Electrical Activity Of Extended Defects Research Articles

(Invited) Defect Engineering for Monolithic Integration of III-V Semiconductors on Silicon Substrates

Implementation of high-mobility channel materials enables to increase the device performance due to the higher carrier mobility compared to silicon devices. III-V based materials such as GaAs and ternary systems (e.g. InxGa1-xAs alloys) are achieving high performing n-channel transistors. The strong progress in hetero-epitaxy using nano ridge engineering [1] leading to monolithic heterogeneous integration of III-V materials on silicon substrates resulted in state-of-the-art FinFETs, gate-all-around (GAA) and horizontal or vertical stacked nanowires (NW) on 300 mm Si wafers [2,3]. Very promising results have also been reported for GaN on Si triggering their use for high power and RF applications [4].One of the main challenges remains a good defect control in order not to degrade the electrical performance of devices and circuits [5]. The nucleation of extended defects is directly related to the hetero-epitaxial growth of layers with a lattice mismatch and their concentration depends on the composition of the layers such as e.g. the In content in InxGa1-xAs and the Al content in AlxGa1-xN. The defects have a direct impact on the generation and recombination lifetime and the leakage current [5], while also the low frequency noise (LFN) performance is influenced [6]. The identification of the defects (energy level ET, capture cross section and concentration) can be determined using Deep Level Transient Spectroscopy (DLTS) and low frequency noise spectroscopy by measuring LFN as a function of temperature.The goal of this work is to review the knowledge about defect engineering and to analyze the electrical activity of extended defects in III-V semiconductors on silicon substrates. Different case studies will be used to illustrate both the defect identification and the electrical activity of the defects. The impact of the used processing schemes to fabricate the devices is also discussed. It will e.g. be shown that defects in GaN/AlGaN MOSHEMTs increase the low frequency noise due to generation-recombination centers in the GaN depletion layer [7]. These traps can lead to a distortion of the current-voltage characteristics of short channel devices. DLTS studies are a powerful tool to identify traps and to investigate their impact on the leakage current of III-V on Si devices. Double correlation DLTS investigations on GaAs/InGaP/GaAs diodes pointed out that traps associated with sidewall interface states can dominate the peripheral diode leakage current. The focus of the presentation will be on the current understanding of defect engineering associated with the monolithic integration of III-V materials on Si and a discussion of recent results concerning the electrical activity of the defects and the defect modeling.[1] M. Baryshnikova et al., Crystals, 10, 330 (2020).[2] X. Sun et al., Digest VLSI Technology, T3-4 (2017).[3] A.P. Milemin et al., Microelectron. Eng., 192, 14 (2019).[4] L. Li et al., IEEE Electron Device Lett., 41, 689 (2020).[5] C. Claeys et al., ECS Solid State Electronics, 9, 03301 (2020).[6] C. Claeys et al., J. Phys. Cond. Ser., 1190, 012001 (2019).[7] K. Takakura et al., IEEE Trans. Electron Dev., 67, 3062 (2020).

Electrical Activity of Extended Defects in Relaxed InxGa1−xAs Hetero-Epitaxial Layers

The electrical activity of extended defects in III–V materials, combining different analysis methods based on lifetime extraction from diode current-voltage characteristics, time resolved photoluminescence (TRPL) and deep level studies using Deep Level Transient Spectroscopy (DLTS) is reviewed. To that purpose p+n junction diodes have been fabricated in In0.53Ga0.47As hetero-epitaxial layers on semi-insulating InP or GaAs substrates. By depositing a strained buffer layer, the Extended Defect Density (EDD) can be varied over several decades, enabling a systematic study of their electrical impact in the same range. The defect densities are determined by High-Resolution X-ray Diffraction (HR-XRD), DLTS and Electron Channeling Contrast (ECCI) techniques. The generation and recombination (GR) lifetimes of the In0.53Ga0.47As layers become dominated by the EDs for densities above about 3 × 107 cm−2, whereby the dominant GR level moves closer to the mid gap position. This is supported by DLTS investigations, showing the occurrence of specific electron traps for defective epi layers, which exhibit a capture behavior that is typical for extended defects.

(Invited) Electrical Activity of Extended Defects in III-V Semiconductors

The electrical activity of a defect in a semiconductor material is usually expressed in terms of the Shockley-Read-Hall (SRH) theory which provides an expression for the generation or recombination lifetime. Along the same lines, one can calculate the leakage current generated by a single defect in the depletion region of a junction, as shown in Fig. 1 [1]. It is clear that for III-V based ternary alloys, like the InxGa1-xAs system, the generation current depends proportionally on the intrinsic carrier concentration ni (see equation in Fig. 1). However, equally important is also the variation of the defect energy level ET as a function of the In content x: for ET pinned to the intrinsic Fermi level Ei(x), the leakage current will follow ni. On the other hand, when ET is pinned to either the valence or conduction band, the leakage current will decrease exponentially with the difference |ET-Ei| [2]. It is thus important to derive the variation of ET with alloy composition x for a certain type of defect and to establish what could be consideredas a kind of Vegard’s law for specific deep levels. In addition, when integrating III-V compounds on a silicon CMOS platform, extended defects will be inevitably introduced [3]; for a sufficiently high density, they will govern the reverse current [3,4]. It is thus of vital importance to study the electrical parameters of extended defects in III-V-on-silicon materials and their evolution with composition x. The aim of the this work is to review what is known about the electrical activity of extended defects in InxGa1-xAs-based hetero-epitaxial layers. Results will be described about a combined p-n diode current-voltage (I-V) and lifetime analysis on a set of nearly strain-free layers where x=0.53 with varying densities of extended defects [5]. Based on this, it is demonstrated that for an extended defect density exceeding ~2×107 cm-2 the SRH lifetime becomes dominated by a near mid-gap trap level, associated with them. A detailed Deep-Level Transient Spectroscopy (DLTS) analysis provides further information about the electrical activity of these extended defects and confirms the presence of a dominant electron trap. The corresponding activation energy is represented in Fig. 2 versus x and compared with available literature data. In addition, it is shown that this deep level indeed belongs to an extended defect, based on the electron capture behavior, varying approximately logarithmically with the capture time [4]. Moreover, it can be shown that the electron traps belong to a one-dimensional band-of-states, associated with a ‘perfect’ extended defect. According to Fig. 2, this level appears to follow approximately Ei(x), so that it will dominate the leakage current of a p-n junction over a wide composition range, at least up to 0.53, when present in a sufficient density. Moreover, the defects will become more efficient leakage centers for increasing x. Finally, the implications of the band-like nature of the energy states of extended defects on the carrier generation/recombination will be discussed. [1] J. Vanhellemont and E. Simoen, J. Electrochem. Soc, 154, H572 (2007). [2] E. Simoen, J. Lauwaert and H. Vrielinck, Semiconductors and Semimetals, Eds. L. Romano, V. Privitera and C. Jagadish, 91, pp. 205-250, Elsevier 2015. [3] E. Simoen, “Impact of defects on the performance of high-mobility semiconductor devices”, In: High Mobility Materials for CMOS Applications, Ed. N. Collaert, Elsevier, Ch. 5, July 2018. [4] C. Claeys et al., ECS J. Solid State Sci. and Technol., 5, P3149 (2016). [5] P.-C. Hsu et al., J. Appl. Phys., 124, 165707 (2018). Figure 1

(Invited) Electrical Activity of Extended Defects in III-V Semiconductors

This paper gives an overview on the electrical activity of extended defects in III-V materials, combining different analysis methods, which are based on lifetime extraction from diode current-voltage characteristics and deep-level studies using Deep-Level Transient Spectroscopy (DLTS). To that purpose p+n junction diodes have been fabricated in In0.53Ga0.47As hetero-epitaxial layers on semi-insulating InP or GaAs substrates. By depositing a strained buffer layer, the Extended Defect Density (EDD) can be varied over several decades, enabling the study of the electrical impact in the same range. It will be shown that the generation and recombination (GR) lifetimes of the In0.53Ga0.47As layers become dominated by the EDs for densities above about 3×106 cm-2, whereby the dominant GR level moves closer to the mid gap position. This is supported by DLTS, showing the occurrence of specific electron traps for defective epi layers, which exhibit a capture behavior which is typical for extended defects.

Electrical Activity of Extended Defects in Multicrystalline Silicon

The excess carrier lifetime (τ) distribution in multicrystalline silicon grown by the Bridgman technique from high-purity metallurgical silicon (HPMG-Si) is studied. The features of the variation in τ, caused by the grain-boundary structure of ingots, are revealed. The grain boundaries, dislocations, and impurity microinclusions are studied by electron probe microanalysis (EPMA) and scanning electron microscopy (SEM) using selective acid etching. The electrical activity of extended defects is measured by the electronbeam- induced-current (EBIC) method.

Электрическая активность протяженных дефектов в мультикремнии

AbstractThe excess carrier lifetime (τ) distribution in multicrystalline silicon grown by the Bridgman technique from high-purity metallurgical silicon (HPMG-Si) is studied. The features of the variation in τ, caused by the grain-boundary structure of ingots, are revealed. The grain boundaries, dislocations, and impurity microinclusions are studied by electron probe microanalysis (EPMA) and scanning electron microscopy (SEM) using selective acid etching. The electrical activity of extended defects is measured by the electronbeam- induced-current (EBIC) method.

Review—Device Assessment of Electrically Active Defects in High-Mobility Materials

The stringent device performance specifications of advanced scaled down technologies necessitates the implementation of high mobility substrates such as SiGe, Strained Si (sSi), Ge, sGe and/or III-V materials like GaAs, InGaAs. The control of the stress-induced defects remains a key challenge. Simple device structures such as capacitors, diodes and transistors are used to assess the electrical activity of extended defects (dislocations; antiphase boundaries; …) in high-mobility channel materials. Beside junction current analyses and lifetime studies, also the use of low-frequency noise characterization is reported. Special case studies are discussed to illustrate the used methodology. The potential of TCAD studies to better understand the electrical defect activity is also briefly addressed.

(Invited) On the Electrical Activity of Extended Defects in High-Mobility Channel Materials

The electrical activity of extended defects (dislocations; antiphase boundaries;...) in high-mobility channel materials (strained-Si; (strained)-Ge, GaAs and InGaAs) is investigated by means of simple device structures (p-n diodes and MOS capacitors). These are fabricated in substrates with a well-controlled density of predominant extended defects, enabling the determination of a specific leakage current contribution per defect. It is shown that there is a linear relationship between the area leakage current density and the threading dislocation density for a wide range of group IV p+n junctions. In the case of antiphase boundaries (APBs) of GaAs on Ge substrates, only a moderate electrical activity has been derived from these studies. On the other hand, a clear band of deep states has been demonstrated for TDs in InGaAs layers on GaAs substrates.

Evidence of electrical activity of extended defects in 3C–SiC grown on Si

In this paper, we demonstrate the high electrical activity of extended defects found in 3C–SiC heteroepitaxially grown layer on (100) silicon substrates. Cross-sectional scanning transmission electron microscopy analysis was performed to reveal the defects while scanning spreading resistance microscopy aimed to study their electrical behavior. Using this technique, complete layer resistance cartography was done. The electrical activity of the extended defects in 3C–SiC was clearly evidenced. Furthermore, the defect activity was estimated to be higher than that of heavily nitrogen doped (5×1018 cm−3) 3C–SiC layer.

Annealing effect on the electrical activity of extended defects in plastically deformed p‐Si with low dislocation density

AbstractIt is shown that after plastic deformation in clean conditions the most efficient recombination defects in Si are dislocation trails. The DLTS spectrum associated with the defects in the dislocation trails in p‐Si are revealed. The thermal annealing effect on the electrical properties of these extended defects has been studied. A complex annealing kinetics of defects in the dislocation trails is revealed by the EBIC and DLTS. It is shown that annealing at 800 °C essentially decreases the EBIC contrast of dislocation trails. The DLTS spectrum associated with dislocation trails is also found to disappear after such annealing. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

IBIC Studies of structural defect activity in different polycrystalline silicon material

In the research of semiconducting materials, the ion beam induced charge collection (IBIC) technique can provide interesting and straightforward information about the different electronic device characteristics. This nuclear microprobe technique was used for the qualitative analysis of the spatial distribution of charge collection efficiency in several types of poly-Si material. We studied the influence of light impurities (oxygen, carbon) on electrical activity of extended defects. It is shown that oxygen segregating close to structural defects influences their electrical activity, while for carbon we did not observe the same effect. We demonstrated that IBIC can be applied to provide spatial information about the position of electrically active defects and its activation during subsequent processing.

Defects in polycrystalline silicon studied by IBICC

In the research of semiconducting materials, ion beam-induced charge collection (IBICC) technique can provide interesting and straightforward information about the different electronic device characteristics. This nuclear microprobe technique was used for the qualitative analysis of charge collection efficiency spatial distribution in three different types of EFG silicon material. Using IBICC technique, we studied the influence of present light impurities (oxygen, carbon) on electrical activity of extended defects. It is shown that oxygen segregating close to structural defects influences their electrical activity, while for carbon we did not observe the same effect. We demonstrated that IBICC technique could be applied to provide spatial information about the position of electrically active defects, and/or their activation or deactivation during subsequent processing.

Transformation of Electrical Activity of Extended Defects in Silicon Polycrystals under Annealing and Hydrogen Plasma Treatment

A possibility to control the electrical activity of extended defects (grain boundaries, dislocations) under annealing and hydrogen plasma treatment by different regimes of silicon ribbons grown with the edge-defined film-fed growth technique was studied. It is shown that the results of hydrogenation of grain boundaries (GBs) significantly depend on two factors: the type of GBs (deviated or general) and the state of ribbons (as-grown or annealed). Heat treatment of polysilicon in different ambients results in a considerable decrease of the electrical activity of dislocation, and special and weakly-deviated GBs too. On the contrary, the activity of general and highly-deviated GBs is enhanced after annealing. Our investigation has revealed that the electrical activity of general GBs is defined significantly by the cooling rate after annealing.

Design, fabrication, and analysis of greater than 18% efficient multicrystalline silicon solar cells

Solar cells with efficiencies as high as 18.6% (1 cm 2 area) and 17.5% (4 cm 2 area) have been achieved by a process which involves impurity gettering and effective back-surface passivation on multicrystalline silicon (mc-Si) grown by the heat exchanger method (HEM). The former efficiency mark represents the highest reported solar cell efficiency on mc-Si to date. PCD analysis revealed that the bulk lifetime in certain HEM samples after phosphorus gettering can be as high as 135 μs. This increases the impact of the back-surface recombination velocity ( S b) on the solar cell performance. By incorporating a deeper aluminum back-surface field (Al-BSF), the S b for solar cells in this study was lowered from 10,000 to 2000 cm/s (for 1 and 10 μm evaporated aluminum layers, respectively, alloyed in a conventional furnace) and finally to 200 cm/s (for screen printed Al-BSFs alloyed in an RTP furnace). It was observed that the screen-printed/RTP alloyed Al-BSF process raised the efficiency of both float zone and relatively defect-free mc-Si solar cells by lowering S b. However, this process increased the electrical activity of extended defects so that mc-Si cells with a significant defect density showed degradation in performance.

Electrical activity of extended defects and gettering of metallic impurities in silicon

Electrical activities of slip dislocations and Frank type partial dislocations in Si were investigated using the temperature dependent electron beam induced current technique. It was found that both types of dislocation are recombination active in the temperature range below about 200 K only and inactive in the higher temperature range if they are free from decoration by metallic impurities. From the temperature dependence of the electron beam induced current contrasts, the energy levels of recombination centres on these dislocations were determined to be less than 0.1 eV. They are not accompanied by any deep levels. Debris of defects generated from moving dislocations has deep levels about 0.3-0.4 eV from the band edge even if there is no decoration with metals. Both slip dislocations and Frank partials become recombination active at high temperatures when they getter metallic impurities. The characteristics of impurity gettering by dislocations depend on both the species of impurities and the cooling rate of a Si crystal after contamination. As a result, the recombination activities of dislocations are influenced by a variety ofexternal parameters. MST/3305

Recombination Activity of Individual Extended Defects in Silicon

ABSTRACTDislocations and point defects introduce energy levels deep in the gap, which dramatically change the material electrical properties. Because of the coexistence of a multitude of dislocation types and dislocation-point defect interaction mechanisms, it would be highly desirable to identify the particular type of defect related to specific traps.The electrical activity of extended defects (planar precipitates and dislocations) is here examined in terms of their recombination activity, investigated by electron as well as light beam induced current methods of scanning microscopy.Besides, a scanning modification of spectroscopy is used to identify traps at individual defects. The method, named quenched infra-red beam induced current, combines the scanning light beam induced current technique with the spectroscopie bulk analysis called “infrared quenching of photoconductivity”.Defect energy levels are found on the basis of the particular features of the beam induced current as a function of injected carrier generation rate, temperature and quenching excitation.

DEVELOPMENTS OF IRBIC AND QIRBIC IN DEFECT STUDIES : A REVIEW

Optical injection, as well as the electronic one, is of great use for semiconductor material and component characterization, and in recent years several papers appeared dealing with the analysis of the depth response of scanning light microscopy, the distribution of the charge carriers generated by a focused light beam as well as the photoinduced current dependence on the measurement configuration and the consequent imaging of defects in semiconductors. In these works a laser source is always used because of its features of monochromaticity, focusing and high intensity. Actually the light microscopy has become a widely accepted wafer mapping technique for investigating inhomogeneities and, besides, a method to evaluate diffusion length and surface recombination velocity of minority carriers. We have applied the same principles of the scanning laser microscopy, but substituting filtered light corning from an halogen lamp to the laser source. This expedient, even though it involves some disadvantages about monochromaticity and focusing, allows, however, to easier handle light beam parameters as photon density and energy. We refer to this method as IRBIC (Infra-Red Beam Induced Current) since the photon energy of the scanning beam lies in the infrared portion of the spectrum. Object of our investigations is the current induced by the infrared light beam and, in more detail, the variations in defect imaging observed by changing penetration depth and intensity of the light. In addition, having a scanning light microswpe at our disposal, we have modified the basic experimental setup so as to irradiate the back surface of the sample by monochromatic sub-band gap light. When the photon energy of the back surface irradiation coincides with the distance E, of a deep level within the forbidden gap from one of the allowed energy bands, a level-band transition occurs and, as a consequence, the concentration of the efficient recombination traps at the level E, changes. This process, involving the defect recombination activity, produces strong variations in the current induced by the beam scanning the opposite surface. The above said phenomenon, known for long time in bulk material examinations and named photoconductivity quenching, has been applied by us to the scanning light microscopy and called that is Quenched Infra-Red Beam Induced Current. Both the methods, IRBIC and QIRBIC, very sensitive to the occupancy factor of the defects, have been used to investigate the electrical activity of extended defects, namely dislocations, and their interaction with impurities and point defects. Besides, investigations have been performed on lamellar structure precipitates and on deformation-induced dislocation loops.

Electrical activity of extended defects in polycrystalline silicon

The analysis of the dependence of the diffusion length of minority carriers on the microstructure in polycrystalline silicon has been extended by considering the influence of oxygen and carbon. These impurities are in fact known to have a definite effect on the electrical activity of dislocations and grain boundaries (GB). The results of this analysis show that a term of the type N D (N O -N C ), where N D is the dislocation density and N O , N C are the concentration of oxygen and carbon, respectively, well accounts for the influence of oxygen and carbon on the diffusion length of minority carriers. Oxygen and carbon, therefore, affect only marginally the recombination losses at GB in polycrystalline silicon, whose average diffusion length is determined almost exclusively by dislocations On etend l'analyse de la relation entre microstructure de Si polycristallin et longueur de diffusion des porteurs minoritaires en y incluant l'influence de C et O, deux impuretes dont on connait l'effet sur l'activite electrique des dislocations et des joints de grains: un terme en N D (N O -N C ) (avec N D : densite de dislocations, N C et N O : concentrations respectives en C et O) rend bien compte de cette influence qui n'est que marginale, alors que la recombinaison aux joints de grains depend presqu'exclusivement des dislocations