Ewa Papis - Academia.edu (original) (raw)
Papers by Ewa Papis
Metal Deposition
(100) GaAs surface treatment prior to contact
Optica Applicata, 2009
The effects of HCl-based chemical and Ar + sputter etching treatment on (100) GaAs surface proper... more The effects of HCl-based chemical and Ar + sputter etching treatment on (100) GaAs surface properties with the aim to develop the procedure of surface preparation before metal deposition have been investigated. Variable angle spectroscopic ellipsometry, X-ray photoelectron spectroscopy, atomic force microscopy and photoluminescence have been used to study the surface characterization. We show that combining chemical etching in 5% HCl with Ar + sputter etching gives the best results for surface cleaning prior to metal deposition. The application of this two-step treatment allows to obtain Ni/AuGe/Ni/Au ohmic contact with r c =2 ×10 –6 Ωcm 2 with excellent adhesion and long-term thermal stability.
Optica Applicata, 2009
This paper reports on the results of optimization of ohmic contacts for GaAs/AlGaAs quantum casca... more This paper reports on the results of optimization of ohmic contacts for GaAs/AlGaAs quantum cascade lasers (QCLs). Technological parameters during optimization concerned surface preparation, evaporation method, and thermal treatment. The aim of this research was to obtain low resistance and time stable ohmic contacts. The average specific contact resistance was 6×10–7 Ωcm–2 with record value below 3×10–7 Ωcm–2. It appears that the crucial role in contact formation is played by the in-situ surface pretreatment and thermal processing. Circular transmission line method (CTLM) was applied for electrical characterization of Ni/AuGe/Ni/Au metallization system. Secondary ion mass spectroscopy (SIMS) was used for determination of Au diffusion into semiconductor. The system presented was used in fabrication of pulse operating QCLs. The lasers mounted with diamond heat spreaders on copper block cooled by liquid nitrogen (LN) achieved optical powers over 1 W, threshold current density values o...
Application of Fractional-Derivative-Spectrum Methods for Optical Analyses of Si and GaAs Semiconductors
ECS Meeting Abstracts
not Available.
Acta Physica Polonica Series a
Optical spectra analysis provides a wealth of information on physical properties of various semic... more Optical spectra analysis provides a wealth of information on physical properties of various semiconductor materials. Fractional derivative spectrum technique is especially interesting when the limitations of the standard treatment occur. In this paper we present the fractional derivative spectrum method for analysis of the optical spectra for both Si and GaAs. The significant changes in critical point parameters in each treated Si and GaAs samples in comparison to that before treatment have been observed. Our investigation illustrates that fractional derivative spectrum is a very good technique to extract basic information on relevant physical quantities from the observed optical spectra, and it has the advantages of flexibility, directness, and sensitivity, which give possibility to obtain the Van Hove singularities (critical point parameters) efficiently with one consent.
InGaAsSb/AlGaAsSb heterojunction photodetectors for wavelength 1.8-2.4 μm grown by LPE
ASDAM '98. Conference Proceedings. Second International Conference on Advanced Semiconductor Devices and Microsystems (Cat. No.98EX172), 1998
The paper reports on progress in the technology of GaSb-based mid-infrared photodetectors. Photod... more The paper reports on progress in the technology of GaSb-based mid-infrared photodetectors. Photodiode structures were made by LPE and fabricate as mesa-type diodes by RIE etching in CCl4/H2 plasma. Mesa passivation was carried out in (NH4)2S water solution. Analysis of PD performance through the measurements of current-voltage and spectral responsivity characteristics have shown that (NH4)2S passivated photodiode structures are characterized
Spin alignment of electrons in PbTe/(Pb, Eu) Te nanostructures
We have measured the transport properties of one-dimensional electron gas fabricated of narrow ga... more We have measured the transport properties of one-dimensional electron gas fabricated of narrow gap semiconductor, PbTe. The Zeeman splitting in this material is comparable to the cyclotron energy and may be as large as 4meV/T. Submicron constrictions have been patterned by electron beam lithography of 50nm PbTe quantum well embedded between Bi-doped Pb0.92Eu0.08Te barriers grown by MBE onto 2.5μm Pb0.92Eu0.08Te-undoped
Physical Review B, 1999
Conductance of submicron constrictions of PbTe:Bi was studied up to 8 T and between 4.2 K and 50 ... more Conductance of submicron constrictions of PbTe:Bi was studied up to 8 T and between 4.2 K and 50 mK. The structures were fabricated by electron beam lithography and chemical etching of high-electron mobility films grown by MBE on BaF2. In the moderately strong magnetic fields perpendicular to the current, B ≥ 1 T, the conductance shows accurate quantization in the units of 1e 2 /h as a function of the side-gate voltage. In the absence of the field, a temperature-independent step structure, with an average step height ≈ e 2 /h, is observed. It is suggested that such a quantization may reflect the lifting of the Kramers degeneracy by the exchange interaction among the electrons, effective despite a large dielectric constant of bulk PbTe.
Liquid phase epitaxy of (100) oriented GaInAsSb with high indium concentration in the liquid phase
LPE growth of quaternary Ga1-xInxAsySb1-y compounds on (100) GaSb substrates has been investigate... more LPE growth of quaternary Ga1-xInxAsySb1-y compounds on (100) GaSb substrates has been investigated for high indium content in the melt x1In = 0.40 - 0.41, growth temperatures To = 590 - 594°C and various amount of supersaturation. Epilayers were characterized by means of XRD, AFM, EPXMA and SIMS. It has been found that LPE growth at To approximately 593°C produces
MRS Proceedings, 1996
ABSTRACTSemiconducting antimonide compounds have received increasing attention as the alternative... more ABSTRACTSemiconducting antimonide compounds have received increasing attention as the alternative materials for mid-infrared photonic devices, with a variety of applications such as remote sensing, pollution monitoring, and molecular spectroscopy. For many, if not all these devices it is necessary to pattern antimonide films into mesa or line structures. While plasma etching techniques have played an increasing role in producing such features, little was reported until now on dry etching of GaSb- and AlSb-containing alloys. In this paper we present the results of our recent work towards the development of the technology for GaSb-based ridge wave-guide laser emitting at 2–2.3 μm at RT. Specifically, we discuss the fabrication of double-channel mesa structure in AlxGai1−xAsySb1−y/GaSb (x=0.2–0.5) heterostructure materials by RIE technique. The effects of gas and material composition, rf power, pressure and temperature on etching characteristics were studied with special attention paid...
Superlattices and Microstructures, 1997
We show that conducting edge channels are formed in free standing wires of PbSe/BaF 2 and PbTe/Ba... more We show that conducting edge channels are formed in free standing wires of PbSe/BaF 2 and PbTe/BaF2 as temperature is lowered. The effect results from spatially inhomogeneous strain caused by a difference between the thermal expansion coefficients of the epilayer and the substrate. The presence of the edge channels can explain anomalous mesoscopic effects observed previously in these wires.
Physical Review B, 2005
Conductance quantization was measured in submicron constrictions of PbTe, patterned into narrow,1... more Conductance quantization was measured in submicron constrictions of PbTe, patterned into narrow,12 nm wide quantum wells deposited between Pb0.92Eu0.08Te barriers. Because the quantum confinement imposed by the barriers is much stronger than the lateral one, the one-dimensional electron energy level structure is very similar to that usually met in constrictions of AlGaAs/GaAs heterostructures. However, in contrast to any other system studied so far, we observe precise conductance quantization in 2e 2 /h units, despite of significant amount of charged defects in the vicinity of the constriction. We show that such extraordinary results is a consequence of the paraelectric properties of PbTe, namely, the suppression of long-range tails of the Coulomb potentials due to the huge dielectric constant.
Study of long-term stability of ohmic contacts to GaN
physica status solidi (c), 2004
We report on low-resistivity thermally stable ohmic contacts to p-GaN using ZrN/ZrB2 metallisatio... more We report on low-resistivity thermally stable ohmic contacts to p-GaN using ZrN/ZrB2 metallisation. Transport properties, thermal conductivity and long-term stability of contacts were examined. p-GaN/ZrN/ZrB2 contacts show excellent stability upon aging in air, indicating their suitability for long-term operation at temperatures up to 150 °C.
physica status solidi (c), 2007
physica status solidi (a), 2007
In this paper we present the results of study of thin oxide films: CdO, ZnO and RuSiO 4 used as t... more In this paper we present the results of study of thin oxide films: CdO, ZnO and RuSiO 4 used as transparent ohmic contacts to GaSb/InGaAsSb/AlGaAsSb photodiodes. Thin oxide films with thickness of 50 nm were deposited by magnetron sputtering. CdO and RuSiO 4 were formed in a reactive process in Ar-O 2 atmosphere, from Cd and Ru 1 Si 1 targets, respectively. ZnO films were deposited directly from ZnO target by rf sputtering. We have shown that application of CdO, ZnO and RuSiO 4 transparent films instead of conventional metal-based contacts enables to improve of photodiode properties. As a result, GaSb/ InGaAsSb/AlGaAsSb photodiodes with detectivity D* increased by factor of 2 and reduced by factor of 3 the series resistance were obtained.
Physica E: Low-dimensional Systems and Nanostructures, 2000
We report on a transport study in modulation-doped CdMnTe=CdMgTe : I heterostructures. In this no... more We report on a transport study in modulation-doped CdMnTe=CdMgTe : I heterostructures. In this novel quantum Hall system electron gas the spin splitting is enhanced due to giant s-d exchange energy. A standard temperature and size scaling of Quantum Hall e ect (QHE) is observed under such conditions. Low-temperature saturation of the QHE scaling observed in wires allows one to evaluate the coherence length for the studied structures.
Ballistic transport in PbTe-based nanostructures
Physica E: Low-dimensional Systems and Nanostructures, 2004
ABSTRACT We describe our study of ballistic transport in nanostructures of lead telluride, PbTe. ... more ABSTRACT We describe our study of ballistic transport in nanostructures of lead telluride, PbTe. Submicron devices have been fabricated by electron beam lithography and chemical etching of wide PbTe single quantum wells embedded between Pb0.92Eu0.08Te barriers grown by MBE on BaF2. The electron concentration in the devices was tuned by the gate voltage applied across an interfacial p–n junction. The most important observation was zero-magnetic field conductance quantization (in multiplies of 2e2/h) in narrow constrictions of dimensions comparable to electron mean free path calculated from transport mobility. This indicates considerable relaxation of requirements for quantum ballistic transport in comparison with other materials. We argue that the huge static dielectric constant of PbTe (ε0=1350 at ) leads to suppression of the long-range Coulomb potentials of charged impurities and, thus, provides favorable conditions for the conductance quantization.
Quantum nanostructures of paraelectric PbTe
Physica E: Low-dimensional Systems and Nanostructures, 2006
ABSTRACT This article provides a review of our results on nanostructurization of lead telluride, ... more ABSTRACT This article provides a review of our results on nanostructurization of lead telluride, PbTe. This IV–VI group narrow-gap semiconductor exhibits paraelectric behaviour leading to a huge dielectric constant ε>1000 at helium temperatures. Because the Coulomb potential fluctuations produced by charged defects are strongly suppressed in PbTe nanostructures, one can reach the quantum ballistic regime at significantly relaxed conditions in comparison with other systems. In particular, we observe precise zero-field conductance quantization in the wires made of modulation doped PbTe/PbEuTe quantum wells where the heavily doped layer is separated from the conducting channel only by a 2 nm thick spacer layer. The second important property is the very large Zeeman splitting. It reaches 4 meV/T. Accordingly, significant spin splitting of the conductance plateaux is observed already at fields below 1 T. Therefore, the system is attractive for the construction of local spin filters. We show that the presence of metal layers does not impair the quantum ballistic properties. Furthermore, we have developed a new method of tuning the PbTe nanostructures, using laterally placed metallic electrodes. We have found that this method is more effective than previous schemes using used p–n junctions and it provides better stability of the nanostructures.
PbTe—A new medium for quantum ballistic devices
Physica E: Low-dimensional Systems and Nanostructures, 2006
Conductance quantization was measured in submicron mesa constrictions, patterned into PbTe/Pb0.92... more Conductance quantization was measured in submicron mesa constrictions, patterned into PbTe/Pb0.92Eu0.08Te quantum wells of thickness 12, 25 and 50nm. The main observation is almost unitary transmission of the one-dimensional quantum modes, despite of significant amount of charged defects in the vicinity of the constrictions. Such an extraordinary result is a consequence of the paraelectric properties of PbTe, namely, the suppression
Physica E: Low-dimensional Systems and Nanostructures, 2004
We report on the observation of the Ising quantum Hall ferromagnet with Curie temperature T C as ... more We report on the observation of the Ising quantum Hall ferromagnet with Curie temperature T C as high as 2 K in a modulation-doped (Cd,Mn)Te heterostructure. In this system field-induced crossing of Landau levels occurs due to the giant spin-splitting effect. Magnetoresistance data, collected over a wide range of temperatures, magnetic fields, tilt angles, and electron densities, are discussed taking into account both Coulomb electron-electron interactions and s-d coupling to Mn spin fluctuations. The critical behavior of the resistance ''spikes'' at T ! T C corroborates theoretical suggestions that the ferromagnet is destroyed by domain excitations.
Metal Deposition
(100) GaAs surface treatment prior to contact
Optica Applicata, 2009
The effects of HCl-based chemical and Ar + sputter etching treatment on (100) GaAs surface proper... more The effects of HCl-based chemical and Ar + sputter etching treatment on (100) GaAs surface properties with the aim to develop the procedure of surface preparation before metal deposition have been investigated. Variable angle spectroscopic ellipsometry, X-ray photoelectron spectroscopy, atomic force microscopy and photoluminescence have been used to study the surface characterization. We show that combining chemical etching in 5% HCl with Ar + sputter etching gives the best results for surface cleaning prior to metal deposition. The application of this two-step treatment allows to obtain Ni/AuGe/Ni/Au ohmic contact with r c =2 ×10 –6 Ωcm 2 with excellent adhesion and long-term thermal stability.
Optica Applicata, 2009
This paper reports on the results of optimization of ohmic contacts for GaAs/AlGaAs quantum casca... more This paper reports on the results of optimization of ohmic contacts for GaAs/AlGaAs quantum cascade lasers (QCLs). Technological parameters during optimization concerned surface preparation, evaporation method, and thermal treatment. The aim of this research was to obtain low resistance and time stable ohmic contacts. The average specific contact resistance was 6×10–7 Ωcm–2 with record value below 3×10–7 Ωcm–2. It appears that the crucial role in contact formation is played by the in-situ surface pretreatment and thermal processing. Circular transmission line method (CTLM) was applied for electrical characterization of Ni/AuGe/Ni/Au metallization system. Secondary ion mass spectroscopy (SIMS) was used for determination of Au diffusion into semiconductor. The system presented was used in fabrication of pulse operating QCLs. The lasers mounted with diamond heat spreaders on copper block cooled by liquid nitrogen (LN) achieved optical powers over 1 W, threshold current density values o...
Application of Fractional-Derivative-Spectrum Methods for Optical Analyses of Si and GaAs Semiconductors
ECS Meeting Abstracts
not Available.
Acta Physica Polonica Series a
Optical spectra analysis provides a wealth of information on physical properties of various semic... more Optical spectra analysis provides a wealth of information on physical properties of various semiconductor materials. Fractional derivative spectrum technique is especially interesting when the limitations of the standard treatment occur. In this paper we present the fractional derivative spectrum method for analysis of the optical spectra for both Si and GaAs. The significant changes in critical point parameters in each treated Si and GaAs samples in comparison to that before treatment have been observed. Our investigation illustrates that fractional derivative spectrum is a very good technique to extract basic information on relevant physical quantities from the observed optical spectra, and it has the advantages of flexibility, directness, and sensitivity, which give possibility to obtain the Van Hove singularities (critical point parameters) efficiently with one consent.
InGaAsSb/AlGaAsSb heterojunction photodetectors for wavelength 1.8-2.4 μm grown by LPE
ASDAM '98. Conference Proceedings. Second International Conference on Advanced Semiconductor Devices and Microsystems (Cat. No.98EX172), 1998
The paper reports on progress in the technology of GaSb-based mid-infrared photodetectors. Photod... more The paper reports on progress in the technology of GaSb-based mid-infrared photodetectors. Photodiode structures were made by LPE and fabricate as mesa-type diodes by RIE etching in CCl4/H2 plasma. Mesa passivation was carried out in (NH4)2S water solution. Analysis of PD performance through the measurements of current-voltage and spectral responsivity characteristics have shown that (NH4)2S passivated photodiode structures are characterized
Spin alignment of electrons in PbTe/(Pb, Eu) Te nanostructures
We have measured the transport properties of one-dimensional electron gas fabricated of narrow ga... more We have measured the transport properties of one-dimensional electron gas fabricated of narrow gap semiconductor, PbTe. The Zeeman splitting in this material is comparable to the cyclotron energy and may be as large as 4meV/T. Submicron constrictions have been patterned by electron beam lithography of 50nm PbTe quantum well embedded between Bi-doped Pb0.92Eu0.08Te barriers grown by MBE onto 2.5μm Pb0.92Eu0.08Te-undoped
Physical Review B, 1999
Conductance of submicron constrictions of PbTe:Bi was studied up to 8 T and between 4.2 K and 50 ... more Conductance of submicron constrictions of PbTe:Bi was studied up to 8 T and between 4.2 K and 50 mK. The structures were fabricated by electron beam lithography and chemical etching of high-electron mobility films grown by MBE on BaF2. In the moderately strong magnetic fields perpendicular to the current, B ≥ 1 T, the conductance shows accurate quantization in the units of 1e 2 /h as a function of the side-gate voltage. In the absence of the field, a temperature-independent step structure, with an average step height ≈ e 2 /h, is observed. It is suggested that such a quantization may reflect the lifting of the Kramers degeneracy by the exchange interaction among the electrons, effective despite a large dielectric constant of bulk PbTe.
Liquid phase epitaxy of (100) oriented GaInAsSb with high indium concentration in the liquid phase
LPE growth of quaternary Ga1-xInxAsySb1-y compounds on (100) GaSb substrates has been investigate... more LPE growth of quaternary Ga1-xInxAsySb1-y compounds on (100) GaSb substrates has been investigated for high indium content in the melt x1In = 0.40 - 0.41, growth temperatures To = 590 - 594°C and various amount of supersaturation. Epilayers were characterized by means of XRD, AFM, EPXMA and SIMS. It has been found that LPE growth at To approximately 593°C produces
MRS Proceedings, 1996
ABSTRACTSemiconducting antimonide compounds have received increasing attention as the alternative... more ABSTRACTSemiconducting antimonide compounds have received increasing attention as the alternative materials for mid-infrared photonic devices, with a variety of applications such as remote sensing, pollution monitoring, and molecular spectroscopy. For many, if not all these devices it is necessary to pattern antimonide films into mesa or line structures. While plasma etching techniques have played an increasing role in producing such features, little was reported until now on dry etching of GaSb- and AlSb-containing alloys. In this paper we present the results of our recent work towards the development of the technology for GaSb-based ridge wave-guide laser emitting at 2–2.3 μm at RT. Specifically, we discuss the fabrication of double-channel mesa structure in AlxGai1−xAsySb1−y/GaSb (x=0.2–0.5) heterostructure materials by RIE technique. The effects of gas and material composition, rf power, pressure and temperature on etching characteristics were studied with special attention paid...
Superlattices and Microstructures, 1997
We show that conducting edge channels are formed in free standing wires of PbSe/BaF 2 and PbTe/Ba... more We show that conducting edge channels are formed in free standing wires of PbSe/BaF 2 and PbTe/BaF2 as temperature is lowered. The effect results from spatially inhomogeneous strain caused by a difference between the thermal expansion coefficients of the epilayer and the substrate. The presence of the edge channels can explain anomalous mesoscopic effects observed previously in these wires.
Physical Review B, 2005
Conductance quantization was measured in submicron constrictions of PbTe, patterned into narrow,1... more Conductance quantization was measured in submicron constrictions of PbTe, patterned into narrow,12 nm wide quantum wells deposited between Pb0.92Eu0.08Te barriers. Because the quantum confinement imposed by the barriers is much stronger than the lateral one, the one-dimensional electron energy level structure is very similar to that usually met in constrictions of AlGaAs/GaAs heterostructures. However, in contrast to any other system studied so far, we observe precise conductance quantization in 2e 2 /h units, despite of significant amount of charged defects in the vicinity of the constriction. We show that such extraordinary results is a consequence of the paraelectric properties of PbTe, namely, the suppression of long-range tails of the Coulomb potentials due to the huge dielectric constant.
Study of long-term stability of ohmic contacts to GaN
physica status solidi (c), 2004
We report on low-resistivity thermally stable ohmic contacts to p-GaN using ZrN/ZrB2 metallisatio... more We report on low-resistivity thermally stable ohmic contacts to p-GaN using ZrN/ZrB2 metallisation. Transport properties, thermal conductivity and long-term stability of contacts were examined. p-GaN/ZrN/ZrB2 contacts show excellent stability upon aging in air, indicating their suitability for long-term operation at temperatures up to 150 °C.
physica status solidi (c), 2007
physica status solidi (a), 2007
In this paper we present the results of study of thin oxide films: CdO, ZnO and RuSiO 4 used as t... more In this paper we present the results of study of thin oxide films: CdO, ZnO and RuSiO 4 used as transparent ohmic contacts to GaSb/InGaAsSb/AlGaAsSb photodiodes. Thin oxide films with thickness of 50 nm were deposited by magnetron sputtering. CdO and RuSiO 4 were formed in a reactive process in Ar-O 2 atmosphere, from Cd and Ru 1 Si 1 targets, respectively. ZnO films were deposited directly from ZnO target by rf sputtering. We have shown that application of CdO, ZnO and RuSiO 4 transparent films instead of conventional metal-based contacts enables to improve of photodiode properties. As a result, GaSb/ InGaAsSb/AlGaAsSb photodiodes with detectivity D* increased by factor of 2 and reduced by factor of 3 the series resistance were obtained.
Physica E: Low-dimensional Systems and Nanostructures, 2000
We report on a transport study in modulation-doped CdMnTe=CdMgTe : I heterostructures. In this no... more We report on a transport study in modulation-doped CdMnTe=CdMgTe : I heterostructures. In this novel quantum Hall system electron gas the spin splitting is enhanced due to giant s-d exchange energy. A standard temperature and size scaling of Quantum Hall e ect (QHE) is observed under such conditions. Low-temperature saturation of the QHE scaling observed in wires allows one to evaluate the coherence length for the studied structures.
Ballistic transport in PbTe-based nanostructures
Physica E: Low-dimensional Systems and Nanostructures, 2004
ABSTRACT We describe our study of ballistic transport in nanostructures of lead telluride, PbTe. ... more ABSTRACT We describe our study of ballistic transport in nanostructures of lead telluride, PbTe. Submicron devices have been fabricated by electron beam lithography and chemical etching of wide PbTe single quantum wells embedded between Pb0.92Eu0.08Te barriers grown by MBE on BaF2. The electron concentration in the devices was tuned by the gate voltage applied across an interfacial p–n junction. The most important observation was zero-magnetic field conductance quantization (in multiplies of 2e2/h) in narrow constrictions of dimensions comparable to electron mean free path calculated from transport mobility. This indicates considerable relaxation of requirements for quantum ballistic transport in comparison with other materials. We argue that the huge static dielectric constant of PbTe (ε0=1350 at ) leads to suppression of the long-range Coulomb potentials of charged impurities and, thus, provides favorable conditions for the conductance quantization.
Quantum nanostructures of paraelectric PbTe
Physica E: Low-dimensional Systems and Nanostructures, 2006
ABSTRACT This article provides a review of our results on nanostructurization of lead telluride, ... more ABSTRACT This article provides a review of our results on nanostructurization of lead telluride, PbTe. This IV–VI group narrow-gap semiconductor exhibits paraelectric behaviour leading to a huge dielectric constant ε>1000 at helium temperatures. Because the Coulomb potential fluctuations produced by charged defects are strongly suppressed in PbTe nanostructures, one can reach the quantum ballistic regime at significantly relaxed conditions in comparison with other systems. In particular, we observe precise zero-field conductance quantization in the wires made of modulation doped PbTe/PbEuTe quantum wells where the heavily doped layer is separated from the conducting channel only by a 2 nm thick spacer layer. The second important property is the very large Zeeman splitting. It reaches 4 meV/T. Accordingly, significant spin splitting of the conductance plateaux is observed already at fields below 1 T. Therefore, the system is attractive for the construction of local spin filters. We show that the presence of metal layers does not impair the quantum ballistic properties. Furthermore, we have developed a new method of tuning the PbTe nanostructures, using laterally placed metallic electrodes. We have found that this method is more effective than previous schemes using used p–n junctions and it provides better stability of the nanostructures.
PbTe—A new medium for quantum ballistic devices
Physica E: Low-dimensional Systems and Nanostructures, 2006
Conductance quantization was measured in submicron mesa constrictions, patterned into PbTe/Pb0.92... more Conductance quantization was measured in submicron mesa constrictions, patterned into PbTe/Pb0.92Eu0.08Te quantum wells of thickness 12, 25 and 50nm. The main observation is almost unitary transmission of the one-dimensional quantum modes, despite of significant amount of charged defects in the vicinity of the constrictions. Such an extraordinary result is a consequence of the paraelectric properties of PbTe, namely, the suppression
Physica E: Low-dimensional Systems and Nanostructures, 2004
We report on the observation of the Ising quantum Hall ferromagnet with Curie temperature T C as ... more We report on the observation of the Ising quantum Hall ferromagnet with Curie temperature T C as high as 2 K in a modulation-doped (Cd,Mn)Te heterostructure. In this system field-induced crossing of Landau levels occurs due to the giant spin-splitting effect. Magnetoresistance data, collected over a wide range of temperatures, magnetic fields, tilt angles, and electron densities, are discussed taking into account both Coulomb electron-electron interactions and s-d coupling to Mn spin fluctuations. The critical behavior of the resistance ''spikes'' at T ! T C corroborates theoretical suggestions that the ferromagnet is destroyed by domain excitations.