Calculation Of Carrier Concentration Research Articles

The method for calculation of carrier concentration in narrow-gap n-type doped Hg1\u2212xCdxTe structures

A simple method for the computation of carrier concentration in n-type doped Hg1−xCdxTe (MCT) structures is proposed. The method is based on the postulate of the existence of donor bands. In our model the donor bands are postulated to have a Gaussian distribution of density of states characterized by two parameters only (mean energy for this distribution and standard deviation). These parameters could be obtained with experimental data, which were comprised of a wide range of doping levels for various kinds of dopants.

The numerical method for solving the transport equations in HgCdTe heterostructures using the non-equilibrium distribution functions

This paper presents a numerical method for solving the set of transport equations in semiconductor heterostructures by using the non-equilibrium distribution function for electrons and holes. This method enables the calculation of carrier concentration, carrier mobility and entropy by integrations in the space of wave vectors. In the same way the electrical current density and density of entropy currents are determined. The influence of quasi-Fermi energy gradients for electrons and holes and the gradient of temperature on the physical parameters of the heterostructure is taken into account.

Electrical design of InAs-Sb/GaSb superlattices for optical detectors using full bandstructure sp3s* tight-binding method and Bloch boundary conditions

InAs-Sb/GaSb type-II strain compensated superlattices (SLS) are currently being used in mid-wave and long-wave infrared photodetectors. The electronic bandstructure of InSb and GaSb shows very strong anisotropy and non-parabolicity close to the Γ-point for the conduction band (CB) minimum and the valence band (VB) maximum. Particularly around the energy range of 45–80 meV from band-edge we observe strong non-parabolicity in the CB and light hole VB. The band-edge dispersion determines the electrical properties of a material. When the bulk materials are combined to form a superlattice we need a model of bandstructure which takes into account the full bandstructure details of the constituents and also the strong interaction between the conduction band of InAs and valence bands of GaSb. There can also be contact potentials near the interface between two dissimilar superlattices which will not be captured unless a full bandstructure calculation is done. In this study, we have done a calculation using second nearest neighbor tight binding model in order to accurately reproduce the effective masses. The calculation of mini-band structure is done by finding the wavefunctions within one SL period subject to Bloch boundary conditions ψ(L)=ψ(0)eikL. We demonstrate in this paper how a calculation of carrier concentration as a function of the position of the Fermi level (EF) within bandgap(Eg) should be done in order to take into account the full bandstructure of broken-bandgap material systems. This calculation is key for determining electron transport particularly when we have an interface between two dissimilar superlattices.

Optical parameters of ZnTe determined using continuous-wave terahertz radiation

The optical parameters of three ZnTe crystal wafers of different thicknesses were determined using transmittance measurements of continuous-wave terahertz radiation from a two-color photomixing source. The parameters are extracted by fitting the transmittance data with theoretical curves generated using a Drude-Lorentz dielectric model of the crystal and a bootstrap statistical analysis of the fits. It was found at room temperature that the low and high frequency dielectric constants are ϵ(0)=9.8±0.2 and ϵ(∞)=7.3±0.6, respectively. The transverse optical phonon frequency was found to be νTO=6.0±1.3 THz. Sample specific properties such as the plasma, collision, and phonon damping frequencies were determined and used for an approximate calculation of carrier concentration. The results are compared with a comprehensive review of earlier values from the literature. Our results are consistent with previous work, falling within the spread of accepted values, and demonstrate that this method is particularly suited for determining the low and high frequency dielectric constants of semiconductor samples.

Drain current reduction by source electrode overlap in hydrogenated amorphous silicon thin-film transistors

The characteristics of hydrogenated amorphous silicon (a-Si:H) thin-film transistors are investigated as a function of the overlap of the source electrode Lovs on top of the passivation layer. The drain current is reduced by Lovs and the effect is dependent on drain voltage and a-Si:H layer thickness. The effect is enhanced at high drain voltage and at thin a-Si:H layer thickness. At high drain voltage, field-effect mobility and threshold voltage decrease as Lovs increases. Numerical calculation of carrier concentration in a-Si:H layer showed that the carrier is depleted under Lovs and that the effective channel length is shortened by the size of Lovs. The nonlinear resistance formed by Lovs is discussed in terms of drain voltage and a-Si:H layer thickness.

Effect of polar vibrations of the crystal lattice on the plasma frequency of heavily-doped semiconductors and correction for calculation of carrier concentration

In heavily-doped polar semiconductors, the polar vibrations of the crystal lattice affect their plasma frequency. Thus, when calculating the carrier concentration from the plasma reflection edge, some correction to the results is necessary.

Calculation of Carrier Concentration in Polycrystalline Films as a Function of Surface Acceptor State Density: Application for ZnO Gas Sensors

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An analytical model for the epitaxial bipolar transistor

In the n + pn − n + transistor, high-current effects in the base and collector regions are linked within the current ranges of practical interest. To describe such effects, we have derived an analytical model that is based primarily on five assumptions: (1) the structure is approximately one-dimensional; (2) recombination is negligible in the base and collector quasi-neutral regions, and in the three space-charge regions; (3) high-current effects are negligible in the emitter and n +-substrate regions; (4) the Fletcher boundary conditions (or the Misawa boundary conditions) can be used for the three space-charge regions; and (5) the ambipolar approach can be used for the base and collector quasi-neutral regions. The primary findings predicted by the n + pn − n + transistor model are: In current ranges of practical interest (usable current gain), the electron concentration profile has a significant “vertical step” located at the collector-base metallurgical junction for all values of collector current. In the limit of extremely-high-current operation, this step tends to vanish. In the current range where the current gain begins to decline rapidly with increasing collector current, the electron concentration at the base boundary of the collector-base space-charge region goes approximately as the square of the hole concentration at the collector boundary of the same region. Because of this relationship, a charge-control calculation is more difficult than a straightforward calculation of carrier concentration for a given degree of accuracy. The n + pn − n + transistor model (which consists of twelve algebraic equations) is particularly useful for the practically important case of an epitaxial bipolar transistor having a very thin, heavily-doped base region.