Origin of photoinduced metastable defects in amorphous chalcogenides.
Origin of photoinduced metastable defects in amorphous chalcogenides.
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DOI：
10.1103/physrevb.46.10062
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发表时间：
1992-10
期刊：
影响因子：
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通讯作者：
Shimakawa;Inami;Kato;Elliott
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文献类型：
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作者：
Shimakawa;Inami;Kato;Elliott
长时间暴露在带隙光下会降低非晶硫属化物（As&S3、As3S7 AsS、As2Se3、GeS2、GeSe2 和 GeSe）退火薄膜的光电导率。这可以归因于光诱导的亚稳态缺陷，它可以充当额外的捕获和/或重组中心。这些亚稳中心通过在玻璃化转变温度附近退火来去除。在缺陷守恒键转换模型中讨论了光照期间光电流随时间变化的动力学。 I. 引言 非晶硫属化物中光致缺陷的产生已经通过光致电子自旋共振（LESR）、“静电复印”、“交流传输和光电流”测量进行了研究。我们早期的研究中提出了一个模型，用于在化学计量的非晶硫属化物中光诱导产生亚稳态深缺陷态[例如，As2S(Se)3，GeS(Se)2]。由光学照明引起的光电导率随时间的可逆变化是由带电缺陷（以前称为自陷激子）的紧密对（IP）的初始产生引起的，随后发生键转换反应，导致广泛分离的亚稳态“随机对”（RP）缺陷。在本文中，通过测量化学计量非晶 As2S3、As2Se3、GeSz 和 GeSe2 薄膜以及非化学计量非晶 As3S7、AsS 和 GeSe 薄膜的光电流 I 与温度相关的下降，使用 IP 和势能图讨论了缺陷守恒键转换 (DCBS) 反应的动力学。 RP 中心。 DCBS 的动力学本质上可能是“分散的”，因此 I 的时间变化可以通过使用拉伸指数项 [exp(Ct )]（其中 0&1）凭经验表示。拟合实验数据可产生有关与知识产权和 RP 中心形成相关的潜在障碍程度的信息。二.光导性研究 将非晶 As2S3、As3S7、AsS、As2Se3、GeS2、GeSe2 和 GeSe 薄膜蒸发到 Corning 7059 基板上。蒸发后，将样品在低于玻璃化转变温度T的适当温度下退火。薄膜的厚度、退火温度 Tn 和 Tauc 间隙 Eo 在表 I 中给出。As-S(Se) 薄膜的实际成分使用 X 射线光电子能谱 (XPS) 测量进行估计，这些结果显示在表 I 的括号中。与起始玻璃相比，总是获得富硫薄膜。使用 Al 触点制造了平面间隙电池电极（间隙间距 40 JLtm，间隙宽度 5 毫米）。对于含S材料，施加的电压为300V；对于含Se材料，施加的电压为5V。卤素灯 (57 mW/cm2) 或用于更宽带隙材料的高压汞灯 (54 mW/cm2) 与 ir-cut 水过滤器一起使用以诱导光电导。每种情况下使用的灯的类型是
Prolonged exposure to band-gap light decreases the photoconductivity of annealed films of amorphous chalcogenides (As&S3, As3S7 AsS, As2Se3, GeS2, GeSe2, and GeSe). This can be attributed to photoinduced metastable defects, which could act as additional trapping and/or recombination centers. These metastable centers are removed by annealing near the glass transition temperature. The kinetics of the temporal change of photocurrent during illumination are discussed in a model of defect-conserved bond switching. I. INTRODUCTION Photoinduced defect creation in amorphous chalcogenides has been studied using light-induced electronspin resonance (LESR), ' xerographic, ' ac transport, and photocurrent ' measurements. A model has been presented in our earlier studies ' for the light-induced creation of metastable deep defect states in stoichiometric amorphous chalcogenides [e.g. , As2S(Se)3, GeS(Se)2]. The reversible time-dependent changes in the photoconductivity caused by optical illumination result from the initial creation of intimate pairs (IP) of charged defects (previously referred to as self-trapped excitons ), followed by bond-switching reactions leading to widely separated, metastable "random pairs" (RP) of defects. In the present paper, through measurements of the temperature-dependent decrease in photocurrent I for stoichiometric amorphous As2S3, As2Se3, GeSz, and GeSe2 films, and off-stoichiometric amorphous As3S7, AsS, and GeSe films, the kinetics of defect-conserved bond-switching (DCBS) reactions are discussed using a potential-energy diagram for IP and RP centers. The kinetics of DCBS may be "dispersive" ' in nature and hence the temporal change in I can be expressed empirically by using the stretched exponential term [exp(Ct )], where 0&1. Fitting to the experimental data produces information about the magnitude of the potential barriers associated with the formation of IP and RP centers. II. PHOTOCONDUCTIVITY STUDIES Thin films of amorphous As2S3, As3S7, AsS, As2Se3, GeS2, GeSe2, and GeSe were evaporated onto Corning 7059 substrates. After evaporation, the samples were annealed at appropriate temperatures below the glasstransition temperature T . The thickness of the films, the annealing temperatures T„and the Tauc gap Eo are given in Table I. The actual compositions of As-S(Se) films were estimated using x-ray photoemission spectroscopy (XPS) measurements and these are shown in parentheses in Table I. Sulfur-rich films compared with the starting glasses were always obtained. Planar gap cell electrodes using Al contacts were fabricated (gap spacing 40 JLtm, gap width 5 mm). The applied voltages were 300 V for S-containing materials and 5 V for Se-containing materials. A halogen lamp (57 mWlcm ), or a highpressure mercury lamp (54 mW/cm ) for wider band-gap matenals, was used with an ir-cut water filter to induce photoconductivity. The type of lamp used in each case is