M. Baj

Determining Curie temperature of (Ga,Mn)As samples based on electrical transport measurements: Low Curie temperature case

In this paper, we show that the widely accepted method of the determination of Curie temperature (TC) in (Ga,Mn)As samples, based on the position of the peak in the temperature derivative of the resistivity, completely fails in the case of non-metallic and low-TC unannealed samples. In this case, we propose an alternative method, also based on electric transport measurements, which exploits temperature dependence of the second derivative of the resistivity upon magnetic field.

Structural and magnetic phase transitions in CoxNi1−xMnGe system under pressure

Abstract The interaction of magnetic (Tc) an first-order distortion-type structural (TD) transitions in the CoxNi1−xMnGe system was investigated using an ac susceptibility method under hydrostatic pressure up to 1.3 GPa. For all compositions TC increases and TD decreases with pressure. At the first triple point (0.3–0.6 GPa depending on x) these transitions go through a simultaneous magnetic-structural transition, as observed by Anzai and Ozawa in NiMnGe. However, for the composition x = 5, at the second triple point (at 0.8 GPa) the magnetic transition separates from the structural one, with TC greater than TD. This appears to be the first example of physically different, first and second-order phase transitions merging at a particular value of an external parameter, i.e. pressure PTR1 and decoupling again at PTR2 > PT1. The (P, T) phase diagrams and the nature of the triple points are discussed using a simple Landau-type theory

Hydrostatic pressure study of the paramagnetic-ferromagnetic phase transition in (Ga,Mn)As

The effect of hydrostatic pressure on the paramagnetic-ferromagnetic phase transition has been studied in (Ga,Mn)As. The variation in the Curie temperature (T-C) with pressure was monitored by two transport methods: (1) measurement of zero-field resistivity versus temperature rho(T) and (2) dependence on temperature of the Hall voltage hysteresis loop. Two specimens of different resistivity characteristics were examined. The measured pressure-induced changes in T-C were relatively small (on the order of 1 K/GPa) for both samples, however they were opposite for the two.

High pressure investigation of ferroelectric phase transition in PbSnTe

Abstract The anomalies in electrical transport properties at the displacive phase transition in Pb1−xSnxTe (x=0.18−0.86) has been investigated. The results of applying pressure point out the multiphonon scattering mechanism caused by the soft TO phonons as responsible for the resistivity anomaly.

The dielectric constant in narrow-gap semiconductors

Abstract We show that a substantial contribution to the dielectric constant ϵ 0 in narrow-gap, zinc-blende semiconductors arises from a small region (about 1.5%) of the Brillouin zone around the Г point. This contribution, calculated from the RPA expression in the 3-band model, dominates the concentration- and pressure-dependence of ϵ 0 in zero-gap or small-gap materials, reducing in the appropriate limit to the one obtained by Liu and Tosatti.

Hydrostatic pressure investigations of resonant tunnelling through X-minimum-related states in a single barrier GaAs/AlAs/GaAs heterostructure

Abstract We have investigated the resonant tunnelling of electrons through X-valley related states in a single AlAs barrier with Si donor & doping. Under high hydrostatic pressure all the peaks observed in the differential conductance-voltage (σ-V) characteristics shift with a pressure rate of -lSmeV/kbar, which is expected for X-minima related electronic states.

Resonant tunnelling through single donor states in GaAs/AlAs/GaAs devices

Our paper is a first step towards tunnelling spectroscopy of individual X-minimum-related shallow donors. We investigated I–V characteristics of submicrometer mesa structures made on GaAs/AlAs/GaAs wafers δ-doped with silicon in the middle of AlAs layer. At 4.2K and magnetic field up to 6T we resolved well-separated peaks attributed to resonant tunnelling via individual donors.

Effect of hydrostatic pressure on degradation of CdTe/CdMgTe heterostructures grown by molecular beam epitaxy on GaAs substrates

We have shown that external hydrostatic pressure leads to the creation of structural defects, mainly in the vicinity of the II-VI/GaAs interface in the CdTe/Cd{sub 1-x}Mg{sub x}Te heterostructures grown by the molecular beam epitaxy method on GaAs substrates. These defects propagating across the epilayer cause permanent damage to the samples from the point of view of their electrical properties. In contrast, photoluminescence spectra are only weakly influenced by pressure. Our results shed light on the degradation process observed even without pressure in II-VI-based heterostructures.

Metastable Donors in GaAs

The presented paper is a short review of some interesting phenomena characteristic for the DX centre in GaAs and AlGaAs as well as the EL2 defect in GaAs. We mainly concentrate on pressure studies of metastable properties of the both defects trying to refer the experimental results to the existing microscopic models of DX and EL2 defects.

Low‐Frequency Noise Measurements of the Tunneling Current in Single Barrier GaAs/AlAs/GaAs Devices

The experimental results of the low temperature (T = 4.2 K) low‐frequency current fluctuations measurements in the single‐barrier resonant tunneling GaAs/AlAs/GaAs vertical devices with Si δ‐doping in the center of the 10‐nm thick AlAs barrier are reported. The dimensions of the device were 200 μm by 200 μm. For the small bias voltages (low transmission of the barrier) there is only the shot noise with Fano factor F close to 1 observed. For higher voltages the generation‐recombination‐like and/or 1/fα noise arises and superimposes on the shot noise.