指数掺杂透射式GaAs光电阴极表面光电压谱研究

通过求解一维稳态少数载流子扩散方程,推导了指数掺杂和均匀掺杂的透射式GaAs光电阴极表面光电压谱理论方程。利用金属有机化学气相沉积(MOCVD)外延生长了发射层厚度相同、掺杂结构不同的两款透射式阴极材料。通过表面光电压谱实验测试和理论拟合发现指数掺杂结构在发射层厚度和后界面复合速率相同的情况下能够有效提高阴极电子扩散长度,这主要由于内建电场能够促使光生电子通过扩散和电场漂移两种方式向表面运动,从而最终提升阴极的发射效率和表面光电压谱。利用能带计算公式和电子散射理论对这两种不同结构材料的表面光电压谱进行了详细分析。     

不同结构的反射式GaAs光电阴极的光谱特性比较

利用分子束外延生长了三种结构的反射式GaAs光电阴极,其中一种为传统结构的反射式GaAs光电阴极,另外两种为具有GaAlAs缓冲层的均匀掺杂和梯度掺杂反射式GaAs光电阴极.激活后的光谱响应测试结果表明,与传统结构的反射式GaAs光电阴极相比,具有GaAlAs缓冲层的均匀掺杂反射式GaAs光电阴极的长波响应更好,而具有...     

高积分光电灵敏度多层Be浓度掺杂的GaAs负电子亲和势光电阴极

研究了变掺杂浓度结构对GaAs负电子亲和势光电阴极积分光电灵敏度的影响.通过MBE生长了两组GaAs同质外延样品.其中一组采用了均匀掺杂的单层结构,Be掺杂浓度为1×1019cm-3;另一组采用了变掺杂的多层结构,从衬底开始Be的掺杂浓度依次为1×1019,7×1018,4×1018和1×1018cm-3.负电子亲和势光电阴极通过在高真空系统中交替通入Cs和O激活得到.在线光谱响应测试曲线表明,多层Be掺杂结构光阴极的积分光电灵敏度比单层Be掺杂结构光阴极的积分光电灵敏度至少提高了50%.两种结构的GaAs样品表现出不同的表面应力情况.     

Cu掺杂Ca3Co4O9+δ中温固体氧化物燃料电池阴极材料

采用固相法制备了Ca₃Co_4-xCu_xO_9+δ(x=0,0.1,0.3,0.5)阴极材料,研究了Cu离子掺杂对材料的物相组成、电极微观形貌、电化学性能、热膨胀系数、电导率及单电池输出性能的影响。结果表明：在900℃的煅烧合成温度下,未掺杂与Cu掺杂量为x=0.1的生成产物具有相同单一物相晶体结构(JCPDS 21-0139),Cu掺杂使晶胞参数略有增加。掺杂量为x=0.1的阴极膜层呈现出最疏松多孔状态,有利于氧气在阴极的扩散传输,相应的极化阻抗最小(700℃时极化阻抗为0.85Ω·cm²,为未掺杂的42.9%),可以高效地催化氧气在阴极处的还原反应,而且具有最高的电子电导率(相比未掺杂的提高了1.6倍),提升了阴极反应过程中的电荷转移效率。采用Ca₃Co_3.9Cu_0.1O_9+δ为阴极的单电池输出性能明显优于其他组分作为阴极时的性能(700℃时功率密度峰值约为79 mW·cm^-2     

Cl掺杂对n-Cu2O的光电性能的影响

在酸性溶液中利用恒电位沉积法在导电玻璃(ITO)上沉积Cu2O薄膜,并以KC1为添加剂对其进行掺杂,采用场发射扫描电子显微镜(FESEM)和X射线衍射谱(XRD)等手段研究了氯掺杂对Cu2O表面形貌和晶体结构的影响.紫外-可见吸收光光谱确定得到的Cu2O和Cl掺杂Cu2O(Cu2 O-C1)样品的禁带宽度分别为1.98和1.95 eV.根据表面光电压谱和相位谱,掺杂前后的Cu2O均为n型,Cu2 O-C1有更强的表面光电压响应.场诱导表面光电压谱结果表明未掺杂C1的Cu2O在加负偏压时易形成反型层;氯离子的掺杂引入杂质能级可以提高n型导电性.光电化学性能测试发现,以Cu2O、Cu2 O-Cl为光阳极组成的光化学太阳电池,在大气质量AM 1.5G、100 mW/cm2标准光强作用下光电转换效率分别为0.12％和0.51％.     

高温AlN模板上p型GaN的生长研究

利用低压金属有机物化学气相沉积技术,采用均匀掺杂和渐变Mg-δ掺杂方法,分别在氮化镓(GaN)和高温氮化铝(HT-AlN)模板上,生长了p型GaN外延材料.生长后,双晶X射线衍射和霍尔测试结果表明:HT-AlN模板上采用渐变Mg-δ掺杂方法生长的p型GaN材料,具有最好的晶体质量和电学性能.该p型GaN样品的(0002)面半峰宽值小至178",其空穴氧浓度为5.78×1017 cm-3.在对Cp2Mg/TMGa进行了优化试验后,p型GaN的空穴氧浓度被提高到8.03×1017 cm-3.     

高温AlN模板上p型GaN的生长研究

利用低压金属有机物化学气相沉积技术,采用均匀掺杂和渐变Mg-δ掺杂方法,分别在氮化镓(GaN)和高温氮化铝(HT-AlN)模板上,生长了p型GaN外延材料.生长后,双晶X射线衍射和霍尔测试结果表明:HT-AlN模板上采用渐变Mg-δ掺杂方法生长的p型GaN材料,具有最好的晶体质量和电学性能.该p型GaN样品的(0002)面半峰宽值小至178",其空穴氧浓度为5.78×1017 cm-3.在对Cp2Mg/TMGa进行了优化试验后,p型GaN的空穴氧浓度被提高到8.03×1017 cm-3.     

氮化镓基薄膜材料的测试和评价

氮化镓基薄膜材料由于外延衬底与氯化镓基薄膜材料之间存在较大的晶格失配，因此氮化镓基薄膜材料，特别是铝镓氮薄膜材料的质量还需要有很大的提高。本文利用紫外可见透射光谱，电流电压特性曲线测试，以及二维透射扫描系统来评价氮化镓基薄膜材料。利用紫外可见透射光谱，可以得到材料的截止波长、吸收边以及在可见光波段的透射率，从而对材料的组分以及材料的异质结界面作出评价；利用简单的电流电压特性曲线测试可以对薄膜材料最表层的电导能力有所了解；而利用搭建的二维透射扫描系统则可以对材料均匀性进行量化的评价。通过以上这些非损伤性的测试评价手段，对氮化镓基薄膜材料的光学、电学以及均匀性等各方面的重要性能作出定性和半定量的评价，从而对薄膜材料生长以及后续的大面阵芯片制作提供极其重要的指导。     

NEA GaN光电阴极的制备与评估

对GaN的结构性质进行了介绍,研究了NEAGaN光电阴极的制备方法,利用MOCVD生长了P型掺杂浓度为1.6×1017cm-3发射层厚度150 am的GaN样品,在进行了GaN表面净化处理得到原子级清洁表面后,在超高真空系统中对GaN光电阴极进行了Cs/O激活,获得了NEAGaN光电阴极.利用实验室制备的多信息量测试系...     

对低温下制得的CdS薄膜电学性质的研究

采用化学水浴沉积法研究在低温条件下以及硫尿浓度不同的溶液中生长出的硫化镉薄膜的电学性质。采用X-射线衍射(XRD)仪确定退火后的样品是六方相,在(002)、(112)和(004)方向优势生长;使用紫外-可见分光光度计发现各样品的光学性质符合硫化镉作为窗口材料的要求;利用原子力显微镜发现各样品的晶粒形状、均匀性和致密性差异较大;利用化学工作站进行样品的电容-电压测试发现,各样品的掺杂浓度差异很大,其中有的样品掺杂浓度为1.2×1017cm-3,这样的掺杂浓度适合制造光电器件。     

Stable gallium arsenide MIS capacitors and MIS field effecttransistors by (NH4)2Sx treatment andhydrogenation using plasma deposited silicon nitride gate insulator

The beneficial effects of sulfur passivation of gallium arsenide (GaAs) surface by (NH₄)₂S_x chemical treatment and by hydrogenation of the insulator-GaAs interface using the plasma-enhanced chemical vapor-deposited (PECVD) silicon nitride gate dielectric film as the source of hydrogen are illustrated by fabricating Al/PECVD silicon nitride/n-GaAs MIS capacitors and metal insulator semiconductor field effect transistors (MISFET). Post metallization annealing (PMA) at temperatures in the range 450-550°C is shown to be the key process for achieving midgap interface state density below 10 ¹¹/cm²/eV and maximum incremental transconductance, which is about 75% of the theoretical maximum limit. MIS capacitors are fabricated on (NH₄)₂S_x treated GaAs substrate using gate dielectrics such as PECVD SiO ₂ and silicon oxynitride to demonstrate that the PMA is less effective with these dielectrics because of their lower hydrogen content. The small signal AC transconductance, g_ms measurements on MISFETs fabricated using silicon nitride, have shown that the low-frequency degradation of g_ms is almost absent in the devices fabricated on (NH₄)₂S_x-treated GaAs substrates and subjected to PMA. The drain current stability in these devices is demonstrated to be excellent, with an initial drift of only 2% of the starting value. The dual role of silicon nitride layer, namely, protection against loss of sulfur and an excellent source of hydrogen for additional surface passivation along with sulfur is demonstrated by comparing the transconductance of MISFETs fabricated on GaAs substrates annealed without the nitride cap after the (NH₄)₂S _x treatment     

Structural,optical and electrical properties of Fe-doped SnO2 fabricated by sol–gel dip coating technique

Nanosized Fe³⁺-doped SnO₂ thin film was prepared by the sol–gel dip coating (SGDC) technique on quartz class substrate and sintered at 800 °C. The microstructures, surface morphology and optical properties of these films were then characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical absorption measurements, respectively. Electrical properties were analyzed, and resistivity, type and number of carrier concentration, Hall mobility measured as a function of Fe³⁺ doping and temperature. The XRD spectrum shows the decrease in peak heights as a result of Fe³⁺-doping while SEM images reveal reduction in crystallite size with increase in Fe³⁺ content. The optical studies showed a direct band gap reducing with increase in Fe³⁺-doping from 3.87 to 3.38 eV. From the electrical measurements, it was found that the resistivity initially increased with Fe³⁺-doping before reducing at higher doping level. Hall mobility measurements showed n-type conductivity at lower Fe³⁺-doping levels and p-type at higher levels. The increase in conductivity with temperature ascertained the semiconducting behavior of these films.     

900nm三叠层隧道级联激光器的结构优化研究

采用金属有机化合物气相淀积方法生长了900nm的三叠层隧道级联激光器。针对隧道级联激光器存在工作电压高、材料各层的光场耦合等问题,分别采用δ掺杂、扩展波导等技术对激光器结构进行了优化,并通过模拟计算对隧道结耗尽区宽度进行了优化。通过优化隧道结δ掺杂的生长条件,得到n+GaAs的掺杂浓度大于1×1019/cm3,使工作电压下降1V;通过采用扩展波导,使垂直发散角由常规结构的35°减小到20°。将900nm的三叠层隧道级联激光器制作成条宽300μm、腔长800μm的条形激光器,采用同轴封装形式,在20A的脉冲工作电流下,输出功率达到55W,斜率效率达到2.9W/A,以上指标是普通激光器的3倍。     

Studying the uniformity of the surface resistance of Ti, Al, Ni, Cr, and Au metal films on silicon

Nanosized Ti, Al, Ni, Cr, and Au films were deposited onto KEF-20 (100)-oriented silicon plates with a diameter of 100 mm using the method of thermal evaporation in a vacuum. The value and uniformity of the distribution of the specific electrical resistance of the metal films were estimated by measuring their thickness and surface electrical resistance via the four-probe method. The specific electrical resistance of such films was shown to be considerably higher than for bulk materials. The observed increase in the surface resistance at the edges of the film was due to both the decrease in the thickness of the film and the increase in the specific electrical resistance of the material of the film. The proved regimes were used to obtain metal layers on gallium nitride substrates.     

SiGe薄膜材料电阻率与掺杂浓度的关系研究

目前，应变Si1-xGex薄膜材料杂质浓度尚未有准确且简便易行的测试方法。为了快速准确地确定应变Si1-xGex薄膜材料的掺杂浓度，在研究应变Si1-xGex材料多子迁移率模型的基础上，采用Matlab编程模拟仿真，求解并建立了不同Ge组分下应变Si1-xGex薄膜材料掺杂浓度与其电阻率的关系曲线，讨论了轻、重掺杂两种情况下该关系曲线的变化趋势。通过Si1-xGex薄膜材料样品的四探针电阻率测试及电化学C-V掺杂浓度测试的对比实验，对本关系曲线进行了验证。     

Selective incorporation of Si along step edges during delta-doping on MOVPE-grown GaAs (001) vicinal surfaces

We investigated the delta-doping (δ-doping) of Si using SiH₄ on MOVPE-grown GaAs (001) vicinal surfaces to explore the possibility of selective incorporation of Si along atomic steps, and to demonstrate doping quantum wires by the combination of multiatomic steps and wire-like doping. It was found that the doping density on vicinal surfaces was enhanced as the misorientation angle was increased, which suggested the enhanced decomposition of SiH₄ and the selective incorporation of Si at step edges. It was also found that this selective incorporation could be enhanced by annealing the surface prior to the δ-doping, which resulted from the reduced incorporation of Si at the terrace regions. Anisotropic electron transport properties which are expected from the wire-like incorporation along step edges are also discussed.     

PbI2掺杂对CH3NH3PbI3光电性能的影响

采用溶液生成法制备了有机铅卤化钙钛矿(CH3 NH3PbI3)晶体粉末,并以过量的PbI2对其进行掺杂,采用X射线衍射谱(XRD)技术研究了掺杂前后样品的晶体结构变化.表面光电压谱(SPS)和相位谱(PS)显示掺杂前后的CH3 NH3 PbI3均为p型半导体,但后者有更强的光伏响应.场诱导表面光电压谱(FISPS)表明:当加正电场时,掺杂前后的CH3NH3PbI3均表现为p型半导体的载流子特性,当加负偏压时掺杂后的CH3NH3PbI3易形成反型层,出现光伏反转,且外加负偏压越大,光伏反转区域越大,表现出双极导电特性.     

Terahertz Semiconductor Quantum Well Devices

For eventually providing terahertz science with compact and convenient devices,terahertz (1～10THz) quantum-well photodetectors and quantum-cascade lasers are investigated. The design and projected detector performance are presented together with experimental results for several test devices,all working at photon energies below and around optical phonons. Background limited infrared performance (BLIP) operations are observed for all samples (three in total) ,designed for different wavelengths. BLIP temperatures of 17,13, and 12K are achieved for peak detection frequencies of 9.7THz(31μm) ,5.4THz(56μm) ,and 3.2THz(93μm) ,respectively. A set of THz quantum-cascade lasers with identical device parameters except for doping concentration is studied. The δ-doping density for each period varies from 3.2 × 1010 to 4. 8 × 1010cm-2. We observe that the lasing threshold current density increases monotonically with doping concentration. Moreover, the measurements for devices with different cavity lengths provide evidence that the free carrier absorption causes the waveguide loss also to increase monotonically. Interestingly the observed maximum lasing temperature is best at a doping density of 3.6 × 1010cm-2.     

高斜率效率隧道结叠层激光器的研制

隧道结叠层激光器技术具有广泛的应用空间,如高斜率效率、高功率密度、多波长激光器等。采用LP-MOCVD系统生长隧道结材料,CCl4作为p型掺杂源,SiH4作为n型掺杂源,并采用δ掺杂技术,使得n+-GaAs的掺杂浓度大于1×1019/cm3,隧道结的面电阻率小于2×10-4Ω.cm2。设计生长了双叠层、三叠层材料,该材料制作的900nm双叠层激光器在200ns脉宽、20A工作电流下输出功率35W,斜率效率1.8W/A,是单层材料的1.8倍,隧穿结引入的压降约为0.15V;860nm三叠层激光器的斜率效率大于2.7W/A,是单层材料的2.7倍。     

Roles of cesium and oxides in the processing of gallium aluminum arsenide photocathodes

The roles of cesium (Cs) and oxides in the processing of gallium aluminum arsenide (GaAlAs) photocathodes have been investigated. The Cs/O activation, Cs/O reactivation and degradation experiments are performed on GaAlAs photocathode. The activated photocurrent, degraded photocurrent and quantum efficiency curves are measured using a self-developed multi-information measurement system. We use the quantum efficiency formula to fit the experimental quantum efficiency curves, and obtain the performance parameters of the photocathode. The results show that the oxide gases play an important role in the degradation of the photocathode, and the Cs atoms could react with the oxides on the degraded surface and the residual oxide gases. Besides, the quantum efficiency of the degraded GaAlAs photocathode could be restored to a good level after Cs/O reactivation.