Full-Band Monte Carlo Simulation of HgCdTe APDs

A full-band Monte Carlo model has been developed for understanding the carrier multiplication process in HgCdTe infrared avalanche photodiodes. The proposed model is based on a realistic electronic structure obtained by pseudopotential calculations and a phonon dispersion relation determined by ab initio techniques. The calculated carrier–phonon scattering rates are consistent with the electronic structure and the phonon dispersion relation, thus removing adjustable parameters such as deformation potential coefficients. The computation of the impact ionization transition rate is based on the calculated electronic structure and the corresponding wavevector-dependent dielectric function. The Monte Carlo model is applied to investigate key performance figures of long-wavelength infrared (LWIR) and mid-wavelength infrared (MWIR) HgCdTe avalanche photodetectors such as carrier multiplication and noise properties. Good agreement is achieved between simulations and experimental results. The multiplication process in LWIR (λ _c = 9.0 μm at 80 K) and MWIR (λ _c = 5.1 μm at 80 K) devices is found to be initiated only by electrons, as expected from excess noise measurements. This single-carrier multiplication behavior can be traced back to the details of the computed valence-band structure and phonon scattering rates.     

HgCdTe反型层电子子能带物理

<正> 本文在4.2K下测定了p-HgCdTe MIS结构样品的量子电容谱,表面磁阻振荡,表面回旋共振以及表面电子自旋共振,确定了HgCdTe反型层电子子能带结构,包括能级位置、费米能级、有效质量、反型层耗尽层厚度等,并推导了由于自旋轨道相互作用而引起的电致自旋分裂子能带的色散关系和朗道能级扇形图,还研究了朗道能级以及自旋能级间的光跃迁问题。     

昆明物理研究所HgCdTe光导探测器的现状及发展

“七五”,“八五”期间,昆明物理研究所成功地研制和发展了ＨｇＣｄＴｅＳＰＲＩＴＥ探测器组件和多元短线列光导ＨｇＣｄＴｅ探测器组件,本文简要报道这两种探测器组件的现状和今后的发展。     

小像元碲镉汞红外焦平面探测器的研究进展

随着红外技术的发展,探测器的尺寸、重量和功耗(SWaP)的减小已成为研究热点。像元尺寸的减小,一方面可以提高器件的分辨率,另一方面可以减小整个探测器系统的体积、重量和功耗,进而大大节约成本。因此,像元尺寸的减小成了研究的重点。本文介绍了小像元红外焦平面器件的技术难点,分别从系统的调制传递函数(Modulation Transfer Function,MTF)、噪声等效温差(Noise Equivalent Temperature Difference,NETD)、像元结构和像元集成互连方面进行了讨论。此外,介绍了国外像元中心距为12?m、10?m、8?m和5?m的HgCdTe红外焦平面探测器的研究进展。     

Study of the Transit-Time Limitations of the Impulse Response in Mid-Wave Infrared HgCdTe Avalanche Photodiodes

The impulse response in frontside-illuminated mid-wave infrared HgCdTe electron avalanche photodiodes (APDs) has been measured with localized photoexcitation at varying positions in the depletion layer. Gain measurements have shown an exponential gain, with a maximum value of M = 5000 for the diffusion current at a reverse bias of V _b = 12 V. When the light was injected in the depletion layer, the gain was reduced as the injection approached the N+ edge of the junction. The impulse response was limited by the diode series resistance–capacitance product, RC, due to the large capacitance of the diode metallization. Hence, the fall time is given by the RC constant, estimated as RC = 270 ps, and the rise time is due to the charging of the diode capacitance via the transit and multiplication of carriers in the depletion layer. The latter varies between t _10–90 = 20 ps (at intermediate gains M < 500) and t _10–90 = 70 ps (at M = 3500). The corresponding RC-limited bandwidth is BW = 600 MHz, which yields a new absolute record in gain–bandwidth product of GBW = 2.1 THz. The increase in rise time at high gains indicates the existence of a limit in the transit-time-limited gain–bandwidth product, GBW = 19 THz. The impulse response was modeled using a one-dimensional deterministic model, which allowed a quantitative analysis of the data in terms of the average velocity of electrons and holes. The fitting of the data yielded a saturation of the electron and hole velocity of v _e = 2.3 × 10⁷ cm/s and v _h = 1.0 × 10⁷ cm/s at electric fields E > 1.5 kV/cm. The increase in rise time at high bias is consistent with the results of Monte Carlo simulations and can be partly explained by a reduction of the electron saturation velocity due to frequent impact ionization. Finally, the model was used to predict the bandwidth in diodes with shorter RC = 5 ps, giving BW = 16 GHz and BW = 21 GHz for x _j = 4 μm and x _j = 2 μm, respectively, for a gain of M = 100.     

弱P型碲镉汞材料和陷阱模式光导探测器

窄禁带碲镉汞(HgCdTe)为电子和空穴混合导电的多载流子体系材料,特别是对于弱p型材料,由于电子和空穴的迁移率相差大约两个数量级,更容易受到少数载流子电子的干扰,因此单一磁场的霍尔测试无法区分迁移率较低性能较差的n型材料和p型材料.通过变温变磁场的霍尔测试对两种碲镉汞材料的磁输运特性进行了测试区分.另外对由弱p型材料...     

Surface degradation mechanism of InP/InGaAs APDs

Bias-temperature tests of InP/InGaAs avalanche photodiodes have been conducted to evaluate long-term reliability at temperatures from 200-250° C. Wearout -failure modes with a gradual increase in dark current occur at all testing levels. Failure analyses using the light-beam-induced current method suggest that the degradation is caused by local avalanche multiplication in the guard-ring periphery. A surface degradation mechanism is proposed, namely, positive charge accumulation in the passivation film above the guard-ring region, followed by local avalanche multiplication at the guard-ring periphery. A tentative activation energy of 1.7 eV is obtained for this failure mode, and the extrapolated median life exceeds 10¹⁰ h in practical use     

GaSb: A New Alternative Substrate for Epitaxial Growth of HgCdTe

In this work, GaSb is proposed as a new alternative substrate for the growth of HgCdTe via molecular beam epitaxy (MBE). Due to the smaller mismatch in both lattice constant and coefficient of thermal expansion between GaSb and HgCdTe, GaSb presents a better alternative substrate for the epitaxial growth of HgCdTe, in comparison to alternative substrates such as Si, Ge, and GaAs. In our recent efforts, a CdTe buffer layer technology has been developed on GaSb substrates via MBE. By optimizing the growth conditions (mainly growth temperature and VI/II flux ratio), CdTe buffer layers have been grown on GaSb substrates with material quality comparable to, and slightly better than, CdTe buffer layers grown on GaAs substrates, which is one of the state-of-the-art alternative substrates used in growing HgCdTe for the fabrication of mid-wave infrared detectors. The results presented in this paper indicate the great potential of GaSb to become the next generation alternative substrate for HgCdTe infrared detectors, demonstrating MBE-grown CdTe buffer layers with rocking curve (double crystal x-ray diffraction) full width at half maximum of ～60 arcsec and etch pit density of ～10⁶ cm^?2.     

微波半导体器件失效物理述评

本文主要论述用于通信、雷达等电子系统中微波半导体器件的常见失效模式,并分析其主要失效机理。为使器件达到高可靠水平,提出可靠性设计的相应对策。     

Effect of dead space on avalanche speed [APDs]

The effects of dead space (the minimum distance travelled by a carrier before acquiring enough energy to impact ionize) on the current impulse response and bandwidth of an avalanche multiplication process are obtained from a numerical model that maintains a constant carrier velocity but allows for a random distribution of impact ionization path lengths. The results show that the main mechanism responsible for the increase in response time with dead space is the increase in the number of carrier groups, which qualitatively describes the length of multiplication chains. When the dead space is negligible, the bandwidth follows the behavior predicted by Emmons but decreases as dead space increases     

碲镉汞表面钝化层研究

本文简要报导了碲镉汞（ＭＣＴ）光导探测器表面钝化层的研究及结果，介绍了阳极氧化膜的制备，氧化膜的化学组成及氧化膜的物理化学性质。阐述了阳极氧化膜的退火处理。经过退火处理，提高了氧化膜的绝缘性能。     

A monolithic dual-band HgCdTe infrared detector structure

A monolithic HgCdTe photoconductive device structure is presented that is suitable for dual-band optically registered infrared photodetection in the two atmospheric transmission windows of 3-5 μm and 8-12 μm, which correspond to the mid-wave and long-wave infrared bands; MWIR and LWIR, respectively. The proposed structure employs a wider bandgap isolating layer between the two photosensitive layers such that an effective electrical barrier is formed thus prohibiting carrier transport between the two infrared absorbing layers of different cutoff wavelengths. The technology is demonstrated using a mature HgCdTe photoconductive device fabrication process. The resulting detectors have an MWIR cutoff of 5.0 μm, and LWIR cutoff of 10.5 μm     

HgCdTe molecular beam epitaxy technology: A focus on material properties

HgCdTe MBE technology is becoming a mature growth technology for flexible manufacturing of short-wave, medium-wave, long-wave, and very long-wave infrared focal plane arrays. The main reason that this technology is getting more mature for device applications is the progress made in controlling the dopants (both n-type and p-type in-situ) and the success in lowering the defect density to less than 2 x 10⁵/cm² in the base layer. In this paper, we will discuss the unique approach that we have developed for growing As-doped HgCdTe alloys with cadmium arsenide compound. Material properties including composition, crystallinity, dopant activation, minority carrier lifetime, and morphology are also discussed. In addition, we have fabricated several infrared focal plane arrays using device quality double layers and the device results are approaching that of the state-of-the-art liquid phase epitaxy technology.     

Independently accessed back-to-back HgCdTe photodiodes: A new dual-band infrared detector

We report the first data for a new two-color HgCdTe infrared detector for use in large dual-band infrared focal plane arrays (IRFPAs). Referred to as the independently accessed back-to-back photodiode structure, this novel dual-band HgCdTe detector provides independent electrical access to each of two spatially collocated back-to-back HgCdTe photodiodes so that true simultaneous and independent detection of medium wavelength (MW, 3–5 μm) and long wavelength (LW, 8–12 μm) infrared radiation can be accomplished. This new dual-band detector is directly compatible with standard backside-illuminated bump-interconnected hybrid HgCdTe IRFPA technology. It is capable of high fill factor, and allows high quantum efficiency and BLIP sensitivity to be realized in both the MW and LW photodiodes. We report data that demonstrate experimentally the key features of this new dual-band detector. These arrays have a unit cell size of 100 x 100 μm², and were fabricated from a four-layer p-n-N-P HgCdTe film grown in situ by metalorganic chemical vapor deposition on a CdZnTe substrate. At 80K, the MW detector cutoff wavelength is 4.5 μm and the LW detector cutoff wavelength is 8.0 μm. Spectral crosstalk is less than 3%. Data confirm that the MW and LW photodiodes are electrically and radiometrically independent.     

研发工作开始注重物理研究——利用“不存在的物质”突破研发瓶颈

电子厂商常用的一些研发方法，诸如材料的反复试验，元器件的微细化以及减少杂质等都已经无法进一步提高产品的特性。厂商们计划从物质的原理开始寻求新的研发方向。他们不再像以前那样为了研发而研发，而是把要开发设计的元器件和产品看作是整个战略的基础。最近，物理学的新成果不断涌现，那些看似不可能存在的物质和现象逐渐被发现。例如。负折射率的人工特异材料“左手材料”、磁化方向由磁场改为电流控制的“自旋反极化电子注入”．利用电子云特异动态的“强相关电子类材料”等。有几家厂商十分关注上述技术，并计划将它们早日运用到实际的研究开发中。[编者按]     

MBE HgCdTe for HDVIP Devices: Horizontal Integration in the US HgCdTe FPA Industry

Molecular beam epitaxy (MBE) growth of HgCdTe offers the possibility of fabricating multilayer device structures with an almost unlimited choice of infrared sensor designs for focal-plane array (FPA) fabrication. HgCdTe offers two major advantages that explain its dominance in the infrared photon detector marketplace. The thermal generation rate per unit volume of the material is lower and the quantum efficiency for photon absorption in the infrared is higher in HgCdTe than in any competing material—it yields devices with quantum efficiencies as high as 0.99. Recently, EPIR Technologies and DRS Infrared Technologies agreed to collaborate and examine: (i) the feasibility of employing MBE HgCdTe in the fabrication of high-density vertically interconnected photodiodes (HDVIPs), which are usually fabricated with liquid-phase epitaxy material, and (ii) the potential benefits of horizontal integration, with EPIR supplying the MBE materials to DRS for device and array fabrication. The team designed and developed passivation–absorber–passivation structures that are heavily used by DRS. This paper provides an overview of the characteristics of HDVIP devices and arrays fabricated from MBE HgCdTe and the anticipated advantages of horizontal integration in the industry. Material growth, device fabrication, and test results are presented.     

利用"不存在的物质"突破研发瓶颈

电子厂商常用的一些研发方法,诸如材料的反复试验、元器件的微细化以及减少杂质等都已经无法进一步提高产品的特性.厂商们计划从物质的原理开始寻求新的研发方向.他们不再像以前那样为了研发而研发,而是把要开发设计的元器件和产品看作是整个战略的基础.最近,物理学的新成果不断涌现,那些看似不可能存在的物质和现象逐渐被发现.例如,负折射率的人工特异材料"左手材料"、磁化方向由磁场改为电流控制的"自旋反极化电子注入"、利用电子云特异动态的"强相关电子类材料"等.有几家厂商十分关注上述技术,并计划将它们早日运用到实际的研究开发中.