Transient Response of Photorefractive Grating in BSO and GaP by Short Light Pulse

(1)研究了BSO和GaP晶体的响应时间和衍射效率与折射率光栅间距的关系。在占据受主的初始条件下，根据统一的能带输运模型对实验数据进行分析，理论与实验符合得很好。在稳态条件下获得最大衍射效率的干涉条纹的特征波数K_O是最重要的参数，因为它不仅表征了衍射效率与K的关系曲线，而且还表征了响应时间与K的关系。(2)利用新提出的“四能级”模型分析了折射率光栅在短光脉冲照射下的时间演化，其中在b-…上考虑了导带与施主能级、电离受主能级和两个浅受主能级之间的载流子动力学。通过测量新研制的光激励电流(LSC)、瞬时光电流和热激励电流(TSC)，研究了BSO和GaP晶体的电学性质与光折变特性的关系。利用去除外加电场后形成的内部电场进行TSC测量，在没有噪声电流的情况下成功地识别了几个深陷阱。(4)通过监测He-Ne激光光束的衍射束强度，研究了BSO晶体在短光脉冲照射下的瞬时光折变特性。以前观察到的在第一次快速上升和第二次缓慢上升之间的特殊响应曲线可以用一个新发展的具有两个浅受主能级、一个非活性电离受主能级和一个施主能级的“四能级”模型来解释。瞬变光折变特性和瞬变光电流的温度依赖关系也支持本模型。较少

(1) Both response time and diffraction efficiency versus index grating spacing characteristics were examined for BSO and GaP crystals. The agreement between the theory and experiments is quite good, when the data are analyzed on the basis of the unified band transport model under the initial condition of occupied acceptors. The characteristic wave number of the interference fringe, K_O, at which maximum diffraction efficiency can be obtained under steady state condition, is the most important parameter because it characterize not only the diffraction efficiency versus K curve but also the response time versus K curve. Some physical parameters of those crystals were estimated from those characteristics.(2) Time evolution of the index grating after illumination of a short light pulse was analyzed by using a newly developed "Four- Level" model, where carrier dynamics between conduction band and a donor level, an ionized acceptor level and two shallow acceptor levels is considered on the b … More asis of thermally stimulated current (TSC) measurement for trap identification.(3) Electrical properties of BSO and GaP crystals relevant to photorefractive properties were studied by measuring a newly developed light-stimulated current (LSC), transient photocurrent and thermally stimulated current (TSC). The internal electric field formed after removal of external applied electric field was utilized for TSC measurements, where several deep traps were successfully identified without suffering from noise current.(4) Transient photorefractive properties of a BSO crystal after illumination by short light pulses were studied by monitoring diffracted beam intensity of a He-Ne laser beam. Previously observed peculiar response curve, having a dip between first fast rise and second slower rise, can be explained by a newly developed "Four-Level" model with two shallow acceptor levels, an inactive ionized acceptor level, and a donor level. Temperature dependences of transient photorefractive properties and transient photocurrent also support the present model. Less