Charge collection microscopy of annealing induced electrically active defects in Si1−xGex/Si strained layer epitaxy

Images of electrically active defects in Si_1−xGe_x strained epilayers onn-type Si(100) have been obtained using charge collection microscopy (CCM) in a scanning electron microscope. Electrically active defects were generated in the defect-free as-grown material by rapid thermal annealing treatments (3 min) over a temperature range of 550 to 850° C. Point-like contrast, attributed to threading dislocations, as well as an additional line contrast due to the formation of an interface misfit dislocation network, were observed as the metastable strained Si_1−xGr_x layers relaxed upon annealing. Cross-sectional and plan-view transmission electron microscopy were used to examine the Si_1−xGe_x epilayers in finer detail. Double crystal x-ray diffraction and Raman scattering spectra were also obtained and the annealing induced peak shifts investigated.     

Investigation of electrically active defects in amorphous barium titanate thin films

DC and AC electrical properties of amorphous barium titanate thin film capacitors have been investigated as a function of temperature. A clear correlation is found between the temperature dependence of DC leakage currents and the temperature variation of the AC loss peaks, showing that these measurement techniques are probing the same electrical defects. Using either of these two techniques in amorphous barium titanate, we were able to detect oxygen vacancies diffusion with activation energy around 1 eV, and electron traps at 0.3 and 0.4 eV.     

Characterization of electrically active defects in photovoltaic detector arrays using laser beam-induced current

One of the main limitations in the operability of modern infrared focal plane arrays of p-n junction diodes formed on molecular-beam epitaxy (MBE)-grown HgCdTe is the effect of localized defects. Such defects, including voids, triangles and microvoids, are a feature of the MBE growth regime and can compromise the performance of devices fabricated within the vicinity of electrically active defects. While such defects can often be identified visually, not all defects are electrically active such that they provide a current leakage path shunting the p-n junction of the individual photodiode. In this paper, the use of laser beam-induced current is proposed as a nondestructive characterization technique, and quantitative aspects of its use in the study of electrically active defects in photodiode arrays are examined.     

PN结电容微分量频谱

本文用单一能级深陷阱模型研究了含深陷阱中心的PN结电容(C)及其微分量((dC)/(dω))与频率(ω)的关系,得到了相应的解析式.理论分析结果表明:电容微分量是一个具有峰值的函数,其峰值、峰位与深陷阱密度及载流子发射时间常数相关.由此提供了一种利用PN结的 C-ω特性确定深陷阱参数的新方法.用此方法,在室温(300K)条件下,测定了 P~+N结中的金受主能级的俘获截面σ_?=(5.6±0.8)×10~(-16)cm~2.     

GaN基LED光电器件的磊层研究与设计

介绍了一种缓解GaN基LED效率下降的器件设计方法,重点研究了采用新方法光电器件中载流子的分布。根据与传统GaN器件的对比,可以发现LED效率提高的原因是空穴的浓度分布的更加均匀。     

A transmission electron microscopy study of microstructure evolution with increasing anneal temperature in Ti/Al ohmic contacts to n-GaN

Al(200 nm)/Ti(20 nm)/n-GaN contacts have been studied using transmission electron microscopy (TEM) and the resulting microstructures correlated with the observed variation in specific contact resistance (ρ_c). A minimum ρ_c value of 7×10⁻⁷ Ωcm² was obtained after annealing at 550°C for 1 min in argon. Bulk metal and interfacial phases have been characterized, and explanations for the observed electrical behavior are proposed. A transition from TiN to AlN at the interface occurs between 650°C and 700°C.     

The influence of dose and protecting mask on electrically active defects induced by ion implantation in silicon

We present a study of electrically active defects induced by ion implantation, for two dopants: arsenic and phosphorous. Our analysis technique is Deep Level Transient Spectroscopy (D.L.T.S.). We have studied the generation of defects by direct implantation, and indirect implantation, that is through an SiO₂ layer. We follow the defect spectrum evolution for different doses (10⁸ to 10¹⁴ atoms/cm²) and for different annealing temperatures (from room temperature up to 800° C). The comparison of our results with other published ones allows us to improve the knowledge about the role of a protecting oxide layer, the influence of moderate thermal annealing, and the effect of oxygen on deep centers produced by ion bombardment.     

Characterization of electrically active defects in high-k gate dielectrics by using low frequency noise and charge pumping measurements

The electrically active defects in high-k/SiO₂ dielectric stacks are examined using a combination of low frequency noise (LFN) and charge pumping (CP) methods. The volume trap profile in the stacks is obtained by modeling the drain current noise spectra and charge pumping currents, with each technique covering a different depth range. The LFN is dependent on both the high-k and interfacial (IL) SiO₂ thicknesses while the CP current is mainly dependent on the IL thickness.     

TDMA卫星通信系统突发同步的性能研究

突发载波捕获和同步是TDMA系统的关键技术,使用数据序列辅助判决可有效缩短该处理过程需要的时间;在低接收信噪比下使用CAZAC序列的相关处理能够获得较高的突发捕获性能;比较了CAZAC序列和"1010"序列的载波和时钟同步误差估计性能,分析了它们在低信噪比门限时对信号快速捕获能力的影响。提出了2种序列组合应用实现载波快速同步的方案,完成信号捕获和载波估计功能。     

Prospects of gallium nitride double drift region mixed tunneling avalanche transit time diodes for operation in F, Y and THz bands

The potential of GaN as a wide band gap semiconductor is explored for application as double drift region mixed tunneling avalanche transit time (MITATT) diodes for operation at 120 GHz, 220 GHz and 0.35 THz using some computer simulation methods developed by our group. The salient features of our results have uncovered some peculiarities of the GaN based MITATT devices. An efficiency of more than 20% right up to a frequency of 0.35 THz (from the GaN MITATT diode) seems highly encouraging but a power output of only 0.76 W is indicative of its dismal fate. The existence of a noise measure minimum at the operating frequency of 0.35 THz is again exhilarating but the value of the minimum is miserably high i.e. more than 33 dB. Thus, although GaN is a wide band gap semiconductor, the disparate carrier velocities prevent its full potential from being exploited for application as MTATT diodes.     

AlGaN/GaN HEMT中慢瞬态的数值解释

观察了AlGaN/GaN HEMT器件在短期应力后不同栅偏置下的一组漏极电流瞬态,发现瞬态的时间常数随栅偏压变化很小,据此判断这组瞬态由电子陷阱的释放引起.为了验证这个判断,采用数值仿真手段计算了上述瞬态.分别考虑了在器件中不同空间位置的电子陷阱,分析了应力和瞬态中相应的陷阱行为,对比和解释了仿真曲线与测量结果的异同.基于上述讨论,提出测量的瞬态可能是表面深陷阱和GaN层体陷阱的综合作用的结果.     

Numerical Explanation of Slow Transients in an AlGaN/GaN HEMT

观察了AlGaN/GaN HEMT器件在短期应力后不同栅偏置下的一组漏极电流瞬态,发现瞬态的时间常数随栅偏压变化很小,据此判断这组瞬态由电子陷阱的释放引起.为了验证这个判断,采用数值仿真手段计算了上述瞬态.分别考虑了在器件中不同空间位置的电子陷阱,分析了应力和瞬态中相应的陷阱行为,对比和解释了仿真曲线与测量结果的异同.基于上述讨论,提出测量的瞬态可能是表面深陷阱和GaN层体陷阱的综合作用的结果.     

Neutralization of electrically active aluminum in recrystallized silicon-on-sapphire films

We report the effect of steam oxidation at 875° C on the electrical resistivity, crystalline quality (measured by ion channeling), and Al concentration (measured by secondary ion mass spectrometry) in 0.25 μm thick, Si-implanted and recrystallized, Si-on-sapphire films. After a deep Si implantation (180 keV, 1.4×l0¹⁵ Si/cm²) at room temperature, and solid-phase epitaxial regrowth from the non-amorphized, 0.03 μm thick surface region, the initially undoped SOS films become doped p-type, and their resistivity decreases from (1−5)xl0¹⁴ ficm to 0.5 Ωcm. The doping is due to electrically active Al, released from the A1₂O₃ by the Si implantation, and present in the recrystallized films at a concentration of ≃2×l0¹⁶ Al/cm³ . After a 75 min steam oxidation at 875 °C, which consumes 0.06 Μm of Si, the resistivity of the recrystallized films increases to over 40 Ωcm, but the Al concentration is unchanged. The oxidation also uncovers higher quality material below the non-recrystallized surface layer. A semi-quantitative model is proposed to explain the electrical data, based on the diffusion of oxygen from the Si/SiO₂ interface into the SOS film during oxidation, and the formation of Al-O-Si neutral complexes. Data on the stability of the high-resistivity films against high-temperature annealing or re-amorphization and annealing is given.     

引入GaN过渡层对Si（111）衬底上生长GaN外延的影响

本文研究了在Si(111)衬底上生长GaN外延层的方法。相比于直接在AlN缓冲层上生长GaN外延层,引入GaN过渡层显著地提高了外延层的晶体质量并降低了外延层的裂纹密度。使用X射线双晶衍射仪、光学显微镜以及在位监测曲线分析了GaN过渡层对外延层的晶体质量以及裂纹密度的影响。实验发现,直接在AlN缓冲层上生长外延层,晶体质量较差, X射线(0002)面半高宽最优值为0.686°,引入GaN过渡层后,通过调整生长条件,控制岛的长大与合并的过程,从而控制三维生长到二维生长过渡的过程,外延层的晶体质量明显提高, (0002)面半高宽降低为0.206°,并且裂纹明显减少。研究结果证明,通过生长合适厚度的GaN过渡层,可以得到高质量、无裂纹的GaN外延层。     

The effect of a post processing thermal anneal on pre-existing and stress induced electrically active defects in ultra-thin SiON dielectric layers

In this work we demonstrate the effects of a post processing high temperature anneal on the reliability of ultra-thin SiON layers fabricated into both nmos and pmos devices in terms of the initial gate leakage current, stress induced leakage current (SILC), and the time dependent dielectric breakdown behaviour. The devices under consideration were annealed at several temperatures up to 500 °C. We show that different mechanisms dominate the leakage behaviour at different temperatures by examining the relative leakage in the low voltage range. In particular for pmos devices, the emptying of electron traps induced by temperature and subsequent annealing of these traps alters the leakage current profiles significantly, dependent on anneal temperature. We show that annealing improves the time dependent dielectric breakdown (TDDB) lifetimes of nmos devices and examine the reasons for this.     

受主型杂质对p型单晶硅中少子衰减过程的影响

少子寿命测试技术是监控单晶硅中杂质和缺陷的数量及性质的重要技术手段.基于常规光电导少子寿命测试的基本参数,研究了不同性质的受主型杂质缺陷对太阳电池用p型单晶硅中少子衰减过程的影响,并重点分析了仅存在受主型电子陷阱或复合中心时,少子衰减过程的变化规律;受主型电子陷阱和复合中心并存时,少子衰减过程的变化规律.研究表明:p型单晶硅中仅存在电子陷阱或复合中心时,二者的密度和俘获截面越小,少子寿命越长,且二者均存在一个最小阈值;当二者并存时,少子电子的衰减过程可根据少子寿命值的不同分成不同的衰减区域.     

The role of the low temperature buffer layer and layer thickness in the optimization of OMVPE growth of GaN on sapphire

In agreement with previous work,¹² a thin, low temperature GaN buffer layer, that is used to initiate OMVPE growth of GaN growth on sapphire, is shown to play a critical role in determining the surface morphology of the main GaN epilayer. X-ray analysis shows that the mosaicity of the main GaN epilayer continues to improve even after several μm of epitaxy. This continuing improvement in crystal perfection correlates with an improvement in Hall mobility for thicker samples. So far, we have obtained a maximum mobility of 600 cm²/V-s in a 6 μm GaN epilayer. Atomic force microscopy (AFM) analysis of the buffer layer and x-ray analysis of the main epilayer lead us to conclude that the both of these effects reflect the degree of coherence in the main GaN epitaxial layer. These results are consistent with the growth model presented by Hiramatsu et al., however, our AFM data indicates that for GaN buffer layers partial coherence can be achieved during the low temperature growth stage.     

DLTS characterization of defects in GaN induced by electron beam exposure

The deep level transient spectroscopy (DLTS) technique was used to investigate the effects of electron beam exposure (EBE) on n-GaN. A defect with activation energy of 0.12 eV and capture cross section of 8.0×10^–16 cm² was induced by the exposure. The defect was similar to defects induced by other irradiation techniques such as proton, electron, and gamma irradiation. In comparison to GaN, the EBE induced defects in other materials such as Si and SiC are similar to those induced by other irradiation methods.     

多晶硅TFT热载流子效应的模拟研究

热载流子效应引起的器件电学特性退化会严重影响电路的工作性能。文章结合多晶硅薄膜晶体管沟道电流的理论模型,讨论了热载流子效应与界面陷阱的关系。沟道载流子在大的漏电场牵引下,运动到漏结附近获得很大的能量从而成为热载流子。如果热载流子能量超过Si-SiO2界面势垒高度,会注入到栅氧层或陷落到界面陷阱,使阈值电压和沟道电流发生退化现象。同时,对多晶硅薄膜晶体管输出特性进行了模拟分析,模拟结果与理论模型基本一致。     

AlGaN/GaN HEMT的恒压电应力退化研究

研究了AlGaN/GaN高电子迁移率晶体管(HEMT)在不同持续恒压电应力条件下的退化机制,制作了一种AlGaN/GaN HEMT。对该器件分别采用恒压开态应力和恒压关态应力,研究了与直流特性相关的重要参数的陷阱产生规律。实验结果表明,在开态应力下,由于存在热载流子效应,发生了阈值电压正漂现象,峰值跨导降低;在关态应力下,由于存在逆压电效应,发生了阈值电压负向漂移现象。