Nonlocal resistance is studied in a two-dimensional system with a simultaneous presence of electrons and holes in a 20 nm HgTe quantum well. A large nonlocal electric response is found near the ...charge neutrality point in the presence of a perpendicular magnetic field. We attribute the observed nonlocality to the edge state transport via counterpropagating chiral modes similar to the quantum spin Hall effect at a zero magnetic field and graphene near a Landau filling factor ν=0.
Accumulation of arsenic implantation-induced donor defects in heteroepitaxial Hg
1−x
Cd
x
Te structures with the composition of the active layer
x
a
= 0.30 was studied with the use of the Hall-effect ...measurements and mobility spectrum analysis. The studies allowed for identifying the carriers in the implantation-damaged
n
+
-layer, namely, electrons with low and intermediate mobility, and for establishing the dependence of their concentration on the ion fluence. The electrically active implantation-induced defects in the studied structures, similar to the case of those with
x
a
= 0.22, were identified as atoms of interstitial mercury captured by dislocation loops and quasi-point defects. In the material with
x
a
= 0.30, a weak dependence of the concentration of low-mobility electrons on the fluence was observed. In general, a substantial difference in the properties of
p
+
–n
junctions formed as a result of arsenic implantation in the structures with
x
a
= 0.30 and
x
a
= 0.22 was established. The difference was explained by the effect of the graded-gap surface layer on the diffusion of charged defects released during the implantation.
We report on the observation of an unconventional structure of the quantum Hall effect (QHE) in a p−type HgTe / CdxHg1−x Te double quantum well (DQW) consisting of two HgTe layers of critical ...thickness. The observed QHE is a reentrant function of magnetic field between two i = 2 states (plateaus at ρyx = h / ie2 ) separated by an intermediate i = 1 state in the shape of a flat-top peak placed on the remarkably long i = 2 plateau. This anomalous i = 1 peak separates two different regimes: (i) a traditional QHE at relatively low fields corresponding to a small density of mobile holes ps and (ii) a high-field QHE with a 2-1 plateau-plateau transition corresponding to a much larger ps. The high-field part is strongly sensitive to external influences such as gate voltages, in contrast to the low-field part, which is much less responsive. We explain the observed behavior by analyzing the calculated trajectories of the Fermi level EF (B) between hole-like and electron-like Landau levels (LLs). At low fields, EF is captured by the lateral maximum (LM) of the valence subband, and only holes in the center of the Brillouin zone contribute to QHE, while holes in the LM are inactive. In contrast, at fields above the reentry, EF rises significantly higher than LM, approaching the zero-mode LLs, and all holes come into play in QHE. At intermediate fields, the reentrance is caused by a combination of two factors in the specific energy spectrum of this DQW: (i) the superposition of an electron-like LL on hole-like LLs and (ii) the stabilizing influence of the LM reservoir on EF (B).
The energy structure of the size quantization levels in multiple Hg
0.3
Cd
0.7
Te/HgTe quantum wells grown via molecular beam epitaxy on a (013)GaAs substrate has been studied. Experimental and ...calculated energy positions of three size quantization levels are obtained.
Heteroepitaxial
n
-Hg
0.78
Cd
0.22
Te films with near-surface graded-gap layers were grown by molecular beam epitaxy and subjected to two-stage thermal annealing in saturated mercury vapor ...atmosphere. The first stage of annealing was carried out for 2 h at a temperature of 360°C. The second stage was carried out at a temperature of 220°C for 24 h. Similar annealing was carried out after As
+
ion implantation to activate the introduced impurity and anneal radiation defects. Based on as-grown and annealed films, metal–insulator–semiconductor (MIS) structures were formed by depositing an Al
2
O
3
dielectric by plasma atomic layer deposition. The admittance of fabricated MIS structures was studied in a wide range of frequencies and temperatures. It was found that after thermal annealing, the properties of the
n
-HgCdTe surface layer are noticeably changed, which is manifested as a decrease in the density of slow states in the transition layer between the dielectric and the semiconductor, and an increase in the generation of minority charge carriers in the
n
-HgCdTe near-surface layer. These changes in the properties of
n
-HgCdTe after thermal annealing are associated with the modification of the defect system of the near-surface layer of the semiconductor and the transition layer between dielectric and semiconductor. No significant changes were detected in the bulk properties of the epitaxial film after thermal annealing. A decrease in the density of states near the interface between HgCdTe and Al
2
O
3
during thermal annealing makes it possible to facilitate the electrical characterization of MIS structures by suppressing hysteresis phenomena.
The effect of As
+
ion implantation on the electrical properties of the near-surface layer of
n
-HgCdTe films grown by molecular beam epitaxy (MBE) on Si (310) substrates was experimentally studied. ...A specific feature of MBE
n
-Hg
0.78
Cd
0.22
Te films is the presence of near-surface graded-gap layers with a high CdTe content, formed during epitaxial growth. The properties of as-grown films and films after As
+
ion implantation with ion energy of 200 keV and fluence of 10
14
cm
−2
were studied. Post-implantation activation annealing was not performed. Test metal–insulator–semiconductor (MIS) structures were created based on as-grown and as-implanted samples by plasma-enhanced atomic layer deposition of Al
2
O
3
insulator films. The admittance of the fabricated MIS structures was measured over a wide range of frequencies and temperatures. When determining the parameters of MIS structures, we used techniques that take into account the presence of near-surface graded-gap layers and series resistance of the HgCdTe film bulk, as well as the high density of slow surface states. It was found that, in as-implanted samples, the donor center concentration in the near-surface layer exceeds 10
17
cm
−3
and increases with distance from the HgCdTe-Al
2
O
3
interface (at least up to 90 nm). After implantation, the conductivity of MBE HgCdTe film bulk increases markedly. It was shown that, for as-implanted samples, the generation rate of minority charge carriers in the MBE HgCdTe surface layer is significantly reduced, which indicates the appearance of a low defect layer with a thickness of at least 90 nm.
The electrical properties of MIS structures based on graded band gap Hg0.77Cd0.23Te grown by the molecular beam epitaxy method with the Al2O3 dielectric formed by the plasma enhanced atomic layer ...deposition method were investigated. It is established that for such structures the recharge of slow states takes place and significantly distorts the form of the capacitance-voltage (C-V) characteristics. A technique is proposed for constructing the C-V curves of HgCdTe MIS structures, which makes it possible to eliminate the effect of slow surface states. It is shown that Al2O3 films are suitable for passivation of infrared detectors due to small flat band voltages leading to the realization of the depletion or weak inversion modes. The hysteresis of electrical characteristics is eliminated when an intermediate CdTe layer with a thickness of about 0.2 μm is grown in situ during the epitaxial growth.
•Graded band gap HgCdTe grown by molecular beam epitaxy on Si and GaAs substrates.•The interface properties of n(p)-HgCdTe with the ALD Al2O3 film are investigated.•C-V curves were obtained by narrow swing method with slow state effect exception.•Growth of a thin (0.2 μm) CdTe interlayer leads to the disappearance of hysteresis.•Al2O3 films are suitable for detector passivation due to small flat band voltages.
We report on the observation of magneto-oscillations of terahertz radiation induced photocurrent in HgTe/HgCdTe quantum wells of different widths, which are characterized by a Dirac-like, inverted, ...and normal parabolic band structure. The photocurrent data are accompanied by measurements of photoresistance (photoconductivity), radiation transmission, as well as magneto transport. We develop a microscopic model of a cyclotron-resonance assisted photogalvanic effect, which describes main experimental findings. We demonstrate that the quantum oscillations of the photocurrent are caused by the crossing of Fermi level by Landau levels resulting in the oscillations of spin polarization and electron mobilities in spin subbands. Theory explains a photocurrent direction reversal with the variation of magnetic field observed in experiment. We describe the photoconductivity oscillations related with the thermal suppression of the Shubnikov-de Haas effect.
We report on magnetospectroscopy of HgTe quantum wells in magnetic fields up to 45 T in a temperature range from 4.2 up to 185 K. We observe intra- and inter-band transitions from zero-mode Landau ...levels, which split from the bottom conduction and upper valence sub-bands and merge under the applied magnetic field. To describe experimental results, realistic temperature-dependent calculations of Landau levels have been performed. We show that although our samples are topological insulators at low temperatures only, the signature of such a phase persists in optical transitions at high temperatures and high magnetic fields. Our results demonstrate that temperature-dependent magnetospectroscopy is a powerful tool to discriminate trivial and topological insulator phases in HgTe quantum wells.
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