Response Time Measurements in Short-Wave Infrared HgCdTe e-APDs

The impulse response time has been measured as a function of reverse bias, gain, and temperature in backside-illuminated short-wave infrared HgCdTe avalanche photodiodes (APDs) with variable junction geometry. The APD geometry was altered using HgCdTe substrates of variable thickness and by variation of device fabrication parameters. This approach allowed study of the drift–diffusion dynamics of the electrons before entering the junction and the electron and hole dynamics during the junction transition in APDs with different carrier collection distances and junction widths. The response time was typically limited by a double exponential decay, which is attributed to contributions from the impedance mismatch between the interconnection circuit and the 50-Ω radiofrequency probe, and a delayed diffusion response from carriers generated far from the junction. These contributions limited the maximum bandwidth of the diodes to about 600 MHz, independently of gain and temperature. The hot carrier velocities are estimated by fitting the measured response with numerical calculations, taking into account contributions from a direct drift–multiplication response and a delayed diffusion response. This analysis shows that the hot carrier dynamics is close to independent of temperature and that the electron drift velocity saturates at the gain onset to a value of 1 × 10⁷ cm/s, decreasing upon a further increase of the electric field E to a value of about 3 × 10⁶ cm/s at E = 100 kV/cm. The hole velocity shows a slow variation from 3 × 10⁶ cm/s at low electric fields to 1.5 × 10⁶ cm/s at high electric fields.     

Short-Wave Infrared HgCdTe Avalanche Photodiodes

Short-wave infrared (SWIR) HgCdTe avalanche photodiodes (APDs) have been developed to address low-flux applications at low operating temperature and for laser detection at higher temperatures. Stable multiplication gains in excess of 200 have been observed in homojunction APDs with cutoff wavelengths down to 2.8???m and operating temperatures up to 300?K, associated with low excess noise F?<?1.3 and low 1/f noise. The measured dark current density at 200?K of 6.2???A/cm² is low enough to enable high-sensitivity single-element light detection and ranging (lidar) applications and time-of-flight imaging. Corresponding APD arrays have been hybridized on a readout integrated circuit (ROIC) designed for low-flux low-SNR imaging with low noise and frame rates higher than 1500?frames/s. Preliminary focal-plane array characterization has confirmed the nominal ROIC performance and showed pixel operability above 99.5% (pixels within ±50% of average gain). The bias dependence of the multiplication gain has been characterized as a function of temperature, cadmium composition, and junction geometry. A qualitative change in the bias dependence of the gain compared with mid-wave infrared (MWIR) HgCdTe has motivated the development of a modified local electric field model for the electron impaction ionization coefficient and multiplication gain. This model gives a close fit to the gain curves in both SWIR and MWIR APDs at temperatures between 80?K and 300?K, using two parameters that scale as a function of the energy gap and temperature. This property opens the path to quantitative predictive device simulations and to estimations of the junction geometry of APDs from the bias dependence of the gain.     

MBE-grown HgCdTe multi-layer heterojunction structures for high speed low-noise 1.3–1.6 µm avalanche photodetectors

HgCdTe is an attractive material for room-temperature avalanche photodetectors (APDs) operated at 1.3–1.6 μm wavelengths for fiber optical communication applications because of its bandgap tunability and the resonant enhancement of hole impact ionization for CdTe fractions near 0.73. The HgCdTe based separate absorption and multiplication avalanche photodetector is designed and fabricated for backside illumination through a CdZnTe substrate. The multi-layer device structure is comprised of seven layers including 1). n ⁺ contact 2). n ⁻ diffusion buffer 3). n ⁻ absorber 4). n charge sheet 5). n ⁻ avalanche gain 6). p to form junction, and 7).p ⁺ contact. Several wafers were processed into 45 μm × 45 μm and 100 (μm × 100 μm devices. The mean value of avalanche voltage is 63.7 V measured at room temperature. At 1 GHz, the device shows a gain of about 7 for a gain-bandwidth product of 7 GHz. This first demonstration of an all molecular beam epitaxially grown HgCdTe multi-layer heterojunction structure on CdZnTe substrates represents a significant advance toward the goal of producing reliable room temperature HgCdTe high speed, low noise avalanche photodetectors.     

High-speed InP/InGaAsP/InGaAs avalanche photodiodes grown bychemical beam epitaxy

High-performance InP/InGaAsP/InGaAs avalanche photodiodes (APDs) grown by chemical beam epitaxy are described. These APDs exhibit low dark current (less than 50 nA at 90% of breakdown), good external quantum efficiency (greater than 90% at a wavelength of 1.3 μm), and high avalanche gain (≃40). In the low-gain regime, bandwidths as high as 8 GHz have been achieved. At higher gains, a gain-bandwidth-limited response is observed; the gain-bandwidth product is 70 GHz     

History-Dependent Impact Ionization Theory Applied to HgCdTe e-APDs

The variation of the gain and the excess noise factor in HgCdTe avalanche photodiodes (APDs) with different junction geometries are compared with published theoretical and numerical work. It is shown that, although some features of the gain curves are reproduced, such as the constant exponential increase in the gain, the theoretical work fails to predict the observed variation of the gain as a function of multiplication layer width. In contrast, a new analytical gain model based on local impact ionization coefficients and a first direct comparison of the prediction of history-dependent impact ionization theory are shown to give a good general fit to the experimental gain data. A generic model of the gain in HgCdTe APDs has been obtained by fitting the analytical local model to gain curves of APDs with various geometries and cut-off wavelengths. The study of different hypotheses on the electric field dependence of the dead-space length and the saturation value of the impact ionization coefficient has shown that a variable dead-space effect has a direct impact on the excess noise of APDs, which is why exact excess noise measurements are necessary to achieve a pertinent estimation of the nonlocal impact ionization function.     

碲镉汞雪崩光电二极管近年研究及应用进展

碲镉汞雪崩光电二极管(HgCdTe APD)因其具有高增益、高带宽、高量子效率、低噪声的优良性能,在主动/被动成像、激光雷达、波前传感和光子计数等低光子探测领域有着广阔的应用前景,国外研究机构在该领域采用不同的技术路线进行了深入研究.本文阐述了APD原理及结构,重点对近年来国外相关研究进展及应用情况进行了介绍,并对国内...     

High-reliability and low-dark-current 10-Gb/s planar superlatticeavalanche photodiodes

For compact and high-sensitivity 10 Gb/s optical receiver applications, we have developed low-dark-current planar-structure InAlGaAs-InAlAs superlattice avalanche photodiodes with a Ti-implanted guard-ring. The APDs exhibited dark current as low as 0.36 μA at a gain of 10. The temperature dependence of the dark current was confirmed to be in a sufficient level for practical 10-Gb/s applications. The APDs also exhibited a quantum efficiency of 67%, a gain-bandwidth-product of 110 GHz, a top 3-dB bandwidth of 15.2 GHz, and a minimum gain for 10-GHz bandwidth of 1.6. Preliminary aging test also showed a stable dark current operation after aging of over 2200 h at 200°C. These high-reliability, low-dark-current, high-speed, and wide-dynamic-range characteristics are promising for 10-Gb/s high-sensitivity optical receiver use     

Integrated amateur band and ultra-wide band monopole antenna with multiple band-notched

This paper presents the integrated amateur band and ultra-wide band (UWB) monopole antenna with integrated multiple band–notched characteristics. It is designed for avoiding the potential interference of frequencies 3.99 GHz (3.83 GHz–4.34 GHz), 4.86 GHz (4.48 GHz–5.63 GHz), 7.20 GHz (6.10 GHz–7.55 GHz) and 8.0 GHz (7.62 GHz–8.47 GHz) with VSWR 4.9, 11.5, 6.4 and 5.3, respectively. Equivalent parallel resonant circuits have been presented for each band-notched frequencies of the antenna. Antenna operates in amateur band 1.2 GHz (1.05 GHz–1.3 GHz) and UWB band from 3.2 GHz–13.9 GHz. Different substrates are used to verify the working of the proposed antenna. Integrated GSM band from 0.6 GHz to 1.8 GHz can also be achieved by changing the radius of the radiating patch. Antenna gain varied from 1.4 dBi to 9.8 dBi. Measured results are presented to validate the antenna performances.     

Dark current reduction in nano-avalanche photodiodes by incorporating multiple quantum barriers

Multiple quantum barriers have been used to suppress the dark current of nanoscale avalanche photodiodes (APDs). The n⁺–π–p⁺-structured Si–3C-SiC heterojunction-based multiple quantum barrier (MQB) APDs are considered and a detailed model of dark current has been developed from the self-consistent solution of the coupled Schrödinger–Poisson equations. Four major types of electron–hole pair (EHP) generation mechanisms such as (1) thermal generation, (2) band-to-band tunnelling generation, (3) trap-assisted tunnelling generation and (4) avalanche generation are considered for calculating variation of the total dark current with reverse bias voltage. It is observed that the dark current can be suppressed significantly by increasing both the number and thickness of quantum barriers. However, the authors have also admitted that both the number and thickness of quantum barriers cannot be increased indefinitely, since it will cause deterioration in spectral response of the device in near-infrared range (λ < 1100 nm).     

Microwave and Millimeter Wave Characteristics and Attenuation of Clouds over some Malaysian Equatorial Stations

Based on radar range height indicator (RHI) measurements, cloud characteristics in relation to radiowave propagation over three locations in different geographical region in western Malaysia have been presented. It is seen that low cloud occurrence over these locations are quite significant. Cloud attenuation and noise temperature can result in serious degradation of telecommunication link performances. This paper presents cloud coverage in different months, 0°C isotherm height and cloud attenuation results at 12 GHz, 20 GHz, 36 GHz, 50 GHz, 70 GHz and 100 GHz over measurement site. The low level cloud over the measurement sites has been found to occur for many days and nights and particularly in the months of April to May and October to December. Such results are useful for satellite communication and remote sensing application in Malaysia.     

New CRLH-Based Planar Slotted Antennas with Helical Inductors for Wireless Communication Systems,RF-Circuits and Microwave Devices at UHF–SHF Bands

Two novel planar slotted-antennas (PSAs) are presented that exhibit good radiation characteristics at the UHF–SHF bands. The proposed antennas are constructed using metamaterial unit-cells constituted from capacitive slots etched in the radiating patch and grounded spiral shaped inductive stubs. The proposed PSA design is fabricated on a commercially available dielectric substrate, i.e. Rogers RO4003 with permittivity of 3.38 and thickness of 1.6 mm. The first PSA comprising five symmetrical unit-cells of slot–inductor–slot configuration operates over a wide bandwidth extending from 1 to 4.2 GHz with a peak gain of 1.5 dBi and efficiency of 35 % at 2 GHz. The second PSA consists of ten asymmetrical unit-cells of slot–inductor configuration on the same size of substrate as the first PSA, enhances the antenna gain by 2 dB and efficiency by 25 % and operates over 0.75–4.5 GHz. The asymmetrical unit-cell effectively increases the aperture size of the antenna without comprising its size. The electrical size of the antenna is 0.083λ₀ × 0.033λ₀ × 0.005λ₀, where free-space wavelength (λ₀) is 1 GHz.     

碲镉汞光子计数型线性雪崩探测器(特邀)

单光子计数技术在弱信号探测和时间测距中具有重大的应用前景。自从20世纪70年代可见光的光子计数系统研发以来,国际上该领域内的研发小组在不断地发展完善光子计数技术,充分放大光子信号,以降低电子设备的读出噪声。电子倍增电荷耦合器件(Electron Multiplying Charge Coupled Devices, EMCCDs)具有更高的量子效率,可替代传统的可见光光子计数系统,但较大的雪崩噪声阻碍了倍增下入射光子数的准确获取。碲镉汞线性雪崩器件(HgCdTe APD)的过剩噪声因子接近1,几乎无过剩噪声;相对于盖革模式的雪崩器件,没有死时间和后脉冲,不需要淬灭电路,具有超高动态范围,光谱响应范围宽且可调,探测效率和误计数率可独立优化,开辟了红外波段光子计数成像的新应用领域,在天文探测、激光雷达、自由空间通信等应用中具有重要价值。美国雷神(Raytheon)公司和DRS技术公司、法国CEA/LETI实验室和Lynred公司、英国Leonardo公司先后实现了碲镉汞线性雪崩探测器的单光子计数。文中总结了欧美国家在碲镉汞光子计数型线性雪崩探测器研究方面的技术路线和研究现状,分析了吸收倍增...     

A 11.2 mW 48–62 GHz Low Noise Amplifier in 65 nm CMOS Technology

In this paper, a wideband low noise amplifier (LNA) for 60 GHz wireless applications is presented. A single-ended two-stage cascade topology is utilized to realize an ultra-wideband and flat gain response. The first stage adopts a current-reused topology that performs the more than 10 GHz ultra-wideband input impedance matching. The second stage is a cascade common source amplifier that is used to enhance the overall gain and reverse isolation. By proper optimization of the current-reused topology and stagger turning technique, the two-stage cascade common source LNA provides low power consumption and gain flatness over an ultra-wide frequency band with relatively low noise. The LNA is fabricated in Global Foundries 65 nm RFCMOS technology. The measurement results show a maximum \(S_{21}\) gain of 11.4 dB gain with a \(-\)3 dB bandwidth from 48 to 62 GHz. Within this frequency range, the measured \(S_{11}\) and \(S_{12}\) are less than \(-\)10 dB and the measured DC power consumption is only 11.2 mW from a single 1.5 V supply.     

Design of a 300 GHz Band TWT with a Folded Waveguide Fabricated by Microelectromechanical Systems

For future broadband wireless links, we have designed a 300 GHz band traveling wave tube (TWT) with a folded waveguide fabricated by microelectromechanical systems (MEMS). The TWT operates at a beam voltage of 12 kV and a beam current of 8.3 mA. The classical large signal simulation code predicts the output power greater than 1 W and gain larger than 20 dB over the bandwidth from 280 to 300 GHz.     

Cloud Attenuation in Millimeter Wave and Microwave Frequencies for Satellite Applications over Equatorial Climate

A propagation experiment has been carried out at Penang using the SUPERBIRD-C satellite beacon. Cloud occurrences were observed during different months and it is seen that the low cloud occurrences over Penang is very significant from October to January. The cloud attenuation results that are presented, which include the testing of models, have been obtained from the data gathered over five years. The specific attenuation of radio wave due to clouds at various frequencies 12 GHz, 20 GHz, 75 GHz, 50 GHz and 100 GHz has been estimated whereby the values varies from 0.14 dB/km at 12 GHz to 10.1 dB/km at 100 GHz.     

Improved frequency response of InP/InGaAsP/InGaAs avalanche photodiodes with separate absorption, grading and multiplication regions

We report very high-speed operation of InP/InGaAsP/InGaAs avalanche photodiodes with separate absorption, grading and multiplication regions (SAGM-APDs). For low multiplication values (M0?7) the bandwidth of these APDs is relatively insensitive to the gain and is determined by the hole transit time and the RC time constant. In this gain region bandwidths as high as 5.5 GHz have been achieved. For higher multiplication values the frequency response exhibits a constant gain-bandwidth product. We have observed gain-bandwidth products as high as 40 GHz, the highest value reported to date for a device of this type.     

HgCdTe MWIR Back-Illuminated Electron-Initiated Avalanche Photodiode Arrays

This paper reports data for back-illuminated planar n-on-p HgCdTe electron-initiated avalanche photodiode (e-APD) 4 × 4 arrays with large unit cells (250 × 250 μm²). The arrays were fabricated from p-type HgCdTe films grown by liquid phase epitaxy (LPE) on CdZnTe substrates. The arrays were bump-mounted to fanout boards and characterized in the back-illuminated mode. Gain increased exponentially with reverse bias voltage, and the gain versus bias curves were quite uniform from element to element. The maximum gain measured was 648 at −11.7 V for a cutoff wavelength of 4.06 μm at 160 K. For the same reverse-bias voltage, the gains measured at 160 K for elements with two different cutoff wavelengths (3.54 μm and 4.06 μm at 160 K) show an exponential increase with increasing cutoff wavelength, in agreement with Beck’s empirical model for gain versus voltage and cutoff wavelength in HgCdTe e-APDs. Spot scan data show that both the V = 0 response and the gain at V = −5.0 V are spatially uniform over the large junction area. To the best of our knowledge, these are the first spot scan data for avalanche gain ever reported for HgCdTe e-APDs. Capacitance versus voltage data are consistent with an ideal abrupt junction having a donor concentration equal to the indium concentration in the LPE film. U.S. Workshop on the Physics and Chemistry of II-VI Materials Newport Beach, California October 10–12, 2006.     

Performance of thin separate absorption, charge, and multiplicationavalanche photodiodes

Previously, it has been demonstrated that resonant-cavity-enhanced separate-absorption-and-multiplication (SAM) avalanche photodiodes (APDs) can achieve high bandwidths and high gain-bandwidth products while maintaining good quantum efficiency. In this paper, we describe a GaAs-based resonant-cavity-enhanced SAM APD that utilizes a thin charge layer for improved control of the electric field profile. These devices have shown RC-limited bandwidths above 30 GHz at low gains and gain-bandwidth products as high as 290 GHz. In order to gain insight into the performance of these APDs, homojunction APDs with thin multiplication regions were studied. It was found that the gain and noise have a dependence on the width of the multiplication region that is not predicted by conventional models. Calculations using width-dependent ionization coefficients provide good fits to the measured results. These calculations indicate that the gain-bandwidth product depends strongly on the charge layer doping and on the multiplication layer thickness and, further, that even higher gain-bandwidth products can be achieved with optimized structures     

An Optimal Design of Fractal Antenna with Modified Ground Structure for Wideband Applications

This paper premeditates an optimal design of fractal antenna with modified ground structure for wideband applications. The proposed antenna has been designed by taking numerous iterations started from 0th to 3rd. To attain the wideband characteristics, the partial ground plane has been introduced in the 3rd iteration, and the length of the ground plane has been varied to enhance the bandwidth. The maximum value of bandwidth has been adorned in the final iteration as 1.88 and 0.20 GHz. Further, this bandwidth has been improved and embellished as 2.48 GHz within the frequency range of 3–6 GHz by employing horizontal and vertical extensions in the partial ground plane. Antenna is simulated by using HFSS and performance parameters of antenna like return loss (S_11?≤???10 dB), gain and radiation efficiency are in the acceptable limits. The maximum value of gain is reported as 5.1 dB and radiation pattern is also omnidirectional. The proposed antenna is useful for the wireless applications as WiMAX (3.4–3.69 GHz) and WLAN (5.15–5.35 and 5.72–5.82 GHz) Simulated and experimental results are also juxtaposed and found in good agreement with each other.     

Compact Dual Band-Notched Monopole Antenna with Modified Radiating Patch for UWB Wireless Applications

Ultra-wideband (UWB) planar antennas with single or multiple notched frequency bands properties have recently been considered for various communications between wireless devices. In this study, a low profile microstrip monopole antenna with double band-filtering function is designed and investigated. FR-4 dielectric with properties of ε = 4.4 and δ = 0.02 has been employed as the antenna substrate. The configuration of the proposed design is composed of a modified fork-shaped radiating patch with inverted Ω-shaped slot and a pair of coupled Γ-shaped parasitic structures, a feed-line and a ground plane. The proposed dual band-notched UWB antenna provides good impedance bandwidth characteristic from 2.89 to 12.43 GHz for VSWR <2 with two notched bands which cover all the 5.2/5.8 GHz of WLAN, 3.5/5.5 GHz of WiMAX and 4-GHz of C bands ranges. The antenna provides good radiation behavior with sufficient gain levels over its operation frequency band.