MnAs dots grown on GaN(0001)-(1x1) surface

MnAs has been grown by means of MBE on the GaN(0001)-(1x1) surface. Two options of initiating the crystal growth were applied: (a) a regular MBE procedure (manganese and arsenic were delivered simultaneously) and (b) subsequent deposition of manganese and arsenic layers. It was shown that spontaneous formation of MnAs dots with the surface density of 1$\cdot 10^{11}$ cm$^{-2}$ and $2.5\cdot 10^{11}$ cm$^{-2}$, respectively (as observed by AFM), occurred for the layer thickness higher than 5 ML. Electronic structure of the MnAs/GaN systems was studied by resonant photoemission spectroscopy. That led to determination of the Mn 3d - related contribution to the total density of states (DOS) distribution of MnAs. It has been proven that the electronic structures of the MnAs dots grown by the two procedures differ markedly. One corresponds to metallic, ferromagnetic NiAs-type MnAs, the other is similar to that reported for half-metallic zinc-blende MnAs. Both system behave superparamagnetically (as revealed by magnetization measurements), but with both the blocking temperatures and the intra-dot Curie temperatures substantially different. The intra-dot Curie temperature is about 260 K for the former system while markedly higher than room temperature for the latter one. Relations between growth process, electronic structure and other properties of the studied systems are discussed. Possible mechanisms of half-metallic MnAs formation on GaN are considered.Comment: 20+ pages, 8 figure

Zinc oxide for electronic, photovoltaic and optoelectronic applications

We demonstrate that the atomic layer deposition (ALD) technique has large potential to be widely used in a production of ZnO films for applications in electronic, photovoltaic (PV) and optoelectronic devices. Low growth temperature makes the ALD-grown ZnO films suitable for construction of various semiconductor/organic material hybrid structures. This opens possibilities of construction of novel devices based on very cheap organic materials. This includes organic light emitting diodes and PV cells of the third generation, as discussed in the present work

Structure Dependent Conductivity of Ultrathin ZnO Films

Zinc oxide lms dedicated for hybrid organic/inorganic devices have been studied. The lms were grown at low temperature (100 • C, 130 • C and 200 • C) required for deposition on thermally unstable organic substrates. ZnO layers were obtained in atomic layer deposition processes with very short purging times in order to shift a structure of the lms from polycrystalline towards amorphous one. The correlation between atomic layer deposition growth parameters, a structural quality and electrical properties of ZnO lms was determined

ZnO as a conductive layer prepared by ALD for solar cells based on n-CdS/n-CdTe/p-Cu₁.₈S heterostructure

ZnO films with high conductivity are obtained by atomic layer deposition for application in solar cells based on n CdS/ n CdTe / p Cu₁.₈S heterostructure. The parameters of solar cells with ZnO electrode are calculated from light and dark currentvoltage characteristics and compared with those obtained for structures with Mo contact. The advantages of ZnO electrode are discussed

Quasi Fermi Levels in Semiconductor Photovoltaic Heterojunction

The photovoltaic heterojunction elements are build of two different semiconductors of n and p type. Under cell illumination the same density of n and p carriers are created in each generation point but it leads to the remarkably higher increase of relative concentration for minority than for majority carriers. It is causing bigger energy change of the quasi Fermi level of minority than of majority carriers. The minority carriers decide of the value of generated photovoltage while the majority carriers contribution to it, in most cases can be neglected. Measured change of the generated open circuit photovoltage versus illumination light intensity allows to estimate corresponding to it increase of the minority carrier concentration. These allows as well to scan the part of the forbidden gap region by the minority carriers quasi Fermi level and in a case of impurity or defect levels located in forbidden gap it can influence on the continuous dependence of generated photovoltage versus light intensity e.g. for pinning of the Fermi level. To create efficient photovoltaic heterojunction it will need to study electronic properties of the used impurities and their proper distribution in the region of junction

ACTA PHYSICA POLONICA A INFRARED ABSORPTION STUDY OF THERMALLY GENERATED SHALLOW DONOR CENTERS IN CZOCHRALSKI SILICON

A comparative study of thermally generated donor centers in boron and aluminum doped Czochralski silicon was performed by means of Fourier transform infrared technique. A detailed study revealed presence of donor centers belonging to the well-known series of thermal donors and shallow thermal donors. For both types of material the same centers could be observed while considerable differences in their generation kinetics occurred. In addition to the previously identified species also new ones could be observed. One of them, with single ionization level at approximately 39.5 meV, was found to exhibit clear dependence of its concentration upon illumination of the sample during cooling from room temperature to liquid He temperature

Infrared Absorption Study of Thermally Generated Shallow Donor Centers in Czochralski Silicon

A comparative study of thermally generated donor centers in boron and aluminum doped Czochralski silicon was performed by means of Fourier transform infrared technique. A detailed study revealed presence of donor centers belonging to the well-known series of thermal donors and shallow thermal donors. For both types of material the same centers could be observed while considerable differences in their generation kinetics occurred. In addition to the previously identified species also new ones could be observed. One of them, with single ionization level at approximately 39.5 meV, was found to exhibit clear dependence of its concentration upon illumination of the sample during cooling from room temperature to liquid He temperature

Thermal Donor Generation in Boron- and Aluminium-Doped Czochralski Silicon

Generation of thermal donor centres in oxygen-rich silicon doped with boron and aluminium acceptors has been studied with the FTIR technique. It has been found that upon annealing 470°C two kinds of absorption series were generated. One of them belonged to the well-known first ionization level of silicon thermal (double) donors (TD's): TD°/TD$\text{}^{+}$ . The second series was identified with the so-called shallow thermal donors (STD's). The generation kinetics of the two series was followed for both kinds of acceptor doping and significant differences has been found. The results of the FTIR investigations were further compared with the magnetic resonance findings allowing for their mutual correlation and more general conclusions