Reduced Annealing Temperature Research Articles

Flexible Substrate-Compatible and Efficiency-Improved Quantum-Dot Light-Emitting Diodes with Reduced Annealing Temperature of NiOx Hole-Injecting Layer

The growing demand for wearable and attachable displays has sparked significant interest in flexible quantum-dot light-emitting diodes (QLEDs). However, the challenges of fabricating and operating QLEDs on flexible substrates persist due to the lack of stable and low-temperature processable charge-injection/-transporting layers with aligned energy levels. In this study, we utilized NiOx nanoparticles that are compatible with flexible substrates as a hole-injection layer (HIL). To enhance the work function of the NiOx HIL, we introduced a self-assembled dipole modifier called 4-(trifluoromethyl)benzoic acid (4–CF3–BA) onto the surface of the NiOx nanoparticles. The incorporation of the dipole molecules through adsorption treatment has significantly changed the wettability and electronic characteristics of NiOx nanoparticles, resulting in the formation of NiO(OH) at the interface and a shift in vacuum level. The alteration of surface electronic states of the NiOx nanoparticles not only improves the carrier balance by reducing the hole injection barrier but also prevents exciton quenching by passivating defects in the film. Consequently, the NiOx-based red QLEDs with interfacial modification demonstrate a maximum current efficiency of 16.1 cd/A and a peak external quantum efficiency of 10.3%. This represents a nearly twofold efficiency enhancement compared to control devices. The mild fabrication requirements and low annealing temperatures suggest potential applications of dipole molecule-modified NiOx nanoparticles in flexible optoelectronic devices.

Low Temperature Niobium Tungsten Oxides as Anodes for Fast Charging Li-Ion Batteries

The development of fast-charging Li-ion batteries is one of the important steps in building electric vehicles that need high power and fast charging. The reduction in the particle size to the nanometre length scale drastically improves the charging rate by increasing the surface area but lowers the volumetric energy density and can potentially result in more rapid degradation of the electrolyte via electrode-catalysed reactions. Recent reports show that niobium tungsten oxides (NbWOs) with µm sized particles serve as good anode materials for Li-ion batteries having high volumetric capacity with good cyclability at high rates while avoiding solid electrolyte interphase formation (SEI). The high rate performance of NbWOs is attributed to the topochemical charge storage mechanism that exhibits (i) minimal, highly reversible structural changes during the charge-discharge cycles, (ii) high Li-ion diffusion coefficients due to the presence of fast conducting tunnels, and (iii) high electronic conductivity upon lithiation.1,2 The NbWOs are known to crystallize into two families of different crystal structures depending on the composition and synthesis conditions. The NbWOs phases can either have tungsten bronze-type structures or block-type structures (commonly referred to as Wadsley-Roth phases). Different NbWO phases are reported in the literature3 which could serve as potential anode materials with better performance.In this work, a series of new NbWO phases have been synthesized at reduced annealing temperatures and the structure of these phases has been established using X-ray and neutron diffraction data. The electrochemical properties of NbWO/Li half cells were examined through a series of galvanostatic (dis)charge tests at varying current rates ranging from 0.2 C to 20 C. The NbWO phases delivers a high reversible capacity of 200 and 130 mAh/g at 0.2C and 10 C respectively vs. Li metal. Here we use operando powder X-ray diffraction to investigate the structural changes occurring at the anode during the charge-discharge process in the newly synthesised NbWO phases. Reference s : 1 K. J. Griffith, K. M. Wiaderek, G. Cibin, L. E. Marbella and C. P. Grey, Nature, 2018, 559, 556–563.2 C. P. Koçer, K. J. Griffith, C. P. Grey and A. J. Morris, Chem. Mater., 2020, 32, 3980–3989.3 N. C. Stephenson, Acta Crystallogr. Sect. B Struct. Crystallogr. Cryst. Chem., 1968, 24, 637–653. Figure 1

Влияние режимов формирования контактной системы Pd/Ge/Au к n-GaAs на ее электрические характеристики

The investigations of Pd/Ge/Au contact system forming regimes influence on the specific contact resistivity to n-type conductivity GaAs layer were carried out. The method of samples surface treatment before the layers evaporation and thermal annealing regimes in H2, N2 and Ar atmosphere influence on contact system parameters was investigated. The specific contact resistivity value 2-3•10-6 Ohm•cm2 at the reduced annealing temperature 190 C was archived.

Forming regimes of Pd/Ge/Au contact system to n-GaAs influence on its electric parameters

The investigations of Pd/Ge/Au contact system forming regimes influence on the specific contact resistivity to n-type conductivity GaAs layer were carried out. The method of samples surface treatment before the layers evaporation and thermal annealing regimes in H2, N2 and Ar atmosphere influence on contact system parameters was investigated. The specific contact resistivity value (2-3)· 10-6 Ohm· cm2 at the reduced annealing temperature 190oC was archived.. Keywords: Pd/Ge/Au, n-GaAs, surface treatment, thermal annealing

Rhenium-based low resistivity and low annealing temperature ohmic contacts to n-GaN

We report an ohmic contact metallization scheme for n-GaN based on a Re–Al–Ni–Au multilayer stack that offers low-resistivity and provides better edge sharpness and lower surface roughness at reduced annealing temperature compared to standard Ti–Al-based metallization. We studied three sets of samples with Re thicknesses of 10, 30, and 60 nm and measured specific contact resistances using the circular transmission line method. We obtained reliable ohmic contacts with specific contact resistance of the order of 10−6 Ω cm2 at 550 °C temperature with the contact stack having a large annealing temperature window of >300 °C for resistivity below 5 × 10−6 Ω cm2. The lowest contact resistivity, below 10−7 Ω cm2, is achieved at annealing temperature around 650–700 °C. A reduction in surface roughness by a factor of 4, with excellent edge definition for Re >30 nm thickness is observed as compared to Ti–Al contacts. Grazing incidence x-ray diffraction and electron dispersive x-ray spectroscopy (EDS) show intermetallic phases of RexNy, Re–Al–Ni, Al–Re, and Al–Au being formed. Atomic force microscope and EDS measurements show the formation of crystalline Re–Al–Ni agglomerates, surrounded by phases of AlAu2 and Al2Au5. The presence of Re seems to suppress the formation of viscous AlAu4 phase, thus minimizing the lateral flow of the metals and providing better edge acuity. The temperature dependence of contact resistivity suggests a field-emission mechanism for current transport across the contact. Our results show that Re-based ohmic contacts, with their lower annealing temperature and excellent edge definition, may offer a promising alternative to Ti–Al contacts.

High resolution physical analysis of ohmic contact formation at GaN-HEMT devices

A low ohmic contact resistance is a key request on AlGaN/GaN HEMT devices especially when dealing with higher frequency applications. In such a GaN material system very high annealing temperatures of up to 900°C are frequently necessary to achieve low ohmic resistance. It is known that high annealing temperatures could reduce electrical performance and reliability of the devices. Therefore, low contact resistances at reduced annealing temperatures are beneficial. In the present work a special SiCl4 plasma treatment was applied prior to the ohm metallisation resulting in sufficiently low ohmic resistances at a significantly reduced anneal temperature of 750°C. High resolution physical analysis by transmission electron microscopy (TEM) and time of flight secondary mass spectroscopy (TOFSIMS) have been performed to understand the structural and chemical differences between the treated ohmic contacts compared to contacts processed under standard conditions. An advanced preparation technique was developed to get access to the reaction interfaces for TOFSIMS analysis from backside. It could be shown that the SiCl4 treated samples reveal less impurities/contaminants on the ohmic metal–GaN/AlGaN interface and a different metal semiconductor alloying. The diffusion of metals like Al and Au into the semiconductor substrate was detected at the front of the TiN forming reaction.

Electrochemical Lithiation and Sodiation of Nb-Doped Rutile TiO2

As anode materials of Li-ion and Na-ion batteries, the electrochemical insertion/extraction reactions of Li and Na were investigated for a rutile-type Nb-doped TiO2 synthesized by a sol–gel method. We changed the particle and crystallite sizes of the Nb-doped rutile TiO2 powders by annealing at various temperatures between 100 and 1000 °C and prepared thick-film electrodes consisting of the powders. The anode performances were remarkably improved not only in the Li-ion battery but also in the Na-ion battery with a reduced annealing temperature of 400 from 1000 °C. We revealed that the Nb-doped TiO2 showing better high-rate performances exhibited a larger ratio of crystallite size to particle size. The size-dependent enhancement in the performance of rutile TiO2 was much more drastic than that of anatase TiO2. These results suggest that rutile’s potential diffusivity of Li and Na appeared more obviously when increasing the ratio because its diffusion coefficient is anisotropic and significantly high.

Investigation of Disilane-Based SiGe-HBT Layers for Low External Base Resistances

In the past decade there has been increased interest in utilizing SiGe-heterojunction bipolar transistors (SiGe-HBT) and in particular SiGe-BiCMOS technologies for applications in the mm-and sub-mm-wave range. High data rate communication systems and optical networks for >100Gb/s, industrial and automotive sensors at 120 GHz for velocity and position control as well as imaging systems at >160 GHz for medical and security systems are some examples for these fields of application. Key elements for the continuous improvement of the high frequency performance of SiGe-HBTs are the scaling of vertical and lateral dimensions as well as design optimization to achieve reduced parasitics. In particular the maximum oscillation frequency fmax could be increased in the last years above 0.5 THz. Beside a sufficient high cut-off frequency fT, a reduced base-collector capacitance CBC and low base resistance RB are beneficial for the fmax performance of a SiGe-HBT. In this work we investigate the behavior of the external base resistance RBext for two different epitaxial processes used in SiGe-HBTs with a silane- (SiH4) and disilane-based (Si2H6) precursor. The SiGe-layers were treated by various rapid thermal annealing (RTA). We processed different wafers with an oxide stack usually used in a standard SiGe-BiCMOS process. After the release of certain silicon regions by reactive-ion-etching the epitaxial layers were deposited. First a selective epitaxial silicon buffer was grown within oxide-free windows followed by non-selective growth of a silicon layer, the in-situ boron doped SiGe base layer and an on top silicon cap layer. For the disilane-based process the SiGe layer grows in an amorphous phase whereas for the silane-based process a poly-crystalline film is formed. The growth of the whole Si-SiGe-Si stack was adapted for disilane process in order to reach the same layer thicknesses for both variants inside oxide free windows (single-crystalline regions) as for the original silane-based process. Sheet resistance (Rs) measurements were performed on 49 points across a wafer on the poly crystalline SiGe layer on an oxide. Figure 1 shows the Rs of silane-based (#1) and disilane-based (#3) SiGe-layer after a rapid thermal annealing at 1010°C for 12s. We observe a decrease of Rs by 60% in comparison to the silane-based SiGe-layer. Even for a reduced annealing temperature of 950°C (#2) the Rs dropped down around 30% in comparison to the silan-based variant. Moreover the standard deviation of the sheet resistance in the poly-crystalline regions across the wafer becomes significantly smaller and decreased by a factor of six down to approximately 50 Ohm/square for the disilane-based SiGe stack. Secondary-ion-mass-spectroscopy (SIMS) measurements were used to characterize the boron doping and SiGe-profile inside the crystalline and poly-crystalline regions of the wafers. In the poly crystalline region the germanium and boron concentration of the disilane-based process corresponds to the distribution of the single crystalline region. However we obtain a difference in the doping distribution after epitaxy (Fig. 2a) in comparison to the silane-based process. This difference becomes more significant after the RTA and we observe a quite homogeneous distribution of Ge and boron for the silane-based SiGe-stack whereas a steeper doping is within poly-crystalline layers for the disilane-based process (Figure 2b). We address this disparity in the Ge and boron distribution to differences in the diffusion behavior for the disilane-based layer stack due to i) the deposition as an amorphous Si/SiGe/Si layer and ii) the grain size of the poly-crystals after the final RTA. For our operation point the loading effect during the disilane-based epi-process leads to a 40% increased boron dose in the external base region compared to the silane-based process and without increasing the B doping inside the single crystalline region. This is beneficial for the behavior of RBext. Finally we applied both variants in a standard SiGe-BiCMOS flow. The overall performance of the SiGe-HBT depends of course on several other aspects like base-emitter and base-collector capacitances and the influence of changing one parasitic component has to be carefully evaluated. Nevertheless the external base resistance as well as the contact resistance dropped by 55% and 45%, respectively, for the disilane-based process and show the benefits for the use of this type of epitaxial layer depositions in advanced SiGe-HBTs. Figure 1

Vertical Graphene Growth from Amorphous Carbon Films Using Oxidizing Gases

Amorphous carbon thin films are technologically important materials that range in use from the semiconductor industry to corrosion-resistant films. Their conversion to crystalline graphene layers has long been pursued; however, typically this requires excessively high temperatures. Thus, crystallization routes which require reduced temperatures are important. Moreover, the ability to crystallize amorphous carbon at reduced temperatures without a catalyst could pave the way for practical graphene synthesis for device fabrication without the need for transfer or post-transfer gate deposition. To this end we demonstrate a practical and facile method to crystallize deposited amorphous carbon films to high quality graphene layers at reduced annealing temperatures by introducing oxidizing gases during the process. The reactive gases react with regions of higher strain (energy) in the system and accelerate the graphitization process by minimizing criss-cross-linkages and accelerating C–C bond rearrangement at de...

Microstructure of V-based ohmic contacts to AlGaN/GaN heterostructures at a reduced annealing temperature

Ohmic contacts with V/Al/Ni/Au and V/Ni/Au metalization schemes were deposited on AlGaN/GaN heterostructures. The dependence of the specific contact resistance on the annealing conditions and the V:Al thickness ratio was shown. For an optimized electrode stack, a low specific contact resistance of 8.9 × 10−6 Ω cm2 was achieved at an annealing temperature of 650 °C. Compared to the conventional Ti/Al/Ni/Au contact, this is a reduction of 150 K. The microstructure and contact formation at the AlGaN/metal interface were investigated by transmission electron microscopy including high-resolution micrographs and energy dispersive X-ray analysis. It was shown that for low-resistive contacts, the resistivity of the metalization has to be taken into account. The V:Al thickness ratio has an impact on the formation of different intermetallic phases and thus is crucial for establishing ohmic contacts at reduced annealing temperatures.

Correlation of the energy product with evolution of the nanostructure in the Y,Dy,Nd–(Fe, Co)–B magnetic alloy

The devitrification behavior of nanocrystalline MRE2(Fe,Co)14B+ZrC (MRE=Nd+Y+Dy) was studied using differential scanning calorimetry (DSC), synchrotron high temperature x-ray diffraction, and analytical transmission electron microscopy (TEM) techniques. Alloy ribbons were melt spun at 25 m/s to obtain an amorphous structure. Optimum hard magnetic properties (Br=7.2 kG, Hc=12.7 kOe and (BH)max=10.8 MG Oe) were obtained in ribbons annealed at 750 °C for 15 min. A reduced annealing temperature of 638 °C and holding time from 0 to 11 min were chosen based on DSC analysis. Large changes in both microstructure and hard magnetic properties were found in a narrow window of annealing time, 4.5–6 min, resulting in a dramatic increase in energy product, remanence and coercivity: 0.96 MG Oe, 5.2 kG, 2.7 kOe to 5.7 MG Oe, 7.2 kG, 8.5 kOe for (BH)max, Br and Hc, respectively. Energy dispersive x-ray spectroscopy and energy filtered TEM analyses indicate that Zr- and C-rich particles (∼5 nm) and thin grain boundary layers (1–2 nm thick) are formed surrounding 2-14-1 hard phase grains when the annealing time is over 6 min. Further annealing resulted in a more distinct hard phase surrounded by a nonmagnetic grain boundary phase ∼1 nm in thickness. The thin grain boundary layer phase starts to disappear with annealing time over 11 min. The partitioning behavior of various elements at different annealing conditions appears to be associated with significant changes in magnetic properties, leading to an improved optimum microstructure.

Defect suppression of indium end-of-range during solid phase epitaxy annealing using Si 1− yC y in silicon

We report on the elimination of defect formation which is associated with high dose indium implantations under solid phase epitaxial regrowth (SPER) annealing conditions of 650–800 °C. This is achieved by incorporating a layer of epitaxially grown Si 1− y C y layer, strategically located at the end-of-range (EOR) of the implant profile. An indium implant of 115 keV at 1 × 10 14 cm − 2 was performed followed by annealing at temperature ranges of 650–800 °C. Samples with the Si 1− y C y layer revealed the elimination of secondary EOR defects with effectively suppressed indium transient enhanced diffusion (TED), indicating the function of carbon as an efficient sink for silicon interstitials at reduced annealing temperatures, in the SPER dopant activation regime.

Texture Control of Sol‐Gel Derived Pb(Mg1/3Nb2/3)O3–PbTiO3 Thin Films Using Seeding Layer

Lead magnesium niobium titanate (PMNT) thin films with a composition near the morphotropic phase boundary were prepared on conventional Pt(111)/Ti/SiO2/Si substrates using a modified sol‐gel process. A PbO seeding layer was introduced to the interface between the PMNT layer and the substrate to enhance the [001]‐preferential orientation of the PMNT film. Single‐phase perovskite PMNT films with highly [001]‐preferential orientation were obtained at reduced annealing temperatures compared with the PMNT films directly deposited on the same substrates. The dielectric and ferroelectric properties of the prepared PMNT films were evaluated as a function of annealing temperature.

Accurate STR Allele Designations at the FGA and vWA Loci Despite Primer Site Polymorphisms

Polymerase chain reaction (PCR)-based STR DNA typing systems are used extensively in the field of human identification. Under optimal PCR conditions, the amplicon yield from both alleles of an STR locus is expected to be approximately equivalent. However, it is reasonable to expect that rare genomic sequence polymorphisms will co-localize with well-designed primer sets and induce allele imbalance or "dropouts". Two samples were identified in the course of genotyping thousands of individuals with AmpF/STR Profiler Plus that showed strong disparity in amplitude peak height of heterozygous peaks at the loci vWA and FGA. These samples were reamplified at reduced annealing temperature in an attempt to balance the peak heights. Nucleotide sequencing documented polymorphisms at the PCR primer binding sites of the affected alleles. The results indicate that reducing the annealing temperature to improve primer-binding efficiency at the mismatch and employing an alternative multiplex enhanced the data from both samples. Reducing annealing temperatures could provide a simple general solution to improving data quality for samples where polymorphisms are suspected to cause allele imbalance. Finally, we report on additional polymorphisms surrounding the vWA locus in a genetically diverse population.

Sol−Gel Fabrication and Electrical Property of Nanocrystalline (RE2O3)0.08(ZrO2)0.92 (RE = Sc, Y) Thin Films

Dense, crack-free, and homogeneous nanocrystalline (RE2O3)0.08(ZrO2)0.92 (RE = Sc, Y) thin films (≈0.58-μm thick) on monocrystalline silicon (100) wafers were fabricated by a simple sol−gel spin-coating method under reduced annealing temperature and were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), Auger electron spectroscopy (AES), and impedance studies. Some key correlative processing parameters such as coating solution composition and gel-firing temperature have been optimized. XRD results indicate that the as-fabricated (Sc2O3)0.08(ZrO2)0.92 thin films can achieve good crystallization in a pure cubic phase at a relatively low annealing temperature not exceeding 800 °C in 2 h and the nanocrystal size grows with elevation of the annealing temperature. AFM and SEM micrographs show that the (RE2O3)0.08(ZrO2)0.92 nanocrystals after undergoing annealing at 950 °C for 2 h are uniform in the size range of 50−60 nm. AES profile analysis suggests that the (Sc2O3)0.08(ZrO2)0.92 thin films are fairly pure with good composition homogeneity in the depth range of 75−500 nm. Impedance measurements reveal that the oxide ion conductivity of the nanocrystalline thin films is 10 times higher than that of the respective bulk material at temperatures beyond 600 °C. A decrease of grain boundary resistance related to interfacial effects is predominately responsible for this electrical conductivity enhancement.

Identification of streptococci isolated from various sources by determination ofcfbgene and other CAMP-factor genes

In the present study, the CAMP-factor (cfb) gene of streptococci of serological group B (Streptococcus agalactiae) and the CAMP-factor (cfu) gene of S. uberis could be amplified by polymerase chain reaction. A cfb specific amplicon could be observed for all 128 phenotypically CAMP-positive S. agalactiae, for the phenotypically CAMP-negative S. agalactiae strain 74-360, and for 2 S. difficile reference strains. A cfu specific amplicon could be observed for all 7 phenotypically CAMP-positive S. uberis. Four S. agalactiae strains isolated from 4 cows with mastitis appeared to be phenotypically CAMP-negative and negative in the cfb gene PCR. The CAMP-positive and CAMP-negative isolates, including both S. difficile, could be identified as S. agalactiae by amplification of a S. agalactiae specific part of the V2 region of the 16S rRNA and a species-specific part of the 16S-23S rRNA intergenic spacer region. Amplification of an internal fragment of the cfb gene with a reduced annealing temperature yielded positive reactions not only for CAMP-positive S. agalactiae, but also for phenotypically CAMP-positive S. pyogenes (n = 4), S. canis (n = 28), and S. uberis (n = 7), indicating a close relation of the CAMP genes of these 4 species. The relation could be further demonstrated by sequencing the internal fragment of the CAMP-factor (cfg) gene of S. canis and comparing the sequence with those of S. agalactiae, S. pyogenes, and S. uberis.Key words: CAMP factor, cfb, cfu, S. canis.

Identification of streptococci isolated from various sources by determination of <i>cfb </i>gene and other CAMP-factor genes

In the present study, the CAMP-factor (cfb) gene of streptococci of serological group B (Streptococcus agalactiae) and the CAMP-factor (cfu) gene of S. uberis could be amplified by polymerase chain reaction. A cfb specific amplicon could be observed for all 128 phenotypically CAMP-positive S. agalactiae, for the phenotypically CAMP-negative S. agalactiae strain 74-360, and for 2 S. difficile reference strains. A cfu specific amplicon could be observed for all 7 phenotypically CAMP-positive S. uberis. Four S. agalactiae strains isolated from 4 cows with mastitis appeared to be phenotypically CAMP-negative and negative in the cfb gene PCR. The CAMP-positive and CAMP-negative isolates, including both S. difficile, could be identified as S. agalactiae by amplification of a S. agalactiae specific part of the V2 region of the 16S rRNA and a species-specific part of the 16S-23S rRNA intergenic spacer region. Amplification of an internal fragment of the cfb gene with a reduced annealing temperature yielded positive reactions not only for CAMP-positive S. agalactiae, but also for phenotypically CAMP-positive S. pyogenes (n = 4), S. canis (n = 28), and S. uberis (n = 7), indicating a close relation of the CAMP genes of these 4 species. The relation could be further demonstrated by sequencing the internal fragment of the CAMP-factor (cfg) gene of S. canis and comparing the sequence with those of S. agalactiae, S. pyogenes, and S. uberis.

Structural studies of the effects of silver and gold on the YBaCuO superconducting films formed from layer structures

Superconducting YBaCuO films have recently been formed using both Ag/Cu/BaO/Y2O3/MgO and Au/Cu/BaO/Y2O3/MgO structures, where MgO is the substrate. The addition of a silver layer in the starting structure improves the film resistances from those using the Cu/BaO/Y2 O3 /MgO structure, especially at lower annealing temperatures. This allows the formation of superconducting films between annealing temperatures of 750 and 900 °C, all with an onset above 85 K. The transition into full superconductive state, however, broadens with decreasing annealing temperatures, with zero resistance between 80 and 60 K. This dependence on annealing temperatures is studied by x-ray diffraction, which shows the diminishing signals of the superconducting YBa2 Cu3 O7 phase at reduced annealing temperatures. A study of the surface morphology provides further information regarding the roles of silver and gold on the superconducting films formed.

Effects of silver and gold on the YBaCuO superconducting thin films with the use of Ag/Cu/BaO/Y2O3 and Au/Cu/BaO/Y2O3 structures

Superconducting YBaCuO films have been fabricated from the Ag/Cu/BaO/Y2O3 and Au/Cu/BaO/Y2O3 layer structures on MgO substrates. Compared to those using only the Cu/BaO/Y2O3 structure, the addition of a silver layer to the starting structures improves the film resistances, especially at reduced annealing temperatures, allowing the study of the dependence of the superconducting transition on the annealing temperatures between 900 and 750 °C. Zero resistance is observed at 80 K for the Ag/Cu/BaO/Y2O3 structure annealed at 900 °C. The use of a gold layer, on the other hand, reduces the temperature for zero resistance to 75 K for a similarly annealed film. All the superconducting films are composed of the YBa2Cu3O7 and the Y2BaCuO7 phases, with starting compositions off that of the former. Structural and morphological analysis of the films is performed to explore the roles of silver and gold in the films formed.

Annealing of Vk-type centres in mixed KBr-KI crystals

The annealing of IBr- and I2-Vk-type centres in mixed KBr-KI crystals with varying iodine concentration has been investigated by the fractional glow technique. It is shown that for an I- concentration exceeding 1-5 mol.% the hole delocalisation from iodine monomers and dimers is characterised by both a reduced activation energy and a reduced annealing temperature. The kinetics of the corresponding thermoactivated recombination process reveals clearly a diffusion-controlled behaviour. A new mechanism of hole migration through chains of spatially separated iodine impurities is proposed.