Hole Capture Research Articles

Capacitance transient study of the deep Fe acceptor in indium phosphide

We present a detailed study of the electrical properties of the deep ${\mathrm{Fe}}^{2+/3+}$ acceptor in InP by deep-level transient spectroscopy. The Fe acceptor transition has been observed in electron and hole emission in $n$- and $p$-type InP. A study of the electron emission signature reveals an electric-field enhancement of the emission rate, which is best explained by a polarization potential model. At 300 K electron and hole capture cross sections of $1.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}$ and $4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}18}{\mathrm{cm}}^{2}$ were determined, respectively, indicating the Fe acceptor being a recombination center. The capture cross sections were found to be temperature dependent in agreement with a multiphonon emission process with activation energies of 138\ifmmode\pm\else\textpm\fi{}13 meV for electron and 161\ifmmode\pm\else\textpm\fi{}15 meV for hole capture. Measurements of the ${\mathrm{Fe}}^{3+/2+}$ electron capture cross section at electric-field strengths above $4\ifmmode\times\else\texttimes\fi{}{10}^{4}\mathrm{V}/\mathrm{c}\mathrm{m}$ reveal an approximately 70 times higher value of $1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}{\mathrm{cm}}^{2}$ than without an electric field due to an electric-field-induced lowering of the capture barrier. This increase of the capture cross section is most likely due to a decreased capture barrier for electrons in the $L$ valleys. Since the capture barrier is close to zero when an electric field is applied, the apparent activation energy of ${E}_{C}\ensuremath{-}0.62$ eV, determined by deep-level transient spectroscopy from the carrier emission in an electric field, has not to be corrected by the zero-field capture barrier energy.

Hole trap generation by thermal treatment of nitrogen doped p-type ZnSe on GaAs characterized by deep level transient spectroscopy

The influence of a thermal treatment on hole trap generation in nitrogen doped ZnSe on GaAs was investigated by means of deep level transient spectroscopy. The samples were grown by molecular beam epitaxy (MBE) on highly zinc doped p-type GaAs(001) substrates. p-type doping of the ZnSe epilayer was performed by applying a rf nitrogen plasma during MBE growth. In order to carry out electrical measurements Schottky contacts were prepared by evaporating gold (Au) on top of the ZnSe. A dominant hole trap with a thermal activation energy of about 0.65 eV, showing a strong temperature dependence of the hole capture cross section, was determined. It was found that the concentration of this trap increases by more than one order of magnitude after an annealing of the Au/ZnSe/GaAs samples at 550 K and that it is responsible for hole compensation effects.

Electronic states in ZnSe/ZnTe type-II superlattice studied by capacitance transient spectroscopy

We have studied the electronic states in N-doped ZnSe/ZnTe type-II superlattice (SL) by deep level transient spectroscopy (DLTS) and isothermal capacitance transient spectroscopy (ICTS). The capture and emission processes of holes between a miniband of the SL and the valence band of ZnSe barrier were investigated. From the analysis of DLTS and ICTS spectra, the activation energy for the hole emission from the miniband energy level was determined to be 0.28±0.03 eV, which is consistent with a theoretical value (0.25 eV) of the band offset between the ZnSe/ZnTe SL calculated based on the Kronig–Penney model. A deep level with an activation energy of 0.48±0.03 eV was observed and has been assumed to originate from an interface defect in the SL region. A deep level located at 0.54±0.03 eV above the valence band of ZnSe was also observed in the ZnSe capping layer.

Dynamics of photoexcited holes in n-doped InGaAs/GaAs single quantum well

We have measured the temporal evolution of the photoluminescence (PL) of a Si δ-doped In0.2Ga0.8As/GaAs quantum wells using the PL up-conversion technique. The luminescence spectrum of this sample displayed the characteristic features of the Fermi edge singularity. The temporal evolution of the luminescence is described in terms of the dynamics of the hole population. From the experiments, we have determined the effective hole capture time (15 ps), the interband relaxation time (3 ps), and the radiative decay time (>1 ns) at T=8 K. We have found that the radiative decay time decreases dramatically with increasing temperature (τr=45 ps at T=125 K) which, we believe, is the result of the smearing of the Fermi edge and the delocalization of the holes that are responsible for the luminescence.

A possible mechanism for improved light-induced degradation in deuterated amorphous-silicon alloy

We have studied light-induced photoconductivity degradation in an intrinsic hydrogenated and deuterated amorphous-silicon (a-Si) alloy. Deuterated a-Si turns out to be more stable under light exposure. A possible mechanism is proposed to explain this phenomenon. It is attributed to the highly efficient coupling between the localized Si–D wagging modes (∼510 cm−1) and the extended Si–Si lattice vibration modes (∼495 cm−1). The energy released from electron or hole capture at silicon dangling bonds causes localized vibrations of nearby Si–D bonds. The energy dissipates quickly to the background lattice and a higher recombination rate at local sites is needed in deuterated a-Si than in hydrogenated amorphous silicon to accumulate enough energy to break the nearby weak bonds.

Trivalent behavior of palladium in silicon

Palladium is known to exhibit an acceptor state at EC−0.22 eV in n-type Si and a donor state at EV+0.31 eV in p-type Si. We have identified a third level at EV+(0.140±0.005) eV and attribute it to the double donor state of substitutional Pd. The Pd level positions are very similar to the corresponding levels for Pt. The double donor states of both metals show an electric field dependence of the emission rates and a thermal activation of the hole capture cross sections.

Simulation of carrier capture in semiconductor quantum wells: Bridging the gap from quantum to classical transport

The effects of lost phase coherence on carrier capture by semiconductor quantum wells are simulated using Schrödinger Equation Monte Carlo. Results are shown for polar-opticalphonon-induced capture of both electrons and holes, and for both monoenergetic and thermal distributions of incident charge carriers. Results suggest that semiclassical modeling of hole capture may be sufficient, provided that quantum mechanical reflection from the individual heterointerfaces still is taken into account. However, for a quantum well laser optimized to operate at an electron capture resonance, semiclassical calculations blind to the resonance structure would underestimate the capture rate, while Golden-Rule calculations, which assume complete phase coherence, could somewhat overestimate it.

Minority-carrier lifetime damage coefficient of irradiated InP

Minority-carrier lifetime damage coefficients for 1 MeV electron, 3 MeV proton, and 6 MeV alpha particle irradiation of n-type (4.5×1015 and 1.3×1017 cm−3) and p-type (2.5×1017 cm−3) InP have been measured using time-resolved photoluminescence. These values are relatively insensitive to carrier type and show a slight increase with increasing carrier concentration. Evidence of comparable electron and hole capture lifetimes is found for the dominant recombination defect. The effect of 3 MeV proton and 6 MeV alpha particles relative to 1 MeV electrons is an increase in the lifetime damage coefficient by factors of about 104 and 105, respectively.

Reversibility of Photoelectrochromism at the TiO2/Methylene Blue Interface

This paper describes the photoelectrochromic bleaching and recoloration of methylene blue in aqueous or methanolic slurry suspensions of Using simple modification of a UV‐visible diode‐array spectrometer setup, the spectral changes undergone by the dye in these solutions were monitored in situ during irradiation of the particles and in the dark. A particular focus of this study was a systematic investigation of factors underpinning the chemical and electrochemical (kinetic) reversibility of the dye bleaching‐recoloration sequence. Thus, choice of solution pH and hole capture agents is shown to be crucial to the suppression of parasitic chemical and photochemical reactions involving the dye. On the other hand, dye adsorption on the surface, the solvent medium itself, and its content are all important factors in dictating the kinetic reversibility of the photoelectrochromic process. Finally, the practical implications of the findings are presented.

Measurement of single interface trap capture cross sections with charge pumping

A technique has been developed using charge pumping to determine electron and hole capture cross sections of individual interface traps in small silicon metal–oxide–semiconductor transistors. Values for both cross sections are ≈10−16 cm2 for the particular trap measured.

Carrier trapping due to Fe3+/ Fe2+ in epitaxial InP

Time-resolved photoluminescence studies were performed on epitaxially grown InP either doped with iron or with iron and sulphur to gain information on the carrier trapping characteristics of Fe3+/Fe2+. The carrier trapping time was found to be dependent on both the iron and sulphur concentrations, from which the electron and hole capture cross sections of the Fe deep centers are determined as σe=1×10−15 cm2 and σh=6×10−15 cm2, respectively.

Estimating the detectable rate of capture of stellar mass black holes by massive central black holes in normal galaxies

The capture and subsequent inspiral of stellar mass black holes on eccentric orbits by central massive black holes is one of the more interesting likely sources of gravitational radiation detectable by LISA. We estimate the rate of observable events and the associated uncertainties. A moderately favourable mass function could provide many detectable bursts each year, and a detection of at least one burst per year is very likely given our current understanding of the populations in cores of normal spiral galaxies.

The origin of persistent photoconductivity in compensated hydrogenated amorphous silicon

The possible origins of persistent photoconductivity (PPC) in compensated hydrogenated amorphous silicon ( a-Si : H) are reexamined by the numerical calculation. PPC behavior with the variation of defect density and active dopants concentration is compared with the previous experimental data. The results show that PPC cannot be induced by the defect generation only, but the deactivation of active boron should be included. The variation of PPC with light soaking is well explained by the deactivation of a boron acceptor and a defect generation induced by a hole capture. This result supports the thermal equilibrium, or the charge trapping model rather than the model based only on Staebler-Wronski effect.

Gain and Threshold of Quantum Dot Lasers: Theory and Comparison to Experiments

A theory for gain and threshold of quantum dot lasers operating with inhomogeneously broadened dot ensembles is developed. Separate vs. simultaneous electron and hole capture and thermal vs. non-thermal carrier distributions and vertically coupled stacks are considered. In realistic lasers thermally distributed carriers allow lower threshold currents than non-thermal ensembles. Stacked quantum dots provide larger maximum gain but have a priori a higher threshold. However, vertical coupling leads to a redistribution of the carrier population and subsequently to similarly low thresholds as for lasers operating with single sheets of dots. Theoretical predictions are compared to experiments on quantum dot lasers operating on self-organized InAs/GaAs quantum dots.

Measurements on a hole trap in neutron-irradiated silicon

High resistivity n-type Si has been neutron irradiated and characterized by Deep Level Transient Spectroscopy (DLTS). In addition to common irradiation induced traps we have observed a hole trap with activation energy around 0.475 eV. For characterizing the trap we have observed the DLTS signal versus filling pulse bias combined with simulations of carrier concentrations. According to these measurements, the capture cross section is very small for holes as well as for electrons; of the order of 10 −18–10 −20 cm 2. The hole capture cross section is temperature dependent in the temperature range covered.

Correlation of electrical and optical properties of the vanadium-related C level in silicon

Gibb's free energies due to hole transitions between the C level of Si:V and the valence band have been determined for eleven different temperatures within the range 190 K\ensuremath{\leqslant}T\ensuremath{\leqslant}270 K on the basis of simultan- eous measurements of corresponding thermal hole capture coefficients and emission rates. Zero-phonon binding energies have been determined from the low-energy part of photoionization cross-section spectra at five different temperatures within the range 75 K\ensuremath{\leqslant}T\ensuremath{\leqslant}170 K. The temperature dependence of these binding energies can be described by a Varshni-type analytical formula with a zero-temperature level position of ${\mathrm{E}}_{\mathrm{v}}$ +0.361 eV (\ifmmode\pm\else\textpm\fi{}0.003 eV). The associated ratio of the temperature-induced change of this level position with respect to the one of the band-gap energy is about 0.80 (\ifmmode\pm\else\textpm\fi{}0.10). The inherent correlation between electrical and optical level position parameters was used to calculate the temperature dependence of the zero-phonon binding energy, ${\mathrm{J}}_{\mathrm{p}}$ (T), the Gibb's free energy, ${\mathrm{G}}_{\mathrm{p}}$ (T), and the enthalpy, ${\mathrm{H}}_{\mathrm{p}}$ (T), from 0 K to room temperature. Using two photoionization cross-section spectra, the associated Franck-Condon shift was estimated to be about 0.04 eV.

Surface electron properties of 6H and 15R modifications of silicon carbide

The temperature dependences of the surface potential on the (0001)Si and (0001)C surfaces of 6H- and 15R-SiC have been studied by the surface photovoltage method. It is found that the depletion layer is at all surfaces and and values are determined by the physical-chemical conditions of the surfaces. For the (0001)Si surfaces of 6H- and 15R-SiC oxidized electrolytically and etched in HF the dependences have an N-like behaviour; for the (0001)C surfaces they have a V-like behaviour. Following from the Hall effect data and dependences we have carried out calculations of temperature dependences of the charge in the surface electron states (SES) and the Fermi level position at surfaces. It is shown that the dependence with decreasing temperature is determined by charging SES with electrons and reconstruction of the SES system. We have found and studied the photomemory effect of the surface potential related to the capture of non-equilibrium holes by surface traps under illumination. The maximum trap concentration of is observed at the (0001)C surface of 15R-SiC and the minimum, at , is at the (0001)Si surface of 6H-SiC etched in HF.

Infrared induced visible emission from porous silicon: the mechanism of anodic oxidation

The visible luminescence caused by anodic oxidation of p-type porous silicon has been studied. It is shown that similar luminescence can be observed in n-type material by illumination with near-infrared light. Addition of a suitable reducing agent to the electrolyte solution can both suppress the oxidation of the porous layer and quench its luminescence. These results confirm a previously suggested mechanism, in which the capture of a valence band hole in a surface bond of the porous semiconductor gives rise to a surface state intermediate capable of thermally injecting an electron into the conduction band.

Radiation Damage in Si Avalanche Photodiodes by 1-Mev Fast Neutrons and 220-Mev Carbon Particles

AbstractResults are presented of a study on the degradation of the electrical and optical performance of n+p Si avalanche photodiodes, subjected to 1-MeV fast neutrons and to a 220-MeV carbon irradiation. The dark current increases after irradiation, while the photo current decreases. Two dominant hole capture levels, which are responsible for the degradation of performance, are after irradiation observed by DLTS (Deep Level Transient Spectroscopy). The degradation caused by neutron irradiation is smaller than that for carbon irradiation. The differences in the radiation damage are explained by the differences in the number of knock-on atoms and the nonionizing energy loss (NIEL). The recovery behavior of the device performance by isochronal annealing is also reported.

Monte Carlo simulations of carrier transport in AlGaInP laser diodes

A self-consistent ensemble Monte Carlo simulation of charge transport in AlGaInP quantum-well (QW) lasers has been developed in an effort to understand the temperature sensitivity of these devices. In particular, the lasing capability of a three-well design has been studied at 300 and 360 K. Although the electron and hole leakage currents are found to increase with the temperature, this does not explain a reduction in the emitted light hole emission time intensity for the particular device studied. Instead, the fall in the light output is due to increased emission from the QW's, since this reduces the net electron and hole capture efficiency.