Delta-doped Layers Research Articles

Improving luminescence response in ZnGeN2/GaN superlattices: defect reduction through composition control

Color-mixed (cm) light-emitting diodes (LEDs) are theoretically the most efficient white light emitters, projected to improve white light luminous efficacy by 34% compared to incumbent phosphor converted LEDs. Since white light technology is pervasive and essential, small improvements in LED technology can result in energy savings. However, cm-LEDs are not yet realized due to poor efficacy in green and amber emitting materials, a spectral region colloquially referred to as the Green Gap. ZnGeN2 is nearly isostructural and closely lattice-matched to GaN and can be heteroepitaxially integrated with existing GaN devices; ZnGeN2/GaN hybrid structures are theorized to emit green (~530 nn) light with a spontaneous emission rate 4.6–4.9 times higher than traditional InGaN LEDs when incorporated into III-N LED structures. In this report we demonstrate the molecular beam epitaxy (MBE) growth of GaN and ZnGeN2 superlattices, an important step towards realizing multiple quantum well structures required for efficient LEDs. Elemental analysis, including atom probe tomography, shows that Ga and Ge are observed in both ZnGeN2 and GaN layers, degrading the structural uniformity. The lack of elemental abruptness also leads to increased defect luminescence and reabsorption of band edge luminescence. The source of unintentional Ga distributed throughout the ZnGeN2 layers was identified as excess flux escaping from around the closed MBE shutter. The source of unintentional Ge, which tended to incorporate as a single delta-doped layer in GaN, was identified as Ge riding along the cyclical metal-rich Ga adlayer used for high quality GaN, incorporating during subsequent nitrogen-rich growth step. Modifying the growth strategy results in improved structural quality, elemental abruptness, and luminescence response. This realization of structurally and elementally abrupt interfaces demonstrates the potential of heteroepitaxially integrated binary and ternary nitrides for energy-relevant devices.

Improvement of p-type ohmic contact of GaN laser diodes by using delta-doped p-GaN contact layer

The p-type ohmic contact of GaN laser diodes has been optimized in several ways. The heavily doped p-GaN contact layer obtained by using delta-doping method, which effectively suppressed the self compensation effect of Mg ions during the heavy doping. By optimizing the delta-doping period, temperature, and thickness of the p-GaN contact layer, the activation energy of Mg atoms is reduced, and the hole concentration in the surface contact layer is further increased. Finally, the specific contact resistivity of the p-type ohmic contact of the GaN laser, measured more accurately by using the transmission line module, was successfully reduced to the order of 1E-3 Ω cm2.

Field effect two-dimensional electron gases in modulation-doped InSb surface quantum wells

We report on transport characteristics of field effect two-dimensional electron gases (2DEGs) in surface indium antimonide quantum wells. The topmost 5 nm of the 30 nm wide quantum well is doped and shown to promote the formation of reliable, low resistance Ohmic contacts to surface InSb 2DEGs. High quality single-subband magnetotransport with clear quantized integer quantum Hall plateaus is observed to filling factor ν = 1 in magnetic fields of up to B = 18 T. We show that the electron density is gate-tunable, reproducible, and stable from pinch-off to 4 ×1011 cm−2, and peak mobilities exceed 24 000 cm2/V s. Large Rashba spin–orbit coefficients up to 110 meV ·Å are obtained through weak anti-localization measurements. An effective mass of 0.019me is determined from temperature-dependent magnetoresistance measurements, and a g-factor of 41 at a density of 3.6 ×1011 cm−2 is obtained from coincidence measurements in tilted magnetic fields. By comparing two heterostructures with and without a delta-doped layer beneath the quantum well, we find that the carrier density is stable with time when doping in the ternary Al0.1In0.9Sb barrier is not present. Finally, the effect of modulation doping on structural asymmetry between the two heterostructures is characterized.

High-Mobility Magnetic Two-Dimensional Electron Gas in Engineered Oxide Interfaces

The engineered interfaces of complex oxides have abundant physical properties and provide a powerful platform for the exploration of fundamental physics and emergent phenomena. In particular, research on the two-dimensional magnetic systems with high mobility remains a long-standing challenge for the discovery of quantum phase and spintronic applications. Here, we introduce a few atomic layers of the delta doping layer at LaAlO3/SrTiO3 interfaces through elaborately controllable epitaxial growth of SrRuO3. After inserting a SrRuO3 buffer layer, the interfaces exhibit a well-defined anomalous Hall effect up to 100 K and their mobility is enhanced by 3 orders of magnitude at low temperatures. More intriguingly, a large unsaturated positive magnetoresistance is created at interfaces. Combining with the density functional theory calculation, we attribute our findings to the electron transfer at interfaces and the magnetic moment of Ru4+ 4d bands. The results pave a way for further research of two-dimensional ferromagnetism and quantum transport in all-oxide systems.

Electric current paths in a Si:P delta-doped device imaged by nitrogen-vacancy diamond magnetic microscopy

The recently-developed ability to control phosphorous-doping of silicon at an atomic level using scanning tunneling microscopy, a technique known as atomic precision advanced manufacturing (APAM), has allowed us to tailor electronic devices with atomic precision, and thus has emerged as a way to explore new possibilities in Si electronics. In these applications, critical questions include where current flow is actually occurring in or near APAM structures as well as whether leakage currents are present. In general, detection and mapping of current flow in APAM structures are valuable diagnostic tools to obtain reliable devices in digital-enhanced applications. In this paper, we used nitrogen-vacancy (NV) centers in diamond for wide-field magnetic imaging (with a few-mm field of view and micron-scale resolution) of magnetic fields from surface currents flowing in an APAM test device made of a P delta-doped layer on a Si substrate, a standard APAM witness material. We integrated a diamond having a surface NV ensemble with the device (patterned in two parallel mm-sized ribbons), then mapped the magnetic field from the DC current injected in the APAM device in a home-built NV wide-field microscope. The 2D magnetic field maps were used to reconstruct the surface current densities, allowing us to obtain information on current paths, device failures such as choke points where current flow is impeded, and current leakages outside the APAM-defined P-doped regions. Analysis on the current density reconstructed map showed a projected sensitivity of ∼0.03 A m−1, corresponding to a smallest-detectable current in the 200 μm wide APAM ribbon of ∼6 μA. These results demonstrate the failure analysis capability of NV wide-field magnetometry for APAM materials, opening the possibility to investigate other cutting-edge microelectronic devices.

(Digital Presentation) Strong Room-Temperature EL Emissions from Strained Sige/Ge-on-Si (111) LEDs

Introduction In recent years, encryption technology has become more and more important, and the method to use the circular polarized light in optical communications has been proposed. Spin LEDs are expected as on-chip circular polarized light generating devices, and we have been focusing on a Ge as an active material because it is capable of being monolithically integrated on a Si substrate and emitting light in the telecommunications wavelength band. Particularly, the (111) surface orientation of Ge allows for the epitaxial growth of high-quality ferromagnetic materials on Ge, making it possible to inject spin-polarized electrons from ferromagnetic materials into Ge (111) [1]. Furthermore, it has been proven that the use of strained-SiGe can increase the spin lifetime because of its ability to suppress intervalley scattering [2]. In this study, we fabricate strained-SiGe/Ge-on-Si (111) LEDs and obtain very strong EL emissions at room temperature. Experimental The sample was prepared using a solid source molecular beam epitaxy (MBE). First, a high-quality tensile-strained Ge layer was grown on a Si (111) substrate using two-step growth method, where a Ge buffer layer of 40 nm was grown on a p-type Si (111) substrate at a temperature of 350℃ and a Ge layer of 500 nm was grown at 700℃. Secondly, a Si0.15Ge0.85 layer of 40 nm and a P-doped Ge layer of 500 nm were grown at lower temperature of 350℃ to prevent relaxation of the SiGe. After the growth of the p-i-n structure, a P delta-doping layer of 2×1014 cm-2 was inserted to obtain a low resistivity Ohmic contact. Before P delta-doping, an ultra-thin Si (UT-Si) layer of 2 monolayers was inserted in order to avoid surface segregation of P atoms [3]. Finally, 7 nm thick Ge was grown for the capping. The fabricated multilayers were defined into a mesa diode by photolithography and reactive ion etching. AuSb and AuGa were deposited as top and back contacts, respectively. Results and Discussions Current-voltage output characteristics were evaluated and good diode characteristics were obtained. Figure 1 shows the room temperature EL spectra for the Si0.15Ge0.85/Ge LEDs with various injected currents. It was found that strong EL emissions covering the communication wavelength band of 1500-1600 nm was obtained. The EL peak intensity increases with the injected current and it is drastically enhanced above 350 mA as shown in inset of Fig. 1. We consider that recombination efficiency can be improved by the strained Si0.15Ge0.85 layer. While exact light emission wavelengths cannot be known with the current experiments due to the detector upper limit, characterizations in the longer wavelength range are now under investigation. Moreover, we expect further enhancements of EL intensity by introducing Si0.15Ge0.85/Ge multiple quantum wells in the active layer. It is also expected that by changing compositions of Si and Ge in SiGe, we can control the emission wavelength range, indicating that the SiGe/Ge LEDs are very attractive for application to on-chip circular polarized LEDs.This work was supported in part by Grant-in-Aid for Scientific Research (19H02175, 19H05616, 20K21009) from MEXT, Japan.[1] K. Hamaya et al., J. Phys. D: Appl. Phys. 51, 393001 (2018).[2] T. Naito et al., Phys. Rev. Appl. 13, 054025 (2020).[3] M. Yamada et al., Appl. Phys. Lett. 107. 132101 (2015). Figure 1

Interfacial charge analysis and temperature sensitivity of germanium source vertical tunnel FET with delta-doped layer

The influence of interface trap charges (ITCs) and reliability of the Germanium source vertical tunnel field effect transistor with delta-doped layer (GSDD vTFET) is investigated in this paper. The analysis is carried out on the GSDD vTFET by evaluating the analog/RF performances under the consideration of donor and acceptor ITCs and temperature variations. The presence of interface trap charges at the silicon channel/gate oxide interface changes the flat-band voltage, affecting the analog and RF performances of the GSDD vTFET. The study is carried out at distinctive donor and acceptor interface trap charges. The findings indicate that as the interface trap charge densities increases, the device's output changes drastically. The off-state current of the GSDD vTFET deteriorates significantly from an order of 10−14 A to 10−8 A in the presence of positive ITC of 1012/cm2. The temperature variations over a wide range shows that OFF-state current as well as subthreshold region gets deteriorated due to dominance of Shockley–Read–Hall effect and the superthreshold region is less affected owing to dependence of band-to-band tunneling. The results reveal that when the temperature is raised from 200 K to 400 K, the ION/IOFF current ratio degrades tremendously from ~1014 to ~108 in the existence of donor ITC. It is also observed that the GSDD vTFET is less susceptible to acceptor interface trap charge in comparison with donor ITC in a temperature sensitive environment. Quantum correction (QC) of GSDD vTFET with ITC shows the same type of variations as the condition without considering QC.

Investigation on Effect of Doped InP Subchannel Thickness and Delta-Doped InP Layer of Composite Channel HEMT

DC performances of a depletion-mode 100-nm In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As/InP composite channel InP-based high-electron-mobility transistor (HEMT) is investigated by using numerical simulation. The transfer, output, and breakdown characteristics of different doped InP subchannel thickness In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As/InP composite channel HEMT are compared. Decreasing the thickness of the doped InP subchannel from 10 to 5 nm results in a decline of the output current. However, the threshold voltage is increased from −0.77 to −0.6 V and the breakdown voltage is improved from 1.99 to 5.69 V at bias of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{{\mathrm {gs}}}-{V}_{{\mathrm {t}}} = -0.5$ </tex-math></inline-formula> V. To enhance the breakdown characteristic of In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As/InP composite channel HEMT, we minimize the thickness of the doped InP layer and replace the doped InP layer with the delta-doped layer. The structure is compared with the conventional double delta-doped structure in the performance of transfer, output, and breakdown characteristics. At ON-state, the electrons of two kinds of structure concentrate in the InGaAs channel. The output current and the threshold voltage of the composite channel structure are at the same level compared with the conventional double delta-doped structure. However, at OFF-state, because of the transfer of electrons into the InP subchannel, part of electric potential will not be concentrated at the drain side of the gate region but distributed in other area of the channel. A higher drain voltage is required to achieve electric field strength enough to breakdown and the breakdown voltage is improved obviously.

High hole mobility in boron delta-doped layers in diamond: why it is not achieved as yet and how it can be achieved

The required parameters of nanometer boron delta-doped layers in diamond for achieving high conductivity and hole mobility are calculated. The boron concentration in such layers has to be sufficient to achieve the insulator--metal phase transition, i. e. metallic conductivity. Then, it is demonstrated that taking into account valence band edge energy shift due to the presence of ionized boron atoms leads to the significant deepening of the potential well formed by the delta-doped layer for holes. It results in much stronger hole confinement than it was expected before. Thus, it is predicted that a significant delocalization-induced increase of hole mobility can be achieved if metallic boron delta-doped layer thickness is of order and smaller than 0.5 nm and compensation ratio does not exceed 42%. Keywords: delta-doped layers, nanostructures, diamond films chemically deposited from the vapor phase, hole mobility, insulator-metal phase transition.

Analytical modeling and simulation of a triple metal vertical TFET with hetero-junction gate stack

In this paper, a new 2D analytical model for surface potential of a gate stacked triple metal Vertical TFET with n + delta doped layer (δ-doped n + SiGe GS-TMG-VTFET) is presented. The parabolic approximation process is used to solve the Poisson equation in terms of channel surface potential and electrical field respectively. The proposed method consists of a dual modulation effect that controls the surface potential at both the interface of the source and drains with the channel. This structure comprises SiO2 and HfO2 as gate-stacked materials to extend the control of the gate terminal over the channel. In addition, the proposed TMG-VTFET outperforms the surface potential results in terms of input and output characteristics like gate-source voltage (VGS) and drain-source voltage (VDS), gate oxide, and SiGe mole fraction. Finally, we obtained the expression of the channel surface potential, which involves the biasing variation of source and drain terminal. Our proposed model is accounting the variable of kane model in respect to extract the drain current characteristics. It can be modeled by integrating band-to-band tunneling generation rate using suitable boundary conditions. Now, efficiency of the proposed model for both the surface potential and drain current has been confirmed by comparing its analytical outcomes with the TCAD results.

Design and Analysis of Triple Metal Vertical TFET Gate Stacked with N-Type SiGe Delta-Doped Layer

Design and Analysis of Triple Metal Vertical TFET Gate Stacked with N-Type SiGe Delta-Doped Layer

Study on induced work-function variation of titanium metal gate on various electrical parameters for delta-doped layer germanium source vertical tunnel FET

Workfunction variation (WFV) in a high-k/titanium metal gate stack vertical tunnel field-effect transistor (FET) with a delta-doped layer in the germanium source is explored using technology computer-aided design simulations. The field-induced quantum confinement effect is also evaluated for the vertical tunnel FET. The impact of the gate area on various electrical parameters such as the ON-current (σION), OFF current (σIOFF), current ratio [σ(ION/IOFF)], subthreshold swing (σSS), threshold voltage (σVT), and analog performance parameters such as the total gate capacitance (σCgg), transconductance (σgm), and cutoff frequency (σfT) due to WFV of the titanium gate metal is evaluated. The results show that the variability in ION and IOFF increases when decreasing the overall transistor gate area for different metal grain sizes. In addition, the variations in the subthreshold swing and threshold voltage also decrease for a larger gate area. The distributions of the electrical parameters show that, when the grain size is comparable to the gate dimension, the distribution is not Gaussian bounded. In addition, the plot of the ratio of the average grain size to the gate area reveals that a slope of more than ~ 120 mV is attained.

Delta-doped β-(AlxGa1−x)2O3/Ga2O3 heterostructure field-effect transistors by ozone molecular beam epitaxy

Heterojunction field-effect transistors based on the β-(AlxGa1−x)2O3/Ga2O3 heterostructure grown by ozone-assisted molecular beam epitaxy were demonstrated for the first time. Al composition ratios in the 14%–23% range were validated using x-ray diffraction on the three samples grown for this study. Electrochemical capacitance-voltage (ECV) measurements showed the presence of a charge sheet in the delta-doped (AlxGa1−x)2O3 barrier layer. Secondary ion mass spectroscopy and ECV measurements also revealed an unintentional Si peak at the (AlxGa1−x)2O3/Ga2O3 interface. Direct current (IDS-VGS) and transconductance (Gm-VGS) measurements demonstrated depletion-mode transistor operation as well as the presence of a parallel conduction channel. A one-dimensional Poisson model suggested that dopant redistribution in the delta-doped region could cause a secondary channel to form in the barrier in addition to the primary channel near the (AlxGa1−x)2O3/Ga2O3 interface under certain conditions met in these samples. Fabricated devices on sample A did not exhibit breakdown up to the measurement limit of 1100 V, with stability after ten cycles. A maximum output drain current density of 22 mA/mm was measured on sample B. Room temperature Hall measurements yielded a sheet carrier density of 1.12 × 1013 cm−2 with corresponding Hall mobility of 95 cm2/V s in sample C.

Investigation of silicon-vacancy center formation during the CVD diamond growth of thin and delta doped layers

A study of the process of diamond doping with silicon during CVD growth is presented. As a result, for the first time, a silicon-doped delta layer with a thickness of 5 nm and a depth localization accuracy of several nanometers was demonstrated.

High Performance and Reliability Analysis of Implant Free Composite Channel In0.53Ga0.47As/InAs/In0.53Ga0.47As Delta-Doped MOSFET

A new approach for implementation of implant free In0.53Ga0.47As/InAs/In0.53Ga0.47As composite delta-doped stepped poly gate MOSFET is one of the challenging devices due to their inherent advantages of large electron mobility as a comparison with conventional bulk MOSFETs. The minimization of the defect density and border traps at the channel interface, due to the InP layer is one of the attractive features of this proposed buried channel MOSFET. So, the channel mobility will be very high due to a high thermally stable oxide semiconductor interface. As results, low leakage current is observed. Further, the proposed device offers a high driving current in extending to the low energy bandgap due to the addition of the delta-doped layer in the channel region. In this work, the electrostatic behavior along with the RF and linearity performance of 15 nm gate length stepped poly gate In0.53Ga0.47As/InAs/In0.53Ga0.47As buried composite channel using delta layer is investigated using 2D TCAD tool. The comparison has been done between stepped poly gate (SG) MOSFET and composite delta (δ) doped stepped poly gate (CDSG) MOSFET, to validate the advantages of the proposed structure for the realization of low power and high frequency applications.

Study of effect of oxide thickness variation on electrical parameters and high frequency characteristics induced by work-function variation for delta-doped germanium-source vertical TFET

In this paper, we use a 3D technology computer-aided design device simulator to conduct an investigation into the impact on oxide thickness variation, based on parameters, such as threshold voltage (σV TH), subthreshold swing (σSS), on current (σI ON), off current (σI OFF), current ratio σ(I ON/I OFF), transconductance (σg m), total gate capacitance (σC gg), and cut-off frequency (σf T), induced by Titanium nitride (TiN) metal gate/high-κ stack work-function variability (WFV) in a delta-doped layer Germanium-source vertical tunnel field-effect transistor (vTFET). We note that WFV has a substantial impact on electrical parameters as well as high frequency characteristics, in relation to gate insulator thickness variation. The distribution of V TH is nearly Gaussian for smaller metal grain sizes, whereas it appears bi-modal for larger grain sizes. However, the average effect has an insignificant impact on the WFV-induced threshold-voltage variation for vTFET architectures.

Novel Ultra Localized and Dense Nitrogen Delta-Doping in Diamond for Advanced Quantum Sensing.

We introduce and demonstrate a new approach for nitrogen-vacancy (NV) patterning in diamond, achieving a deterministic, nanometer-thin, and dense delta-doped layer of negatively charged NV centers in diamond. We employed a pure nitridation stage using microwave plasma and a subsequent in situ diamond overgrowth. We present the highest reported nitrogen concentration in a delta-doped layer (1.8 × 1020 cm-3) while maintaining the pristine diamond crystal quality. This result combined with the large optically detected magnetic resonance contrast can pave the way toward highly sensitive NV-based magnetometers. We further employed this delta-doping technique on high-quality fabricated diamond nanostructures for realizing a topographic NV patterning in order to enhance the sensing and hyperpolarization capabilities of NV-based devices.

Optical investigation of as-grown NV centers in heavily nitrogen doped delta layers in CVD diamond

In this paper, we realize growth of the delta doped layer (3 nm thick) with high concentration of nitrogen atoms (about 1.4 × 1019 cm−3) during CVD diamond growth process. We experimentally investigate the distribution of the nitrogen inside the grown layer and formation of the NV centers during such growth. Using confocal microscopy, we analyze the spatial distribution of the NV centers and investigate the formation efficiency of the NV centers in delta doped layers. The spatial distribution is measured by two methods, using second-order correlation function and emission volume analysis, and NV center concentration is found to be 3.9 ± 0.6 and 2.7 ± 0.2 μm-2 consequently. The divergence between the methods is discussed. As-grown NV centers formation efficiency was found to be 30 times lower than in the case of uniform doped diamond growth. Nevertheless, coherence time of an electron spin for a single NV center inside the delta layer was found to be around 1 μs which is quite reasonable given the concentration of the nitrogen in the sample.

Temperature performance of InGaAs/InGaAlAsTemperature performance of InGaAs/InGaAlAs laser diodes with δ-doping active region

The optical gain performance of 1530-1565 nm laser diodes with active regions containing p-doped barrier layers has been investigated. We have studied the threshold current density and differential quantum efficiency in wide temperature range and compared modal gain behaviour of laser diodes made of heterostructure with delta-doped barrier layers by carbon at level of 1012 cm-2 and heterostructure with undoped barrier layers.

Electrothermal Characteristics of Delta-Doped $\beta$ -Ga2O3 Metal–Semiconductor Field-Effect Transistors

A 2-D electrothermal model of delta-doped b eta-gallium oxide ( $\beta $ -Ga2O3) metal–semiconductor field-effect transistor (MESFET) is developed by using TCAD Sentaurus to investigate its electrical and thermal characteristics. The temperature and electric field-dependent electron mobility model is incorporated to predict I – V characteristics of the FET, which are in good agreement with the measured I – V characteristics. We investigated the effect of bias voltages on an electric field, a current path, a volumetric heat generation profile, and a peak temperature at a given total heat dissipation. The peak temperature is observed to be significantly different at the same power dissipation but different bias conditions, e.g., the peak temperature is ~9 K higher when the drain-to-source voltage ( V ds) = 25 V and the gate-to-source voltage ( V gs) = −6 V compared with V ds = 8.3 V and V gs = 2 V at the total power dissipation of 1.16 W/mm. This difference is attributed to the change in the electron Joule heating profile with the applied bias voltage. The effects of the location of the delta-doping layer, the gate–drain spacing, and the source–drain spacing are investigated to guide a future device fabrication. The variation in these parameters mainly affects electrical characteristics such as ON-resistance, saturation current, threshold voltage, and so on. The thermal characteristics, such as peak temperature, temperature profile, and so on, are not significantly affected at a low-power dissipation.