Measurement of Dielectric Properties for Low-Loss Materials at Millimeter Wavelengths

We describe here a system for accurate measurement of the dielectric properties of very low-loss materials in the 130 to 170 GHz frequency range. This system utilizes an open resonator with a quality factor ∼ 1 × 10⁶. Resonance curves for this resonator are acquired with a commercial spectrum analyzer equipped with an external millimeter-wave harmonic mixer. The excitation source is a backward-wave oscillator locked to the spectrum analyzer local oscillator via a digital phase-locked loop. This system permits rapid and accurate measurement of resonance curve line widths, permitting determination of loss tangents down to the 10^-6 range. Results are reported for silicon carbide (SiC), CVD diamond, sapphire, and quartz.     

Nanosecond Laser-Driven Semiconductor Switch for 70 GHz Microwave Radiation

We study a new type of semiconductor switches for microwave radiation driven by laser emission. The switches comprise a plate of plain semiconductor built in a hollow metallic waveguide resonator. The plate can be illuminated by laser emission changing the resonator properties due to photoconductivity and therefore switching between two stable states. A sample switch has been built and experimentally investigated, demonstrating nanosecond level of switching performance. The results of numerical simulation by the FDTD method are compared with the experimental data. Typical laser pulse energies sufficient for switching are from 1 nJ to 100 nJ, switched radiation frequency tuning range is about 10 % around 70 GHz. The switching operation was observed in wide range of the driving 100-femtosecond laser parameters - for pulse energy from 6 pJ to 250 μJ, and laser emission wavelength from 0.75 μm to 2 μm.     

Electrical and luminescence properties of silicon-based tunnel transit-time light-emitting diodes p +/n +/n-Si:Er

The electrical and luminescence properties of silicon-based tunnel transit-time light-emitting diodes (LEDs) p ⁺/n ⁺/n-Si:Er, emitting under reverse bias on the p ⁺/n ⁺ junction in the breakdown regime, have been investigated. The room-temperature emission power at the wavelength λ ≈ 1.5 μm (∼5 μW), external quantum efficiency (∼10⁻⁵), and excitation efficiency of erbium ions (∼2 × 10⁻²⁰ cm² s) have been determined. At the same excitation efficiency, tunnel transit-time LEDs exhibit higher emission power in comparison with p ⁺/n-Si:Er diode structures. The experimental results are compared with the model predictions for these structures. The factors limiting the electroluminescence intensity and impact excitation efficiency for erbium ions in tunnel transit-time LEDs are discussed.     

热激励硅梁谐振器研究

作者利用微电子机械加工技术成功研制出用于高精度压力传感器的硅梁谐振器。采用热激励方式,测定了谐振梁的开环振动幅频特性:室温真空中谐振峰-3dB带宽1.2Hz,Q值大于33000。从理论和实验两方面讨论了低热激励功率条件下激励功率与谐振频率的线性关系,二者符合较好。     

Study of Spatial Distribution of Piezoelectric Properties of ZnO Films by Acoustic Resonator Spectroscopy

Using broadband acoustic resonator spectroscopy, an almost twofold increase in the frequency of optimal excitation of the composite microwave resonator of shear bulk acoustic waves is found when the distance from the substrate to the magnetron axis during the deposition of a ZnO film by magnetron sputtering is changed. The frequency characteristics of the resonator structure are simulated and an explanation of the change in the optimal excitation frequency by the inhomogeneity of the inclination of the ZnO film texture’s axis over the thickness is proposed.

     

Novel Design of a High-gain and Wideband Fabry-Pérot Cavity Antenna Using a Tapered AMC Substrate

A high-gain and wideband electromagnetic bandgap (EBG) resonator antenna with a tapered artificial magnetic conductor (AMC) ground plane is presented. The proposed EBG resonator antenna is comprised of a frequency selective surface (FSS) superstrate with a strip dipole array and an AMC ground plane with tapered rectangular patches. The realized gain and the bandwidth of the antenna can be improved simultaneously by using the tapered AMC where the phase difference of the reflected waves from the patches with different length is within 180° and the destructive interference among them can be considerably reduced. The maximum gain is increased about 2∼3 dB and the bandwidth is improved about 2.5 times compared to when the uniform AMC is used.     

Application of the smith chart in the analysis of the relaxation properties of magnetostatic oscillations and spin waves in ferrite films

The relaxation properties of three main types of magnetostatic oscillations in a magnetostatic film resonator and nonlinear processes (parametric excitation of spin waves in the first and second bands in the presence of the tangential magnetization of the gallium-substituted yttrium-iron garnet film and foldover in the regime of normal magnetization) are studied in the frequency range 0.8–4.5 GHz. An original method is proposed for the determination of thresholds of the parametric excitation of spin waves using the deformations of Smith chart caused by variations in the measurement power level. The method is used in the highaccuracy analysis of the frequency dependences of threshold power in the presence of tangential magnetization in the regimes of resonances of both surface and backward volume magnetostatic waves. The frequencyfield dependences of the absorption spectra of three main types of magnetostatic oscillations in the linear regime are used to determine the saturation magnetization, anisotropy fields, and unloaded Q factors of resonator at each mode and to calculate the relaxation parameters of the corresponding magnetostatic oscillations. The experimentally measured threshold pump powers are used to calculate the relaxation line widths of the parametrically excited spin waves with the aid of the improved theory of parametric processes that takes into account both cubic and uniaxial anisotropy of the film.     

Very high-speed ultraviolet photodetectors fabricated on GaN

We report on the temporal and the frequency response of both metal-semiconductor-metal (MSM) and p-i-n ultraviolet photodetectors fabricated on single-crystal GaN. The best MSM devices show a fast 10–90% rise-time of ∼28 psec under comparatively low ultraviolet excitation of ∼0.1 W/cm² averagerirradiance. The fast-Fourier transform (FFT) of the pulse response data indicates a bandwidth, f_3dB, of ∼3.8 GHz at a reverse bias of 25 V. This agrees well with the direct frequency response measurement value of ∼3.5 GHz. For the p-i-n devices, we measured a rise-time of ∼43 psec at 15 V reverse bias for a 60 μm diameter mesa with 1 μm thick intrinsic region. The FFT of the p-i-n pulse response obtains f_3dB ≈1.4 GHz. Analysis in terms of reverse bias and geometric scaling indicates that the MSM photodetectors are transit-time limited. The p-i-n devices also show evidence of transit-time limited effects based on trends with respect to reverse bias and intrinsic region thickness. However, our larger area p-i-n devices show clear evidence of RC-limited behavior. Modeling of the temporal behavior indicates that a slow component in the time and frequency response data is a consequence of the hole drift velocity. We have also found preliminary evidence of microplasmic effects in the p-i-n devices.     

Ultrafast Relaxation of Charge Carriers Induced Switching in Terahertz Metamaterials

We demonstrate ultrafast switching of resonant mode in terahertz metamaterials through optical excitation of radiation-damaged silicon placed in the gap of a split-ring resonator. Upon optical excitation, we observe the dynamic transition of the fundamental resonance from ON-to-OFF state on a timescale of 4 picoseconds (ps) and then fast recovery of the resonance to the ON-state within the next 20 ps. Electric field distributions in the metamaterial unit cell derived through numerical simulations clearly support our experimental observations, showing that the high electric field at the resonator gaps, responsible for inductive-capacitive (LC) resonance, completely disappears and switches OFF the resonance after being optically excited. The ultrafast switching of the metamaterial resonance is attributed to the relaxation of the photo-carriers through the defect states of radiation-damaged silicon layer. Such ultrafast material–based active control of metamaterials can lead to the ultrafast terahertz metaphotonic devices.     

Resonant optical second harmonic generation and mixing

Experimental and theoretical results are described on the enhancement of optical second harmonic generation (SHG) and mixing in KDP by the use of optical resonance. Both resonance of the harmonic and of the fundamental are considered. Large enhancements are possible for resonators with low loss. Using a planoconcave harmonic resonator containing 1.23 cm of KDP, the authors achieved a loss < 4 percent per pass. This resulted in an enhancement of ∼ 500 times the harmonic power internal to the resonator and ∼ 10 times external to the resonator. When resonating, the fundamental enhancements of ∼ 5 were observed. The theory includes the effect of double refraction. This results in a coupling coefficient of the generated harmonic power to the transverse modes of the harmonic resonator. The experimental results are in substantial agreement with the theory.     

Ultrahigh-power picosecond current switching by a silicon sharpener based on successive breakdown of structures

Ultrafast current switching by a silicon sharpener based on successive breakdown of structures has been experimentally implemented and theoretically studied. A voltage pulse with an amplitude of 180 kV and a rise time of 400 ps was applied to a semiconductor device containing 44 series-connected diode structures positioned in a 50-Ω transmission line. After device switching, pulses with an amplitude of 150 kV and a rise time of 100 ps were obtained in the transmission line. Numerical simulation showed that the electric field near the p-n junction reaches the Zener breakdown threshold (∼10⁶ V/cm) at an input voltage rise rate of more than 4 × 10¹³ V/s per structure achieved in the experiment, even when the diode structure contains technological impurities with deep ionization levels and a concentration of 10¹¹ cm⁻³.     

Bistability in a nonlinear magnetoacoustic resonator

The characteristics of a nonlinear magnetoacoustic resonator are studied. The resonator is fabricated from an antiferromagnetic hematite (α-Fe₂O₃) monocrystal. The amplitude-and phase-bistability loops are investigated experimentally when an exciting signal has a cyclically variable frequency and a fixed power or a cyclically variable power and a fixed frequency. Bistability is induced by strong coupling between the acoustic and magnetic subsystems of hematite. This coupling results in renormalization of both linear and nonlinear elastic moduli of the crystal and causes the resonator frequency to depend on the external magnetic field and the power level of the exciting signal. At low power levels, the resonator’s transmission characteristic is a Lorentzian curve and the frequency can be tuned over an interval of 65% of the initial value as the field ranges from 0 to 3 kOe. An increase in the signal power results in a distortion of the characteristic and in the frequency shift of the maximum transmission factor by 2.1%. Analytical expressions for the amplitude and phase bistable characteristics of a nonlinear magnetoacoustic resonator are obtained. Calculated and measured data are in quantitative agreement.     

Intraband light absorption in quasi-two-dimensional systems in external electric and magnetic fields

Intraband light absorption in parabolic quantum wells is studied with an electric field directed along the spatial quantization axis and a magnetic field parallel to the plane of the size-confined system. In such a geometry direct optical transitions between the quantum-well levels are possible, the peak light absorption coefficient reaches large values (∼3×10² cm⁻¹), and the frequency of the absorption maximum depends on magnetic field strength. It is shown for the normal incidence of electromagnetic waves that the level of absorption decreases with increasing electric field strength and that it is incorrect to confine the calculations to the Born approximation in strong magnetic fields. Fiz. Tekh. Poluprovodn. 33, 828–831 (July 1999)     

Specific Features and Nature of the 890 nm Photoluminescence Band Detected in SiO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Films after Low-Temperature Annealing

A band with a peak at 890 nm is detected in the photoluminescence spectra of SiO _x (x ≈ 1.3) films deposited by thermal evaporation of SiO and annealed in air at 650–1150°C. The 890-nm band appears after low-temperature (∼650°C) annealing and exhibits a number of features: (i) as the annealing temperature is elevated to 1150°C, the position of the band peak remains unchanged, whereas the intensity increases by two orders of magnitude; (ii) the effects of the annealing atmosphere (air, vacuum) and the excitation wavelength and power density on the intensity of the 890-nm band differ from the corresponding effects on the well-known bands observable in the ranges 600–650 and 700–800 nm; and (iii) the photoluminescence decay is first fast and then much slower, with corresponding lifetimes of ∼9 and ∼70 μs. The observed features are inconsistent with the interpretation of photoluminescence observed in SiO _x so far. Specifically, the earlier observed photoluminescence was attributed to transitions between the band and defect states in the matrix and between the states of band tails, transitions inside Si nanoclusters, and intraion transitions in rare-earth impurity ions. Therefore, we consider here the possibility of attributing the 890-nm band to transitions in local centers formed by silicon ions twofold- and/or threefold-coordinated with oxygen; i.e., we attempt to interpret the 890-nm band in the same manner as was done for luminescence in SiO₂ glasses and films slightly deficient in oxygen.     

Characteristics of surface states at the insulator-semiconductor interface in the thin-film electroluminescent structures based on ZnS:Mn

Distributions of the density of occupied surface electron states at the cathode interface between the insulator and phosphor in thin-film electroluminescent emitters are simulated in relation to the energy on the basis of experimental data. The dependences of the above distributions on the conditions of excitation of emitters are obtained. It is shown that these distributions shift to deeper levels of surface states as the frequency of excitation voltage is decreased and the pause between two neighboring switched-on states of emitters is increased, which corresponds to the cascade mechanism of relaxation of electrons captured by surface states. The coefficient of cascade capture of electrons prior to relaxation ((4−5) × 10⁻¹² cm²/s), instantaneous lifetime of electrons prior to relaxation (0.2–0.25 s), cross section for capture of electrons to deeper levels of surface states (in excess or on the order of (6.7−8.3) × 10⁻²¹ cm²), largest values of the densities of occupied surface states at the cathode boundary from which electron tunnel (∼2.5 × 10¹³ cm⁻²), and energy density of above-specified surface states (7 × 1014 cm⁻² eV⁻¹) have been determined. The values of the quasi-equilibrium Fermi level at the surface in the course of the activity of electroluminescent emitters varies in the range from 0.9 to 1.35 eV, depending on conditions of excitation.     

Use of electron cyclotron resonance plasmas to prepare CdZnTe (211)B substrates for HgCdTe molecular beam epitaxy

Without any additional preparation, Cd_1−yZn_yTe (211)B (y∼3.5%) wafers were cleaned by exposure to an electron cyclotron resonance (ECR) Ar/H₂ plasma and used as substrates for HgCdTe molecular beam epitaxy. Auger electron spectra were taken from as-received wafers, conventionally prepared wafers (bromine: methanol etching, followed by heating to 330–340°C), and wafers prepared under a variety of ECR process conditions. Surfaces of as-received wafers contained ∼1.5 monolayers of contaminants (oxygen, carbon, and chlorine). Conventionally prepared wafers had ∼1/4 monolayer of carbon contamination, as well as excess tellurium and/or excess zinc depending on the heating process used. Auger spectra from plasma-treated CdZnTe wafers showed surfaces free from contamination, with the expected stoichiometry. Stoichiometry and surface cleanliness were insensitive to the duration of plasma exposure (2–20 s) and to changes in radio frequency input power (20–100 W). Reflection high energy electron diffraction patterns were streaked indicating microscopically smooth and ordered surfaces. The smoothness of plasma-etched CdZnTe wafers was further confirmed ex situ using interferometric microscopy. Surface roughness values of ∼0.4 nm were measured. Characteristics of HgCdTe epilayers deposited on wafers prepared with plasma and conventional etching were found to be comparable. For these epilayers, etch pit densities on the order of 10⁵ cm⁻² have been achieved. ECR Ar/H₂ plasma cleaning is now utilized at Night Vision and Electronic Sensors Directorate as the baseline CdZnTe surface preparation technique.     

A monolithic sigma-delta fractional-N frequency synthesizer with implicit dual-path filter and phase switching multi-modulus frequency divider

A fully integrated Sigma-delta fractional-N frequency synthesizer is realized in TSMC 0.18 μm MM/RF 1P6M Salicide 1.8V/3.3V technology. The proposed implicit dual-path loop filter with enhanced trans-conductor can eliminate the charge pump mismatch of the conventional dual-path loop filter and suppress the effect of parasitic poles and zero as well as reduce the area of the loop filter. A simple frequency divider based on phase switching technique is employed to reduce the area and power dissipation. The frequency synthesizer consumes 21 MW power from 1.8 V power supply voltage with area 1.80  ×  2.0 mm². The achieved phase noise is −82 dBc/Hz at 10 kHz offset, −108 dBc/Hz at 100 kHz offset and −128 dBc/Hz at 1 MHz offset respectively with frequency switching time 95 μs.     

Pulse-switchable microwave resonator on a basis of monocrystal hexaferrite

In this paper it is considered an idea of application specificities of hysteresis loop of frequency-field dependence of ferromagnetic resonance of good monocrystal hexaferrite materials for creation of pulse-switchable resonator for millimeter wavelength range. The essence of principle of this device lies in possibility of quick change of the hexaferrite resonator frequency from higher frequencies to lower and inversly, “switching” the hexaferrite onto definite magnetic states. The idea was realized in a prototype device with resonator from barium hexaferrite BaFe₁₂O₁₉. It is stated experimentally that maximal tuning range can achieve 3.5 GHz, and the time for tuning is about 200 μs in case of magnetic field pulse is about 1.5 kOe.     

Dual-Wavelength Pulse Train Generation Based on Silicon-on-Insulator Optical Waveguides

In this paper, we present and numerically study a method with pump-probe configuration to generate ∼4.17-THz dual-wavelength ultrahigh-repetition-rate pulse train from the continuous-waves (CW) based on the submicron silicon-on-insulator (SOI) optical waveguides. An original ∼4.17 THz repetition rate pulsed pump, with femtosecond pulse duration, at 2900 nm (mid-wave infrared wavelength-MWIR) and 2-channel CW lights at 1450 nm and 1650 nm (near infrared wavelengths) are simultaneously launched into the silicon waveguide. Results show that, when both of CW lights with high intensity pulsed pump are co-propagating along the SOI waveguide, the CW lights will, respectively, experience normal and anomalous group velocity dispersion (GVD) regimes, leading to developing into two inverted ∼4.17 THz repetition rate pulse train by the combined effects of GVD and nonlinear frequency chirp induced by pulsed pump inside the waveguide. Moreover, the outcome pulse trains have short pulse duration and high extinction ratio (ER) comparing with the original pulsed pump if the systems parameters such as input power and waveguide length are judiciously adjusted.     

基于声表面波的喇曼型声光移频器的研究

A Raman acousto-optic frequency shifter （AOFS） based on surface acoustic wave （SAW） is presented. It consists of a double-ended SAW resonator and optical waveguide system. The structure parameters of the SAW resonator are optimized using COM software and the optical waveguide system is designed using an effective index method. The AOFS prototype fabricated using MEMS technology is detected. The optical beat signals su- perimposed by ± 1st-order and ±2nd-order diffracted beams are detected. The frequency shift of 78.2201 MHz related to the 1 st-order diffracted beams and 156.2306 MHz related to the 2nd-order diffracted beams are obtained respectively.