This article proposes a novel modeling approach for the analysis of the microwave power performance of GaN HEMTs. By combining Technology Computer-Aided Design (TCAD) physical and circuit design standard compact trap models, surface and buffer traps can be directly correlated, for the first time, with power-added efficiency (PAE) and output power ( $\textit{P}_\text{out}$ ). A new trap model topology is created with an RC subnetwork and nonlinear scaling functions, encouraged by TCAD analysis on trap localization. The effects of surface trapping were quantified using a TCAD-based extraction of the proposed trap model, observing a loss on $\textit{P}_\text{out}$ of 3 dBm and a maximum PAE ( $\text{PAE}_\text{MAX}$ ) loss of 12% due to surface traps. In addition, the correlation of 2-D electron gas (2DEG) at the drain access region with $\text{PAE}_\text{MAX}$ and the 1-dB compression point of $\textit{P}_\text{out}$ ( $\text{OP}_\text{1\,dB}$ ) is investigated and transformed into a correlation between the density of traps ( $\textit{N}_\text{T}$ ) and $\text{PAE}_\text{MAX}$ and $\text{OP}_\text{1\,dB}$ , creating a new direct method to connect TCAD with RF large-signal simulations.

We present first principles calculations of the interface between GaN and strained AlN, using a slab model in which polarization is compensated via surface fractional-charge pseudo-hydrogen atoms. We show that an interface two-dimensional carrier electron or hole gas emerges naturally in response to different compensating surface charges, but that this need not involve in-gap surface states.

The parasitic gate tunnelling of electrons into surface traps is shown to be responsible for the current collapse in GaN high electron mobility transistors. Simulations with and without surface traps are compared to pulsed output and gate leakage measurements and showed that the detrimental effect of surface traps is evident at positive gate voltages. Moreover, an apparent relationship between 2-dimensional electron density and Schottky reverse gate current is revealed in the presence of surface traps.

We demonstrate enhanced Andreev reflection in a Nb/InGaAs/InP-based superconductor-semiconductor hybrid device resulting in increased Cooper-pair injection efficiency, achieved by Cooper-pair tunneling into a semiconductor quantum well resonant state. We show this enhancement by investigating the differential conductance spectra of two kinds of samples: one exhibiting resonant states and one which does not. We observe resonant features alongside strong enhancement of Cooper pair injection in the resonant sample, and lack of Cooper pair injection in the nonresonant sample. The theoretical modeling for measured spectra by a numerical approach agrees well with the experimental data. Our findings open a wide range of directions in condensed matter physics and in quantum technologies such as superconducting light-emitting diodes and structures supporting exotic excitations.

Trap-induced dispersive effects play an important role in PAs and robust LNAs based on AlGaN/GaN-HEMTs. In this paper, the influence of scaling gate-source (GS) and gate-drain (GD) separation is studied through pulsed DC measurements and TCAD physical device simulations. In view of PA-applications, dynamic on-resistance and drain current in the knee region after high drain voltage stress are investigated. The de-embedding of pure scaling effects shows that adverse effects due to trapping are largely independent of the transistor GS/GD separation. Likewise, with regard to robust LNAs, the shift of threshold voltage under large negative gate voltages, typical for RF input overdrive conditions, shows a strong dependence on quiescent stress, but not on device scaling. This is in line with TCAD physical device simulations which suggest that trapping of electrons as well as the extension of the depletion region is affected mainly by the heterostructure and trap properties but not GS or GD separation. The findings aid RF designers to optimize the performance and reliability of GaN-MMICs for the specific application.

If neither traps nor a back-barrier is included in an ideal GaN heterojunction field-effect transistor, its performance is severely degraded by space charge limited current through the buffer layer. This effect is analyzed here by simulation, showing that it results in significant current leakage in the off state not only in short channel devices but also in long channel devices. The output resistance at saturation is also set primarily by space charge limited current through the buffer.

Conductive metal nitrides are widely used in the microelectronics industry as interconnects, thin film resistors, electrodes, and diffusion barriers. These films are commonly prepared by sputtering and chemical vapor deposition, which are suitable for planar geometries. However, conformal deposition onto 3D and complex structures requires the use of atomic layer deposition (ALD). In this work, we compare the electrical and structural properties of various metallic nitrides (namely, TiNx, ZrNx, HfNx, and TaNx) prepared by ALD from metalorganic precursor and H2/Ar plasma. Despite similar bulk resistivity values of these films, we find significant differences in their measured resistivity for the thin film (by ALD). TiNx and ZrNx show metallic behavior with a positive temperature coefficient of resistance (TCR), whereas HfNx and TaNx show semiconducting behavior with negative TCR values. Microstructure and film chemistry of deposited films are investigated by x-ray photoelectron spectroscopy and transmission electron microscopy, and the correlation between the electrical and structural parameters of the deposited films is discussed. It is shown that a high concentration of carbon contamination is related to smaller grain size and higher electrical resistivity. TiNx exhibits the lowest carbon contamination, largest degree of crystallinity and lowest resistivity (∼60 μΩ cm) highlighting its potential as ALD-grown metal. Other nitrides and their combinations can be used to tailor specific resistivity and TCR values for thin film resistor applications in 3D and complex geometries such as deep trenches. Overall, this study provides useful guidelines toward the development of ALD nitrides for use in the microelectronics industry.

Buffer traps in GaN RF heterostructure field-effect transistors (HFETs) provide a high dc output resistance on one hand but induce the current collapse effect on the other hand. Here, we show that traps do not merely confine the carriers into the channel, but serve to pin the Fermi level. Only by pinning the Fermi level a high saturated dc output resistance can be obtained in short channel devices. If carriers are confined into the channel by a back-barrier, and no traps are present, then short channel effects still severely reduce the saturated dc output resistance. In addition, we show that the buffer-related current collapse, which manifests as an output conductance under RF or pulse conditions, can straightforwardly be explained by a simple capacitive coupling model between the drain and the channel under the gate. The trapped charge under the gate results in a pulse voltage step-dependent shift in threshold voltage. Based on this picture, current collapse at pulsed condition can be approximately evaluated from dc simulations or from capacitance measurements.

The authors deposited titanium nitride (TiN) films by plasma-enhanced atomic layer deposition on various types of amorphous, polycrystalline, and single crystalline substrates and found that the crystallinity of the substrate strongly affects the morphology, orientation, and resistivity of the films. An appropriate substrate choice yields TiN films with bulk resistivity values of about ∼20 μΩ cm. The preferred crystallographic orientation of the films, either (111) or (001), does not affect film resistivity.

The large-signal RF power performance of an AlGaN/GaN heterostructure field-effect transistor (HFET) is simulated by technology computer-aided design (TCAD) software, and compared to measurement. A clear procedure for extraction of the simulation physical parameters is described. Trapping effects are included, but temperature effects are not. Good agreement between simulation and measurement is demonstrated, paving the way for efficiency optimization of GaN HFETs using TCAD.

Various applications in the rapidly growing field of quantum information science require reliable and effective quantum light sources. We proposed an efficient approach for generation of entangled photons, based on Cooper-pair luminescence in semiconductors, which does not require isolated emitters. Semiconductor quantum wells, remove the light-heavy-hole degeneracy, allowing efficient photon entanglement generation in simple electrically-driven structures, taking advantage of the superconducting macroscopic coherence [1]. We analyzed a new effect of enhanced light amplification in electrically-driven semiconductor-superconductor structures, including Cooper-pair based two-photon gain [2]. We also proposed a compact and highly-efficient scheme for a complete Bell-state analysis using two-photon absorption in a superconducting proximity region of a semiconductor avalanche photodiode [3]. This Cooper-pair based two-photon absorption results in a strong detection preference of a specified entangled state.

This data set includes a complete COMSOL simulation file, for the bending of a tapered InP/InAs core-shell structure. Also the manual curvature analysis of a nanowire, based on its TEM is shown.

We have evaluated the density of interface trap states (Dit) at the surface of a GaN/AlGaN/GaN heterojunction by the previously described gated van der Pauw experiments, as well as by a UV-assisted gated van der Pauw method, described in this paper. The obtained Dit values are about two orders of magnitude lower than the assumed by the surface-donor theory and three orders of magnitude lower than the required to compensate the polarization surface charge in GaN. Previous experimental studies using a variety of other techniques reported similarly low Dit values. We, hence, conclude that the variable midgap surface charge is not responsible for the formation of the 2-D electron gas, and cannot compensate for the large surface polarization charge in GaN. A yet unexplained polarization self-compensating (PSC) surface charge must be invoked to account for experiments. A few comments about the physical nature of the proposed PSC charge are provided.

Controlling nanomaterial shape beyond its basic dimensionality is a concurrent challenge tackled by several growth and processing avenues. One of these is strain engineering of nanowires, implemented through the growth of asymmetrical heterostructures. Here, we report metal–organic molecular beam epitaxy of bent InP/InAs core/shell nanowires brought by precursor flow directionality in the growth chamber. We observe the increase of bending with decreased core diameter. We further analyze the composition of a single nanowire and show through supporting finite element simulations that strain accommodation following the lattice mismatch between InP and InAs dominates nanowire bending. The simulations show the interplay between material composition, shell thickness, and tapering in determining the bending. The simulation results are in good agreement with the experimental bending curvature, reproducing the radius of 4.3 µm (±10%), for the 2.3 µm long nanowire. The InP core of the bent heterostructure was found to be compressed at about 2%. This report provides evidence of shape control and strain engineering in nanostructures, specifically through the exchange of group-V materials in III–V nanowire growth.

Zincblende-wurtzite polytypism in III-V nanowires has been of great interest for a long time. However, full understanding and control over the crystal phase is still lacking. Here, we propose a model for the morphologies and related crystal phases of vapor-liquid-solid III-V nanowires by considering the minimum surface energies of different side wall facets as a function of the droplet contact angle. On the basis of the recent experimental data and earlier theoretical calculations of the surface energies, a simple classification of the possible growth modes is presented. It shows that the wurtzite phase forms in vertical nanowires at intermediate contact angles whereas the zincblende phase is predominant for vertical or inverse-tapered nanowires with a truncated top at larger contact angles. The small stable contact angle corresponds to faulted wurtzite zincblende intermix. Pure zincblende phase is possible for even smaller contact angles only in the kinetic growth regimes. The wurtzite and zincblende domains are highly sensitive to surface energetics. Using the model, we explain why most gold-catalyzed GaAs nanowires are wurtzite whereas most gallium-catalyzed GaAs nanowires are zincblende and why it is more difficult to obtain pure wurtzite GaP nanowires. We present experimental data on such GaP NWs grown by gold-catalyzed metal organic molecular beam epitaxy and interpret them within the model. Overall, the proposed picture gives a clear route for the crystal phase engineering in III-V nanowires.

The authors report on the properties of various conductive nitride (TiN, ZrN, and TaN) films prepared by plasma enhanced atomic layer deposition using either quartz or sapphire inductively coupled plasma (ICP) sources. Different reactive gases (N2, NH3, and H2) and various pressures during the plasma half-cycle were examined. The sapphire based ICP source enabled higher deposition rates, better crystallization, lower film resistivity, and lower oxygen contamination. The effect of the ICP source material depends strongly on the reactive gas species and pressure. Optimal deposition conditions for both ICP source materials are determined.

Direct bandgap wurzite (WZ) GaP nanowires (NWs) are projected as a non-nitride solution to the green gap in the LED technology. Here, we report on the growth of 5 μm long pure WZ GaP NWs having a diameter of 200 nm by a two-step core-clad approach. Transmission electron microscopy indicates the absence of any planar defects in the NWs. The low temperature photoluminescence (PL) spectrum of the NWs differs markedly from their non-pure counterparts, previously reported. From the PL spectrum, the bandgap of wurtzite GaP at 10 K is 2.13 eV. This value differs from previously reported values.

The authors report on the role of various reactive gases on the structure and properties of TiN thin films prepared by plasma enhanced atomic layer deposition (PEALD) from tetrakis(dimethylamido)titanium. The reactive gas plays an important role determining the film structure and properties. Nitrogen-based plasma (N­2 and NH3) resulted in low oxygen (∼3%) and carbon (∼2%) contamination and well-defined columnar grain structure. A nitrogen excess (∼4%) was found in the films deposited using N2 plasma. The stoichiometric films and lowest resistivity (∼80 μΩ cm) were achieved using NH3 plasma. Deposition using H2 plasma resulted in higher carbon and oxygen contamination (∼6% for each element). The reactive gas also plays an important role in determining the grain size and preferential orientation. By varying the plasma chemistry, either (111) or (100) oriented films can be obtained. A mechanism determining the PEALD TiN preferential orientation is proposed. Finally, plasma induced degradation of the underlying dielectric layer is evaluated.

We experimentally demonstrate Cooper-pair injection into a superconducting light-emitting diode by observing Andreev reflection at the superconductor-semiconductor interface, overcoming the contradicting requirements of an electrically transparent interface and radiative recombination efficiency. The device exhibits electroluminescence enhancement at the quasi-Fermi energy at temperatures below Tc. The theoretically predicted conductance and electroluminescence spectra based on Cooper-pair injection into the semiconductor correspond well to our experimental results. Our findings pave the way for practical superconductor-semiconductor quantum light sources.

We have evaluated the density of interface trap states ( ${D}_{textsf {it}}$ ) at the surface of a GaN/AlGaN/GaN heterojunction by the previously described gated van der Pauw experiments, as well as by a UV-assisted gated van der Pauw method, described in this paper. The obtained ${D}_{textsf {it}}$ values are about two orders of magnitude lower than the assumed by the surface-donor theory and three orders of magnitude lower than the required to compensate the polarization surface charge in GaN. Previous experimental studies using a variety of other techniques reported similarly low ${D}_{textsf {it}}$ values. We, hence, conclude that the variable midgap surface charge is not responsible for the formation of the 2-D electron gas, and cannot compensate for the large surface polarization charge in GaN. A yet unexplained polarization self-compensating (PSC) surface charge must be invoked to account for experiments. A few comments about the physical nature of the proposed PSC charge are provided.