Damage In Ge Research Articles

Dynamic annealing in Ge studied by pulsed ion beams

The formation of radiation damage in Ge above room temperature is dominated by complex dynamic annealing processes, involving migration and interaction of ballistically-generated point defects. Here, we study the dynamics of radiation defects in Ge in the temperature range of 100–160 °C under pulsed beam irradiation with 500 keV Ar ions when the total ion fluence is split into a train of equal square pulses. By varying the passive portion of the beam duty cycle, we measure a characteristic time constant of dynamic annealing, which rapidly decreases from ~8 to 0.3 ms with increasing temperature. By varying the active portion of the beam duty cycle, we measure an effective diffusion length of ~38 nm at 110 °C. Results reveal a major change in the dominant dynamic annealing process at a critical transition temperature of ~130 °C. The two dominant dynamic annealing processes have an order of magnitude different activation energies of 0.13 and 1.3 eV.

Implantation-induced damage in Ge: strain and disorder profiles during defect accumulation and recovery

We present an experimental study of structural lattice damage in Ge induced by ion implantation. From the strain and disorder profiles, calculated from x-ray diffraction and ion channelling experiments we have investigated the defect accumulation as a function of ion fluence, mass, energy and current density as well as the damage recovery and recrystallization of the implanted region upon annealing. The damage accumulation process can be divided into three different regimes, based on the ion fluence. In the lowest fluence regime, the strain and the defect fraction are linearly proportional to the ion fluence, and the number of defects in the implanted layer is directly related to the deposited energy that is converted into the creation of vacancies. In the second regime, the damage accumulation process is more efficient, due to the increased defect density in the implanted layer. The third fluence regime starts at the critical fluence for amorphization, and this value has been determined for a wide range of ion masses and energies. The recovery study of the implantation-induced damage has revealed two distinct annealing steps. Rapid thermal annealing at temperatures as low as 100 °C results in the removal of isolated defects, which are present in the low-fluence implanted samples, as well as in the tail of the implantation profile of heavily damaged samples. Annealing at 350 °C results in the recrystallization of amorphous Ge at the amorphous–crystalline interface at a rate of 14 ± 3 nm min−1. Although Ge amorphizes at much lower fluences than Si, the influence of the studied implantation parameters on the damage accumulation process is comparable for both group IV semiconductors. This extended experimental overview of implantation-induced structural damage partly fills the large knowledge gap on implantation-related issues in Ge, and provides relevant and complementary information for defect studies in Ge and, in general, for any study using implanted Ge.

A study of ion implantation into crystalline germanium

We report an experimental and simulation study for introducing dopant ions into (1 0 0) germanium in the energy range from 5 to 40 keV. The successful calibration of our Monte Carlo ion implantation simulator for amorphous and crystalline Ge targets is demonstrated by comparison of predicted boron profiles with SIMS data. The implantation profile in Ge is shallower than in Si for a given energy due to the larger nuclear and electronic stopping power of Ge atoms. The generated point defects and amorphized regions in the crystal are calculated by a modified Kinchin–Pease model. We found that the higher displacement energy in Ge, the stronger backscattering effect, and the smaller energy transfer from the ion to the primary recoil of a cascade are mainly responsible for the significantly reduced implantation damage in Ge. The point responses for boron implantations in Si and Ge are compared with each other. Finally the simulation results for the formation of interdigitated Ge-on-Si PIN-photodiodes are presented.

Structure and low-temperature thermal relaxation of ion-implanted germanium.

The structure of implantation-induced damage in Ge has been investigated using high resolution extended X-ray absorption fine structure spectroscopy (EXAFS). EXAFS data analysis was performed with the Cumulant Method. For the crystalline-to-amorphous transformation, a progressive increase in bond-length was observed without the presence of an asymmetry in interatomic distance distribution (RDF). Beyond the amorphization threshold the RDF was dose dependent and asymmetric, where the bond-length and asymmetry increased as functions of ion dose. Such an effect was attributed to the formation of three- and five-fold coordinated atoms within the amorphous phase. Low-temperature thermal annealing resulted in structural relaxation of the amorphous phase as evidenced by a reduction in the centroid, asymmetry and width of the RDF, as consistent with a reduction in the fraction of non four-fold coordinated atoms. The results have been compared to other EXAFS studies of amorphous Ge, and it is suggested that the range of bond-lengths reported therein is related to the sample preparation method and state of relaxation.

Investigation of radiation damage in germanium induced by MeV Si+

Polished germanium Ge (100) was irradiated with 1.0–2.0 MeV Si+ at different doses from 4×1013 to 1×1014 ions/cm2 under different angles: 7°, 45°, and 60°. The radiation damage is studied by the Rutherford backscattering/channeling technique. The experimental damage distribution is extracted from the spectrum based on the procedure by Feldman et al. The experimental damage distributions are compared with the result from the TRIM (transport of ions in matter) code. The results show that (1) it is easier to amorphize Ge than Si, and the damage in Ge (100) induced by MeV Si+ depends on the dose, energy, irradiation angle, and annealing temperature also; (2) the shape of damage profile in Ge (100) induced by 2.0 MeV Si+ under 60° irradiation can be described well by the TRIM prediction, except the near-surface region where the experimental damage ratio is higher than that given by the TRIM prediction; (3) after 800 °C annealing, damaged Ge (100) trends to be recrystallized.

Can recoil distribution models account for end-of-range damage?

A quantitative evaluation of two existing models for end-of-range damage in Ge + implanted silicon is presented. The models propose that the amount of end-of-range damage is related to either (1) the number of ions or (2) the number of recoiling Si atoms that come to rest beyond the amorphous/crystalline (α/c) interface. TRIM (Monte Carlo) simulations of the implants studied were used to obtain the predictions of each model. These predictions were compared to experimental results obtained from implants at 30, 100 and 150 keV and doses of 5 × 10 14, 1 × 10 15 and 2 × 10 15. Plan view and cross-sectional TEM observations were used to determine the concentration of atoms bound by the end-of-range dislocation loops and the location of the α/c interface. Increasing the energy or dose resulted in significant increases in the amount of end-of-range damage. Neither model was able to consistently predict these trends at the lower doses and energies where ion beam induced epitaxial crystallization was suppressed. However, the recoil model was found to be superior overall to the ion model when compared to data from a wider range of implant conditions.

The effect of implant energy, dose, and dynamic annealing on end-of-range damage in Ge+-implanted silicon

A study of the effect of Ge+ implantation energy, dose, and temperature on the concentration of atoms bound by the extrinsic end-of-range dislocation loops in Si 〈100〉 wafers is presented. Plan-view and cross-sectional transmission electron microscopy observations of both the as-implanted and annealed (900 °C, 30 min) morphology were made. The implant energy was varied from 30 to 150 keV, the dose varied from 2×1014 to 1×1016/cm2, and the temperature was varied by using three different wafer-cooling methods during the implantation. Increasing the implant energy, dose, or wafer temperature all resulted in significant increases (as much as two orders of magnitude) in the concentration of atoms bound by the end-of-range loops. Recent models have suggested that the concentration of end-of-range defects is related to the integrated recoil concentration beyond the amorphous/crystalline (a/c) interface. Correlation of trim-88 calculations with measured a/c depths show that the integrated recoil concentration beyond the a/c interface can explain both qualitatively and quantitatively the dependence of the ‘‘trapped interstitials’’ on the implant energy. However, this model can only qualitatively explain the temperature dependence of the defects, and it fails to account for the strong dose dependence when wafer heating is suppressed.

Radiation damage in Ge and Si detected by carrier lifetime changes: Damage thresholds

Abstract Minority carrier lifetime, τ, in semiconductors is shown to be more sensitive, by a factor of 104, to radiation-induced defects than is the conductivity. Thus, in some cases, the introduction of as few as 1010 defects cm−3 can be detected by its effect on τ. Both direct measurements of τ and measurements of dependent parameters (such as the photovoltaic effect and the particle effect) are described for Si and Ge. Using such parameters, and an electron accelerator, the minimum energy needed to produce a Frenkel defect was found to be 14.5 ± 0.4 eV in Ge and 12.9 ± 0.6 eV in Si. An analysis of the phenomenon shows how the location of the radiation-induced energy levels and the relative minority carrier capture cross-sections can be determined experimentally. The shape of the curve of the displacement cross-section vs. the incident particle energy is compared with calculations from collision theory. Qualitative explanations for the observed “tail” on this curve are presented. Calculations based on these explanations fail to yield complete agreement with the experimental curves.

Radiation damage in Ge induced by Te + implantation near channeling conditions

Samples of (100), (111) and (110) oriented Ge-crystals were implanted with 40 keV Te + ions at fluences between 5 × 10 13 and 5 × 10 14 cm −2. The beam alignment during the implantation was α = 0 ° or within 6 to 7° from the surface normal. The disorder depth profiles were analysed by using conventional and high depth resolution RBS channeling of 2 MeV helium ions. The damage profiles for implantation at α smaller than the critical angle for axial channeling (ψ c) show an increase in the average penetration depth and a reduction in the damage peak in comparison to the case of α exceeding ψ c. In parallel, a MARLOWE based computer code is applied to simulate the atomic collision cascades and resulting impurity and disorder depth distributions.

Elimination of end-of-range and mask edge lateral damage in Ge+ preamorphized, B+ implanted Si

The problems of residual extended defects due to end-of-range ion implantation damage and mask edge lateral damage have been solved in this study for shallow boron junctions preamorphized via germanium ion implantation. Defect elimination has been achieved by adjusting the germanium ion energy, dose, and annealing temperature and ambient to minimize the local interstitial point defect concentration and optimize the role of the free surface in defect annihilation. For the combination of shallow, low dose 40 or 60 keV/2×1014 cm−2 Ge+ and 8 keV/1×1015 cm−2 B+ implants, a defect-free structure was obtained following a 1050 °C, 10 s rapid thermal anneal (RTA) in a nonoxidizing Ar ambient. For these samples, boron profiles determined using secondary ion mass spectroscopy (SIMS) showed the junction depth to be approximately 0.17 μm at a background doping of 1×1017 cm−3 with a sheet resistance of 136 Ω/⧠.

A comparison of 252Cf and 238Pu, Be neutron sources for partial-body in vivo activation analysis

A comparison is made of the isotopic neutron sources 252Cf and 238Pu, Be for partial-body in vivo neutron activation analysis. Depth distributions of thermal neutron fluences in a water phantom are very similar for the two sources. The peak depth occurs at 5 cm. This value is approximately 2 cm less than the values obtained with uncollimated neutrons produced in broad-beam irradiations. With respect to the fluence-to-dose ratio, the 252Cf neutrons have an advantage of approximately 1.4 over the 238Pu, Be source. The use of 252Cf offers two additional advantages for the investigator. First, it minimises the on-line fast-neutron damage in Ge(Li) semiconductor detectors. Secondly, it is subject to much less stringent transport regulations than 238Pu, Be. The latter feature takes on particular importance in view of the increasing usefulness of transportable instruments for in vivo cadmium measurements at the workplace.

Optical heating in semiconductors: Laser damage in Ge, Si, InSb, and GaAs

A comprehensive theory developed previously for optical heating in semiconductors is applied to the calculation of laser damage thresholds in Ge, Si, InSb, and GaAs. The calculated thresholds agree well with the experimental values over a broad range of laser wavelengths and pulse durations. The results demonstrate that the dynamic nature of the material’s optical and transport properties with changing temperature and laser-generated carrier density has a significant effect on the heating process, particularly at short pulse durations.

Calculated laser damage thresholds of Ge:Hg photoconductive detectors

Thermal damage in laser irradiated mercury-doped germanium detectors is investigated. Threshold levels of 10.6 μm laser radiation corresponding to onset of irreversible damage in Ge:Hg crystals are measured. The dependence of the damage thresholds on irradiaton time agrees favorably with thermal model predictions. Thresholds for both onset of irreversible damage and complete loss of photoresponse for Ge:Hg detectors are then calculated as a function of irradiation time, using parameters obtained from experimental results on laser damage in Ge:Hg crystals.

Laser (cw CO 2)-induced electrical damage in Ge and Si

Laser (cw CO 2)-induced electrical damage in Ge and Si

Laser (cw CO2) -induced electrical damage in Ge and Si

This paper presents the experimental results on the electrical studies of cw CO2 laser-induced damage in Ge and Si. The damage first appears at the surface of the semiconductor and penetrates the bulk, creating defects that cause carrier removal and mobility degradation. The defects so created are more active at lower temperatures than at room temperature, as seen from the mobility-vs-temperature curves before and after laser damage. Carrier removal and mobility degradation curves appear qualitatively to be similar to those observed for electron, neutron, and γ-ray damage. The experimental results can be satisfactorily explained by assuming the creation of vacancy and interstitial pairs and applying the model of James and Lark-Horovitz.

Radiation damage in Ge produced and removed by energetic Ge ions

Abstract Single crystals of Ge (110) were bombarded by 40 keV Ge ions at a dose rate of 6.0 × 1013 ions/cm2 sec in the temperature region 50–500°C. The secondary electron emission yield was used to study the state of disorder. In accordance with Chadderton's damage center nucleation model the growth of disorder can be divided into several dose intervals. Radiation enhanced and thermal annealing characteristics have also been studied using a probe ion beam of dose rate 6.0 × 1011 ions/cm2 sec. Evidence for both bombardment enhanced and thermal annealing are established. The bombardment enhanced annealing of a continuous disordered layer occurs at the inner region of the layer. The temperature dependence of the bombardment enhanced annealing indicates that a thermal step is included in the annealing process.

Radiation enhanced annealing of radiation damage in Ge

Abstract Ge (110) single crystals heated to a temperature of 228°C have been bombardment disordered by 40 keV ions at a dose rate of 6 × 1011 ions/cm2 sec. The enhanced annealing caused by 40 keV Ge ions at a dose rate of 6 × 1011ions/cm2 sec was studied as a function of dose by measuring the secondary electron yield. The depth distribution of damage was determined by the channeling technique using 500 keV He ions. It is shown that enhanced annealing occurs at the inner part of the damage region and proceeds outwards towards the crystal surface. The dose necessary to completely anneal a disordered layer is about 3.0 × 1015 ions/cm2. A model for the annealing process is discussed. The maximum path length of the secondary electrons emitted from Ge during the bombardment with 40 keV Ge ions has been determined to be equal to approximately 40 A.

Radiation damage in ge produced by noble gas ions investigated by the secondary electron emission method

Abstract 40 keV Ne, A, Kr and Xe ions have been used to bombard Ge single crystals at perpendicular incidence to (110) under clean target conditions. The temperature, dose and dose rate dependences of the accumulation of disorder have been determined. In a low temperature interval, 50–150°C, small temperature and dose rate effects on the accumulation of disorder were detected for Ne and A but for the other ions there was no such dependence. At temperatures above 150°C the temperature and dose rate for all types of ions used influence the accumulation of disorder. Different temperatures for the transition from a crystalline to a disordered region were detected for the various dose rates and ions used. Activation energies of 1.45 ± 0.15 eV for the observed defects have been calculated.

A study of the production and removal of radiation defects in Ge using secondary electron emission

Abstract The production and removal of radiation defects in Ge (110) single crystals are studied by measuring the variation in the kinetic secondary electron emission yield during bombardment by 40 keV Ge ions. A strong dose rate effect has been found in the temperature dependence of the defect production. An activation energy of 1.44 eV has been calculated for the defect which plays an important role in the removal of damage in Ge.

Annealing of ion bombardment damage in Ge

Sputtered atom ejection patterns have been used to detect the temperature dependent amorphous to crystalline transition in Ge(111) crystals. An activation energy for defect annealing has been calculated from the results.