New observation on the luminescence of CdS clusters in zeolite-Y

The excitation spectrum of CdS dusters in zeolite-Y is consistent with their absorption spectrum, both showing two absorption bands that are assigned to the Is-is and Is-lp transitions, respectively. A new emission at 400 nn is considered to be the recombination of the bounded excitons. The emission firstly increases then decreases with increasing cluster size or loading. The emission by excitation into the Is-is band is stronger and sharper than that by excitation into the Is-lp band. This phenomenon is attributed to the size inhomogeneity and the strong electron-phonon interaction of the dusters. Copyright (C) 1996 Elsevier Science Ltd

Absorption and Raman spectra of Se-8-ring clusters in zeolite 5A

Samples with different weight ratio of Se to zeolite 5A (Se composition) have been prepared by loading Se into the cages of zeolite 5A and the measurements of the absorption and Raman spectra have been carried out for the prepared samples. The measured absorption edges of the samples close and blue shifted to the value for monoclinic Se containing Se-8-ring, suggesting the formation of Se-8-ring clusters dagger in the cages. The continuous and broadening features of the absorption spectra are interpreted by the strong electron-phonon coupling in Se-8-ring clusters. The sample with high Se composition has a red shift of the absorption band edge relative to the samples with less Se composition. It is tentatively attributed to the reason that with different Se composition, single Se-8-ring clusters and double Se-8-ring clusters are formed in the cages of zeolite 5A. A single broad band at about 262 cm(-1) is observed in the Raman spectra, that gives the further support of the formation of Se-8-ring clusters. Copyright (C) 1996 Elsevier Science Ltd

Some new observation on the formation and optical properties of CdS clusters in zeolite-Y

CdS clusters in zeolite-Y have been prepared by the exchange of Cd2+ into the zeolite following by sulfurization with Na2S in solution. Blue-shifts from the bulk caused by quantum size effect and the change of absorption upon CdS loading are observed. Two absorption bands are detected for one of the sample and are assigned to the 1s-1s band and exciton transition, respectively. The exciton feature is more pronounced in the excitation spectrum than in the absorption spectrum, and the luminescence excited at the exciton band is stronger than that at the 1s-1s band. Copyright (C) 1996 Elsevier Science Ltd

New observation on the formation of PbS clusters in zeolite-Y

PbS clusters in zeolite-Y have been prepared with the reaction of Pb2+-ion-exchanged zeolite-Y with Na2S in solution at room temperature. Their absorption spectra show dramatic blue shifts from that of the bulk PbS. Obvious change of both the absorption edges and peak positions upon PbS concentrations have been observed. These phenomena provide evidences that PbS clusters have been formed within the zeolite. The absorption spectra show featureless structure and have no tails near the absorption edges. As the PbS loading density becomes higher, the absorption bands become stronger and sharpen. Order PbS clusters lattice with high quality might be formed in the supercages of zeolite-Y. (C) 1996 American Institute of Physics.

穿透型V形坑对GaN基p-i-n结构紫外探测器反向漏电的影响

研究了GaN基p-i-n(p-AlGaN/i-GaN,n-GaN)结构紫外探测器的漏电机理.实验发现,在位错密度几乎相同的情况下,基于表面有较高密度的V形坑缺陷材料制备的器件表现出较高的反向漏电.进一步的SEM测试发现,这种V形坑穿透到有源区i-GaN、甚至n-GaN层.在制备p-AlGaN电极时,许多金属会落在V形坑中,从而与i-GaN形成了肖特基接触.有些甚至直接和n-GaN形成欧姆接触.正是由于并联的肖特基接触和欧姆接触的存在导致了漏电的增加.

以弱p型为有源区的新型p-n结构GaN紫外探测器

提出了以弱p型(p~--GaN)为有源区的p-n结构GaN紫外探测器.由于弱p型层的载流子浓度较低,很容易增加耗尽区的宽度,从而可以增加器件的量子效率.通过模拟计算,研究了金属与p~--GaN层的肖特基接触势垒高度、p~--GaN层厚度等参数对器件性能的影响.研究结果表明,降低金属与p~--GaN层的接触势垒高度、适当减小p~--GaN层厚度能够实现有源层方向单一的内建电场,从而提高器件的量子效率.要制备出具有良好性能的p-n结构紫外探测器,必须减小p~--GaN层厚度,降低金属与p~--GaN层的接触势垒高度.

Ni基电极淀积前后表面处理对p-GaN欧姆接触的影响

在p-GaN上蒸发Ni/Au电极前,采用王水、HCl、缓冲HF进行前表面处理,O_2气氛下退火后,比较各电极样品的I-V特性和表面形貌.结果显示无表面处理时接触电阻最小,且溶剂处理后残留的电解质会影响电极的电流特性和稳定性.用俄歇电子能谱(AES)测试不同元素随深度分布情况,发现高温退火过程中NiO的形成有自动清洁p-GaN表面的作用,因此对于Ni基电极前表面处理不是必需的.再将样品用10%草酸溶液处理,其I-V特性显示接触电阻率明显下降;X射线光电子能谱(XPS)测试显示草酸溶液处理后电极表面Ni含量显著减少,而Au元素信号峰增强,说明表面高阻P型NiO被有效除去,对改善接触性能具有实际意义.

NiO removal of Ni/Au Ohmic contact to p-GaN after annealing

The Ni/Au contact was treated with oxalic acid after annealing in O_2 ambient, and its I-V characteristic showed the property of contact has been obviously improved. An Auger electron spectroscopy (AES) depth pro-file of the contact as-annealed showed that the top layer was highly resistive NiO, while an X-ray photo-electron spectroscopy (XPS) of oxalic acid treated samples indicated that the NiO has been removed effectively. A scanning electron microscope (SEM) was used to observe the surface morphology of the contacts, and it was found that the lacunaris surface right after annealing became quite smooth with lots of small Au exposed areas after oxalic acid treatment. When the test probe or the subsequently deposited Ti/Au was directly in contact with these small Au areas, they worked as low resistive current paths and thus decrease the specific contact resistance.

p型掺杂1.3 μm InAs/GaAs量子点激光器的最大模式增益特性的研究

对p型掺杂1.3 μm InAs/GaAs量子点激光器的最大模式增益进行了实验和理论分析.实验上,测量了不同腔长激光器阈值电流密度与总损耗的对应关系,拟合出的最大模式增益为17.5 cm~(-1),与相同结构非掺杂量子点激光器的最大模式增益一致.同时理论分析表明,p型掺杂对InAs/GaAs量子点激光器的最大模式增益并无影响,并且最大模式增益的计算结果与实验值相符.具有较小高度或高宽比的量子点能达到更高的最大模式增益,而较高的最大模式增益对p型掺杂1.3 μm InAs/GaAs自组织量子点激光器在光通信系统中的应用具有重要意义.

两步合金法制作p-GaN高反电极

利用两步合金法获得了能与p-GaN形成良好欧姆接触的高反射电极。电极的构成采用透明电极+高反射金属方案,厚的Ag层或Al层覆盖在合金后的Ni/Au上以提高电极的反射率,以Pt和Au作为覆盖层,可有效地防止Ag的氧化和团聚,短时间的热处理有助于Ag基电极反射率的提高。可靠性测试表明Ag基电极的稳定性较好,对于Al基电极,热处理后反射镜上出现暗斑,导致其反射率的下降。最终获得了波长在460nm处反射率为74%的Ag基高反射电极。

p-GaN层厚度对GaN基p-i-n结构紫外探测器性能的影响

研究了p-GaN层厚度对GaN基pin结构紫外探测器性能的影响.模拟计算表明:较厚的p-GaN层会减小器件的量子效率,然而同时也会减小器件的暗电流,较薄的p-GaN层会增加器件的量子效率,但是同时也增加了器件的暗电流.进一步的分析表明,金属和p-GaN之间的结电场是出现这种现象的根本原因.在实际的器件设计中,应该根据实际需要选择p型层的厚度.

n-GaAs和p-GaN晶片的直接键合

采用直接键合的方法成功实现了n-GaAs和p-GaN晶片的高质量键合.扫描电子显微镜观测结果表明,键合界面没有空洞.键合前后光致发光谱测试表明,键合工艺对材料质量影响不大.室温下界面的电流-电压特性表明,键合得到的n-GaAs/p-GaN异质结为肖特基二极管并且理想因子为1.08.n-GaAs和p-GaN材料直接键合的成功对于集成GaAs和GaN材料制备光电集成器件有重要意义.

表面处理对p-GaN欧姆接触的影响

分别用稀盐酸、王水以及(NH_4)_2S溶液处理p-GaN表面,通过测试样品表面Ols的X射线光电子能谱(XPS),比较了这些溶液去除p-GaN表面氧化层的能力;在经不同溶液处理后的样品表面,以相同的条件制作Ni/Au电极,并测试其与p-GaN的比接触电阻,结果表明经稀盐酸处理后的样品表面,由于其氧含量较高,不能与Ni/Au形成良好的欧姆接触,而经王水和(NH_4)_2S溶液处理后的p-GaN表面,能与Ni/Au形成良好的欧姆接触;最后,通过比较样品表面的Ga/N原子浓度比,探讨了王水处理p-GaN表面能够形成良好欧姆接触的原因.

PECVD沉积SiO_2和SiN_x对p-GaN的影响

在等离子增强化学气相沉积法（PECVD）沉积SiO_2和SiNx掩蔽层过程中，分解等离子体中浓度较高的H原子使Mg~-受主钝化，同时在p-GaN材料表面发生反应形成浅施主特性的N_v~+，空位。高能量离子轰击造成的材料深能级缺陷增多以及沉积形成致密的SiO_2和SiN_x材料，阻碍了H原子向外扩散，使H原子在Ni／Au电极与p-GaN的界面处聚集，造成p-GaN近表面附近区域Mg-H络合物密度的提高，空穴浓度急剧下降，导致Ni／Au透明电极I-V特性严重恶化。选择较低的射频功率（15W，13．56MHz）沉积模式，经过适当的退火，可以减小沉积SiO_2过程对p-GaN的影响。

微量掺碳ne-SiC:H薄膜用于p-i-n太阳电池的窗口层

采用等离子增强化学气相沉积方法(PEVVD)制备了微量掺碳的p型纳米非晶硅碳薄膜(p-nc-SiC:H),反应气体为硅烷和甲烷,掺杂气体采用硼烷,沉积温度分别采用333 K,353 K和373 K.测量结果表明随着沉积温度增加和碳含量的增加,薄膜的光学带隙增加;薄膜具有较宽的带隙和较高的电导率,同时有较低的激活能(0.06 eV).Raman和XRD测量结果表明薄膜存在纳米晶.优化的p型纳米非晶硅碳薄膜作为非晶硅p-i-n太阳电池的窗口层,使得太阳电池的开路电压达到0.94 V.