P-type HgCdTe Research Articles

Influence of annealing on the surface structure evolution of intrinsic p-type HgCdTe films.

In this study, scanning electron microscopy, atomic force microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and the Hall effect were used to characterize the microscopic morphology, structural features and electrical properties of a HgCdTe film surface before and after annealing. The effect of annealing on the surface quality of the films was studied in detail. The results showed that the annealing treatment reduced the roughness, improve the denseness and uniformity and ameliorate the surface crystallinity. It also eliminated the defects, such as stress and stacking layer errors, caused by lattice distortion during the growth of the HgCdTe films. An increase in surface carrier concentration and mobility after annealing and improved electrical properties of the intrinsic p-type HgCdTe materials were also observed. It is therefore shown that annealing had a significant effect on improving the surface quality of HgCdTe films.

Photoluminescence Study of As Doped p-type HgCdTe Absorber for Infrared Detectors Operating in the Range up to 8 µm

A HgCdTe photodiode grown by chemical vapor deposition (MOCVD) on a GaAs substrate operating in the long-wave infrared (LWIR) range was characterized using photoluminescence (PL) measurements. At high temperatures, the PL spectrum originates from a free-carrier emission and might be fitted by a theoretical expression being the product of the density of states and the Fermi–Dirac distribution. At low temperatures, the PL spectrum consists of multiple emission peaks that do not originate solely from the energy gap. Such spectra are not unambiguous to interpret due to the prominence of different optical transitions. Spectral response (SR) measurements were used to determine the energy gap (Eg) and extract the band-to-band transition from the PL spectra. PL peaks visible within the band gap were fitted by a Gaussian distribution. To identify the sources of individual emission peaks, excitation power dependence analysis was conducted. Band-to-band, free-to-bound, acceptor-bound exciton, and defect-bound exciton transitions were identified. At low temperatures, transitions are mainly impurity-related, with shallow impurity levels estimated to be 6 meV and 16 meV for the donor and acceptor, respectively, while deep-level impurities were associated with VHg. The latter transition with an energy of about 78 meV does not vary with temperature. Its relative positions with respect to the energy gap is 0.8 Eg at 18 K and 0.67 Eg at 80 K.

Structural, compositional, morphological and electrical characteristics of thermally evaporated Au Ohmic Contact on p-type HgCdTe substrate for possible infrared detectors

Gold (Au) thin films were deposited over the HgCdTe (mercury cadmium telluride) surface by a thermal-evaporation deposition technique. The thermally grown Au films were investigated using different characterization techniques, X-ray diffraction (XRD), energy dispersive X-ray (EDX) analysis, atomic force microscopy (AFM), scanning electron microscopy (SEM), and current-voltage (I–V)/resistance measurement. The maximum film growth occurs along with the preferred orientation (111). The grown Au film possesses a cubic fcc structure, desired elemental compositions, and purity. The AFM confirms that the films were uniform, dense, and had very low roughness. The films attained the desired grain size of film-forming particles. The optimized Au films were established and further employed to fabricate the transfer length method (TLM) structure with configuration (Au/p-HgCdTe). The I–V and resistance measurements of the as-deposited TLM structure produced the Ohmic Au-contact with low specific contact resistance (ρc) of 2.73 × 10−3 Ω cm2. Annealing treatment (contacts annealed for 2 h at 80 °C in the air) was applied to the as-deposited TLM structure and the measured value of specific contact resistance (ρc) for the annealed Au contact (Ohmic behaviour) is 7.11 × 10−4 Ω cm2 that is relatively low than the as-deposited contacts. Thermal annealing has reduced the magnitude of ρc by about one order. TLM structures (as-deposited and annealed) exposed the efficiency of Au thin films as an effective Ohmic contact. Thus, Au thin films could be used to create a compelling and appropriate Ohmic p-contact to fabricate HgCdTe infrared detectors.

Nano-scale structural studies of defects in arsenic-implanted n and p-type HgCdTe films

Bright–field and high-resolution transmission electron microscopy were used for nano-scale structural studies of defects induced by implantation of arsenic ions with 190 keV energy and 1014 cm–2 fluence in n and p-type Hg0.78Cd0.22Te films grown by molecular-beam epitaxy. A similarity in defect pattern formed by arsenic implantation in n and p-type material was observed. The electrical properties of the implanted layers in n and p-type films also appeared to be similar, confirming the results of microscopic observations.

Effect of Surface Recombination on the Parameters of Photodiodes Based on HgCdTe Semiconductor Structures

The surface recombination rates for p-type HgCdTe layers with different dopant concentrations and trap densities Nt are calculated. It is shown that, at the given initial parameters, the surface recombination rate Smax lies in the range of 10–104 cm/s. The current sensitivity for p-type HgCdTe is simulated using the dependence of quantum efficiency in the approximation of large lifetimes τn0 and large diffusion lengths Ln of minority charge carriers, taking into account the effect of the surface recombination rate.

Maximum entropy mobility spectrum analysis of LPE-grown and anodic oxidated Hg1-xCdxTe(x=0.237)

In this paper, magneto-transport properties of the LPE-grown and anodic oxidated p-type Hg1-xCdxTe(x=0.237) films have been studied by using maximum entropy mobility spectrum analysis (ME-MSA) technique. It can be found that the high-mobility electron (μe∼2 × 104cm2/Vs) has considerable contributions to the conduction of anodic oxidated Hg1-xCdxTe(x=0.237) film, but not in LPE-grown Hg1-xCdxTe(x=0.237) film. The high-mobility electron maintains dominant contributions from 11k to 150k, which can be attributed to two-dimensional electron gas in the inversion layer of anodic oxidated p-type Hg1-xCdxTe(x=0.237) film. In addition, we also observe the nonphysical contributions of low mobility electrons (μe∼0.08 × 104cm2/Vs) in mobility spectrum of both LPE-grown and anodic oxidated p-type HgCdTe films. The low-mobility electrons, so-called mirror peaks, can be interpreted as a consequence of magnetic freeze-out of holes in vacancy-doped HgCdTe, which disappeared at T=150k.

Theoretical utmost performance of the (1 0 0) long-wave HgCdTe Auger suppressed photodetectors grown on GaAs

The vast majority of HgCdTe detectors designed to detect long wavelength (8–14μm) infrared radiation must be cooled to achieve the required performance. It must be stressed that cooling requirement is both expensive and bulky and the main objective is to reach higher operating temperature condition preserving near background limited performance and high speed response. In order to reach that goal the thermal generation rate needs to be reduced below the photon generation rate. Except Auger 7, p-type HgCdTe active layers are mostly limited by technology dependent Shockley-Read-Hall generation-recombination processes. One of the ways to reduce of the trap density is a growth of the (100) HgCdTe epilayers on GaAs substrates. In addition, that orientation allows reaching lower carrier concentration in comparison to the commonly used (111) orientation (5×1015–1016cm−3). In this paper we report on theoretical utmost performance of (100) HgCdTe Auger suppressed photodetectors grown on GaAs substrates. (100) HgCdTe orientation allows to reduce p-type doping to the level of ∼5×1014cm−3 in analyzed long wavelength range. In addition Shockley-Read-Hall traps could be reduced to the level of ∼4.4×108cm−3 resulting in suppression of the dark current by nearly two orders of magnitude within the range ∼20÷0.31A/cm2 and detectivity, ∼1010−1011cmHz1/2/W at temperature 230K, voltage 200mV.

Magnetotransport property of negative band gap HgCdTe bulk material

In recent years, spintronic devices have attracted more and more attention because of their good characteristics. The spin-orbit coupling of HgCdTe is one of the most important parts in the study of narrow gap semiconductors. The magneotransport properties of the Hg0.9Cd0.1Te bulk material with an inverted band structure have been hardly reported so far. The spin-orbit coupling strength of HgCdTe is closely related to the band gap. The strength of the spin-orbit coupling increases with the width of the band gap decreasing. Thus, Hg0.9Cd0.1Te should have strong spin-orbit coupling. Meanwhile it should be one of the most suitable materials to fabricate spintronic devices. The main propose of our experiments is to prove this inference. Inside the sample, Rashba spin-orbit interaction (SOI) strongly influences the spin-splitting due to the lack of structural inversion symmetry. In other words, Rashba SOI is the main part of the zero field spin splitting △0. The band structure of Hg1-xCdxTe can be precisely tuned by changing the composition of Cd which keeps an inverted band order when 0 x Γ8 band lying below the Γ6 band (or equivalently a positive band gap) when x0.165. In this paper, the p-type HgCdTe bulk material with Cd component of 0.1 is grown by single crystal. Anodic oxidation is used to induce an inversion layer on the HgCdTe bulk, and indium is used to facilitate Ohmic contacts. The magnetoresistance is measured in the van der Pauw configuration, and the magnetic field is applied perpendicularly to the film. All measurements are carried out in an Oxford Instruments He cryogenic system. At 1.5 K and zero gate voltage, the carrier density n is 1.3×1016 m-2. Clear Shubnikov-de Haas (SdH) oscillation in ρxx and quantum Hall plateaus of Rxy are observed in the Hg0.9Cd0.1Te bulk material with an inverted band structure is investigated in magnetotransport experiment. This indicates that our sample is a good transistor. Fast Fourier transformation is used to deduce the zero-field spin-splitting △0 which is about 26.55 meV. By studying the beating patterns in SdH oscillations we find that the effective g-factor is about-11.54. Both the large zero field spin splitting and the negative effective g-factor suggest that Hg0.9Cd0.1Te has really strong spin-orbit coupling. The investigation of SOI in Hg0.9Cd0.1Te can increase our knowledge of Hg-based narrow-gap semiconductors and benefit the field of spintronics.

Theoretical utmost performance of (100) mid-wave HgCdTe photodetectors

HgCdTe detectors designed to detect mid-wavelength (3–5 μm) infrared radiation must be cooled to reach the required performance. The cooling requirement makes the sensor system both expensive and bulky and the fundamental goal is to reach higher operating temperature condition preserving near background limited performance with high detectivity and high speed response at the same time. In order to reach higher operating temperature condition the thermal generation rate must to be suppressed under the photon generation rate. Except Auger 7 generation-recombination process, p-type HgCdTe is mostly limited by technology dependent Shockley-Read-Hall generation-recombination mechanism. One of the ways to reduce the trap density is a growth of the (100) HgCdTe on GaAs substrates. That orientation allows reaching lower carrier concentration ~5 × 1014 cm−3 in comparison to the commonly used (111) orientation ~5 × 1015 cm−3 in mid-wavelength infrared range. In addition, it was presented that Shockley-Read-Hall traps density could be reduced to the level of ~4.4 × 108 cm−3. The theoretical simulations related to the utmost performance of the (100) HgCdTe Auger suppressed structures are presented. Dark current is reported to be reduced by more than one order of magnitude within the range ~6 × 10−2–3 × 10−3 A/cm2. Detectivity increases within range ~3–12 × 1011 cm Hz1/2/W (wavelength ~5 μm) at temperature 200 K and voltage 200 mV.

Dense Array Effects in SWIR HgCdTe Photodetecting Arrays

This paper presents results from three-dimensional quantitative modeling on dense, moderately doped [ND (NA) = 5 × 1015 cm−3] short-wave infrared (SWIR) p+n and n+p Hg1−xCdxTe double planar heterostructure photodetecting arrays with absorber x = 0.451 and cap x = 0.55. At uniform reverse bias, the competition for minority carriers between closely spaced diodes preserves densities below equilibrium levels throughout the absorber. This carrier suppression has several consequences in addition to suppressing dark current by constraining the minority-carrier gradients at each diode junction. First, the dense arrays maintain volume-average negative net radiative recombination rates (negative luminescence) roughly an order of magnitude larger than comparably biased isolated diodes. Second, the negative excess minority-carrier densities suppress the volume-average net Auger recombination rate by roughly an order of magnitude in dense n-type HgCdTe arrays compared with a single diode. Third, the long minority electron diffusion lengths in the p-type HgCdTe absorber not only suppress lateral diffusion currents, but do so in a manner that provides negative differential resistance. By suppressing intrinsic recombination rates, or lateral diffusion currents, each effect can contribute to increasing R0A products in SWIR HgCdTe dense arrays. These effects should be considered when optimizing device structures for pitch, thickness, feature size, doping, and bias points.

Temperature-sensitive junction transformations for mid-wavelength HgCdTe photovoltaic infrared detector arrays by laser beam induced current microscope

In this paper, we report on the disappearance of the photosensitive area extension effect and the unusual temperature dependence of junction transformation for mid-wavelength, n-on-p HgCdTe photovoltaic infrared detector arrays. The n-type region is formed by B+ ion implantation on Hg-vacancy-doped p-type HgCdTe. Junction transformations under different temperatures are visually captured by a laser beam induced current microscope. A physical model of temperature dependence on junction transformation is proposed and demonstrated by using numerical simulations. It is shown that Hg-interstitial diffusion and temperature activated defects jointly lead to the p-n junction transformation dependence on temperature, and the weaker mixed conduction compared with long-wavelength HgCdTe photodiode contributes to the disappearance of the photosensitive area extension effect in mid-wavelength HgCdTe infrared detector arrays.

Novel signal inversion of laser beam induced current for femtosecond-laser-drilling-induced junction on vacancy-doped p-type HgCdTe

In this paper, experimental results of temperature-dependent signal inversion of laser beam induced current (LBIC) for femtosecond-laser-drilling-induced junction on vacancy-doped p-type HgCdTe are reported. LBIC characterization shows that the traps induced by femtosecond laser drilling are sensitive to temperature. Theoretical models for trap-related p-n junction transformation are proposed and demonstrated using numerical simulations. The simulations are in good agreement with the experimental results. The effects of traps and mixed conduction are possibly the main reasons that result in the novel signal inversion of LBIC microscope at room temperature. The research results provide a theoretical guide for practical applications of large-scale array HgCdTe infrared photovoltaic detectors formed by femtosecond laser drilling, which may act as a potential new method for fabricating HgCdTe photodiodes.

Electrical characteristics of electroless gold contacts on p-type Hg1−xCdxTe

High contact resistance of the order of 10−3Ωcm2 observed in p-type HgCdTe is one of the practical problems in the production of fine pitch high operating temperature and avalanche photodiode detector array. Electrical and compositional measurements on Au/p-HgCdTe are reported to understand the difficulties in reducing the contact resistance in HgCdTe detectors. Characterization of Au contacts on p-type Hg1−xCdxTe (x=0.3) formed by electrode-less (electroless) process and current transport mechanism are discussed. SIMS depth profiling of interfacial layer formed by the reaction of gold chloride with HgCdTe have been analyzed. Extent of the interfacial layer containing Au, Te, O and Cl is found to increase with increasing deposition time. Effect of annealing on the migration of Au across the contact region and electrical characteristics are presented. Heavily doped HgCdTe region with NA=1017cm−3 is produced beneath the contact regions after annealing at 80°C leading to an order of magnitude improvement in the specific contact resistance. These results are useful for the creation of Au/p-HgCdTe contacts in a controlled and reproducible manner.

Structural and Energetic Analysis of Group V Impurities in p-Type HgCdTe: The Case of As and Sb

Although molecular beam epitaxy technology-based arsenic-doped Hg1−x Cd x Te has been extensively studied, according to the newly proposed framework of the defect-complex-based p-type doping mechanism, heavier group V elements such as antimony (Sb) should have a different doping behavior because of their larger radius which can cause larger lattice distortion. In this work, we performed first-principles calculations and took As and Sb as examples to study this issue. The substitutional doping, interstitial doping (including split, tetrahedral, and hexagonal interstitial sites), and defect complex doping forms for arsenic and antimony are all investigated. A significant lattice distortion is found in hexagonal and split-site interstitial-Sb-doped Hg0.75Cd0.25Te due to the larger covalent radius of Sb. Compared with As, Sb can lead to a more complicated configuration change in the case of SbHg-V Hg-SbHg tridoping, and the interstitial Sb is found to be stable even with the coupling of Hg vacancies through detailed energetic calculations, indicating that the interstitial Sb has greater ability to form stable defect complexes, and thus great potential to be a more appropriate p-type dopant. This study provides more complementary understanding of the behaviors of group V impurities in HgCdTe.

Design of Phosphorus-Containing MWIR Type-II Superlattices for Infrared Photon Detectors

Type-II strained layer superlattices (SLSs) offer a broad range of design degrees of freedom to help optimize their properties as absorber layers of infrared photon detectors. We theoretically examine a new class of mid-wavelength infrared (2-5 μm bandpass) Type-II structures with two-layer InGaSb/InPSb and four-layer InAs/GaSb/InAs/InPSb SLS periods. Phosphorous-containing SLSs are a promising approach to improving infrared photon detector performance due to providing a new set of material properties, including favorable valence band offsets. P-based SLSs of four-layer type InAs/GaSb/InAs/InPSb were found to be among the best 5-μm gap SLSs that we have modeled. Among the studied designs, the lowest dark current in an ideal structure is predicted for a four-layer 23.6 A InAs/20 A GaSb/23.6 Å InAs/60 Å InP 0.62Sb0.38 SLS. Its predicted ideal dark current is about 35 times lower than an n-type HgCdTe-based photodiode absorber and six times lower than a p-type HgCdTe one for the same bandgap, temperature, and dopant concentration. We also discuss a defect mitigation strategy that involves positioning the SLS gap in an energy range that avoids defect levels and show how this applies to the aforementioned P-containing SLS.

Scanning tunneling spectra for the etched surface of p-type HgCdTe

PDF HTML阅读 XML下载 导出引用 引用提醒 液相外延p型碲镉汞表面区与腐蚀凹坑的不同扫描隧道谱特征 DOI: 作者: 作者单位: 上海大学理学院物理系和微结构实验室,上海市上大路号,上海大学理学院物理系和微结构实验室,上海市上大路号,上海大学理学院物理系和微结构实验室,上海市上大路号,上海大学理学院物理系和微结构实验室,上海市上大路号,上海大学理学院物理系和微结构实验室,上海市上大路号,上海大学理学院物理系和微结构实验室,上海市上大路号 作者简介: 通讯作者: 中图分类号: 基金项目: 上海市重点学科建设无线电物理专项基金（S30105） Scanning tunneling spectra for the etched surface of ptype HgCdTe Author: Affiliation: Dept of Physics and Laboratory for Microstructures,Shanghai University,Dept of Physics and Laboratory for Microstructures,Shanghai University,Dept of Physics and Laboratory for Microstructures,Shanghai University;China,Dept of Physics and Laboratory for Microstructures,Shanghai University,China,Dept of Physics and Laboratory for Microstructures,Shanghai University,Dept of Physics and Laboratory for Microstructures,Shanghai University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:利用超高真空扫描隧道显微镜对经过溴甲醇溶液腐蚀处理的液相外延碲镉汞材料进行了表征.发现经过腐蚀处理（3%浓度，2.5 min）的样品表面出现高密度的凹坑结构，凹坑深度约几十纳米，横向尺度在几十到几百纳米之间.扫描隧道谱测量表明，腐蚀样品表面平坦区呈现较大表观带隙，需考虑针尖诱导的能带弯曲效应，而凹坑区在零偏压区的扫描隧道谱线则近似为线性变化，说明该区域包含较高的带隙态并直接参与隧穿，从而掩盖了带隙信息. Abstract:Ultrahigh vacuum scanning tunneling microscopy（STM） and spectroscopy （STS）were used to characterize Hg1-xCdxTe grown by liquidphase epitaxy (LPE) method. The sample was etched with 3% Brominemethanol in 2.5 minutes. The STM images display submicrometersized pit structures with depths ranging from a few tens to a few hundreds nanometers. The scanning tunneling spectra show a larger apparent gap than the energy band gap of the bulk material due to the tipinduced band bending effect. In contrast, the scanning tunneling spectra of the pits show a finite slope through zero volt, implying the contribution of high density of band gap states which blur out the band gap information. 参考文献 相似文献 引证文献

The bulk generation-recombination processes and the carrier lifetime in mid-wave infrared and long-wave infrared liquid nitrogen cooled HgCdTe alloys

Comprehensive study of the bulk generation-recombination mechanisms and the carrier lifetime in long wavelength and mid wavelength infrared indium-doped as well as arsenic- and mercury vacancies-doped HgCdTe ternary alloys at liquid nitrogen temperature has been done. The excess minority carrier lifetime in HgCdTe materials has been calculated by solving the set of non-linear transport equations under conditions of small deviation from equilibrium. The results of numerical calculations of the carrier lifetime determined by the Auger 1, Auger 7, and Shockley-Read-Hall mechanisms related to mercury vacancies have been compared with experimental data available in the literature. We re-examine the carrier lifetime, including the impact of the electrical screening on Coulomb interaction of carriers in the Auger process to explain certain inconsistency between theoretical prediction and experimental data especially in highly doped p-type HgCdTe material. Moreover, the marginal significance of the interband radiative recombination has been indicated.

Performance of Mid-Wave Infrared HgCdTe e-Avalanche Photodiodes

HgCdTe has been shown to be the first semiconductor exhibiting single-carrier multiplication in avalanche photodiodes (APDs) up to multiplication factors larger than 1000 and with close to zero excess noise. These results have opened a new horizon for low-flux and/or versatile imaging from visible wavelengths up to the infrared cutoff wavelength of the APDs. In this paper we report the first results on mid-wave infrared (MWIR) cutoff wavelength APDs manufactured at Sofradir in collaboration with CEA-LETI. These APDs display high gain and low dispersion on and between wafers. In particular, a record avalanche gain M of over 10,000 is observed for some diode structures. This result provides an additional demonstration of the stability of single-carrier multiplication in HgCdTe and shows that the technological processes used at Sofradir are well adapted to APD manufacturing. A dedicated readout integrated circuit (ROIC) with 384 × 288 format and l5 μm pitch was developed to address both passive amplified imaging and active laser-assisted imaging. Arrays were produced using p-type HgCdTe films grown by liquid-phase epitaxy on CdZnTe substrates. Focal-plane array (FPA) performance is reported for ROICs hybridized with APD arrays manufactured at Sofradir. Operability of the best devices exceeds 99.7% for gains up to 55. Relative dispersions of the gain and ROIC output voltage are lower than 4%. The excess noise factor is lower than 1.4 over this range of gains.

Temperature dependent characteristics of HgCdTe variable-area photovoltaic detectors on Si substrates

The variable-area HgCdTe/Si photovoltaic detector was investigated in this paper.By analyzing the relationship of dark current density(J) and the ratio of perimeter to area(p/A) under different reverse bias,it is indicated that the n-on-p type HgCdTe/Si photovoltaic detector has a significant surface leakage current under larger reverse bias.The minority carrier diffusion length at different temperature can be obtained by fitting the relationship between the product of zero-bias resistance and area(R0A) and p/A.It shows that the minority carrier diffusion length increases with the increase of temperature below 200 K,while the minority carrier diffusion length decreases with the increase of temperature above 200 K.The minority carrier lifetime of Hg-vacancy p-type HgCdTe on Si substrate was calculated from the minority diffusion length at different temperature.It was concluded that the lifetime of HgCdTe/Si minority carrier and its relationship with the temperature is the same as that of HgCdTe/CdZnTe material by comparing the minority carrier lifetime for these two kinds of materials.

Study on p-type HgCdTe single crystals by mobility spectrum analysis

Very-narrow-gap HgCdTe single crystals were multicarrier semiconductor material with multiple electron and hole species in the conduction band.Especially,for p-type HgCdTe single crystals,the evaluation based on conventional measurements at a single magnetic field could lead to erroneous conclusions because of the large ratio of the electron mobility to hole mobility(b=μe/μh≈102).Variable-magnetic-field Hall measurements were performed on bulk-grown HgCdTe single crystals at various temperatures.The mobility spectrum analysis(MSA) technique were employed in this paper.An accurate determination of both the carriers type and the carriers mobility usually involves multicarrier characterization.At the same time,the effect of the autoxidation for the HgCdTe multicarrier system was investigated.