Metal–insulator–semiconductor (MIS) structures based on HgCdTe were fabricated after various stages of pn junction formation using As+ implantation and activation annealing. The energy of As+ ions ...was 200 keV with the fluence of 1014 cm−2. Heteroepitaxial HgCdTe films with near-surface graded-gap layers were grown by molecular beam epitaxy (MBE) on silicon substrates. It was shown that the electron concentration in the near-surface semiconductor layer increases after implantation to values of about 1017 cm−3, and after implantation and annealing in the near-surface semiconductor layer, a p+ layer appears with a hole concentration of more than 1.5 × 1018 cm−3. The generation rate of minority charge carriers in the space charge region after implantation is low, which indicates a low defectiveness of the thin near-surface MBE HgCdTe layer. After implantation and annealing, the generation rate increases significantly, which may be due to high defectiveness near the interface between Al2O3 and MBE HgCdTe. Dopant profiles were constructed in the near-surface HgCdTe layers after various technological procedures. It was shown that after implantation in films, the dopant concentration increases with distance from the interface to the depth of 0.1 μm.
•Surface HgCdTe properties were modified by As implantation and thermal annealing.•Metal–insulator–semiconductor structures were created and their admittance studied.•Concentration profiles in HgCdTe after various procedures were determined.•After As implantation, a low-defect layer appears near the interface HgCdTe-Al2O3.•Activation annealing leads to a decrease in the density of slow states.
Abstract
In this study, we employed several experimental techniques to investigate structure and magnetic properties of poly(
p
-xylylene)–MnSb composites synthesized by low-temperature vapor ...deposition polymerization technique and MnSb films deposited at various temperatures. The presence of MnSb nanocrystallites in the studied films was verified by the results of X-ray diffraction, electron microscopy and Raman spectroscopy studies. The obtained data revealed the formation of Sb-rich sublayer with well-oriented Sb grains near the susbtrate, which seems to act as a buffer for the consequent poly(
p
-xylylene)–MnSb or MnSb layer growth. Increasing the polymer content results in qualitative change of surface morphology of studied films. At high polymer content the hybrid nanocomposite with MnSb nanoparticles embedded into poly(
p
-xylylene) matrix is formed. All investigated samples demonstrated detectable ferromagnetic response at room temperature, while the parameters of this response revealed a complex correlation with nominal composition, presented crystal phases and surface morphology of studied films. Estimated values of the Curie temperature of the samples are close to that of bulk MnSb.
Metal–insulator–semiconductor structures based on HgCdTe are grown by molecular-beam epitaxy. Near-surface graded-gap layers with a high CdTe content are inserted on both sides of the epitaxial ...HgCdTe film. The capacitance–voltage characteristics of these structures are studied experimentally. The main characteristics of these graded-gap HgCdTe structures are determined taking into account the effect of the non-uniform composition of the near-surface layers on the measured parameters. The capacitance–voltage characteristics of the graded-gap HgCdTe structures with various insulators are examined and the densities of surface states, densities of fixed and mobile charges are evaluated. The properties of the interface for CdTe grown in situ are found to be fairly good. We found that for structures based on HgCdTe–CdTe typical of very low density of mobile charges, the density of fixed charge does not exceed a 5.5×1010cm−2.
► The metal–insulator–semiconductor structures based on HgCdTe were studied. ► A method is proposed for investigation of these graded-gap structures. ► The properties of the interface HgCdTe with some insulators were investigated. ► The properties of the interface for CdTe are found to be fairly good.
In this study, wide-angle X-ray diffraction, X-ray absorption spectroscopy, and transmission electron microscopy were employed to address the crystalline structure and morphology of ...poly(p-xylylene)–PbS nanocomposite thin films prepared by vapor deposition polymerization as well as their evolution upon thermal annealing. It was found that as-synthesized samples with different PbS contents demonstrate similar diffraction patterns that cannot be fully ascribed to a decrease in crystallite size, indicating distorted crystal structure of PbS nanoparticles compared to the bulk PbS. X-ray absorption spectroscopy reveals wide distribution of Pb–S bond lengths with a minimum value of 2.67 Å, which can be attributed to the presence of molecular (PbS) n clusters in the studied films. It was shown that thermal annealing can be used to control the size of PbS nanoparticles and, as a consequence, optical properties of the composite films. The UV–vis absorption spectra demonstrate pronounced red shift of the absorption edge correlated with the growth of PbS nanoparticles upon annealing. Comprehensive analysis of several theoretical models describing the effect of nanoparticles size on optical band gap of the composite material has been performed and compared with the experimental data.
Results of the Hall-effect studies of surface properties of n–type HgCdTe films modified with arsenic ion implantation and thermal annealing are reported on. A complete annihilation of ...implantation-induced extended defects (dislocation loops), quasi-point defects and related donor centers was observed as a result of a two-stage arsenic activation annealing. A high degree of activation of implanted arsenic was achieved with the annealing. In some cases, the annealing was found to lead to the modification of the properties of the ‘base’ layers not affected by implantation due to activation of uncontrolled acceptor defects and resulting changes in the degree of electrical compensation.
•Modification of the surface of HgCdTe films with arsenic implantation and annealing was studied.•Annealing was shown to annihilate structural defects induced by implantation.•High degree of activation of arsenic as a result of post-implantation annealing was achieved.•Activation of residual acceptor impurities by post-implantation annealing was discovered.
The capacitive characteristics of metal–insulator-semiconductor (MIS) structures based on the compositionally graded Hg
1−x
Cd
x
Te created by molecular beam epitaxy have been experimentally ...investigated in a wide temperature range (8–77 K). A program has been developed for numerical simulation of ideal capacitance–voltage (C–V) characteristics in the low-frequency and high-frequency approximations. The concentrations of the majority carriers in the near-surface semiconductor layer are determined from the values of the capacitances in the minima of low-frequency C–V curves. For MIS structures based on
p
-Hg
1−x
Cd
x
Te, the effect of the presence of the compositionally graded layer on the hole concentration in the near-surface semiconductor layer, determined from capacitive measurements, has not been established. Perhaps this is due to the fact that the concentration of holes in the near-surface layer largely depends on the type of dielectric coating and the regimes of its application. For MIS structures based on
n
-Hg
1−
x
Cd
x
Te (
x
= 0.22–0.23) without a graded-gap layer, the electron concentration determined by the proposed method is close to the average concentration determined by the Hall measurements. The electron concentration in the near-surface semiconductor layer of the compositionally graded
n
-Hg
1−
x
Cd
x
Te (
x
= 0.22–0.23) found from the minimum capacitance value is much higher than the average electron concentration determined by the Hall measurements. The results are qualitatively explained by the creation of additional intrinsic donor-type defects in the near-surface compositionally graded layer of
n
-Hg
1−
x
Cd
x
Te.
Dark currents in medium-wave
nBn
structures based on HgCdTe grown with the aid of molecular beam epitaxy on the (013) GaAs substrates are studied. The passivation of the surface of the side walls of ...the mesastructures is performed using Al
2
O
3
films formed by plasma atomic layer deposition. It is shown that the volume component of the dark current dominates in the
nBn
structures with a composition in the barrier layer of 0.84. The activation energy of the current is close to the band gap of the absorbing layer. Comparison of the experimental results with the results of the Rule07 empirical model shows that the diffusion limitation of the dark current takes place in the fabricated structures in a temperature interval of 180–300 K. The results indicate that the molecular beam epitaxy of HgCdTe on alternative substrates is a promising method for fabrication of unipolar barrier detectors for a spectral interval of 3–5 µm.
We analyze the current state of research in the field of creating unipolar semiconductor barrier structures based on various materials for infrared photodetector arrays, which make it possible to ...reduce the dark currents and thereby improve the threshold characteristics and ensure operation at high cooling temperatures. The main ways of minimizing a barrier for holes in the valence band are considered by the example of a photosensitive structure based on the
n
-CMT layer. It is shown that the
nBn
barrier structures are an alternative for creating photodiode sensing matrices for the mid- and far-infrared photodetector arrays.
Metal–insulator–semiconductor structures based on HgCdTe are grown by molecular-beam epitaxy. Near-surface graded-gap layers with high CdTe content are formed on both sides of the epitaxial HgCdTe ...film. Photoelectrical characteristics of these structures are studied experimentally and theoretically. For structures based on n-Hg1−xCdxTe (x=0.21–0.23), the formation of a near-surface graded-gap layer leads to an increase in the differential resistance of the space charge region due to the suppression of tunneling. The temperature dependences of the differential resistance calculated with account to different mechanisms of generation of minority charge carriers are similar to the experimental dependences of the photoelectromotive force.
•The metal–insulator–semiconductor structures based on HgCdTe were studied.•Photoelectrical properties of such structures were investigated.•Mechanisms of generation of minority carriers were studied.•Creation of near-surface graded-gap layers suppresses tunneling.
Mid-wave infrared nBn structures based on HgCdTe grown by molecular beam epitaxy on GaAs (013) substrates were fabricated. The composition in the absorbing layer was 0.29, and in the barrier layer it ...was 0.67. It was shown that the dark currents of the created nBn structures are limited by the surface leakage component. To study the bulk component of the dark current, it was proposed to use the admittance measurements of test metal-insulator-semiconductor (MIS) devices based on fabricated nBn structures in the case of the formation of a backward contact to the absorbing layer. It was established that surface leakage does not affect the dynamic resistance of the MIS device barrier. The dependence of the dynamic resistance of the barrier layer (
R
b
) of the MIS device in the accumulation mode on the area of the front electrode (
A
), voltage, and temperature was determined. It was shown that, with the exclusion of surface leakage, the values of the
R
b
A
product in a temperature range of 230–300 K at forward biases are determined by the diffusion current of holes from the contact layer, and at reverse biases, by the diffusion current from the absorbing layer. It was found that at temperatures of 210–300 K,
R
b
A
values exceeding the values of this parameter determined according to the empirical model Rule 07 were realized in the fabricated structures.
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