Growth and characterization of Cd-Doped InGaAsP/InP double heterostructure lasers

The liquid phase epitaxial growth of Cd-doped InGaAsP/InP double heterostructure lasers (1.3 μm) has been studied. Cd has been found to have a smoothing effect on the morphology of the quaternary layers and a typical terracing effect on that of InP found also by doping with Zn. The defects, revealed by etching, were found to propagate in one to one correspondence from the substrate throughout the whole structure with no generation of defects even in a highly doped material. Electrical saturation at p ~2.10^l8Cm^-3 was found in InP by Hall measurements while no saturation was found in the quaternary up to a hole concentration of ~2.10^l9cm^-3. A lattice mismatch which is linearly dependent on the amount of Cd in the liquid was found by X-ray analysis. Cd was found to greatly facilitate the location of the p-n junction within the active region because of its low diffusion. Low threshold, very high external differential quantum efficiency, and high uniformity characterize the lasers made of this material. The results obtained in this work suggest that Cd should be considered as a promising candidate for a p-type dopant in fabrication of quaternary devices.     

A comparison between atomic concentration profiles and defect density profiles in GaAs annealed after implantation with beryllium

Semi-insulating chromium-doped GaAs was implanted with 100 keV Be ions to fluences of 5 × 10¹³ and 1 × 10¹⁵ ions/cm². Specimens were annealed at 800°C for thirty minutes. Beryllium atomic concentration profiles, as determined by secondary ion mass spectrometry (SIMS), were compared to the defect density profiles obtained from transmission electron stereomicroscopy techniques for the annealed samples. A major redistribution of Be was observed compared to the as-implanted distribution after annealing at the higher fluence, whereas only a slight redistribution of Be occurred for the lower fluence. A major difference in the defect density profiles was observed with the fluences used for this study in the region where the annealed specimens were compared. The distribution of defects throughout the implanted-annealed layer was examined in GaAs annealed after implantation with the higher fluence using sectioned specimens. The relationships between the atomic Be concentration profile, the defect density profile, and the distribution of some specific defects were compared in these sectioned layers. The distribution and size of defects appear to be directly influenced by the Be concentration and its associated implantation induced damage.     

Diffusion of zinc into ion-implanted gallium arsenide

A study has been made of the diffusion of zinc, from a vapour source, into GaAs slices which had been previously implanted with various ion species. A radiotracer sectioning technique was used to measure the zinc diffusion profiles. It was found that the various implanted ion species (H⁺, He⁺, N⁺, Zn⁺, As⁺) had different effects on the zinc diffusion. The results could not be attributed solely to native defects produced by radiation damage. The heavier ion species increased the zinc concentration in the implanted region, but not beyond. The lighter species substantially increased the zinc diffusion rate and altered the resultant concentration profiles. Uphill diffusion was seen in slices which had been given a single high energy H⁺ implant. The results obtained are compared to those of Radiation-Enhanced-Diffusion experiments. It is suggested that the rate of incorporation of dopant species into the host semiconductor lattice is an important influence on the diffusion mechanism and the shape of the concentration profile.     

Diffusion-profile measurement in InP with Schottky diodes

Measurements of the doping profile resulting from the diffusion of Cd into lowly-doped n-type InP are reported. The measurements were taken with Au Schottky contacts. In order to probe the doping profile in its entirety with the limited resolution depth of the Schottky diodes, thin layers of the diffused samples were removed by chemical etching in a well-controlled fashion. The etching procedure leading to smooth crystal surfaces is described in detail. The diffusion profile of Cd is characterized by a flat portion in the low 10¹⁸ cm^?3 extending to a sharp gradient coinciding with the shallow diffusion front detectable by cleaving and stain etching. Between the shallow and second diffusion front very low p-type doping is found whereas beyond the second diffusion front the n-type conductivity of the substrate is attained. Thus Cd leads to a p⁺pn transition in n^?-InP.     

Diffusion of Cd And Zn In InP between 550 and 650°C

A large number of diffusions have been carried out in sealed quartz ampoules in the temperature range 550–650°C using Zn and Cd in InP. Three-fronted profiles were observed at 650°C for both Cd and Zn and the diffused samples were extensively analysed using Hall measurements, electron beam induced current, electrochemical carrier concentration profiling and thermal probing. These electrical measurements identified the p/n junction unambiguously and indicated a region of high compensation between the p/n junction and the third line. The weight of P added to the ampoule had little effect up to 0.4mg in 0.75cm³ volume at which point a dramatic reduction in diffusion depth for all fronts occurred for increasing P. Diffusion coefficients for Cd and Zn were estimated and plotted as a function of temperature.     

Secondary defect profile related to low energy implanted boron measured up to 3.5 µm depth into Si-substrates

Low energy implantation is one of the most promising options for ultra shallow junction formation in the next generation of silicon BiCMOS technology. Among the dopants that have to be implanted, boron is the most problematic because of its low stopping power (large penetration depth) and its tendency to undergo transient enhanced diffusion and clustering during thermal activation. This paper reports an experimental study of secondary defect profiles of low energy B implants in crystalline silicon. Shallow p⁺n junctions were formed by low energy B implantation—10¹⁵ cm⁻² at 3 keV—into a reference n-type crystalline silicon or pre-amorphized n-Si with germanium −10¹⁵ cm⁻² at 30 keV, 60 keV, and 150 keV. Rapid Thermal Annealing (RTA) for 15 s at 950°C was then performed. Secondary defect profiles induced by this process are measured with isothermal transient capacitance in association with Deep Level Transient Spectroscopy (DLTS). Relatively high concentrations of electrically active defects have been obtained up to 3.5 μm into the crystalline silicon bulk. The relation of these defects with boron is discussed. The results of this study are in agreement with boron transient enhanced diffusion in Si-substrate as has been reported by Collart using Secondary Ion Mass Spectrometry (SIMS) measurements.     

Faster Diffusion of Oxygen Along Dislocations in (La,Sr)MnO3+δ Is a Space-Charge Phenomenon

In displaying accelerated oxygen diffusion along extended defects, (La,Sr)MnO_3+δ is an atypical acceptor-doped perovskite-type oxide. In this study, ¹⁸O/¹⁶O diffusion experiments on epitaxial thin films of La_0.8Sr_0.2MnO_3+δ and molecular dynamics (MD) simulations are combined to elucidate the origin of this phenomenon for dislocations: Does diffusion occur along dislocation cores or along space-charge tubes? Transmission electron microscopy studies of the films revealed dislocations extending from the surface. ¹⁸O penetration profiles measured by secondary ion mass spectrometry indicated (slow) bulk diffusion and faster diffusion along dislocations. Oxygen tracer diffusivities obtained for temperatures 873 ≤ T [K] ≤ 973 were over two orders of magnitude higher for dislocations than for the bulk. The activation enthalpy of oxygen diffusion along dislocations, of (2.95 ± 0.21) eV, is surprisingly high relative to that for bulk diffusion, (2.67 ± 0.13) eV. This result militates against fast diffusion along dislocation cores. MD simulations confirmed no accelerated migration of oxide ions along dislocation cores. Faster diffusion of oxygen along dislocations in La_0.8Sr_0.2MnO_3+δ is thus concluded to occur within space-charge tubes in which oxygen vacancies are strongly accumulated. Reasons for and the consequences of space-charge zones at extended defects in manganite perovskites are discussed.     

The annealing of Cd1−xZnxTe in CdZn vapors

As-grown CdZnTe usually contains defects, such as twins, subgrain boundaries, dislocations, and Te precipitates. It is always important to anneal CdZnTe slices in Cd vapor to eliminate these defects, especially Te precipitates. The exchange of Zn atoms between the slices and the vapor plays an important role during the annealing process. In this paper, the effects of Zn partial pressure on the properties of the annealed slices are studied carefully by measuring the concentration profiles, the infrared (IR) transmission spectra, and the x-ray rocking curves. It was found that a surface layer with different compositions and possibly different structure from the bulk crystal formed during the annealing of CdZnTe samples in the saturated Zn vapor. The accumulation of excess Te in the surface layer helps to increase the IR permeability of the bulk crystal greatly. To improve the crystallization quality, a lower Zn-pressure annealing should be used following the high Zn-pressure annealing. The diffusion of Zn in the bulk crystal has also been analyzed at the temperatures of 700°C and 500°C. Calculations determined that D_Zn (700°C)=4.02 × 10⁻¹² cm²s⁻¹ and D_Zn (500°C)=1.22 × 10⁻¹³ cm²s⁻¹.     

Study on the diffusion of Cd and Zn IN InP

 The study on the diffusion of Cd and Zn in InP at a temperature range of 450—700℃ and their compared results are described in this paper.The effects of various impurity sources,such as Cd and Zn as well as their compounds on the results of diffusion are investigated intensively.Using X_j~2/t ratio defined by the square of the diffusion depth X_j~2 and time t as a measure of the diffusion velocity,we show the plots of X_j~2/t vs temperature T.It is found that the diffusion velocity of Cd, especially CdP_2 diffusion sources is slower and thus easier to control the diffusion depth and concentration.However they are more ideal diffusion impurity sources.We explain the complication phenomena of Cd-and Zn-diffusion in InP with neutral complex presented by Tien(1979).     

Two series of “dislocation” photoluminescence bands in cadmium telluride crystals

Generation of dislocations in CdTe crystals induces new lines in the radiative recombination spectra, so-called “dislocation” photoluminescence bands. The spectral distribution of the “dislocation” photoluminescence bands and the spatial distribution profiles of their intensity in the vicinity of the points of indentation on the (111) and (001) faces are obtained. From the comparison of the profiles with the crystallographic structure of dislocations, the types of defects responsible for two groups of emission bands are identified. One of the groups (with the main peak at 841 nm) is controlled by the electron states of 60° dislocations with extra half-planes framed by tellurium atoms, referred to as Te(g) dislocations. The emission lines of the other group (with the peak at 806 nm) correspond to the ordered structures of point defects generated by the steps on the screw segments of dislocation half-loops with the Cd(g) head dislocations.     

Ag/Ni Metallization Bilayer: A Functional Layer for Highly Efficient Polycrystalline SnSe Thermoelectric Modules

The structural and electrical characteristics of Ag/Ni bilayer metallization on polycrystalline thermoelectric SnSe were investigated. Two difficulties with thermoelectric SnSe metallization were identified for Ag and Ni single layers: Sn diffusion into the Ag metallization layer and unexpected cracks in the Ni metallization layer. The proposed Ag/Ni bilayer was prepared by hot-pressing, demonstrating successful metallization on the SnSe surface without interfacial cracks or elemental penetration into the metallization layer. Structural analysis revealed that the Ni layer reacts with SnSe, forming several crystalline phases during metallization that are beneficial for reducing contact resistance. Detailed investigation of the Ni/SnSe interface layer confirms columnar Ni-Sn intermetallic phases [(Ni₃Sn and Ni₃Sn₂) and Ni_5.63SnSe₂] that suppress Sn diffusion into the Ag layer. Electrical specific-contact resistivity (5.32 × 10^?4 Ω cm²) of the Ag/Ni bilayer requires further modification for development of high-efficiency polycrystalline SnSe thermoelectric modules.     

Boron implantation and epitaxial regrowth studies of 6H SiC

Implantation of B has been performed into an epitaxially grown layer of 6H SiC, at two different B concentrations, 2×10¹⁶ cm⁻³ and 2×10¹⁸ cm⁻³. Subsequently, an epitaxial layer was regrown on the B implanted layer. The samples were investigated by transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS). In the highly B-doped layers plate-like defects were found, associated with large strain fields, and an increased B concentration. These defects were stable at the originally implanted region during regrowth and at anneal temperatures up to 1700°C. In the samples implanted with the lower B concentration, no crystal defects could be detected by TEM. No threading dislocations or other defects were observed in the regrown epitaxial layer, which shows the possibility to grow a layer with high crystalline quality on B implanted 6H SiC. By SIMS, it was found that B piles up at the interface to the regrown layer, which could be explained by enhanced diffusion from an increased concentration of point defects created by implantation damage in the region. B is also spread out into the original crystal and in the regrown layer at a concentration of below 2×10¹⁶ cm⁻³, with a diffusion constant estimated to 1.3×10⁻¹² cm²s⁻¹. This diffusion is most probably not driven by implantation damage, but by intrinsic defects in the grown crystal. Our investigation shows that the combination of implantation and subsequent regrowth techniques could be used in SiC for building advanced device structures, with the crystal quality in the regrown layer not being deteriorated by crystal defects in the implanted region. A device process using B implantation and subsequent regrowth could on the other hand be limited by the diffusion of B.     

The electrical properties of zinc diffused indium phosphide

The electrical properties of p-type layers of InP, formed by the diffusion of zinc into n-type material, are studied. A wide range of diffusion conditions are used and both homogeneously doped specimens and those containing a zinc atom concentration gradient are produced. The impurity atom distribution of the diffused crystals is characterised by radiotracer analysis. p?n junction measurements on non-homogeneously doped specimens indicate that the number of zinc atoms in a diffused layer is much greater than the number of shallow acceptors. This non-correspondence of atom and carrier concentrations is confirmed by four point resistivity, Hall effect and capacitance-voltage measurements. The first two of these techniques are used to produce carrier concentration profiles which are compared with corresponding radio-tracer profiles. The carrier profiles are achieved by both serial sectioning and multiple specimen techniques. A gold probe point contacting procedure is developed for the Hall Effect measurements from which a plot of carrier mobility versus carrier concentration, in the range 5 × 10¹⁸ – 5 × 10¹⁹cm^?3, is produced for p-type InP.     

Low-temperature Zn- and Cd-diffusion profiles in InP and formation of guard ring in InP avalanche photodiodes

Zn and Cd diffusion in InP were studied in the wide temperature range of 350-580°C to realize a guard ring in InP avalanche photodiodes (APD's). Hole-concentration profiles for Zn and Cd diffusions at various temperatures were found to be expressed by a unified empirical curve, which decreases exponentially with the distance from the surface, and abruptly decreases at the diffusion front. A graded junction can be formed by diffusion at temperatures lower than 500°C for the n-InP background carrier concentration of 1016cm-3, while an abrupt junction can be formed by higher temperature diffusion. Breakdown voltages for the graded-junction diodes formed by low-temperature diffusion were confirmed to be higher than those for the abrupt-junction diodes formed by the higher temperature diffusion. A guard ring formed by the low-temperature Cd diffusion enabled planar-type InP and InGaAs/InP APD's to have uniform multiplication in the photosensitive area without any edge breakdown.     

Tunable Oxygen Diffusion and Electronic Conduction in SrTiO3 by Dislocation‐Induced Space Charge Fields

Plastic strain engineering was applied to induce controllable changes in electronic and oxygen ion conductivity in oxides by orders of magnitude, without changing their nominal composition. By using SrTiO₃ as a model system of technological importance, and by combining electrical and chemical tracer diffusion experiments with computational modeling, it is revealed that dislocations alter the equilibrium concentration and distribution of electronic and ionic defects. The easier reducibility of the dislocation cores increases the n‐type conductivity by 50 times at oxygen pressures below 10^?5 atm at 650 °C. At higher oxygen pressures the p‐type conductivity decreases by 50 times and the oxygen diffusion coefficient reduces by three orders of magnitude. The strongly altered electrical and oxygen diffusion properties in SrTiO₃ arise because of the existence of overlapping electrostatic fields around the positively charged dislocation cores. The findings and the approach are broadly important and have the potential for significantly impacting the functionalities of electrochemical and/or electronic applications such as thin film oxide electronics, memristive systems, sensors, micro‐solid oxide fuel cells, and catalysts, whose functionalities rely on the concentration and distribution of charged point defects.     

Electrical activity of iodine-diffused CdTe

The electrical activity of iodine in CdTe is discussed when iodine is introduced into the CdTe by diffusion from the vapour phase. It is compared both with the total concentration of iodine in the diffused CdTe slices and with the electrical activity in CdTe slices which have been annealed under Cd- and Te-saturated vapour pressures. Iodine-diffused slices of CdTe were profiled by secondary ion mass spectrometry (SIMS) to obtain the total iodine concentration and by capacitance-voltage (C-V) techniques to obtain the net concentration of electrically active iodine. After annealing with iodine in the form of Cdl₂, the slices were p-type, similar to those obtained when CdTe was annealed in either excess Te or Cd vapour, and they showed no significant increase in electrical activity. If Cd was added to the Cdl₂ diffusion source or the CdTe was given a subsequent anneal in cadmium vapour, the slices became n-type. The results indicated that in all cases a neutral layer composed of Cd _nI_m (m and n are integers) formed on the surface layers, whereas if Cd was involved in the diffusion, some of the iodine existed in an electrically active form deeper into the slice with a maximum concentration of active carriers given by N_D - N_A ≈ 10¹⁷ cm⁻³. © 1997 John Wiley & Sons Ltd.     

Electric current effects on Sn/Ag interfacial reactions

The effect of electric current on the Sn/Ag interfacial reaction was studied at 140°C and 200°C, by examining the growth of phase (ε-Ag₃Sn) in the Sn/Ag reaction couples with a constant current density. Only at 140°C was the growth of phase affected by the passage of electric current. The growth rate was enhanced when diffusion of Sn and electron flow were in the same direction, and retarded when they were in the opposite direction. It was found that the diffusion coefficient of Sn through Ag₃Sn was 3.37 μm²/h and the apparent effective charge for Sn in Ag₃Sn was −90, at 140°C.     

Ag and Cu migration phenomena on wire-bonding

After storing a plastic packaged sample at 250°C for 588 h, the Au plus 1% Pd wire composition was found to be changed. The Ag and Cu atoms can migrate from the wedge bond through the wire surface and arrive at the ball bond. At the same time, Ag and Cu atoms diffuse into the gold wire itself and form a layer type structure. The atom migration phenomena are due to three driving forces: diffusion, alloy formation, and Galvanic effect. The obtained diffusion rate constant is in the order of 10⁻¹² cm square per sec, which corresponds to an activation energy of 0.7∼0.76 eV. The phases sequence formed by diffusion is inconsistent with the equilibrium Ag-Au-Cu phase diagram which indicates that the present diffusion layer has reached thermodynamic equilibrium.     

Study of the distribution profile of iron ions implanted into silicon

Iron ions with energies of 90 and 250 keV and a dose of 10¹⁶ cm^–2 are implanted into a silicon single crystal with the (110) orientation. The method of Rutherford backscattering in combination with channeling is used to study the distribution profiles of the introduced impurity and also the profiles of the distribution of radiation-induced defects in the crystal lattice. Experimental data are compared with the results of simulation performed using the TRIM software package. It is shown that, at an energy of 4.6 keV/nucleon, the average projected ranges coincide; however, at an energy of 1.6 keV/nucleon, the difference amounts to 35%. In addition, it is shown that the calculation incorrectly takes into account the dose dependence at energies of 1.6–4.6 keV/nucleon.     

Effects of S,Si, or Fe dopants on the diffusion of Zn in InP during MOCVD

Diffusion of Zn in InP during growth of InP epitaxial layers has been investigated in layer structures consisting of Zn-InP epilayers grown on S-InP and Fe-InP substrates, and on undoped InP epilayers. The layers were grown by metalorganic chemical vapour deposition (MOCVD) atT = 625° C andP = 75 Torr. Dopant diffusion profiles were measured by secondary ion mass spectrometry (SIMS). At sufficiently high Zn doping levels ([Zn] ≥8 × 10¹⁷ cm⁻³) diffusion into S-InP substrates took place, with accumulation of Zn in the substrate at a concentration similar to [S]. Diffusion into undoped InP epilayers produced a diffusion tail at low [Zn] levels, probably associated with interstitial Zn diffusion. For diffusion into Fe-InP, this low level diffusion produced a region of constant Zn concentration at [Zn] ≈ 3 × 10¹⁶ cm⁻³, due to kick-out of the original Fe species from substitutional sites. We also investigated diffusion out of (Zn, Si) codoped InP epilayers grown on Fe-InP substates. The SIMS profiles were characterised by a sharp decrease in [Zn] at the epilayer-substrate interface; the magnitude of this decrease corresponded to that of the Si donor level in the epilayer. For [Si] ≫ [Zn] in the epilayer no Zn diffusion was observed; Hall measurements indicated that the donor and acceptor species in those samples were electrically active. All these results are consistent with the presence of donor-acceptor interactions in InP, resulting in the formation of ionised donor-acceptor pairs which are immobile, and do not contribute to the diffusion process.