Cd1-xZnxTe晶体中由本征缺陷引起的导电类型转变界面研究

在富Te生长条件下,采用垂直布里奇曼法（vertical Bridgman method, VB）生长的部分碲锌镉（Cd_1-xZn_xTe, CZT）晶体内存在导电类型转变界面。为深入探讨碲锌镉晶体导电类型转变界面形成的原因,结合晶体导电类型和红外光谱透过率的测试结果与第一性原理的理论计算进行分析,结果表明,碲锌镉晶体内的导电类型转变界面是晶体生长过程中形成的Cd空位（V_Cd）缺陷与Cd间隙（Cd_i）缺陷导致的。在富Te条件的生长过程中,Cd空位缺陷易于形成,碲锌镉晶体材料中含有大量的Cd空位缺陷,材料的导电型为p型。在晶体生长结束阶段的降温过程中,Cd原子会扩散至碲锌镉晶体中,促进了Cd间隙缺陷的形成,在碲锌镉晶体材料中形成Cd间隙缺陷,导致晶体材料的导电性转变为n型。     

高质量HgCdTe薄膜的液相外延生长

用固态HgTe作为Hg补偿源，采用开管、水平滑块推舟的富Te液相外延(LPE)方法在碲锌镉(Cd1-yZnyTe，y=0．04)衬底上外延生长大面积Hg1-xCdxTe(x=0．2)薄膜材料，通过适当的生长条件得到组分均匀、结构完整、表面形貌良好的长波碲镉汞薄膜。测试结果表明本方法生长的HgCdTe薄膜能满足目前研制红外焦平面器件的要求。     

碲锌镉晶体第二相夹杂物特性研究

高质量的碲锌镉单晶是制备碲镉汞红外焦平面器件的理想衬底材料,然而目前碲锌镉材料中的第二相夹杂物严重制约着晶体的质量.根据红外透射形貌的描述和表征,碲锌镉晶体的常见夹杂物被分成了五类,并在此基础上讨论了各自的形成机制,A、B和C类夹杂物与化学配比及其变化密切相关,而D和E类夹杂物与源材料中或者在生长工艺控制过程中氧含量相关.进一步的研究表明大尺寸、高密度的Te夹杂物将会严重降低红外透过率,同时腐蚀坑密集分布在与Cd夹杂对应的六重对称线上,该结果揭示了第二相夹杂物会产生其他缺陷的增殖,但夹杂物引起的应力影响区域是局限的.     

大尺寸碲锌镉基碲镉汞材料分子束外延技术研究

针对高质量、大规模碲镉汞红外焦平面探测器需求的持续增加,本文开展了使用分子束外延方式在50 mm×50 mm(211)B碲锌镉衬底上外延碲镉汞材料技术的研究.通过对碲锌镉衬底改进湿化学腐蚀、碲锌镉衬底预处理、碲锌镉衬底缓冲层生长、碲锌镉基碲镉汞材料工艺开发等方面的研究,开发出了能够稳定获得碲锌镉基碲镉汞材料的工艺.材料...     

掺砷碲镉汞的研究进展

掺砷碲镉汞是一科用于制作p-on-n器件和实现高性能碲镉汞探测器及多色红外焦平面阵列的关键材料。对掺砷碲镉汞的相关文献进行了归纳分析。砷渺活效率与退火条件及砷的浓度直接相关。对于掺砷浓度在10^16-10^18cm-3范围内的碲镉汞,通过300℃／16h和240℃／4sh两步退火可将样品前表面激活为P型材料,但汞空位的浓度相对于背面较高。样品背面靠近衬底处可能存在AsT和AsHg缺陷。     

50 mm×50 mm高性能HgCdTe液相外延材料的批生产技术

采用富碲垂直液相外延技术实现了50 mm×50 mm×3高性能碲镉汞外延材料的制备.外延工艺的样品架采用了三角柱体结构,并设计了防衬底背面粘液的样品夹具.为保证大面积材料的均匀性,工艺中加强了对母液温度均匀性和组分均匀性的控制,50 mm×50 mm外延材料的组分均方差达到了0.000 4,厚度均方差达到了0.4μm.在批量生产技术中,加强了对单轮次生长环境的均匀性和生长轮次之间生长条件一致性的控制,同一轮次生长的3片材料之间的组分偏差小于0.000 4,厚度偏差小于0.1μm,不同生长轮次之间材料的组分之间的波动在±0.002左右,厚度之间的波动在±2μm左右.工艺中对碲锌镉衬底的Zn组分、缺陷尺寸和缺陷密度也加强了控制,以控制大面积外延材料的缺陷,晶体双晶衍射半峰宽(FWHM)小于30弧秒,外延材料的位错密度小于1×105cm~(-2),表面缺陷密度小于5 cm~(-2).外延材料经过热处理后,汞空位型的P型Hg0.78Cd0.22Te外延材料77 K温度下的载流子浓度被控制在8~20×1015cm-3,空穴迁移率大于600 cm2/Vs.材料整体性能和批生产能力已能满足大规模碲镉汞红外焦平面探测器的研制需求.     

碲镉汞富汞热处理技术的研究

利用自行研制的垂直开管富汞热处理设备，研究了碲镉汞（HgCdTe）富汞热处理技术。经富汞条件下3000C热处理和后续的常规N型热处理，As掺杂的Hg1-xCd，Te分子束外延材料中的As原子已被激活成P型受主，As原子激活率同石英管封管热处理试验的结果基本一致。对包括3in Si基衬底在内的材料退火前后表面形貌进行的比较显示，样品表面形貌可得到很好的保护。研究结果表明，碲镉汞开管富汞热处理技术可用于第三代碲镉汞红外焦平面技术所需大面积多层掺杂异质外延材料的制备。     

原位退火对碲锌镉晶体第二相夹杂缺陷的影响

采用传统布里奇曼法生长碲锌镉晶体,在配料过程中添加适当过量的Cd,并在晶体生长结束阶段的降温过程中加入晶锭原位退火工艺,晶体的第二相夹杂缺陷得到了有效抑制。根据晶体第二相夹杂缺陷的形成机理,结合热扩散理论和碲锌镉晶体的P-T相图,研究了退火温度对晶体第二相夹杂缺陷密度和粒度（尺寸）的影响,获得了抑制碲锌镉晶体第二相夹杂缺陷的退火条件。利用优化的退火条件制备碲锌镉晶体,晶体第二相夹杂缺陷的尺寸小于10 μm,密度小于250 cm－2。     

中国电科11所碲镉汞薄膜材料制备技术进展

碲镉汞材料具有响应速度快、量子效率高、带隙连续可调等优点,广泛应用于红外探测领域,本文报道了近年来中国电科11所在碲镉汞薄膜材料制备方面的技术进展。在碲锌镉衬底材料制备方面,已突破135mm碲锌镉晶体生长技术,碲锌镉衬底平均位错腐蚀坑密度(EPD) <1×104cm-2,具备了80mm×80mm规格碲锌镉衬底的批量生产能力。在液相外延碲镉汞薄膜制备方面,富碲水平液相外延碲镉汞薄膜平均位错腐蚀坑密度EPD<4×104cm-2,具备80mm×80mm规格碲镉汞薄膜的制备能力;富汞垂直液相外延实现高质量双层异质结碲镉汞薄膜材料批量化制备,该种材料的半峰宽(FWHM)控制在(20～40)arcsec范围内,碲镉汞薄膜厚度极差≤±06μm。在分子束外延碲镉汞薄膜方面,实现了6 in硅基碲镉汞材料制备,组分标准偏差≤00015,表面宏观缺陷密度≤100cm-2;碲锌镉基碲镉汞材料已具备50mm×50mm制备能力,组分标准偏差为0002,厚度标准偏差为0047μm。从探测器验证结果来看,基于富碲水平液相外延碲镉汞薄膜实现了1 k×1 k、2 k×2 k等规格红外焦平面探测器的工程化制备;采用双层异质结碲镉汞薄膜实现了高温工作、长波及甚长波探测器的制备;使用分子束外延制备的碲镉汞薄膜实现了27 k×27 k、54 k×54 k、8 k×8 k等规格红外焦平面探测器研制,在宇航领域有巨大的应用潜力。     

碲锌镉晶体中微观缺陷分析

碲锌镉晶体(CdZnTe)是一种性能优异的红外焦平面探测器衬底材料,其质量的优劣将直接影响外延层的结构与性能,而晶体中的微观缺陷常常是影响衬底材料质量的主要因素之一。本文采用红外透射显微镜、金相显微镜、X射线形貌仪、扫描电镜、白光干涉仪等仪器系统地检测和研究了碲锌镉晶体中存在的微观缺陷。研究发现碲锌镉晶体样品中主要存在层错、孪晶界和包裹物等微观缺陷,结合晶体缺陷理论详细地分析了碲锌镉晶体中微观缺陷的形成机制。     

Engineering Interface Composition for Passivation of HgCdTe Photodiodes

A compositionally graded surface layer has been created for the passivation of Hg_1-xCd_xTe photodiodes. The graded CdTe-Hg_1-xCd_xTe interface was created by deposition of CdTe and subsequent annealing. It was found that the composition gradient and width of the graded region could be tailored by adopting a suitable annealing procedure. The effect of grading on the interface electrical properties and photoelectrical properties was studied by X-ray photoelectron spectroscopy (XPS), photoconductive decay, and C-V measurements. Insulator fixed-charge density and interface-trap density could be reduced to 3times10¹⁰ cm ^-2 and 2times10¹⁰ cm^-2middoteV^-1, respectively, by creating a graded interfacial composition. The interface conditions so engineered led to a low surface recombination velocity ~3000 cm/s. A direct correlation has been established between the process conditions, interfacial composition, and the electrical/photoelectrical properties of the CdTe-Hg_1-xCd_xTe heterostructures. The passivation layer formed by this method is shown to be suitable for the fabrication of high-performance infrared detectors     

High-density photogenerated free-carrier spin relaxation processesin Wurtzite semiconductors: CdSe and semimagnetic semiconductorCd1-xMnxSe

Picosecond time-resolves spin relaxation kinetics of high-density free carriers is investigated at low temperatures on CdSe (x=0) and in the dilute semimagnetic semiconductor Cd_1-xMn_x Se for x=0.05 and 0.10. The fast spins relaxation observed in CdSe results from a mechanism associated with the noncentrosymmetric character of the band structure for this material. This process is similar to the one proposed by M.I. D'yakonov and V.I. Perel' (1971) for the zinc blende crystal structures. The spin relaxation times in CdSe are on the order of 30 ps. The spin relaxation time are <20 ps in semimagnetic semiconductor Cd_1-xMnSe and are consistent with spin-flip Raman scattering measurements. The increase in spin relaxation rate relative to CdSe is explained in terms of the carrier spin exchange between the carriers and the magnetic spin sites. A probable cause for the reduction in the observed spin polarization factor for carriers in Cd_1-xMn_xSe ( x≠0) is presented     

Heterojunction blocking contacts in MOCVD grown Hg1-xCdxTe long wavelength infrared photoconductors

The theoretical and experimental performance of Hg_1-xCd _xTe long wavelength infrared (LWIR) photoconductors fabricated on two-layer heterostructures grown by in situ MOCVD has been studied. It is shown that heterojunction blocking contact (HBC) photoconductors, consisting of wider bandgap Hg_1-xCd_x Te on an LWIR absorbing layer, give improved responsivity, particularly at higher applied bias, when compared with two-layer photoconductors incorporating n⁺/n contacts. An extension to existing device models is presented, which takes into account the recombination rate at the heterointerface and separates it from that occurring at both the contact-metal/semiconductor and passivant/semiconductor interfaces. The model requires a numerical solution to the continuity equation, and allows the device responsivity to be calculated as a function of applied electric field. Model predictions indicate that a change in bandgap across the heterointerface corresponding to a compositional change of Δx⩾0.04 essentially eliminates the onset of responsivity saturation due to minority carrier sweepout at high applied bias. Experimental results are presented for frontside-illuminated n-type Hg_1-xCd_xTe photoconductive detectors with either n⁺/n contacts or heterojunction blocking contacts. The devices are fabricated on a two-layer in situ grown MOCVD Hg_1-xCd_xTe wafer with a capping layer of x=0.31 and an LWIR absorbing layer of x=0.22. The experimental data clearly demonstrates the difficulty of forming n ⁺/n blocking contacts on LWIR material, and indicates that heterojunctions are the only viable technology for forming effective blocking contacts to narrow bandgap semiconductors     

Diluted magnetic semiconductors

Diluted magnetic semiconductors (DMSs), i.e. semiconducting crystals whose lattice is made up in part of substitutional magnetic ions (e.g. Cd_1-xMn_xTe, Hg_1-xFe_x Se, Zn_1-xCo_xS), are reviewed. The focus is on materials of the type A_1-x^II Mn_xB ^VI, which are the most thoroughly understood. However, the similarities and differences between these materials and the A_1-x ^IIFe_xB^VI and A_1-^IICo_xB^VI systems are discussed wherever information on the latter system is available. The band structure of the materials, which determines their basic semiconducting properties, is examined. Special attention is given to exchange interactions between the magnetic ions themselves (the d -d interaction) and the interaction between the magnetic ions and band electrons (the sp-d interaction). Magnetic phenomena in DMS alloys are considered. Special attention is given to the physics of layered structures, such as quantum wells and superlattices, involving DMS materials. The prospects of device applications made possible by the properties of DMS alloys are assessed     

Hg1-xCdxTe metal-semiconductor-metal (MSM)photodetectors

Metal-semiconductor-metal (MSM) detectors with active layers of Hg _1-xCd_xTe (x=0.62-0.74) and electrode spacings of 2, 4, and 6 μm have been fabricated and characterized. Direct-current measurements have shown a low dark current and high responsivity from 0.15 to 1.5 A/W at 10-V bias. The lowest values of dark current (0.16 mA cm²) were obtained for detectors which incorporated an overlayer of CdTe. For detectors without the overlayer, increasing the Cd mole fraction resulted in a decrease in the dark current and a reduction in the 300-nm responsivity. Measurements of frequency response for these detectors show a maximum loss of 8 dB to 20 GHz. These results compare favorably with high-performance MSM detectors based on In_0.53Ga_0.47As with a lattice-matched barrier layer of In_0.52Al_0.48As     

980 nm compact optical isolators using Cd1-x-yMnxHgyTe single crystals for high power pumping laserdiodes

The author have developed compact optical isolators operating at 480 nm wavelength with an insertion loss of 1.0 dB, isolation of 30 dB, size of 4φ×4.5 mm and endurance against laser power of ~500 mW using Cd_1-x-yMn_xHg_yTe single crystals for the first time     

Hg0.4Cd0.6Te 1.55-μm avalanche photodiodenoise analysis in the vicinity of resonant impact ionization connectedwith the spin-orbit split-off band

The authors describe the electrical and optical characterization of three Hg_1-xCd_xTe avalanche photodiodes manufactured using planar technology with composition parameter x near 0.6. This alloy composition leads to devices that are well suited for 1.55-μm detection. From the noise analysis under multiplication, the authors show the tight dependence of the ratio β/α (of the hole; and electron ionization coefficient, respectively) upon x and the ratio Δ/E_g where Δ is the spin-orbit splitting energy and E _g is the bandgap energy. It turns out that in these alloys around x=0.6, Δ is very close to the bandgap energy so β/α reaches its maximum value. Owing to this property, which is characteristic of II-VI compounds, Hg_1-xCd_xTe is a good candidate for 1.3-μm to 1.6-μm avalanche photodiodes     

Low-temperature annealing of polycrystallineSi1-xGex after dopant implantation

Hall effect measurement was employed to study the isothermal annealing of boron or phosphorus implanted polycrystalline Si_1-x Ge_x thin films, with x varying from 0.3-0.55. X-ray diffraction and cross-sectional transmission electron microscopy were used to study the crystal structure, whereas X-ray photoelectron spectroscopy was used to determine the film composition and the chemical bonding states of the elements. In low-temperature (⩽600°C) annealing, the conductivity, the dopant activation, and the Hall effect mobility decreased during extended annealing. The effective activation of phosphorus was less than 20% and decreased with increasing Ge content. Boron activation could reach above 70%. It was also found that Si_1-xGe_x could be oxidized at 600°C in a conventional furnace even with N₂ protection, especially for phosphorus doped films with high Ge content. Consequently, a low-temperature SiO₂ capping layer is necessary during extended annealing     

Spatial integration of direct band-to-band tunneling currents ingeneral device structures

A simplified integration technique for direct band-to-band tunneling current calculation in semiconductor devices of 1- or 2-D general device structures is described. The integration, along part of the depletion region, is of a tunneling generation function which depends on the local electric field. The simplified integration scheme relies on Kane's parabolic shaped gap barrier which accurately applies to such narrow-bandgap semiconductors as InSb and Hg_1-xCd_xTe. Tunneling current and zero bias resistance calculations in 1-D Hg_1-xCd_xTe p-n junctions using the proposed technique are presented. The extension of the technique to 2-D potential structures is demonstrated by modeling peripheral surface tunneling currents. The results compare well with measured reverse breakdown currents of InSb gate-controlled diodes