Ultraviolet semiconductor laser structures with pseudomorphic ZnCdSSe quaternary alloys on GaP substrates

For short-wavelength laser diodes operating in the ultraviolet region, a ZnCdSSe/ ZnSSe or ZnCdSSe/ZnCdS quantum well (QW) structure on a GaP substrate is proposed. The physical parameters of Zn_1−xCd_xS_ySe_1−y alloys in the range of 0 ≤ x ≤ 0.3 and 0.7 ≤ y ≤ 1 are estimated to design the device structure. It is shown that this system can be grown coherently on GaP substrates and is expected to possess the so-called type I QW structures that allow the effective confinement of both electrons and holes. ZnCdSSe/ZnSSe double heterostructures grown by gas-source molecular beam epitaxy exhibited relatively strong photoluminescence from the quaternary active layer at 4.2K, which suggested carrier confinement in the active layer.     

GaP中替代缺陷对的A1对称性深能级波函数

本文在Koster-Slater格林函数方法和在位(onsite)势近似的基础上,提出了一个计算替代杂质对的完整方法,并成功地应用于GaP中O替代杂质对。第一次给出了O-Zn和O-Cd对的波函数。我们发现波函数主要集中在O周围4个格点并指向O的化学键上。然而在这4个键上,波函数的分量并不相等,在O—杂质键上的分量要比其它键上的值小。杂质的排斥势越大,则分量值的不平衡越明显。而波函数的其余部分较为平坦地分布在一相当大的空间内。 关键词： GaP     

A dislocation etchant for {100} gallium phosphide

An etchant has been developed which produces etch pits with a well-defined crystallographic structure on {100} gallium phosphide surfaces. Scanning electron microscope (SEM) studies using both the emissive and cathodoluminescent (CL) modes of operation have established that there is a precise 1:1 correlation between etch pits and dark dots seen in the CL micrographs. Since the dark dots in the CL image are produced at the sites of emergent dislocations, it is therefore concluded that the etch pits are dislocation etch pits. The described etchant makes possible a rapid and easy assessment of the degree of crystalline perfection of {100} gallium phosphide epitaxial layers. Formerly with Ferranti Ltd., Chadderton, Lancashire.     

GaP/GaPN核壳纳米线阵列修饰的硅光阴极的光电化学制氢反应（英文）

能够大规模同时提升电极的催化效率和稳定性对光电化学分解水系统的开发具有重要意义.硅是一种地球储量丰富且成熟的工业材料,由于其合适的带隙(1.1 eV)和优异的导电性,已被广泛用于光电化学制氢反应.然而,缓慢的表面催化反应和在电解液中的不稳定性限制了其在太阳能制氢中的实际应用.III-IV族半导体材料也具有较高的载流子传输特性且被广泛用于光电器件.其中,GaP的直接带隙和间接带隙分别为2.78和2.26 eV,可与硅组成串联型光电极用于光电化学分解水.然而,GaP的光腐蚀电位位于禁带中,很容易在光电催化过程中发生光腐蚀而导致性能大幅下降.本文报道了一种新型的GaP/GaPN核/壳纳米线修饰的p型硅(p-Si)串联型光阴极,同未修饰的p-Si相比,其光电化学制氢性能更高.这可归因于以下几点:(1)p-Si和GaP纳米线之间形成的p-n结促进了电荷分离;(2)GaPN相对于GaP具有更低的导带边位置,进一步促进了光生电子向电极表面的转移;(3)纳米线结构既缩短了光生载流子的收集距离,又增加了比表面积,从而加快了表面反应动力学.此外,在GaP中引入氮元素还提高了体系的光吸收和稳定性.我们所提出的高效、简便的改进策略可应用于其他的太阳能转换体系.利用简单的化学气相沉积法制备GaP/GaPN核/壳纳米线修饰的p-Si光阴极.首先在p-Si衬底上利用Au纳米颗粒作为催化剂生长GaP纳米线;然后,去除Au催化剂,并在氨气中退火便形成了GaP/GaPN核壳纳米线.高分辨透射电子显微镜,拉曼光谱和X射线光电子谱的表征结果均证实了氨气退火使得GaP纳米线表面形成了GaPN的薄壳层,同时证明了GaP/GaPN核壳纳米线具有可调的核壳结构.在模拟太阳光下作为光阴极用于光解水制氢反应时,GaP/GaPN核壳纳米线修饰的p-Si光阴极的起始电位为~0.14 V,而未修饰的p-Si电极的起始电位大约在?0.77 V.而且,GaP/GaPN核/壳纳米线修饰的p-Si光阴极比未修饰的p-Si光阴极具有更高的光电流密度,在水的还原电位下,其光电流密度为?0.3 mA cm^-2,且饱和光电流密度在?0.76 V时达到了?8.8 mA cm^-2.此外,GaP/GaPN核/壳纳米线修饰的p-Si光阴极的光电化学活性在10 h内没有发生明显下降.由此可见GaP/GaPN核/壳纳米线可以规模化有效地提升Si光电极的催化效率和稳定性.     

Efficient excitation and amplification of the surface plasmons

One dimensional (1D) grating has been fabricated (using focused ion beam) on 50 nm gold (Au) film deposited on higher refractive index Gallium phosphate (GaP) substrate. The sub-wavelength periodic metal nano structuring enable to couple photon to couple with the surface plasmons (SPs) excited by them. These grating devices provide the efficient control on the SPs which propagate on the interface of noble metal and dielectric whose frequency is dependent on the bulk electron plasma frequency of the metal. For a fixed periodicity (Λ = 700 nm) and slit width (w = 100 nm) in the grating device, the efficiency of SPP excitation is about 40% compared to the transmission in the near-field. Efficient coupling of SPs with photon in dielectric provide field localisation on sub-wavelength scale which is needed in Heat Assisted Magnetic recording (HAMR) systems. The GaP is also used to emulate Vertical Cavity Surface emitting laser (VCSEL) in order to provide cheaper alternative of light source being used in HAMR technology. In order to understand the underlying physics, far-and near-field results has been compared with the modelling results which are obtained using COMSOL RF module.Apart from this, grating devices of smaller periodicity (Λ = 280 nm) and slit width (w = 22 nm) has been fabricated on GaP substrate which is photoluminescence material to observe amplified spontaneous emission of the SPs at wavelength of 805 nm when the grating device was excited with 532 nm laser light. This observation is unique and can have direct application in light emitting diodes (LEDs).