Accumulation Of Minority Carriers Research Articles

Research on the Negative Resistance Characteristics of Silicon-based Trench MOS Barrier Schottky Diodes

The negative resistance characteristics of Trench MOS Barrier Schottky (TMBS) diodes were studied by simulation and theoretical calculation. A reasonable simulation model was established according to the experimental results of Schottky Barrier Diodes (SBD), which were utilized to simulate the TMBS diodes. A theoretical calculation model of TMBS diodes under forward bias was constructed based on existing SBD theoretical analysis to systematically understand the simulation results. Both simulation and theoretical calculation demonstrate that the negative resistance characteristics of TMBS diodes under forward bias are caused by the accumulation of minority carriers at the epitaxial region and the accumulation of majority carriers at the epitaxial region and oxide layer.

The Origin of the High Off-State Current in p-Type Cu 2 O Thin Film Transistors

There is a need for a good quality p-type accumulation-mode thin film transistor (TFT) using a metal oxide semiconducting channel. P-type cuprous oxide (Cu2O) has been proposed as a suitable semiconductor, but such TFTs have suffered from unacceptably high off-state currents. This letter studies the main origin of this high off-state current. Capacitance–voltage characteristics reveal the accumulation of minority carriers (electrons) in the off-state regime (i.e., for a positive gate voltage). The activation energy extracted from the temperature dependence of the drain current as a function of gate voltage shows an abrupt lowering of the activation energy and pinning of the Fermi energy in the off-state region, which is attributed to subgap states at 0.38 eV from the conduction band minimum. This suggests that an electron flow in the off-state causes the high off-state current in p-type Cu2O TFTs and not an inability to deplete the channel of holes.

AC hot carrier effect of the thin-film silicon-on-insulator power n-MOSFET

In this paper, we describe the hot carrier (HC) effect of the thin-film silicon-on-insulator (SOI) power n-MOSFET under DC and AC stress. We clarify that the HC effect is enhanced by AC stress because of both drain avalanche hot carriers (DAHC) and channel hot carriers (CHC). In addition, the parasitic bipolar effect which is enhanced by minority carrier accumulation under AC stress, causes device degradation at low frequencies.

Development and research of MIS varicaps with charge transfer

A new type of a double-electrode MIS varicap with a carrier transfer has been proposed. It is shown that in a device of this type, there are no negative effects associated with the processes of thermal generation and accumulation of minority carriers. This makes it possible to increase the limiting frequency and improve the temperature stability of varicap operation. Two designs of the device are considered. The characteristics of the varicaps that were measured experimentally agree with the results of the calculations.

The impedance spectroscopy of CuIn3Se5 photoabsorber films prepared by high vacuum evaporation technique

Abstract Thin films of CuIn3Se5 photoabsorber were deposited from the stoichiometric polycrystalline precursor onto glass/ITO substrates by using the high vacuum evaporation technique and following annealing in argon. The chalcopyrite structure of obtained films of CuIn3Se5 were confirmed by the XRD spectroscopy. The SEM micrographs, Raman spectra and EDS data confirm the enhanced morphology and composition of prepared CuIn3Se5 films. The obtained glass/ITO/CuIn3Se5/graphite sandwich structures demonstrate diode-shape I-V characteristics and photosensitivity. The annealed CuIn3Se5 films have a p-type of conductivity with the free carriers’ concentration in the range of 1016–1017 cm−3. An electrical equivalent circuit consisting of constant phase elements was used for modeling of the impedance spectroscopy measurements. Both impedance modeling and capacitance-voltage ( C − V ) curves show that there is a strong minority carrier accumulation process taking place at forward potentials.

Geometry effects and frequency dependence in scanning capacitance microscopy on GaAs Schottky and metal–oxide–semiconductor-Type junctions

In this work, the influence of the tip-geometry and an unusual low frequency behavior in scanning capacitance microscopy is investigated experimentally and theoretically on metal–oxide–semiconductor (MOS) and Schottky type junctions on gallium–arsenide (GaAs). Using a two-dimensional model we find that on Schottky type junctions the electric field around the tip is screened by the surface states and that the essential parameters entering the capacitance versus voltage C( V) characteristics are the doping level and the contact area only. On a MOS-type junction, the electric field from the tip penetrates into the semiconductor and the tip geometry effects are much larger. C( V) spectra are fitted to the experimental data and allowed a quantitative determination of doping levels, oxide thickness, and contact area without moreover calibration measurements. Furthermore, we show that the natural surface depletion field on GaAs generates a permanent minority carrier accumulation around the tip–apex. In contrast to thermally generated minority carriers in the space charge region of a large area device, the minority carrier distribution around the SCM tip–apex is detected up to much higher excitation frequencies. An analytic approach to estimate the transition frequency between the low and high frequency regime is also given.

55 W peak power from 1100 nm wavelength 60 µm broad-area laser diodes enabled by reduced carrier accumulation in the waveguide

Optical power from 1100 nm broad-area laser diodes is found to be limited by the accumulation of minority carriers in the waveguide layer, caused by a small effective barrier between the quantum wells and the GaAs waveguide. This effect is visible as enhanced spontaneous emission at high currents. We show that increasing the number of QWs mitigates this effect and leads to higher emitted powers. Optimized devices deliver more than 55 W per 60 µm stripe width under 300 ns pulse operation. In this paper we present the experimental results of our study.

Investigation of Minority Carrier Distribution in Semiconductor-Controlled Rectifier Devices and the Impact on Electrostatic Discharge Applications

In this paper, a physical mechanism is proposed where the holding voltage of the semiconductor-controlled rectifier (SCR) is predominated by the accumulation of minority carriers. Two-dimensional simulation is used to demonstrate this mechanism where the carrier distribution of SCR devices is calculated and analyzed. It has been clearly proven that the distribution of minority carriers highly correlates to holding voltage. Accordingly, a layout approach has also been designed and experiments have confirmed that an increment in holding voltage can be performed. It can be concluded that the optimization of the topological structure will markedly increase holding voltage and eventually prevent the complementary metal–oxide–semiconductor (CMOS) integration circuit from minimizing the latch-up effect. Moreover, because of its high current capabilities, the optimized SCR can be used as an ideal candidate for electrostatic discharge protection (ESD) applications.

The role of interface in photo processes in photoconductive heterophase composites based on monolayer dispersions of molybdenum disulfide

Two-layer heterostructures with a high yield of charged current carriers were obtained and investigated. The heterostructures comprised monolayer dispersions of MoS2 in polyvinyl alcohol as the lower layer and the upper p-, n-, or bipolar transport layer (TL). It was found that dark conductivity of the two-layer heterostructures increased considerably compared with the conductivity of reference samples based on TL but containing no MoS2. After excitation from the TL side, maximum photoelectric sensitivity was obtained where TL long-wave absorption decreased and there was a high concentration of TL excited states at the interface that interacted with the surface of MoS2 particles. This interaction quenched the luminescence of TL transport centers and led to the photogeneration of both positively and negatively charged current carriers at the interface. Luminescence quenching could be of 50–60% at high MoS2 contents in the lower layer (90–100 wt %). This was evidence that the contact area of MoS2 particles with the polymeric transport layer exceeded the geometric interface dimensions and the interface had a relief surface (was fairly thick). It was found that the donor-acceptor properties of both MoS2 and the polymeric TL were very important for the photogeneration of charge carriers at the interface. When the MoS2 content in the lower layer was maximum, the effectiveness of the accumulation of minority carriers increased because of the formation of an alternative transport network associated with MoS2 particles. The conclusion was drawn that the photogeneration of charges at the interface resulted from the phototransfer of electrons between MoS2 particles and TL excited states.

Capacitance characteristics in PbSrSe thin films

We report bias- and frequency-dependent capacitance characteristics in Pb 1− x Sr x Se thin films with Sr composition from 0.066 to 0.276 grown by molecular beam epitaxy on BaF 2 substrates. A grain boundary barrier model has been presented, which can well explain the experimental observation of the capacitance in relation with the bias, frequency, as well as the Sr composition. Negative capacitance phenomenon has been observed for samples with different Sr compositions under different bias and frequency conditions. The origin of this negative capacitance effect is believed to be due to the accumulation of minority carriers at the grain boundaries, which produces an additional dynamic capacitance with an opposite sign. In addition, the success in explaining the Sr composition dependent dark current characteristics gives further evidence for the model.

Minority Carrier Accumulation and Interfacial Kinetics in Nanosized Pt-Dotted Silicon Electrolyte Interfaces Studied by Microwave Techniques

Photoinduced microwave conductivity (PMC) measurement allows the determination of the excess densities of accumulating minority carriers in the potential region of the kinetically limited, increasing photocurrent. Compared with PMC signals obtained with slightly oxidized naked silicon interfaces, those for the Pt-dotted silicon interfaces have a bell shaped narrow distribution and are negatively shifted with respect to the photocurrent-potential curve. It is shown that minority carrier accumulation is essentially controlled by the peculiar Si/Pt particle interfacial barrier which can be easily overcome by holes at increasingly positive potential to take advantage of the Pt-mediated reactivity. The potential and light dependent transfer rate of minority carriers at the interface strongly increases with the applied potential. Electrochemical corrosion essentially leads to a gradual modification of this barrier through formation of a Si-SiO x -Pt structure. The influence of Fe 2 + /Fe 3 + concentration on the minority carrier accumulation profile as well as the photon flux dependence of the PMC signals can be explained as being due to a transport limitation phenomenon in the solution near the Pt particles.

Minority Carrier Dynamics and Interfacial Kinetics at the ZnO/Electrolyte Interface Studied by Combined Photocurrent/Microwave Photoconductivity Measurements

A pronounced peak of microwave photoconductivity (PMC), observed in the region of onset of photocurrents through a ZnO (0001)/aqueous electrolyte interface, is studied in dependence of electrolyte composition, electrochemical pretreatments, and light intensity. The amplitude, position, and shape of the peak were found to depend on interfacial kinetics, and the peak converts into a plateau with limiting PMC in the presence of an organic electrolyte. The PMC peak can be understood as an accumulation of minority carriers, the surface lifetime of which has increased due to limiting interfacial reactivity in charge transfer or recombination. The theory allows the determination of interfacial rate constants from parallel potentiodynamic PMC and photocurrent measurements. An exponential dependence of the charge transfer rate constant (kr) on the applied voltage was found for ZnO in contact with different aqueous electrolytes at low electrode bias. This is in contradiction with classical models on photoelectrochemical charge-transfer which assume potential independent rate constants (Gärtner model as applied to electrodes: kr → ∞; Marcus−Gerischer model, kr = const). The conclusion is that these models cannot be applied and that the condition of weak interaction during electron transfer is not fulfilled. The latter condition can however be approached with an organic electrolyte containing ferrocene/ferrocenium+.

Photocurrent effect on the zero-Bias dynamic resistance of HgCdTe photodiode

A new physical model is presented for the illumination-dependence of the zero-bias resistance-area product (R0A) of HgCdTe photodiode. The model is based on three independent mechanisms. They are the depletion region volume change with the applied bias, the diffusion distance change with the moving depletion region edge, and the minority carrier accumulation in the depletion region which affects the minority carrier diffusion. Analytic equations are derived for the photodiode current-voltage characteristics and R0A products. The results of the model have been compared with experimental data obtained from several Hg0.7Cd0.3Te diodes with an identical diode structure having different absorbing amount of light. The model showed good agreement with the experimental data.

Current-induced light emission by narrow-gap semiconductors in a magnetic field

Morimoto and Chiba (1991 J. Phys. Soc. Japan. 60, 2446) have observed a threshold behaviour of current-induced interband light emission from n-InSb samples in a magnetic field, attributing this to the onset of stimulated emission. We show that their experimental results can be explained quite satisfactorily by the combined effect of sample heating by current and surface accumulation of minority carriers under the action of the Lorentz force. We also derive for intrinsic narrow-gap semiconductors the condition for achieving population inversion within a narrow accumulation layer by passing current in a transverse magnetic field.

Temperature dependence of 1/f noise in Hg/sub 1-x/Cd/sub x/Te MIS infrared detectors

We measured 1/f noise on Hg/sub 0.71/Cd/sub 0.29/Te Metal-Insulator-Semiconductor (MIS) infrared detectors operated over the temperature range of 40 K to 90 K under 300 K Infrared (IR) radiation. The purpose of the study was to identify the sources of 1/f noise, especially in relation to the dark current. The devices were operated in the correlated double sampling mode where the voltage across the MIS capacitor was sampled at empty potential well and right after the accumulation of minority carriers in the well due to IR radiation generation. The noise power spectral density for the charge integrated in the MIS well was investigated in relation to the dominant component of dark current. At lower temperatures T/spl les/65 K, the charge noise power spectral density was found to depend quadratically on the dark current. At higher temperatures, this quadratic dependence did not exist. We attribute the dark current to a mixture of tunneling and depletion-region-originated minority carrier generation which seems to be responsible for 1/f fluctuations in these structures for temperatures below 65 K. >

Minority carrier accumulation at high-low junctions

The semiconductor transport equations have been solved for lifetime semiconductors under the assumption of quasineutrality which is calculated to be valid up to relatively high current densities. The effective diffusion length of minority carriers is shown to be (strongly) current dependent. Of the four nonequilibrium processes, minority carrier accumulation is treated analytically in greater detail, showing current dependent resistance decreases which are confirmed by both numerical solutions of the transport equations and experiments.

An analysis of positive and negative resistance characteristics in the high-current-density region of Schottky diodes

A number of different diode characteristics are observed in small-area silicon Schottky diodes under forward-biased and high-current-density conditions. These characteristics, such as positive resistance, negative resistance, and normal diode characteristics, are analyzed. The analysis demonstrates that the variations are due to the minority-carrier accumulation in the epitaxial region of the diodes, which is mainly controlled by Schottky barrier heights and the resistivity of the semiconductor epitaxial region. >

Minority-carrier accumulation at the base edge of a junction space-charge region under short-circuit conditions

A new boundary condition is derived for the base edge of a p n junction space-charge region of a solar cell subjected to short-circuit conditions. This condition is expressed as an effective surface recombination velocity for minority carriers which equals the ratio of the diffusion coefficient to the extrinsic Debye length. The same condition applies at the collector edge of a quasi-neutral base of a transistor in the forward active mode. The accumulation of minority carriers due to the finite value of the recombination velocity can affect transient responses especially in solar cells that are lightly doped or at low temperatures. Further, this accumulation and the associated space-charge-region recombination current can decrease the short-circuit current in some cells.

Evidence of optical generation of minority carriers from saturated MOS transistors

Minority carrier injection into the substrate by a MOS transistor operating in saturation presents a reliability problem in dynamic memory circuits such as RAM's and CCD's. The effect has been studied by measuring the substrate and drain currents of stressed transistors as a function of gate and drain voltages, firstly by the accumulation of minority carriers in a charge coupled device, and secondly by the direct detection of light from the drain region of a transistor. These results suggest that light emission associated with multiplication in the drain region is more important than the secondary impact ionization mechanism in the generation of minority carriers.

Photoconductivity of an inhomogeneous semiconductor

Photoconductivity of an inhomogeneous semiconductor is analyzed using the barrier model. The barriers are caused by an inhomogeneous distribution of donors in a p-type crystal. The conductivity is controlled both, by the carrier trapping to donors and by the minority carrier accumulation in the barrier region. The steady-state photoconductivity is calculated as function of temperature and light intensity. The conductivity relaxation after the end of illumination is studied. In the case of a shallow donor level photoconductivity characteristics typical of amorphous semiconductors are obtained. The photoconductivity in CdS thin films and crystalline Se is explained in terms of conducting minority carrier channels.