Development of Cd1-xMgxTe thin films for application as an electron reflector in CdS/CdTe solar cells

2014 Summer.Efficiencies of CdS/CdTe photovoltaic cells significantly lag behind their theoretical limit, primarily because open-circuit voltage (VOC) of record efficiency cells (872 mV) is well below what is expected for the CdTe band gap (1.5 eV). A substantial VOC improvement can be achieved through addition of an electron reflector (ER) layer to CdTe devices. The ER layer forms a conduction-band barrier that reflects minority-charge carriers (i.e. electrons in p-type CdTe) away from the back surface. Similar to back-surface fields in c-Si, III-V, and CIGS solar cells, the ER strategy is expected to reduce back-surface recombination and is estimated to increase CdTe VOC by about 200 mV based on numerical simulation. The presented research investigates the addition of a thin layer of wider band gap Cd1-xMgxTe (CMT) to achieve a CdTe ER structure. First, a novel co-sublimation process was developed for deposition of Cd1-xMgxTe thin films that demonstrates excellent experimental capabilities, commercial viability, and improved alloy control over other techniques. Next, the effects of processing on material properties of CMT deposition onto CdS/CdTe structures were investigated. It was discovered that substrate temperature during CMT deposition is a critical parameter for achieving uniform CMT film coverage on polycrystalline CdTe. Furthermore, CMT film growth was found to be epitaxial on CdTe where the CMT films retain the same microstructural features as the underlying CdTe grains. Despite film uniformity, significant Mg loss from the CMT film, oxide formation, and a reduction of the optical band gap was found after CdCl2-based passivation treatments. Preliminary process optimization found that band gap degradation can be minimized by utilizing MgCl2 in addition to CdCl2 as a treatment source material. Finally, development of CdS/CdTe/Cd1-xMgxTe electron reflector devices demonstrated a barrier behavior at high voltage bias and improved voltage when CdTe thickness is held below 1 μm. Additional electro-optical characterization and device modeling was used to understand the source of this device behavior. The results suggest the CdTe/Cd1-xMgxTe interface is likely free of detrimental electronic defects and the barrier behavior comes from a larger than expected valence band offset for the material system. Finally, future work to improve ER device performance is suggested

Dispersion and decay of collective modes in neutron star cores

We calculate the frequencies of collective modes of neutrons, protons and electrons in the outer core of neutron stars. The neutrons and protons are treated in a hydrodynamic approximation and the electrons are regarded as collisionless. The coupling of the nucleons to the electrons leads to Landau damping of the collective modes and to significant dispersion of the low-lying modes. We investigate the sensitivity of the mode frequencies to the strength of entrainment between neutrons and protons, which is not well characterized. The contribution of collective modes to the thermal conductivity is evaluated.Comment: 10 pages, 4 figure

Synthesis, Structure, and Magnetic Properties of an Al2O3/Ge-p/Al2O3/Co Thin-Film System

Abstract—Structural and magnetic measurements are made of an Al2O3/Ge-p/Al2O3/Co thin-film system. The structure is synthesized via ion-plasma deposition and can be used as a tunnel heterostructure. The dependences of the magnetic properties of cobalt on the rate of its deposition and the rates of deposition of preceding layers are established

Parametric localized modes in quadratic nonlinear photonic structures

We analyze two-color spatially localized modes formed by parametrically coupled fundamental and second-harmonic fields excited at quadratic (or chi-2) nonlinear interfaces embedded into a linear layered structure --- a quasi-one-dimensional quadratic nonlinear photonic crystal. For a periodic lattice of nonlinear interfaces, we derive an effective discrete model for the amplitudes of the fundamental and second-harmonic waves at the interfaces (the so-called discrete chi-2 equations), and find, numerically and analytically, the spatially localized solutions --- discrete gap solitons. For a single nonlinear interface in a linear superlattice, we study the properties of two-color localized modes, and describe both similarities and differences with quadratic solitons in homogeneous media.Comment: 9 pages, 8 figure

Decoherence of Bose-Einstein condensates in microtraps

We discuss the impact of thermally excited near fields on the coherent expansion of a condensate in a miniaturized electromagnetic trap. Monte Carlo simulations are compared with a kinetic two-component theory and indicate that atom interactions can slow down decoherence. This is explained by a simple theory in terms of the condensate dynamic structure factor.Comment: 5 pages, 4 figure

Higher-order nonlinear modes and bifurcation phenomena due to degenerate parametric four-wave mixing

We demonstrate that weak parametric interaction of a fundamental beam with its third harmonic field in Kerr media gives rise to a rich variety of families of non-fundamental (multi-humped) solitary waves. Making a comprehensive comparison between bifurcation phenomena for these families in bulk media and planar waveguides, we discover two novel types of soliton bifurcations and other interesting findings. The later includes (i) multi-humped solitary waves without even or odd symmetry and (ii) multi-humped solitary waves with large separation between their humps which, however, may not be viewed as bound states of several distinct one-humped solitons.Comment: 9 pages, 17 figures, submitted to Phys. Rev.

ВЗАИМОСВЯЗЬ МАРКЕРОВ АПОПТОЗА (P53, BCL-2, BAX) С КЛИНИКО-МОРФОЛОГИЧЕСКИМИ ПАРАМЕТРАМИ И ВЫЖИВАЕМОСТЬЮ ПРИ НЕМЕЛКОКЛЕТОЧНОМ РАКЕ ЛЕГКОГО

The purpose of the study was to analyze the relationship between expression of the р53, bcl-2 and bax genes and clinical-morphological parameters and survival in patients with non-small cell lung cancer (NSCLC). Expression of bcl-2 and р53 was found to be higher in patients with squamous cell carcinoma, bax expression was higher in patients with adenocarcinoma and bcl-2 level was higher in patients with stage I NSCLC and in patients having no lymph node metastases. Survival of patients with NSCLC depended on the expression of p53, bcl-2 and depended no on the bax expression. Survival rates were increased in bcl-2 expression and decreased in p63 expression. Survival rate of patients with NSCLC was higher in –p53/+bcl-2 and –p53/+bcl-2/–bax immune phenotypes and lower in +p53/+bax and +p53/–bcl-2/+bax immune phenotypes. The unifactor regression analysis showed that bcl-2 and р53 were prognostic factors. The multifactor regression analysis revealed no relationship between bcl-2, р53, bax and prognosis of NSCLC.Исследована экспрессия р53, bcl-2 и bax во взаимосвязи с клинико-морфологическими параметрами и выживаемостью при немелкоклеточном раке легкого (НМКРЛ). Отмечается взаимосвязь экспрессии р53, bcl-2 и bax с клинико-морфологическими параметрами НМКРЛ: экспрессия bcl-2 и р53 выше при плоскоклеточном раке, экспрессия bax выше при аденокарциноме, экспрессия bcl-2 выше при отсутствии лимфогенных метастазов и при НМКРЛ I стадии. Показатели выживаемости больных НМКРЛ зависят от экспрессии p53, bcl-2 и не зависят от экспрессии bax, показатели выживаемости повышаются при экспрессии bcl-2 и снижаются при экспрессии p53. Уровень выживаемости больных НМКРЛ взаимосвязан с взаимным содержанием bcl-2, р53 и bax, он выше при иммунофенотипах –p53/+bcl-2 и –p53/+bcl-2/–bax и ниже при иммунофенотипах +p53/+bax и +p53/–bcl-2/+bax. При однофакторном регрессионном анализе bcl-2 и р53 являлись факторами прогноза. Многофакторный регрессионный анализ не выявил взаимосвязи bcl-2, р53 и bax с прогнозом НМКРЛ