Ultraviolet laser-induced photovoltaic effects in miscut ferroelectric LiNbO_3 single crystals

This paper investigates the photovoltaic properties of miscut LiNbO3 single crystal with different thicknesses under irradiation of a 248 nm ultraviolet laser pulse with 20 ns duration without an applied bias. Nanosecond photovoltaic response is observed and faster rise time is obtained in thinner samples. In accord with the 248 nm laser duration, the full width at half maximum of the photovoltaic signals keeps a constant of ~ 20 ns. With decrease of the crystal thickness, the photovoltaic sensitivity was improved rapidly at first and then decreased, and the maximum photovoltage occurred at 0.38 mm-thick single crystal. The present results demonstrate that decreasing the LiNbO3 single crystal thickness can obtain faster response time and improve the photovoltaic sensitivity.

Fast lateral photovoltaic effect in ferroelectric LiNbO_3 single crystals

We report the fast lateral photovoltaic effect in pure congruent LiNbO3 crystal induced by pulsed laser and continuous wave laser with wavelengths of 355, 532, and 1064 nm. A typical ultrafast photovoltage can be observed on the surface perpendicular to the c axis, With the rise time of 1.5 ns and the full-width at half-maximum of 1-2 ns, when the laser pulse inhomogeneously irradiates on the crystal. The peak open-circuit photovoltages show a linear dependence on the incident laser intensities. The mechanism of the photovoltaic characteristics is proposed.

Ultraviolet laser-induced voltages in LaSrAlO_4 single crystal

Laser-induced ultrafast photovoltaic effect is observed in LaSrAlO4 single crystal at ambient temperature without any applied bias. An open-circuit photovoltage is obtained when the wafer is irradiated by a 248-nm-KrF laser pulse of 20 ns duration. The response time and full width at half maximum of the photovoltage pulse are 6 ns and 19 ns, respectively, indicating that LaSrAlO4 single crystal has potential application in ultraviolet detector.

Infrared active phonon modes and ionicity of single crystal MgAl2O4

Near-normal incident infrared reflectivity spectra of （100） MgAl2O4 spinel single crystal have been measured at different temperatures in the frequency region between 50 and 6000 cm^-1. Eight infrared-active phonon modes are identified, which are fitted with the factorized form of the dielectric function. The dielectric property and optical conductivity of the MgAl2O4 crystal are analysed. From TO/LO splitting, the effective Szigeti charges and Born effective charges at different temperatures are calculated for studying the ionicity and the effect of polarization. Based on the relationship between the （LO-TO）1 splitting, which represents the transverse and longitudinal frequencies splitting of the highest energy phonon band in the reflectivity spectrum, and the ionic-covalent parameter, the four main phonon modes are assigned. MgA1204 can be considered as a pure ionic crystal and its optical characters do not change with decreasing temperature, so it may be used as a suitable substrate for high-Tc superconducting thin films.

中子辐照的单晶硅参数研究

在不同温度和红外光照下，测量了经中子辐照的单晶硅表面光电压，确定了其深能级的位置和少子扩散长度；由双能级复合理论，推导了中子辐照单晶硅的深能级复合中心和寿命的计算公式；计算了热中子辐照和高能中子辐照单晶硅后的深能级密度、费米能级和其他有关重要参数。

分子束外延Mn_(4)N单晶薄膜的反常霍尔效应研究

Mn_(4)N是立方相的反钙钛矿型晶体,具有显著的亚铁磁性和反常霍尔效应.该文利用等离子辅助分子束外延在MgO(100)衬底上生长厚度为40 nm的Mn_(4)N(100)单晶薄膜,通过X射线衍射θ扫描和φ扫描,证实外延层的结构符合Mn_(4)N单晶的空间结构特征;化学态测试结果表明Mn_(4)N(100)薄膜内部存在Mn^(0)、Mn^(2+)和Mn^(4+)等几种价态,其实际化学式为Mn_(3.6)N,薄膜中存在富余的N元素;电学测试数据表明Mn_(4)N(100)薄膜具有以电子为载流子的反常霍尔效应(在正磁场中得到负的霍尔电阻率),正常霍尔效应的贡献约占千分之六,其反常霍尔电阻率随着测试温度升高5 K~350 K单调增大,说明温度升高导致电子散射现象加剧.通过对测试数据分析可以推断,在5 K~50 K和50 K~75 K温度范围,反常霍尔效应的来源可分别归结为电子斜散射机制和电子边跳机制.在75 K~350 K这一温度范围内,反常霍尔效应主要来源于与能带结构相关的内禀机制.