Spectroscopic Studies of III-V Semiconductor Materials for Improved Devices

Defects in semiconductor crystals and at their interfaces usually impair the properties and the performance of devices. These defects include, for example, vacancies (i.e., missing crystal atoms), interstitials (i.e., extra atoms between the host crystal sites), and impurities such as oxygen atoms. The defects can decrease (i) the rate of the radiative electron transition from the conduction band to the valence band, (ii) the amount of charge carriers, and (iii) the mobility of the electrons in the conduction band. It is a common situation that the presence of crystal defects can be readily concluded as a decrease in the luminescence intensity or in the current flow for example. However, the identification of the harmful defects is not straightforward at all because it is challenging to characterize local defects with atomic resolution and identification. Such atomic-scale knowledge is however essential to find methods for reducing the amount of defects in energy-efficient semiconductor devices. The defects formed in thin interface layers of semiconductors are particularly difficult to characterize due to their buried and amorphous structures. Characterization methods which are sensitive to defects often require well-defined samples with long range order. Photoelectron spectroscopy (PES) combined with photoluminescence (PL) or electrical measurements is a potential approach to elucidate the structure and defects of the interface. It is essential to combine the PES with complementary measurements of similar samples to relate the PES changes to changes in the interface defect density. Understanding of the nature of defects related to III-V materials is relevant to developing for example field-effect transistors which include a III-V channel, but research is still far from complete. In this thesis, PES measurements are utilized in studies of various III-V compound semiconductor materials. PES is combined with photoluminescence measurements to study the SiO2/GaAs, SiNx/GaAs and BaO/GaAs interfaces. Also the formation of novel materials InN and photoluminescent GaAs nanoparticles are studied. Finally, the formation of Ga interstitial defects in GaAsN is elucidated by combining calculational results with PES measurements.Kidevirheet puolijohdekiteissä ja rajapinnoissa yleensä heikentävät laitteiden ominaisuuksia. Kidevirhe voi olla esimerkiksi vakanssi (puuttuva atomi), välisija-atomi (ylimääräinen atomi hilapaikkojen välissä) ja epäpuhtausatomi. Kidevirheet voivat alentaa (i) säteilytehoa, (ii) varauksen kuljettajien määrää ja (iii) elektronien nopeutta johtovyöllä. On yleistä, että kidevirheiden olemassaolo voidaan päätellä esimerkiksi heikentyneestä luminesenssistä tai virrankulusta. Ei kuitenkaan ole yksinkertaista tunnistaa minkälaatuisista virheistä on kyse, sillä on haastavaa karakterisoida paikallisia virheitä atomitarkkuudella. Sellainen tieto on kuitenkin välttämätöntä, että voidaan löytää menetelmiä kidevirheiden vähentämiseksi. Kidevirheet, joita muodostuu ohuissa rajapintakerroksissa, ovat erityisen haastavia tunnistaa, sillä ne sijatsevat näytteen pinnan alla ja ovat amorfisia. Karakterisointimenetelmät, jotka ovat hyödyllisiä kidevirheiden tutkimisessa, usein vaativat hyvin järjestäytyneen näytteen. Fotoelektronispektroskopia yhdistettynä fotoluminesenssimittaukseen tai sähköisiin mittauksiin on potentiaalinen lähestymistapa rajapinnan kidevirheiden tunnistamiseen. On välttämätöntä yhdistää fotoelektronispektroskopiamittaus muihin mittausmenetelmiin, jotta muutokset spektrissä voidaan ymmärtää paremmin. Parempi ymmärrys III-V kiteisiin liittyvistä kidevirheistä on välttämätöntä III-V kanavan sisältävien transistorien kehitystyön kannalta ja paljon on vielä opittavaa. Tässä väitöskirjatutkimuksessa fotoelektronispektroskopiaa hyödynnettiin III-V yhdistepuolijohteiden tutkimisessa. Se yhdistettiin fotolumisenssimittauksiin, kun tutkittiin SiO2/GaAs, SiNx/GaAs ja BaO/GaAs rajapintoja. Myös InN:n ja valoa tuottavien GaAs nanopartikkelien valmistamista tutkittiin. Lopuksi esitellään laskennallisia ja kokeellisia tuloksia Ga välisija-atomien muodostumisesta GaAsN:ssä.Siirretty Doriast

Adoptive cancer immunotherapy using DNA-demethylated T helper cells as antigen-presenting cells

A critical determinant of tumor eradication by adoptive immunotherapy is the tumor associated antigen recognized by cytotoxic T lymphocytes. Here the authors generate ex vivo autologous cytotoxic T lymphocytes by exposure to antigens induced by DNA demethylation and report the results of a phase 1 trial of 25 patients with recurrent glioblastoma multiforme with tumor regression in three patients

The Changing Landscape for Stroke\ua0Prevention in AF: Findings From the GLORIA-AF Registry Phase 2

Background GLORIA-AF (Global Registry on Long-Term Oral Antithrombotic Treatment in Patients with Atrial Fibrillation) is a prospective, global registry program describing antithrombotic treatment patterns in patients with newly diagnosed nonvalvular atrial fibrillation at risk of stroke. Phase 2 began when dabigatran, the first non\u2013vitamin K antagonist oral anticoagulant (NOAC), became available. Objectives This study sought to describe phase 2 baseline data and compare these with the pre-NOAC era collected during phase 1. Methods During phase 2, 15,641 consenting patients were enrolled (November 2011 to December 2014); 15,092 were eligible. This pre-specified cross-sectional analysis describes eligible patients\u2019 baseline characteristics. Atrial fibrillation disease characteristics, medical outcomes, and concomitant diseases and medications were collected. Data were analyzed using descriptive statistics. Results Of the total patients, 45.5% were female; median age was 71 (interquartile range: 64, 78) years. Patients were from Europe (47.1%), North America (22.5%), Asia (20.3%), Latin America (6.0%), and the Middle East/Africa (4.0%). Most had high stroke risk (CHA2DS2-VASc [Congestive heart failure, Hypertension, Age  6575 years, Diabetes mellitus, previous Stroke, Vascular disease, Age 65 to 74 years, Sex category] score  652; 86.1%); 13.9% had moderate risk (CHA2DS2-VASc = 1). Overall, 79.9% received oral anticoagulants, of whom 47.6% received NOAC and 32.3% vitamin K antagonists (VKA); 12.1% received antiplatelet agents; 7.8% received no antithrombotic treatment. For comparison, the proportion of phase 1 patients (of N = 1,063 all eligible) prescribed VKA was 32.8%, acetylsalicylic acid 41.7%, and no therapy 20.2%. In Europe in phase 2, treatment with NOAC was more common than VKA (52.3% and 37.8%, respectively); 6.0% of patients received antiplatelet treatment; and 3.8% received no antithrombotic treatment. In North America, 52.1%, 26.2%, and 14.0% of patients received NOAC, VKA, and antiplatelet drugs, respectively; 7.5% received no antithrombotic treatment. NOAC use was less common in Asia (27.7%), where 27.5% of patients received VKA, 25.0% antiplatelet drugs, and 19.8% no antithrombotic treatment. Conclusions The baseline data from GLORIA-AF phase 2 demonstrate that in newly diagnosed nonvalvular atrial fibrillation patients, NOAC have been highly adopted into practice, becoming more frequently prescribed than VKA in Europe and North America. Worldwide, however, a large proportion of patients remain undertreated, particularly in Asia and North America. (Global Registry on Long-Term Oral Antithrombotic Treatment in Patients With Atrial Fibrillation [GLORIA-AF]; NCT01468701