Majority Carrier Trap Research Articles

Investigation of deep level defects in copper irradiated bipolar junction transistor

Commercial bipolar junction transistor (2N 2219A, npn) irradiated with 150MeV Cu11+-ions with fluence of the order 1012ionscm−2, is studied for radiation induced gain degradation and deep level defects. I–V measurements are made to study the gain degradation as a function of ion fluence. The properties such as activation energy, trap concentration and capture cross-section of deep levels are studied by deep level transient spectroscopy (DLTS). Minority carrier trap levels with energies ranging from EC−0.164eV to EC−0.695eV are observed in the base–collector junction of the transistor. Majority carrier trap levels are also observed with energies ranging from EV+0.203eV to EV+0.526eV. The irradiated transistor is subjected to isothermal and isochronal annealing. The defects are seen to anneal above 350°C. The defects generated in the base region of the transistor by displacement damage appear to be responsible for transistor gain degradation.

Anomalous deep-level transients related to quantum well piezoelectric fields inInyGa1−yN∕GaN-heterostructure light-emitting diodes

The anomalous inversion of capacitance transients was observed during deep level transient spectroscopy characterization of $\mathrm{In}\mathrm{Ga}\mathrm{N}∕\mathrm{Ga}\mathrm{N}$ based blue light-emitting diodes. Deep level C $({E}_{C}\ensuremath{-}{E}_{T}=0.25\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$, a majority carrier trap related to isolated point defects, has a negative transient when the bias stimulates it only in the bulk region and has a positive transient when the filling pulse is such that the quantum well (QW) region is probed. We explain this observation by a model based on the confining effects of QW piezoelectric fields on the charge emitted by deep levels. Instead of being collected by the junction, this charge is rearranged in conduction band states of the multi-QW region, shifting its center of mass toward the bulk. We measured the strength of piezoelectric fields $(2.3\phantom{\rule{0.3em}{0ex}}\mathrm{MV}∕\mathrm{cm})$ and the QW In fraction $(x=0.15)$ by means of photocurrent spectroscopy, and we tested the accuracy of our model by comparing a Schr\odinger-Poisson simulation with our experimental data, finding substantial agreement.

Analysis of generation and annihilation of deep level defects in a silicon-irradiated bipolar junction transistor

A commercial bipolar junction transistor (2 N 2219 A, npn), irradiated with 120 MeV Si9+ ions with a fluence of the order of 1012 ions cm−2, is studied for radiation-induced gain degradation and deep level defects. I–V measurements are made to study the gain degradation as a function of ion fluence. Properties such as activation energy, trap concentration and capture cross section of deep levels are studied by deep level transient spectroscopy (DLTS). Minority carrier trap energy levels with energies ranging from EC − 0.160 eV to EC − 0.581 eV are observed in the base-collector junction of the transistor. Majority carrier trap levels are also observed with energies ranging from EV + 0.182 eV to EV + 0.401 eV. The identification of the defect type is made on the basis of its finger prints such as activation energy, annealing temperature and capture cross section by comparing with those reported in the literature. New energy levels for the defects A-center, di-vacancy and Si-interstitial are also observed. The irradiated transistor is subjected to isothermal and isochronal annealing. The defects are seen to anneal above 250 °C. The defects generated in the base region of the transistor by displacement damage appear to be responsible for transistor gain degradation.

Effects of a low-energy proton irradiation on n +/p-AlInGaP solar cells

For the first time, by deep-level transient spectroscopy, 30 keV proton irradiation-induced defects in n + /p-AlInGaP solar cells have been observed. After the 30 keV proton irradiation, new deep-level defects such as two majority-carrier (hole) traps HP1 ( E V + 0.9 8 eV , N T = 3.8 × 1 0 1 4 cm - 3 ) and HP2, and two minority-carrier (electron) traps EP1 ( E C - 0.7 1 eV , N T = 2.0 × 1 0 1 5 cm - 3 ) and EP2 have been observed in p-AlInGaP. The introduction rate of majority-carrier trap center (HP1) is 380 cm −1, which is lower than that (1500 cm −1) in 100 keV proton-irradiated p-InGaP. From the minority-carrier injection annealing for HP1 defect and carrier concentration in 30 keV proton-irradiated p-AlInGaP, HP1 defect is likely to act as a recombination center as well as a compensator center.

Defect states investigation in poly(2-methoxy,5-(2′ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV)

In this study, application of the charge based Deep Level Transient Spectroscopy (Q-DLTS) has been extended to poly(2-methoxy,5-(2′ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) single layer diodes, whose cathode consisted of aluminium and anode of indium tin oxide (ITO). The results reveal a broad Q-DLTS spectrum, with at least two maxima, consistent with a complex distribution of trap states. Only the Q-DLTS maximum with the shortest relaxation time could be fully resolved over the temperature range used here (100–300 K), yielding activation energies and capture cross sections in the ranges 0.3–0.4 eV and 10 − 20–10 − 18 cm 2, respectively. It will be shown that this energy level is likely related to a majority-carrier (hole) trap, consistent with a Poole–Frenkel injection mechanism and p-type doping of the MEH-PPV film. The origin of the second (non-resolved) Q-DLTS peak will also be discussed.

Deep-level defects introduced by 1 MeV electron radiation in AlInGaP for multijunction space solar cells

Presented in this paper are 1 MeV electron irradiation effects on wide-band-gap (1.97 eV) (Al0.08Ga0.92)0.52In0.48P diodes and solar cells. The carrier removal rate estimated in p-AlInGaP with electron fluence is about 1cm−1, which is lower than that in InP and GaAs. From high-temperature deep-level transient spectroscopy measurements, a deep-level defect center such as majority-carrier (hole) trap H2 (Eν+0.90±0.05eV) was observed. The changes in carrier concentrations (Δp) and trap densities as a function of electron fluence were compared, and as a result the total introduction rate, 0.39cm−1, of majority-carrier trap centers (H1 and H2) is different from the carrier removal rate, 1cm−1, in p-AlInGaP. From the minority-carrier injection annealing (100mA∕cm2), the annealing activation energy of H2 defect is ΔE=0.60eV, which is likely to be associated with a vacancy-phosphorus Frenkel pair (Vp-Pi). The recovery of defect concentration and carrier concentration in the irradiated p-AlInGaP by injection relates that a deep-level defect H2 acts as a recombination center as well as compensator center.

Radiation-resistant properties of Ga-doped Si analyzed by DLTS

Using deep-level transient spectroscopy (DLTS), we have studied the effect of Ga impurities upon defect generation and annealing behavior of radiation-induced defects, and carrier removal and minority-carrier lifetime degradation in Si single crystals irradiated with 1MeV electrons at room temperature. It is found that compared to the B impurity in p-type Si, the Ga impurity strongly suppresses the generation of the EC−0.18–0.21eV and EV+0.36eV defect centers, which play a dominant role in carrier removal as a deep donor state and act as a majority-carrier trapping center, and a recombination center. The effectiveness of the Ga impurity for suppressing the carrier removal effect with irradiation is also found in comparison to the B impurity.

Distinguishing metastable changes in bulk CIGS defect densities from interface effects

The deep defect distributions affecting majority carrier trapping in polycrystalline CuIn 1− x Ga x Se 2 (CIGS) have been studied using drive level capacitance profiling. This technique provides, a spatial and energetic profile of sub-band gap defect transitions in the CIGS layer of working photovoltaic devices, while remaining insensitive to surface states. The bulk response was dominated by a defect which varied between 0.1 and 0.3 eV, according to the Meyer-Neldel rule. Devices grown at reduced substrate temperatures had smaller grain sizes and additional defect response. The effect of a light-soaking treatment, using near-band gap optical excitation, was studied. Both the free carrier density and the density of deeper defects were increased by this treatment. Device quality was degraded, predominantly due to a decreased fill factor.

Determination of Traps in Poly(p-phenylene vinylene) Light Emitting Diodes by Chargebased Deep Level Transient Spectroscopy

AbstractCharge-based deep level transient spectroscopy (Q-DLTS) has been used to study the defect states that exist within poly(p-phenylene vinylene) (PPV), a semiconducting polymer with a band gap of about 2.4 eV. The technique allows the determination of activation energies, capture cross-sections and trap concentrations. In some circumstances, it is also possible to distinguish between minority and majority carrier traps. The structures investigated here consisted of ITO/PPV/MgAg light emitting diode (LED) devices. Two types of trapping centres were found. The first type has activation energies in the range 0.49 – 0.53 eV and capture cross-sections of the order of 10-16 – 10-18 cm2. It shows a Poole-Frenkel, field assisted-emission process. This level has been identified as a bulk acceptor-like majority carrier (i.e., hole) trap. The second type has activation energies in the range 0.40 – 0.42 eV and capture cross-sections of the order of 10-19 cm2. This level has been identified as a minority carrier (i.e., electron) trap. This second trap type is therefore expected to limit minority carrier injection into the PPV layer within the LED, and hence reduce electroluminescence under forward bias conditions.

Deep-level transient spectroscopy analysis of proton-irradiated n +/p InGaP solar cells

Defects in p-InGaP produced by low-energy protons have been investigated by deep-level transient spectroscopy (DLTS). A new majority-carrier (hole) trap HP1 has been observed in low-energy proton-irradiated p-InGaP at 0.90±0.05 eV above the valance band for the first time. The HP1 introduction rate for 100-keV proton-irradiated p-InGaP is 1500 cm −1, which is 6 times higher than that (260 cm −1) for the 380-keV proton-irradiated one. Isochronal annealing is found to annihilate the proton-induced HP1 defect above 300°C that is higher than the annealing stage (100°C) for 1-MeV electron-induced H2 center in p-InGaP. The carrier removal rates are found to be 61433 and 8640 cm −1 for 100 and 380-keV proton irradiation, respectively. Proton energy-dependent effects include decrease in both the carrier removal rate and in the defect introduction rate with increase in proton energy by creating HP1 trap.

Determination of traps in poly(p-phenylene vinylene) light emitting diodes by charge-based deep level transient spectroscopy

Charge-based deep level transient spectroscopy has been used to study the defect states that exist within poly(p-phenylene vinylene) (PPV), a semiconducting polymer with a band gap of about 2.4 eV. The technique allows the determination of activation energies, capture cross sections, and trap concentrations. In some circumstances, it is also possible to distinguish between minority and majority carrier traps. The structures investigated here consisted of indium–tin–oxide (ITO)/PPV/MgAg light emitting diode (LED) devices. Two types of trapping centers were found. The first type has activation energies in the range 0.49–0.53 eV and capture cross sections on the order of 10−16–10−18 cm2. It shows a Poole–Frenkel, field assisted–emission process. This level has been identified as a bulk acceptor-like majority carrier (i.e., hole) trap. The second type has activation energies in the range 0.40–0.42 eV and capture cross sections on the order of 10−19 cm2. This level has been identified as a minority carrier (i.e., electron) trap. This second trap type is therefore expected to limit minority carrier injection into the PPV layer within the LED, and hence reduce electroluminescence under forward bias conditions.

Electrical, electronic and optical characterisation of ion beam synthesised β-FeSi 2 light emitting devices

β-FeSi 2/Si light emitting devices (LEDs) have been attracting great interest since the first successful demonstration of an ion beam synthesised (IBS) device operating at a wavelength of 1.5 μm . We report here on a study of the electrical, electronic and optical properties of devices produced by Fe implantation into epitaxial silicon layers. The devices have been characterised by current–voltage ( I– V), capacitance–voltage ( C– V), deep level transient spectroscopy (DLTS) and electroluminescence (EL) measurements. DLTS showed the presence of a majority carrier trapping centre, with an activation energy of 200±25 meV. Room temperature EL was observed from β-FeSi 2/Si LEDs. Preliminary analysis of the EL results suggests its quench ratio depends on device structure; the quenching is thought to be related to surface recombination.

DLTS measurements on CuInS 2 solar cells

Deep-level transient spectroscopy (DLTS) was used in this work to reveal information about deep defect levels in CuInS 2 based solar cells. A strong variation of the defect spectrum from sample to sample was found. A minority carrier trap at 0.25 eV and a majority carrier trap at 0.35 eV were identified as bulk traps by variation of pulse height. Two majority carrier traps at 0.24 and 0.8 eV were confirmed as interface traps.

Deep-level transient spectroscopy (DLTS) of CdS/CuIn 1− xGa xSe 2-based solar cells prepared from electroplated and auto-plated precursors, and by physical vapor deposition

We fabricated high-efficiency thin-film CuIn 1− x Ga x Se 2-based solar cells from solution-based electroplated, auto-plated precursors and by physical vapor deposition. The devices were characterized by deep-level transient spectroscopy (DLTS). DLTS recorded a new electron trap level in addition to two hole (majority-carrier) trap levels and one electron (minority-carrier) trap level for low-efficiency devices. We believe that the additional electron trap level is an effective recombination center, which leads to the poor performance of the device.

Analysis of the gate capacitance measurement technique and its application for the evaluation of hot-carrier degradation in submicrometer MOSFETs

The use of gate-to-drain capacitance ( C gd) measurement as a tool to characterize hot-carrier-induced charge centers in submicron n- and p-MOSFET’s has been reviewed and demonstrated. By analyzing the change in C gd measured at room and cryogenic temperature before and after high gate-to-drain transverse field (high field) and maximum substrate current ( I bmax) stress, it is concluded that the degradation was found to be mostly due to trapping of majority carriers and generation of interface states. These interface states were found to be acceptor states at top half of band gap for n-MOSFETs and donor states at bottom half of band gap for p-MOSFETs. In general, hot electrons are more likely to be trapped in gate oxide as compared to hot holes while the presence of hot holes generates more interface states. Also, we have demonstrated a new method for extracting the spatial distribution of oxide trapped charge, Q ot, through gate-to-substrate capacitance ( C gb) measurement. This method is simple to implement and does not require additional information from simulation or detailed knowledge of the device’s structure.

Electrically Active Defects in Silicon after various Optical Thermal Processing

Schottky diodes have been made on virgin n-type monocrystalline silicon annealed by various optical thermal processes including lasers and incoherent light heat-pulses. The electrical characteristics of the diodes have been measured as a function of the laser energy density. A strong change in all their electrical parameters occurs for energy density equal or higher than a fluence threshold at which the processed silicon surface layer turns into melt. Capacitance measurements and DLTS analyses show that laser irradiations introduce a large density of deep levels related to donor defects in the processed surface region. DLTS analyses performed on samples processed with incoherent light heat-pulses show that deep levels related to majority carrier trap defects are also generated by this new thermal process. The results have been compared to those obtained from parallel analyses carried out on p-type silicon processed using either rapid or conventional thermal annealing mode.

Deep level analysis of radiation-induced defects in Si crystals and solar cells

Deep level transient spectroscopy (DLTS) analysis of radiation-induced defects in p-type Si crystals and solar cells has been carried out to clarify the mechanism of the anomalous degradation of Si n+–p–p+ structure space cells induced by high-energy, high-fluence electron/proton irradiations. A large concentration of a minority-carrier trap with an activation energy of about 0.18 eV has been observed in irradiated p-Si using DLTS measurements, as well as the majority-carrier traps at around Ev+0.18 eV and Ev+0.36 eV, Correlations between DLTS data and solar-cell properties for irradiated and annealed Si diodes and solar cells have shown that type conversion of p-Si base layer from p-type to n-type is found to be mainly caused by introduction of the 0.18 eV minority-carrier trap center, that is, this center acts as a deep-donor center. The Ev+0.36 eV majority-carrier trap center is thought to also act as a recombination center that decreases minority-carrier lifetime (diffusion length). Moreover, origins of radiation-induced defects in heavily irradiated p-Si and generation of deep-donor defect has also been discussed.

Electrical Activity of Defects Induced by Oxygen Precipitation in Czochralski-Grown Silicon Wafers

Majority and minority carrier traps introduced in p-type Czochralski-grown silicon (CZ-Si) wafers during two-step low-high temperature annealing procedures were investigated using deep level transient spectroscopy (DLTS). It was determined that the platelike silicon oxide precipitate surface and the punch-out dislocations introduce majority carrier traps having deep energy levels (EV+0.43 eV and EV+0.26 eV, repectively) in the Si band gap in concentrations proportional to the relevant defect density. The minority carrier traps are positioned at EC-0.42 eV and EC-0.22 eV. The majority carrier trap density on the surface of the platelike precipitate was estimated as ∼3×109 cm-2 and the linear trap density for the punch-out dislocations as ∼ 4×104 cm-1.

Effects of Annealing on Type Converted Si and Space Solar Cells Irradiated with Heavy Fluence 1 MeV Electrons

We present a detailed quantitative study of the thermal annealing characteristics of deep level defects in Si and space solar cells with boron-doped p-Si base layer, introduced by 1 MeV electrons irradiation. Present isochronal annealing provides an overall different annealing behavior of the defects in type converted (n-type) heavy dose electrons (φ=1×1017 e/cm2) irradiated samples, contrary to earlier low dose electrons studies. Isochronal annealing provides evidence that the minority carrier trap (EC-0.18 eV) and majority carrier trap (EC-0.71 eV) that appear after type conversion play a dominant role in carrier removal and are the major defects responsible for the type conversion as well as the severe degradation of space solar cells. This study also sheds light on the fact that heavy electron irradiation not only changes the structure of the device (p to n-type) but also makes the defect structure more complex as compared to simple defects structure in low dose samples.

Analysis of deep levels in a phenylenevinylene polymer by transient capacitance methods

Transient capacitance methods were applied to the depletion region of an abrupt asymmetric n+−p junction of silicon and unintentionally doped poly[2-methoxy, 5 ethyl (2′ hexyloxy) paraphenylenevinylene] (MEH-PPV). Studies in the temperature range 100–300 K show the presence of a majority-carrier trap at 1.0 eV and two minority traps at 0.7 and 1.3 eV, respectively. There is an indication for more levels for which the activation energy could not be determined. Furthermore, admittance data reveal a bulk activation energy for conduction of 0.12 eV, suggesting the presence of an additional shallow acceptor state.