Effect of successive implantation of Ag+(Cu+) and Xe+ ions on the recombination properties of CdxHg1−x Te crystals

The effect of successive double implantation of Ag⁺(Cu⁺) and Xe⁺ ions on the recombination properties of Cd_xHg_1−x Te (0.2<x<0.3) crystals has been investigated. It is shown that after implantation of ions of one chemical element, followed by diffusion thermal annealing at temperatures below 150–200 K, recombination through local levels lying 30±5 meV below the conduction band bottom dominates. Successive double implantation of Ag⁺(Cu⁺) and Xe⁺ ions followed by diffusion thermal annealing changes the course of the temperature dependence of the lifetime of the nonequilibrium charge carriers. It was determined that for Cd_xHg_1−x Te crystals with x⋍0.20–0.25 in the temperature interval 700–200 K the lifetime of the nonequilibrium charge carriers is low (τ<0.15 μs) and does not depend on the temperature. For Cd_xHg_1−x Te crystals with x⋍0.3 recombination of nonequilibrium charge carriers occurs through two types of levels: in the temperature range 140–200 K — deep levels E _t1⋍E _c −51 meV and at lower temperatures (77–140 K) — through shallower levels E _t2⋍E _c −(16±2) meV. Fiz. Tekh. Poluprovodn. 31, 786–789 (July 1997)     

Lpe growth of Hgl−xCdxTe using conventional slider boat and effects of annealing on properties of the epilayers

The epitaxial layers of Hg_1−xCd_xTe (0.17≦×≦0.3) were grown by liquid phase epitaxy on CdTe (111)A substrates using a conventional slider boat in the open tube H₂ flow system. The as-grown layers have hole concentrations in the 10¹⁷− 10¹⁸ cm⁻³ range and Hall mobilities in the 100−500 cm²/Vs range for the x=0.2 layers. The surfaces of the layers are mirror-like and EMPA data of the layers show sharp compositional transition at the interface between the epitaxial layer and the substrate. The effects of annealing in Hg over-pressure on the properties of the as-grown layers were also investigated in the temperature range of 250−400 °C. By annealing at the temperature of 400 °C, a compositional change near the interface is observed. Contrary to this, without apparent compositional change, well-behaved n-type layers are obtained by annealing in the 250−300 °C temperature range. Sequential growth of double heterostructure, Hg_l−xCd_xTe/Hg_l−yCd_yTe on a CdTe (111)A substrate was also demonstrated.     

Physico-chemical properties of Ga and In dopants during liquid phase epitaxy of CdxHg1−xTe

This work deals with the study by means of radioactive tracers and autoradiography, as well as measuring of galvanomagnetic properties, of Ga and In doping of epitaxial Cd_xHg_1−xTe layers during their crystallization from a Te-rich melt. Ga and In were introduced in the form of Ga⁷² and In¹¹⁴ master alloys with Te. The effective distribution coefficients of Ga and In during the crystallization of the Cd_xHg_1−xTe solid solutions with x=0.20 to 0.23 were determined by cooling the Te-base melt to 515–470°C. Depending on the concentration of the dopants and the time-temperature conditions of Cd_xHg_1−xTe growth, these ratios for Ga and In were 1.5–2.0 and 1.0–1.5, respectively. The electrical activity of Ga and In was determined after annealing of the Cd_xHg_1−xTe layers in saturated Hg vapor at 270–300°C. In doping of the epitaxial layers to (3–8)×10¹⁴ cm⁻³ with subsequent annealing in saturated Hg vapor at ∼270°C increases the carrier lifetime approximately by a factor of two as compared with the undoped material annealed under the same conditions.     

Nearly Perfect Electrical Activation Efficiencies from Silicon-Implanted Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>N with High Aluminum Mole Fraction

Electrical activation studies of Al _x Ga_1−x N (x = 0.45 and 0.51) implanted with Si for n-type conductivity have been made as a function of ion dose and anneal temperature. Silicon ions were implanted at 200 keV with doses ranging from 1 × 10¹⁴ cm⁻² to 1 × 10¹⁵ cm⁻² at room temperature. The samples were subsequently annealed from 1150°C to 1350°C for 20 min in a nitrogen environment. Nearly 100% electrical activation efficiency was successfully obtained for the Si-implanted Al_0.45Ga_0.55N samples after annealing at 1350°C for doses of 1 × 10¹⁴ cm⁻² and 5 × 10¹⁴ cm⁻² and at 1200°C for a dose of 1 × 10¹⁵ cm⁻², and for the Al_0.51Ga_0.49N implanted with silicon doses of 1 × 10¹⁴ cm⁻² and 5 × 10¹⁴ cm⁻² after annealing at 1300°C. The highest room-temperature mobility obtained was 61 cm²/V s and 55 cm²/V s for the low-dose implanted Al_0.45Ga_0.55N and Al_0.51Ga_0.49N, respectively, after annealing at 1350°C for 20 min. These results show unprecedented activation efficiencies for Al _x Ga_1−x N with high Al mole fractions and provide suitable annealing conditions for Al _x Ga_1−x N-based device applications.     

Electrical Activation Studies of Silicon-Implanted Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>N with Aluminum Mole Fraction of 11% to 51%

Electrical activation studies of Si-implanted Al _x Ga_1−x N with an Al mole fraction of 11% to 51% have been carried out as a function of ion dose and annealing temperature. The Al _x Ga_1−x N samples were implanted at room temperature with Si ions at 200 keV in doses ranging from 1 × 10¹⁴ cm⁻² to 1 × 10¹⁵ cm⁻², and subsequently annealed from 1100°C to 1350°C for 20 min in a nitrogen environment. The maximum electrical activation efficiencies for the Al _x Ga_1−x N samples with an Al mole fraction less than 40% were obtained for samples implanted with the highest Si dose of 1 × 10¹⁵ cm⁻². On the other hand, for the Al _x Ga_1−x N samples with an Al mole fraction more than 40%, nearly perfect activation efficiencies of 99% and 100% were obtained for the samples implanted with the lowest Si dose of 1 × 10¹⁴ cm⁻². The mobility of the Si-implanted Al _x Ga_1−x N samples increased with increasing annealing temperature in spite of the increased number of ionized donors and thus increased impurity scattering, indicating that a greater amount of lattice damage is being repaired with each successive increase in annealing temperature. These results provide suitable annealing conditions for Si-implanted Al _x Ga_1−x N-based devices with an Al mole fraction from 11% to 51%.     

Measurement of minority carrier lifetime in n-type MBE HgCdTe and its dependence on annealing

Results are presented for minority carrier lifetime in n-type molecular beam epitaxy Hg_1−xCd_xTe with x ranging from 0.2 to 0.6. It was found that the lifetime was unintentionally degraded by post-growth annealing under Hg saturated conditions in a H₂ atmosphere that was both time and temperature dependent. This effect was minimal or non-existent for x∼0.2 material, but very strong for x ≥ 0.3. Hydrogen was identified as responsible for this degradation. Identical annealing in a He atmosphere avoids this degradation and results in neartheoretical lifetime values for carrier concentrations as low 1 × 10¹⁵ cm⁻³ in ≥0.3 material. Modeling was carried out for x∼0.2 and x∼0.4 material that shows the extent to which lifetime is reduced by Shockley-Real-Hall recombination for carrier concentrations below 1 × 10¹⁵ cm⁻³, as well as for layers annealed in H₂. It appears that annealing in H₂ results in a deep recombination center in wider bandgap HgCdTe that lowers the lifetime without affecting the majority carrier concentration and mobility.     

Optical and Magnetic Properties of ZnO:V Prepared by Ion Implantation

We report on the optical and magnetic properties of the magnetic semiconductor Zn(V)O fabricated by implantation of 195 keV ₅₁V⁺ ions into bulk ZnO:Al grown by a hydrothermal technique. Two sets of the samples, containing N _d –N _a ∼ 10¹⁵ cm⁻³ and 10¹⁸ cm⁻³, were implanted to doses of 1 × 10¹⁵ cm⁻², 3 × 10¹⁵ cm⁻², and 1 × 10¹⁶ cm⁻². The ion implantation was performed at 573 K. To remove irradiation-induced defects, the samples were annealed in air at 1073 K. Photoluminescence (PL) measurements of Zn(V)O films were carried out at temperatures from 10 K to 300 K. The effects of implantation dose and free carrier concentration on the magnetic properties of Zn(V)O were studied using a superconducting quantum interference device magnetometer. Ferromagnetism has been observed in annealed highly conductive samples implanted to 1 × 10¹⁶ cm⁻². The PL studies of ZnO bulk samples implanted with V⁺ have revealed that thermal annealing at 1073 K restores to a large extent the optical quality of the material. A new emission line centered at 3.307 eV has been found in the PL spectrum of the highly conductive samples implanted to the dose of 1 × 10¹⁶ cm⁻², which is most probably due to complexes involving V ions.     

Synthesis and Thermoelectric Properties of InzCo4?xFexSb12 Skutterudites

The thermoelectric properties of In-filled and Fe-doped CoSb₃ (In _z Co_4−x - Fe _x Sb₁₂) skutterudites prepared by encapsulated induction melting were examined. A single δ-phase was obtained successfully by subsequent annealing at 823 K for 120 h. The Hall and Seebeck coefficients of the In _z Co_4−x Fe _x Sb₁₂ samples had positive signs, indicating p-type conduction. The electrical conductivity was increased by Fe doping, and the thermal conductivity was decreased by In filling due to phonon scattering. The thermoelectric properties were improved by In filling and Fe doping, and were closely related to the optimum carrier concentration and phonon scattering.     

Multi-step rapid thermal annealing of boron and indium implanted Hg1−xCdxTe

In this work, we are reporting the use of a two-step rapid thermal annealing (RTA) process (250°C, 100s+340°C, 30s) for the annealing of Hg_1−xCd_xTe (MCT) implanted layers over p-type (x=0.22) substrates. We report a high value of electrical activation (70%) of the indium implants after this short RTA treatment in inert Ar atmosphere. The need of two RTA steps in the annealing recipe is shown, and so the role played by each of them: the first step annihilates the implantation damage, while the second one produces the impurity electrical activation. However, for the boron case, no electrical activity was found after several annealing processes, behaving as an inert species for the case of this bulk MCT material. We also point out the change on the substrate electrical characteristics induced by the thermal treatments, and report the convenience of a subsequent low temperature furnace annealing (200°C, 72 h) to reduce back the bulk carrier concentration to values low enough to achieve an n⁺-p IR detector structure.     

Exfoliation and blistering of Cd<Subscript>0.96</Subscript>Zn<Subscript>0.04</Subscript>Te substrates by ion implantation

As part of a series of wafer bonding experiments, the exfoliation/blistering of ion-implanted Cd_0.96Zn_0.04Te substrates was investigated as a function of postimplantation annealing conditions. (211) Cd_0.96Zn_0.04Te samples were implanted either with hydrogen (5×10¹⁶ cm⁻²; 40–200 keV) or co-implanted with boron (1×10¹⁵ cm⁻²; 147 keV) and hydrogen (1–5×10¹⁶ cm⁻²; 40 keV) at intended implant temperatures of 253 K or 77 K. Silicon reference samples were simultaneously co-implanted. The change in the implant profile after annealing at low temperatures (<300°C) was monitored using high-resolution x-ray diffraction, atomic force microscopy (AFM), and optical microscopy. The samples implanted at the higher temperature did not show any evidence of blistering after annealing, although there was evidence of sample heating above 253 K during the implant. The samples implanted at 77 K blistered at temperatures ranging from 150°C to 300°C, depending on the hydrogen implant dose and the presence of the boron co-implant. The production of blisters under different implant and annealing conditions is consistent with nucleation of subsurface defects at lower temperature, followed by blistering/exfoliation at higher temperature. The surface roughness remained comparable to that of the as-implanted sample after the lower temperature anneal sequence, so this defect nucleation step is consistent with a wafer bond annealing step prior to exfoliation. Higher temperature anneals lead to exfoliation of all samples implanted at 77 K, although the blistering temperature (150–300°C) was a strong function of the implant conditions. The exfoliated layer thickness was 330 nm, in good agreement with the projected range. The “optimum” conditions based on our experimental data showed that implanting CdZnTe with H⁺ at 77 K and a dose of 5×10¹⁶/cm² is compatible with developing high interfacial energy at the bonded interface during a low-temperature (150°C) anneal followed by layer exfoliation at higher (300°C) temperature.