Resonant Impurity Level Research Articles

The investigation of hydrostatic pressure dependent optoelectronic properties of GaAsNBi spherical quantum dot

The electronic band structure of GaAsNBi spherical quantum dot (QDs) have been calculated under hydrostatically induced pressure using 16 band k.p model and considering the band anticrossing (BAC) interaction between the valence band (VB) of the host material with the N and Bi related resonant impurity level. It has a linear variation in bandgap with different Bi concentration and non-linear in bandgap with varying pressure, for 2.3%N in both the cases. However, small differences are observed in valance band offset (VBO), whereas more considerable changes can be seen in the conduction band offset (CBO) with an increasing hydrostatic pressure, which implies a stronger confinement of charge carriers. Finally, we also studied the percentage of strain distribution and its related properties of GaAsNBi spherical QDs along the radial direction, lattice misfit under biaxial and hydrostatic strain. These QDs are also being used in many applications, including selective frequency operation for optoelectronic devices by tuning distinct mole fraction and pressure.

Temperature and pressure coefficients of iron resonant impurity level in PbTe

We investigate temperature dependences of galvanomagnetic parameters in weak magnetic fields (4.2 ≤ T ≤ 300 K, B ≤ 0.07 T) in the p-Pb1−yFeyTe alloy from the middle part of the single-crystal ingot, where the Fermi level is pinned by the resonant impurity level lying under the top of the valence band. Experiments are performed under hydrostatic compression up to 10 kbar. Using scanning electron microscopy, we find microscopic inclusions of the secondary phase enriched with iron and show that the main phase is characterized by a good uniformity of the spatial distribution of impurities. A monotonous increase of the free hole concentration at liquid-helium temperature under pressure and anomalous temperature dependences of the Hall coefficient in the whole investigated pressure range are revealed. Experimental results are explained by a model assuming pinning of the Fermi level by the impurity level and a redistribution of electrons between the valence band and impurity states with increasing temperature and under pressure. In the framework of the two-band Kane dispersion law, theoretical temperature dependences of the Hall coefficient under pressure, which are in satisfactory agreement with the experimental ones at low temperatures, are calculated and temperature and pressure coefficients of the iron deep level are determined. Diagrams of the electronic structure rearrangement with increasing temperature for Pb1−yFeyTe at pressures up to 10 kbar are proposed.

Galvanomagnetic properties and electronic structure of iron-doped PbTe

We synthesize an iron-doped PbTe single-crystal ingot and investigate the phase composition and distribution of the iron impurity along the ingot as well as galvanomagnetic properties in weak magnetic fields (4.2 K ≤ T ≤ 300 K, B ≤ 0.07 T) of Pb1−yFeyTe alloys. We find microscopic inclusions enriched with iron and regions with a chemical composition close to FeTe in the heavily doped samples, while the iron impurity content in the main phase rises only slightly along the length of the ingot reaching the impurity solubility limit at approximately 0.6 mol. %. Samples from the initial and the middle parts of the ingot are characterized by p-type metal conductivity. An increase of the iron impurity content leads to a decrease in the free hole concentration and to a stabilization of galvanomagnetic parameters due to the pinning of the Fermi level by the iron resonant impurity level EFe lying under the bottom of the valence band (Ev − EFe ≈ 16 meV). In the samples from the end of the ingot, a p-n inversion of the conductivity type and an increase of the free electron concentration along the ingot are revealed despite the impurity solubility limit being reached. The kinetics of changes of charge carrier concentration and of the Fermi energy along the ingot is analyzed in the framework of the six-band Dimmock dispersion relation. A model is proposed for the electronic structure rearrangement of Pb1−yFeyTe with doping, which may also be used for PbTe doped with other transition metals.

Fermi level pinning in Fe-doped PbTe under pressure

We synthesize an iron-doped PbTe single-crystal ingot and investigate the phase and the elemental composition as well as galvanomagnetic properties in weak magnetic fields (4.2 K≤T≤300 K, B ≤ 0.07 T) of Pb1−yFeyTe alloys upon varying the iron content, at atmospheric pressure and under hydrostatic compression up to 10 kilobars. We find an increase of iron concentration along the length of the ingot and the appearance of microscopic inclusions enriched with iron in the heavily doped samples. Lightly doped alloys are characterized by the p-type metal conductivity. An increase of the iron impurity content leads to a decrease in the free hole concentration, a stabilization of galvanomagnetic parameters, indicating the pinning of the Fermi energy by the iron resonant impurity level lying under the bottom of the valence band, and to the p-n inversion of the conductivity type. Under pressure, the free hole concentration in the sample, in which the stabilization of galvanomagnetic parameters takes place, increases by approximately a factor of four due to the flow of electrons from the valence band to the iron-induced resonant level. Using the two-band Kane and the six-band Dimmock dispersion relations, the pressure dependence of the Fermi energy is calculated. The model of the electronic structure rearrangement of Pb1−yFeyTe under pressure is proposed. The energy position and the pressure coefficient of the resonant iron impurity level are determined.

Scandium resonant impurity level in PbTe

We synthesize a scandium-doped PbTe single-crystal ingot and investigate the phase and the elemental composition as well as galvanomagnetic properties of Pb1-yScyTe alloys in weak magnetic fields (4.2 K ≤ T ≤ 300 K, B ≤ 0.07 T) upon varying the scandium content (y ≤ 0.02). We find that all investigated samples are single-phase and n-type. The distribution of scandium impurities along the axis of the ingot is estimated to be exponential. An increase of scandium impurity content leads to a monotonous growth of the free electron concentration by four orders of magnitude (approximately from 1016 cm−3 to 1020 cm−3). In heavily doped alloys (y > 0.01), the free electron concentration at the liquid-helium temperature tends to saturation, indicating the pinning of the Fermi energy by the scandium resonant impurity level located on the background of the conduction band. Using the two-band Kane and six-band Dimmock dispersion relations for IV-VI semiconductors, dependences of the Fermi energy measured from the bottom of the conduction band Ec on the scandium impurity content are calculated and the energy of the resonant scandium level is estimated to be ESc ≈ Ec + 280 meV. Diagrams of electronic structure rearrangement of Pb1-yScyTe alloys upon doping are proposed.

Smearing of the coulomb blockade by resonant tunneling

We study the Coulomb blockade in a grain coupled to a lead via a resonant impurity level. We show that the strong energy dependence of the transmission coefficient through the impurity level can have a dramatic effect on the quantization of the grain charge. In particular, if the resonance is sufficiently narrow, the Coulomb staircase shows very sharp steps even if the transmission through the impurity at the Fermi energy is perfect. This is in contrast to the naive expectation that perfect transmission should completely smear charging effects.

Image of local density of states fluctuations in disordered metals in the differential conductance of tunneling via a resonant impurity level

Differential conductance of the resonant-tunneling structure with a single impurity level studied in the current plateau regime undergoes fluctuations around a zero average manifesting the energy dependence of the local density of states in a disordered electrode. Although the rms value of dI/dV depends on disorder and barrier transparencies, it is almost independent of temperature and, as a function of bias voltage, has a correlation function scaled by the intrinsic width of the resonance, which can be regarded as a tool to measure this quantity beyond the main differential-conductance peak. The analysis is extended to the regime of classically high magnetic fields where both the amplitude and correlation magnetic field are expected to increase.

DX-Like behavior of Se-impurity centers in gasb under hydrostatic pressure

Abstract Hall coefficient (RH) and electrical resistivity measurements have been performed as a function of temperature (between 77 K and 300 K) and under hydrostatic pressures (up to 15 kbar) on a set of Se-doped GaSb samples with impurity concentrations in the range 8×1017 cm−3 - 1×1018 cm−3. With increasing pressure at 300 K, the electrons are strongly trapped into a resonant impurity level. The pressure induced occupation of this level leads to time-dependent effects at T B = 300×30 meV gives clear evidence for a large lattice relaxation around the impurity centers characteristic for DX-like behavior.

Short-range resonant electron scattering in Se- and S-doped GaxIn1-x Sb under hydrostatic pressure

Abstract Electron scattering mechanisms have been investigated in Se- and S-doped GaxIn1-xSb alloys by measuring the Hall mobilities as a function of hydrostatic pressures up to 25 kbar at temperatures down to 4.2 K. The analysis of the data shows that the Brooks-Herring theory of ionized impurities scattering could fit the experimental variations only overa narrow range of low pressures before carrier freeze-out into a resonant impurity level sets in. At higher pressures, good agreement between theory and experiment could be obtained by introducing an additional scattering mechanism due to the short-range central cell impurity potential.

Characterisation under hydrostatic pressure of narrow-gap Hg1-xCdxTe and Hg1-xZnxTe

The authors have performed transport experiments under hydrostatic pressure on samples of two different narrow-gap mercury telluride mixed compounds: Hg1-xCdxTe (x=0.27, 0.28, 0.30) and Hg1-xZnxTe (x=0.15). The investigated samples of HgCdTe are n-type samples grown by the molecular beam epitaxy technique on GaAs/CdTe substrates and doped with In during the growth. The experiments, performed at liquid helium temperature in the magnetic field range B=0-5 T and under hydrostatic pressure up to P=11 kbar, allow them to conclude that this doping process does not induce any resonant impurity level as previously observed for boron-implanted samples. They used the same experimental techniques (0<B<19 T, 0<P<9 kbar, 1.68<T<300 K) to study HgZnTe samples grown by the travelling heating method. This open-gap material (x=0.15) is a high-mobility semiconductor (n=6.8*1014 cm-3 and mu =1.8*106 cm2 V-1 s-1). Nevertheless, its pressure behaviour in zero magnetic field and in the high-magnetic-field regime shows the existence of two impurity levels.

Hydrostatic pressure investigation of the metastable character of S and Se impurity states in Ga 0.78In 0.22Sb mixed crystals

Hall effect and resistivity measurements have been made on S-doped and Se-doped Ga x In 1- x Sb ( x = 0.78) at hydrostatic pressure up to 15 kbar. With increasing pressure at T = 300 K, in both kind of samples, the electrons are strongly trapped into a resonant impurity level. Moreover, the occupation of this level leads to time-dependent effects at T < 110 K. The activated thermal electron emission, with a potential barrier of ∼180 meV in S-doped and ∼240 meV in Se-doped samples, gives clear evidence for a large lattice relaxation around the impurity centers similar to that responsible for presistent photoconductivity observed in many semiconductor compounds and alloys.

Resonant and deep impurity levels under hydrostatic pressure in pure n-type InAs

Hall coefficient ( R H) and electrical resistivity (ϱ 0) were measured as a function of hydrostatic pressure up to 18 kbar, in the 4.2 K–120 K temperature range, on nominally undopted n-type InAs with free carrier concentration ∼2 × 10 16 cm −3. In the 4.2–30 K range, R H and ϱ 0 versus pressure variations indicate the deionization of impurity states which are resonant in the Γ 1c band at normal pressure. The position and the pressure variation of the resonant impurity level are discussed. At T>30 K, evidence is made for the existence of a donor-like impurity level lying ∼10 meV below the Γ 1c band minimum and moving with pressure at the rate of −1.8 meV/kbar with respect to this band.

High-magnetic-field and high-hydrostatic-pressure investigation of hydrogenic- and resonant-impurity states in n-type indium arsenide.

Hall-effect and transverse-magnetoresistance measurements were performed on pure n-type InAs samples (n\ensuremath{\simeq}2\ifmmode\times\else\texttimes\fi{}${10}^{16}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$) under magnetic fields up to 180 kG and hydrostatic pressures up to 18 kbar in the temperature range 2.7\char21{}8 K. At P13 kbar, the magnetic freezeout takes place into a shallow-donor level which shifts downward from the \ensuremath{\Gamma} conduction-band minimum with the pressure coefficient -0.077 meV/kbar. At Pg13 kbar, additional magnetic freezeout into a resonant-impurity level was observed. This resonant level lies at 68\ifmmode\pm\else\textpm\fi{}1 meV above the \ensuremath{\Gamma} conduction band and moves with pressure at the rate of -4 meV/kbar with respect to this minimum. An extra deepening of the shallow-donor level takes place when the pressure and the magnetic field are sufficiently high to induce the occupation of the resonant states.