This study presents a refined approach to computing the electronic structure of indium antimonide (InSb) using advanced ab initio techniques with the In and Sb 4d10 semicore electrons included in the valence states. These states are modeled using fully relativistic projector augmented waves (PAW) and optimized norm-conserving Vanderbilt (ONCV) pseudopotentials. However, standard Kohn-Sham density-functional theory (DFT) calculations with these pseudopotentials often produce nonphysical band inversions and incorrect band gaps at the P point because of 5p-4d repulsion and self-interaction errors (SIE). To resolve these issues, we apply a combination of hybrid Heyd-Scuseria-Ernzerhof (HSE) exchange-correlation (XC) functionals, many-body perturbation theory (MBPT) via quasiparticle G0W0, and DFT + U, significantly improving the accuracy of the band structure over previous studies. A Bayesian optimization framework is used to refine key parameters, including the inverse screening length (mu) and Hartree-Fock (HF) exchange fraction (alpha) in HSE-based XC functionals, as well as the Hubbard U parameters in DFT + U, leading to significantly improved band structure predictions. This approach yields highly precise band gaps, bulk moduli, effective masses, Luttinger parameters, valence bandwidth, and 4d band positions, achieving unprecedented agreement with experimental data. The resulting model resolves a long-standing incomplete description of InSb's electronic band structure and provides a transferable computational framework for accurate electronic structure predictions across diverse material systems, offering valuable insights for future electronic, optoelectronic, and quantum applications.

The frequency band of the electromagnetic spectrum between microwaves and infrared is nowadays defined as the Terahertz band (1 THz corresponds to 1012 Hz). The development of specific applications for this area requires the use of devices able to operate (for instance, as emitters, detectors, amplifiers, etc.) in this domain of extremely high frequencies. For this purpose, it is necessary to cleverly combine favourable materials and charge transport properties with specific physical mechanisms and appropriate device topologies in order to reach electrical operation in conditions that, with respect to standard electronics, can be considered as extreme. Alternative strategies (not treated in this chapter) involve either the use of optical devices or a combination of electrical and optical systems. Here, we present an overview of the main electronic devices used for applications in the Terahertz frequency domain subdivided into two-terminal devices (such as Gunn, Schottky and resonant-tunnelling diodes) and three-terminal devices (such as field-effect, heterojunction bipolar and complementary metal oxide semiconductor transistors). A section devoted to non-conventional devices exploiting ballistic transport concludes the survey.

The integrated THz pattern over any MMIC appears to be a good opportunity to enclose calibration kit suitable for accurate measurements. An original technology based on polymer has been developed. Sub-millimeter single-mode conductor-backed coplanar waveguides using benzocyclobutene polymer and interconnecting via between ground planes are processed and measured up to 760 GHz. The experimental performances show good agreement with analytical and numerical modeling. A two-tier Thru-Reflect-Line correction and a square root of Thru de-embedding are applied to extract the attenuation factor of about 3 dB/mm at 600 GHz, the relative phase velocity to light of about 0.716 and the characteristic impedance around 50 omega. The fundamental propagating mode remains unique in this wide frequency range, enabling this technological to be integrated over existing circuit for THz applications. The loss performance of the coplanar waveguide ranges in the state-of-the-art opening the road for fully integrated THz circuits.

In this paper the design, measurements and retro-simulations of a 110-GHz 5 th -order Chebyshev filter, based on substrate integrated waveguide in a $30-\mu\mathrm{m}$ thick BenzoCycloButene (BCB) above-IC technology, are presented. A center frequency of 101.5 GHz, corresponding to a 8.5-GHz frequency shift towards low frequencies, and 11.8% of fractional bandwidth are measured. The filter presents 4.6-dB of insertion loss and a low return loss of 17.5 dB in the passband. Thanks to optical profilometer measurements, a deformation of the top metallic cover of the SIW structures was observed. Electromagnetic simulations taking this top surface deformation into account allows recovering the measured filter behaviour with the center frequency shift. Thus, this BCB above-IC technology seems promising for the design of passive circuits at higher frequencies, at which substrate heights of $30\ \mu\mathrm{m}$ are more appropriate.

We investigate the use of an InP-based double-heterojunction bipolar transistor as a detector for wireless communications around 300~GHz. The sensitivity of the detector, along with its complex output impedance are characterized for a transistor (un)coupled to a log-spiral antenna, at different biases. A real-time uncompressed high-definition video signal is successfully transmitted at 1.5 Gbps in a heterodyne configuration.

This paper introduces an experimental characterization of substrate integrated waveguide (SIW) components integrated in a benzocyclobutene-based interposer for WR10-band applications. High performance SIWs were experimentally validated, with a measured attenuation constant of 0.39 dB/mm and a quality factor of 27 at 90 GHz. The attenuation constant remains equal to 0.4 dB/mm between 85 GHz and 110 GHz and the quality factor reaches 40 in the upper end of the band. These results show the benefits offered by using benzocyclobutene 3D packaging for the realization of high performance passive circuits with lower cost and higher electrical performance as compared to standard CMOS technologies and concurrent packaging technologies.

A straight front face constrained lens is used to excite a leaky-wave antenna (array of slots) at 300 GHz. The supporting polymer of the antennas is Benzocyclobutene (BCB). The lens is fabricated using substrate integrated waveguide (SIW) technology, while the radiating slots are etched on the polymer by photolithography. Numerical results show a reflection coefficient lower than -15 dB and a realized gain larger than 15 dBi over a 20% fractional bandwidth, spanning from 260 GHz to 330 GHz. The antenna efficiency is estimated equal to 25% by taking into account dielectric and conductive losses.

Conductor-backed coplanar waveguide on 30-μm-thick BCB polymer is fabricated. In order to eliminate unwanted propagation modes for these lines designed for frequencies up to 1 THz, electroplated vias interconnect each coplanar ground to the backed conductor. Transmission line properties are extracted here up to 67 GHz, showing a characteristic impedance of about 50 Ω, but with high conduction losses for this frequency range due to the thin metal layer used. Thru-reflect-line correction and a de-embedding with electrical circuit of accesses are applied to extract line properties. The comparison with a coplanar waveguide model leads to a relative permittivity of 2.676 for the BCB in this low-frequency range.

A process for microelectronic technology is developed for integration of passive devices with existing active device technology for submillimeter wave and THz frequency range applications. Performances of a conductor-backed coplanar waveguide on BCB polymer and interconnecting via between ground planes are presented up to 67 GHz with a 50 Ω characteristic impedance and a BCB relative permittivity of 2.676.

We present a reliable technique to model the influence of DC current-crowding in bipolar transistors on the variation of emitter width (W-E,W-ef) as a function of collector current density (J(C)) in silicon-germanium-carbon heterojunction bipolar transistors (SiGe:C HBTs). This method avoids using geometrical assumptions that may be invalid for highly scaled devices. We point out that according to the scientific literature consulted, this is the first time that the evolution of W-E,W-ef with J(C) extracted from measurements of S-parameters, high frequency noise and small-signal electric modelling is reported for a bipolar transistor technology (homojunction or heterojunction). The investigated SiGe:C HBTs have eight different base layer configurations, varying in base doping level and Ge content. The results show that W-E,W-ef decreases with J(C) for all devices. This behaviour is directly linked to the current-crowding effect. The procedure was used to identify the base configuration layer from the batch of eight SiGe:C HBTs that minimized current-crowding. This method could be applied to state-of-the-art SiGe:C HBTs to determine the base layer technological configuration that mitigates current-crowding and improves the reliability of SiGe:C HBTs. Finally, knowledge of the effective emitter width as a function of bias opens the road to thoroughly analyse the self-heating impact on ultra-fast SiGe:C HBTs.

Before designing a detector circuit, the electrical parameters extraction of the Schottky diode is a critical step. This article is based on a Monte-Carlo (MC) solver of the Boltzmann Transport Equation (BTE) including different transport mechanisms at the metal-semiconductor contact such as image force effect or tunneling. The weight of tunneling and thermionic current is quantified according to different degrees of tunneling modelling. The I-V characteristic highlights the dependence of the ideality factor and the current saturation with bias. Harmonic Balance (HB) simulation on a rectifier circuit within Advanced Design System (ADS) software shows that considering non-linear ideality factor and saturation current for the electrical model of the Schottky diode does not seem essential. Indeed, bias independent values extracted in forward regime on I-V curve are sufficient. However, the non-linear series resistance extracted from a small signal analysis (SSA) strongly influences the conversion efficiency at low input powers. (C) 2017 Elsevier Ltd. All rights reserved.

We show that direct band gap germanium can be obtained with external silicon nitride stressor layers. The cross-over from indirect to direct band gap is found to occur for an equivalent 1.67% biaxial tensile strain. Both whispering gallery modes and quasi-radial modes are observed with tensile-strained Ge microdisks. Quality factors up to 7100 have been measured around 2 µm wavelength. We demonstrate that circular Bragg reflectors can significantly enhance the quality factors of quasi-radial modes in strained germanium microdisks.

We show that direct band gap germanium can be obtained with external silicon nitride stressor layers. The cross-over from indirect to direct band gap is found to occur for an equivalent 1.67% biaxial tensile strain. Both whispering gallery modes and quasi radial modes are observed with tensile-strained Ge microdisks. Quality factors up to 7100 have been measured around 2 p.m wavelength. We demonstrate that circular Bragg reflectors can significantly enhance the quality factors of quasi-radial modes in strained germanium microdisks.

The influence of temperature (300 K and 40 K) on intrinsic transit times and microwave noise performances of silicon germanium (SiGe) heterojunction bipolar transistors (HBTs) is investigated. At 300 K, we compared measured and modelled S-parameters and four noise parameters, and we found a good agreement. At 40 K, we compared measured and modelled S-parameters, and we deduced noise performances from the S-parameter measurements. The electric model includes correlated junction noise sources and a proper extraction of the transit times involved in these sources. Moreover, the microwave noise model considers all the physical phenomena that impact noise performances in SiGe HBTs. We analysed three devices having different Ge content (10%–20%, 10%–25% and 10%–30%). At 40 K, the device with 10%–25% reaches one of the lowest base transit times (τ B), the lowest minimum noise figure (NFmin), and the lowest equivalent noise resistance (R n), for operation frequencies up to the maximum device dynamic performances (f ≈ f T) These results demonstrate the excellent potential to develop cryogenic applications of SiGe HBTs.

Germanium is an indirect band gap material. This property is a significant disadvantage to realize an efficient laser emitter with this material. This feature can nonetheless be circumvented by strain engineering of the band structure. It is well known that tensile strain can reduce the energy difference between the conduction band valleys and ultimately lead to a band inversion. With a direct band gap material, one should expect to obtain optical gain with a significantly reduced threshold as compared to unstrained or weakly-strained Ge. Consequently, the integration of a group IV emitter on a silicon chip could become more realistic. In this presentation, we will show that direct band gap germanium can be obtained by transferring tensile strain with nitride stressor layers. We have experimentally determined when the cross-over from indirect to direct band gap occurs using temperature-dependent photoluminescence measurements. This cross-over was found to occur for a biaxial tensile strain of 1.67%, the theoretical values varying between 1.5 and 2% in the literature. We will show that this level of strain transfer is compatible with the fabrication of optical micro-resonators with germanium microdisks. Tensile-strained germanium microdisks with circular Bragg reflectors have been successfully fabricated. They exhibit high quality factors for the quasi-radial modes. These types of structures are ideal candidates to realize microlasers with pure germanium. We will discuss the latest progress in this direction.

In this paper, we present sensitivity measurement as well as measured and calculated absorption spectra for AlGaN/GaN THz plasmonic detector made of a metallic grating in-between two ohmic contacts. Detectors with different grating patterns have been fabricated and their sensitivity, reaching 1.9 μA/W at 77 K and 0.7 μA/W at 300 K, measured with a voltage applied between the ohmic contacts. It is the first time that such a detector shows THz detection with no voltage applied on the grating, namely with a bidimensional electron gas (2DEG) having a homogeneous electron density. These results are consistent with detection by drag-effect rectification. Measurements held between 0.648 and 0.690 THz show that the dependence of the sensitivity on the frequency follows the absorption spectrum, indicating that absorption is a crucial step in the detection process. Further simulations of absorption spectra show the tunability offered by such detector and allow us to predict frequency behavior for grating-biased detectors as well, in which the rectification is mainly governed by ratchet effect.

The optical emission of germanium-based luminescent and/or laser devices can be enhanced by tensile strain and n-type doping. In this work, we study by simulation the interplay between electrical transport and optical gain in highly n-doped and intrinsic germanium p-n heterostructure diodes under tensile strain. The effects of strain and doping on carrier mobilities and energy distribution are taken into account. Whereas the n-doping of Ge enhances the filling of the indirect L and Brillouin zone-center conduction band states, the n-doping also reduces the carrier injection efficiency, which is detrimental for the achievement of optical gain at reduced current densities. For applied biaxial strains larger than 1.25%, i.e., far before reaching the cross-over from indirect to direct band gap regime, undoped germanium exhibits a lower optical gain threshold as compared to doped germanium. We also show that the threshold current needed to reach transparency in germanium heterostructures has been significantly underestimated in the previous works.

We investigate plasmonic THz detectors on Al-GaN/GaN hetero-structures for different configurations of the grating (symmetric or asymmetric pattern) and spatial modulation of the electron sheet density. The absorption spectra have been calculated for the different configurations and a few detectors have freshly been fabricated and the transmission and reflection spectra have been measured for one of them. It appears that these detectors could be the ideal candidate for an on-chip, electrically tunable, room-temperature operating and cheap THz detector.

We report room temperature electroluminescence of tensile-strained germanium microdisks. The strain is transferred into the microdisks using silicon nitride stressors. Carrier injection is achieved with Schottky contacts on n-type doped germanium. We show that a biaxial tensile-strain up to 0.72% can be transferred by optimizing the carrier injection profile. The transferred strain is measured by the electroluminescence spectral red-shift and compared to finite element modeling. We discuss the impact of this strain level to achieve population inversion in germanium.