Reduction In Hole Concentration Research Articles

Continuous wave operated 3.2 µm type-I quantum-well diode lasers with the quinary waveguide layer

GaSb-based diode lasers with type-I quantum-well active region located either in the center of quinary AlInGaAsSb broadened waveguide or shifted to the p-cladding side were fabricated and characterized. Devices with narrower ‘p-side waveguide’ demonstrate better performance. We explain the phenomenon by reduced hole concentration in the waveguide region of the device. At 12 °C, lasers with optimized design generate above 65 mW of continuous wave output power at 3.2 µm.

Mechanisms of unexpected reduction in hole concentration in Al-doped 4H-SiC by 200 keV electron irradiation

The hole concentration in Al-doped p-type 4H-SiC was found to be significantly reduced by electron irradiation when compared to the hole concentration in Al-doped p-type Si; this is an unexpected result. The temperature dependence of the hole concentration p(T) in Al-doped 4H-SiC irradiated with 200 keV electrons at various fluences was measured. Only substitutional C atoms in SiC can be displaced by irradiation with 200 keV electrons. The reduction in p(T) by the electron irradiation was found to be mainly due to a decrease in Al acceptors and not due to an increase in defects (e.g., C vacancies) located around the middle of the bandgap in SiC. Based on the analysis of p(T), two types of acceptor species were detected and the density and energy level of each acceptor species were determined. An equation describing the fluence dependence of each acceptor density is proposed. The results suggest that for the 200 keV electron irradiation, a substitutional C atom bonded to an Al acceptor was more easily displaced than a substitutional C atom bonded to four Si atoms.

Mechanisms of Reduction in Hole Concentration in Al-Implanted p-Type 6H-SiC by 1 MeV Electron Irradiation

The reduction in temperature-dependent hole concentration p(T) in Al-implanted p-type 6H-SiC by 1 MeV electron irradiation is investigated. By analysis of p(T), the density (NA), level position (EA) in the bandgap and nature of the acceptor are determined, and this acceptor is assigned to an Al acceptor. EA is independent of irradiation fluence (Φ), while NA is strongly dependent on Φ. We derived an analytical expression for the fluence dependence of NA and we estimated the removal coefficient (i.e., removal cross-section) of NA to be 6.4×10-18 cm2 for 1 MeV electron irradiation. The reduction in p(T) by electron irradiation is found to be mainly due to the decrease in NA, not to the increase in the density of deep-level defects in the bandgap, because the decrement in NA is much larger than the increment in the density of deep-level defects.

The Characteristics of Kink Effect Suppressed Thin Film Transistor by Using Symmetric Dual-Gate

In this paper, a symmetric dual-gate single-Si thin film transistor (TFT), which includes three split floating n+ zones, is simulated. This structure drastically reduces the kink-effect and improves the on-current. This is due to the separated floating n+ zones, the transistor channel region is split into four zones with different lengths defined by a floating n+ region. This structure allows effective reduction in the kink-effect, depending on the length of the two sub-channels. The on-current of the proposed dual-gate structure is 0.9 mA, while that of the conventional dual-gate structure is 0.5 mA, at both 12 V drain and 7 V gate voltages. This result shows an 80% enhancement in on-current. In addition, the reduction of electric field in the channel region compared to a conventional single-gate TFT and the reduction of the output conductance in the saturation region, is observed. In addition, the reduction in hole concentration, in the channel region, in order for effectively reducing the kink-effect, is also confirmed.

Electrical characteristics of single-silicon TFT structure with symmetric dual-gate for kink-effect suppression

In this paper, a symmetric dual-gate single-Si TFT, which is composed of three split floating n+ zones, is simulated. This structure remarkably reduces the kink-effect and improves the on-current. Due to the separated floating n+ zones, the transistor channel region is split into four zones with different lengths defined by the floating n+ region. This structure allows effective reduction in the kink-effect, depending on the length of the two sub-channels. The on-current of the proposed dual-gate structure is 0.9mA, while that of the conventional dual-gate structure is 0.5mA, at both 12V drain and 7V gate. This result demonstrates 80% enhancement in on-current. In addition, the reduction of electric field in the channel region compared to conventional single-gate TFT and the reduction in output conductance in the saturation region, is observed. In addition, the reduction of hole concentration in the channel region, in order to effectively reduce the kink-effect, is confirmed.

Electrical Characteristics of Single-silicon TFT Structure with Symmetric Dual-gate for Kink Effect Suppression

In this paper, a Symmetric Dual-gate Single-Si TFT, which includes three split floating n+ zones, is simulated. This structure drastically reduces the kink-effect and improves the on-current. This is due to the separated floating n+ zones, the transistor channel region is split into four zones with different lengths defined by a floating n+ region. This structure allows effective reduction in the kink-effect, depending on thy length of the two sub-channels. The on-current of the proposed dual-gate structure is 0.9 mA, while that of the conventional dual-gate structure is 0.5 mA, at both 12 V drain and 7 V gate voltages. This result shows an 80% enhancement in on-current. In addition, the reduction of electric field in the channel region compared to a conventional single-gate TFT and the reduction of the output conductance in the saturation region, is observed. In addition, the reduction in hole concentration, in the channel region, in order for effectively reducing the kink-effect, is also confirmed.

Relationship between defects induced by irradiation and reduction of hole concentration in Al-doped 4H–SiC

From the temperature dependence of the hole concentration in lightly Al-doped 4H–SiC epilayers, a shallow acceptor with E V + 0.2 eV , which is an Al atom ( Al Si ) at a Si sublattice site, and an unknown deep defect with E V + 0.35 eV are found, where E V is the valence band maximum. In unirradiated epilayers, moreover, the density ( N Defect ) of this defect is close to the Al acceptor density ( N Al ) . With irradiation of 0.2 MeV electrons, the N Al is reduced, while the N Defect is increased. Judging from the minimum electron energy required to displace a substitutional C atom ( C s ) or Al Si , the bond between Al Si and its nearest neighbor C s is broken due to the displacement of the C s by this irradiation. Moreover, the displacement of the C s results in the creation of a complex ( Al Si – V C ) of Al Si and its nearest neighbor C vacancy ( V C ) , indicating that the possible origin of the defect with E V + 0.35 eV is Al Si – V C .

Mechanisms of reduction in hole concentration in Al-doped 4H-SiC by electron irradiation

From the temperature dependence of the hole concentration in unirradiated lightly Al-doped 4H-SiC epilayers, an Al acceptor with E V + 0.2 eV, which is an Al atom (Al Si) at a Si sublattice site, and an unknown deep acceptor with E V + 0.35 eV are found, where E V is the top of the valence band. Both the densities are similar. With irradiation of 0.2 MeV electrons the Al acceptor density is reduced, while the unknown deep acceptor density is increased. Judging from the minimum electron energy required to displace a substitutional C atom (C s) or the Al Si, the bond between the Al Si and its nearest neighbor C s is broken due to the displacement of the C s by this irradiation. Moreover, the displacement of the C s results in the creation of a complex (Al Si–V C) of Al Si and a carbon vacancy (V C), indicating that the possible origin of the deep acceptor with E V + 0.35 eV is Al Si–V C.

THE MAGNETIC AND ELECTRICAL PROPERTIES OF RARE-EARTH Sm3+ SUBSTITUTED Bi1.7Pb0.3Sr2Ca2-xSmxCu3O12 SYSTEM

In the present work, the magnetic properties of high-Tc Bi 1.7 Pb 0.3 Sr 2 Ca 2-x Sm x Cu 3 O 12 system (x = 0.03) have been investigated, for different temperatures below Tc. Substitution of Sm 3+ for Ca 2+ is found to change the superconducting properties of the system, despite the weak paramagnetic nature of the Sm 3+ ion. The dc magnetization measurements performed on the compound reveal that the superconducting regions decrease with increasing temperature and magnetic field. The results are explained on the basis of a possible reduction of hole concentration with trivalent rare-earth ion substitution, and also on the basis of the magnetic nature of the substituted Sm 3+ ions.

Time evolution of the electric field at electrode interfaces with conducting polymers

Time-resolved scanning Kelvin probe microscopy (SKPM) and Raman microscopy have been used to investigate processes occurring at the interface between indium tin oxide (ITO) electrodes and inkjet printed polyethylenedioxythiophene: polystyrene sulphonic acid (PEDOT:PSS). SKPM reveals a slow, reversible polarisation process (time constant ∼12s) occurring at the electrodes caused by the drift of Na+ and∕or H+ ions in the polymer. Raman microscopy shows that the resulting field enhancement at the electrodes increases the concentration of holes in the polymer at the anode, while at the cathode there is a significant reduction in hole concentration. Such effects have implications for both the short- and long-term stability of devices utilising PEDOT:PSS.

Influence of microstructure on the carrier concentration of Mg-doped GaN films

Room-temperature Hall effect measurements of (0001) Mg-doped GaN films grown on sapphire substrates by metalorganic chemical vapor deposition show a reduction in hole concentration for Mg concentrations greater than 1020 cm−3. A combination of secondary ion mass spectrometry and transmission electron microscopy indicates a steadily increasing Mg incorporation during growth and the formation of inversion domains at these high concentrations. We discuss mechanisms that could give rise to a reduction of the hole concentration at high Mg doping levels.

Effect of gamma-irradiation on the electronic structure of (Bi1.65Pb0.35)Sr2Ca2Cu3O10 superconductor

Abstract An XPS investigation was carried out on (Bi 1.65 Pb 0.35 )Sr 2 Ca 2 Cu 3 O 10 superconductors, in an effort to study the effect of gamma-irradiation. There is no significant change in the binding energies of Bi 4f, Ca 2p, Cu 2p, O 1s, Pb 4f, and Sr 3p core levels up to the gamma dose of 50 Mrad. However, for the gamma dose of 60 Mrad, the Bi 4f region shows two sets of spin-orbit split levels, one set at about 1.3 eV lower and the other at about 1.7 eV higher binding energies than that of the low-dose samples. Furthermore, for this high-dose sample, (i) the O 1s region clearly shows the evidence of the removal of O by gamma irradiation and (ii) the Cu 2p region shows no satellite, which is typical of Cu 2+ valence states and a low energy shoulder that is a signature of Cu 1+ valence states, in contrast to the low-dose samples. These observations suggest a reduction of hole-concentration in the Cu–O planes through the O removal at a gamma dose between 50 and 60 Mrad.

Electrical Characterization of MOVPE-Grown P-Type GaN:Mg Against Annealing Temperature

Hall effect measurements have been applied for the electrical characterization of p-type Mg-doped GaN grown by metalorganic vapor-phase epitaxy on sapphire substrates in terms of annealing temperature for dehydrogenation (N2 annealing) and hydrogenation (H2 annealing) of the acceptors. With the N2 annealing temperature from 600 to 900 °C for dehydrogenation, both hole concentration and mobility increases, showing more activation of acceptors and less incorporation of unfavorable scattering centers probably originating from Mg-H bondings. The N2 annealing at higher than the growth temperature results in reduced hole concentration, but the mobility gets higher. Some defects compensating acceptors may be induced at high temperature annealing, but they seem to be no scattering centers and be inactivated by successive hydrogenation and re-dehydrogenation at the optimum dehydrogenation temperature 900 °C. The electrical degradation of GaN due to thermal damage is not very destructive and can be well recovered by annealing treatments.

Doping effects arising from Fe and Ge for Mn in La0.7Ca0.3MnO3

Structural, magnetic, and transport properties of polycrystalline La0.7Ca0.3Mn1−xFexO3 and La0.7Ca0.3Mn1−xGexO3 are experimentally studied. Single-phase samples are obtained in the range x=0–0.12 for Fe, and x=0–0.06 for Ge. There are no appreciable structure changes due to the introduction of Fe and Ge. The Mn-site doping favors a reduced magnetic/resistive transition, at rates of ∼22 K for 1% Fe and ∼28 K for 1% Ge, and an elevated resistivity. No metal–insulator transition occurs when the content of Fe exceeds ∼0.1. The enhanced doping effects in La0.7Ca0.3Mn1−xGexO3 can be ascribed to the reduced hole concentration noting that the presence of Fe and Ge influence the contents of mobile eg electrons and holes in the compounds, respectively. Equivalence of the effects from Fe and Ge doping, respectively, to those due to eg electron and hole trapping and the relation between Mn- and O-site doping are discussed.

Electrical Characterization of MOVPE-GROWN P-Type GaN:Mg Against Annealing Temperature

AbstractHall effect measurements have been applied for the electrical characterization of p-type Mg-doped GaN grown by metalorganic vapor-phase epitaxy on sapphire substrates in terms of annealing temperature for dehydrogenation (N2 annealing) and hydrogenation (H2 annealing) of the acceptors. With the N2 annealing temperature from 600 to 900°C for dehydrogenation, both hole concentration and mobility increases, showing more activation of acceptors and less incorporation of unfavorable scattering centers probably originating from Mg-H bondings. The N2 annealing at higher than the growth temperature results in reduced hole concentration, but the mobility gets higher. Some defects compensating acceptors may be induced at high temperature annealing, but they seem to be no scattering centers and be inactivated by successive hydrogenation and re-dehydrogenation at the optimum dehydrogenation temperature 900°C. The electrical degradation of GaN due to thermal damage is not very destructive and can be well recovered by annealing treatments.

Milli-Kelvin magneto-transport studies of two-dimensional hole systems under illumination

We present evidence for the occurrence of an insulating phase both at zero and high magnetic fields, observed in extremely dilute two-dimensional hole systems in GaAsAl 1− x Ga x As quantum wells. At the highest hole concentrations the insulating phase is consistent with the magnetically-induced Wigner solid. As the hole concentration is persistently reduced by illumination of the structures, an insulator-metal-insulator transition develops in the magneto-transport around filling factor v = 1 and eventually the structure becomes insulating at all magnetic fields. The zero-field insulator emerges at a critical value of the dimensionless inter-particle separation, r s , of around 14, the highest value yet reported for this transition. We discuss these observations in the light of recent studies of the Wigner solid and the Hall insulator and invoke a model of the recombination kinetics of our experiments which accounts for the reduction in hole concentration under illumination.

Evidence for enhanced zinc interstitial concentration in strain-relaxed heteroepitaxial indium phosphide

Heteroepitaxial InP films grown on GaAs substrates by metalorganic chemical vapor deposition are demonstrated to have a higher concentration of zinc occupying interstitial sites than do equivalent homoepitaxial InP layers. A zinc interstitial-related donor-to-acceptor photoluminescence peak is observed in heteroepitaxial InP films which is absent in the homoepitaxial sample spectra. Capacitance–voltage measurements yield a lower hole concentration in the heteroepitaxial layers versus the homoepitaxial layers, which is attributable to a higher fraction of zinc in interstitial sites within the heteroepitaxial layers. Additionally, the hole concentration of the heteroepitaxial layers is found to be lower near the heterojunction as compared with the film surface region, correlating with a higher dislocation density near the heterojunction as seen by transmission electron microscopy. We conclude that the increased zinc interstitial concentration and the reduced hole concentration are due to dislocation-zinc solute interactions.

Effect of base dopant species on heterojunction bipolar transistor reliability

The electrical activation of carbon in GaAs grown by metal-organic molecular beam epitaxy has been shown to be excellent in as-grown material. At very high doping levels, however, the activation can be reduced substantially by annealing, even at rather moderate temperatures. This reduction in hole concentration combined with the reduction in gain observed with increasing dopant level in the base suggests a practical limit of less than 10 20 cm −3 for base doping in GaAs/AlGaAs heterojunction bipolar transistors (HBTs). Using moderate base doping, p ≈ 7 × 10 19 cm −3 , carbon-doped devices do not exhibit short-term degradation at current densities less than or equal to 2.5 × 10 4 A cm −2 , even at operating temperatures up to 200 °C, unlike Be-doped HBTs which typically degrade much more rapidly even at twice lower base doping levels. Operation of carbon-doped devices at higher current densities for longer periods of time, however, can result in current-induced decreases in d.c. gain which are correlated with the amount of hydrogen incorporated in the base layer during growth. During device operation, minority carrier injection induced debonding of hydrogen from neutral C-H complexes leads to an increase in effective base doping level and therefore to a decrease in gain. Post-growth in situ or ex situ annealing eliminates this effect by breaking up the C-H complexes. Properly designed HBTs are stable during operation at 125 °C even for very high collector current densities (10 5 A cm −2).

Effect of annealing temperature on the hole concentration and lattice relaxation of carbon-doped GaAs and AlxGa1−xAs

Measurements of the hole density in carbon-doped GaAs and AlxGa1−xAs as a function of the annealing temperature are presented. It is shown that after sample annealing at low temperatures (T<550 °C), the hole concentration increases in all samples doped ≥1×1019 cm−3 with a simultaneous decrease in the hole mobility. However, sample annealing at higher temperatures (T≳600 °C) results in a reduction of the hole concentration in all samples doped with carbon at concentrations higher than ≊5×1019 cm−3. The reduction in hole concentration is also accompanied by an increase in lattice parameter of the carbon-doped epilayer. The observed changes in the electrical and microstructural properties are explained in terms of two different mechanisms: (1) the passivation of carbon acceptors by the incorporation of hydrogen during growth, and (2) the change in the lattice site location of carbon atoms upon annealing. Direct determination of the lattice site location of carbon in samples doped ≥5×1019 cm−3 showed that the fraction of interstitial carbon after annealing at T≳600 °C is at least 70% higher than in the as-grown samples.

Effects of Li doping on the superconducting properties of Bi-based superconducting whiskers

The effects of Li doping on the superconductivity of Bi-based superconducting whiskers have been investigated. The Li doping is effective in increasing T c of both the Bi 2Sr 2CaCu 2O x (2223) whiskers. The Li-doped 2212 whiskers show a T c at 82 K, which is higher than that of the undoped 2212 whiskers by 5 K. The Li-doped and undoped 2223 whiskers have been prepared by the Conversion by Annealing in Powder (CAP) method. An enhancement of T c by 1.2 K is achieved by Li doping of the 2223 whiskers. The T c of the 2223 phase is commonly accepted to be lowered by a reduction of hole concentration, which is opposite to the situation of the 2212 phase. Therefore, the mechanism of the enhancement of T c is not due to the optimization of the hole concentration. From the compositional analysis and the measurement of the c-axis lattice parameter, the Li doping is thought to be effective in increasing the Sr/Ca ratio for both kinds of whiskers, which causes the enhancement of T c.