High Doping Densities Research Articles

Influence of the modulation doping to the mobility of two-dimensional electron gases in Si/SiGe

The influence of the doping densities to the low temperature mobility of 2DEG in Si/SiGe is investigated. The SiGe modulation doped quantum well structures are realized by the method of molecular beam epitaxy (MBE). Different concepts for the needed virtual substrate are implemented to assess the influence from the quality of the samples to the mobility behavior. The modulation doping is varied between 6 ⁎ 10 13/cm 2 and 3 ⁎ 10 12/cm 2. In contrast to the theory of remote Coulomb scattering, it is observed that the low temperature mobility of two-dimensional electron gas in Si-channels increases with higher doping density.

Electrical and electrothermal transport in InN: The roles of defects

The transport properties of Mg doped and undoped InN films are studied with capacitance-voltage, thermopower, and Hall mobility measurements. A positive Seebeck coefficient is observed for Mg doped InN confirming p-type conductivity, though high doping and structural defect density can lead to n-type films. Transport measurements of undoped films are analyzed employing Rode's iterative Boltzmann equation method. Observed thermopower, Hall mobility, and dislocation density data for undoped films are consistent with calculations including the effects of charged line defect (donor-type dislocation) scattering.

Quantum Efficiency Analysis of InAs–GaSb Type-II Superlattice Photodiodes

We compare the experimentally measured and theoretically calculated quantum efficiency (QE), where an analytical drift-diffusion photocurrent model is used, of n+ -on-p InAs-GaSb superlattice (SL) photodiodes. With inputs of the transport parameters obtained by the electron-beam-induced current technique and absorption coefficient spectra calculated by the eight-band kldrp method for the p-SL, n+ -SL, and depletion region, taking into account the band filling effect, we show that the drift-diffusion photocurrent model is a good approximation for the InAs-GaSb type-II SL photodiodes, which implies that the SL depletion region in InAs-GaSb SL photodiodes is as effective as that in bulk semiconductor photodiodes in terms of collecting the photo-excited electron-hole pairs. Using this theoretical model, we also find that the high doping density in n-type SL degrades the QE by reducing the absorption coefficient. As a result, the n-type doping density is suggested to be below 1times1017cm-3 in order to optimize the QE for the studied InAs-GaSb SL photodiodes.

Electrical characteristics of Mg-doped GaAs epitaxial layers grown by molecular beam epitaxy

The electrical characteristics of magnesium (Mg)-doped GaAs epitaxial layers grown with different substrate temperatures have been investigated by Hall effect and capacitance–voltage (C–V) measurements at room temperature. The carrier concentration obtained by Hall measurements was decreased from 1.4×1019 to 3.4×1016 cm−3 when increasing the substrate temperature in the range 460–540 °C, and thus the maximum attainable doping density was NA–ND=1.4×1019 cm−3. The depth profiles of doping density, obtained by C–V measurements, show that carriers largely out-diffused toward the surface. This could be attributed to the surface segregation effect, which was predominant in the samples with a high doping density than those with a low doping density. Mg-doped GaAs layers have higher mobility than Be-doped GaAs layers around NA–ND=1018 cm−3. Thus, it is expected that Mg could be effectively used as p-type dopants for highly doped nanostructured semiconductors.

Linear optical responses of one-dimensional electron systems: Comparison of theories with experiments

We present a systematic study on the linear optical spectra of n-doped GaAs quantum wire. A Coulomb-correlated band-edge absorption peak appears at low doping density evolving from the exciton resonance. The Fermi-edge singularity is observed at high doping density. Based on theoretical calculations, we clarify the mechanism of the crossover among exciton, the band-edge and the Fermi-edge singularities.

Manipulation of strain relaxation in metamorphic heterostructures

The authors have discovered that high doping densities in an alloy graded InGaAs buffer have dramatic effects on strain relaxation dynamics and consequently surface and optical qualities in metamorphic heterostructures. Compared with undoped graded buffers, the use of Be doping significantly improves structural, surface, and optical qualities while the use of Si doping deteriorates all these properties. This discovery is significant for the realization of metamorphic optoelectronic devices.

Effect of exchange–correlation potential on the plasmon dispersions in a doped symmetrical double quantum well

AbstractWe have calculated the plasmon dispersion relations in a doped double quantum well with and without exchange–correlation potential added to the effective potential of the system. The calculations were done for high and low doping densities by solving the Schrödinger and Poisson equations self‐consistently. Our numerical results show that the exchange–correlation potential is quite important at high doping densities of donor impurities for plasmon dispersions at large wave vectors. On the other hand, the ratio of subband populations ni to donor density ND is more affected at low densities. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Tuning the structural, electrical and optical properties of Ti(III)-doped nanocrystalline TiO 2 films by electrophoretic deposition time

Doped nanocrystalline TiO 2 films were prepared by electrophoretic deposition of colloidal aqueous suspensions on optically transparent electrodes followed by annealing in air. Characterization experiments of the resulting films indicate that several properties can be tuned by electrophoresis time as a consequence of the electrochemically promoted insertion of Ti(III) atoms into the TiO 2 lattice that takes place during the synthetic protocol. In this way, while structural parameters such as thickness, particle size, pore diameter, and electrical conductivity, were shown to change as a function of the electrophoresis time, the band edges of the films showed a constant red-shift due to the high doping density of the semiconductor material (∼ 10 20 cm − 3 ).

High Doping Density Schottky Diodes in the 3MM Wavelength Cryogenic Heterodyne Receiver

The paper describes a 3mm cryogenic mixer receiver using high doping density (“room-temperature”) Schottky diodes. The measured equivalent noise temperature Teq of the diodes is 109 K at 20 K, which is much higher than the Teq of the low doping density (“cryogenic”) diodes. In spite of this, the double-sideband (DSB) noise temperature of the cryogenic receiver developed is 55 K at 110 GHz, owing to the low conversion loss of the mixer and ultra-low noise of the PHEMT IF amplifier. This is the lowest noise temperature ever reported for a Schottky diode mixer receiver. The results obtained are useful for the development of submm receivers in which high doping density Schottky diodes are used.

Quantum Potential Approach to Modeling Nanoscale MOSFETs

We propose a novel parameter-free quantum potential scheme for use in conjunction with particle-based simulations. The method is based on a perturbation theory around thermodynamic equilibrium and leads to an effective potential scheme in which the size of the electron depends upon its energy. The approach has been tested on the example of a MOS-capacitor by retrieving the correct sheet electron density. It has also been used in simulations of a 25 nm n-channel nanoscale MOSFET with high substrate doping density. We find that the use of the quantum potential approach gives rise to a threshold voltage shift of about 220 mV and drain current degradation of about 30%.

Effect of free-carrier absorption on the threshold current density of GaAs∕(Al,Ga)As quantum-cascade lasers

Ga As ∕ Al 0.33 Ga 0.67 As quantum-cascade lasers with plasmon-assisted waveguides exhibit a decreasing threshold current density jth with increasing wave number ν0 of the laser line, which changes as a function of the injector doping density. We have developed an analytical approach based on the effective dielectric tensor component for the p-polarized light emitted from a quantum-cascade laser, which explains the observed dependence of jth(ν0) in terms of losses due to free-carrier absorption predominantly in the doped waveguides αWG(ν0). A contribution to the losses by free-carrier absorption in the quantum-cascade structure itself and subsequently to jth can be neglected except for very high injector doping densities. The calculated values for αWG(ν0) are in good agreement with the experimental data. Our approach quantitatively predicts the observed decrease of jth from 17to7kAcm−2 with increasing ν0 between 900 and 1100cm−1. In addition to achieving a direct physical insight into the influence of free-carrier absorption on the laser performance, the proposed analytical approach provides a simple tool for the determination of the waveguide losses for any quantum-cascade laser without adopting a numerical solver.

Transcritical Hopf bifurcation and breathing of limit cycles in sequential tunnelling of superlattices

Within a discrete drift model, we study the evolution of the self-sustained current oscillation (SSCO) solutions (limit cycles) in sequential tunnelling of superlattices under dc bias. We propose two possible modes: one is co-existence of both fixed point and limit cycle solutions, exchanging stabilities at the bifurcation point, termed the transcritical Hopf bifurcation and the other is that, at high doping densities and inside SSCO regime, the breathing motion of the limit cycles, in which the amplitude and frequency of SSCOs oscillate as a function of an applied dc bias, in contrast with a square-root dependence expected in a conventional Hopf bifurcation.

Doping effect on the intermixing in GaInAsP/InP multiple quantum well structures grown using all solid sources

We report the doping effect on the intermixing in the GaInAsP/InP multiple quantum well structures with doping densities of 5×10 16, 10 17, 5×10 17, 10 18, 5×10 18 cm −3 in their wells, respectively. It was found that the lattice mismatch and the energy band gap increased with the annealing temperature and time, and the high doping density in the wells of the multiple quantum well structures degraded the intermixing. The mismatch and the blue shift of the energy band gap in the wells can be explained by the out-diffusion of phosphorus from the InP barriers, and the reduction of the intermixing at high doping can be attributed to the interface roughness and inhomogeneity in the wells caused by high doping.

The Influence of Doping Levels and Surface Termination on the Electrochemistry of Polycrystalline Diamond

AbstractThe influence of surface chemistry and boron doping density on the redox chemistry of Fe(CN)$\rm{ {_{6}^{3-/4-}}}$ at CVD polycrystalline diamond electrodes is considered. It is demonstrated that for this couple both the doping density and the surface chemistry are important in determining the rate of charge transfer at the electrode/electrolyte interface. For hydrogen terminated CVD diamond metallic electrochemical behavior is always observed, even at boron doping densities as low as 7×1018 cm−3. In contrast, the electrochemical behavior of oxygen terminated CVD diamond varies with doping density, a metallic response being observed at high doping density and semiconductor behavior at low doping density. It is shown that the results attained may be explained by a surface state mediated charge transfer mechanism, thus demonstrating the importance of controlling surface chemistry in electroanalytical applications of diamond.

Interface roughness scattering and its impact on electron transport in relaxed and strained Si n-MOSFETs

In this paper we focus on the problem of interface roughness scattering which is treated non-perturbatively by incorporating the effects of scattering as a boundary condition for the Boltzmann transport equation. The scattering probability is derived and implemented in an ensemble Monte Carlo simulation of electron transport in relaxed and strained Si n-MOSFETs. We compare the internal device behaviour as a function of the interface quality between short channel relaxed and strained Si n-MOSFETs. We provide further evidence that the strained Si/SiO2 interface is less rough, requiring a longer correlation length and smaller rms height for the strained Si/SiO2 interface. The high doping densities encountered necessitate the self-consistent use of degenerate (Fermi–Dirac) statistics.

Infrared quantum well intersubband modulator

A modulator based on intersubband transition in asymmetrical quantum wells having a large linear Stark shift is demonstrated. Using a high doping density and a large number of quantum wells, a strong intersubband absorption (∼85%) is achieved. With an appropriate asymmetrical quantum well design, a large linear Stark shift is obtained.

Spatial correlation effects in the charged impurity distribution on the electronic properties of δ‐doped structures

AbstractIn this paper we will show that the δ‐doped GaAs/AlGaAs/GaAs quantum barrier is an ideal system to study deep centers in narrow doping layers with high doping density. By varying the Al content in the barrier, the distance between the Fermi‐level and the deep level can be tuned and therefore the number of populated states. By applying hydrostatic pressure this number can be further increased. Our measurements show that in these δ‐doped barrier structures electrons are trapped under hydrostatic pressure and that the quantum mobility is enhanced. This mobility enhancement can be explained by MC calculations which include the effect of the spatial correlation of the charge distribution when the deep state is the DX center and has a negative charge state. The fact that we do not observe a PPC effect or a significant change in the mobility after illumination at high pressure suggest that the Fermi‐level is pinned by a non‐metastable deep state like the A1 state or that the DX center is modified.

Characterization of Electrical Properties of Micro-Schottky Contacts on Epitaxial Lateral Overgrowth GaN

Current-voltage characteristics of micro-Schottky contacts fabricated on Epitaxial lateral overgrowth (ELO) GaN have been measured. The obtained characteristics are classified into two groups; good contacts with small ideality factor (n-value) and poor contacts with large n-value. By comparing the distribution of I-V characteristics of the micro-Schottky contact array with the distribution of dislocations revealed by molten KOH etching, it was concluded that the dislocations are not responsible for the poor I-V characteristics of the Schottky contacts. Regarding the origin of the poor I-V characteristics, the high doping density area formed at the top surface of the as-grown wafer was suggested.

QWIPs DESIGNED FOR HIGH ABSORPTION AND HIGH OPERATING TEMPERATURE

For the majority of applications involving detection of weak signals or thermal imaging, the quantum well infrared photodetector (QWIP) is designed to have the highest possible detectivity and operating temperature. The device parameters, such as the doping density, are chosen accordingly. In a different direction, the intrinsic short carrier lifetime (~ 5 ps) makes QWIPs well suited for high speed and high frequency applications. In such cases, since lasers are normally used, a high dark current can be tolerated. The most important parameter is then the absorption efficiency. For system simplicity and potential wide use, room temperature or near room temperature (reachable by thermo-electric cooling) operations are desirable. This paper discusses the QWIP design for high absorption and elevated temperature operation, and present a systematic experimental study on a set of GaAs/AlGaAs QWIPs with different doping densities. High absorption (~ 100%) and up to room temperature operation are achieved in devices having high doping densities and 100 quantum wells.

Numerical modeling of highly doped Si:P emitters based on Fermi–Dirac statistics and self-consistent material parameters

We have established a simulation model for phosphorus-doped silicon emitters using Fermi–Dirac statistics. Our model is based on a set of independently measured material parameters and on quantum mechanical calculations. In contrast to commonly applied models, which use Boltzmann statistics and apparent band-gap narrowing data, we use Fermi–Dirac statistics and theoretically derived band shifts, and therefore we account for the degeneracy effects on a physically sounder basis. This leads to unprecedented consistency and precision even at very high dopant densities. We also derive the hole surface recombination velocity parameter Spo by applying our model to a broad range of measurements of the emitter saturation current density. Despite small differences in oxide quality among various laboratories, Spo generally increases for all of them in a very similar manner at high surface doping densities Nsurf. Pyramidal texturing generally increases Spo by a factor of five. The frequently used forming gas anneal lowers Spo mainly in low-doped emitters, while an aluminum anneal (Al deposit followed by a heat cycle) lowers Spo at all Nsurf.