film Division of IUVSTA (chair: Professor Dr Alberto Tagliaferro), IUVSTA, VSJ and other cooperating societies, and to all of the supporting organizations and enterprises. We would also like to express our thanks to all of the participants, secretariat members and members of the supporting staff. I am very pleased to welcome you to ICTF-15 and Kyoto! Director Professor Dr Osamu Takai Chairperson of ICTF-15 EcoTopia Science Institute, and Department of Materials, Physics and Energy Engineering Graduate School of Engineering Nagoya University Japan

In order to analyze effect of the dicing process on the GaN epitaxial layer, the GaN-wafer is cut in sizes of the 0.7 mm square and the 1.7 mm square. The crystal characteristics of the GaN-chips have been measured using X-ray measurements and Raman spectra measurements. The full-width half maximum (FWHM) values of the X-ray rocking curves of (0002), (10–13) and (10–12) of the 0.7 mm square GaN-chip become wider than that of before the dicing process. The E2 (high) peak of Raman spectra at the edge in the 0.7mm square GaN-chip is shifted to lower wave number. In consideration of crystallography, we infer from these results that both the crystal strains and the screw dislocations have been generated during the dicing process.

We have grown Eu-doped GaN on a freestanding GaN substrate by organometallic vapor phase epitaxy and investigated its red luminescence that is due to intra-4f shell transitions of Eu3+ ions. The optimum growth temperature for Eu luminescence was 50 °C higher than that of Eu-doped GaN on a sapphire substrate. The highest emission intensity was more intense than that on the sapphire substrate, while the Eu luminescence lifetime was identical for both substrates. These results indicate that energy transfer from the GaN host to the Eu3+ ions occurs more efficiently in Eu-doped GaN on the GaN substrate because of a low dislocation density.

In order to investigate the magnetic properties of GaAs:Er,O, we performed X-band ESR measurement on three different Er-concentration samples in the temperature region from T = 4.6 K to 18 K. Three types of Er-related ESR signals were observed below 18 K. The temperature dependence of the signal intensities and the result of the line shape analyses suggest that the luminescent related Er centers have a singlet-like ground state: that is, the Er-related centers are not homogenously distributed in GaAs:Er,O, and Er3+ ions can be antiferromagnetically coupled via the super exchange interaction. Moreover, we have shown that the Er-concentration dependence of intensities of ESR absorption has a strong correlation with the Er-concentration dependence of the PL intensities of GaAs:Er,O

We investigated the optical properties of Eu-implanted GaN and related-alloy semiconductors by photoluminescence (PL) and time resolved PL measurements at room temperature (RT). After thermal annealing, the red emission was observed in each sample due to the intra-4f transitions in Eu3+ ions. The PL intensity increases with Al incorporation into GaN while it decreases with In incorporation into GaN, indicating that the emission efficiency depends on the host materials while the emission wavelength is independent of the host materials. Since the decay times of Eu emission of the samples are found to be similar by time resolved PL measurements, the origin of the Eu emission of each sample is supposed to be same. Therefore, the difference in the PL intensity is attributed to the difference in the energy transfer efficiency because of the ion implantation damage and/or bandgap energy of the host materials.

Growth of GaAs by MOVPE (Metal-Organic Vapor-Phase Epitaxy) at a much lower temperature than conventional conditions of 650°C required to produce highly resistive buffer layers and molecular-layer-level abrupt heterojunctions and doped-layer interfaces. It has been widely recognized that growth at 550~600°C causes poor morphological surfaces on the grown layers. This paper describes a fundamental improvement of the low-temperature growth of GaAs, resulting in smooth surfaces with very low impurity concentrations. Excellent GaAs layers can be grown at 500°C by increasing partial pressure of AsH3 during growth. The method has been applied to high quality epitaxial layers for electronic device production.

We have fabricated two types of 1.5 μm light-emitting devices based on Er,O-codoped GaAs (GaAs:Er,O) using organometallic vapor phase epitaxy (OMVPE). In a device exhibiting a room-temperature lasing at the GaAs band-edge, the threshold current density increased with Er concentration. The Er intensity rose up steeply and then decreased gradually in the spontaneous emission region. In the stimulated emission region, it remained almost constant, reflecting ultrafast energy transfer to Er ions. In a device exhibiting a room-temperature lasing from strained GaInAs quantum wells (QWs) embedded in GaAs:Er,O, on the other hands, the lasing wavelength was designed to tune to the energy separation between the second excited states 4I11/2 and the ground state 4I15/2 of Er3+ ions. The Er intensity revealed initially steep increase with injected current density in the region for spontaneous emission from the GaInAs QWs. In the stimulated QW emission region, however, the intensity continued to increase with the current density.

Band structure of β-FeSi2 epitaxial and polycrystalline films was investigated by photoreflectance (PR) measurements. In the PR spectra, two critical points were obtained at Eg = 0.918 eV and Ei = 0.895 eV in the films. The Eg consistent with the direct transition energy at Y point in the Brillouin zone of β-FeSi2. The Ei was assigned as a transition-energy between conduction band and the acceptor-level originating from Si vacancies in β-FeSi2. The energy from top of valence band to the acceptor-level was determined to be 23 meV.

We investigated the relationship between optical properties and crystal quality of Eu-implanted GaN-based semiconductors. Emission peaks that are due to intra-4f shell transitions in Eu3+ ions were observed in Eu-implanted GaN, InGaN, and AlGaN. Emission wavelengths from the Eu ions were constant regardless of the matrix materials. The emission peak intensity in the Eu-implanted AlGaN was higher than that in the Eu-implanted InGaN or GaN because of less matrix damage by ion implantation.

Er-doped ZnO (ZnO:Er) thin films were grown by metalorganic chemical vapor deposition. Subsequent annealing improved the crystallinity of the ZnO:Er by suppressing nonradiative centers in the films. The annealed ZnO:Er showed clear 1.54 μm PL originating from the 4I13/2 → 4I15/2 transitions of Er3+ ions. This was in addition to luminescence from the ZnO host. Er-related PL intensity increased when prepared with annealing temperatures of 800–900 °C, while annealing at 1000 °C reduced the intensity. PL of 1.54 μm with high intensity was obtained in the ZnO:Er film that exhibited band-edge emission of free- or bound-excitons.

Optical properties of GaInP/GaAs:Er,O/GaInP double heterostructure (DH) laser diodes (LDs) grown by organometallic vapor phase epitaxy (OMVPE) were investigated. The Er-doped LDs showed laser emission of the GaAs band-edge. The threshold current density (Jth) was 3.6 kA/cm2 on the n-type GaAs substrates and 15.8 kA/cm2 on the p-type at 77 K. The Er-doped LDs on the n-type substrate showed a strong sulfur (S)-related emission in the near-infrared region. Conversely, the S-related emission was strongly suppressed in the LDs on the p-type substrates. This was achieved by preventing the incorporation of S atoms into the GaAs active layer. For the electroluminescence (EL) properties, 1.54 μm-emission from Er3+ ions was clearly observed in the Er-doped LDs on p-type substrates. The dependence of EL intensities on the current density showed that the suppression of an energy transfer from the Er3+ ion to the S-related emission was necessary for efficient Er3+ emission at the stimulated emission region of the GaAs band-edge.

InGaAs epitaxial layers lattice-matched to InP substrates are studied by photoluminescence measurements modulated by far-infrared radiation under the condition of cyclotron resonance or impurity cyclotron resonance. Based on the experimental results, the ionization energy of shallow donors is estimated to be 2.3 meV, which is lower than the value of 3.0 meV obtained from the effective mass approximation. In order to explain the difference between the two values, we propose a model of the existence of a Ga-rich region in samples. In addition to electron cyclotron resonance, hole cyclotron resonance is observed. The effective masses of electron and light hole are estimated to be 0.041m0 and 0.051m0, respectively.

Thermal quenching of Er-related photoluminescence (PL) due to intra-4f shell transitions of Er3+ ions has been investigated in Ga x In1-x P (0≤x≤1) doped with Er by organometallic vapor phase epitaxy (OMVPE). In GaInP grown on GaP and InP, the 4.2 K PL intensity gradually increases with increasing Ga composition, while the spectral shape remains unchanged. In GaInP grown on GaAs, the 4.2 K PL spectrum is dominated by three emission lines whose relative intensity depends on the Ga composition. Thermal quenching of the Er-related luminescence gradually decreases with increasing Ga composition, i.e., increasing band gap. PL lifetimes and their temperature variations are discussed in relation to deep-level properties of Er in the excitation mechanism of the 4f shell.

We have investigated nanoscale ErP islands formed on InP(001) during Er exposure in organometallic vapor-phase epitaxial growth by means of atomic force microscopy and scanning tunneling microscopy. Different features of surface morphologies are observed depending on the growth temperature and the ErP coverage. The generation of misfit dislocation arrays along the [1\bar0] direction leads to anisotropic strain relaxation that originates from the anisotropy of the atomic bonds at the interface. The residual strain of partially relaxed islands is ∼2% for growth at 530°C, which corresponds to the minimum of total areal energy of the strained film. Current imaging tunneling spectroscopy shows a high tunnel current at dislocations and ErP island edges suggesting the existence of high-density surface states near the Fermi level and the decrease in tunneling barrier height.

It has been found that there is a threshold growth temperature between 550°C and 580°C for the change of local structure around Er atoms in InP doped Er atoms grown by organometallic vapor phase epitaxy (OMVPE). To understand whether the structure change is induced at the growing surface or during the growth as an in situ annealing, the thermal stability of the local structures around the Er atoms doped in InP by the OMVPE at 530°C has been investigated by the extended X-ray absorption fine structure (EXAFS). The EXAFS analysis revealed that the local structure around the Er atoms, which existed substitutionally on In sites in the InP lattice, was stable against the post-growth annealing even for 1 h at 650°C. Therefore, it is concluded that the local structures are formed on the growth front, and not in the volume of InP by thermal annealing during or after the growth.

We have fabricated periodic arrays of InP pillars for two-dimensional (2D) photonic crystals by reactive ion etching (RIE) with SiCl4/Ar inductively coupled plasma (ICP) and Cl2 electron cyclotron resonance (ECR) plasma chemistry. Prior to the fabrication of the arrays, photonic band structures for electromagnetic waves are calculated theoretically, and photonic band gaps are predicted to appear in the optical wavelength region. Periodic arrays of InP micron pillars with fairly smooth etched surfaces are fabricated by ICP-RIE with SiCl4/Ar. The reflective properties of the arrays have been characterized in the optical wavelength region by Fourier-transformed infrared reflection absorption spectrometry (FTIR-RAS). FTIR-RAS spectra of the arrays exhibit characteristic features such as a blue shift with decreasing period of pillars. In ECR-RIE, we systematically investigate InP etch characteristics as functions of various etching parameters, and successfully fabricate periodic arrays of vertical submicron pillars with smooth surfaces.

The effects of growth temperature on Er-related photoluminescence (PL) have been investigated in Er-doped InP (InP:Er) and GaAs (GaAs:Er) grown by organometallic vapor phase epitaxy (OMVPE) using tertiarybutylphosphine (TBP) and tertiarybutylarsine (TBAs). In InP:Er, the PL spectra exhibit strong dependence on the growth temperature, and the intensity increases drastically in specimens prepared at temperatures lower than 550° C. Similar dependence of PL intensity on the growth temperature is observed in GaAs:Er. The activation energy obtained is about 3 eV in both materials. The activation energy is discussed based on atomic configurations of Er-related luminescence centers.

Visible photoluminescence (PL) has been systematically investigated in laterally anodized porous silicon. The PL peak position was dependent on the distance from the meniscus and shifted towards a shorter wavelength with increasing anodization current density. A PL spectrum exhibiting several structures was observed inside the mirrorlike region on the sample surface, which was interpreted by multiple reflection of the luminescence, not by the quantum size effects. Through the analysis of the PL spectrum, the Si density of the porous layer was roughly estimated to be 37% by means of the effective-medium model.

We have investigated the light-induced degradation of visible photoluminescence (PL) and its recovery in porous silicon. It has been found that the exposure of the porous sample to UV and visible laser light results in the drastic quenching of the PL intensity. Furthermore, the PL intensity in the photodegraded sample is effectively recovered by annealing at low temperature up to 200°C, rather than by HF etching. Based on the recovery behavior of the PL fatigue through the low-temperature annealing, the origin of the visible luminescence in porous silicon is discussed.