Scanning Deep Level Transient Spectroscopy Research Articles

Correlative Defect Characterization in Semiconductors via Electron Channeling Contrast Imaging and Scanning Deep Level Transient Spectroscopy

Correlative Defect Characterization in Semiconductors via Electron Channeling Contrast Imaging and Scanning Deep Level Transient Spectroscopy

Tutorial: Junction spectroscopy techniques and deep-level defects in semiconductors

The term junction spectroscopy embraces a wide range of techniques used to explore the properties of semiconductor materials and semiconductor devices. In this tutorial review, we describe the most widely used junction spectroscopy approaches for characterizing deep-level defects in semiconductors and present some of the early work on which the principles of today's methodology are based. We outline ab-initio calculations of defect properties and give examples of how density functional theory in conjunction with formation energy and marker methods can be used to guide the interpretation of experimental results. We review recombination, generation, and trapping of charge carriers associated with defects. We consider thermally driven emission and capture and describe the techniques of Deep Level Transient Spectroscopy (DLTS), high resolution Laplace DLTS, admittance spectroscopy, and scanning DLTS. For the study of minority carrier related processes and wide gap materials, we consider Minority Carrier Transient Spectroscopy (MCTS), Optical DLTS, and deep level optical transient spectroscopy together with some of their many variants. Capacitance, current, and conductance measurements enable carrier exchange processes associated with the defects to be detected. We explain how these methods are used in order to understand the behaviour of point defects and the determination of charge states and negative-U (Hubbard correlation energy) behaviour. We provide, or reference, examples from a wide range of materials including Si, SiGe, GaAs, GaP, GaN, InGaN, InAlN, and ZnO.

Application of scanning deep level transient spectroscopy for characterisation of multicrystalline silicon

Minority carrier trap levels in cast p-type multicrystalline silicon solar cell material were identified by means of scanning deep level transient spectroscopy. The material was investigated in the as-grown state and after the solar cell process. Additionally iron diffused samples (1050 °C), quenched or slow-cooled, were used. Two levels in the as-grown material were detected at E C -0.2 eV and E C -0.45 eV. The E C -0.45 eV level is also found with comparable defect density in the material after the solar cell process and after iron diffusion, respectively. In the quenched samples the iron-boron level at E C -0.29 eV is observed. Spatially resolved measurements for the E C -0.45 eV level reveal an inhomogeneous defect distribution in the iron diffused and quenched samples which is not related to crystal defects like grain boundaries or dislocations.

Scanning Deep Level Transient Spectroscopy Measurements of Extended Defects in Silicon

Scanning Deep Level Transient Spectroscopy Measurements of Extended Defects in Silicon

Quantitative electron-beam tester for defects in semiconductors (CL/EBIC/SDLTS system)

A pulsed electron beam testing system was developed for quantitative analysis of optical and/or electrical properties of defects in semiconductors. This system can control not only the electron beam but also detect and record the absolute values of light intensity: cathodoluminescence (CL), electron-beam-induced current (EBIC), and scanning deep level transient spectroscopy (SDLTS). Several improvements were made to enable accurate quantitative measurement. An optical system with an ellipsoidal mirror of low magnification was designed to make uniform collection efficiency of CL over a wide specimen area. A photon counting system and a lock-in amplifying system were implemented to measure absolute value of light intensity. A quantitative EBIC or SDLTS system was also incorporated to this system. The combined system of CL/EBIC/SDLTS can both image the distribution of defects and study their characteristics.

Scanning deep-level transient spectroscopy investigations on gallium arsenide

The present state of the art of the application of the scanning deep-level transient spectroscopy (SDLTS) technique is reported. Special attention is given to the theoretical modelling of the signal generation process, yielding important information on the factors influencing the spatial resolution to be attained. The experimental possibilities of the dedicated SDLTS equipment available now are described. This system was used to investigate point defects generated by plastic deformation in GaAs p+-n junctions induced by diamond indentations made at room temperature. A cloud of point defects (hole traps at Ev + 0.5 eV) up to a distance of approximately 20 μm from the indentations has been detected by SDLTS. Interestingly, the deformation-induced point defects are localized in regions outside the slip bands rather than within the slip bands of the deformation-induced dislocations. Annealing experiments seem to contradict their interpretation as the second charge state of the EL2 level.

Scanning‐DLTS, EBIC, and CL Investigations of Diamond Indentations in GaAs p+n Junctions

AbstractDiamond indentations have been carried out on Zn‐diffused GaAs p+n junctions on (100) oriented material. Electron‐beam induced current (EBIC) investigations revealed the well‐known dislocation slip bands in 〈110〉 directions. Scanning deep level transient spectroscopy (SDLTS) imaging proved a deformation‐induced point‐defect level at Ey + 0.5 eV, which is preferentially concentrated in the dislocation‐free regions between the slip bands rather than within the slip bands. Monochromatic cathodolumines‐cence (CL) imaging at 10K using different wavelengths revealed only the dislocation‐induced recombination activity but not any point‐defect luminescence corresponding to the 0.5 eV level found by SDLTS.

Characterization of EL2 in GaAs wafers by scanning isothermal transient spectroscopy

The authors have developed a novel scanning deep level transient spectroscopy system based on laser-excited junction capacitance or current transient measurements under isothermal conditions (scanning isothermal transient spectroscopy or SICTS). By applying the system to the measurement of deep levels in GaAs, they have successfully obtained precise information on the spatial distribution of EL2 in n-type GaAs wafers.

Scanning deep level transient spectroscopy (SDLTS) investigations of deep level spatial distribution in implanted silicon

A model describing SDLTS signal formation in the case of majority carrier capture is proposed. In the frame of this model, the calculations of signal and spatial resolution dependences on beam current have been computed. The computation results are compared with experimental data obtained on Si and GaAs crystals.

Electron beam induced current and cathodoluminescence imaging of the antiphase domain boundaries in GaAs grown on Si

Electrical and optical properties of antiphase domain boundaries (APBs) in GaAs epitaxial layers grown on Si substrates have been investigated using cathodoluminescence, electron beam induced current, and scanning deep level transient spectroscopy. It was found that APBs reduce near-band-gap luminescence and minority-carrier lifetime. In contrast to recombination at threading dislocations in GaAs films, the nonradiative recombination processes at APBs are not due to deep traps but rather to a continuum of band-gap states introduced by APBs.

Spatial Inhomogeneities of the Luminescence and Electrical Properties of Mbe Grown GaAs on Si

AbstractSpatial homogeneity of the luminescence and electrical properties of gallium arsenide films grown directly on silicon substrates (GaAs/Si) by molecular beam epitaxy (MBE) have been investigated with microscopic scanning photoluminescence (PL), cathodoluminescence (CL), electron beam induced current (EBIC), and scanning deep level transient spectroscopy (SDLTS). It was found that GaAs/Si exhibits a highly nonuniform lateral distribution of speckled appearance in CL and PL images. These centers are also responsible for short minority carrier lifetimes as determined by EBIC. The observed nonuniformities appear to be a fundamental material property which is not altered by post-growth annealing. Correlations between the luminescence and electrical inhomogeneities and structural defects will be discussed.

Analysis of scanning deep level transient spectroscopy

Fundamental processes such as charge generation, trapping and emission, and collection in scanning deep level transient spectroscopy (SDLTS) are analyzed. It is concluded that SDLTS is more sensitive to minority-carrier traps than to majority-carrier traps and that a two-dimensional map of SDLTS peak signal magnitude, i.e., SDLTS image, of minority-carrier traps does not necessarily show the trap concentration distribution. A practical equation for trap concentration is derived by utilizing an electron beam induced current. Concentration of a hole trap with an activation energy 0.45 eV in an n-type as-grown liquid encapsulated Czochralski GaAs is calculated to be 1×1016 cm−3.

Characterization of defects in semiconductors by combined application of SEM(EBIC) and SDLTS*

SUMMARYBesides the characterization of the geometrical structure of defects in semiconductors by TEM the estimation of their electrical activity is of importance. SEM(EBIC) and SDLTS (scanning deep level transient spectroscopy) are especially suitable for this purpose; they allow the inspection of electronic properties with a spatial resolution in the micron‐range. On the one hand, SEM(EBIC) yields information on the recombination efficiency of defects in the crystal volume adjacent to a pn junction or a Schottky barrier; on the other hand, SDLTS enables the detection to be carried out of the distribution and the energetic levels of deep level defects lying in the space charge region. Accordingly, the combined application of these techniques is very promising for investigating physical processes implying an inhomogeneous incorporation of deep level defects in semiconductor crystals.In comparison to the widely used SEM(EBIC) technique SDLTS has only rarely been applied, a fact that is due to the high detection sensitivity necessary for measuring capacity transients. The application of a highly sensitive (10—6 pF) micro‐computer‐controlled SDLTS system in combination with a conventional EBIC system allows a reliable inspection of semiconductor materials and devices, based on A3B5 compounds and on silicon. A typical application of the above technique is the investigation of the impurity distribution around extended crystal defects, like dislocations and precipitates, to study their gettering activity.

Scanning deep level transient spectroscopy (SDLTS)

AbstractScanning Deep Level Transient Spectroscopy (SDLTS) is a current SEM technique for the detection of the local distribution of deep level centres in semiconductors. It is based on the application of the widely used Deep Level Transient Spectroscopy (DLTS), which enables capacitance changes (or current changes) to be measured in a space charge structure after an excitation pulse as a function of the temperature. This makes it possible to detect the energy levels and the concentration of electronic states in the band gap. By means of scanning DLTS–i.e. the excitation of the levels by an electron probe–deep level states can be investigated with a spatial resolution of a few microns. Scanning the pulsed electron beam (at a temperature selected according to an interesting energy level) yields an SDLTS image. Based on the general principle of the measurement and on the necessary instrumentation the practice of the SDLTS signal generation analysis is presented and experimental examples are discussed.

COMBINED ELECTRON MICROSCOPICAL AND DLTS (ESP, DSLTS) INVESTIGATIONS IN SEMICONDUCTORS

COMBINED ELECTRON MICROSCOPICAL AND DLTS (ESP, DSLTS) INVESTIGATIONS IN SEMICONDUCTORS

The influence of intrisic defects on the degradation and luminescence of GaAs and other III–V compounds

A significant contribution to the degradation of GaAs-based lasers and light-emitting diodes arises from the formation of so-called dark line defects. It is shown that these defects are accumulations of non-radiative recombination centres around dislocations. The centres are identified as As vacancies, which are emitted by climbing dislocations, concomitantly with the absorption of Ga interstitials. From scanning deep-level transient spectroscopy observations it is concluded that the so-called DX centres are Ga interstitials. The driving force for dislocation climb and thus for dark-line-defect formation is a supersaturation of Ga interstitials originating from the growth of the GaAs crystals under Ga-rich conditions as a consequence of the high volatility of As. Phenomena in other III–V compound semiconductors related to the formation of dark line defects in GaAs are also discussed.

Recombination-Enhanced Interactions between Point Defects and Dislocation Climb in Semiconductors

The interaction between $〈100〉$ climb-induced dislocation networks and a naturally occurring deep level (the $\mathrm{DX}$ center) in ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ has been analyzed by scanning deeplevel transient spectroscopy. The concentration of $\mathrm{DX}$ centers was observed to decrease markedly in the vicinity of climb-induced $〈100〉$ networks, but remained nearly unchanged near glide-induced $〈110〉$ dislocation networks.

Investigation of Semiconductor Materials and Devices by High Voltage STEM Techniques

AbstractThis paper reviews work carried out in‐situ on semiconductor devices by means of a high voltage electron microscope equipped with facilities for scanning transmission electron microscopy, electron beam induced conductivity and energy loss spectrometry. These combined techniques have allowed simultaneous and unambiguous correlations to be established between crystallographic, electrical and elemental properties of semiconductor materials and devices. Examples of these correlations are given, and mention is made to facilities (scanning deep level transient spectroscopy and cathodoluminescence) which may further increase the potential of high voltage scanning transmission electron microscopy.

A new spectroscopic technique for imaging the spatial distribution of nonradiative defects in a scanning transmission electron microscope

A new spectroscopic technique for imaging the spatial distribution of nonradiative defects in semiconductor materials is presented. The technique combines the versatility and sensitivity of deep-level transient spectroscopy (DLTS) with the capability for defect analysis at high resolution of the scanning transmission electron microscope. This scanning DLTS method (SDLTS) is illustrated by observing Cu-related defect centers in Ga1−xAlxAs epitaxial layers. A high sensitivity (3×1015 Cu defects cm−3 have been detected) and a spatial resolution of 2 μ or better illustrate the potential of the technique for the study of the electrical behavior of defects in semiconductor devices.