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We report a high performance UVB photodetector with a metal–semiconductor–metal device structure based on high crystal quality SnO2 microwires prepared by chemical vapor deposition.

Background Remnant cholesterol (remnant-C) and inflammation are considered risk factors for in-stent restenosis (ISR). We evaluate the combined impact of remnant-C and high-sensitivity C-reactive protein (hsCRP) on ISR. Methods A total of 1,503 patients were consecutively enrolled in this study. Baseline and follow-up remnant-C and hsCRP concentrations were obtained. The individual and combined effects of remnant-C and hsCRP on ISR were examined. Results The median (interquartile range) follow-up for all patients was 2.0 (0.9, 3.9) years, and 244 patients (16.2%) were diagnosed with ISR. Multivariate Cox analysis showed that the risk of ISR was higher in patients at the highest quartile of remnant-C (Q4 vs. Q1: adjusted hazard ratio HR 1.482, 95% confidence interval CI 1.013–2.168, p = 0.042, p for trend 0.020) and hsCRP (Q4 vs. Q1: adjusted HR 1.620, 95% CI 1.121–2.339, p = 0.010, p for trend 0.006). Moreover, the combination of high remnant-C and hsCRP produced a higher predictive value (adjusted HR: 1.904; 95% CI: 1.328–2.729; p p = 0.005) in patients with LDL-C levels ≤ 1.8 mmol/L. Conclusions Our results show that elevated remnant-C or hsCRP is associated with a high risk of ISR. The combined analysis of remnant-C and hsCRP could improve risk identification since high levels significantly increase the risk of ISR.

Rutile-phase titanium dioxide (TiO2) nanosheets with a thickness of 4 nm were successfully prepared. Excellent visible light catalytic degradation effects have been observed from these nanosheets. To enhance the catalytic performance, aurum nanorods (AuNRs) were incorporated with the TiO2 nanosheets. Compared with sole TiO2 nanosheets, the Janus structures of the combined TiO2 and AuNRs (TiO2@AuNRs) showed three times the reaction rate for the degradation of Rhodamine B under visible and near-infrared light (> 410 nm, 300 W). This is attributed to the wide response range of AuNRs, which is demonstrated by the absorption spectra of the AuNRs colloids. The introduction of AuNRs with different aspect ratios in TiO2@AuNRs revealed better catalytic activities for AuNRs with larger aspect ratios. To study the physical mechanism of photocatalytic enhancement, the finite difference time domain method has been performed to simulate the optical properties of TiO2@AuNRs. The simulation results showed that the photocatalytic improvement of TiO2@AuNRs was caused by the longitudinal localized surface plasmon resonance mode of AuNR. Through the excitation of the longitudinal mode, 40 times enhancement of the near-field intensity can be observed. The results indicate that AuNRs can be used to improve the photocatalytic activity of TiO2 nanosheets through the injection of hot electrons from AuNR into TiO2.

Wide band gap semiconductors are promising UV photodetector materials due to their suitable bandgap, high crystal quality, strong absorption and large carrier mobility. Up to now, deep UV photodetectors are mainly based on epitaxial thin films, which have some undesired properties such as p-type doping difficulty. Lattice mismatch hinders the further development of these devices. Here, a high performance self-powered solar-blind UV photodetector was realized by a facile combination of a centimeter-sized single crystal β-Ga2O3 microwire and polyaniline. Owing to the excellent organic/inorganic hybrid p–n junction, the device shows an ultrahigh responsivity of 21 mA W−1 at 246 nm with a sharp cut-off wavelength of 272 nm without an external power supply. Moreover, the dark current is 0.08 pA, which is smaller than those of almost all the previous metallic oxide based solar-blind UV photodetectors. The photodetector also shows a high UV/visible rejection ratio (102) at zero bias voltage. Finally, a physical model of the self-powered photodetector is also proposed. This work provides a simple, low-cost, and effective method for preparing high performance self-powered solar-blind UV photodetectors based on organic/inorganic heterojunctions.

The authors report the conversion of conduction type from n-type to p-type in the Al–N co-doped ZnO thin films by using thermal annealing treatment under argon atmosphere. The samples were deposited on fused silica by radio frequency magnetron sputtering. X-ray diffraction measurements showed that ZnO thin films have (002)-preferred orientation and the lattice constant decreases with the increase of nitrogen partial pressure. The average optical transmittance of these films is over 80%. The hole density is around 1.58 × 1017 cm−3 with an annealing temperature of 700°C. After exposing the samples in air for 1 year, the conduction type remains p-type with only a slight decrease of hole density, which indicates that the p-type ZnO with Al–N co-dopants has good electrical stability.

We calculated the adsorption behaviors of Au clusters on different crystal planes of SnS2 via first principles methods. Due to the surface dangling bonds and surface atomic arrangements, the (101) plane shows lower formation energy (−5.29 eV) to Au clusters as compared to the (001) surface (−3.77 eV) of SnS2. This indicates the Au clusters prefer to stick on the (101) surface of SnS2, which is further confirmed by the experimental results. The calculated HOMO and LUMO reveal the excited electron transfer behavior between Au clusters and the (101) surface of SnS2. The photoluminescence spectra, photocurrent and photocatalytic experiments of AuNCs and SnS2 nanoparticles support the electron transfer mechanisms.

We compare the visible light extinction difference of Janus and core-shell structures for several typical semiconductors and gold nanoparticles (AuNPs) and found out better extinction behavior of the Janus type with visible light response for narrow bandgap semiconductors. Following the predictions, we designed and prepared the Janus and core-shell heterostructures of SnS2 (Eg = 2.1–2.4 eV) and AuNPs (SnS2@AuNPs). Excellent visible light catalytic performance in Janus structures compared with SnS2 and the core-shell structures can be observed, which was attributed to the enhanced localized surface plasmon resonance (LSPR) and the increased lifetime of photo generated carriers. The absorption spectrum revealed more significant LSPR intensities for the Janus structures compared to SnS2 and the core-shell structures. The Photoluminescence (PL) spectrum of the core-shell and Janus structures showed a half and a quarter the intensities of the SnS2. The shorter lifetime in Janus structures (1.16 ns) may result from the fast depopulation of photo-generated electrons from SnS2 into Au. Due to the LSPR enhancement and the photo generated carriers separation in the Janus structures, the visible light catalytic performance of SnS2 has been improved effectively.

Wide band gap semiconductors are promising UV photodetector materials due to their suitable bandgap, high crystal quality, strong absorption and large carrier mobility. Up to now, deep UV photodetectors are mainly based on epitaxial thin films, which have some undesired properties such as p-type doping difficulty. Lattice mismatch hinders the further development of these devices. Here, a high performance self-powered solar-blind UV photodetector was realized by a facile combination of a centimeter-sized single crystal β-Ga2O3 microwire and polyaniline. Owing to the excellent organic/inorganic hybrid p-n junction, the device shows an ultrahigh responsivity of 21 mA W-1 at 246 nm with a sharp cut-off wavelength of 272 nm without an external power supply. Moreover, the dark current is 0.08 pA, which is smaller than those of almost all the previous metallic oxide based solar-blind UV photodetectors. The photodetector also shows a high UV/visible rejection ratio (102) at zero bias voltage. Finally, a physical model of the self-powered photodetector is also proposed. This work provides a simple, low-cost, and effective method for preparing high performance self-powered solar-blind UV photodetectors based on organic/inorganic heterojunctions.

The design, growth, and characterizations of ZnCdSe/ZnCdMgSe semiconductor multilayer quantum-well structures for two-color quantum-well infrared photodetectors (QWIPs) are reported. The energy band and quantum well states are computed in a ZnCdSe/ZnCdMgSe single quantum well for both infrared detection regions. The sample has been grown in a multichamber molecular beam epitaxy system. The good crystalline quality of sample and its lattice matching to the InP substrate are investigated by high-resolution x-ray diffraction and transmission electron microscopy analysis. These structural measurements also confirm the good agreement between the design and the grown structure. The band-to-band and interband transition energies are experimentally determined by photoluminescence and contactless electroreflectance, respectively. The intersubband absorption spectra are investigated by Fourier transform infrared spectroscopy at room temperature. This multilayer structure represents a significant technological validation of the capabilities and potential of InP-based II-VI materials for engineering two-color QWIP devices. This paper provides a detailed methodology for the growth and in-depth characterization of such a complex high precision multilayered structure.

The authors report the fabrication of p-type ZnO thin films with improved thermal stability. The p-type ZnO thin films were obtained by oxidizing Zn3N2:Al thin films in an oxygen ambient. Both Zn3N2:Al and Zn3N2 thin films were deposited on fused silica substrates at 100 °C by megnetron sputtering. X-ray diffraction (XRD) measurements showed that the ZnO thin films obtained from by oxiding Zn3N2:Al, have preferred (002) orientation. On the other hand, ZnO films obtained by oxidizing Zn3N2 are polycrystalline. The optical band gap of ZnO (3.294 eV) obtained by annealing Zn3N2:Al thin films is narrower than that of the ZnO (3.31 eV) obtained by annealing Zn3N2. P-type ZnO films were formed by annealing Zn3N2:Al at temperatures above 600 °C. A maximum hole density of 1.4 x 1016 cm-3 was obtained in a film annealed at 800 °C. In contrast, only n-type ZnO can be produced from oxidizing Zn3N2. Our results indicate that the Al can stabilize the nitrogen acceptors in ZnO thin films. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The authors report, for the first time, the new two-color quantum well infrared photodetectors (QWIPs) from a non-III-V semiconductor material system. The samples were grown on InP substrate by molecular beam epitaxy. X-ray diffraction and photoluminescence measurements showed high structural and optical quality of the samples. Two intersubband (ISB) absorption peaks in two different wavelength regions are observed in Fourier transform infrared measurements. The two-color photodetectors can be turned on separately or simultaneously in the two spectral regions. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This chapter reviews the molecular beam epitaxy (MBE) growth of wide band gap II–VI semiconductor quantum structures and their applications in intersubband (ISB) photonic devices. It consists of three parts, with the first part dedicated to the growth and characterization of quantum-well infrared photodetectors (QWIPs). The QWIPs were made from ZnCdSe/ZnCdMgSe multiple quantum wells (MQWs) grown lattice matched on InP substrates and work in the two important mid-infrared (mid-IR) spectral regions—the long wave IR (LWIR) and medium wave IR (MWIR) regions. The second part describes the realization of short wavelength ISB absorption in the material system through band structure engineering. By using coupled quantum wells and optimizing the MgSe barrier layer thickness, ISB absorption in the optical communication wavelength of 1.55 μm has been achieved. The third part summarizes our effort on the growth and characterization of ZnO/ZnMgO QWs. Mid-IR ISB absorption was observed for the first time in ZnO-based quantum structures, making them promising for ISB devices as well.

The authors report the growth of ZnO/ZnMgO multiple quantum well (MQW) structures by plasma-assisted molecular beam epitaxy. A set of three MQW samples with different well thicknesses were grown on c -plane sapphire substrates. Structural and optical properties of the samples were characterized by reflection high-energy electron diffraction, high-resolution x-ray diffraction (XRD) and photoluminescence measurements. Clear superlattice satellite peaks and thickness fringes observed in XRD measurements indicate the formation of periodic structure with good interfacial quality and high crystalline quality. Mid infrared absorptions around 3 μm are observed from Fourier transform infrared spectroscopy measurement. The polarization-dependent absorption proves that the absorptions are originated from intersubband transitions.

In order to increase the conduction band offset of the ZnCdMgSe-based material system we studied the incorporation of strained CdSe layers to obtain deeper quantum wells for shorter wavelength intersubband transitions than those obtained in lattice-matched structures. Five CdSe/ZnSe/ZnCdMgSe multi-quantum wells (QW) samples grown by molecular beam epitaxy are studied in detail by transmission electron microscopy (TEM), X-ray diffraction (XRD), cw-photoluminescence (PL), and Fourier Transform Infrared (FTIR) absorption experiments. TEM and XRD results confirmed good structural quality of the samples. All the multi-QW PL energies were below the ZnCdSe lattice-matched to InP alloy bandgap (2.1 eV), which serves as first evidence of having achieved deeper quantum wells. FTIR absorptions from 3.83 to 2.56 μm were measured, shorter than those achieved by the lattice matched system. Simulations based on these results predict that absorptions as low as 2.18 μm can be obtained with these materials.

Background Outcomes of patients with autoimmune diseases after percutaneous coronary intervention (PCI), as compared to those without autoimmune disease, remain unclear. Methods We searched Medline, EMBASE, and the Cochrane Library from their inception to 1 April 2017. All studies comparing the following outcomes of patients with and without autoimmune diseases after PCI were included: long-term mortality, major adverse cardiovascular events (MACE), repeat revascularisation, myocardial ischaemia or myocardial infarction (MI), restenosis, and in-hospital mortality. The Newcastle-Ottawa Quality Assessment Scale (NOS) and the quality assessment form of the Agency for Healthcare Research and Quality (USA) (AHRQ) were used for assessing the risk of bias, and the certainty of evidence was rated by the Grading of Recommendations Assessment, Development, and Evaluation (GRADE). Results A total of 11 studies were included in our analysis. Compared with patients without autoimmune diseases, those with autoimmune diseases carried an increased risk of MACEs (relative risk (RR): 2.24, 95% confidence interval (CI): 1.20–4.16; heterogeneity: p = 0.128, I2 = 56.9%), repeat revascularisation (RR: 1.66, 95% CI 95%: 1.01–2.72; heterogeneity: p = 0.057, I2 = 65.1%), ischaemia or MI (RR: 2.80, 95% CI: 1.38–5.65; heterogeneity: p = 0.871, I2 = 0.0%), and restenosis (RR: 2.06, 95% CI: 1.39–3.07; heterogeneity: p = 0.665, I2 = 0.0%) during the one-year follow-up after PCI, and carried an increased risk of MACEs (RR: 1.10, 95% CI: 1.04–1.17) and death (RR: 1.38, 95% CI: 1.25–1.51) during the 11-year follow-up after PCI. Conclusions Evidence of very low quality showed that during the one-year follow-up period, patients with autoimmune diseases after PCI were more likely to experience MACEs, repeat revascularisation, myocardial ischaemia or MI, and restenosis. During the 11-year follow-up period, patients with autoimmune diseases after PCI were more likely to die. It is therefore important to watch for restenosis, repeat ischaemia or MI and other adverse events more carefully in patients with autoimmune diseases after PCI.

An independently controllable, two-color ZnCdSe/ZnCdMgSe quantum well infrared detector spanning 4.3–5.4 μm and 6.7–8.2 μm is experimentally demonstrated with a dark current limited detectivity of 2.9×108 cm√Hz/W and 2.7×107 cm√Hz/W at 80 K, respectively.

ZnO thin films were grown by plasma-assisted MBE on GaAs substrates with ZnSe buffer layers. GaAs with different orientations: (001), (111) A, and (111) B were investigated. X-ray diffraction measurements showed that ZnO grown on (111) B GaAs substrates have the best structural quality. All the samples showed good optical qualities as indicated by room temperature photoluminescence measurements. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Typically, II–VI heterostructures and devices are grown on commercially available III–V substrates. Often these substrates have strong absorption at the emission energy of the epitaxial layer, a problem when transmission measurements are required, as well as for some device applications. By removing the epilayers from the substrate the layer properties can be examined unhindered by the presence of the substrate. In this paper we present a selective etching technique for the removal of InGaAs/InP substrates from ZnMgCdSe-based epitaxial structures. Characterization of the materials after etching indicated the material is not damaged in the etching process. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

ZnO thin films have been grown by plasma-assisted molecular beam epitaxy on (111) ZnS substrates. The films grown on Zn-face substrates showed better structural and optical properties compared with those grown on S-face substrates, as demonstrated by x-ray diffraction and photoluminescence measurements. Scanning electron microscopy measurements indicated that ZnO films grown on Zn-face substrates also have smoother surface morphology. It is also found that higher growth temperature yields films with better quality.

Quantum cascade (QC) lasers operating in the mid-infrared (IR) are being intensely pursued for environmental sensing and other important technological applications. Having demonstrated mid-IR (3 μm to 5 μm) electroluminescence (EL) from a II–VI intersubband device based on wide-band-gap (2.9 eV) Zn0.24Cd0.26Mg0.5Se on InP, there has been a drive towards production of a QC laser from these materials. To achieve lasing, waveguiding layers that straddle the active region used in the EL structure must be included. Initial attempts to grow this more complex structure resulted in degradation of the material quality. This paper presents the optimization steps required for the growth of the full QC laser structure and discusses possible mechanisms for the degraded quality.

The authors report that the growth rate of ZnO can be significantly increased by modifying the oxygen plasma conditions in plasma-assisted molecular beam epitaxy. Both the aperture diameter and the distance between the plasma source and the substrate affect the growth rate and the quality of the ZnO films. A short source to substrate distance is essential in achieving higher growth rate, which is explained by reduced chance of oxygen atom collisions to accommodate the short oxygen mean free path at high background pressure. At a shorter source to substrate distance, the growth rate is higher with a larger aperture diameter. The quality of the ZnO thin films grown under different conditions is assessed by x-ray diffraction and room-temperature photoluminescence measurements.

Background This study aimed to investigate the expression of ZEB1 in osteosarcoma tissues and to discuss the relationship between ZEB1 expression and osteosarcoma metastasis. Methods Using RT-PCR and Western blotting, the mRNA and protein expressions of ZEB1 in the osteosarcoma and normal bone tissues were detected. Using the RNA interference technique, the expression of ZEB1 in the human osteosarcoma MG-63 cell line was downregulated, and the changes in the invasion of MG-63 cells were examined. Results The positive mRNA expression rate of ZEB1 in the osteosarcoma tissues was significantly higher than that in normal bone tissue (P

Previous research has shown that vitamin D could suppress proliferation, migration and invasion of cancers, but the effects of vitamin D may be related to the expression of Snail-1, which could inhibit the expression of the vitamin-D gene receptor (VDR). Snail-1 is overexpressed in osteosarcoma, this study was conducted to determine whether inhibiting Snail-1 could increase the role of vitamin D as an anti- osteosarcoma agent. We used stable transfection of the SaOS₂ cell line as in vitro model to study the effect of 1,25(OH)-D₃, which is the most active metabolite of vitamin D. The in vitro antiproliferative, pro-apoptotic and inhibiting of invasion effects were examined. The effects of 1,25(OH)-D₃ on the expression of β-catenin signaling pathways were also studied. Then in vivo antiproliferative effect of 1,25(OH)-D₃ was also detected in nude mice injected with either mock-infected or Snail-1 SaOS₂ cells. We found that inhibition of Snail-1 signaling by transfection could increase the expression of VDR, enhance the anti-proliferative activity of 1,25(OH)-D₃ in osteosarcoma cells, and induce apoptosis and lower invasion in vitro. The effect of 1,25(OH)-D₃ was also associated with decreased expression of β-catenin signaling, which is related to VDR signaling. In vivo, the effect of antiproliferative was higher in mice injected with either Snail-1-infected cells than with mock-infected cells. Our findings suggest that canonical Snail-1/VDR/β-catenin signaling reflects an important underlying mechanism of osteosarcoma progression. Therefore, strategies to suppress Snail-mediated signaling may lead to the better action of 1,25(OH)-D₃ as an anti osteosarcoma treatment.

We report the effects of varying growth parameters on the photoluminescence (PL) and time-resolved photoluminescence (TRPL) emission from layered Zn-Se:Te structures with submonolayer quantities of ZnTe grown by a combination of migration-enhanced epitaxy (MEE) and molecular beam epitaxy (MBE). Dependences on Te effusion cell temperature (T Te source) and “wait time” (duration for which all shutters are closed, t all-off) are investigated to show that these parameters contribute towards changing the size and/or composition of the quantum dots (QDs). Optical studies showed that increasing T Te source resulted in the formation of larger QDs. Increasing t all-off from 0 s to 3 s contributed towards the formation of larger QDs, while further increasing t all-off to 9 s led to desorption of Te adatoms which resulted in smaller QDs. These parameters are easy to control, and thus understanding their effects should help us to gain better control towards obtaining high-quality QDs.

An independently controllable, two-band quantum well infrared photo-detector (QWIP) based on the ZnCdSe/ZnCdMgSe material system is characterized. The two-band detector consists of two stacks of quantum wells absorbing in the mid- and long-wavelength infrared regime. Photocurrent and responsivity measurements resulted in 11 mA/W and 7 mA/W peak responsivities at 80 K with corresponding detectivities of 2 × 108 cm√Hz/W and 2 × 107 cm√Hz/W centered at 4.8 μm (258 meV) and 7.6 μm (163 meV). The two-band device can also perform as a broadband detector covering wavelengths from 4.4 μm (281 meV) to 8.2 μm (151 meV) at 80 K with a full width at half maximum of 130 meV. Two-band QWIP is tested for an absolute temperature detection application and good agreement is observed between theoretical calculation and experimental results.

Diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), has evolved resistance to various kinds of insecticides in the field. Chlorantraniliprole, which is a new pesticide of the anthranilic diamide group, provides potent and broad-spectrum activity within the insect order Lepidoptera. This insecticide provides a new option for control of P. xylostella populations resistant to other chemicals. The susceptibility of 16 field populations and seven laboratory maintained strains of P. xylostella to chlorantraniliprole were determined through leaf dip bioassay. The susceptibility variation among 16 field populations was low (five-fold), with median lethal concentrations (LC50 values) varying from 0.221 to 1.104 mg/liter. However, wider ranges of variation in LC50 values (10-fold) were observed among seven laboratory strains. Low level tolerance (six- to 10-fold) was detected in two laboratory-selected strains and three field-collected populations when compared with the susceptible Roth strain. A discriminating concentration (15 mg/liter) was calibrated from pooled toxicological data of the 16 field populations, as an important first step in resistance management, for the routine monitoring of resistance in the future. When assessed at the established discriminating dose 15 mg/liter, seven laboratory strains and five field populations showed an average mortality of 99.75% (from 98 to 100%). Synergism assays showed metabolic enzymes might be involved in chlorantraniliprole detoxification in the susceptible Roth strain, but not in the additional observed tolerance of strains selected for resistance with other insecticides.

CdTe layers were grown on (0 0 1) GaAs substrates with a ZnSe buffer layer by molecular beam epitaxy. The high-quality ZnSe (0 0 1) epitaxy on GaAs allows us to control the II–VI/III–V heterovalent interface prior to the CdTe deposition. By subsequently adjusting the interface between ZnSe and CdTe, it was possible to selectively obtain the growth of either (0 0 1) or (1 1 1) CdTe epitaxial layers on the (0 0 1) ZnSe/GaAs substrate. Reflection high energy electron diffraction indicates that the nucleation of the CdTe epitaxial layers turns two-dimensional within a few seconds of initiating the growth. X-ray diffraction and photoluminescence measurements indicate that both the (1 1 1) and the (0 0 1) CdTe films are of high structural quality despite the large lattice constant mismatch of 14.6% between CdTe and the (0 0 1) ZnSe/GaAs substrate.

In this paper, we present our recent progress towards the realization of short wavelength intersubband devices with wide band gap II–VI selenide semiconductors. Intersubband electroluminescence at 4.8 μm was observed in a ZnCdSe/ZnCdMgSe quantum cascade structure at temperatures up to room temperature. We also developed a new ZnCdSe/MgSe quantum structure with metastable MgSe barriers. Intersubband absorption in the 3–5 μm range was observed. Calculations suggest that with this structure intersubband transitions as short as 1.55 μm may be achieved.

The authors report the effect of a low-temperature buffer layer of Cu 2 O (LTB-Cu 2 O) on the growth of Cu 2 O thin films. The samples were prepared by radio frequency-magnetron sputtering. It was found that with the introducing of LTB-Cu 2 O, the linewidth of the X-ray diffraction peak decreases and the Cu 2 O thin films have preferred (1 1 1) orientation. By introducing LTB-Cu 2 O, the grain size sufficiently increases and the surface flatness improves, as indicated from the atomic force microscopy measurement. Under the optimum growth conditions, hole mobility of 256 cm 2 V −1 s −1 , which is the highest value reported so far, with the hole concentration of 1×10 14 cm −3 was achieved.

We report growth by molecular beam epitaxy of a Zn x Cd (1− x ) Se/Zn x ′ Cd y ′ Mg (1− x ′− y ′) Se quantum cascade (QC) structure that was designed for electroluminescence (EL) at ∼4.5 μm. The QC active region is comprised of a two-well asymmetric coupled quantum well (ACQW) structure, which was thoroughly investigated to establish the growth conditions for the QC structure. After growth of several ACQW test samples, the conditions for growth were optimized for the QC structure. In-situ RHEED, photoluminescence (PL), high-resolution X-ray diffraction (HR-XRD) and Fourier transform infrared (FTIR) spectroscopy results were used for characterization. The QC structure grown under these conditions exhibited EL at 4.8 μm, in excellent agreement with the design value.

Two heavily doped n-type Zn0.46Cd0.54Se/Zn0.24 Cd0.25Mg0.51Se multiple quantum well (MQW) structures have been grown on InP (0 0 1) substrates by molecular beam epitaxy. Photoluminescence (PL), time-resolved PL, and Fourier transform infrared (FTIR) spectroscopy were performed to characterize their interband and intersubband (ISB) properties. These two MQW samples have similar structures except for different well widths and a different number of periods. Excitation-intensity-dependent PL shows no electronic coupling between the multiquantum wells. The integrated PL intensities and the PL decay times of the MQWs were measured as functions of temperature in the range from 77 to 290 K. Theoretical fittings of temperature dependences of integrated PL intensities and PL decay times indicate that the nonradiative recombination processes observed in our samples can be well described by hole capture by acceptor-like defect centers through multiphonon emissions. ISB absorption spectra of the samples were measured by FTIR and show peak absorption at wavelengths of 3.99 and 5.35 mum for the MQWs with well widths of 28 and 42 A, respectively. Theoretical calculations based on the envelope function approximation confirm that these peaks are due to the transitions from the ground state E1 to the first excited state E2.

Optical and morphological studies are used to investigate the effects of chemical composition and, in particular, the magnesium content of the Zn x Cd y Mg 1− x − y Se barrier layers on the size, density and uniformity of CdSe self-assembled quantum dots (QDs). A reduction of the uncapped QD size, as well as a blue shift of the capped QD photoluminescence peak position by increasing Mg concentration in the Zn x Cd y Mg 1− x − y Se barrier has been demonstrated by changing the Mg cell temperature during growth. In addition, a more uniform and more densely packed QD layer has been observed with an increase of the MgSe fraction in the Zn x Cd y Mg 1− x − y Se barrier layer using three-dimensional topographic atomic force microscopy images of the surface of uncapped QDs. Results point to Mg as a chemical factor that induces QD formation, either by increasing the density of atomic steps or/and by changing the energy of the Zn x Cd y Mg 1− x − y Se surface.

Quantum well infrared photodetectors (QWIPs) from wide bandgap II-VI compounds are promising as high quantum efficiency detectors in the mid-IR. A series of Cl-doped Zn x Cd (1-x) Se/Zn x' Cd y' Mg (1-x'-y') Se multiple-quantum-wells (MQW) with different quantum well (QW) thicknesses have been grown by MBE lattice-matched to InP substrates. The high material quality of the samples was demonstrated by X-ray diffraction (XRD), steady-state photoluminescence (PL), and time-resolved photoluminescence (t-PL) measurements. Contactless electroreflectance (CER) measurements were performed to investigate high order transitions within the QWs. From these transitions, intersubband transition energies were predicted and compared with the theoretical calculations, a very useful result for device design. Our results indicate that this material system is very promising for intersubband device applications such as QWIPs operating in the 3-5 μm region.

Properties of ferromagnetic (Ga,Mn)As layers grown epitaxially on a GaAs (4 1 1)A substrate were investigated. X-ray double-crystal diffraction showed the presence of shear strain due to lattice mismatch between substrate and the epitaxial layer. The magnetotransport measurements showed that the easy axis of magnetization was in the (1 0 0) plane. The results indicate that the origin of the magnetic anisotropy is dominated by the lattice strain.

Depending on the shutter sequence used to initiate CdTe deposition, either (100) or (111) CdTe layers can be reproducibly grown on (100) ZnSe/GaAs substrates. Using a hexagonal surface model for (111) CdTe we propose a mechanism for the crystalline orientation selectivity. We use time-resolved Kerr rotation to monitor the electron spin dynamics in these films. While the spin lifetime is found to depend on material quality, only (100) films show a clear temperature dependence, a peculiar feature we believe to arise from different residual strains in the layers with the two different orientations. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)