Photoluminescence of GaAs/AlGaAs quantum wells

In this thesis is studied the influence of uniaxial deformation of GaAs/AlGaAs quantum well structures to photoluminescence. Uniaxial deformation was applied along [110] and polarization ratio of photoluminescence at T = 77 K and 300 K was measured. Also the physical origin of photoluminescence lines in spectrum was determined and the energy band splitting value between states of heavy and light holes was estimated. It was found that the dependencies of polarization ratio on uniaxial deformation for bulk GaAs and GaAs/AlGaAs are different. Two observed lines in photoluminescence spectrum are induced by free electron recombination to energy sublevels of valence band corresponding to heavy and light holes. Those sublevels are splited due to the combination of size quantization and external pressure. The quantum splitting energy value was estimated. Also was shown a method, which allows to determine the energy splitting value of sublevels at room temperature and at comparatively low uniaxial deformation, when the other method for determining of the splitting becomes impossible.

Magnetic and transport properties of InGaAs quantum wells with Mn

In the present work structural, magnetic and transport properties of InGaAs quantum wells (QW) prepared by MBE with an remote Mn layer are investigated. By means of high-resolution X-ray diffractometry the structure of the samples is analyzed. It is shown that Mn ions penetrate into the QW. Influence of the thickness of GaAs spacer and annealing at 286 ºС on the properties of the system is shown. It is shown that annealing of the samples led to Mn activation and narrowing of the Mn layer. Substantial role of 2D holes in ferromagnetic ordering in Mn layer is shown. Evidence for that is observation of maximum at 25 – 55 K on the resistivity temperature dependence. Position of maximum, which is used for quantitative assessment of the Curie temperature, correlates with calculations of the Curie temperature for structures with indirect interaction via 2D holes’ channel. Dependence of the Curie temperature on the spacer thickness shows, that creation of applicable spintronic devices needs high-precision equipment to manufacture extra fine structures. The magnetotransport measurements show that charge carrier mobility is very low. This leads to deficiency of the anomalous Hall effect. At the same time, magnetic field dependences of the magnetization at different temperatures demonstrate that systems are ferromagnetically ordered. These facts, most probably, give evidence of presence of the ferromagnetic MnAs clusters.

Investigations of GaAs based heterostructures for spintronics

In the present work are reported investigations of structural, magnetic and electronic properties of GaAs/Ga1-xInxAs/GaAs quantum wells (QW) having a 0.5 - 1.8 monolayer thick Mn layer, separated from the quantum well by a 3 nm thick spacer. The structure of the samples is analyzed in details by photoluminescence and high-resolution X-ray difractometry and reflectometry, confirming that Mn atoms are practically absent from the QW. Transport properties and crystal structure are analyzed for the first time for this type of QW structures with so high mobility. Observedconductivity and the Hall effect in quantizing magnetic fields in wide temperature range, defined by transport of holes in the quantum well, demonstrate properties inherent to ferromagnetic systems with spin polarization of charge carriersin the QW. Investigation of the Shubnikov ¿ de Haas and the Hall effects gave the possibility to estimate the energy band parameters such as cyclotron mass andFermi level and calculate concentrations and mobilities of holes and show the high-quality of structures. Magnetic ordering is confirmed by the existence of the anomalous Hall effect.

Transforming Bodies, Wandering Desires. Intra-actions of Gender and Sexuality in Non-heterosexual Transgender Embodiment

Pro gradu -tutkielmani käsittelee sukupuolen ja seksuaalisuuden keskinäisiä intraaktiivisia vuorovaikutussuhteita elettyjen, ei-heteroseksuaalisten transsukupuolisten ruumiiden kokemuksissa. Tutkielmani haastaa sukupuolen ja seksuaalisuuden pysyvyyden käsityksiä sekä niihin liittyviä yhteiskunnallisia normeja kuvaten tapoja, joilla seksuaalisuuden ja sukupuolen kokeminen ja käytännöt liikkuvat, kehittyvät ja vuorovaikuttavat eletyissä transsukupuolisuuden ruumiillistumissa. Haastattelen kuutta suomalaista, syntymässä naiseksi määriteltyä transsukupuolista henkilöä liittyen heidän kokemuksiinsa sukupuolesta, seksuaalisuudesta ja näiden muutoksista heidän tähänastisen elämänsä aikana. Tarkastelen nauhoitettuja ja litteroituja haastattelutekstejä transtutkimusta, queer-teoriaa ja feminististä uusmaterialistista filosofiaa yhdistävän teoreettisen kehyksen kautta keskittyen siihen, miten sukupuoli ja seksuaalisuus vaikuttavat toistensa kehitykseen, muutokseen ja materialisoitumiseen eri elämänvaiheissa ja tilanteissa. Erityisen tärkeiksi teoreettisiksi vaikuttajiksi tutkielmassani muodostuvat Judith Butlerin Gender Trouble (2006 [1990]) -teoksessaan hahmottelema performatiivisen sukupuolen teoria, Sara Ahmedin analyysi teoksessa Queer Phenomenology. Orientations, Objects, Others (2006) ja Karen Baradin teoksessa Meeting the Universe Halfway. Quantum Physics and the Entanglement of Matter and Meaning (2007) teoretisoima toimijuudellinen realismi. Päästäkseni kiinni sukupuolen ja seksuaalisuuden yhtymäkohtiin erittelen ensin niitä ominaisuuksia ja kokemuksia, jotka näyttäytyvät haastatteluteksteissäni oleellisina seksuaalisuuden ja sukupuolen kannalta. Tarkastelen seksuaalisuutta suuntautumisen, halun ja seksuaalisten käytäntöjen näkökulmasta: vaikka nämä seksuaalisuuden aspektit ovat kiinteästi kytköksissä toisiinsa, niitä ei voi kokonaan palauttaa toisiinsa. Sukupuolta käsittelen performatiivisuuden näkökulmasta painottaen transsukupuolisiin ruumiisiin ja niiden materiaalisuuteen liittyviä erityispiirteitä. Sukupuolen ja seksuaalisuuden suhteita toisiinsa tarkastelen sekä sellaisissa tilanteissa, joissa niitä on vaikea erottaa toisistaan, että sellaisissa, joissa niiden voidaan nähdä tuottavan toinentoisiaan. Tutkielmallani on etnografisia, filosofisia ja poliittisia ulottuvuuksia. Yhtäältä tahdon kuvata ja analysoida elettyjä transsukupuolisia kokemuksia ja tuottaa tietoa vähän tutkitun ihmisryhmän todellisuudesta. Toisaalta osallistun sukupuolifilosofiseen keskusteluun ruumiillisuudesta ja sukupuolen ja seksuaalisuuden olemuksesta. Lähestyn tutkimusprosessiani niin sanotusta transgender standpoint -näkökulmasta; kirjoitan transsukupuolisena ruumiina, transsukupuolisia ruumiita koskien, pyrkimyksenäni edistää elävien transsukupuolisten ruumiiden asemaa, toimijuutta ja näkyvyyttä yhteiskunnassa.

Covariant Phase Observables in Quantum Mechanics

The aim of this thesis is to present a solution to the quantum phase problem of the single-mode optical field. The solution is based on the use of phase shift covariant normalized positive operator measures. These measures describe realistic direct coherent state phase measurements such as the phase measurement schemes based on eight-port homodyne detection or heterodyne detection. The structure of covariant operator measures and, more generally, covariant sesquilinear form measures is analyzed in this work. Four different characterizations for phase shift covariant normalized positive operator measures are presented. The canonical covariant operator measure is definded and its properties are studied. Finally, some other suggested phase theories are introduced to investigate their connections to the covariant sesquilinear form measures.

Intra-specific variation in cell wall constituents of needle age classes of Pinus sylvestris in relation to soil fertility status in Southwest England

Abstract

Quantum transport phenomena and shallow impurity states in CdSb

This work is dedicated to investigation of the energy spectrum of one of the most anisotropic narrow-gap semiconductors, CdSb. At the beginning of the present studies even the model of its energy band structure was not clear. Measurements of galvanomagnetic effects in wide temperature range (1.6 - 300 K) and in magnetic fields up to 30 T were chosen for clarifying of the energy spectrum in the intentionally undoped CdSb single crystals and doped with shallow impurities (In, Ag). Detection of the Shubnikov - de Haas oscillations allowed estimating the fundamental energy spectrum parameters. The shapes of the Fermi surfaces of electrons (sphere) and holes (ellipsoid), the number of the equivalent extremums for valence band (2) and their positions in the Brillouin zone were determined for the first time in this work. Also anisotropy coefficients, components of the tensor of effective masses of carriers, effective masses of density of states, nonparabolicity of the conduction and valence bands, g-factor and its anisotropy for n- and p-CdSb were estimated for the first time during these studies. All the results obtained are compared with the cyclotron resonance data and the corresponding theoretical calculations for p-CdSb. This is basic information for the analyses of the complex transport properties of CdSb and for working out the energy spectrum model of the shallow energy levels of defects and impurities in this semiconductor. It was found out existence of different mechanisms of hopping conductivity in the presence of metal - insulator transition induced by magnetic field in n- and p-CdSb. Quite unusual feature opened in CdSb is that different types of hopping conductivity may take place in the same crystal depending on temperature, magnetic field or even orientation of crystal in magnetic field. Transport properties of undoped p-CdSb samples show that the anisotropy of the resistivity in weak and strong magnetic fields is determined completely by the anisotropy of the effective mass of the holes. Temperature and magnetic field dependence of the Hall coefficient and magnetoresistance is attributed to presence of two groups of holes with different concentrations and mobilities. The analysis demonstrates that below Tcr ~ 20 K and down to ~ 6 - 7 K the low-mobile carriers are itinerant holes with energy E2 ≈ 6 meV. The high-mobile carriers, at all temperatures T < Tcr, are holes activated thermally from a deeper acceptor band to itinerant states of a shallower acceptor band with energy E1 ≈ 3 meV. Analysis of temperature dependences of mobilities confirms the existence of the heavy-hole band or a non-equivalent maximum and two equivalent maxima of the light-hole valence band. Galvanomagnetic effects in n-CdSb reveal the existence of two groups of carriers. These are the electrons of a single minimum in isotropic conduction band and the itinerant electrons of the narrow impurity band, having at low temperatures the energies above the bottom of the conduction band. It is found that above this impurity band exists second impurity band of only localized states and the energy of both impurity bands depend on temperature so that they sink into the band gap when temperature is increased. The bands are splitted by the spin, and in strong magnetic fields the energy difference between them decreases and redistribution of the electrons between the two impurity bands takes place. Mobility of the conduction band carriers demonstrates that scattering in n-CdSb at low temperatures is strongly anisotropic. This is because of domination from scattering on the neutral impurity centers and increasing of the contribution to mobility from scattering by acoustic phonons when temperature increases. Metallic conductivity in zero or weak magnetic field is changed to activated conductivity with increasing of magnetic field. This exhibits a metal-insulator transition (MIT) induced by the magnetic field due to shift of the Fermi level from the interval of extended states to that of the localized states of the electron spectrum near the edge of the conduction band. The Mott variablerange hopping conductivity is observed in the low- and high-field intervals on the insulating side of the MIT. The results yield information about the density of states, the localization radius of the resonant impurity band with completely localized states and about the donor band. In high magnetic fields this band is separated from the conduction band and lies below the resonant impurity bands.