Thickness Of Depletion Region Research Articles

ПЕРЕХІДНИЙ ШАР І ЛАТЕРАЛЬНА ФОТОЕРС В НАПІВПРОВІДНИКОВІЙ ГЕТЕРОСИСТЕМІ

A photo-emf in the NbN–GaAs Schottky contact samples studied. This photo-emf is generated along the metalsemiconductor interface. It is shown that a semiconductor transition layer formed near the Schottky contact interface has a pronounced effect on the form of spectral characteristics. The feature of the photoemf spectral characteristics is a variations its appearance when changing the thermal annealing temperature of the studied heterosystems. If the spectral characteristic has one maximum and amplitude, which several times exceeds the amplitude of a significant characteristic, which means the formation of a transition layer in the Schottky contact depletion area with high conductivity, compared with a quasine-neutral region of a semiconductor. A complicated alternating form of spectral characteristics of the photo-emf is related to contributions to the measured signal from several components that are generated at potential barriers of the metalsemiconductor heterosystem. Illumination of samples on the metal side results in change of the form of spectral characteristics and reversal of sign of photo-emf. This is caused by variation of interrelation between the photo-emf components that are generated in the heterosystem layers with different conductivities. For the samples annealed at Т = 900 С, the photo-emf changes its sign near the GaAs absorption edge. It was found that thermal annealing at Т = 950 С results in increase of relative nonuniformity of the depletion region thickness, while the sign of the photo-emf spectral curve does not change. In this case, considerable effect of band bending nonuniformity in the depletion region of the heterosystem under investigation on the character of lateral photo-emf distribution is retained.

Single event transient effect of frontside and backside illumination image sensors under proton irradiation

Complementary metal oxide semiconductor (CMOS) image sensor is susceptible to proton single event effect when being applied to space environment. Proton irradiation experiments with different energy values are carried out on a commercial FSI and BSI CMOS image sensors. The proton single event effect is analyzed by on-line testing, the maximum proton energy is 200 MeV, and the total fluence is 10<sup>10 </sup>particle/cm<sup>2</sup>. The single-event transient bright spots of different shapes are observed in the pixel array. By extracting the deposition energy and size, the effects of different energy protons on transient bright spot characteristics are compared, and the transient bright spot characteristics between FSI and BSI are also compared. Finally, the energy deposition distribution of the transient bright spot generated by proton in CMOS image sensor pixel unit is predicted by comparing the simulation method with the experimental results. The simulation results verify that the decrease of PPD depletion region thickness and the thinning of epitaxial layer are the main factors leading the proton energy deposition distribution to shift leftward in BSI image sensor.

Si−doped In0.145Ga0.855As0.123Sb0.877: A novel p−type quaternary alloy with high crystalline quality

Antimonide−based p−n junctions are particularly attractive for a wide variety of optoelectronic applications in the near and mid-infrared wavelength range. In this work, novel p−type Si−doped In0.145Ga0.855As0.123Sb0.877 epitaxial layers were grown on GaSb(100) substrates by Liquid Phase Epitaxy (LPE) technique. The XPS spectra measured on Si−doped In0.145Ga0.855As0.123Sb0.877 layers indicate that Si atoms behave as acceptors. The analysis of the surface depletion region and its relationship with phonon−plasmon L_ coupling were investigated using Raman spectroscopy, giving an acceptor concentration of NA ∼ 5.8 × 1017 cm−3 for a depletion region thickness of d ∼ 9.4 nm. Low temperature photoluminiscence (PL) spectrum for the Si−doped In0.145Ga0.855As0.123Sb0.877 layers showed a bound excitonic emission peak associated to neutral Sb acceptors, with an activation energy of ∼10meV and a donor−acceptor transition. It was observed that the Si doping reduces the excitonic emission intensity and increases the donor−acceptor pair recombination intensity.

Simulation Study of Silicon-Based Single-Photon Avalanche Diodes with Double Buried Layers and Deep Trench Electrodes

In this paper we present a study of a silicon-based Single-Photon Avalanche Diode (SPAD) in the near-infrared band with double buried layers and deep trench electrodes fabricated by the complimentary metal–oxide semiconductor (CMOS) technology. The deep trench electrodes aim to promote the movement of carriers in the device and reduce the transit time of the photo-generated carrier. The double buried layers are introduced to increase the electric field in the avalanche area and withstand a larger excess bias voltage as its larger depletion region. The semiconductor device simulation software TCAD is used to simulate the performance of this SPAD model, such as the I-V characteristic, the electric field and the Photon Detection Efficiency (PDE). Further optimization of the structure are studied with influence factors such as the doping concentration and depletion region thickness. Based on the results in this study, the designed a structure that can provide a high detecting efficiency in the near-infrared band.

Frequency response optimization of P-I-N photodiode based on InGaAsN lattice matched to GaAs for High-Speed photodetection applications

This paper reports on pin photodiode frequency response optimization based on InxGa1-xAs1-yNy quaternary lattice matched to GaAs. Two transparent layers are placed on p-side and n-side in order to manage the photodiode frequency response limitations. The lattice matching condition is calculated in order to obtain stable structure. The physical and optical parameters calculations are performed at room temperature showing the impact of nitrogen on the absorption coefficient. A stable structure, having 2 % of nitrogen and 6% of indium, allows to achieve a cutoff frequency of about 116 GHz and a capacitance of 5.21fF while the quantum efficiency is 41.59% for a depletion region thickness of about 0.55 µm. However, in case of depletion region thickness of about 0.625 µm, the cutoff frequency degrades to 98 GHz while the capacitance diminishes to 4.58fF and the quantum efficiency increases to 51.56%. In addition, a comparative study with literature results has been carried out in order to show the advantages of the proposed photodiode. This comparison affirms that the proposed photodiode based on InGaAsN lattice matched to GaAs exhibits high-speed photo-detection. This work allowed us to obtain a p-i-n photodiode with stable structure suitable for photo-detection at 1.15 µm.

Enhanced Band Edge Luminescence in GaAs with Sulfur Passivation

In this work, we perform a sulfur chemical passivation on GaAs substrate, which leads to a change in the photoluminescence (PL) owing to a reduction of surface states. By varying the reaction time of passivation, we can modify the chemical bonds of the GaAs surface and reduce the surface depletion region thickness, which strongly affects the emission efficiency of the GaAs band edge. Based on systematic PL measurements and energy band model with surface states, the sulfur passivation also enhances the number of free and bound excitons. Therefore, sulfur passivation is important to improve the performance of GaAs-based optoelectronics devices.

Diagnostics for ultrashort X-ray pulses using silicon trackers

The spectrum of laser–plasma generated X-rays is very important, it characterizes electron dynamics in plasma and is basic for applications. However, the accuracies and efficiencies of existing methods to diagnose the spectrum of laser–plasma based X-ray pulse are not very high, especially in the range of several hundred keV. In this study, a new method based on electron tracks detection to measure the spectrum of laser–plasma produced X-ray pulses is proposed and demonstrated. Laser–plasma generated X-rays are scattered in a multi-pixel silicon tracker. Energies and scattering directions of Compton electrons can be extracted from the response of the detector, and then the spectrum of X-rays can be reconstructed. Simulations indicate that the energy resolution of this method is approximately 20% for X-rays from 200 to 550 keV for a silicon-on-insulator pixel detector with 12 μm pixel pitch and 500 μm depletion region thickness. The results of a proof-of-principle experiment based on a Timepix3 detector are also shown.

Effect of Channel Engineering on Quasi-Static Capacitance-Voltage Characteristics of Double-Gate MOSFET

The quasi-static capacitance–voltage (QSCV) characteristics of 10-nm-gate-length double-gate N-type metal–oxide–semiconductor field-effect transistors (NMOSFETs) with Si, Ge, InAs, $$ {\hbox{In}}_{0.53} {\hbox{Ga}}_{0.47} {\hbox{As}} $$ , and GaAs as channel materials are studied and simulated using Silvaco ATLAS three-dimensional (3D) technology computer-aided design (TCAD) software. The QSCV approach offers the advantage of immunity against frequency dependence effects and the ability to measure small capacitances in the 100 fF range. In this device, we consider the self-consistent solution of Schrodinger’s equation with Poisson’s equation. The splitting of the conduction band into multiple subbands is considered, while there is no doping in the channel region. The effects of metal gate electrode engineering, channel engineering (Si, Ge, GaAs, $$ {\hbox{In}}_{0.53} {\hbox{Ga}}_{0.47} {\hbox{As}} $$ , and InAs), and different channel thicknesses with $$ \left( {{\hbox{Al}}_{2} {\hbox{O}}_{3} } \right) $$ as gate oxide having thickness of 0.8 nm on the QSCV characteristics are studied. A comparison of the QSCV characteristics is carried out for the above-mentioned channel materials, revealing a significant reduction in the inversion-mode QSCV characteristics for all the materials due to quantization that results in a decrease in the overall gate-to-channel capacitance and hence increases the threshold voltage of the MOS device. The QSCV characteristics are also useful to measure the oxide thickness, flat-band voltage, threshold voltage, maximum depletion region thickness, charge distribution in the dielectric, interface trap charge, and interface states between the channel and gate oxide before device fabrication.

High frequency noise calculation in Schottky metal-semiconductor-metal structure and parameter retrieval of nanometric CdTe structure

An analytical model to calculate the noise spectral density in Metal-Semiconductor-Metal (M-S-M) structure of Schottky contacts has been developed. The model based on the linearization of Langevin approach of carrier motion inside a bulk semiconductor, and taking into account the fluctuations in the leakage current through the structure due to the barrier lowering by the image force effect. Particularly, the calculations describe two quantities of noise: electric field and total current spectral densities. The results obtained from the Au-CdTe-Au Schottky structure exhibit sharp resonances due to the effect of plasma frequency oscillations and the relative thickness of the depletion region below the anode. Moreover, the noise current spectrum exhibits Lorentzian behavior when the M-S-M has the form of a homogenous structure (thickness of depletion region≈0). These results are in agreement with that reported by Monte Carlo technique of metal Schottky structure. The discussion of the noise spectra as a function of structure parameters revealed that the nanometric M-S-M structures with undoped CdTe can be used as Schottky detectors/emitters in Terahertz frequency applications.

Quantum efficiency calibration for low energy detector in hard X-ray modulation telescope satellite

Low energy X-ray telescope, working over 0.7-15 keV energy band, is one of the main payloads in the hard X-ray modulation telescope satellite. The primary scientific objectives are to survey large sky area to investigate galactic X-ray transient sources as well as the cosmic X-ray background, and to observe X-ray binaries or black holes for studying the dynamics and emission mechanism in strong gravitational or magnetic field. The detector of low energy X-ray telescope is CCD236, a new generation of swept charge device, which has good time and energy resolution. Quantum efficiency (QE) of the detector has a crucial influence on X-ray spectrum fitting and absolute luminosity calculation. To provide valuable scientific data, QE should be calibrated in detail. In this paper, QE calibration is accomplished with respect to a silicon drift detector (SDD), using an Fe-55 radioactive source, at energy points Mn-Kα (5.899 keV) and Mn-Kβ (6.497 keV). The energies of Mn-Kα and Mn-Kβ are near that of iron-K, which is an important line in X-ray observation. Additionally, Mn-Kα and Mn-Kβ X-ray will partially pass through the depletion region of CCD236, and these energy points can be used to measure the depletion thickness. This experiment is set up in a vacuum cooling chamber. The X-ray source perpendicularly illuminates SDD and CCD236 through a small hole, whose area is far less than those of two detectors; therefore, QE measurements are irrelevant to neither the distance nor the azimuth angle between the X-ray source and the detector. For CCD236, split events should be corrected. Energy spectra of SDD and CCD236 are fitted with two Gaussian distributions, respectively, to obtain peak positions and standard variations of Mn-Kα and Mn-Kβ. With known structure of SDD, the QE of CCD236 can be calculated. QE values at Mn-Kα and Mn-Kβ are 71% and 62%, respectively. QE and temperature are uncorrelated with each other in a temperature range from -95 ℃ to -30 ℃. According to the specific structure of CCD236 and the measured QE, without considering the effect of channel stop, the best-fit thickness of depletion region is obtained to be 38 μm. When CCD236 is applied with different driving or substrate voltages, no obvious variation of QE is observed. It indicates that the thickness values of depletion region with high and low level voltages are equal. Furthermore, it shows that working CCD236 is deep depleted, and the thickness of depletion region will not change because it reaches its maximum, the edge of epitaxial layer and substrate layer.

The Electrical Characteristics Model of GaN/InGaN/GaN Heterostructure in InGaN-based LED

The calculation model of tunneling current through GaN/InGaN/GaN heterostructure in InGaN-based LED using the transfer matrix method employed to verify the result of calculation of tunneling current implemented analytically. The analytical method applied through solving theoretically the Schrodinger equation, whereas, the transfer matrix method divided the solution area into a less size of N segment compared to the observed potential width size, where the potential energy of each segment was assumed constant. Verification employed to the thickness of depletion region and bias voltage variations. The obtained result has shown that the analytical result of calculation simmilar with the calculation result using transfer matrix method. The calculation model was then extended to calculate the tunneling current for different temperature.

Optimization design of GaN betavoltaic microbattery

Betavoltaic radioisotope microbatteries have gradually become the research direction of micro-power sources because of their several advantages, including small scale, stable output performance, long service life, high energy density, strong anti-jamming capability, and so on. Based on the theory of semiconductor physics, the current paper presented a design scheme of isotope microbattery with wide-gap semiconductor material GaN and isotope 147Pm. In consideration of the isotope’s self-absorption effect, the current paper studied and analyzed the optimization thickness of semiconductor and isotope source, junction depth, depletion region thickness, doping concentration, and the generation and collection of electron hole pairs with simulation of transport process of beta particles in semiconductor material using Monte Carlo simulation program MCNP. In the proposed design scheme, for a single decay, an average energy of 28.2 keV was deposited in the GaN, and the short circuit current density, open circuit voltage, and efficiency of a single device were 1.636 μA/cm2, 3.16 V, and 13.4%, respectively.

Transport mechanisms and photovoltaic properties of zinc tetraphenylporphyrin/n-type silicon heterojunction solar cell

The DC electrical measurements on Au/ZnTPP/Au planar structure showed two regimes of electrical conductivity depending on temperature, at low temperatures the activation energy is 0.24 eV and variable range hopping in localized states near Fermi level is the operating conduction mechanism, at high temperatures the activation energy is 0.998 eV and phonon-assisted hopping of small polarons is the operating conduction mechanism. The capacitance-voltage measurements on Au/ZnTPP/n-Si/Al showed that the formed junction is linearly graded one. The thickness of depletion region in ZnTPP and n-Si has been determined and the built-in potential is 0.85 V. The concentration gradient of holes and electrons is 2.6 × 1020 holes/m4 and 0.3 × 1020 electrons/m4, respectively. Thermoelectric power measurements showed that ZnTPP films are p-type semiconductor and polaron activation energy is 0.37 eV. A hybrid solar cell of Au/ZnTPP/n-Si/Al had been constructed by growing ZnTPP film via thermal evaporation technique on n-Si wafer. Dark current-voltage measurements of the device at different temperatures showed that there are three conduction mechanisms operating in the device. The dominance of any of them depends on applied potential. The photovoltaic properties of Au/ZnTPP/n-Si/Al hybrid solar had been evaluated.

Ultralow-frequency photocurrent oscillation in ZnO nanowires

We report experimental results of ultralow frequency photocurrent oscillation in individual ZnO nanowires. Consecutive photocurrent and photoluminescence measurements corroborate the process of capture and release of photogenerated holes by surface trap states. The dynamic process results in the oscillation of the thickness of surface depletion region, which is believed to be responsible for the observed photocurrent oscillation.

Modeling of Inversion Layer Centroid and Polysilicon Depletion Effects on Ultrathin-Gate-Oxide MOSFET Behavior: The Influence of Crystallographic Orientation

An empirical expression is developed for the inversion layer centroid and the polysilicon-gate depletion region thickness for bulk MOSFETs with different crystallographic orientations. In particular, results for the most commonly used wafer orientations, i.e., (100), (110), and (111), are given. These expressions are used to accurately model the inversion charge (Qinv) and the gate-to-channel capacitance (Cgc) of MOSFETs with gate oxides of nanometric thickness (tox < 1 nm) and different surface orientations. The Poisson and Schrodinger equations are self-consistently solved for different values of silicon and polysilicon doping concentrations in these devices. The results show important reductions of both Qinv and Cgc because of the polysilicon depletion effect and the displacement of the inversion charge centroid from the interface to the silicon bulk as a consequence of quantum effects. These effects are very noticeable for gate-oxide thicknesses of around 1 nm and must be taken into account in the development of accurate MOSFET models. The authors show that this task can be performed by means of a corrected gate-oxide thickness, which includes both the effect of the inversion layer centroid ZI and the polydepletion region thickness Z D. To do this, the authors have developed an accurate model for ZI as a function of the inversion charge concentration, the depletion charge concentration, and the silicon doping concentration for the (100), (110), and (111) wafer orientations. The in-plane channel directions have been swept for each wafer orientation in order to study the validity of the model in depth. Similarly, an expression for ZD as a function, of the polydoping concentration is provided. The gate-to-channel capacitance is also carefully and extensively analyzed. An analytical model for Cgc is provided and tested for different values of oxide thickness, polysilicon doping, substrate doping, and gate voltage

Conduction in lead phthalocyanine films with aluminium electrodes

Electronic conduction has been investigated in evaporated lead phthalocyanine thin films with aluminium electrodes. In contrast to previously investigated samples where the injecting electrode was a gold ohmic contact, these samples did not exhibit space-charge-limited conductivity, but showed carrier excitation via a field-lowering mechanism with a log J∝ V 1/2 current density–voltage ( J– V) characteristic. Both polarities showed two regions in the J– V characteristics having different slopes, leading to the conclusion that conduction is via Schottky and Poole–Frenkel emission at lower and higher voltages, respectively. The Schottky barrier height was 1.03 eV and the depletion region thickness was typically 100 nm for forward bias and 77 nm for reverse bias. In the presence of air there was a decrease in conductivity, which was attributed to the effects of oxygen establishing an interfacial region at the electrodes. The reverse bias conductivity was higher than that for forward bias when exposed to air; this effect was associated with different values of the hole injection efficiency at the two electrodes consequent on the effects of the oxygen exposure.

Fringing field of high-voltage planar p-i-n diodes with a nonuniformly doped guard ring

An exact analytical solution to the problem of the electric-field distribution in a plane capacitor with infinitely long interelectrode space, thin electrodes, and a nonuniform surface charge at the boundary of an insulator that fills the capacitor was derived. Such a capacitor represents an adequate model of a p-i-n diode with shallow planar junctions, a stopper ring, and a lightly doped guard ring. It is shown that a guard ring with the surface charge density Q s varying over the semiconductor-free space interface makes it basically possible to reduce the largest value of the fringing field to the bulk value E0. To this end, it is necessary that (i) the width of the guard ring is at least three times as large as the depletion region thickness d and (ii) the quantity Q s is equal to-E0ɛ0(ɛ+1/2) in the internal region of the guard ring and increases gradually to E0ɛ0(ɛ+3/2) (if there is a stopper ring) or to zero (if there is no stopper ring) in a band that has a width no less than d and is located at the outer boundary of the guard ring. The results of calculations can be also used to optimize the doping profile in the diodes fabricated using silicon-on-insulator technology.

Sensing Mechanism of a Carbon Monoxide Sensor Based on Anatase Titania

This paper reports results on a (anatase)‐based CO sensor and proposes a possible surface‐controlled sensing mechanism. The complex plane analysis of the ac electrical data provides quantitative evidence supporting the mechanism. The grain‐boundary capacitance and conductance, extracted from the impedance plane, were observed to increase with the CO concentration. This effect is attributed to a change in the depletion region thickness and barrier height at the intergranular contact. The analysis of the electrical data combined with x‐ray diffraction and x‐ray photoelectron spectroscopy observations support the proposed sensing mechanism involving CO adsorption and ionization on the titania surface, and not an oxidation‐reduction type reaction as observed in most oxide‐based sensors.

Theory of electrical characteristics of a Schottky barrier having exponentially distributed impurity states and metal-insulator-metal structures

The metal-insulator or metal-amorphous semiconductor blocking contact is still not well understood. Here, the author discusses the steady state characteristics of a non-intimate metal-insulator Schottky barrier. He considers an exponential distribution (in energy) of impurity states in addition to impurity states at a single energy level within the depletion region. He presents analytical expressions for the electrical potential, field, thickness of depletion region, capacitance, and charge accumulated in the depletion region. He also discusses ln I versus Vap data. Finally, he compares the characteristics in three cases: (i) impurity states at only a single energy level; (ii) uniform energy distribution of impurity states; and (iii) exponential energy distribution of impurity states. In general, the electrical characteristics of Schottky barriers and metal-insulator-metal structures with Schottky barriers depend strongly on the energy distribution of impurity states.

Production of detector-grade silicon using high-current electron accelerators

With the development of new silicon detectors (SD) with a large working-surface area and depletion-region thickness [13], the requirements on starting-material quality have risen [4, 5]. Along with high resistivity p and charge-carrier lifetime T, homogeneity of the electrophysical properties of single-crystal silicon with large ingot diameters is acquiring principal importance. The acceptable resistivity fluctuation 6,0 over the volume of ingots of detector silicon with a diameter of greater than 50 mm is =20% at a nominal 3-10 kQ .cm. High-resistivity homogeneous silicon cannot be produced by conventional metallurgical methods, due to large fluctuations 6,0 and a small yield of single crystals with specified p [6]. Improvement of the volume homogeneity of resistivity and more-accurate control of the charge-carrier concentration and it space distribution are achieved by nuclear doping of the silicon by a phosphorous donor impurity or an aluminum acceptor impurity and irradiation of the starting single crystals by neutrons or gamma quanta, respectively [7]. The promise of the use of neutron-doped silicon in various types of SDs has been shown in some publications 12-5, 8]. Here, we shall present the results of a study of nuclear doping by means of bremsstrahlung gamma quanta [7, 9-11] to produce detector-grade silicon.