Defects In Semiconductor Materials Research Articles

Controlling Unintentional Defects Enables High‐Efficient Antimony Selenide Solar Cells

AbstractDeep‐level defects in semiconductor materials usually induce carrier trapping and non‐radiative recombination. However, defects caused by unintentional contaminants in antimony selenide (Sb2Se3) solar cells have rarely been reported. Herein, the correlation between defect properties and unintentional impurities in the Sb2Se3 absorber is investigated, which is prepared by injection vapor deposition with Sb2Se3 source purities ranging from 99.9% to 99.9999%. The analysis of deep‐level transient spectra reveals that an increase in impurity concentration does not result in new defect types. Nevertheless, the higher impurity level causes an increase in both the defect density and the capture cross section of the original defect. To address this challenge, defect engineering is developed to regulate the growth of the Sb2Se3 absorber. This strategy completely suppresses deepest defect states E3, a mixture of intrinsic defect (SbSe) and impurity Si related defect. As a result, the carrier lifetime increases significantly from 0.37 to 3.4 ps. This enables to fabricate Sb2Se3 solar cells with a power conversion efficiency of 10.41%. This work uncovers the characteristics of unintentional contaminant‐related defects, and provides a strategy for fabricating highly efficient Sb2Se3 solar cells with low‐purity source materials.

Local defect and mid-gap state analysis of GaN using monochromated EELS combined with nanodiffraction and atomic-resolution imaging

Defects in semiconductor materials significantly impact their inherent properties, making the evaluation of local defects and their energy levels crucial for controlling device performance. With advancements in monochromators, electron energy loss spectroscopy (EELS) combined with scanning transmission electron microscopy (STEM) has emerged as a promising approach for assessing crystal and band structures of semiconductor materials at the nanoscale. However, there is limited experimental research investigating the relationship between actual defective structures in local regions and mid-gap states. In this study, we conducted high-energy resolution EELS (HR-EELS) measurements with an energy resolution of less than 100 meV to detect the mid-gap states of GaN. Various defects were intentionally induced through Ga-ion implantation, and the defect concentration varied in the depth direction. To understand the origin of the mid-gap states, we performed 4D-STEM analysis and atomic-resolution STEM observations. The HR-EELS measurements provided insights into the depth-dependent valence-loss spectra, revealing that the intensities corresponding to mid-gap states gradually increased toward the surface, whereas the slope at the onsets corresponding to interband transition decreased. Furthermore, local structural analysis unveiled the presence of structural disorder and defective structures, indicating the existence of extended defects such as stacking faults and domain boundaries. Observably, these defective structures were abundant near the surface and less pronounced in deeper regions. Based on these experimental findings, we concluded that the variations in valence-loss spectra can be utilized to qualitatively evaluate the crystal imperfections at the nanoscale.

Machine learning-enhanced detection of minor radiation-induced defects in semiconductor materials using Raman spectroscopy

Radiation damage in semiconductor materials is a crucial concern for electronic applications, especially in the fields of space, military, nuclear, and medical electronics. With the advancements in semiconductor fabrication techniques and the trend of miniaturization, the quality of semiconductor materials and their susceptibility to radiation-induced defects have become more important than ever. In this context, machine learning (ML) algorithms have emerged as a promising tool to study minor radiation-induced defects in semiconductor materials. In this study, we propose a sensitive non-destructive technique for investigating radiation-induced defects using multivariate statistical analyses combined with Raman spectroscopy. Raman spectroscopy is a contactless and non-destructive method widely used to characterize semiconductor materials and their defects. The multivariate statistical methods applied in analyzing the Raman spectra provide high sensitivity in detecting minor radiation-induced defects. The proposed technique was demonstrated by categorizing 100–500 kGy irradiated GaAs wafers into samples with low and high irradiation levels using linear discrimination analysis ML algorithms. Despite the high similarity in the obtained Raman spectra, the ML algorithms correctly predicted the blind testing samples, highlighting the effectiveness of ML in defect study. This study provides a promising approach for detecting minor radiation-induced defects in semiconductor materials and can be extended to other semiconductor materials and devices.

Antisite Defect SiC as a Source of the DI Center in 4H‐SiC

DI center, as a widely existed defect in 4H‐SiC, has attracted much attention in recent years, while the origin of it is still unclear. Herein, by comparing first‐principles calculated potential point defects‐related zero‐phonon lines (ZPLs) and nonradiative capture cross‐sections with the DI center‐related values in the experiment, it is proposed that the transition from the bound exciton states about 57 meV below the CBM to the “+1/+2” level of antisite defect SiC is responsible for the DI center in 4H‐SiC. This work describes the temperature and transition energy level dependence of the hole capture cross‐section of antisite defect in 4H‐SiC, which provides an idea for the optimal design of point defects in semiconductor materials.

Lattice Strain and Defects Analysis in Nanostructured Semiconductor Materials and Devices by High-Resolution X-Ray Diffraction: Theoretical and Practical Aspects.

The reliability of semiconductor materials with electrical and optical properties are connected to their structures. The elastic strain field and tilt analysis of the crystal lattice, detectable by the variation in position and shape of the diffraction peaks, is used to quantify defects and investigate their mobility. The exploitation of high-resolution X-ray diffraction-based methods for the evaluation of structural defects in semiconductor materials and devices is reviewed. An efficient and non-destructive characterization is possible for structural parameters such as, lattice strain and tilt, layer composition and thickness, lattice mismatch, and dislocation density. The description of specific experimental diffraction geometries and scanning methods is provided. Today's X-ray diffraction based methods are evaluated and compared, also with respect to their applicability limits. The goal is to understand the close relationship between lattice strain and structural defects. For different material systems, the appropriate analytical methods are highlighted.

Effect of electrodeposition temperature on the thin films of ZnO nanoparticles used for photocathodic protection of SS304

Abstract Films of ZnO nanoparticles were electrodeposited on indium-doped tin oxide (ITO) glass under different temperatures between 40 and 80 °C to study their photogenerated cathodic protection to stainless steel 304 (SS304). Morphology, crystallographic information and optical performance of the ZnO films were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), UV–vis spectroscopy and photoluminescence (PL) spectroscopy, respectively. The photocathodic protection of ZnO films on SS304 were evaluated by electrochemical methods. It was found that the ZnO films obtained at 40 °C is cauliflower-like in microstructure, while those obtained between 60 and 80 °C are hexagonal nanorods. The films prepared at 40 °C cause the most negative shift of the open circuit potential (OCP) of SS304 and produce photocurrent more than 10 times greater than those of the films obtained at higher temperatures. The excellent photocathodic performance of the ZnO nanoparticles prepared at 40 °C is attributed to the abundance of defects in its microstructure, which greatly reduces the electron-hole recombination rate upon UV illumination. The findings in this paper reveal that the defective ZnO nanoparticles obtained at low electrodeposition temperature display more efficient photocathodic protection and controlling the defects in semiconductor material may be a feasible way to improve its photoactivity.

Efficiency enhancement of perovskite solar cells based on Al2O3-passivated nano-nickel oxide film

Interface passivation plays a significant role in reducing surface defects in semiconductor materials. In this paper, we present a kind of Al2O3-passivated nickel oxide (NiO) film as hole transport layer for the perovskite solar cells (PSCs). The optimal Al2O3 insulating film between the NiO and perovskite active layers has a capability to decrease the defect states density at the surface of NiO and suppress the carriers recombination at NiO/perovskite interface. The passivation process could apparently improve the efficiencies of corresponding PSCs from 5.64 to 7.12%. Steady-state photoluminescence and transient time-resolved photoluminescence (TRPL) results demonstrate the restraint of charge recombination at the NiO/perovskite interface with passivation. The Hall effect test further shows that the electrical properties of the NiO film can be improved by adjusting the precursor concentration of the Al2O3, which has a certain significance for the application of interface engineering in PSCs. Furthermore, this method has the advantages of simple operation, low cost, and strong reproducibility, which is also good for the working stability of PSCs.

Identification of Burgers vectors of dislocations in monoclinic β-Ga2O3 via synchrotron x-ray topography

Dislocations are major structural defects in semiconductor materials, and they have negative impacts on the performance and reliability of electronic devices. The Burgers vector (b→) of a dislocation is one of the most important characteristics that determines its behavior in an operating device. In this study, we used synchrotron x-ray topography (XRT) to perform systematic observations of dislocations in β-Ga2O3, which is a promising wide-bandgap semiconductor for power device applications. By applying the g→⋅b→ invisibility criterion to dislocation contrasts in XRTs taken at multiple reciprocal lattice vectors g→, we identified 12 types of Burgers vectors, including 11 types theoretically predicted by Yamaguchi et al. [Superlattice Microst. 99, 99 (2016)] and b→=⟨100⟩. Some of these Burgers vectors, such as b→=⟨101¯⟩,12⟨132⟩,12⟨13¯2⟩,⟨001⟩, and ⟨100⟩, were confirmed experimentally for the first time.

The Photocatalytic Properties of VZn–N Co-doped ZnO: A First-Principles Investigation

Research work has found that doping or forming defects in semiconductor materials can enhance their catalytic efficiency in the visible light region. Therefore, the first-principles study is used to systematically research the electronic structures and the photocatalytic properties in the visible region of pure ZnO, N–ZnO, VZn–ZnO, and VZn–N–ZnO. The analytical results show that the ZnO is a semiconductor of direct band gap, and its absorption edge is in the ultraviolet region, while N doping, VZn, or both can make the ZnO show light absorption coefficient in the region of visible light, the absorption coefficient of VZn–N–ZnO system in the visible light is the largest, which imply that co-doping of N and VZn is benefit for improving the photocatalytic efficiency of ZnO in the visible range. According to the analysis of the density of states, the visible light absorption is mainly caused by the intra-band transitions of the electrons in O 2p and N 2p.

Electron irradiation-induced defects and photoelectric properties of Te-doped GaSb

Electron irradiation causes atomic displacement damage and produces point defects in semiconductor materials. The formation and variation of defects determine the optical properties of semiconductors during the irradiation process. In this paper, Te-doped GaSb was irradiated by 1 MeV electrons, with fluence of 1 × 1015 electrons cm−2, and its optical properties investigated by temperature-dependent photoluminescence (PL) before and after irradiation. After irradiation, the peak position had a blue-shift and intensity was significantly enhanced. The carrier concentration increased from 4.14 × 1017 to 7.82 × 1017 cm−3 but mobility decreased from 2690 to 1780 cm2 V−1 s−1. These phenomena could be explained by the complex mechanism of defect decomposition, that is, the VGaGaSbTeSb defect decomposed into two independent VGaGaSb and TeSb defects. To verify this mechanism, undoped GaSb was irradiated under the same conditions and PL results indicated that electron irradiation had little effect on optical properties of undoped GaSb.

Optically-active metastable defects in volumetric nanoplasmonic composites

Metastable defects in semiconductor materials have been well known for decades, but have only recently started to attract attention for their potential applications in information technology. Here, we describe active and passive nanoplasmonic materials with optically active metastable defects that can be switched on or off by cooling with or without laser illumination, respectively. To the best of our knowledge, this is the first report of metastable defects in either passive or active nanoplasmonic materials, and, more generally, in non-semiconducting materials. The nanocomposites are made of a sodium-boron-phosphate glass matrix doped with silver nanoparticles (nAg) or co-doped with nAg and Er3+ ions by NanoParticle Direct Doping method. We further show that the different origins of the two types of defect-related luminescence behaviour are attributable to either a metal-glass defect (MG1) or a metal-glass-rare-earth ion defect (MGR1). Such materials could potentially be used for data writing and erasing using laser illumination with a ‘tight’ focus such as direct laser writing.

Metastable defect response in CZTSSe from admittance spectroscopy

Admittance spectroscopy is a useful tool used to study defects in semiconductor materials. However, metastable defect responses in non-ideal semiconductors can greatly impact the measurement and therefore the interpretation of results. Here, admittance spectroscopy was performed on Cu2ZnSn(S,Se)4 where metastable defect response is illustrated due to the trapping of injected carriers into a deep defect state. To investigate the metastable response, admittance measurements were performed under electrically and optically relaxed conditions in comparison to a device following a low level carrier-injection pretreatment. The relaxed measurement demonstrates a single capacitance signature while two capacitance signatures are observed for the device measured following carrier-injection. The deeper level signature, typically reported for kesterites, is activated by charge trapping following carrier injection. Both signatures are attributed to bulk level defects. The significant metastable response observed on kesterites due to charge trapping obscures accurate interpretation of defect levels from admittance spectroscopy and indicates that great care must be taken when performing and interpreting this measurement on non-ideal devices.

Identification of Semiconductor Defects through Constant-Fermi-Level Ab Initio Molecular Dynamics: Application to GaAs

We show that constant-Fermi-level ab initio molecular dynamics can be used as a computer-based tool to reveal and control relevant defects in semiconductor materials. In this scheme, the Fermi level can be set at any position within the band gap during the defect generation process, in analogy to experimental growth conditions in the presence of extra electrons or holes. The scheme is illustrated in the case of GaAs, for which we generate melt-quenched amorphous structures through molecular dynamics at various Fermi levels. By a combined analysis which involves both the atomic structure and a Wannier-function decomposition of the electronic structure, we achieve a detailed description of the generated defects as a function of the Fermi level. This leads to the identification of As-As homopolar bonds and Ga dangling bonds for Fermi levels set in the vicinity of the valence band. These defects convert into As dangling bonds and Ga-Ga homopolar bonds, as the Fermi level moves toward the conduction band. This demonstrates a computer-aided procedure to identify semiconductor defects in an unbiased way.

Intrinsic "Vacancy Point Defect" Induced Electrochemiluminescence from Coreless Supertetrahedral Chalcogenide Nanocluster.

A deep understanding of distinct functional differences of various defects in semiconductor materials is conducive to effectively control and rationally tune defect-induced functionalities. However, such research goals remain a substantial challenge due to great difficulties in identifying the defect types and distinguishing their own roles, especially when various defects coexist in bulk or nanoscale material. Hereby, we subtly selected a molecular-type semiconductor material as structural mode composed of supertetrahedral chalcogenide Cd-In-S nanoclusters (NCs) with intrinsic vacancy point defect at the core site and antisite point defects at the surface of supertetrahedron and successfully established the correlation of those point defects with their own electrochemiluminescence (ECL) behaviors. The multichannel ECL properties were recorded, and the corresponding reaction mechanisms were also proposed. The predominant radiation recombination path of ECL emission peak at 585 nm was significantly distinguished from asymmetrically broad PL emission with a peak at 490 nm. In addition, the ECL performance of the coreless supertetrahedral chalcogenide nanocluster can be modulated by atomically precise doping of monomanganese ion at the core vacant site. A relatively high ECL efficiency of 2.1% was also gained. Actually, this is the first investigation of ECL behavior of semiconductor materials based on supertetrahedral chalcogenide nanocluster in aqueous solution. Current research may open up a new avenue to probe the roles of various different defects with defined composition and position in the NC. The versatile and bright ECL properties of Cd-In-S NC combined with tunable ECL potential and ECL peak suggest that the new kind of NC-based ECL material may hold great promising for its potential applications in electrochemical analysis, sensing, and imaging.

Comprehensive Characterization of Extended Defects in Semiconductor Materials by a Scanning Electron Microscope.

Extended defects such as dislocations and grain boundaries have a strong influence on the performance of microelectronic devices and on other applications of semiconductor materials. However, it is still under debate how the defect structure determines the band structure, and therefore, the recombination behavior of electron-hole pairs responsible for the optical and electrical properties of the extended defects. The present paper is a survey of procedures for the spatially resolved investigation of structural and of physical properties of extended defects in semiconductor materials with a scanning electron microscope (SEM). Representative examples are given for crystalline silicon. The luminescence behavior of extended defects can be investigated by cathodoluminescence (CL) measurements. They are particularly valuable because spectrally and spatially resolved information can be obtained simultaneously. For silicon, with an indirect electronic band structure, CL measurements should be carried out at low temperatures down to 5 K due to the low fraction of radiative recombination processes in comparison to non-radiative transitions at room temperature. For the study of the electrical properties of extended defects, the electron beam induced current (EBIC) technique can be applied. The EBIC image reflects the local distribution of defects due to the increased charge-carrier recombination in their vicinity. The procedure for EBIC investigations is described for measurements at room temperature and at low temperatures. Internal strain fields arising from extended defects can be determined quantitatively by cross-correlation electron backscatter diffraction (ccEBSD). This method is challenging because of the necessary preparation of the sample surface and because of the quality of the diffraction patterns which are recorded during the mapping of the sample. The spatial resolution of the three experimental techniques is compared.

Comprehensive Characterization of Extended Defects in Semiconductor Materials by a Scanning Electron Microscope

Extended defects such as dislocations and grain boundaries have a strong influence on the performance of microelectronic devices and on other applications of semiconductor materials. However, it is still under debate how the defect structure determines the band structure, and therefore, the recombination behavior of electron-hole pairs responsible for the optical and electrical properties of the extended defects. The present paper is a survey of procedures for the spatially resolved investigation of structural and of physical properties of extended defects in semiconductor materials with a scanning electron microscope (SEM). Representative examples are given for crystalline silicon. The luminescence behavior of extended defects can be investigated by cathodoluminescence (CL) measurements. They are particularly valuable because spectrally and spatially resolved information can be obtained simultaneously. For silicon, with an indirect electronic band structure, CL measurements should be carried out at low temperatures down to 5 K due to the low fraction of radiative recombination processes in comparison to non-radiative transitions at room temperature. For the study of the electrical properties of extended defects, the electron beam induced current (EBIC) technique can be applied. The EBIC image reflects the local distribution of defects due to the increased charge-carrier recombination in their vicinity. The procedure for EBIC investigations is described for measurements at room temperature and at low temperatures. Internal strain fields arising from extended defects can be determined quantitatively by cross-correlation electron backscatter diffraction (ccEBSD). This method is challenging because of the necessary preparation of the sample surface and because of the quality of the diffraction patterns which are recorded during the mapping of the sample. The spatial resolution of the three experimental techniques is compared.

Random telegraph noise: The key to single defect studies in nano-devices

A review is given of the different methods to extract the main parameters from a Random Telegraph Signal (RTS) occurring in the channel current of small-area Metal-Oxide-Semiconductor Field-Effect Transistors, namely, its amplitude and its average up and down time constants. The advantages of using a so-called colored Time Lag Plot will be illustrated, enabling the detection of single defects in semiconductor materials and devices with high sensitivity. It will finally be shown that a detailed modeling of the RTS amplitude in vertical polycrystalline silicon transistors can yield the position of the trap in the channel with high accuracy.

Temperature dependence of the point defect properties of GaN thin films studied by terahertz time-domain spectroscopy

The dielectric functions of GaN for the temperature and frequency ranges of 10-300 K and 0.3-1 THz are obtained using terahertz time-domain spectroscopy. It is found that there are oscillations of the dielectric functions at various temperatures. Physically, the oscillation behavior is attributed to the resonance states of the point defects in the material. Furthermore, the dielectric functions are well fitted by the combination of the simple Drude model together with the classical damped oscillator model. According to the values of the fitting parameters, the concentration and electron lifetime of the point defects for various temperatures are determined, and the temperature dependences of them are in accordance with the previously reported result. Therefore, terahertz time-domain spectroscopy can be considered as a promising technique for investigating the relevant characteristics of the point defects in semiconductor materials.

Diagnostics and lithography of semiconductor structures for nanoelectronics

A complex of metrological, diagnostic, and technological support of investigations and innovations in the field of nanotechnologies based on the Nanostructures joint service center is presented. Results of the study of the atomic structure of the surface, interfaces, and structural defects in semiconductor materials; the development of modern electron and scanning probe microscopy methods; and the fabrication of low-dimensional solid-state systems for nanoelectronics are reviewed. The emphasis is on the development of physicochemical fundamentals of the nanostructuring of semiconductor materials, analysis of the main features of growth and defect formation in low-dimensional systems, and the fabrication of experimental elements of nanoelectronics for studying quantum, electron interference, and single-electron effects. The results provide the basis of nanotechnologies for controlled synthesis of nanostructures with tailored configurations and the required electrical, mechanical, and other properties.

M-Center in Low-Dose Proton Implanted 4H-SiC; Bistability and Change in Emission Rate

Electrically active point defects in semiconductor materials are important because they strongly affect material properties like effective doping concentration and charge carrier lifetimes. This thesis presents results on point defects introduced by ion implantation in silicon and silicon carbide. The defects have mainly been studied by deep level transient spectroscopy (DLTS) which is a quantitative, electrical characterization method highly suitable for point defect studies. The method is based on measurements of capacitance transients and both standard DLTS and new applications of the technique have been used. In silicon, a fundamental understanding of diffusion phenomena, like room-temperature migration of point defects and transient enhanced diffusion (TED), is still incomplete. This thesis presents new results which brings this understanding a step closer. In the implantation-based experimental method used to measure point defect migration at room temperature, it has been difficult to separate the effects of defect migration and ion channeling. For various reasons, the effect of channeling has so far been disregarded in this type of experiments. Here, a very simple method to assess the amount of channeling is presented, and it is shown that channeling dominates in our experiments. It is therefore recommended that this simple test for channeling is included in all such experiments. This thesis also contains a detailed experimental study on the defect distributions of vacancy and interstitial related damage in ion implanted silicon. Experiments show that interstitial related damage is positioned deeper (0.4 um or more) than vacancy related damage. A physical model to explain this is presented. This study is important to the future modeling of transient enhanced diffusion. Furthermore, the point defect evolution in low-fluence implanted 4H-SiC is investigated, and a large number of new defect levels has been observed. Many of these levels change or anneal out at temperatures below 300 C, which is not in accordance with the general belief that point defect diffusion in SiC requires high temperatures. This thesis also includes an extensive study on a metastable defect which we have observed for the first time and labeled the M-center. The defect is characterized with respect to DLTS signatures, reconfiguration barriers, kinetics and temperature interval for annealing, carrier capture cross sections, and charge state identification. A detailed configuration diagram for the M-center is presented.