Results of the studies of relaxation of electhcal properties of As- and Sb-doped CdxHg1-xTe epitaxial layers, which were
converted into n-type by ion milling (TM), are presented. It is demonstrated that donor complexes, which are formed
under IM and are responsible for p-to-n conductivity type conversion, are not stable, and their concentration decreases
upon storage even at the room temperature. The relaxation at room temperature results in electron concentration in
converted layers decreasing from the initial value of ~(2-3)x 1015 cm right after the milling down to the value of ~l015
cm-3. Increasing the temperature of the storage speeds up the relaxation. The process responsible for the relaxation
appeared to be the disintegration of the donor complexes, which starts after the end of the IM and is caused by the
decrease in concentration of interstitial mercury atoms, generated by milling.
The main features of passively Q-switched microchip lasers development are considered. The active medium of laser is an epitaxial structure combining an epitaxial layer of saturable absorber Cr4+:Y3Al5O12 (Cr:YAG) grown on substrate of generating crystal Nd:YAG by liquid phase epitaxy. The modulator layer has an initial optical absorption of 36 cm-1 at wavelength of lasing (1064 nm). The epitaxial layer grown on unworking side was mechanically removed and this substrate side was optically polished. The other one was processed precisely to needed thickness. The cavity's mirrors were deposited by electron beam technique directly on each side of the structure to form a rugged, monolithic resonator. Diode laser Model ATC-C4000 with lasing wavelength 808 nm provided the CW end pumping. The output pulses parameters were investigated by means of test bench consisting of photoelectric transducer FEK-15 and Digital Phosphor Oscilloscope TDS 5052B. The obtained laser parameter are as follows: pulse width (FWHM) about 1.3 ns, repetition rate 5.5 kHz, average output power about 10 mW, pulse energy 1.0 μJ, pick power 1.2 kW. The possible solutions for laser parameter improving and optimization are discussed.
Effect of iso-valency doping with S, Se or Zn dopants on Hg1-xCdxTe mechanical, structural and photoelectric properties is considered. It was revealed that iso-valency doping reduced the etch pit density and increased the microhardness in
Hg1-xCdxTe single crystals. Such doping also improved the photoelectric properties, especially increased the excess
carrier lifetime. Taking into account the value of equilibrium concentration of S, Se and Zn iso-valency dopants in Hg1-xCdxTe single crystals it was concluded that the most suitable iso-valency dopant is Se.
P-n conductivity type conversion under ion milling in MOCVD p-CdxHg1-xTe/GaAs multi-layer hetero-structures is considered. It was revealed that CdTe (1 μm thick) passivation layer displayed the protective properties regarding ion milling action on active layer. P-n conversion at ion milling was observed in structures with 0.1-0.2 μm thick CdTe passivation layer; however, the converted depth (7 μm) was smaller than that in the similar homogeneous samples (15 μm). It was shown that the main properties of the converted p-n structures with thin CdTe layer were the same as in homogeneous samples. Ion milling resulted in forming of the typical n+- n - p+ structure with damaged n+-layer and main converted n-layer characterised by very low electron concentration. The relaxation of p-n structure electrical properties was also studied.
The main features of p-n conductivity type conversion by ion milling in vacancy-doped p-CdxHg1-xTe are considered. A diffusion model of the Hg interstitials source formation in MCT crystals under IM was proved through investigation of conversion depth dependence on composition. The model explains, both quantitatively and qualitatively, conversion depth dependencies on the IM temperature and the alloy composition. The most important factor, which defines these dependencies, is an electric field located at the interface between the p-type defect layer and the n type converted layer and in the grad band region. It was demonstrated that main features of carrier distribution over the p-n structure depth remained after 10 years samples storage. The relaxation of electrical properties of the n-layer main part after IM was explained by dissociation of donor complexes and centers formed by Hg interstitials with residual I and V group acceptor impurities. It was also demonstrated that IM results in forming a complex damaged n+-layer including several sub-layers with different nature of electron conductivity. An analysis of how electrons concentration relax in the n+-layer allows interpreting the nature of conductivity in one sub-layer through trapping mercury interstitials by dislocations and dislocation loops. The conductivity relaxation in this sub-layer occurs because the structure of such defects is rebuilt, with donor properties being lost.
Properties of n+-n-p+ structures formed in Hg1-xCdxTe single crystals and epitaxial films by ion milling (IM) followed by isothermal and isochronous annealing were investigated. It was demonstrated that the intricateed electrical properties relaxation of these structures and kinetics relations depend on the samples composition and the technology of their preparation.
It was demonstrated that the ion milling of Hg1xCdxTe layers results in forming a complex n+-layer which contains several sub-layers with different electron conductivities. The analysis of the processes of electron relaxation in theses sub-layers under isothermal aging (at room temperature) and (or) isochronous annealing, has allowed the interpretation of the nature of conductivities in them. The analysis of times and activation energies of relaxation process confirms the relaxation of electrical characteristics of these structures is caused by decomposition of donor centers formed by Hg interstitial atoms with I and V impurities.
Carried out analysis of the electrical characteristics of MCT layers subjected to IM has shown, that in spite of its simplicity for p-n-junctions manufacturing, the grounded technology of IM application for forming stable p-n-junctions requires further study of its optimization.
Investigations and comparative analysis of p-to-n type conductivity processes on the identical samples of vacancy doped p-CdxHg1-xTe (x≈0.2) under IBM and anodic oxide annealing and on the identical samples of As-doped p-CdxHg1-xTe (x≈0.22) under IBM and anodic oxide annealing have been carried out. The conversion of type of conductivity has been observed at the considerable depth of the vacancy doped material both under IBM or under anodic oxide annealing while in the case with As-doped material ony under IBM. It was considered that conversion in all these processes was determined by the mercury interstitial diffusion from corresponding mercury diffusion source and recombination with its native acceptors - cationic vacancies (in the first case) or with donor complex formations (in the second one). It has been shown that in the vacancy doped p-CdxHg1-xTe the effective diffusion coefficients for the mercury interstitials that determines the depth of the converted layer are equal each other at equal temperatures either under thermal annealing in the saturated mercury vapour or anodic oxide annealing. It proves the identity of the mercury concentration in the diffusion source. Absence of the conversion under anodic oxide annealing in the As-doped p-CdxHg1-xTe is explained by insufficient Hg concentration in the source and it matches well with necessary condition for donor complex formation as it takes place under IBM.
An analysis of the relaxation process for cation defects in Hg1-xCdxTe that form in the thermal spike at ion-beam milling (IBM) taking into account the neutral mercury bi-vacancies has been performed. It has been enabled to define a correct expression for concentration of the interstitial mercury created at IBM in the mercury diffusion source that is a boundary condition for equations of the diffusion kinetics. Expressions for depth of the p-n conductivity type conversion in both vacancy-doped p-Hg1-xCdxTe and one doped with As, Sb were obtained. There was a good accord between computed dependence of the conversion depth on the ion dose for vacancy-doped Hg1-xCdxTe (x≈0.2) with available literature experimental data. This fact well confirm the model adequacy.
The influence of a light hole band nonparabolicity on the transport properties of CdxHg1-xTe and InSb in both intrinsic and extrinsic conductivity regions is investigated. The parameters of heavy and light holes (concentration and mobility) for homogeneous samples of p-CdxHg1-xTe (x equals 0,2 - 0,23) are determined from the Hall coefficient field dependencies. These parameters and similar data for InSb available in the literature have been compared with results of analytical computations based on the recent concepts of material parameters.
The influence of thermal annealing on electrical properties of the p-n structures formed by ion beam milling (IBM) on usually vacancy doped CdxHg1-xTe single crystals with p(77K) equals 5.8 X 1015 cm-3 was investigated. After IBM of the initial samples the n-type layers were created with the thickness about 10 (mu) and electron concentration of the mane part of n-type layers 5 X 1014 cm-3. P-n structures were annealed on air at 85, 120 and 160 degrees C during 1, 2 and 4 hours. Degradation of the p-n structure after every annealing step was estimated on changes of the Hall coefficient magnetic field dependence. It was revealed that degradation of the p- n structure took place due to progressive thickness decreasing of n-layer through Hg passing to intersites and vacancy creation. The critical temperature during technology steps is equal about 100 degrees C.
The influence of thermal annealing on electrical properties of p-n structures formed by ion beam milling (IBM) on vacancy doped CdxHg1-xTe (x equals 0.205) single crystals with p (77 K) equals 5.8(DOT)1015 cm-3 was investigated. After IBM of the initial samples the n-type layers were created with the thickness about 10 (mu) and electron concentration of the main part of n-type layers 5(DOT)1014 cm-3. P-n structures were annealed in air at 85, 120 and 160 degree(s)C during 1, 2, and 4 hours. Degradation of the p-n structure after every annealing step was estimated on changes of the Hall coefficient dependence of magnetic field. It was revealed that degradation of the p-n structure took place due to progressive thickness decreasing of n-layer through Hg passing to intersites and vacancy creation. The critical temperature during technology steps is equal about 100 degree(s)C.
Results of complex investigations of n- and p-type Hg1-xCdxTe (MCT) etching in RF mercury glow discharge have been presented. Discharge was induced in quasi-closed volume. Results of technology parameter influence onto velocity of etching have been presented. It has been shown that MCT treatment by mercury ions can be carried out with etching velocity up to 30 micrometers /hour. Surface heating under these conditions slightly increases the temperature (up to 50 degree(s)C) and stoichiometry deviations are absent. It has been found that the width of disturbed layer depends on bias voltage and is smaller than 2.5 micrometers . Electrophysical parameters of n- and p-type MCT after processing have been studied. Etching of n-MCT forms the n+-n structure. The width of n+-layer corresponds to the width of disturbed zone. In the case of p-MCT, there exists inversion of conductivity type at depths exceeding those corresponding to the case of argon ions etching. It is supposed that high inversion velocity is caused by saturation of MCT surface by mercury ions during treatment.
Ion beam milling effect on electrical properties of usual vacancy doped and especially In compensated p-CdxHg1-xTe has been investigated. In all cases after ion beam milling by low energy neutralized. Ar ions n-p structure with thickness of n-layers that depended on initial hole concentration and irradiation dose has been created. It was shown that in the usual vacancy doped CdxHg1-xTe the electron concentration in n-layers well agrees with concentration of residual donors. For the especially doped samples the electron concentration was determined by the In donor impurities' concentration. The possibility of the n-p+ CdxHg1-xTe photodiode fabrication with optimum required carriers' concentration both in n- and p-regions has been demonstrated by ion beam milling of the especially doped samples.
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