长波碲镉汞材料As掺杂激活研究

利用离子注入工艺实现长波碲镉汞材料的As掺杂,As作为掺杂介质表现出两性掺杂行为,而As只有占据Te位成为受主才能形成P型碲镉汞材料。通过对砷掺杂碲镉汞材料在汞气氛中进行退火,分析注入退火引起的样品电学性质的变化,对砷激活退火采用的汞压、温度及时间进行了研究,利用霍尔测试和二次离子质谱仪(SIMS)等手段分析激活效果,研究发现,高温富汞热退火可以实现碲镉汞As激活。     

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。     

MBE生长碲镉汞的砷掺入与激活

采用As掺杂和激活技术制备的p+-on-n异质结材料是获得高性能长波碲镉汞红外焦平面器件的关键技术之一,得到了广泛关注.采用变温IV拟合的方法,对不同As掺入浓度与器件结性能相关性进行了分析,发现降低结区内As掺杂浓度可以有效抑制器件的陷阱辅助隧穿电流.拟合结果表明,较高浓度的Nt很可能与高浓度As掺入相关.因此As的稳定均匀掺入和激活被认为是主要技术挑战.实验研究了分子束外延过程中Hg/Te束流比与As掺入效率的关系,发现相对富Hg的外延条件有助于提高As掺杂效率.研究还发现As的晶圆内掺杂均匀性与Hg/Te束流比的均匀性密切相关.对As的激活退火进行了研究,发现在饱和Hg蒸汽压中采用300℃/16h+420℃/1 h+240℃/48 h的退火条件能明显提升碲镉汞中As原子的激活率.     

分子束外延碲镉汞薄膜的砷掺杂技术

Ⅴ族元素 As 在碲镉汞中具有较小的扩散系数,在非本征 p 型掺杂中得到广泛应用,在 p-on-n型高性能探测器及双色或多色探测器应用方面优势明显。对分子束外延掺 As 碲镉汞薄膜的几种生长技术的基本原理进行了简单介绍,并对各方法存在的优缺点进行了对比分析;同时对 As 杂质在碲镉汞材料中的掺杂形态、杂质激活退火工艺及杂质激活率等进行了总结分析。对 MBE As 掺杂在第三代多层膜结构器件的应用方面提出了建议。     

中波碲镉汞p-on-n高温工作技术研究

针对碲镉汞中波p-on-n技术进行研究,采用二次离子质谱仪分析注入后及退火后As离子在碲镉汞材料中的浓度分布,使用透射电镜表征激活退火后离子注入损伤修复状态,通过半导体参数测试仪评价pn结的IV特性,将探测器芯片装在变温杜瓦中测试其不同温度下的焦平面技术指标。研究结果表明,As离子注入后在碲镉汞体内形成大量缺陷,经过富汞退火后缺陷得到修复,同时As离子进一步向内扩散,制备的pn结工作稳定表明As离子得到有效激活,制备的中波p-on-n探测器芯片在120 K温度下有效像元率可以达到99%以上。     

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。     

砷离子注入体材料碲汞的二次离子质谱分析

用二次离子质谱（ＳＩＭＳ）分析了低能注放（１５０ｋｅＶ）砷在体材料碲镉汞中的分布和注入砷原子在碲镉汞中的热扩散情况,砷在碲镉汞中的分布表现出复杂的多元扩散机制。在缺陷密度（ＥＰＤ）比较低的碲镉汞材料中,砷扩散的主体符合恒定扩散系数的有限源扩散模型,呈现出浓度随深度的高斯分布。而在缺陷密度比较大的碲镉汞材料中,砷的分布呈多段指数型分布,表面出更复杂的多机制扩散特性。     

中短波HgCdTe金属接触的退火研究

为制备良好的碲镉汞金属接触,研究了热退火处理对中短波Hg空位掺杂碲镉汞金属接触的影响。对中短波HgCdTe-Sn/Au接触及中波HgCdTe-Cr/Au接触经不同条件退火后的接触进行了测量。对于短波碲镉汞,p型HgCdTe-Sn/Au接触经95℃,30 min退火可降低比接触电阻2个量级,而经125℃,30 min退火可降低3个量级;离子注入的n型HgCdTe-Sn/Au接触则容易形成欧姆接触。对于中波碲镉汞,退火前p型HgCdTe-Sn/Au接触平均比接触电阻为10-1Ωcm2量级,经适当条件退火可以降低3个量级;此外,Sn/Au比Cr/Au更适合作为中波HgCdTe的接触金属。因而HgCdTe金属接触可通过一定退火处理得到改善。     

中短波HgCdTe金属接触的退火研究

为制备良好的碲镉汞金属接触,研究了热退火处理对中短波Hg空位掺杂碲镉汞金属接触的影响。对中短波HgCdTe-Sn/Au接触及中波HgCdTe-Cr/Au接触经不同条件退火后的接触进行了测量。对于短波碲镉汞,p型HgCdTe-Sn/Au接触经95 ℃,30 min退火可降低比接触电阻2个量级,而经125 ℃,30 min退火可降低3个量级;离子注入的n型HgCdTe-Sn/Au接触则容易形成欧姆接触。对于中波碲镉汞,退火前p型HgCdTe-Sn/Au接触平均比接触电阻为10-1 Ωcm2量级,经适当条件退火可以降低3个量级;此外,Sn/Au比Cr/Au更适合作为中波HgCdTe的接触金属。因而HgCdTe金属接触可通过一定退火处理得到改善。     

非晶态碲镉汞的暗电导率和吸收边(英文)

研究了非晶态碲镉汞(x=0.2)薄膜的暗电导率随温度变化关系,发现非晶态结构的碲镉汞材料具有明显的半导体特性,其室温禁带宽度在0.88～0.91eV之间,与通过光学方法获得的结果相符。在80～240K的温度区间非晶态碲镉汞(x=0.2)的暗电导率从1×10—8Ω—1.cm—1缓慢增大到5×10-8Ω—1.cm—1,温度大于240K时,其电导率剧烈增大到1×10—5Ω—1.cm—1,说明在240K附近非晶态碲镉汞材料的导电机制发生了变化,这对非晶态碲镉汞材料的应用研究具有重要意义。还研究了退火过程对非晶态碲镉汞薄膜电导率的影响,结果表明140℃退火后非晶态碲镉汞薄膜发生了部分晶化。     

应对第三代红外焦平面技术挑战的HgCdTe分子束外延

叙述了围绕第三代红外焦平面的需求所进行的HgCdTe分子束外延的一些研究结果.75mm HgCdTe薄膜材料的组分均匀性良好,80K下截止波长偏差为0.1μm.对所观察到的HgCdTe表面缺陷成核机制进行了分析讨论,获得的75mm HgCdTe材料平均表面缺陷密度低于300cm-2.研究发现As的表面黏附系数很低,对生长温度十分敏感,在170℃下约为1×10-4.计算表明,As在HgCdTe中的激活能为19.5meV,且随(Na∑Nd)1/3的增大呈线性下降关系,反比系数为3.1×10-5meV·cm.实验发现Hg饱和蒸汽压下,对应不同的温度240,380,440℃,As在HgCdTe中的扩散系数分别为(1.0±0.9)×10-16,(8±3)×10-15,(1.5±0.9)×10-13cm2/s.采用分子束外延生长的HgCdTe材料已用于红外焦平面探测器件的研制,文中报道了一些初步结果.     

As在HgCdTe分子束外延中的表面粘附系数

报道了用二次离子质谱分析 (SIMS)方法对As在碲镉汞分子束外延中的掺入行为的研究结果 .发现As在CdTe、HgCdTe表面的粘附系数很低 ,并与Hg的介入密切相关 .对于单晶HgCdTe外延 ,在 170℃生长温度下As的粘附率相对于多晶室温淀积仅为 3× 10 -4,在此生长温度下 ,通过优化生长条件获得了表面形貌良好的外延材料 .通过控制As束源炉的温度可以很好地控制As在HgCdTe层中的原子浓度 .     

Dependence of porosity, charge recombination kinetics and photovoltaic performance on annealing condition of TiO2 films

Effect of annealing temperature, time of nanocrystalline TiO2 film on porosity, electron transport/recombination and photovoltaic performance on dyesensitized solar cell (DSSC) had been investigated in this article. Photocurrent density was slightly higher as annealing at 550℃ compared to those of annealing at 450℃ and 500℃ under the given annealing time of 60 min, which was correlated with the amount of adsorbed dye. Thermogravimetric analysis showed there was a more weight loss between 500℃ and 550℃, which revealed there were more sites for dye adsorption. Given the annealing temperature of 550℃, as annealing time varied from 60 to 90 and 120 min, results showed that the average size of pore and surface area decreased with longer annealing time, which deteriorated photocurrent density due to less dye loading. Electron diffusion rate remained almost unchanged regardless of annealing condition.However, electron recombination was influenced by annealing condition, it became slower with the increase of the annealing temperature under the given annealing time. In the contray, the electron recombination developed faster for the longer annealing time at a given annealing temperature. These results suggested that heat treatment of TiO2 film at 550℃ for 60 min in air would be the optimal annealing condition to achieve high efficiency DSSC.     

Ⅲ-Ⅴ族半导体化合物快速热退火扩Zn方法研究

以GaAs和InP材料为例,对化合物半导体材料中的快速热退火扩Zn可行性进行比较分析,研究表明,化合物半导体材料中快速热退火扩Zn可行性与化合物半导体材料的分解温度有着密切关系。化合物半导体材料分解温度越低,对扩散源、帽层和阻挡层要求越高。针对InP材料高于360℃就分解、低温Zn扩散困难的特点,提出了直接溅射Zn层在410℃低温扩散的方法。对InP快速热退火扩散结果进行分析,初步分析表明其掺杂机理是形成合金结。     

退火工艺对La-Nb共掺杂Bi_4Ti_3O_(12)薄膜结构的影响

采用sol-gel法制备了Si基Bi3.25La0.75Ti2.94Nb0.06O12.03(BLTN)铁电薄膜,研究了退火温度、升温速率和退火时间对BLTN薄膜微观结构的影响。结果表明:制备的BLTN薄膜具有单一的钙钛矿结构,且为随机取向,表面平整致密;退火温度由550℃升高到750℃时,薄膜的衍射峰强度增强,晶粒尺寸由65 nm增大到110 nm;退火升温速率由10℃/min提高为20℃/min时,薄膜的晶化程度降低;退火时间对薄膜的晶相结构影响不大,但时间超过30 min会造成薄膜表面孔洞增多、致密性下降。     

ULSI Cu互连CoSiN扩散阻挡薄膜的研究

CoSiN薄膜可以作为超大规模集成电路Cu布线互连材料使用。利用磁控溅射技术制备了CoSiN/Cu/CoSiN/SiO2/Si薄膜,利用四探针测试仪、薄膜测厚仪、原子力显微镜、X射线光电子能谱仪等来检测多层膜电阻率、薄膜厚度、表面形貌、元素含量及价态等。考察亚45 nm级工艺条件下CoSiN薄膜对Cu的扩散阻挡性能。实验结果表明,在氩气气氛条件下经500℃,30 min热退火处理后多层膜的电阻率和成分没有发生明显变化,CoSiN薄膜能够保持良好的铜扩散阻挡性能;经600℃,30 min热退火处理后,Cu大量出现在表面,CoSiN薄膜对Cu失去扩散阻挡性能。     

分子束外延HgCdTe薄膜As掺杂P型激活研究

报道了利用As4作为掺杂源获得原位As掺杂MBE HgCdTe材料的研究结果．利用高温退火技术激活As使其占据Te位形成受主．对原位As掺杂MBE HgCdTe材料进行SIMS及Hall测试,证实利用原位As掺杂及高温退火可获得P型MBE HgCdTe材料．     

Simulation of HgTe/CdTe interdiffusion using fundamental point defect mechanisms

A numerical model for interdiffusion in HgTe/CdTe systems based on fundamental point defect mechanisms has been developed. The model includes continuity equations for the flux of Hg and Cd on substitutional sites, cation vacancies, and Hg and Cd interstitials. Interdiffusion is modeled by simulating the coupled diffusion and interaction of these species. The Hg vacancy concentration used in the model was fit to measured hole data as a function of annealing temperature, Hg pressure, and composition. The Cd and Hg interstitial diffusion coefficients and concentrations were determined as a function of temperature and composition from low temperature Hg and Cd self-diffusion data. With this model, interdiffusion is simulated over a range of initial and annealing conditions. At high temperatures and/or Te saturated conditions, interdiffusion is dominated by diffusion via a vacancy mechanism. Interdiffusion is controlled by the flux of Cd interstitials at lower temperatures and/or higher Hg pressures.     

P-type doping of double layer mercury cadmium telluride for junction formation

Extrinsic p-type doping of long wavelength infrared-HgCdTe double layer heterostructure for p-on-n device application requires good control of the p-type dopant, regardless of the doping technique. The approach is to place the electrical junction ahead of the compositional interface, thus avoiding quantum efficiency reduction. This research addresses the As and P doping of HgCdTe by an implant/diffusion process. The data demonstrates an enhanced atomic diffusion process for As and P from an ion implanted source, within the single phase domain, with a diffusion rate orders of magnitude higher than the rate under Hg-saturated conditions at the same temperature. This work also reveals a new phenomenon, namely, a transition in the enhanced diffusion of both As and P from an exponential to a Gaussian redistribution. This transition is controlled by temperature at a given P_Hg. Gaussian diffusion dominates at high temperatures, T >400°C. The diffusion coefficient of the Gaussian mechanism decreases as the P_Hg increases, from D_p ~2 x 10^-11 cm²/s at P_Hg ~0.02 atm to D_p ~3 x 10^-14 cm²/ s under Hg-saturated conditions (quartz ampoule) at 440°C. The difference in the diffusion coefficients between open tube and closed tube (quartz ampoule), under nominally Hg-saturated conditions, indicates that P_Hg is undersaturated regardless of the Hg-source proximity. The deviation of P_Hg from saturation is estimated from the annealing furnace temperature profile up to a maximum of 50%. Variation of the diffusion coefficient close to Hg saturation appears to be sharply dependent on the actual P_Hg value (example: D_p ~1 x 10^-12 cm²/s in open-tube anneal vs D_p ~3 x 10^-14 cm²/s in closed tube at nominally the same temperature, T = 440°C). Comparative anneals of As and P showed faster diffusion rates for P than for As in both mechanisms.     

Characterization of GaN Buffer Layers and Its Epitaxial Layers Grown by MOCVD

Low-pressure MOCVD has been used to investigate the properties of low-temperature buffer layer depodition conditions and their influence on the properties of high-temperature GaN epilayers grown subsequently.It is found that the surface morphology of the as-grown buffer layer after thermal annealing at 1030℃and 1050℃ depends strongly on the thickness of the buffer layer.In particular when a thick buffer layer is used, large trapezoidal nuclei are formed after annealing.