Structural and optical properties of vertically aligned InP nanowires grown by metal organic vapor phase epitaxy

Vertically aligned InP nanowires were successfully grown by metalorganic vapor phase epitaxy under metal-catalyzed vapor–liquid–solid growth processes. Au nanoparticles with a nominal diameter of 20 nm were used as the seed to control the diameter of the nanowires. Scanning and transmission electron microscopic studies showed highly dense nanowires with uniform diameters along the length direction, and the zinc-blende structure of the nanowires with 1 1 1 growth direction, respectively. Cathodeluminescence measurements showed a significant blueshift in the spectral peak position compared to bulk InP due to the quantum confinement of the carriers in the nanowires.     

Thermodynamic analysis of the shape, anisotropy and formation process of InAs/InP(0 0 1) quantum dots and quantum sticks grown by metalorganic vapor phase epitaxy

This study describes the origin of the size and shape anisotropy of InAs/InP(0 0 1) quantum dots (QDs) grown by metalorganic vapor phase epitaxy (MOVPE). The geometry of the QDs is determined by carefully analyzing transmission electron microscopy (TEM) images. An analytical model adapted to our QD geometry is used to understand the formation mechanism of the QDs, and to describe the origin of their size dispersion. A shape transition from QDs to elongated quantum sticks (QS) is observed under As-poor growth conditions. This transition, driven by thermodynamics, is clearly described by our model.     

Spectroscopy on single columns of vertically aligned InAs quantum dots

We have investigated the carrier relaxation dynamics in single columns of tenfold stacked vertically aligned InAs quantum dots by micro-photoluminescence measurement. The excitation spectrum in the stacked dots is much different from that in the single dot characterized by the existence of a zero-absorption region and sharp multiple phonon emission lines. We have observed a broad continuum absorption far below the wetting layer band edge in the spectrum of the single columns although we have confirmed the existence of a zero-absorption region in the same sample with reduced number of dot layers to almost single, realized by surface etching. The broad absorption feature suggests the existence of additional carrier relaxation channels through non-resonant tunneling between the dots.     

Growth by molecular beam epitaxy and electrical characterization of GaAs nanowires

We report on structural and electrical properties of GaAs nanowires (NWs) grown by molecular beam epitaxy (MBE) on GaAs and SiO₂ substrates using Au as growth catalyst. Au–Ga particles are observed on the top of the NWs by transmission electron microscopy (TEM). In most of the observed cases, individual particles contain two Au–Ga compositions, in particular orthorhombic AuGa and β′ hexagonal Au₇Ga₂. The wires grown on GaAs are regularly shaped and tidily oriented on both (1 0 0) and (1 1 1)B substrates. TEM also reveals that the NWs have a wurtzite lattice structure. Electrical transport measurements indicate that nominally undoped NWs are weakly n-type while both Be- and Si-doped wires show p-type behaviour. The effect of the lattice structure on impurity incorporation is briefly discussed.     

Characteristics of high responsivity 8.5 μm InGaAs/InP QWIPs grown by metalorganic vapour phase epitaxy

Higher responsivity of quantum well infrared photodetectors based on In_0.53Ga_0.47As–InP material system compared to the well established GaAs–AlGaAs material system is analyzed. It is shown that the higher responsivity of the former results mainly from its smaller capture probability, p_c, than that of the latter. Both transport as well as L valley occupancy appear important in determining the p_c.     

EPR measurement on Er-doped InP grown by organometallic vapor phase epitaxy

We have performed X-band ESR measurements on InP:Er epitaxial layers grown by organometallic vapor phase epitaxy, which were grown at the substrate temperatures of 530°C (sample A) and 580°C (sample B). Sample A shows a slightly anisotropic resonance aroundg = 6 with hyperfine structure due to the¹⁶⁷Er (I = 7/2) isotope at 3 K. This result is similar to the result for Erdoped bulk InP and it indicates that Er³⁺ ions are located in In tetrahedral sites. On the other hand, we do not see such a resonance for sample B, suggesting that the local symmetry of Er in sample B is different from sample A. The difference between samples A and B is consistent with the fluorescence-detected extended X-ray absorption fine structure results that the coordination number of Er depends on the growth temperature.     

Synthesis and optical characterization of vertically grown ZnO nanowires in high crystallinity through vapor-liquid-solid growth mechanism

The gas-phase growth and optical characteristics of 1-dimensional ZnO nanostructure have been investigated. The ZnO nanowires (NWs) were grown vertically on Au coated silicon substrates by vapor-liquid-solid (VLS) growth mechanism using chemical vapor deposition (CVD). The ZnO NWs were grown in the crystal direction of [0 0 0 1]. The ZnO NWs exhibit the uniform size of less than 100 nm in diameter and up to 5 μm in length. Photoluminescence (PL) spectrum of ZnO NWs shows the strong band-edge emission at ∼380 nm (∼3.27 eV) without significant deep-level defect emission. The exciton lifetime of ZnO NWs was measured to be approximately 150 ± 10 ps.     

Selective growth of ZnO nanodots prepared by metalorganic chemical vapor deposition on focused-ion beam-nanopatterned substrates

Selective formation of ZnO nanodots grown by metalorganic chemical vapor deposition (MOCVD) was achieved on focused-ion beam (FIB)-nanopatterned SiO₂ and Si substrates. The selective formation characteristics, dimension, and density of ZnO nanodots on FIB-nanopatterned substrates strongly depended on the FIB-patterning and MOCVD-growth conditions. The mechanism of the selective formation of ZnO nanodots on FIB-nanopatterned SiO₂ substrates is attributed to a surfactant effect of the implanted Ga which leads to the formation of the preferred nucleation sites for the growth of ZnO nanodots, while that of ZnO nanodots on nanopatterned Si substrates is mainly considered in terms of the generation of surface atomic steps and kinks, which are created by Ga⁺ ion sputtering, on the patterned Si areas.     

Fabrication of p-CuGaS2/n-ZnO:Al heterojunction light-emitting diode grown by metalorganic vapor phase epitaxy and helicon-wave-excited-plasma sputtering methods

Greenish-white electroluminescence (EL) was observed from the heterojunction light-emitting diodes (LEDs) composed of p-type (001) CuGaS₂ chalcopyrite semiconductor epilayers and preferentially (0001)-oriented polycrystalline n-type ZnO thin films. The CuGaS₂ layers were grown on a (001) GaP substrate by metalorganic vapor phase epitaxy and the ZnO films were deposited by the surface-damage-free helicon-wave-excited-plasma sputtering method. The n-ZnO/p-CuGaS₂ LED structure was designed to enable an electron injection from the n-type wider band gap material forming a TYPE-I heterojunction. The EL spectra exhibited emission peaks and bands between 1.6 and 2.5 eV, although their higher energy portions were absorbed by the GaP substrate. Since the spectral lineshape resembled that of the photoluminescence from identical CuGaS₂ epilayers, the EL was assigned to originate from p-CuGaS₂.     

InGaAsP multiple quantum well edge-emitting light-emitting diode showing low coherence characteristics using selective-area metalorganic vapor phase epitaxy

Low coherence multiple-quantum well edge-emitting light-emitting diodes were obtained using selective-area metalorganic vapor-phase epitaxial growth, which utilized growth rate enhancement on an open stripe region between mask stripes. An optical absorption region, which was controlled by selective-area growth, was introduced to suppress optical feedback. At a driving current of 100 mA and an ambient temperature of 25°C, a power of 55 μW was coupled into a single-mode fiber, and a broad spectrum without spectral ripple was observed. Low coherence characteristics and very small temperature dependence were obtained in the temperature range from -40°C to 85°C. The modulation bandwidth was 210 MHz at a bias current of 100 mA.     

Optical spectroscopy of single InAs/InP quantum dots around λ=1.55 μm

We discuss the preparation and spectroscopic characterisation of a single InAs/InP quantum dot suitable for long-distance quantum key distribution applications around λ=1.55 μm. The dot is prepared using a site-selective growth technique which allows a single dot to be deposited in isolation at a controlled spatial location. Micro-photoluminescence measurements as a function of exciton occupation are used to determine the electronic structure of the dot. Biexciton emission, shell filling and many-body re-normalization effects are observed for the first time in single InAs/InP quantum dots.     

Lateral electron transport through single InAs quantum dots grown by molecular beam epitaxy

The transport properties of single InAs quantum dots (QDs) grown by molecular beam epitaxy have been investigated by metallic leads with nanogaps. It was found that the uncapped InAs QDs grown on the GaAs surfaces show metallic conductivities, indicating that even the exposed QDs are not depleted. On the contrary, it was found that no current flows through the exposed wetting layers. For the case of the QDs covered with GaAs capping layers, clear Coulomb gaps and Coulomb staircases have been observed at 4.2 K.     

In situ optical monitoring of metalorganic vapor phase epitaxy growth of C-doped GaAs

20 cm^-3 and above) induce oscillations in the reflected intensity. The evolution of the layers morphology is shown to depend on two effects: (i)the locally high surface concentration of carbon which blocks locally the growth and hence induces holes at the surface, (ii)the occurrence of dislocations at thicknesses larger than the critical thickness which are revealed chlorides produced by the decomposition of CCl₄ (the carbon precursor) and form deep etch pits. Received: 13 February 1998 / Accepted: 26 October 1998     

Enhanced ferromagnetism by preventing antiferromagnetic MnO2 in InP:Be/Mn/InP:Be triple layers fabricated using molecular beam epitaxy

The p-type InP:Be/Mn/InMnP:Be triple epilayers were prepared using MBE to increase T_c (>300 K) by preventing MnO₂. After milling 1–3 nm of epilayers thickness from the top surface, the transmission electron microscopy (TEM) and X-ray diffraction (XRD) revealed no MnO₂ and precipitates, and TEM and XRD results coincide with results of ferromagnetism. The enhanced ferromagnetic transition at >300 K corresponds to InMnP:Be. The increased ferromagnetic coupling without MnO₂ is considered to originate from the increased p–d hybridation. These results demonstrate that InP-based ferromagnetic semiconductor layers having enhanced ferromagnetism can be formed by above process.     

Well-aligned ZnO nanowires grown on Si substrate via metal–organic chemical vapor deposition

ZnO nanowires were grown on silicon substrate by metal–organic chemical vapor deposition (MOCVD) without catalysts. The scanning electron microscopy (SEM) observations along with X-ray diffraction (XRD) results suggest that the ZnO nanowires are single crystals vertically well-aligned to silicon substrate. Room-temperature photoluminescence (PL) measurement reveals strong UV emission and weak green emission, which demonstrates that the nanowires are of good optical properties. The mechanism of the catalyst-free growth of ZnO nanowires on silicon substrate is proposed.     

Multiple quantum well structures and high-power lasers of gaas- algaas grown by metalorganic vapor phase epitaxy (MOVPE)1

GaAs/AlGaAs GRIN-SCH type multiple quantum well lasers with four wells of 11 nm GaAs, grown in an MOVPE chimney reactor, exhibit an output power as high as 110 mW/facet (CW, 30°C; 5 μm stripe) and 1.3 W/facet (pulsed, 30°C; 53 μm stripe) until catastrophic optical damage occurs. 2000 hours life tests conducted at 60°C and 15 mW CW show no noticeable degradation for the 5 μm stripe laser with a reflective coating on both facets. Raman spectroscopy on similar multiple quantum well structures with 65 GaAs wells is used to ascertain that the wells have minimum residual aluminum- content.     

Photoluminescence and growth mechanism of amorphous silica nanowires by vapor phase transport

Amorphous silica [SiO_x (1<x<2)] nanowires were fabricated on silicon substrate in an acidic environment by heating the mixture of ZnCl₂, and VO₂ powders at 1100 °C. The length of SiO_x nanowires ranges from micrometers to centimeters, with uniform diameters of 10–500 nm depending on substrate temperature. Room-temperature photoluminescence spectra of the SiO_x nanowires showed two strong luminescence peaks in the red and green region, respectively. The photoluminescence was suggested to originate from nonbridging oxygen hole center (red band), and hydrogen-related species in the structure of SiO_x (green band). The study on chemical reactions and growth of the SiO_x nanowires revealed the formation process of silica nanowires in acidic environment was closely related to the vapor–solid–liquid mechanism.     

Multiple quantum well structures and high-power lasers of gaas- algaas grown by metalorganic vapor phase epitaxy (MOVPE)1

GaAs/AlGaAs GRIN-SCH type multiple quantum well lasers with four wells of 11 nm GaAs, grown in an MOVPE chimney reactor, exhibit an output power as high as 110 mW/facet (CW, 30°C; 5 μm stripe) and 1.3 W/facet (pulsed, 30°C; 53 μm stripe) until catastrophic optical damage occurs. 2000 hours life tests conducted at 60°C and 15 mW CW show no noticeable degradation for the 5 μm stripe laser with a reflective coating on both facets. Raman spectroscopy on similar multiple quantum well structures with 65 GaAs wells is used to ascertain that the wells have minimum residual aluminum- content.     

Tellurium delta‐doped InGaP layers grown by metalorganic vapour phase epitaxy

Heavily n‐type doped and several nanometres thick In_0.485Ga_0.515P layers are necessary for various devices. We studied the delta‐doping of this ternary with tellurium; the layers were grown by metalorganic vapour phase epitaxy (MOVPE), and diethyltelluride was used as the precursor. A maximum Hall sheet concentration of 2.75 × 10¹³ cm^–2 was achieved in our samples grown at 560 °C. The Te profiles were analyzed with secondary ion mass spectrometry (SIMS), and a very narrow spectrum with a full width at half maximum of 7.5 nm was measured. This value indicates that the memory effect, referred to in the literature, was practically eliminated with appropriate growth conditions. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)