Deep Level Transient Spectroscopy Study Research Articles

Avoidance of surface-related defects in MOVPE-grown InGaP layers

Deep-level transient spectroscopy studies of n-type InGaP/GaAs structures revealed an electron trap E1 with a thermal activation energy of 0.75 eV. From the shape of the depth profiles for this deep level an extrinsic defect can be concluded, which moves from the air exposed InGaP surface via interstitial sites into empty substitutional sites of the InGaP lattice. By comparison of InGaP samples grown at 580 °C with different V/III input ratios as well as at 650 °C, it is suggested that the most probable candidate for the E1-related defect is oxygen on phosphorus site. It is shown that this defect is due to an extrinsic defect. The concentration of the E1-related defect depends on the concentration of phosphorus vacancies, which are due to thermal degradation of the growing InGaP layer surface as a result of insufficient stabilization. The in-diffusion of oxygen is promoted by particular intrinsic defects, probably antiphase boundaries, in the InGaP layer determined by the growth condition. With a sufficiently thick GaAs cap layer or by adequately chosen growth conditions for InGaP, the surface-related defect E1 can be avoided.

Defect production in γ-irradiated silicon at different temperatures

A deep level transient spectroscopy (DLTS) study of electrically active defects in γ-irradiated, n-type, Czochralski-grown silicon samples at different temperatures has been performed. It is shown that upon irradiation at low temperatures the migration of primary defects is very limited, resulting in formation of only vacancy–oxygen (VO) centres. At higher temperatures these centres continue to form but the profile of the peak suggests that complex clustering of primary defects around VO centres occurs, contributing to the stress in material. After irradiation at higher temperatures the vacancies become more mobile contributing to the formation of multivacancy-related defects. Besides formation of divacancies, a deep level at E c–0.32 eV has been detected in the DLTS spectra. This level is identified as a divacancy–oxygen V 2O complex.

Annealing of defects in irradiated silicon detector materials with high oxygencontent

A deep level transient spectroscopy (DLTS) study of electrically active defects in electronirradiated silicon detectors has been performed. Two types of materials havebeen studied and compared: carbon-lean magnetic Czochralski (MCZ-) Si, andhigh purity, diffusion oxygenated float-zone (DOFZ-) Si. In both materials weobserved an earlier reported shift in position of peaks associated with the divacancy(V2) at250–325 °C, indicating a gradualtransition from V2 to thedivacancy–oxygen complex (V2O). Heat treatments at higher temperatures reveal a difference in annealingbehaviour of defects in DOFZ- and MCZ-Si. It is observed that VO andV2O anneal with a higher rate in DOFZ-Si. The appearance of a hydrogen related level only inthe DOFZ-Si reveals a small presence of H and it is suggested that the difference inannealing behaviour is due to defect interaction with H in the DOFZ-Si. Our findingsalso suggest that dissociation may be a main mechanism for the annealing ofV2O in MCZ-Si.

Short term instabilities of InGaN GaN light emitting diodes by capacitance–voltage characteristics and junction spectroscopy

We present a combined capacitance-voltage, Deep Level Transient Spectroscopy (DLTS) and electroluminescence (EL) study of short-term instabilities of InGaN/GaN LEDs submitted to forward current aging tests at room temperature. In the early stages of the aging tests at low forward current levels (15 and 20 mA), LEDs present a decrease in optical emission, which stabilizes within the first 50 hours and never exceeds 20% (measured at an output current of 1 mA after stressing the LEDs for 50 hours with 15 mA stress). The spectral distribution of the EL intensity does not change with stress, while C-V profiles detect changes consisting in apparent doping and/or charge concentration increase within quantum wells. This increase is correlated with the decrease in optical power. DLTS has been carried out to clarify the DC aging induced generation/modification of the energy levels present in the devices. Remarkable changes occur after the stress, which can be related to the doping/charge variation and thus to the efficiency loss. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Deep level transient spectroscopy studies on BaTiO3 and Ba1–xCaxTiO3 thin films deposited on Si substrates

Laser ablation grown BaTiO3 and Ba1–xCaxTiO3 thin films were studied in the metal–ferroelectric–semiconductor configuration by the deep level transient spectroscopy (DLTS) technique. The capture cross section, bulk and interface traps were determined from the DLTS technique. The distributions of calculated interface states were mapped with the silicon energy band gap for both the thin films. The interface states of the Ba1–xCaxTiO3 thin films were found to be higher than the BaTiO3 thin films. The substitution of Ca2+ into the Ba2+ sites of BaTiO3 results in a decreased lattice constant, thereby leading to shrinkage in the unit cell. This might be one of the reasons for the higher density of interface states present in Ba1–xCaxTiO3, as it leads to a large number of unsaturated bonds at the interface of Si substrate–thin films. The calculated capture cross section of the interface traps in both the BaTiO3 and Ba1–xCaxTiO3 thin films was very low in the range of 10−21 cm2.

Role of deep levels in DC current aging of GaN/InGaN Light-Emitting Diodes studied by Capacitance and Photocurrent Spectroscopy

AbstractWe present a combined Capacitance-Voltage (C-V), Deep Level Transient Spectroscopy (DLTS) and Photocurrent (PC) study of short-term instabilities of InGaN/GaN LEDs submitted to forward current aging tests at room temperature. C-V profiles detect changes consisting in apparent doping and/or charge concentration increase within the quantum wells. This increase is correlated to dramatic modifications in the DLTS spectrum when the reverse bias and filling pulse are properly adjusted in order to probe the quantum well region. The new distribution of the electronic levels detected by DLTS could explain the observed decrease in the light emission efficiency [1,2] of the device, as the deep levels generated during the stress may provide alternative recombination paths for free carriers. The photocurrent spectra do not change in shape during stress, although their amplitude slightly decreases. This is related to a decrease of the device yield, in this photodetector configuration, with increasing aging time. Thus, we can suggest that the introduction of new defect levels in the bulk material lowers the free carrier mobility.

DLTS and PL study of defects in InAlAs/InP heterojunctions grown by metal organic chemical vapor deposition

Deep level transient spectroscopy (DLTS) and photoluminescence (PL) techniques are used to study the defects present in InAlAs/InP layers grown by metal organic chemical vapor deposition (MOCVD). In DLTS technique, different reverse bias and different heights and widths of the filling pulse are applied to the samples; the measurements have revealed the presence of four defects labelled A–D, which are found to be in a good agreement with the results of the photoluminescence (PL) technique. In fact, a detailed study of the defect (D) by photoluminescence (PL) technique has led to the same results as those determined by DLTS.

Electrical and optical properties of rod-like defects in silicon

Self-interstitials in silicon can aggregate to form rod-like defects (RLDs) having both electrical and optical activity. We carry out local density functional calculations for both {113} and {111} RLDs to determine their structures and electrical activity. We find that small {113} RLDs are more stable than {111} RLDs but this reverses for larger defects. We attribute the electrical activity of {113} RLDs found in deep level transient spectroscopy studies with the bounding dislocations and the 0.903 eV photoluminescence to vacancy point defects lying on the habit plane.

Electronic properties of deep defects in n-type GaN

The recurrent presence of deep levels in n-type hexagonal GaN films grown by metal organic chemical vapour deposition (MOCVD) is testified by Fourier transform deep level transient spectroscopy (FTDLTS) studies performed in various samples. Some of these electron traps are systematically detected with emission rates showing activation energies in the range 0.94–1.30 eV and apparent capture cross sections from 10 −15 to 10 −12 cm 2. These properties are deduced from an Arrhenius diagram where data coming from samples of different origins are close to the same straight line, assessing a common physical identity for the corresponding defects. However, isothermal spectroscopy and trap filling kinetics characteristics contradict these capture cross section values and even show nonmonotonic variations which must be ascribed to the emission and capture rates of interactive multiple deep levels. Fine structure of the energy levels, although it is never resolved by standard FTDLTS, is indeed revealed by a high resolution DLTS method (HRDLTS) which relies on a time domain treatment of the transients recorded over a large range of time. Multiple levels are well evidenced in this way and both their ionisation energy and capture cross sections turn out to be much less than those measured by standard FTDLTS, respectively in the ranges 0.26–0.90 eV and near 10 −17 cm 2 on the one hand or less than 10 −20 cm 2 on the other hand, suggesting that these defects can capture two electrons, leading to three charge states and negative charges at least when filled with 2 electrons. Correlation of the concentration of these defects both with the shallow donor concentration and dislocation density suggest that they are due to the doping impurities in dislocation sites.

Identification of deep levels in GaN associated with dislocations

To establish a correlation between dislocations and deep levels in GaN, a deep-level transient spectroscopy study has been carried out on GaN samples grown by metalorganic chemical vapour deposition. In addition to typical undoped and Si-doped GaN samples, high-quality crack-free undoped GaN film grown intentionally on heavily doped cracked Si-doped GaN and cracked AlGaN templates are also chosen for this study. The purpose of growth of such continuous GaN layers on top of the cracked templates is to reduce the screw dislocation density by an order of magnitude. Deep levels in these layers have been characterized and compared with emphasis on their thermal stabilities and capture kinetics. Three electron traps at Ec–ET∼0.10–0.11, 0.24–0.27 and 0.59–0.63 eV are detected common to all the samples while additional levels at Ec–ET∼0.18 and 0.37–0.40 eV are also observed in the Si-doped GaN. The trap levels exhibit considerably different stabilities under rapid thermal annealing. Based on the observations, the trap levels at Ec–ET∼0.18 and 0.24–0.27 eV can be associated with screw dislocations, whereas the level at Ec–ET∼0.59–0.63 eV can be associated with edge dislocations. This is also in agreement with the transmission electron microscopy measurements conducted on the GaN samples.

Annealing of defect density and excess currents in Si-based tunnel diodes grown by low-temperature molecular-beam epitaxy

Deep-level transient spectroscopy (DLTS) measurements were performed in order to investigate the effects of post-growth heat treatment on deep level defects in Si layers grown by low-temperature molecular-beam epitaxy (LT-MBE) at 320 °C. In the LT-MBE as-grown samples, two dominant divacancy-related complex defects, of which the possible origins are suggested as P–V (E center)+V–V (0/−) and V–V (−2/−) and others, were observed in P-doped n layers. When the as-grown samples were annealed at 700, 800, and 900 °C for 60 s by rapid thermal annealing, the total density of defects were decreased without generating other defects and most defects were annihilated at 900 °C. This study also compared the DLTS trends with performance of Si-based resonant interband tunnel diodes (RITDs) in terms of peak current density, valley current density, and peak-to-valley current ratio, which are closely related to the deep-level defects. The active regions of the RITDs were grown at the same substrate growth temperature and annealed at similar temperatures used in this DLTS study.

DLTS study of silicon-on-insulator structures irradiated with electrons or high-energy ions

Results of deep-level transient spectroscopy (DLTS) study of radiation defects in silicon layers, Si/SiO/sub 2/ interface traps, and a charge in buried oxide formed under irradiation with 2.0 MeV electrons (10/sup 5/-10/sup 6/ rad.) or 245 MeV Kr (2.2/spl times/10/sup 8/ cm/sup -2/ and 1.4/spl times/10/sup 9/ cm/sup -2/) ions in silicon-on-insulator (SOI) structures are presented and discussed. SOI was fabricated by the wafer bonding and hydrogen cutting. It was found that electron irradiation leads to transformation of energy spectrum of the interface traps (relaxation of the bonded interface) in SOI. The main effect of high-energy Kr ion irradiation consists in formation of radiation defects in the top silicon layer as well as in the substrate. The fixed positive charge is introduced in the buried oxide under irradiation in both cases.

DLTS Studies of high-temperature electron irradiated Cz n-Si

This paper reports on a Deep Level Transient Spectroscopy (DLTS) study of both oxygen-related thermal donors (OTDs) and radiation-induced defects (RDs) formed in high-temperature 1 MeV electron irradiated n-type Czochralski silicon. The heating of Si samples is done in-situ by the electron beam. The formation of deep levels is studied on both heat-treated and irradiated at high temperature sides of samples. The interaction between OTDs and RDs is investigated. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Ion Implantation and 1 MeV Electron Irradiation of 4H-SiC---Comparison Studies

AbstractArgon ions (Ar+) were implanted into n-type 4H-SiC epitaxial layers at 600 °C. The energy of the ions was 160 keV and at a dose of 2 × 1016 cm−2. After post-implantation annealing at 1600 °C, Schottky diodes were fabricated on the ion implanted samples. Bulk n-type 4H-SiC samples were irradiated at room temperature with 1 MeV electrons at doses of 1 × 1016 to 5.1 × 1017 el/cm2. The current density of the beam was 0.91 μA/cm2. Deep Level Transient Spectroscopy (DLTS) was used to characterize the induced defects. DLTS studies of Ar+ implanted samples showed six defect levels at EC – 0.18 eV, EC – 0.23eV, EC – 0.31eV, EC – 0.38 eV, EC – 0.72 eV, and EC – 0.81 eV. Z1/Z2 defect is the dominant defect in the electron irradiated sample and anneals out completely after 10 minutes at 1000 °C. However, Z1/Z2 defect in Ar+ implanted samples was stable up to 1600 °C. It is suggested that the annealing behavior of Z1/Z2 depends on the source of its formation.

Deep-level transient spectroscopy study on double implanted n+–p and p+–n 4H-SiC diodes

Planar n+–p and p+–n junction diodes, fabricated in 4H-SiC epitaxial layers using a double-implantation technology (a deep-range acceptor followed by a shallow-range donor implantation and vice versa), are characterized using capacitance deep-level transient spectroscopy (DLTS) to detect deep levels, which may influence device electrical performance. Either Al or B was used as the acceptor, while N or P was used as the donor, with all implants performed at 700 °C and annealed at 1600–1650 °C with an AlN protection cap. Different traps were observed for the various dopants, which are believed to be related to different impurity-defect complexes. A trap at ∼EV+0.51 eV was observed in nitrogen-implanted samples, while an acceptor trap at ∼EV+0.28 eV and a donor trap at ∼EC−0.42 eV were observed in Al-implanted samples. A prominent boron-related D-center trap at ∼EV+0.63 eV is seen in the DLTS spectra of B-implanted diodes. In diodes with implanted phosphorus, three traps at ∼EV+0.6 eV, EV+0.7 eV, and EV+0.92 eV, are seen, which are not observed for implantations of other species.

Evidence for identification of the divacancy-oxygen center in Si

A deep level transient spectroscopy (DLTS) study of electronic defect levels in 15 MeV electron irradiated n-type float-zone Si samples with different oxygen contents has been performed. Heat treatment at 250 \ifmmode^\circ\else\textdegree\fi{}C results in a shift of both the singly negative and doubly negative divacancy $({\mathrm{V}}_{2})$ related DLTS peaks. This is due to annealing of ${\mathrm{V}}_{2}$ and the formation of a new double acceptor center. The formation of the new center has a close one-to-one correlation with the annealing of ${\mathrm{V}}_{2}.$ The annealing rate of ${\mathrm{V}}_{2}$ and the formation rate of the new center are close to proportional with the oxygen content in the samples. The new center is identified as a divacancy-oxygen complex.

Deep level transient spectroscopy study of electron-irradiated CuInSe2 thin films

Irradiation of high-energy (2-MeV and 3-MeV) electrons on single-crystalline n-CuInSe2 films has been investigated. From Hall-effect measurements of the film, the carrier density and mobility were decreased by increasing the electron fluence above 1×1017 cm−2. In both as-grown and electron-irradiated CuInSe2 films, the deep level transient spectroscopy (DLTS) peak, indicating electron trap, was found at around 180 K. However, Arrhenius plots of the observed DLTS peaks in as-grown and electron-irradiated films showed different behavior, suggesting the presence of electron traps introduced by high-energy electron irradiation.

Effects of grain boundary on impurity gettering and oxygen precipitation in polycrystalline sheet silicon

The effects of grain boundaries (GB) in polycrystalline sheet silicon on impurity gettering and oxygen precipitation were investigated by electron beam induced current (EBIC), deep level transient spectroscopy (DLTS), micro-Fourier-transform infrared spectroscopy (FTIR), and preferential etching/Normaski optical microscopy techniques. Both as-grown and thermally processed wafers were studied. A correlation between GB density and transition metal concentration was quantitatively established by combining DLTS and EBIC studies. It was found that four deep levels arising from Fe–B, Fe–Al, Cr–B, and Fei were present in the as-grown sample, and their concentrations decrease with increasing GB density. GB gettering was further verified by the presence of an EBIC image contrast halo around the GB. Preferential etching also revealed a precipitate density of 2×107 cm−2 on the GB. After processing, a clearly defined oxygen precipitate denuded zone formed around the GB with the interstitial oxygen concentration [Oi] decreased from 14.4 to 2.2×1017 cm−3. Micro-FTIR showed that, for both processed and as-grown samples, more silicon oxynitride appears in the GB than in the intragrain region. Since nitrogen enhances oxygen precipitation, it is likely that nitrogen preferentially precipitated on the GB during the wafer formation process and resulted in a nitrogen depletion zone, where oxygen precipitation was further suppressed and a denuded zone formed.

GaAs 기판 위에 EDMIn과 TBP로부터 성장되고 양극산화 처리된 InP Schottky Diode

Au/oxide/n-InP Schottky diodes were fabricated from heteroepitaxial InP layers grown on GaAs substrates by the metalorganic vapor phase epitaxy (MOVPE) method from a new combination of source materials: ethyldimethylindium (EDMIn) and tertiarybutylphosphine (TBP). Anodic oxidation technique by using a solution of 10 g of ammonium pentaborate in 100 cc of ethylene glycole as the electrolyte was used to deposit a thin oxide layer. The barrier heights determined from three different techniques, current-voltage (I-V) measurements at room temperature and in the temperature range of 273 K - 373 K, and room temperature capacitance-voltage (C-V) measurements are in good agreement, 0.7 - 0.9 eV which is considerably high as compared to the 0.45 - 0.55 eV in Au/n-InP Schottky diode without a Passivation layer. The ideality factors of 1.1 - 1.3 of the Schottky diodes were also determined from the I-Y characteristics. Deep level transient spectroscopy (DLTS) studies revealed only one shallow electron state at 92.6 meV below the bottom of the conduction band and no deep state in the heteroepitaxial InP layers grown from EDMIn and TBP.

Deep level defect in Si-implanted GaN n+-p junction

A deep level transient spectroscopy (DLTS) study has been performed on a GaN n+-p junction fabricated by implanting Si into a Mg-doped p-type GaN epilayer. A high concentration of a deep level defect has been revealed within the interfacial region of the junctions by the unusual appearance of a minority peak in the majority carrier DLTS spectra. The deep level defect appears to be an electron trap at EC-0.59 eV in the p-side region of the junction and has tentatively been attributed to the VN–Mg complex. The high concentration of this electrically active deep level defect in the depletion layer of the Si-implanted GaN n+-p junction diodes suggests the need for further investigations.