Search

Silicon nitride (SiN x ) films deposited by direct plasma-enhanced chemical vapor deposition (PECVD) are widely used in silicon solar cell fabrication as passivation layers, yielding very low surface recombination velocities on crystalline Si (c-Si) material. So far, there have been some reports on deep-level transient spectroscopy (DLTS) of as-deposited SiN x layers on Si, but the impact of rapid thermal anneal (RTA) processing step and the textured surface has not been investigated yet. In this paper, low frequency direct PECVD Si-SiN x interface properties with and without plasma NH 3 pre-treatment, with and without RTA on both flat (100) and (111) orientations and textured n-type silicon samples have been investigated with DLTS.

In this work we have employed deep level transient spectroscopy (DLTS) for studies of electrically active centers in solar-grade Si. The purpose of the work is to develop robust experimental routines for detecting and identifying the dominant recombination centers. DLTS measurements have been performed prior and after heat treatments corresponding to such technological processes as contact firing and rapid thermal processing (RTP). Multi-crystalline (mc-Si) and Cz-Si with p-type doping and the resistivity in the 1–6 Ohm range have been investigated. Firstly, the effect of Fe has been investigated. In order to ensure that the carrier recombination is determined by Fe, the samples have been intentionally enriched by Fe via in-diffusion from the surface. It has been observed by DLTS that a heat treatment corresponding to the contact firing process leads to activation of Fe in the interstitial form (Fe i ) with a donor state at 0.43 eV above the valence band. Secondly, RTP has received a considerable attention recently due to increasing control in diffusion profile for the emitter formation in solar cells. However, electrically active defects and impurities may be introduced or activated by RTP due to the high temperatures of the treatment followed by rapid cooling, when the impurities can be quenched with concentrations above the solubility level. It is found that RTP at 1000°C for 2 minutes results in formation of two dominant hole traps at ∼0.3 and ∼0.4 eV above the valence band edge with concentrations in the range 5×1012–5×1013 cm−3. The observed levels exhibit Poole-Frankel effect suggesting the acceptor nature of the centers.

We report investigation of electron traps in AlGaN/GaN HEMTs, grown on silicon by molecular beam epitaxy. Deep levels analysis was performed by conductance deep level transient spectroscopy (CDLTS) under a drain pulse. CDLTS measurements reveal three traps with the energy levels of 0.11, 0.17 and 0.22 eV.

The properties of traps at SiO2/Si and Si3N4/Si interfaces were examined and compared using deep level transient spectroscopy (DLTS). Small pulse DLTS was used to determine the effective electron capture cross-section of the interface states. Similar trends are found for both systems with the capture cross-section decreasing rapidly towards the band edge. The effective capture cross-section and energy level is also given for the Si≡Si3 defect at the Si3N4/Si interface.

Deep level transient spectroscopy (DLTS) and laplace DLTS (LDLTS) measurements have been carried out on very shallow implanted p-n junctions in Si. Lightly doped n or p type Si was implanted with high doses at low energy of B or As, followed by implants of lower doses at higher energies of n or p dopants respectively, to simulate a doping well. The double implants resulted in p+/n/n- or n+/p/p- structures, which calculation showed had two depletion regions, one at the end of range of each implanted region. The electric fields in the two depletion regions act in the opposite sense, and by selecting the correct bias conditions it was possible to measure DLTS at the end-of-range of the two implanted regions. DLTS of the n+/p diodes displayed a high temperature peak due to the end of range of the shallow As implant, together with a defect originating much deeper behind the surface observed at low temperatures. LDLTS of the defect in the end-of-range of the As implant revealed two closely spaced energy levels, indicative of a complex defect structure in this region. The DLTS also showed a minority emission peak in all of the p+/n/n- and n+/p/p- samples. Their emission rate in LDLTS did not change with measurement temperature, and is discussed in terms of a small region at the shallow junction that is efficiently confining carriers.

High resolution Laplace deep level transient spectroscopy (LDLTS) at temperatures up to 450 K has been applied to thin polycrystalline semiconducting diamond films deposited on n-type silicon. Such structures form p-n diodes and can be characterised by capacitance DLTS. The boron doped diamond films were grown by hot filament chemical vapour deposition and the diamond film thickness was 3-4 microns. The boron concentration in the diamond films ranged from 7times1018 cm-3 to 1times1019 cm-3. In the LDLTS an isothermal measurement of thousands of capacitance transients was made and then averaged, and the result was inverse transformed to find the trap emission rate. The temperature was chosen as the maximum of the conventional DLTS emission peak. Conventional DLTS showed a combination of majority and minority carrier emission from deep levels. Multiple peaks in the LDLTS spectra suggest that some of the defects are located in a strain field. Capture cross section measurements also show that these peaks exhibit a time dependent capture cross section, which is indicative of carriers being trapped at a large electrically active defect. It is shown in the paper that a combination of LDLTS and direct capture cross section measurements can be applied to semiconducting diamond and can be used to understand whether defects possess single or multiple energy levels, and whether the trapping is at an isolated point defect or in defects in the strain field of an extended defect.

Deep Level Transient Spectroscopy (DLTS) and high resolution Laplace DLTS (LDLTS) have been used to distinguish the difference between electrically active point and extended defects in MOVPE-grown n-type GaN. Three dominant features are observed in the conventional DLTS spectrum, with energies in the region of 40 meV, 550 meV and 1.46 eV. However, detailed examination with LDLTS shows that all these peaks consist of multiple emission rates. The low energy feature consists of three point defects closely spaced in energy, which are identified as ON, and SiGa. The feature at around 550 meV is shown to be due to defects in the strain field of a dislocation, which is deduced because the activation energy is dependent upon DLTS fill pulse length. LDLTS of this peak shows a very complicated spectrum, also indicative of a system of defects in a dislocation strain field. When applied to the very deep level of 1.46 eV, LDLTS shows multiple emission rates but they behave as point-defect like states.

DLTS analysis of radiation-induced defects in p-type GaInNAs and GaNAs solar cell structures are presented. The DLTS spectra of GaInNAs indicates one dominant electron emitting trap E1 (0.30 eV) and three-hole emitting traps H1 (0.27 eV), H2 (0.33 eV) and H3 (0.67 eV). Also, one dominant electron emitting trap E2 (0.20 eV) and two-hole emitting traps H4 (0.28 eV) and H5 (0.60 eV) were observed in GaNAs. After 1 MeV electron irradiation, the concentrations of E1, H1, H2, H3, and H5 increase significantly. The concentration of E2 decreases significantly and H4 decreases partially. Thermal annealing study shows the complete annealing of E1 and E2, and the significant decrease in concentrations of H2, H3, H4 and H5, whereas H1 increases in concentration. It is observed that GaNAs shows more radiation-resistance than GaInNAs and the possibility of using this material as the third-junction in high-efficiency four-junction solar cells for space applications appears to be very promising.

Difficulties and their solutions found during the determination of parameters of impurities in thin GalnNAs solar cells, by means of spectroscopic capacitance measurements, are presented in this work. The parameters of impurities present in the GalnNAs pn junctions are determined by an iterative method, comparing experimental capacitance transients with calculated ones. The results disagree with the ones obtained by applying the classical expressions associated to the capacitance deep level transient spectroscopy (DLTS). The parameters of the centers are used to determine the hole diffusion lengths in the semiconductor. The agreement between the hole diffusion lengths obtained with our method and results found in literature means that DLTS must be used with care when determining recombination centers in thin pn junctions. An expression to be included in the DLTS technique, that incorporates these effects, is proposed.

Constant capacitance deep-level transient spectroscopy (CC-DLTS) has been used to study bulk traps and interface states in Si metal-oxide semiconductor (MOS) capacitors with 50 nm thick thermally-grown oxides on an n-type substrate. Both as-grown and P-implanted samples were studied. The P implants were performed at 50 keV to a dose of 1 × 10 10 cm-2. Thermal anneals in the temperature range 200-400°C were performed on implanted and as-grown samples to examine the dynamics of trap annealing

In this paper, we report a newly developed scanning capacitance transient spectroscopy (SCTS) that enables the electrical characterization of semiconductor wafers by contactless and nondestructive fashion. The validity of the developed system has been demonstrated using a partially Au-doped Si wafer.

A new modification of DLTS applicable to semi-insulating (SI) materials based on simultaneous capacitance C(t) and ac conductance G(t) transient analysis, Admittance Transient Spectroscopy (ATS), is introduced. Formulas for C(t), G(t), their differential dC(t), dG(t) and correlated Sc(T), SG(T) forms are presented. The most important features of the ATS based on the simulation are summarized. ATS was applied to the investigation of deep-level states in bulk undoped and low temperature MBE SI GaAs. Some of the results are briefly discussed in the context of the previously published ones.

The effect of implantation angle on the profile of vacancy-related defects, represented by the divacancy and vacancy-phosphorus centres, in n-type Cz-Si implanted with 450 keV P or 600 keV Si ions to a dose of 2 /spl times/ 10/sup -9/ ions/spl middot/cm/sup -2/ , has been examined using deep level transient spectroscopy depth profiling. Implants were performed with samples aligned with 10/spl deg/ twists from the [110] planar direction and various tilts from the axis. The peak depth of the VP/V/sub 2/ profile exhibits a systematic variation with the implantation angle: shifting towards the surface, narrowing and increasing in peak concentration as the implantation angle is progressively varied from the aligned direction. For well-channeled 450 keV P ions, the peak in the defect profile is approximately 0.9 microns deeper than the peak in the vacancy profile predicted using the binary collision codes MARLOWE and Crystal-TCAS. The effect of the surface proximity on defect concentrations has been considered by comparing those profiles obtained for 450 keV P implanted samples with those of 600 keV Si implanted samples.

We have used deep level transient spectroscopy to detect traps in p-type GaAsN grown by metal-organic chemical vapor deposition. Although minority-carrier electrons are not intentionally injected into the depletion region of the measured samples, electron traps are detected in both Schottky barrier and p-n junction devices. The electron-trap signal can exist using only reverse biases during measurement, and checks of series resistance and minority-carrier injection using an optical source also confirm the electron-trap signal. For dilute-nitrogen p-n junction samples, the electron trap gives the dominant signal peak. The peak's magnitude, which corresponds to trap density, correlates to amounts of nitrogen incorporated during growth and reduced open-circuit voltage during light-characterization. The p-type GaAsN layers have net acceptor carrier concentrations in the mid-10/sup 16/ to low-10/sup 17/ cm/sup -3/, as determined by capacitance voltage profiling. The electron-trap concentration is dependent on the N content, but values, when traps are filled to saturation, range from 10/sup 15/ to 10/sup 16/ cm/sup -3/. The electron signal peak shows a shoulder peak on some samples, giving another close energy level. The electron-trap activation energy is somewhat dependent on the trap filling time, but ranges from about 0.15 to 0.30 eV, and is usually near 0.2 eV for the largest peak when filled to saturation.

In this paper, we present reliable guidelines allowing to maximize the detection and analysis of deep defects in semiconductors by introducing a new method of analysis that we named MLM-DLTS (modified Levenberg-Marquardt deep level transient spectroscopy) based on the Levenberg-Marquardt algorithm that we modified deliberately and associated with two other high-resolution techniques, i.e., the matrix pencil algorithm and Prony's method recently revised by Osborne. The performances of the method were first assessed with a procedure of simulation by generating multi-exponential capacitance transients with a changing signal-to-noise ratio. These different tests have demonstrated to what extent such a method of analysis is more efficient than classic correlation methods based on DLTS spectra and than three high-resolution methods already existing in the literature. Finally, when the signal-to-noise ratio is low, and in the aim of getting precise results, a few smoothing algorithms were tested. Our findings evidence how the smoothing quality can be controlled under certain conditions while avoiding both the distortions in the shape of the capacitance transients and the DLTS spectra.

Deep levels in undoped semi-insulating (SI) GaAs and Fe-doped SI InP investigated by photoinduced transient spectroscopy (PITS). It is demonstrated that the resolution of this method can be improved by direct computer fitting of digitally recorded photocurrent decays.

A new technique, channel conductance transient spectroscopy (CCTS), for measuring traps at the SiO/sub 2/-Si interface and in the bulk of small-sized MOSFETs is introduced in detail. Constant capacitance deep level transient spectroscopy (CC-DLTS) can not be applied to small-sized MOSFETs due to their small gate capacitance depending on their gate area. CCTS offers the solution for this fundamental problem. The channel conductance of the MOSFET in linear region strongly depends upon the the gate voltage rather than the gate area. Trapped carriers in interface traps and bulk traps influence the threshold voltage and as a result change the channel conductance. The exponential emission of carriers out of traps causes corresponding transients of channel conductance. The channel conductance transients are correlated with lock-in correlator. Interface trap density (D/sub it/) and concentration(N/sub t/) of bulk traps can be evaluated. This new measurement technique is very sensitive and reliable. CCTS is a unique measurement technique which can characterize not only the interface state but also the bulk traps in small-sized MOSFETs. The results of ZMR-SOI-MOSFETs are presented. >

The deep-level transient spectroscopy (DLTS) system is fabricated using low-frequency capacitance measurements and is applied to GaN thin layers to characterize electron traps. The frequency dependence of the capacitance gives the capacitance measurement frequency of 10 kHz in DLTS for the Schottky diodes fabricated on 1-/spl mu/m-thick Si-doped GaN layers due to the high series resistance. DLTS using W-kHz capacitance measurements reveals three electron traps with the energy levels of E/sub c/ - 0.23, E/sub c/ - 0.31 and E/sub c/ -0.61 eV in addition to the broader signals in the temperature range from 350 to 500 K. The concentrations of these traps are found to be in the range of 10/sup 14/ cm/sup -3/.

Defect levels in CdTe/CdS have been characterized using correlation deep level transient spectroscopy. The devices studied were processed under various conditions in an effort to identify defect levels and correlate their presence to key processes and impurities. Process variations included the CdCl/sub 2/ treatment, as this process is very common to most CdTe technologies, and the back contact. The back contact often relies on the use of copper, an impurity known to be critical for the formation of effective back contacts, but which has also been associated with device degradation in CdTe solar cells. Several hole and electron traps were identified and are presented in this paper.

The technique of photoinduced transient spectroscopy (PITS) has been applied to the study of deep-level traps in SIMOX (separation by implantation of oxygen) silicon

In order to study deep defects in undoped LEC-grown GaAs, photo induced current transient spectroscopy (PICTS) has been carried out on materials with a depletion region. Five main traps were observed. In addition to positions in the gap, it is shown that the nature of carrier traps can also be identified. Contributions from the surface and the bulk of the material in the PICTS signal, are compared. Also, effects from the excitation light wavelength on PICTS spectra, are reported.

The interface hole trap distribution in nitrided oxide (NOX), re-oxidized nitrided oxide (RNOX), and thermal oxide are studied and are compared in detail utilizing the deep level transient spectroscopy (DLTS) measurement. Results show that nitrided oxides have larger amount of hole traps than the thermal oxide. Most of the hole trapping centers in NOX layers are due to the oxygen deficiency as a result of oxygen removal during the nitridation. For RNOX sample, the amount oxygen deficiency centers are reduced by re-oxidation and the non-bridging oxygen could be a major source of hole traps. In addition, we found that the hole emissions of the trapping centers in NOX and RNOX samples also follow the lattice relaxation multiphonon emission model as used in thermal oxide.

Semi-insulating (SI) InP substrate is the key element for both high speed microelectronic devices and for optoelectronic integrated circuits (OEICs). Up to now, crystals have been doped with a transition element, which acts as a deep acceptor. Iron has in particular been used to generate deep level in the forbidden gap of InP, which is very effective in decreasing the free carrier concentration. Today, Fe doping during liquid encapsulation Czochralski (LEC) growth is the only reliable technique for the fabrication of InP crystals with high resistivity. The defect characterization of these substrate is of great importance to have successful devices. The Photo Induced Current Transient Spectroscopy (PICTS), first reported by Hurtes et al., is a useful technique for the characterization of deep levels in high resistivity semiconductors. It is based on the analysis of the thermal behaviour of the photocurrent transient induced by periodic light pulses. In this study, we investigate the evolution of the defects in LEC InP with the concentration of Fe introduced in the melt. >

In order to investigate defects in monocrystalline CuInSe/sub 2/ solar cells DLTS (deep level transient spectroscopy) measurements were performed on both In- or Bi-diffused homojunctions and Al-CuInSe/sub 2/ Schottky junctions made on this material. Two hole trap levels, one at 250+or-15 meV and the other at 520+or-15 meV from the valence band edge, were found on either homojunction or Schottky junctions. The trap densities in the homojunctions were on the order of 10/sup 13/ cm/sup -3/, but the value was found to be one order magnitude larger in the Schottky junctions fabricated on the same substrate. During the DLTS measurements, another hole trap level with an energy of 186+or-3 meV from the valence band edge was found in two other Schottky junctions. The stoichiometry of the samples used to fabricate these devices was believed to be responsible for the difference. >

In this work, the deep level band structure of unintentionally doped n-type GaN grown by HVPE and MOVPE is demonstrated. Optical-isothermal capacitance transient spectroscopy (O-ICTS) is used to simultaneously observe thermal and optical emission processes from deep levels. The key benefit of this technique found when applied to GaN is that deep levels can be distinguished spectroscopically by their characteristic emission time constant. The O-ICTS spectra can be deconvoluted to estimate the concentrations and ionization energies of deep levels with a high degree of confidence.

Electrical characterization of rapid thermal oxides on Si/sub 0.887/Ge/sub 0.113/ and Si/sub 0.8811/Ge/sub 0.113/C/sub 0.0059/ alloys were carried out using the capacitance versus voltage (C-V) and deep level transient spectroscopy (DLTS) techniques. A high interface trap density (/spl sim/10/sup 12/ eV/sup -1/ cm/sup -2/) and a high apparent doping level were obtained from the C-V measurements for the SiO/sub 2//Si/sub 0.8811/Ge/sub 0.113/C/sub 0.0059/ samples. The interface state density for the SiO/sub 2//Si/sub 0.887/Ge/sub 0.113/ system was found to be 3.15/spl times/10/sup 11/ eV/sup -1/ cm/sup -2/. The C-V results at different temperatures showed that the high apparent doping levels of the SiO/sub 2//Si/sub 0.8811/Ge/sub 0.113/C/sub 0.0059/ samples might be due to the formation of SiC-related defects introduced by the high temperature oxidation process.

Deep Level Transient Spectroscopy (DLTS) spectra of Schottky diodes on both [100] and [111] GaP substrates were measured. The parameters of one hole and three electron traps were determined. The set of the charge carrier traps was found to depend upon the orientation of the substrate. These traps are suggested to be formed during the high-energy ion implantation and electrochemical processing.

The capacitance of a metal-insulator-metal (MIM) system with a trapped space charge in the insulator has been derived under various conditions. On the basis of the transient behavior of the capacitance as a function of temperature, we have determined the trap parameters in polyimide films. In this paper we describe briefly the theory and present some experimental results.

Self-assembled quantum dots (QD) are attracting widespread interest due to the potential they offer in the device application such as low-threshold lasers, detectors and optical memory structures. We report on the electron-filling photoreflectance and photoluminescence investigation in the 1.5-3 eV photon energy range and at temperatures from 10 to 330 K on stacked layers of Si quantum dots. We observed clear and well-resolved structures, which we attribute to the optical response of different QD families. It is shown that Coulomb interaction can account for the observed optical response of QD families with different morphology coexisting in the semiconductor barrier.

A comparative study on light-induced negative-bias stress stabilities in amorphous In-Ga-Zn-O (a-IGZO) thin film transistors (TFTs) was performed by means of photoinduced transient spectroscopy (PITS). When the a-IGZO thin films were deposited with 4% O 2 partial pressure (P/P), a dominant peak with a maximum of around 100 K was clearly observed from the sample. There was a flow rate of SiH 4 /N 2 O of 4/100 sccm for the ESL deposition, while the PITS spectra from the sample with a flow rate of SiH 4 /N 2 O of 6/150 sccm possessed a broader peak of around 115 K and an apparent shoulder of around 200–280 K was observed. This shoulder of around the 200–280 K was clarified when the a-IGZO thin film was deposited with an O 2 P/P of 20 % In accordance with the changes in the electronic structures in the a-IGZO thin films due to the ESL deposition, the stability of the TFTs against the negative bias thermal Illumination stress (NBTIS) was degraded; the value of the V th shift after the 2h-NBTIS test was increased from 2.5 to 6.0 V The decreasing the compensating acceptors and/or the increasing the hydrogen-related donors could be the origin of the negative V th shift during the NBTIS test.

This paper highlights electrical characterization of Schottky structures prepared on AlGaN/GaN designed for HEMT's using Deep Level Transient Fourier Spectroscopy (DLTFS) method with electrical and optical excitation. In case of electrical excitation the density of minority and majority carrier traps had strong effect on the evaluation, whereas preliminary DLTFS with optical excitation (MCDLTFS) measurements made possible to identify minority carrier defects with higher precision. Parameters of two electron-like defects EL1 (0.47 eV), EL2 (0.54 eV) and three hole-like defects HL1 (1.13 eV), HL2 (0.93 eV) and HL3 (0.49 eV) were identified. HL1 andHL2 were confirmed by both methods: DLTFS and MCDLTFS. These are connected to a Carbon interstitial defect and well-know threading dislocations. Experimental results confirmed the benefits of different method utilizations in complex defect identifications.

Trapping effects still limit the application of GaN-based high-electron mobility transistors (HEMTs). This paper further characters traps in GaN HEMTs based on the drain current transients. A hybrid transient, which contains more valuable information of traps than the single trapping or detrapping transient was detected and analyzed. Three traps with different time constants were determined and their possible mechanisms were discussed. In particular, a dynamic capturing and releasing process during the current transient was proposed, by which a more appropriate measured condition for analyzing current transients can be acquired.