Reduction of deep levels in MOCVD-regrown AlxGa1−x as interfaces by (NH4)2S passivation and in-situ HCl etching

The effects of surface preparation usinginsitu HCl etching and (NH₄)₂S passivation of Al_xGa_1-xAs episurfaces prior to regrowth by MOCVD are analyzed by deep level transient spectroscopy (DLTS), electrochemical profiling (C-V) and room-temperature photoluminescence (PL). Four electron traps were found from the DLTS measurements; a DX-center and three traps previously reported for oxygen-contaminated MOCVD systems. Electrical and optical measurements on quantum well lasers containing a regrown interface in the optical confinement region are also presented. It is demonstrated that both (NH₄)₂S passivation and HClin-situ etching improve the electrical and optical quality of the regrown Al_xGa_1-xAs interfaces, with the best results being obtained when the two methods are used in tandem.     

ZnSe/ZnSxSe1−x heterojunction valence band discontinuity measured by x-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy was used to measure the valence band discontinuity at the ZnSe/ZnS_xSe_1−x interface as a function of alloy composition. Due to the large lattice mismatch, the experimental values have to be corrected in order to account for strain in the ZnSe layers. We find the valence band discontinuity to vary between 0 and 0.76 eV as a function of S content x. This result is in excellent agreement with theoretical calculations. It also shows that the conduction band discontinuity is not negligibly small.     

In0.53Ga0.47As表面氮化和硫钝化对其Al/Al2O3/InGaAs MOS电容特性的影响

本文通过对比频散特性和滞回特性,计算界面态密度D_it和有效边界缺陷密度ΔN_bt,分析界面缺陷和漏电流等方法,系统的研究了In_0.53Ga_0.47As表面氮化和硫钝化对其Al/Al₂O₃/InGaAs结构MOS电容特性的影响。实验结果表明,这两种方法都能够在InGaAs表明形成一层界面钝化层。相比较于未处理的样品,经过氮气等离子体处理的样品表现出较好的界面特性,得到了最小的积累区频散、滞回电压,以及良好的I-V性能。经过(NH₄)₂S_x处理的样品则获得了最小的平带电压区频散以及最低的界面态密度Dit=2.6E11cm_-2eV_-1.     

Impurity-induced disordering of AlxGa1−xAs-GaAs quantum well heterostructures with (Si2)x(GaAs)1−x barriers

Recent work indicates that the alloy (Si₂)_x(GaAs)_1−x can be formed within the GaAs quantum well of an Al_xGa_1−xAs-GaAs quantum well heterostructure (QWH) and results in a shift of laser operation to higher energy. In this paper we show, by SIMS and EDS measurements, that the Si concentration in the (Si₂)_x(GaAs)_1−x layer far exceeds typical “doping” levels. The stability of these QWHs has been investigated with respect to thermal annealing and Zn impurity-induced layer disordering (Zn-IILD). Data are presented showing that the (Si₂)_x(GaAs)_1−x alloy is stable against thermal annealing unless a rich source of Ga vacancies is provided, and that relatively low temperature Zn diffusion greatly enhances the disordering process of the alloy layer.     

Effects of surface treatments on the electrical and the microstructural changes of Pd contact on p-type GaN

We investigated the effects of surface treatments by aqua regia and (NH₄)₂S_x on the electrical and the microstructural changes of Pd contact on p-type GaN during annealing. The formation of a surface oxide was suppressed by the (NH₄)₂S_x treatment, and S-Ga and S-N bonds with binding energy of 162.1 eV and 163.6eV were formed, degrading the structural ordering of Pd. After 300°C annealing, the contact resistivity in the aqua regia-treated sample increased significantly. This could be attributed to the outdiffusion of N atoms leaving N vacancies below the contact, as confirmed by the increase of the Pd (111) plane spacing probably due to the dissolution of N atoms in Pd interstitial sites. Meanwhile, the contact resistivity in the (NH₄)₂S_x-treated sample was not degraded and no change was observed in the Pd (111) plane spacing. These results suggest that S-Ga and S-N bonds formed on (NH₄)₂S_x-treated GaN could act as a diffusion barrier for the outdiffusion of N atoms. The contact resistivity for the aqua regia-treated sample decreased again, probably due to the outdiffusion of Ga as well as N atoms at 500°C.     

( NH4) 2Sx 溶液改善GaAs MESFETs 击穿特性的机理研究

使用（NH4）2Sx溶液对GaAs MESFETs进行处理。处理后，器件各栅偏压下的源漏饱和电流降低了，栅漏击穿电压有了显著提高。我们认为负电荷表面态影响着栅边缘的电场，负电荷表面态密度的增大会提高器件的击穿电压，这就是（NH4）2Sx溶液处理可改善GaAs MESFET击穿电压的原因。     

用于白光LED的KNaCa2(PO4)2:Eu2+蓝色荧光粉的发光特性

采用高温固相法合成了蓝色荧光粉KNaCa₂(PO₄)₂:Eu²⁺,利用X射线衍射(XRD)和光谱技术等表征了材料的性能。结果显示,少量Eu 2+的掺入并没有影响KNaCa₂(PO₄)₂的晶体结构。 在399nm近紫外光激发下,KNaCa₂(PO₄)₂:Eu²⁺材料发 射蓝光,发射光谱为400～600nm, 主发射峰位于471nm,对应Eu²⁺的4f^65d1→ 4f⁷跃迁发射;471nm发射峰,对应的激发光 谱为250～450nm,主激发峰位于399nm,与近紫外芯片匹配很好。 以365nm近紫外光作为 激发源时,KNaCa₂(PO₄)₂:Eu²⁺材料的发射强度约为商用蓝色荧光粉BAM:Eu 2+的85%;而以 399nm近紫外光作为激发源时,相较于BAM:Eu²⁺,KNaCa₂(P O₄)₂:Eu²⁺材料具有更强的发射强 度。此外,KNaCa₂(PO₄)₂:Eu²⁺和BAM:Eu²⁺的CIE色坐标接近,均位于蓝 色区域,色坐标分别 为(0.154,0.154)和(0.141,0.112)。研究结果 表明,KN aCa₂(PO₄)₂:Eu²⁺是一种在三基色白光LED中有应用前景的蓝色荧光粉。     

Fabrication and electrical characteristics of ultrathin (HfO2)x(SiO2)1−x films by surface sol-gel method and reaction-anneal treatment

Hafnium oxide (HfO₂) films were deposited on Si substrates with a pre-grown oxide layer using hafnium chloride (HfCl₄) source by surface sol-gel process, then ultrathin (HfO₂)_x(SiO₂)_1−x films were fabricated due to the reaction of SiO₂ layer with HfO₂ under the appropriate reaction-anneal treatment. The observation of high-resolution transmission electron microscopy indicates that the ultrathin films show amorphous nature. X-ray photoelectron spectroscopy analyses reveal that surface sol-gel derived ultrathin films are Hf-Si-O alloy instead of HfO₂ and pre-grown SiO₂ layer, and the composition was Hf_0.52Si_0.48O₂ under 500 °C reaction-anneal. The lowest equivalent oxide thickness (EOT) value of 0.9 nm of film annealed at 500 °C has been obtained with small flatband voltage of −0.31 V. The experimental results indicate that a simple and feasible solution route to fabricate (HfO₂)_x(SiO₂)_1−x composite films has been developed by means of combination of surface sol-gel and reaction-anneal treatment.     

Study of thick film Ni(1−x)CoxMn2O4,(0?x?1) using overlay technique on thick film microstrip ring resonator

The effect of thick film Ni_(1−x)Co_xMn₂O₄ in-touch overlay on the X band resonance characteristics of thick film microstrip ring resonator is studied. The thick film overlay decreases the resonance frequency and increases the peak output. From the frequency shift the dielectric constant of the thick film Ni_(1−x)Co_xMn₂O₄ has been calculated. For the first time Ag thick film microstrip ring resonator has been used to study thick film Ni_(1−x)Co_xMn₂O₄ in the X band.     

近紫外基白光LEDs用NaY(MoO4)2:Eu3+材料的发光特性

采用固相法于550℃灼烧4h,合成了Eu³⁺ 单掺杂的NaY(MoO₄)₂材料,研究了材料的 发光特性。X射线衍射(XRD)结果显示,掺杂少量杂质的材料仍为纯相的NaY(MoO₄)₂。以 393nm波长 近紫外光作为激发源时,NaY(MoO₄)₂:Eu³⁺可以发射主峰位于616nm波长的红色光,对应Eu³⁺的 ⁵D₀-⁷F₂跃迁发射。研究发现,增大Eu³⁺掺杂量 时,对应材料的发射强度会逐渐增大,但是 未发现浓度猝灭现象,通过相应的衰减曲线解释了此结果。测量不同Eu³⁺掺杂量下 , NaY(MoO₄)₂:Eu³⁺的色坐标结果显示,色坐标基本不变,位于红色区域。上述 结果表明, NaY(MoO₄)₂:Eu³⁺在白光LEDs领域有一定的应用潜力。     

Sn掺杂对(In0.95-xSnxFe0.05)2O3薄膜的结构、电学及磁特性的影响

我们利用脉冲激光沉积的方法制备了一系列(In0.95-xSnxFe0.05)2O3 (x=0~0.09)薄膜,并在其中发现了室温铁磁性。X射线衍射结果表明锡与铁离子已掺入氧化铟晶格。随着锡的掺入,样品内的载流子浓度得到了很大的提高,但相应的铁磁性却几乎没有变化。我们认为氧空位相关的束缚磁极化子模型能够跟好的解释我们的铁掺杂氧化铟薄膜中的铁磁耦合的机制,而载流子传导的RKKY相互作用则不适用于这一系统。