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Undoped nanocrystalline anatase p-type TiO2 thin film was deposited by sol–gel method on thermally oxidized p-Si (2–5 Ω cm, 〈1 0 0〉) substrates. The thin film was characterized by X-ray Diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) to confirm the formation of nanocrystalline anatase titania and to determine the crystallite size (∼7 nm). The resistive sensor structure was fabricated employing two lateral Pd electrodes on top of the TiO2 sensing layer. The developed sensor was tested in the temperature range of 50–200 °C for the detection of low ppm acetone (0.5–50 ppm). The maximum response of ∼115% was obtained at 150 °C with response/recovery time of 14 s/22 s at 50 ppm acetone (in air). Moreover, the sensors were capable of detecting acetone as low as 0.5 ppm with acceptable response magnitude. As titania acetone sensors are mostly n-TiO2 based, the acetone sensing mechanism for p-TiO2 is yet to be established authentically. To address the issue, an equivalent circuit model, based on the corresponding band diagram of nanocrystalline p-TiO2 with Pd electrode, was developed to describe the electron transfer mechanism through grain, grain boundary and Pd electrode under the influence of acetone vapor.

The present paper reports the fabrication and detailed electrical characterization of p-ZnTe/n-CdTe heterojunction diodes prepared by vacuum deposition method. The possible conduction mechanisms of the heterojunction diode were determined by analyzing the I – V characteristics. The C – V characteristics of the heterojunction diodes were studied to determine the barrier height, carrier concentration and thickness of the depletion region in the heterojunction. A theoretical band diagram of the heterojunction was drawn based on Anderson’s model.

In this paper, we report a conduction-type-tunable carbon nanotube field effect transistor (CNT-FET) with double-gate structure (DG CNT-FET). In this study, a specially designed narrow top-gate is created to modulate the energy band in the middle region of a single CNT. In the proposed DG device structure, the top-gate and bottom-gate biases exhibit independent modulation behaviors. Depending on whether a positive or negative bias is applied to the top-gate, the CNT-FET can be operated in either n- or p-type conduction. Energy band diagram conducive to the physical mechanisms of the proposed DG CNT-FET device structure is proposed. Based on the proposed hypothesis, ambipolar CNT-FETs can indeed be converted to n- or p-type-like behaviors.

ZnO p–n homojunctions have been fabricated by depositing p-type ZnO thin films using an innovative CVD method on n-type ZnO films produced by conventional D.C sputtering on glass substrates. The individual oxides have been characterized for ohmic contact by current–voltage ( I – V ) measurements and the semiconducting electrical parameters have been determined by resistivity and Hall effect measurements at room temperature. The formation of ZnO p–n homojunctions has been studied by I – V characteristics at 30, 300 and 400 °C. Rectifying nature was observed in the measured I – V curves. The ideality factor, saturation current and the barrier height for the forward bias have been calculated as a function of temperature. The improvement of the junction properties was observed from the decrease in the value of the ideality factor with the increase in temperature. A qualitative energy band diagram of the homojunction has been constructed in order to explain the interband carrier tunneling mechanism.

An expression that can be used to determine the thickness of an interfacial oxide layer between a high-K dielectric and Si substrate has been derived using the photoelectron intensity ratio of high resolution X-ray photoelectron spectroscopy (HRXPS). Experimental results show the interfacial silicon oxide thickness obtained with the expression fits very well with Ellipsometer measurements. We also studied the formation of an interfacial layer between a high-k HfO2 film and a Si substrate as well as its thermal stability. The results have revealed that: (i) the interfacial oxide formation requires the existence of thermally energized oxygen in an environment to break the H–Si bonds first for hydrogen terminated Si surface and (ii) the thermodynamic stability of the oxide interfacial layer depends on its initial formation process. The valence band structures of Si, SiO2, and HfO2 have been analyzed using HRXPS and an energy band diagram of HfO2/SiO2/Si has been constructed.

In this study the temporal characteristics of the current through thin silicon oxide films have been analyzed applying pulsed voltages of different height to the device under test. In addition to low and high field stress measurements, we also have included pre-tunneling voltages to compare several voltage stress tests. We have shown for the first time, that there is a steady transition in the variation of the current characteristic going from pre-tunneling voltages to high voltage stressing. This current characteristic has been explained by the superposition of two current components. The measurement results have been discussed with the aid of a model based on the energy band diagram. Furthermore, we will show that the temporal transient current component can also be seen in the Fowler–Nordheim tunneling plot.

Plasma-induced energy shifts of the conduction band minimum and of the valence band maximum have been calculated for 3C-, 2H-, 4H-, 6H-, 6H–SiC and Si. The resulting narrowing of the fundamental band gap and of the optical band gap are presented. The method utilized is based on a zero-temperature formalism within the random phase approximation. Electron–electron, hole–hole, electron–hole, electron–optical phonon and hole–optical phonon interactions have been taken into account. The calculations are based on band structure data from a relativistic, full-potential band structure calculation.

A study of the electric and photoelectric behaviour of electrodeposited Au/n-CdTe Schottky diodes in a wide temperature range is presented. The dependence of quantum efficiency on photon energy, temperature, and bias is used to determine the Schottky barrier height, the built-in voltage, the space charge layer width, the field strength and the bulk carrier concentration. The built-in voltage is strongly temperature dependent. At temperatures above 100 K there is no surface inversion. Several arguments indicate the existence of interface states at the Au/CdTe interface. All information is combined to establish the band diagram of the structure and to determine parameters relevant for solar-cell applications.

The electronic band structure of the InP-lattice matched alloys In0.53Ga0.47As and In0.52Al0.48As is investigated using a non-local empirical pseudopotential including spin–orbit interaction. Pseudopotential parameters are obtained by fitting the virtual crystal band structure immediately to available experimental data for the alloys. Results are presented for the band structures and effective masses in In0.53Ga0.47As and In0.52Al0.48As. Comparison of the band structures is made against available results from a quasiparticle calculation and a model pseudopotential calculation within the coherent potential approximation.

A simple electrical method is presented for the characterization of the inversion layer in p-channel MOSFET's with either p+ poly gate (surface-channel, SC) or n+ poly gate (buried-channel, BC). The dc centroid of the inversion layer profile, Xc, represents the effective thickness of the inversion layer in the SC device or the physical location of the buried-channel in the BC device. For the first time, it is well demonstrated that, based on the small-signal gate-to-channel capacitance measurement, the global inversion layer hole profiles in both types of p-MOSFET's can be constructed from three elements, i.e., Xc (dc centroid), Xw (band diagram characteristic width) and ΔNinv (increment of net carrier area density).

A new ZnSe Si heterojunction bipolar transistor was successfully fabricated by vapor phase epitaxy (VPE). The unintentionally doped ZnSe layer was used as an emitter layer. Due to the large valence-band discontinuity at the ZnSe Si heterointerface, we obtain a common-emitter current gain of 10 with a thick base width of 5 μm and a base-to-emitter doping ratio of 50. In addition, the device has a large light-sensitivity area which exhibits a strong sensitivity to visible light. In response to blue (470 nm) illumination, we obtain a responsivity of 1.3 μA/lx with a dark current as small as 1.8 pA/μm2. A qualitative band diagram has been developed to describe the device performance in this study. Together with VLSI technology, the development of a ZnSe Si visibility-sensitive bipolar transistor shows high-potential for applications in photo-receivers that require short-wavelength detection.

A methodology for calculating the energy band diagrams of abrupt heterostructures using the band discontinuities and the interface charge density as parameters is presented. The calculations are based on two basic equations which are universally accepted—the lineup of the bands relative to the common Fermi level (which embodies the valence band discontinuity) and the charge neutrality (which embodies the interface charge density). The two equations, with the aid of Poisson's equation, yield the total band bending on each side of the interface and the dependence of the energy bands on the position (i.e. the band diagram). The methodology is illustrated for the HgTeCdTe semimetal-semiconductor heterostructure, and demonstrates the interplay of band offsets and interface charges in establishing the nature of a heterostructure (either rectifying or ohmic) and in determining the potential barrier height, for both n -type and p -type CdTe. The methodology presented in this study is general and can be applied to additional semiconductor-semiconductor and semimetal-semiconductor heterostructures.

We derive a simple analytical model for the field and temperature dependence of Shockley-Read-Hall lifetimes in silicon from a microscopic level, where the capture of carriers at recombination centers is assumed to be a multiphonon process. Strong electric fields, as often present in modern devices, cause trap assisted tunneling, i.e. the multiphonon recombination path is no longer purely vertical in a band diagram, but has a horizontal branch at an effective energy which is given by the maximum of the transition probability. Applying reasonable approximations we calculate this effective recombination path as a function of field strength and temperature. Field enhancement factors of the inverse carrier lifetimes are then presented that require no integration, iteration or higher mathematical functions. The anisotropy and multi-valley nature of the silicon conduction band is carefully taken into account. We discuss all approximations and physical effects by means of the gold acceptor level. The model is able to describe the pre-breakdown behaviour of trap tunneling leakage and is suitable for the implementation into simulation packages.

A precise and effective numerical procedure to model the band diagram of modulation doped multiquantum well heterostructures is presented. This method is based on a self-consistent iterative solution of the Schroedinger equation and the Poisson equation. It can be used rather easily in any arbitrary modulation-doped structure. In addition to confined energy subbands, the unconfined states can be calculated as well. Examples on realistic device structures are given to demonstrate capabilities of this procedure. The numerical results are in good agreement with experiments. With the aid of this method the transitions involving both the confined and unconfined conduction subbands in a modulation doped AlGaAs/GaAs superlattice, and in a strained layer InGaAs/GaAs superlattice are identified. These results represent the first observation of unconfined transitions in modulation doped multiquantum well structures.

The general density-voltage relations at the boundaries of the space-charge region of a degenerate n+-p junction with position-dependent band structure are derived. The results are valid for a variety of materials including graded composition semiconductors, heterojunctions, and devices with high doping. The following special cases of interest are considered: nondegenerate limit, rigid band model, uniform band structure and the classical case. The effect of carrier degeneracy in materials with parabolic uniform band structure is discussed in detail. In this case, for most junction voltages, a linear relationship is shown to exist between the actual minority carrier density and the values predicted by the classical theory. There is a significant departure from classical results. A plot for a correction factor as a function of doping is also given.

Computation of the equilibrium electrostatic potential and energy band diagram of semiconductor devices with nonuniform composition is considered. We first establish the relationship between the electrostatic potential and the energy band edges and then derive a Poisson-Boltzmann equation for the electrostatic potential. Although the equation is more general, we consider only the simple example of an abrupt heterojunction diode in detail. An analytical solution for doubly-intrinsic, abrupt heterojunctions is also presented. The modeling approach is then generalized to include Fermi-Dirac statistics for free carriers. We also discuss the application of the formulation to a variety of heterojunction devices (e.g. heavily doped silicon and gate-modulated devices).

It is demonstrated that CVD Si-nitride films as transparent dielectric satisfy all requirements for achieving MIS/IL solar cells with high efficiency and long term stability. Deposited on silicon by the SiH4/NH3 reaction at temperatures lower than usual (between 600° and 650°C) fixed positive interface charge densities QN/q up to 7 × 1012 cm−2 with excellent stability have been obtained. Utilizing the Si-nitride charge storage effect, the highest known QN/q values (> 1013cm−2) combined with low values of Nit have been achieved. The charge distribution is discussed and an energy band diagram modified according to new analytical results is presented. MIS/IL solar cells with AM1 efficiencies of 15% (active area) and high UV sensitivity have been obtained.

Junctions between amorphous a -CdS and crystalline n -Si have been prepared. It is found that the junctions are rectifying with a coefficient k r = 10 2 −10 3 at room temperature. The temperature dependence of k r , the J - V characteristics and the spectral intensity dependence of the photocurrent have been measured. The results are interpreted on the basis of carrier injection from c -Si to a -CdS and the assumption that C 1 − states in a -CdS define the reverse current flow. An energy band diagram of the heterojunction is proposed.

An analysis of an instrinsic abrupt heterojunction in equilibrium is given. We review the concepts necessary to construct the energy band diagram and present an analytic solution for the electrostatic potential and transition capacitance. The discontinuity in the conduction and valence band edges is derived. The results, contrary to recent works by Adams and Nussbaum and by von Roos, are in agreement with the Anderson affinity rules. Extension of results to the extrinsic case are indicated.

Two types of heterojunctions have been prepared by electroless deposition of Pb 1− x Hg x S ( x = 0–0.33) films with α′ and β′ structures on n -type silicon single crystal substrates. Functional behaviour of the forward characteristics is explained on the basis of band to band tunnelling coupled with the recombination processes. The energy band diagram is given for both types of Pb 1− x Hg x S/Si heterojunctions in agreement with the experimental results.

A solution method for the nonlinear Poisson equation used in numerical modeling of III–V compound semiconductor heterostructures is presented. The method is based on a nonlinear iterative algorithm and is shown to be globally convergent and suitable for implementation on a computer with small main memory capacity. The rate of convergence also makes the solution method computationally efficient. As an application example, the equilibrium energy band diagram of a GaAs/AlGaAs double heterojunction bipolar transistor is calculated, and computer experiments are performed in order to demonstrate the convergence properties of the algorithm.

A negative photoresponse in p lightly doped GaAs-n heavily doped (AlGa)As heterojunctions is observed. The a.c. spectral response is presented as a function of d.c. bias and illumination. A model for negative photocurrents is proposed as due to electron diffusion into the p side. The photoresponse sign reversal is caused by the existence of the notch-spike discontinuity and of a notch population. Estimations of the band diagram are made from photoresponse and electrical measurements.

For short-channel insulated-gate field-effect transistors (IGFET) operating with source-to-substrate reverse bias, the threshold voltage is in general a function of channel length and drain-to-source voltage. It is shown in this analysis that these dependences can be attributed to the two-dimensional distribution of the depletion charges. Starting from two fundamental relations, the overall charge neutrality and the voltage relations based on the energy band diagram, a generalized threshold voltage equation in integral form is derived. A closed-form threshold equation is then obtained using a regional approximation with a simplified piecewise-linear depletion profile. The equation includes as new factors, the channel length, junction depth and drain voltage, and passes to the conventional form for increasing channel length. The theoretical threshold voltage expression is found to predict the correct tendencies and is shown to be in reasonable agreement with experimental measurements.

The influence of grain boundary barrier height is of great importance for polycrystalline electronic devices and solar cells. The g.b. barrier height is computed in a forward biased one-sided step junction. Within the base, it is calculated by means of analytical expressions which depend on the interface state distribution. Within the space charge region, the population of the interface states is considerably changed on taking the band bending into account. In this region, the g.b. barrier height is obtained by means of a numerical solution of the two-dimensional Poisson's equation. The energy band diagram of the junction in the vicinity of the boundary is given. The variation of the g.b. barrier height as a function of the distance from the junction has been determined for monoenergetic and uniform interface state distributions and for different direct bias voltages.

The photovoltaic response of the nGe-n Si diodes are in agreement with the I-V characteristics and the band diagram postulated by Oldham and Milnes. (Author)

By incorporation of a thin layer of near intrinsic semiconductor, one can change a metal-semiconductor ohmic contact into a retifying junction. This concept is demonstrated by inserting an amorphous silicon film of less than 40 A between aluminum and silicon. The resulting diode's forward current is found to be controlled by majority carrier tunneling, and its reverse current is governed by minority carrier diffusion. From experimental data of I - V and C - V measurements, we find a flat-band condition at zero bias and deduce a tunneling barrier height of 0.67 eV at room temperature. The energy band diagram is presented to illustrate the operation principle of the tunnel diode.