Nitrogen vibrational mode spectra, Hall mobilities, and minority carrier diffusion lengths are examined for InGaAsN (≈ 1.1 eV bandgap) grown by molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD). Independent of growth technique, annealing promotes the formation of In-N bonding, and lateral carrier transport is limited by large scale (Ęmean free path ) material inhomogeneities. Comparing solar cell quantum efficiencies for devices grown by MBE and MOCVD, we find significant electron diffusion in the MBE material (reversed from the hole diffusion occurring in MOCVD material), and minority carrier diffusion in InGaAsN cannot be explained by a “universal”, nitrogen-related defect.

Here we present our results of structural, optical, and magnetic measurements of Zn1−xMnxO thin films. These films were grown epitaxially on (0001) sapphire substrates by using pulsed laser deposition technique. The maximum Mn content (x=0.36) is found to be much higher than allowed by thermal equlibrium limit (x∼0.13) due to the non-equilibrium nature of the pulsed laser deposition. All the films investigated here were found to be single phase with <0001> orientation epitaxial relationship. A linear increase in the c-axis lattice constant was observed with increase in Mn concentration. Optical transmittance measurements showed an increase in the insulating band-gap (Eg) with increase in Mn concentration. DC magnetization measurements showed that there is no long range ferromagnetic ordering down to 10 K.

A series of ZnO thin films with various deposition temperatures were prepared on (100) GaAs substrates by radio-frequency magnetron sputtering using ZnO target. The ZnO films were studied by field emission scanning electron microscope(FESEM), x-ray diffraction(XRD), photoluminescence(PL), cathodoluminescence(CL), and Hall measurements. The structural, optical, and electrical properties of the films were discussed as a function of the deposition temperature. With increasing temperature, the compressive stress in the films was released and their crystalline and optical properties were improved. From the depth profile of As measured by secondary ion mass spectrometry(SIMS), As doping was confirmed, and, in order to activate As dopant atoms, post-annealing treatment was performed. After annealing treatment, electrical and optical properties of the films were changed.

The evidence of a parabolic potential well in quantum wires and dots was reported in the literature, and a parabolic potential is often considered to be a good representation of the “barrier” potential in semiconductor quantum dots. In the present work, the variational and fractionaldimensional space approaches are used in a thorough study of the binding energy of on-center shallow donors in spherical GaAs-Ga1-xAlxAs quantum dots with potential barriers taken either as rectangular [V b (eV) ??1.247 x for r >] or parabolic [Vb (r) ??β2?r2] isotropic barriers. We define the parabolic potential with a β?parameter chosen so that it results in the same E0 groundstate energy as for the spherical quantum dot of radius R and rectangular potential in the absence of the impurity. Calculations using either the variational or fractional-dimensional approaches both for rectangular and parabolic potential result in essentially the same on-center binding energies provided the dot radius is not too small. This indicates that both potentials are alike representations of the quantum-dot barrier potential for a radius R quantum dot provided the parabolic potential is defined with?β?chosen as mentioned above.

The construction and the parameters of a new-strain dependent empirical pseudopotentials method are described and provided, respectively. This method is shown to reproduce with a very high accuracy some observed unusual properties in various complex anion-mixed nitride alloys. This method is also used to predict and understand anomalous effects that remain to be experimentally discovered in Ga1−yInyAs1−xNx quaternaries and GaAs0.5−xP0.5−xN2x solid solutions.

This work is to present results of flash evaporation of PbTe directly over single crystals p-type Si substrates, in order to produce heterojunction infrared detectors (HIRD), working at 4.3μm IR wavelength. The evaporation was performed on modified JEOL vacuum equipment, model JEE4B(a), working with vacuum pressure around 10−5 torr, using diffusion pump. The HIRDs produced with this method presented the same detectivity (D*) values of HIRDs made with Hot Wall Epitaxial System (HWE)(b), in which PbTe epitaxial layers were grown directly over the same Si substrates, where an ionic pump reached about 10−7 torr as vacuum pressure. The best results, were obtained with PbTe layers grown with Molecular Beam Epitaxial (MBE) method(c) directly over Si substrates, where the vacuum pressure is around 10−9 torr, also using an ionic pump. The advantage of growing PbTe directly over Si wafers is that the HIRDs perform at room temperature. The detectivity values of HIRDs obtained with methods (a) and (b), were D*≈4,8 × 105 cm.Hz1/2 W−1 and with method (c), D* ≈ 6,7 × 106 cm.Hz1/2 W−1. Different technologies: (a) very low costs, (c) high technology; not very different results.

We present fabrication of 3D photonic band gap woodpile crystals from photosensitive chalcogenide glass with the help of interference lithography and layer by layer construction. The alignment method is described, which is scalable to extremely small feature sizes required for photonic crystals in the visible region.

A novel ultrabroadband AlGaAs/CaF2 semiconductor saturable absorber mirror (SESAM) covering nearly the entire Ti:sapphire gain spectrum is demonstrated. This device supports sub-10-fs pulse operation of a laser. In contrast to previous SESAMs of comparable bandwidth, our device can be monolithically grown by molecular beam epitaxy and requires no post-growth processing. GaAs is used as semiconductor saturable absorber material. The high defect concentration of the material is due to the lattice-mismatched growth on a fluoride surface with (111) orientation. With a time response of 1.2 ps for carrier trapping, a saturation fluence of 36 μJ/cm2 and a modulation depth of up to 2.2% , the GaAs saturable absorber is well-suited for all-optical switching in SESAM devices used for ultrashort pulse generation.

We describe a technique for obtaining effective second order non-linearity χ2 in non centro-symmetric Photonic Crystal made from centro-symmetric materials (e.g. glass, Ge or Si). The effect is based on the electric quadrupole transition, strong electromagnetic mode deformation and different contributions to the volume polarization from different parts of the photonic crystal1.

InGaAsP/InP multiple quantum wells have been prepared by Impurity-Free Vacancy Disordering (IFVD). The luminescent characteristics was investigated using photoluminescence (PL) and photoreflectance (PR), from which the band gap blue shift was observed. Si3N4, SiO2 and SOG were used for the dielectric layer to create the vacancies. All samples were annealed by rapid thermal anne aling (RTA). The results indicate that the band gap blue shift varies with the dielectric layers and annealing temperature. The SiO2 capping was successfully used with an InGaAs cladding layer to cause larger band tuning effect in the InGaAs/InP MQWs than the Si3N4 capping with an InGaAs cladding layer. On the other hand, samples with the Si3N4-InP cap layer combination also show larger energy shifts than that with SiO2-InP cap layer combination.

We describe the operation of lasers having active regions composed of InP selfassembled quantum dots embedded in In0.5Al0.3Ga0.2P grown on GaAs (100) substrates by MOCVD. InP quantum dots grown on In0.5Al0.3Ga0.2P have a high density on the order of about 1–2×10 cm−2 with a dominant size of about 10–15 nm for 7.5 ML growth.[1] These In0.5Al0.3Ga0.2P/InP quantum dots have previously been characterized by atomic-force microscopy, high-resolution transmission electron microscopy, and photoluminescence.[2] We report here the 300K operation of optically pumped red-emitting quantum dots using both double quantum-dot active regions and quantum-dot coupled with InGaP quantum-well active regions. Optically and electrically pumped 300K lasers have been obtained using this active region design; these lasers show improved operation compared to the lasers having QD-based active regions with threshold current densities as low as Jth ∼ 0.5 KA/cm2.

We describe briefly a cheap and non polluting technique to grow epitaxial GaAs layers, several hundred microns thick, in a matter of hour. Detectors consisting of a p+/i/n+ structure have been realised with these layers and we present their characteristics obtained from currentvoltage, capacitance-voltage measurements as well as their response versus the energy and flux of X-rays.

Depth profiling for the amount of lattice damage using a Confocal Micro-Raman (CMR) spectrometer is demonstrated in this paper. Samples of n-type silicon carbide were implanted with 2 MeV He and O ions at both room temperature and 500 °C, and fluences between 1015 and 1017 ions/cm2. Post-implantation annealing at 1000 °C was also performed in order to study the damage evolution. Optical Absorption Spectrophotometry (OAS) was used for establishing the opacity (and therefore the probing depth) of the damaged layer to the 632.8 nm wavelength of the He-Ne laser used for CMR throughout this study. The methodology used and the results obtained are presented herein. Total dissipation of amorphous carbon islands was observed even at low annealing temperatures of the RT implanted samples, along with an increase in the size of the amorphous silicon islands.

We study changes in the optical constants of a-Si:H films caused by the thermal annealing involved in solid phase crystallization. The aim is to examine the growth mechanism, since changes in refractive index are most probably caused by a change in the network structure. The refractive index change was studied from interference fringes in transmitted light at normal incidence, and shows differing dependence on temperature in different thermal ranges. DSC measurement was also performed to examine changes in the network structure with temperature. Changes in optical and thermal properties induced by an increase of temperature reveal frequent network changes of a-Si:H below 470°C and of a-Si in the range 470 to 570°C. We also found crystallization at about 570°C, and grain growth above the crystallization temperature. Knowledge of network changes in a-Si film allows orientation control by an external seed.

Conditions necessary for the reproducible deposition of pristine In2S3 thin films on TO-glass substrates by low temperature solution deposition have been identified. Baths containing carboxylic acids yield adherent, specular and crystalline films, within a defined pH range, dependent on the particular acid employed. Films have been characterised by XRD, SEM, XPS and electronic spectroscopy. As–deposited films were found to crystallise as tetragonal β-In2S3, no evidence for incorporation of hydroxy-indium species was found by XPS measurements.

AlxGa(1−x)As/GaAs quantum well lasers have been demonstrated via organometallic chemical vapor deposition (OMCVD) on relaxed graded GexSi(1−x) virtual substrates on Si. Despite unoptimized laser structures with high series resistance and large threshold current densities, surface threading dislocation densities as low as 2×106 cm−2 enabled cw room-temperature lasing at a wavelength of 858nm. The laser structures are oxide-stripe gain-guided devices with differential quantum efficiencies of 0.16 and threshold current densities of 1550A/cm2. Identical devices grown on commercial GaAs substrates showed differential quantum efficiencies of 0.14 and threshold current densities of 1700A/cm2. This comparative data agrees with our previous measurements of near-bulk minority carrier lifetimes in GaAs grown on Ge/GeSi/Si substrates. A number of GaAs/Ge/Si integration issues including thermal expansion mismatch and Ge autodoping behavior in GaAs were overcome.

InAs/AlGaAs quantum dot infrared photodetectors based on bound-to-bound intraband transitions in undoped InAs quantum dots are reported. AlGaAs blocking layers were employed to achieve low dark current. The photoresponse peaked at 6.2 μm. At 77 K and –0.7 V bias the responsivity was 14 mA/W and the detectivtiy, D*, was 1010 cmHz1/2/W.

Positron lifetime technique and photoluminescence (PL) were employed to study the vacancy type defects in p-type Zn-doped and undoped GaSb samples. In the positron lifetime study, Ga vacancy related defect was identified in these materials and it was found to anneal out at temperature of about 350°C. For the PL measurement on the as-grown undoped sample performed at 10K, a transition peak having a photon energy of about 777meV was observed. This transition peak was observed to disappear after a 400°C annealing. Our results is consistent with the general belief that the 777meV transition is related to the VGaGaSb defect, which is the proposed residual acceptor of GaSb.

The results of an experimental research of the dependence of photoluminescence (PL) intensity in region about 800 nm for silicon nanoinclusions (quantum dots) obtained by Si ion implantation in SiO2 on the dose of Si ions at two temperatures of an annealing ?ann = 1000 and 1100° ? are presented. It is established that in both cases the dependences have the shape of the curves with a maximum. For 1100° ? the maximum is shifted to the lower dose. The influence of an additional ion doping by the phosphorus on intensity of PL is investigated depending on the dose (concentration) of P and the dose of the silicon at ?ann = 1000° ?. It is shown, that in all the investigated region of P doses, the presence of P enhances the PL. The degree of the enhancement increases with the P dose, but the rate of the intensity enhancement goes down. With the growth of Si dose at the constant dose of P, the degree of the enhancement decreases. In an approximation of an effective mass, the energy spectra of a quantum dot are calculated at the presence of one or several P atoms for various their arrangement.

Using pulsed laser deposition technique, nGaAs-nInSb heterojunctions (HJs) are obtained. Their electrical properties are studied. The Current-Voltage characteristics show that obtained HJs possess rectifying properties. The rectification coefficient depends strongly on the doping level of GaAs substrate. The linear dependence of C−2 (V) curve in Capacitance-Voltage characteristics, as well as the change of photo-response sign with wavelength, indicates that the HJs have abrupt interface, which is, to the best of our knowledge, a novel result for these HJ materials. The full number of interface states arising due to the lattice mismatch is determined which is in agreement with Hall measurements. Current-Voltage characteristics of obtained HJs are analogous to those of metal-semiconductor junction. Based on the obtained results the energy band diagrams of nGaAs-nInSb HJ is constructed taking into account the interface states.