Wyniki wyszukiwania - Biblioteka Nauki

1

First X-Ray Evidence of Heterogeneous Impurity Correlations in Very Highly Doped n-GaAs

100%

Słupiński T. , Zielińska-Rohozińska E.

|

nr 5

971-975

EN

Measurements of X-ray scattering from very highly doped GaAs:Te single crystals as a function of doping level and thermal treatment (annealing temperature) are reported. Reversible diffuse X-ray scattering occurs after sample annealing below a certain temperature. Presented results indicate an inhomogeneous arising of impurity-impurity correlations in GaAs:Te solid solution. Observed features of diffuse X-ray scattering in reciprocal space can be well understood within Krivoglaz theory of scattering due to spatial fluctuations of solute atoms pair correlation function and related lattice deformations. Good coincidence of diffuse X-ray scattering with the free electron concentration changes caused by an annealing is reported. Free electron concentration drop accompanying impurity correlation strongly suggests a certain form of impurity bonding.

2

Free Carrier Scattering in Metallic n-GaAs in the Presence of Static Lattice Distortions Due to a Partial Chemical Order of Impurities

80%

Słupiński T. , Molas M. , Papierska J.

Acta Physica Polonica A

|

2009

|

tom 116

|

nr 5

979-982

EN

Simple electric transport versus T = 20-400 K in metallic n-GaAs annealed single crystals with Te impurity concentration ∿(0.4-1.7) × 10^{19} cm^{-3}, which is above the equilibrium doping limit, is reported and compared with modern theory of electron mobility in degenerated n-GaAs by Szmyd, Hanna, Majerfeld. An overcome of the equilibrium doping limit in annealed n-GaAs is manifested by a lowered electrical activation of Te donors and by an onset of ≈ 0.1-1 μm regions of local strain in the crystal lattice known from high resolution X-ray studies. These preliminary results of transport show that the electron mobility μ(T) measured for n-GaAs with local strains is not consistent with predictions of Szmyd et al. model for any degree of compensation assumed. This surprising result indicates that electric transport in materials above the equilibrium doping limit is not well understood assuming the scattering by ionized impurities. The nature of defects responsible for an observed strong reduction of free carrier concentration (here ≈ 80%) in annealed heavily doped n-GaAs seems not to be related with electrical compensation. We point here at the possible role of effects of free carrier scattering due to static lattice distortions (local strains) related to a chemical aggregation of impurity atoms. We also notice that transport in metallic n-GaAs with local strains shows features similar to a weak localization σ_{xx} ∝ log T.

3

On the Pinning of the Fermi Level by Germanium A_{1}^{0/+} Deep Donor State in GaAs Codoped with Ge and Te

80%

Słupiński T. , Nowak G. , Przybytek J. , Stępniewski R.

|

nr 4

807-811

EN

We present the possibility of GaAs:Ge,Te crystals growth from the melt (liquid encapsulated Czochralski method) with partially occupied, at ambient pressure, the A_{1} localized electronic state of Ge_{Ga} impurity. In as-grown crystals the amphotericity of Ge and creation of defects (deep acceptor complexes, precipitates etc.) during cooling after growth limit the free electron concentration below the value necessary to populate the A_{1}^{0/+} level. Special annealing of the samples, which enlarges the free electron concentration, was used. The occupation of A_{1}^{0/+} level, at ambient pressure, was observed by pressure dependent Hall effect measurements.

4

Deep Level Transient Spectroscopy Measurements of an Acceptor-like State of Metastable EL2 in GaAs and GaAsP

80%

Babiński A. , Wysmołek A. , Słupiński T.

|

nr 4

673-676

EN

The results of deep level transient spectroscopy measurements of an acceptor-like state of metastable EL2 in GaAs and GaAs_{0.97}P_{0.03} are presented. The uniaxial stress in GaAs was applied in order to find the deep leve1 transient spectroscopy signal. It was found that the deep level transient spectroscopy signal depended on the stress direction. In GaAs_{0.97}P_{0.03} the deep level transient spectroscopy peak related to an acceptor-like state of metastable EL2 was observed without external stress.

5

Hole Transport in Impurity Band and Valence Bands Studied in Moderately Doped GaAs:Mn Single Crystals

80%

Słupiński T. , Caban J. , Moskalik K.

|

nr 2

325-330

EN

We report on a simple experiment on temperature-dependent Hall effect measurements in GaMnAs single crystalline samples with Mn composition estimated at 0.05-0.3 at.% which is slightly below the onset of ferromagnetism. Impurity band transport is visible for Mn compositions of ≈0.3 at.% as a clear metallic behaviour. The results show an interesting situation that the metal-insulator transition in GaAs:Mn occurs within the impurity band which is separated from the valence bands for Mn concentrations studied here. We also discuss on the equilibrium high temperature solubility limit of Mn in GaAs, unknown precisely in the literature.

6

Studies of Magnetoresistance in GaAs:Te Crystals with Structural Disorder at Doping Limit

80%

Tarkowski T. , Słupiński T. , Karpierz K.

|

nr 5

726-728

EN

Transverse magnetoresistance was studied in monocrystalline GaAs:Te doped above the equilibrium doping limit and annealed to partially deactivate donor impurities. It is shown that in a sample with partial deactivation of Te impurities, which exhibits structural fluctuations in microscale, both strong positive and some negative magnetoresistances arise, which are difficult to understand within the relaxation time approximation in degenerated homogeneous semiconductor. It is discussed that a consideration of the role of spatial fluctuations (in carrier concentration, conductivity, etc.), e.g. as proposed by Herring, allows for an understanding of positive component of magnetoresistance observed in the sample with a distinct microscopic structural disorder. With the aim to better understand the transport in GaAs:Te, a model material doped above the doping limit, we discuss both positive and negative components of measured magnetoresistance.

7

Highly Compensated GaAs Crystal Obtained by Molecular CO Doping

61%

Bożek R. , Korona K. , Nowak G. , Wasik D. , Słupiński T. , Kaczor P.

|

nr 4

669-672

EN

GaAs:C crystal was grown by liquid encapsulated Czochralski technique with large partial pressure of CO in ambient atmosphere p_{CO}/p_{tot} = 0.2 and investigated using near and infrared absorption, photoluminescence, photoconductivity, photo-induced current transient spectroscopy and photo-Hall measurements. High resistivity of the crystal was found in electrical measurements (10^{7} Ω cm, the Fermi level at 0.67 eV below conduction band at 300 K). Local vibrational mode revealed increased concentration of carbon acceptor and presence of oxygen related complexes. Photoluminescence spectra were dominated by two bands with peak energies at 1.49 eV and 0.8 eV. The near band gap emission shifts with excitation intensity up to 4 meV/decade. In photocurrent spectrum a strong photoionization band with E = 0.55 eV is observed.

8

MBE Growth of CdTe/ZnTe Quantum Dots with Single Mn Ions

51%

Gietka K. , Kobak J. , Rousset J. , Janik E. , Słupiński T. , Kossacki P. , Golnik A. , Pacuski W.

|

nr 6

1056-1058

EN

We report MBE growth and properties of samples with self assembled quantum dots with single manganese ions and low density of quantum dots. Manganese concentration was calibrated using magneto-reflectivity measurements and the giant Zeeman effect in (Cd,Mn)Te and (Zn,Mn)Te layers. Successful incorporation of Mn in the CdTe/ZnTe quantum dots was confirmed using micro-photoluminescence measurements: single manganese ion in quantum dot manifests in sixfold splitting of exciton emission lines due to s, p-d exchange interaction.