N-type Doping Density Research Articles

Formula omitted]-type doping modulation of double GaAs/AlGaAs quantum wells

Utilizing the FEniCS Project and Python programming, we conduct a comprehensive characterization and analysis of the n-type doped layer in double quantum wells made of GaAs and featuring AlGaAs barriers through self-consistent Schrödinger–Poisson simulations. The main findings reveal that the dimensions of the system and the doping layer significantly influence the electronic properties, energy levels, Fermi energy, wave functions, and electron density. Upon doping the intermediate barrier, electrons exhibit notable migration from the doping region to the quantum well zones, particularly pronounced for thin barriers. Conversely, for large barriers, the emergence of a new well, akin to a real quantum well, imposes constraints on the movement of charge carriers. The electron density varies in accordance with the impurity density, which assumes significant importance as the quantum well and barrier width are reduced. The Fermi energy level, which play a crucial role in semiconductors, rises with a decrease in quantum well width or an increase in doped layer width and n-type doping density, remaining almost unaffected by variations in barrier width.

Unveiling charge dynamics of visible light absorbing oxysulfide for efficient overall water splitting

Oxysulfide semiconductor, Y2Ti2O5S2, has recently discovered its exciting potential for visible-light-induced overall water splitting, and therefore, imperatively requires the probing of unknown fundamental charge loss pathways to engineer the photoactivity enhancement. Herein, transient diffuse reflectance spectroscopy measurements are coupled with theoretical calculations to unveil the nanosecond to microsecond time range dynamics of the photogenerated charge carriers. In early nanosecond range, the pump-fluence-dependent decay dynamics of the absorption signal is originated from the bimolecular recombination of mobile charge carriers, in contrast, the power-law decay kinetics in late microsecond range is dominated by hole detrapping from exponential tail trap states of valence band. A well-calibrated theoretical model estimates various efficiency limiting material parameters like recombination rate constant, n-type doping density and tail-states parameters. Compared to metal oxides, longer effective carrier lifetime ~6 ns is demonstrated. Different design routes are proposed to realize efficiency beyond 10% for commercial solar-to-hydrogen production from oxysulfide photocatalysts.

Modelling and optical response of a compressive-strained AlGaN/GaN quantum well laser diode

The effects of the quantum well (QW) width, carrier density, and aluminium (Al) concentration in the barrier layers on the optical characteristics of a gallium nitride (GaN)-based QW laser diode are investigated by means of a careful modelling analysis in a wide range of temperatures. The device’s optical gain is calculated by using two different band energy models. The first is based on the simple band-to-band model that accounts for carrier transitions between the first levels of the conduction band and valence band, whereas the second assumes the perturbation theory (k.p model) for considering the valence intersubband transitions and the relative absorption losses in the QW. The results reveal that the optical gain increases with increasing the n-type doping density as well as the Al molar fraction of the AlxGa1–xN layers, which originate the GaN compressive-strained QW. In particular, a significant optical gain on the order of 5000 cm–1 is calculated for a QW width of 40 Å at room temperature. In addition, the laser threshold current density is of few tens of A/cm2 at low temperatures.

V-groove trench gate SiC MOSFET with a double reduced surface field junction termination extensions structure

We have developed V-groove trench gate SiC MOSFETs (VMOSFETs) with a double reduced surface field junction termination extensions structure (DR-JTEs) to reduce JFET resistance by using a high n-type doping density in a surface drift layer. Simulation results showed that the DR-JTEs structure for an optimized current spreading layer doping of 5 × 1016 cm−3 has a breakdown voltage that corresponds to 94% of the ideal 1D parallel-plane value. The VMOSFETs with a DR-JTEs structure demonstrated both a breakdown voltage of 1610 V and a specific on-resistance of 2.4 mΩcm2 with a threshold voltage of 5.1 V.

Understanding the $C-V$ Characteristics of InAsSb-Based nBn Infrared Detectors With N- and P-Type Barrier Layers Through Numerical Modeling

Capacitance–voltage ( C–V ) profiling is a useful technique for accurate and non-destructive determination of carrier concentrations in semiconductor materials. Recently, this measurement has been applied to the infrared barrier detector to determine the doping densities of the absorber and contact layers. This paper provides three contributions to the development of barrier detectors. First, we develop a physics-based semi-analytical model for computing the C–V characteristics derived from metal–oxide–semiconductor and heterojunction device physics and show that it is in agreement with results obtained from drift-diffusion simulations. Second, we assess the possibility of using the developed model to determine not only the absorber and contact doping densities, but also the doping density and thickness of the barrier layer. Lastly, we use the same drift-diffusion methodology to conduct a comprehensive parametric study of the C–V profile for a variety of absorber n-type doping densities, barrier N- and P-type doping densities, barrier thicknesses, and contact layer n-type doping densities. We also offer an extensive discussion of the role of the various device parameters on shaping the C–V profile. While this paper uses the InAsSb and AlAsSb material system, the analysis can be extended to other materials used to implement barrier devices, such as HgCdTe or superlattices.

Ultraviolet Light-Induced Persistent and Degenerated Doping in MoS2 for Potential Photocontrollable Electronics Applications.

Efficient modulation of carrier concentration is fundamentally important for tailoring the electronic and photoelectronic properties of semiconducting materials. Photoinduced doping is potentially a promising way to realize such a goal for atomically thin nanomaterials in a rapid and defect-free manner. However, the wide applications of photoinduced doping in nanomaterials are severely constrained by the low doping concentration and poor stability that can be reached. Here, we propose a novel photoinduced doping mechanism based on the external photoelectric effect of metal coating on nanomaterials to significantly enhance the achievable doping concentration and stability. This approach is preliminarily demonstrated by an MX2 (M is Mo or Re; X is S or Se) nanoflake modified through a simple process of sequentially depositing and annealing an Au layer on the surface of the flake. Under ultraviolet (UV) light illumination, the modified MX2 achieves degenerated n-type doping density of 1014 cm-2 rapidly according to the experimentally observed >104 times increment in the channel current. The doping level persists after the removal of UV illumination with a nonobservable decrease over 1 day in vacuum (less than 23% over 7 days under an ambient environment). This photoinduced doping approach may contribute a major leap to the development of photocontrollable nanoelectronics.

Deactivation of electrically supersaturated Te-doped InGaAs grown by MOCVD

Achieving and sustaining the highest doping level possible in InGaAs is critical for the reduction of contact resistance in future microelectronic applications. Tellurium (Te) is a very promising n-type dopant with high reported n-type doping densities. However, the stability of this dopant during post-growth thermal processing is unknown. Supersaturated Te-doped InGaAs layers were grown by MOCVD at 500 °C. The electrically active concentration of Te doping was 4.4 × 1019 cm−3 as grown. The thermal stability of the Te was investigated by studying the effect of post-growth annealing between 550 and 700 °C on the electrical activation. At all temperatures, the electrical activation decreased from its starting electron concentration of 4.4 × 1019 cm−3 down to 6–7 × 1018 cm−3. The rate of deactivation was measured at each temperature, and the activation energy for the deactivation process was determined to be 2.6 eV. The deactivation could be caused by either Te–Te clustering or a Te-point defect reaction. HAADF-STEM images showed no visible clustering or precipitation after deactivation. Based on previous ab initio calculations that suggest the VIII population increases as the Fermi level moves toward the conduction band, it is proposed that formation of isolated point defect complexes, possibly a Te–VIII complex, is associated with the deactivation process.

20% efficient solar cells fabricated from epitaxially grown and freestanding n-type wafers

The quality and cost of a wafer are important prerequisites for a high-efficiency, low-cost solar cell. Standard wafers are fabricated using a dicing process, which leads to the loss of a substantial amount of material (up to 40%), the kerf loss. The kerf loss is costly, but in standard technologies, it is unavoidable. As the wafer thickness decreases, these losses become more significant. Using an alternative approach, by applying a sacrificial detachment layer on top of a thin seed layer made of porous silicon for a follow-on thick epitaxial growth, so-called EpiWafers can be produced, and kerf losses can be avoided. An advantage of this EpiWafer production process is that the thickness of the wafers can be deliberately chosen according to requirements, e.g. between 50µm and 250µm. The wafer production costs are lower than standard wafering techniques if high-throughput porosification tools and chemical vapour deposition reactors are used. In this work, solar cells with n-type wafers epitaxially grown in an atmospheric pressure chemical vapour deposition reactor are presented. The processed wafers feature an n-type doping density of 3×1016cm−3 and a mean thickness of 150µm. The best EpiWafer cell reached an open circuit voltage of 657mV, a short circuit current of 39.6mA/cm2 and a fill factor of 77%. A detailed analysis of the losses caused by stacking faults and cell process issues is presented. The resulting energy conversion efficiency of 20% proves the high efficiency potential of this material.

Recent progress in Ge and GeSn light emission on Si

Si-based optical interconnection is expected to solve the problems caused by electric interconnection with increasing the density of integrated circuits, due to its merits of high speed, high bandwidth, and low consumption. So far, all of the key components except light source of Si-based optical interconnection have been demonstrated. Therefore, the light source has been considered as one of the most important components. Ge and GeSn based on Si have emerged as very promising candidates because of their high compatibility with Si CMOS processing, and the pseudo direct-bandgap characteristic. The energy difference between the direct and indirect bandgap of Ge is only 136 meV at room temperature. Under tensile strain or incorporation with Sn, the energy difference becomes smaller, and even less than zero, which means that Ge or GeSn changes into direct bandgap material. What is more, using large n-type doping to increase the fraction of electrons in valley, we can further increase the luminous efficiency of Ge or GeSn. In this paper, we briefly overview the recent progress that has been reported in the study of Ge and GeSn light emitters for silicon photonics, including theoretical models for calculating the optical gain and loss, several common methods of introducing tensile strain into Ge, methods of increasing the n-type doping density, and the method of fabricating luminescent devices of Ge and GeSn. Finally, we discuss the challenges facing us and the development prospects, in order to have a further understanding of Ge and GeSn light sources. Several breakthroughs have been made in past years, especially in the realizing of lasing from GeSn by optically pumping and Ge by optically and electrically pumping, which makes it possible to fabricate a practical laser used in silicon photonics and CMOS technology.

Computational modeling and analysis of thermoelectric properties of nanoporous silicon

In this paper, thermoelectric properties of nanoporous silicon are modeled and studied by using a computational approach. The computational approach combines a quantum non-equilibrium Green's function (NEGF) coupled with the Poisson equation for electrical transport analysis, a phonon Boltzmann transport equation (BTE) for phonon thermal transport analysis and the Wiedemann-Franz law for calculating the electronic thermal conductivity. By solving the NEGF/Poisson equations self-consistently using a finite difference method, the electrical conductivity σ and Seebeck coefficient S of the material are numerically computed. The BTE is solved by using a finite volume method to obtain the phonon thermal conductivity kp and the Wiedemann-Franz law is used to obtain the electronic thermal conductivity ke. The figure of merit of nanoporous silicon is calculated by ZT=S2σT/(kp+ke). The effects of doping density, porosity, temperature, and nanopore size on thermoelectric properties of nanoporous silicon are investigated. It is confirmed that nanoporous silicon has significantly higher thermoelectric energy conversion efficiency than its nonporous counterpart. Specifically, this study shows that, with a n-type doping density of 1020 cm–3, a porosity of 36% and nanopore size of 3 nm × 3 nm, the figure of merit ZT can reach 0.32 at 600 K. The results also show that the degradation of electrical conductivity of nanoporous Si due to the inclusion of nanopores is compensated by the large reduction in the phonon thermal conductivity and increase of absolute value of the Seebeck coefficient, resulting in a significantly improved ZT.

Impact of compound doping on hole and electron balance in p-i-n organic light-emitting diodes

The fluorescent and phosphorescent p-i-n organic light-emitting diodes (OLEDs) with well controllable compound doping have been systematically investigated, where MoO3 and LiF are the effective p-type and n-type dopants, respectively. For both the bulk and interfacial doping, the hole and electron balance in the devices is found to be strongly dependent on the doping configuration, which could either facilitate or compromise the device power efficiency. The impact of the compound doping on the charge balance is further confirmed by the change of the emission region with different doping configuration. The modulation of p-type and n-type doping densities and position is thus essential for optimizing hole and electron balance in p-i-n OLEDs.

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.

Minority carrier lifetime and noise in abrupt molecular-beam epitaxy-grown HgCdTe heterostructures

The steady-state lifetime of photogenerated minority carriers has been investigated in heterostructure HgCdTe devices fabricated on molecular-beam epitaxy (MBE) grown material. A wider bandgap capping layer (Hg(1−x)Cd(x)Te, x = 0.44) was grown on a narrower bandgap absorbing layer (Hg(1−x)Cd(x)Te, x = 0.32, λco,80K = 4.57 µm) material in an uninterrupted MBE growth to create an abrupt heterointerface. Steady-state lifetime as a function of temperature over the range 80–300 K was extracted from photoconductive responsivity at an optical wavelength corresponding to the peak responsivity at that temperature. At 80 K, the photoconductors exhibit a specific detectivity of 4.5 × 1011 cm Hz−1/2W−1 (chopping frequency of 1 kHz). For each measurement temperature, the steady-state excess carrier lifetime determined experimentally was compared to the theoretical bulk lifetime for material with x = 0.32 and effective n-type doping density of 3.7 × 1014 cm−3. Theoretical calculations of the Auger-1 lifetime based on expressions developed by Pratt et al. were not able to account for the reduction in lifetime observed at temperatures above 180 K. Two approaches have been attempted to resolve this discrepancy: A semiempirical expression for Auger lifetime attributed to Meyer et al. was used to fit to the data, with the Auger coefficient γ as a fitting parameter. However, the resulting Auger coefficient found in this work is more than an order of magnitude higher than that reported previously. Alternatively, the reduction in effective lifetime above 180 K may be understood as a “loss” of carriers from the narrow bandgap absorbing layer that are promoted across the potential barrier in the conduction band into a low lifetime, wider bandgap capping layer. The reduction in lifetime as a function of inverse temperature for temperatures above 180 K may be fitted by a “cap lifetime” that has an activation energy equal to the change in bandgap across the heterostucture and scaled by a fitting constant.

Estimation of doping density in HgCdTe p-n junctions using scanning laser microscopy

Quantitative assessment of p- to n- type conversion due to reactive ion etching (RIE) of p-type Hg0.71Cd0.29Te is presented using laser-beam-induced-current (LBIC) measurements. For the RIE processing conditions used (390 mT, CH4/H2, 0.4 W/cm2), n-type conversion was observed in extrinsic arsenic-doped p-type Hg0.71Cd0.29Te which had previously undergone a Hg anneal to eliminate Hg vacancies. Effective doping density of the n-type converted region is determined by fitting a theoretically determined LBIC signature to the measured LBIC signal over a temperature range 80–300 K. Effective n-type doping density is the only fitting parameter used in the simulation, which was carried out using a commercial semiconductor device modeling package (SEMICAD™ DEVICE). This noncontact experimental technique promises to be a useful tool in the characterization of p-n junction diodes in HgCdTe, and for studying the precise nature of p to n conversion in p-type HgCdTe.