DLTS Study Research Articles

A DLTS Study on Deep Trench Processing-Induced Trap States in Silicon Photodiodes

A DLTS Study on Deep Trench Processing-Induced Trap States in Silicon Photodiodes

Chemical cyanide treatment of polycrystalline p-Cu2O/n-ZnO solar cell

Cuprous oxide (Cu2O) and zinc oxide (ZnO) hold a very crucial position in the field of materials research because of their immense potential in many acoustic, electronic and optical applications. Cu2O is a direct-gap semiconducting material with forbidden energy gap around 2.0 eV. It has been considered as one of the most promising materials for photovoltaic applications, especially for use at the top in a cascade cell structure. The enchantment of Cu2O and ZnO as photovoltaic materials is due to fact that their constituent materials are nontoxic, abundantly available and of relatively low cost. In this work, Cu2O thin films in polycrystalline form were prepared in radio-frequency (rf) reactive magnetron sputtering route on glass substrates at different substrate temperatures. After the samples were prepared, these were taken through a crown-ether cyanide (CN) treatment. Presence of oxygen in excess compared to stoichiometry is the major active impurity in Cu2O and consequently holes are the majority charge carriers in it. With the aid of crown-ether cyanide treatment of the prepared samples, hole-mobility was found to increase and resistivity was found to decrease considerably. Finally, polycrystalline p-Cu2O/n-ZnO heterojunctions were fabricated for use in solar cells. Results of Hall measurement strongly support the observations made from DLTS studies and photocurrent measurements. Thus, our present study confirms the improvement of device performance of the p-Cu2O /n-ZnO heterojunctions on chemical cyanide treatment.

DLTS study of the influence of annealing on deep level defects induced in xenon ions implanted n-type 4H-SiC

DLTS study of the influence of annealing on deep level defects induced in xenon ions implanted n-type 4H-SiC

Current–Voltage, Capacitance–Voltage–Temperature, and DLTS Studies of Ni|6H-SiC Schottky Diode

Current–Voltage, Capacitance–Voltage–Temperature, and DLTS Studies of Ni|6H-SiC Schottky Diode

Deep level defects in β-Ga2O3 pulsed laser deposited thin films and Czochralski-grown bulk single crystals by thermally stimulated techniques

Thermally stimulated techniques—thermally stimulated current (TSC) spectroscopy and thermally stimulated depolarization current (TSDC) spectroscopy—were used to comparatively study the electrical properties and deep level defects in β-Ga2O3 pulsed laser deposited thin films and Czochralski-grown bulk crystals. It was found that the samples are highly resistive and each sample may have different dark current activation energy. Deep level defects revealed by the thermally stimulated techniques vary from sample to sample. In addition to the common traps E1 (∼0.56 eV), E2 (∼0.84 eV), and E3 (∼0.99 eV), reported in the literature and revealed by DLTS studies of Ga2O3 bulk crystals, that were also found in our samples by the thermally stimulated techniques, a trap at ∼110 meV and several other traps are revealed specifically by TSDC between 105 and 225 K.

Laplace DLTS study of deep defects created in neutron-irradiated n-type 4H-SiC

This paper presents the characterization of the electrically active defects created by epithermal and fast neutrons in epitaxial n-type 4H-SiC material using Laplace Deep Level Transient Spectroscopy (Laplace DLTS). While the deep level related to the carbon vacancy has been observed in as-grown material, we observed that epithermal and fast neutron irradiation introduces additional simple defect complexes, with energy levels at EC – 0.40 eV and EC – 0.70 eV.

DLTS study of InGaAs and GaAsN structures with different indium and nitrogen compositions

In this article Deep Level Transient Fourier Spectroscopy experiments and various evaluation procedures were used to study emission and capture processes of deep energy levels in intentionally undoped InGaAs and GaAsN semiconductor structures. The examined samples, grown by Atmospheric Pressure Metal Organic Vapour Phase Epitaxy on GaAs substrates, were analyzed at various indium and nitrogen concentrations. Main attention was focused on differences in defect distributions, relations in possible composition and growth condition sensitive defect states. Valuable characteristics of particular In/N contents capable to eliminate or reduce specific impurities are discussed. A possible indium dependent dual state InGaAs complex and a nitrogen and growth condition dependent dual type GaAsN complex was introduced/confirmed. The most balanced samples for further utilizations were achieved for In = 8.9% and N = 1%.

(Invited) DLTS Studies of Defects in n-GaN

We have studied electron and hole traps in Si-doped n-GaN grown by metal organic chemical vapor deposition on n+-GaN, sapphire, SiC and Si substrates. DLTS using bias pulses, MCTS using above-band-gap light pulses and ODLTS using below-band-gap light pulses have been employed for fabricated Schottky diodes. The energy levels and capture cross sections of four electron traps and three hole traps are reported. A variation of dominant traps in concentration between wafers and among diodes on each wafer is observed, which is discussed based on the dependence of trap concentrations on the growth conditions.

Identification of carbon‐hydrogen complexes in n‐ and p‐type silicon

AbstractThe origin of several deep traps E42, E90, E262, and H180 in hydrogenated n ‐type and p ‐type FZ and CZ Si is investigated. Comparing the depth profiles of these defects in samples with different C, O, H, and shallow donor (acceptor) concentrations we conclude that they belong to carbon‐hydrogen‐related defects consisting of one C and one H atom. The similar annealing behavior and identical depth profiles of E42 and E262 correlate them with two different charge states of the same defect. From a comparison with earlier calculations we attribute E42 to the double acceptor and E262 to the single acceptor state of the CH1AB complex. In good agreement with the results of previous studies E90 is assigned to the acceptor state of the CH1BC complex. Our preliminary Laplace DLTS studies on SiGe with a Ge content <5% show different local Ge environments for E90 and H180 in the nearest and second‐nearest neighborhood. We interpret this as an indication for a different origin of these defects. After annealing the samples under reverse bias at 320 K another CH‐related defect (CHB) can be detected by Laplace DLTS in n ‐type Si. Previously, this defect was often wrongly assigned to the single donor state of CH1BC. The field dependence of the emission rate of CHB identifies the level as a single donor state. However, the depth distribution of CHB differs clearly from that of E90. Our results on the carbon‐hydrogen complex give a conclusive explanation of previously reported controversial experimental data. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Molybdenum nano‐precipitates in silicon: A TEM and DLTS study

AbstractThe quest for low cost solar cells has resulted in attempts to use lower purity silicon rather than conventional electronic grade material. The metallic content of such ‘solar silicon’ is usually much higher than electronic grade material and this compromises the efficiency of photovoltaic conversion via a variety of recombination mechanisms. Molybdenum is a common metallic contaminant in Si which is difficult to getter because of its low diffusivity. It is known that Mo incorporates into the Si lattice as single interstitial atoms, introducing a deep donor level into the gap. In this work, we show that Mo in silicon can also form nano‐precipitates which may represent a new general class of efficient recombination centres. We have observed the Mo precipitates by TEM as 5–10 nm clusters in Si samples into which molybdenum was introduced during growth or by ion implantation and annealing. In general, such precipitates can form in Si samples containing metals with low diffusivity during high‐temperature treatments and subsequent cooling. We report the carrier capture and emission properties of Mo nano‐precipitates, which show that these could be very effective recombination centres for minority carriers in p‐type Si. In particular we present data and analysis of minority carrier charge exchange at these nano‐dimension metallic defects.

A DLTS study of a ZnO microwire, a thin film and bulk material

ABSTRACTWe have investigated the electrical properties of a ZnO microwire grown by carbo-thermal evaporation, a ZnO thin film grown by pulsed-laser deposition on an a-plane sapphire, and a hydrothermally grown Zn-face ZnO single crystal (Tokyo Denpa Co. Ltd.). The samples were investigated by means of current-voltage measurements, capacitance-voltage measurements, and deep-level transient spectroscopy.The defects T2 [1,2] and E3 [1,3,4] were identified in all three sample types. Additionally, in the single crystal and thin film samples E64 [5] and E4 [1] were detected. These findings support the common opinion that T2 is an intrinsic defect since it is found in all the samples investigated and thus its occurrence is not related to any growth technique.

A re‐examination of the interstitial Ti levels in Si

AbstractUsing high‐resolution Laplace DLTS studies we demonstrate that three Ti‐related levels (E40, E150 and H180) previously assigned to the different charge states of the interstitial Ti belong to different Ti defects. The enhancement of the emission rates of E40 and H180 as a function of the electric field (Poole‐Frenkel effect) shows that these defects are charged before they capture a majority carrier in n‐ and p‐type Si, respectively. In contrast to the previous studies we did not observe the Poole‐Frenkel effect for E150. The inconsistence is correlated with the presence of H‐related defects close to E150, which cannot be distinguished by using the conventional DLTS technique. The absence of the Poole‐Frenkel effect for E150 indicates that the defect is an acceptor in n‐type Si. The origin of the defects will be discussed. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

C–V and DLTS studies of radiation induced Si–SiO2 interface defects

Interface traps at the Si–SiO2 interface have been and will be an important performance limit in many (future) semiconductor devices. In this paper, we present a study of fast neutron radiation induced changes in the density of Si–SiO2 interface-related defects. Interface related defects (Pb centers) are detected before and upon the irradiation. The density of interface-related defects is increasing with the fast neutron fluence.

C-V - and DLTS-Investigations of Pyramid-Shaped Ge Quantum Dots Embedded in N-Type Silicon

We investigate self-assembled pyramid-shaped Ge Quantum Dots (QDs) with lateral dimensions of 15 nm, and heights of 2.5-3 nm. These Ge QDs were grown by Molecular Beam Epitaxy (MBE) on n-type Si(100) substrates using the Sb-mediated growth mode. The resistivity of the substrates was about 5 Ωcm. The Si buffer layer below the QDs and the Si capping layer above them were doped up to 1018cm-3by Sb. Cross-section transmission electron microscopy shows the QDs and the Sb delta-doped layers. Using standard photolithographic techniques, a 0.3 mm2Au Schottky contact was applied to the epilayer, while an Ohmic contact was formed on the back side of the substrate. Plotting C-2vs. V plot reveals the nominal doping of 1018cm-3. DLTS studies revealed two levels with fitted activation energies of 49 meV and 360-390 meV. They are related to the Sb doping and the Pb interface states, respectively. The simulation suggests a deep level with a volumetric concentration of 2.55×1015cm-3. Multiplying this value by the thickness of the depletion region obtained from the CV measurements, we find that the deep level capture about 5.8×109electrons per cm2.

Formation of Copper-Related Deep-Level Centers in Irradiated P-Type Silicon

Results of a DLTS study on the deep-level centers in the copper-contaminated electron-irradiated FZ-Si are presented. Copper was diffused from the Cu-contaminated surface into previously irradiated samples at 350 K. The most abundant Cu-related complexes formed due to this procedure are the same as in the case of previously studied Cu-diffused Cz-Si.

Electrical Study of Self-Assembled Ge Quantum Dots Embedded in P-Type Silicon. Temperature Dependent Capacitance Voltage and DLTS Study

The electrical properties of dome-shaped and pyramid-shaped Ge Quantum Dots (QDs) embedded in p-type Silicon are reported. Capacitance-Voltage (T-CV) characteristics are reported for the temperature range of 35 K to 296 K. The T-CV results showed the desired charge carrier density of the Silicon, on the order of 1016 cm-3, at room temperature. Two shoulders are observed in the CV curves between 270 K and 175 K. They are explained as charge stored in the dome- and pyramid-shaped QDs. Below 175 K, only one shoulder is observed in the CV measurements, attributed to charge trapped in dome-shaped QDs. The DLTS study confirms these results. Using a reverse bias between -0.1 V and -1 V two peaks are seen at 50 and 70 K. They are explained in terms of the boron state (the one at 50 K) and charged stored on pyramid-shaped Ge QDs (the one at 70 K). Increasing the reverse bias from -1 V to -1.4 V shows the appearance of a peak around 60 K, attributed to dome-shaped Ge QDs. At the same time, a shoulder appears around 100 K for -1 V, which extends to larger temperatures as the reverse bias magnitude is increased. The activation energies found are around 50 meV (due to Boron), 150 to 250 meV (due to pyramid-shaped Ge QDs), 300 to 350 meV (due to dome-shaped Ge QDs) and 425 meV (due to both dome- and pyramid-shaped Ge QDs).

The influence of inhomogeneous trap distribution on results of DLTS study

A model is developed to describe how a narrow distribution of deep traps adjacent to quantum dots (QDs) influences the trap-related signals measured by frequency scanned deep level transient spectroscopy (FS-DLTS). By comparison with experiment, it is demonstrated that traps with a steep concentration gradient, positioned in the so called transition layer close to the edge of the depletion region (“ λ-effect”), have a strong influence on DLTS signal amplitudes. This is manifested by an extreme sensitivity to the change in the Fermi-level position when temperature is varied.

Giant Poole-Frenkel effect for the shallow dislocation-related hole traps in silicon

The results of a theoretical calculation of the Pool-Frenkel effect due to the strain field of screw and 60° dislocations upon the valence band in silicon, and of a detailed DLTS study of the electrical field impact on carrier emission from the dislocation-related states of two types of bonded samples are presented and discussed. A good agreement between the theory and experiment was established. It is concluded that the large Pool-Frenkel coefficient value that significantly exceeds the value for a Coulomb-like potential is a new distinguishing feature of the hole thermo-emission from dislocation-related levels in silicon.

A DLTS Study of SiO2 and SiO2/SiNx Bi-Layer Surface Passivation of Silicon

not Available.

Minority carrier injection limited current in Re/4H‐SiC Schottky diodes

AbstractCurrent–voltage–temperature, capacitance–voltage, and Fourier transform‐deep level transient spectroscopy (FT‐DLTS) measurements have been employed to gain insights into the conduction mechanism in Re/4H n‐silicon carbide (SiC) Schottky diodes. A power law dependence of current on voltage has been observed in the Re/4H‐SiC Schottky diodes at large forward bias. DLTS studies of the diodes reveal the presence of a deep trap at an energy $E_{\rm c} - E_{\rm t} = 0.6\,{\rm eV}$. The electron trap center is tentatively associated with the prominent Z1 defect level, and the obtained trap density and capture cross‐section values correlate well with available literature values. Excess capacitance has been observed under forward bias suggesting that minority carrier injection is the mechanism responsible for the observed characteristics.