Physical modeling and design of thin-film SOI lateral PIN photodiodes

Lateral PIN diodes on thin-film silicon-on-insulator (SOI) substrates are photodetectors of prime interest for UV and fast IR applications. We present numerical simulations and a simple but accurate way to implement 1-D internal physical modeling of such devices. This modeling allows for the optimization of their external and macroscopic performances such as quantum efficiency and output current as a function of design parameters such as intrinsic length of the diode. Speed and dark current performances versus the intrinsic length are also addressed, and design tradeoffs are illustrated by concrete applications. For diodes with intrinsic lengths between 2 to 4 /spl mu/m, our results predict quantum efficiencies of 56% to 60% at a 400-nm wavelength, with bandwidth of 1 to 10 GHz and a dark current of around 1 pA for a total diode area of 75/spl times/75 /spl mu/m/sup 2/ in a 0.12 /spl mu/m partially depleted SOI technology.     

Wide dynamic range CMOS pixels with reduced dark current

The sensitivity of logarithmic pixels at low light levels is limited by the dark current that flows through the load transistor in the pixel in addition to the photocurrent. This dark current also degrades the performance of cameras containing these pixels by increasing the residual fixed pattern noise following fixed pattern noise correction. The performance of logarithmic pixels will therefore be improved if the dark current can be reduced. A review of the sources of dark current has led to the design of a new layout for a logarithmic pixel. Results are reported that show that this layout significantly reduces the dark current in the pixel. In addition, a simple change to the bias voltages applied to the proposed pixel means that the new layout can simultaneously exhibit a linear response at low light levels and a logarithmic response at higher light levels. Experimental results from both modes of operations are presented.     

不同退火处理的台面型In0.83Ga0.17As pin光电二极管暗电流分析

为了研究延伸波长In0.83Ga0.17As pin光电二极管的暗电流机制。采用两种不同工艺制备了台面型延伸波长In0.83Ga0.17As pin光电二极管。第一种工艺(M135L-5)是:台面刻蚀后进行快速热退火(RTA)。第二种工艺(M135L-3)是:台面刻蚀前进行快速热退火(RTA)。采用IV测试,周长面积比(P/A),激活能和暗电流成分拟合方法对器件暗电流机制进行分析。结果显示,在220~300 K之间,M135L-3器件暗电流低于M135L-5器件的,并且具有较低表面漏电流。在-0.01~-0.5 V之间和220~270 K之间,M135L-5器件的暗电流主要是扩散电流。在250~300 K之间,M135L-3器件的暗电流主要是扩散电流,而在-0.01~-0.5 V之间和220~240 K之间,其暗电流主要是产生复合电流和表面复合电流。与此同时,暗电流成分拟合结果也得出一致的结论。研究表明,在降低器件暗电流方面,M135L-3器件优于M135L-5器件,这主要是因为快速热退火降低了器件的体电流。     

A resonant tunneling quantum-dot infrared photodetector

A novel device-resonant tunneling quantum-dot infrared photodetector-has been investigated theoretically and experimentally. In this device, the transport of dark current and photocurrent are separated by the incorporation of a double barrier resonant tunnel heterostructure with each quantum-dot layer of the device. The devices with In/sub 0.4/Ga/sub 0.6/As-GaAs quantum dots are grown by molecular beam epitaxy. We have characterized devices designed for /spl sim/6 /spl mu/m response, and the devices also exhibit a strong photoresponse peak at /spl sim/17 /spl mu/m at 300 K due to transitions from the dot excited states. The dark currents in the tunnel devices are almost two orders of magnitude smaller than those in conventional devices. Measured values of J/sub dark/ are 1.6/spl times/10/sup -8/ A/cm/sup 2/ at 80 K and 1.55 A/cm/sup 2/ at 300 K for 1-V applied bias. Measured values of peak responsivity and specific detectivity D/sup */ are 0.063 A/W and 2.4/spl times/10/sup 10/ cm/spl middot/Hz/sup 1/2//W, respectively, under a bias of 2 V, at 80 K for the 6-/spl mu/m response. For the 17-/spl mu/m response, the measured values of peak responsivity and detectivity at 300 K are 0.032 A/W and 8.6/spl times/10/sup 6/ cm/spl middot/Hz/sup 1/2//W under 1 V bias.     

Dark current reduction in stacked-type CMOS-APS for charged particle imaging

A stacked CMOS-active pixel sensor (APS) with a newly devised pixel structure for charged particle detection has been developed. At low operation temperatures (<200 K), the dark current of the CMOS-APS is determined by the hot carrier effect. A twin well CMOS pixel with a p-MOS readout and n-MOS reset circuit achieves low leakage current as low as 5/spl times/10/sup -8/ V/s at the pixel electrode under liquid nitrogen temperature of 77 K. The total read noise floor of 0.1 mV/sub rms/ at the pixel electrode was obtained by nondestructive readout correlated double sampling (CDS) with the CDS interval of 21 s.     

Mid-wavelength infrared p-on-n Hg1−xCdxTe heterostructure detectors: 30–120 kelvin state-of-the-Art performance

We report on Hg_1−xCd_xTe mid-wavelength infrared (MWIR) detectors grown by molecular-beam epitaxy (MBE) on CdZnTe substrates. Current-voltage (I-V) characteristics of HgCdTe-MWIR devices and temperature dependence of focal-plane array (FPA) dark current have been investigated and compared with the most recent InSb published data. These MWIR p-on-n Hg_1−xCd_xTe/CdZnTe heterostructure detectors give outstanding performance, and at 68 K, they are limited by diffusion currents. For temperatures lower than 68 K, in the near small-bias region, another current is dominant. This current has lower sensitivity to temperature and most likely is of tunneling origin. High-performance MWIR devices and arrays were fabricated with median R_oA values of 3.96 × 10¹⁰ Ω-cm² at 78 K and 1.27 × 10¹² Ω-cm² at 60 K; the quantum efficiency (QE) without an antireflection (AR) coating was 73% for a cutoff wavelength of 5.3 μm at 78 K. The QE measurement was performed with a narrow pass filter centered at 3.5 μm. Many large-format MWIR 1024 × 1024 FPAs were fabricated and tested as a function of temperature to confirm the ultra-low dark currents observed in individual devices. For these MWIR FPAs, dark current as low as 0.01 e⁻/pixel/sec at 58 K for 18 × 18 μm pixels was measured. The 1024 × 1024 array operability and AR-coated QE at 78 K were 99.48% and 88.3%, respectively. A comparison of these results with the state-of-the-art InSb-detector data suggests MWIR-HgCdTe devices have significantly higher performance in the 30–120 K temperature range. The InSb detectors are dominated by generation-recombination (G-R) currents in the 60–120 K temperature range because of a defect center in the energy gap, whereas MWIR-HgCdTe detectors do not exhibit G-R-type currents in this temperature range and are limited by diffusion currents.     

Thermal cycling-induced changes in excess dark current in very long-wavelength HgCdTe photodiodes at low temperature

We have observed cooldown-to-cooldown changes in the reverse-bias dark current of some very long-wavelength (cutoff >14 μm) HgCdTe P-on-n heterojunction photodiodes operated at very low temperatures (40–45 K). Other photodiodes in the same arrays are stable between cooldowns. The unstable ones have high dark currents, in the tail of the dark current distribution. Current-voltage analysis indicates that the high dark current is caused by trap-assisted tunneling and that the number of traps changes from cooldown to cooldown. Devices with negligible trap-assisted tunneling current, limited by diffusion and band-to-band tunneling currents at reverse bias, are stable between cooldowns. Both types of devices are stable within a given cooldown over periods of at least 24 h.     

Improvement in HgCdTe diode characteristics by low temperature post-implantation annealing

Hg_1−xCd_xTe diodes (x∼0.22) with different carrier concentrations in p type materials have been fabricated by employing an ion-implantation technique. The performances of the diodes, prior to and after low temperature postimplantation annealing, have been investigated in detail by model fitting, taking into account dark current mechanisms. Prior to the annealing process, dark currents for diodes with relatively low carrier concentrations are found to be limited by generation-recombination current and trap-assisted tunneling current, while dark currents for diodes with higher carrier concentrations are limited by band-to-band tunneling current. These dark currents in both diodes have been dramatically decreased by the low temperature annealing at 120∼150°C. From the model fitting analyses, it turned out that trap density and the density of the surface recombination center in the vicinity of the pn junction were reduced by one order of magnitude for a diode with lower carrier concentration and that the carrier concentration profile in a pn junction changed for a diode with higher carrier concentration. The improvements are explained by changes in both carrier concentration profile and pn junction position determined by interaction of interstitial Hg with Hg vacancy in the vicinity of the junction during the annealing process.     

Long-wavelength In0.53Ga0.47As metamorphicp-i-n photodiodes on GaAs substrates

Metamorphic In_0.53Ga_0.47As p-i-n photodiodes on GaAs substrate exhibiting the lowest dark current ever reported were fabricated and characterized. Their dark current, DC and RF performances were measured and compared for devices of different sizes. Typical dark current for 15-μm-diameter devices was 600 pA under 5-V reverse bias, corresponding to a dark current density of 3.40×10^-4 A/cm². Typical responsivity measured with 1.55-μm optical radiation was 0.55 A/W corresponding to an external quantum efficiency of 44%. The electrical 3 dB bandwidths of the photodiodes with diameters smaller than 20 μm were over 20 GHz     

High-responsivity intersubband infrared photodetector usingInGaAsP/InP superlattice

A 4-7-μm infrared detector made of an InGaAsP/InP short-period superlattice is demonstrated with materials grown by metalorganic chemical vapor deposition (MOCVD). A single current blocking layer of InP is used to reduce the dark current. At 40 K, the detector shows a low dark current of less than 4 pA at a bias voltage of 4 V. At 35 K, a peak responsivity of 4.0 A/W is obtained at 5.6 μm at a bias of 1 V     

MCT infrafed detectors with close to radiatively limited performance at 240 K in the 3–5 µm band

Results are reported on infrared photodiodes which have been designed to minimize the dark diffusion currents for operating temperatures above 200 K in the MWIR (3–5 μm) waveband. It is shown that by adjusting the doping and composition profiles, the dark currents due to Auger and contact diffusion mechanisms can be controlled leading to devices which are close to being radiatively limited. The radiatively-generated current has been calculated as a function of temperature from the measured spectral response and this indicates that the radiative contribution increases from about 53% at 240 K to 65% at 300K. In addition, it is shown that these internally-generated radiative currents can be reduced using negative luminescence. This result is the first experimental verification that the internally-generated radiative mechanism can contribute to the diffusion current.     

500 GHz cutoff frequency SiGe HBTs

A current gain cutoff frequency f_T of 508 GHz is reported for a SiGe heterojunction bipolar transistor (HBT) operating at 40 K. This 63% increase over the 311 GHz value measured at room temperature results from the overall decrease of the transit and charging times. Two HBTs are compared to highlight the importance of the topology of the HBT to reach maximum performances.     

Low Dark Count Rate and High Single-Photon Detection Efficiency Avalanche Photodiode in Geiger-Mode Operation

An In_0.53Ga_0.47As-InP avalanche photodiode with very low dark current (0.15 pA at 95% breakdown voltage, 200 K) has been characterized in gated mode for single-photon detection. The temperature dependence of dark current and dark count yields activation energy of ~0.4 eV from 240 K to 297 K. High single-photon detection efficiency (SPDE) at telecom wavelengths with very low dark count rate (DCR) (e.g., DCR =12 kHz at SPDE =45% at 1.31 mum and 200 K) was achieved     

Cryogenic performance of a high-speed GaInAs/InP p-i-n photodiode

The cryogenic performance of a high-speed GaInAs/InP p-i-n photodiode, with graded bandgap layers at the heterostructure interfaces, was investigated for the first time. DC measurements show that the dark current of the diode decreases sharply as the temperature decreases from 300 to 200 K. A factor of 1000 in dark current reduction was found for this photodiode, when it was cooled from room temperature to about 150 K. Similar modulation bandwidths were found for this device for temperatures between 9 and 300 K, with a bandwidth greater than 20 GHz. No degradation was found in performance at cryogenic temperature compared to room temperature. This enables direct integration of high-speed photodiodes with superconductive and other cryogenic electronics     

A 0.8 V CMOS amplifier design

A low-voltage operational amplifier design in a standard CMOS process is presented for operation at ±0.4 V. The design incorporates a low voltage level shift current mirror using forward body-biased MOSFETs limited to a maximum of 0.4 V to minimize latchup and hot carrier effects. Some of the measured performances are as follows: 58 dB open-loop gain, 30 kHz bandwidth, 50° phase margin and 80 μW power dissipation and are in close agreement with the corresponding design and SPICE simulated values.     

Conceptual design of an electrical machine with both low and high Tc superconductors

The emergence of high T_c superconducting (HTS) wires with large critical current densities allows the design and construction of many applications, for example, rotating electrical machines. Nevertheless, the current “state of the art” of Bi “powder in tube” wires, the most advanced HTS conductor, is not adequate for an ac operation. We thus propose a fully superconducting synchronous machine with an NbTi stationary 4 K armature and a rotating Bi-2223 field winding at 20 or 40 K. Thanks to the armature cryogenic environment, the cooling of the Bi coils is very simple. The conceptual design of a typical machine is suggested and several electromagnetic designs are presented. The first one deals with a Bi field winding adapted to an existing NbTi armature of a tenth of kYA. Afterwards, large torque motors are theoretically designed comparing the high (at 20 and 40 K) and low T_c field winding solutions. The results are comparable for NbTi and Bi at 20 K. But with a Bi field winding operating at 40 K, the performances are degraded. Otherwise, at 4 or 20 K fully superconducting motors show high performances in terms of weight, volume, and efficiency. Nevertheless, the Bi field windings require a large amount of material indicating that improvements in critical current density are needed     

γ辐照导致中波碲镉汞光伏器件暗电流退化的机理研究

针对红外探测器在空间应用中受到高能粒子辐照后暗电流退化的问题,开展射线对中波碲镉汞（HgCdTe）光伏器件暗电流影响的研究。在室温和77 K温度下,利用60Co-射线对HgCdTe器件进行辐照试验,辐照试验结束后对低温辐照器件进行77 K低温退火和室温退火。通过比较辐照前后和退火后器件的I-V特性、R-V特性和零偏动态电阻R0参数,分析了辐照对HgCdTe器件暗电流的影响机制。试验结果表明:在总剂量为7 Mrad（Si）照条件下,器件暗电流未出现明显的退化;在77 K温度辐照条件下,器件暗电流随着总剂量的增加而增加,且暗电流退化幅度与辐照过程中的偏置有关。研究表明暗电流的退化源于辐照在器件中造成电离损伤,导致器件HgCdTe化层中的界面态和空穴陷阱电荷密度增加。     

Hydrogen desorption and diffusion in PECVD silicon nitride. Application to passivation of CMOS active pixel sensors

Presented either as a source or as a barrier to hydrogen, plasma deposited silicon nitride can impact microelectronic device performances. The objective of this paper is to clarify the hydrogen behavior in silicon nitride in order to optimize film characteristics for each microelectronic application. A design of experiments methodology was used to statistically discriminate films properties which govern hydrogen diffusion and desorption from PECVD silicon nitride. Finally, we confirm, thanks to trials on CMOS active pixel sensor devices and dark current measurements, the role of the SiN passivation layer on Si remaining defect and we propose an optimized passivation stack.     

Type II Superlattice Infrared Detector Technology at SCD

Semi-Conductor Devices’ long-wave infrared 640?×?512/15-μm pitch type II superlattice detector is based on an XBp design with an InAs/GaSb absorbing layer and an InAs/AlSb barrier layer. The barrier architecture ensures a low, diffusion-limited, dark current and allows stable passivation to all fabrication steps. It is shown that the dark current is about 10 times the Rule 07 value and corresponds to a minority carrier lifetime of about 10 ns, while the quantum efficiency can approach within 10% of the HgCdTe value for realistic detector parameters. Detectors are now being manufactured with a reasonable yield for an operability above 99.5%, and a stable and reproducible noise equivalent temperature difference of <?15 mK when operated at 30 Hz, F/2.7 and 77 K.     

分子束外延InAlSb红外探测器光电性能的温度效应

采用分子束外延生长方法在InSb （100）衬底上生长p+-p+-n-n+势垒型结构的In1-xAlxSb外延层。运用X射线衍射对材料的晶体质量及Al组分进行测试和表征,InAlSb外延层的半峰宽为0.05,表明外延材料的单晶性能良好,并通过布拉格方程和维戈定律计算出Al组分为2.5%。然后将外延材料制备成多元红外探测并测得77~210 K下的光谱响应曲线,实验发现探测器的截止波长从77 K时的4.48 m增加至210 K时的4.95 m。通过数据拟合得出In0.975Al0.025Sb禁带宽度的Varshni关系式以及其参数Eg（0）、和的值分别为0.238 6 eV,2.8710-4 eV/K,166.9 K。经I-V测试发现,在110 K,-0.1 V偏压下,器件的暗电流密度低至1.0910-5 A/cm-2,阻抗为1.40104 cm2,相当于77 K下InSb探测器的性能。同时分析了温度对器件不同类型的暗电流的影响程度,并得到器件的扩散电流与产生-复合电流的转变温度约为120 K。